CN108350540A

CN108350540A - The low-temperature flexibility of welding heat affected zone is inhibited to deteriorate the non-quenched and tempered steel plate with high-yield strength with the hardness of welding heat affected zone

Info

Publication number: CN108350540A
Application number: CN201680064618.1A
Authority: CN
Inventors: 仓田皓至; 川野晴弥; 田代喜郎; 田代喜一郎; 柿崎元树
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 2015-12-04
Filing date: 2016-11-24
Publication date: 2018-07-31
Also published as: EP3385399A1; WO2017094593A1; EP3385399A4; KR20180085791A; JP2017106107A

Abstract

A kind of non-quenched and tempered steel plate with high-yield strength for the low-temperature flexibility deterioration and the hardness of welding heat affected zone inhibiting welding heat affected zone is provided.It is a kind of that the low-temperature flexibility of welding heat affected zone is inhibited to deteriorate the non-quenched and tempered steel plate with high-yield strength with the hardness of welding heat affected zone, it is characterized in that, contain ingredient in defined steel, the Ceq of following formula (1) defined is less than 0.44, the A values of following formula (2) defined are 2.50 or more, B values with following formula (3) defined are 2.37 or more, and in 1/4 position of the plate thickness of steel plate, the area occupation ratio of following metal structures meets bainite：80 area % or more and island-like martensite：0 area % or more and 0.26 area % are hereinafter, the highest hardness of the bainite is 270HV or more.Ceq=C+Mn/6+ (Cu+Ni)/15+ (Cr+Mo+V)/5 ... (1) value=1.15 A × Mn+2.20 × Mo+6.50 × Nb ... (2) value=1.20 B × Mn+0.50 × Ni+4.25 × Nb ... (3).

Description

The low-temperature flexibility of welding heat affected zone is inhibited to deteriorate the hardness with welding heat affected zone The non-quenched and tempered steel plate with high-yield strength

Technical field

The present invention relates to having for the hardness of the low-temperature flexibility deterioration and welding heat affected zone that inhibit welding heat affected zone The non-quenched and tempered steel plate of high-yield strength.In more detail, it is to be related to having used in the conveying line pipe of oil, natural gas etc. There is the non-quenched and tempered steel plate of the high-yield strength of X80 grades of API specifications.

Background technology

In the line pipe of long distance delivery natural gas and crude oil, it is reduced to target to be laid with expense and pipage, makes pipe Former material high intensity itself and limit the increase of wall thickness this upswing in demand.Currently, American Petroleum Institute (American Petroleum Institute, API) in, as high yield stress steel, X80 grades of steel are standardized, are practical.

As the steel plate that above-mentioned such line pipe uses, other than wishing that it has high-yield strength, it is also desirable to high-ductility Property, casual labourer's phase, low cost can enumerate controlled rolling as the manufacturing method for meeting these.Controlled rolling is by appropriate Temperature and reduction ratio when controlled rolling etc. and make crystal grain miniaturization, and implement to accelerate cooling technology after hot rolling.It is controlling In rolling, after accelerating cooling need not heat etc. quenched.The steel plate obtained by this method is commonly referred to as non-tune Matter steel plate.

About the high-yield strength steel plate of Micro Alloying, the exploitation of various technologies has been carried out all the time.Such as in patent text In offering 1~4, the manufacturing method of Micro Alloying and the steel plate of the high-yield strength with X80 grades of API specifications is disclosed.

Existing technical literature

Patent document

Patent document 1：Japanese Unexamined Patent Publication 2006-328523 bulletins

Patent document 2：No. 2010/052927 pamphlet of International Publication No.

Patent document 3：Japanese Unexamined Patent Publication 2006-169591 bulletins

Patent document 4：Japanese Unexamined Patent Publication 2008-261012 bulletins

But line pipe, which also has, is much laid on cold district, therefore welding heat affected zone (Heat Affected Zone, HAZ low-temperature flexibility) must be excellent.In addition it from the viewpoint of welding procedure, is strongly desired to inhibit welding hot shadow in recent years The hardness in sound portion.

But the steel plate described in patent document 1 and patent document 2, not by the toughness of welding heat affected zone and hardness Evaluation index, i.e. Ceq control very low, therefore there are the deteriorations of the toughness of welding heat affected zone and the hardening of welding heat affected zone It may.

In addition in the method described in patent document 3 and patent document 4, because a large amount of additions can make welding heat affected zone The ingredient B of low-temperature flexibility deterioration, so there is the low-temperature flexibility that can make welding heat affected zone to deteriorate.

Invention content

The present invention is done in view of such situation, it is intended that providing a kind of low temperature inhibiting welding heat affected zone Toughness deteriorates and the non-quenched and tempered steel plate with high-yield strength of the hardness of welding heat affected zone.

The low-temperature flexibility for inhibiting welding heat affected zone that can solve the present invention of the above subject deteriorates and welding hot shadow The non-quenched and tempered steel plate with high-yield strength of the hardness in sound portion, what is had will be intended to, and in terms of quality %, contain C：It is higher than 0.04% and below 0.10%, Si：0.15~0.50%, Mn：1.20~2.50%, P：Higher than 0% and 0.020% with Under, S：Higher than 0% and below 0.0050%, Nb：0.020~0.100%, Ti：0.003~0.020%, N：0.0010~ 0.0075%, Zr：0.0001~0.0100%, Ca：0.0005~0.0030%, REM：0.0001~0.0050%, Al： 0.010~0.050% and B：0.0003% or less (containing 0%), also contain from Mo：Higher than 0% and below 0.30%, Cu：It is high In 0% and below 0.30%, Ni：Higher than 0% and below 0.30%, Cr：Higher than 0% and below 0.30% and V：It is higher than 0% and the group that is constituted below 0.050% in select more than one, surplus is made of iron and inevitable impurity, by Ceq as defined in following formula (1) is less than 0.44, and the A values as defined in following formula (2) are 2.50 or more, and the B values as defined in following formula (3) It is 2.37 or more, and in 1/4 position of the plate thickness of steel plate, the area occupation ratio of following metal structures meets bainite：80 area % More than and island-like martensite：0 area % or more and 0.26 area % hereinafter, the highest hardness of the bainite meet 270HV with On.

Ceq=C+Mn/6+ (Cu+Ni)/15+ (Cr+Mo+V)/5 ... (1)

Value=1.15 A × Mn+2.20 × Mo+6.50 × Nb ... (2)

Value=1.20 B × Mn+0.50 × Ni+4.25 × Nb ... (3)

Wherein, C, Mn, Cu, Ni, Cr, Mo, V and Nb indicate respectively in terms of quality %, C, Mn, Cu, Ni, Cr, Mo, V and The content of Nb.

In the preferred embodiments of the present invention, above-mentioned non-quenched and tempered steel plate is used for line pipe.

According to the present invention, by using above-mentioned composition, the low-temperature flexibility for the welding heat affected zone that can be inhibited deteriorates With the non-quenched and tempered steel plate with high-yield strength of the hardness of welding heat affected zone.

Description of the drawings

Fig. 1 is the figure for the relationship for indicating bainite area occupation ratio and yield strength.

Fig. 2 is the figure of the relationship of the highest hardness and yield strength that indicate bainite.

Fig. 3 is to indicate that the area occupation ratio of island-like martensite (hereinafter, having the case where island-like martensite is known as MA) and surrender are strong The figure of the relationship of degree.

Specific implementation mode

First, the present inventors study for dominating the factor of the yield strength of non-quenched and tempered steel plate.Itself as a result, it has been found that, Each area occupation ratio and bainite of bainite and island-like martensite in the yield strength and metal structure of non-quenched and tempered steel plate are most Big hardness has close correlativity, if control can be obtained in defined range X80 grades of API specifications height it is in the wrong Take intensity.

In addition, the present inventors are in order to realize high-yield strength and further suppress the low-temperature flexibility of welding heat affected zone The non-quenched and tempered steel plate of the hardness of deterioration and welding heat affected zone, and studied from various angles.Itself as a result, it has been found that, if with Meet the mode of the relationship of above-mentioned formula (1)~(3) to control chemical composition composition, then the low-temperature flexibility of welding heat affected zone deteriorates It is suppressed, can additionally reduce the hardness of welding heat affected zone, so as to complete the present invention.

In addition, such non-quenched and tempered steel plate, preferably manufactures in the following way, that is, heating meet as defined at being grouped as Steel and after carrying out hot rolling, with average cooling rate：It is 10~50 DEG C/sec, cooling from 730 DEG C or more of the beginning of cooling temperature To 370~550 DEG C of cooling stopping temperature.

In the present specification, so-called " high-yield strengths that X80 grades of API specifications " mean bending for the plate width direction of steel plate It is 555MPa or more and 705MPa or less to take intensity.

It is illustrated firstly, for the tissue of the non-quenched and tempered steel plate of the present invention.

For the non-quenched and tempered steel plate of the present invention in 1/4 position of the plate thickness t of steel plate, each tissue is full relative to metal structure totality Sufficient bainite：80 area % or more, island-like martensite：0 area % or more and 0.26 area % are hereinafter, the maximum with bainite is hard Degree：270HV or more.

Bainite：80 area % or more

Bainite contributes to the tissue of yield strength raising, is for ensuring that the high-yield strength of X80 grades of API specifications Vital tissue.If bainite is less than 80 area %, yield strength reduces.For this purpose, setting the area of metal structure totality as 100% When, the lower limit of the area occupation ratio of bainite is 80 area % or more.The lower limit of the area occupation ratio of bainite is preferably 82 area % or more, More preferably 84 area % or more.

Fig. 1 is the steel grade A~X for indicating the table 1 using aftermentioned embodiment, with the manufacturing condition system of No.1~24 of table 2 The figure of the area occupation ratio of bainite in non-quenched and tempered steel plate obtained from making and the relationship of yield strength.As shown in Figure 1, meeting uncommon The embodiment of the high-yield strength of the 555MPa or more of prestige, the bainite area occupation ratio in metal structure, can all 80% or more Know to meet high-yield strength, bainite area occupation ratio is effectively increased to 80% or more.In Fig. 1, although also there is bayesian Bulk area rate is 80% or more, but yield strength is unsatisfactory for the example of 555MPa or more, but these are aftermentioned bainite hardness Less than the example that 270HV or MA area occupation ratios are higher than 0.26%.

The highest hardness of bainite：270HV or more

The highest hardness of bainite for inhibit the deviation of yield strength and stably obtain it is critically important in high-yield strength, Need control in 270HV or more.Thereby, it is possible to stablize the high-yield strength for ensuring X80 grades of API specifications.The maximum of bainite is hard The lower limit of degree is preferably 275HV or more.But if considering to be shaped as the formability of steel pipe, the highest hardness of bainite it is upper Limit is preferably 310HV hereinafter, more preferably 300HV or less.

Fig. 2 is the steel grade A~X for indicating the table 1 using aftermentioned embodiment, with the manufacturing condition system of No.1~24 of table 2 The figure of the highest hardness of bainite in non-quenched and tempered steel plate obtained from making and the relationship of yield strength.As shown in Fig. 2, meeting The embodiment of desired 555MPa or more, the bainite highest hardness in metal structure is all in 270HV or more, it is known that in order to full Bainite highest hardness is effectively increased to 270HV or more by sufficient high-yield strength.Although here, also there is bainite maximum Hardness is in 270HV or more, but yield strength is unsatisfactory for the example of 555MPa or more, but these are that bainite area occupation ratio is less than 80% or MA area occupation ratios are higher than 0.26% example.

So-called herein " highest hardness of bainite " means and measures bainite by the method described in aftermentioned embodiment Upper 3 points of average value when Vickers hardness.Present inventors found that the highest hardness by controlling bainite, can stablize Obtain high-yield strength.

Island-like martensite：0 area % or more and 0.26 area % or less

Island-like martensite is the tissue for making yield strength reduce, therefore needs to make in order to ensure desired high-yield strength MA area occupation ratios are reduced.Set thus the area of metal structure totality as 100% when, the upper limits of MA area occupation ratios be 0.26 area % with Under.The upper limit of MA area occupation ratios is preferably 0.25 area % or less.

Fig. 3 is the A~X for indicating the table 1 using aftermentioned embodiment, with the manufacturing condition manufacture of No.1~24 of table 2 The figure of the area occupation ratio of island-like martensite in obtained non-quenched and tempered steel plate and the relationship of yield strength.As shown in figure 3, meeting The embodiment of 555MPa or more, the MA area occupation ratios in metal structure are all 0.26% hereinafter, understand strong in order to meet high yield Degree, effectively by the control of MA area occupation ratios below 0.26%.Here, also have although MA area occupation ratios 0.26% hereinafter, bend The example that intensity is but unsatisfactory for 555MPa or more is taken, but these are that bainite area occupation ratio is less than 80% or bainite highest hardness Example less than 270HV.

The tissue of the non-quenched and tempered steel plate of the present invention is as described above.Surplus tissue other than the above be ferrite, martensite or Pearlite.

Next, being illustrated for ingredient in steel.

First, illustrate Ceq, A value indicated by above-mentioned formula (1)~formula (3) and B values, with the low-temperature flexibility for taking intensity, HAZ With the relationship of the hardness of HAZ.

Ceq：Less than 0.44

Ceq=C+Mn/6+ (Cu+Ni)/15+ (Cr+Mo+V)/5 ... (1)

Wherein, C, Mn, Cu, Ni, Cr, Mo and V indicate that in terms of quality %, C, Mn, Cu, Ni, Cr, Mo and V's contains respectively Amount.

The Ceq defined by above-mentioned formula (1) is the important index of the hardness for the low-temperature flexibility and HAZ for determining HAZ.If Ceq Reach 0.44 or more, then the low-temperature flexibility of HAZ and the hardness property of HAZ drastically deteriorate, can be true if Ceq is less than 0.44 Protect the hardness of the low-temperature flexibility and the portions HAZ of good HAZ.For this purpose, the upper limit of Ceq is made to be less than 0.44.The upper limit of Ceq is preferably 0.43 hereinafter, more preferably 0.42 or less.On the other hand, if considering, the lower limit etc. of the content of each element, the lower limit of Ceq are preferred It is 0.37 or more, more preferably 0.38 or more.

A values：More than 2.50

Value=1.15 A × Mn+2.20 × Mo+6.50 × Nb ... (2)

Wherein, Mn, Mo and Nb are indicated respectively in terms of quality %, the content of Mn, Mo and Nb.

A values are originally found by the present inventors, are used to inhibit iron among the element for being control composition Ceq above-mentioned Each content of ferritic phase transformation effective Mn and Mo, the also content of Nb, to be allowed to meet the parameter of above-mentioned formula (2).By making A values It is 2.50 or more, the rising of Ceq can be inhibited on one side, ensures important bayesian bulk area on realizing high-yield strength on one side Rate.In order to make bainite area occupation ratio rise, the higher the better for A values, in order to ensure X80 grades of high-yield strength of API specifications, makes A values Lower limit be 2.50 or more.The lower limit of A values is preferably 2.52 or more, and more preferably 2.54 or more.On the other hand, if considering each member The upper limit etc. of the content of element, then the upper limit of A values is preferably 3.00 hereinafter, more preferably 2.95 or less.

B values：More than 2.37

Value=1.20 B × Mn+0.50 × Ni+4.25 × Nb ... (3)

Wherein, Mn, Ni and Nb are indicated respectively in terms of quality %, the content of Mn, Ni and Nb.

B values are originally found by the present inventors, are controlled by making the phase transition temperature of bainite reduce, and to leading Each content for entering highdensity dislocation effective Mn, Ni, Nb is allowed to meet the parameter of above-mentioned formula (3).By making B values be 2.37 More than, the rising of Ceq can be inhibited on one side, ensure the highest hardness of bainite on one side.In order to make in the highest hardness of bainite It rises, the higher the better for B values, and in order to ensure X80 grades of high-yield strength of API specifications, it is 2.37 or more to make the lower limit of B values.Under B values Limit preferably 2.39 or more.On the other hand, if considering the upper limit etc. of the content of each element, the upper limits of B values be preferably 2.70 with Under, more preferably 2.68 or less.

C：Higher than 0.04% and below 0.10%

C is for ensuring that the high-yield strength of base material (steel plate) and essential element, needs the lower limit for making C amounts thus Higher than 0.04%.The lower limit of C amounts is preferably 0.05% or more, and more preferably 0.06% or more.But if C amounts become superfluous, Island-like martensite is easy to generate, and yield strength reduces, and makes welding procedure reduction, it is therefore desirable to make the upper limit of C amounts be 0.10% or less.The upper limit of C amounts is preferably 0.09% hereinafter, more preferably 0.08% or less.

Si：0.15~0.50%

Si has deoxidation, and is effective element for the raising of the yield strength of base material, makes thus under Si amounts It is limited to 0.15% or more.The lower limit of Si amounts is preferably 0.18% or more, and more preferably 0.20% or more.But if Si amounts become Surplus then makes welding procedure, the low-temperature flexibility deterioration of HAZ, it is therefore desirable to which it is 0.50% or less to make the upper limit of Si amounts.Si amounts The upper limit is preferably 0.45% hereinafter, more preferably 0.40% or less.

Mn：1.20~2.50%

Mn is effective element for the yield strength raising of base material, need to make thus the lower limit of Mn amounts for 1.20% with On.The lower limit of Mn amounts is preferably 1.50% or more, and more preferably 1.70% or more.But if Mn amounts become superfluous, welding is applied Work deteriorates, therefore the upper limit of Mn amounts is made to be 2.50% or less.The upper limit of Mn amounts is preferably 2.20% hereinafter, more preferably 2.00% or less.

P：Higher than 0% and below 0.020%

P be in steel unavoidably by comprising element, if P amounts be higher than 0.020%, keep the low-temperature flexibility of HAZ notable Deterioration.The upper limit of P amounts is 0.020% or less thus.The upper limit of P amounts be preferably 0.015% hereinafter, more preferably 0.010% with Under.In addition, P be in steel unavoidably by comprising impurity, make its amount reach 0% in industrial production can not possibly.

S：Higher than 0% and below 0.0050%

S and above-mentioned P are coarse if S amounts are higher than 0.0050% again it is to the element that the low-temperature flexibility of HAZ has an impact Sulfide generate and so that the low-temperature flexibility of HAZ is deteriorated.It is 0.0050% or less to make the upper limit of S amounts thus.The upper limit of S amounts is preferred For 0.0030% hereinafter, more preferably 0.0020% or less.In addition, S be in steel unavoidably by comprising impurity, so that its amount is existed It can not possibly in industrial production to 0%.

Nb：0.020~0.100%

Nb will not be such that welding procedure deteriorates, and be effective member for the low-temperature flexibility for improving yield strength and base material Element needs that the lower limit of Nb amounts is made to be 0.020% or more thus.The lower limit of Nb amounts is preferably 0.030% or more, more preferably 0.040% or more.But if Nb amounts become superfluous and are higher than 0.100%, the low-temperature flexibility of HAZ is set to deteriorate, therefore make Nb amounts The upper limit be 0.100% or less.The upper limit of Nb amounts is preferably 0.070% hereinafter, more preferably 0.060% or less.

Ti：0.003~0.020%

Ti is effective element for the yield strength raising of base material, in addition, it is precipitated in steel as TiN, it is to weld The low-temperature flexibility required element of HAZ is improved when connecing by the coarsening of the HAZ austenite grains inhibited.In order to play this The effect of sample needs that the lower limit of Ti amounts is made to be 0.003% or more.The lower limit of Ti amounts is preferably 0.005% or more, more preferably 0.007% or more.But if Ti amounts become superfluous, it is dissolved the increase of Ti and TiC precipitates, the low-temperature flexibility of HAZ deteriorates, because This makes the upper limit of Ti amounts be 0.020% or less.The upper limit of Ti amounts is preferably 0.018% hereinafter, more preferably 0.016% or less.

N：0.0010~0.0075%

N in steel as TiN be precipitated, be inhibit welding when HAZ austenite grain coarsening and improve the low of HAZ The warm required element of toughness.In order to play such effect, need that the lower limit of N amounts is made to be 0.0010% or more.The lower limit of N amounts Preferably 0.0020% or more, more preferably 0.0030% or more.But if N amounts become superfluous, due to being dissolved the presence of N Cause the low-temperature flexibility of HAZ to deteriorate, therefore the upper limit of N amounts is made to be 0.0075% or less.The upper limit of N amounts be preferably 0.0070% with Under, more preferably 0.0065% or less.

Zr：0.0001~0.0100%

Zr forms oxide and disperses, and contributes to the element that the low-temperature flexibility of HAZ improves, needs to make under Zr amounts thus It is limited to 0.0001% or more.The lower limit of Zr amounts is preferably 0.0003% or more, and more preferably 0.0005% or more.But if Zr Amount becomes superfluous, then forms coarse field trash and the low-temperature flexibility of HAZ is made to deteriorate, it is therefore desirable to the upper limit of Zr amounts be made to exist 0.0100% or less.The upper limit of Zr amounts is preferably 0.0050% hereinafter, more preferably 0.0030% or less.

Ca：0.0005~0.0030%

Ca has the function of controlling the form of sulfide, the formation of MnS is controlled by forming CaS, is the low temperature for making HAZ The element that toughness improves needs that the lower limit of Ca amounts is made to be 0.0005% or more thus.The lower limit of Ca amounts be preferably 0.0006% with On.But if Ca amounts become superfluous higher than 0.0030%, the low-temperature flexibility deterioration of HAZ, therefore make the upper limit of Ca amounts be 0.0030% or less.The upper limit of Ca amounts is preferably 0.0028% hereinafter, more preferably 0.0026% or less.

REM：0.0001~0.0050%

As the REM of rare earth element, the form control for sulfide is effective element, is inhibited to the low of HAZ The generation of the harmful MnS of warm toughness.In order to play such effect, it is 0.0001% or more to make the lower limit of REM amounts.REM amounts are excellent It is selected as 0.0003% or more, more preferably 0.0005% or more.But even if REM is made largely to contain, effect is also saturation, because The upper limit of this REM amount is 0.0050% or less.The upper limit of REM amounts be preferably 0.0040% hereinafter, more preferably 0.0030% with Under.In addition, in the present invention, so-called REM means lanthanide series (15 kinds of elements from La to Lu) and Sc (scandium) and Y (yttrium). Among these elements, preferably comprise at least one element selected from the group of the composition of Ce, La and Nd, further preferably Ce and At least one of La.

Al：0.010~0.050%

Al is strong deoxidant element, in order to obtain deoxidation effect, needs that the lower limit of Al amounts is made to be 0.010% or more.Al amounts Lower limit is preferably 0.015% or more, and more preferably 0.018% or more.But if Al amounts become superfluous, AlN is largely generated, TiN amount of precipitations are reduced, and the low-temperature flexibility of HAZ is impaired, it is therefore desirable to which it is 0.050% or less to make the upper limit of Al amounts.The upper limit of Al amounts Preferably 0.045% hereinafter, more preferably 0.042% or less.

B：0.0003% or less (containing 0%)

B amounts are the elements for making the low-temperature flexibility of HAZ significantly deteriorate, and it is 0.0003% or less to make the upper limit of B amounts thus.B amounts The upper limit be preferably 0.0002% hereinafter, more preferably 0.0001% or less.In addition, when adding B higher than 0.0003%, Mo Compound addition can cause base material yield strength excessive rising.

From Mo：Higher than 0% and below 0.30%, Cu：Higher than 0% and below 0.30%, Ni：Higher than 0% and 0.30% or less, Cr：Higher than 0% and below 0.30% and V：It is selected in the group constituted higher than 0% and below 0.050% More than one

Mo, Cu, Ni, Cr and V are effective elements for yield strength raising.These elements can be added individually, also may be used It is used in combination with two or more.The range setting reason of the content of these elements is as follows.

Mo：Higher than 0% and below 0.30%

Mo is effective element for the raising of the yield strength of base material, thus the lower limit of Mo amounts be preferably 0.01% with On.The lower limit of Mo amounts is more preferably 0.05% or more, further preferably 0.10% or more.But if Mo amounts are higher than 0.30%, The then low-temperature flexibility of HAZ and welding procedure deterioration, therefore the upper limit of Mo amounts is made to be 0.30% or less.The upper limit of Mo amounts is preferably 0.25% hereinafter, more preferably 0.20% or less.

Cu：Higher than 0% and below 0.30%

Cu is effective element for improving yield strength, and the lower limit of Cu amounts is preferably 0.01% or more thus.Cu amounts Lower limit is more preferably 0.05% or more, further preferably 0.10% or more.But it if Cu amounts become superfluous, is easy to generate MA, therefore the upper limit of Cu amounts is made to be 0.30% or less.The upper limit of Cu amounts is preferably 0.27% hereinafter, more preferably 0.25% or less

Ni：Higher than 0% and below 0.30%

Ni is effective element for the raising of the yield strength of base material, thus the lower limit of Ni amounts be preferably 0.01% with On.The lower limit of Ni amounts is more preferably 0.05% or more, further preferably 0.10% or more.But if Ni amounts become superfluous, It is easy to generate MA.In addition, because as structural steel extremely high price, from the viewpoint of economy, make the upper of Ni amounts It is limited to 0.30% or less.The upper limit of Ni amounts is preferably 0.27% hereinafter, more preferably 0.25% or less.

Cr：Higher than 0% and below 0.30%

Cr is effective element for the raising of yield strength, and the lower limit of Cr amounts is preferably 0.01% or more thus.Cr amounts Lower limit be more preferably 0.05% or more, further preferably 0.10% or more.But it if Cr amounts are higher than 0.30%, is easy MA is generated, therefore the upper limit of Cr amounts is made to be 0.30% or less.The upper limit of Cr amounts is preferably 0.27% hereinafter, more preferably 0.25% Below.

V：Higher than 0% and below 0.050%

V is effective element for the raising of yield strength, and the lower limit of V amounts is preferably 0.001% or more thus.V amounts Lower limit is more preferably 0.002% or more, further preferably 0.003% or more.But it if V amounts are higher than 0.050%, is easy MA is generated, therefore the upper limit of V amounts is made to be 0.050% or less.The upper limit of V amounts is preferably 0.030% hereinafter, more preferably 0.010% or less.

Element is for example above-mentioned in steel used in the present invention, and surplus is substantially iron.But allow certainly because of raw material, goods and materials, system The situation of manufacturing apparatus etc. and mixed inevitable impurity is included in steel.As above-mentioned inevitable impurity, for example, can Enumerate As, Sb, Sn, O, H etc..

Next, being illustrated for the manufacturing method of above-mentioned steel plate.

The steel plate of the present invention, for example, can manufacture in the following way：The slab of slab etc. is made, heating is obtained Slab carries out acceleration cooling again after carrying out hot rolling.

Hereinafter, being described in detail for each process.

First, in casting process, in order in the form of REM and Ca control sulfide, preferably add Al and Zr, make Al₂O₃ It is formed after carrying out deoxidation with ZrO, then adds REM and Ca.Especially Ca is to be easy to form the element of oxide.In addition Ca is compared Oxide (CaO) is more readily formed for formation sulfide (CaS), returns sulphur from CaS in order to prevent, preferably controls to casting and finish Time.Therefore, in molten steel treatment process, when adding Al, Zr, REM and Ca in order, preferably 200 minutes from Ca additions Within so that solidification is finished and is made slab.But after addition REM, to the Ca for adding sulfide Forming ability ratio REM high when Between preferably ensure that at 4 minutes or more.Process in this way, Ca and REM will not form oxide, and be easy to deposit as sulfide .

After being cast in the above described manner, slab is heated, carries out hot rolling.

Heating temperature when heating slab is preferably 1000~1200 DEG C.If heating temperature is too low, the Nb in steel can not Fully solid solution, cannot ensure high-yield strength, therefore the lower limit of heating temperature is more preferably 1100 DEG C or more, further preferably 1120 DEG C or more.But if excessively improving heating temperature, austenite grain coarsening, the low-temperature flexibility deterioration of base material, therefore The upper limit of heating temperature is more preferably 1180 DEG C or less.

Then hot rolling is carried out.Hot rolling start temperature is preferably 900~1100 DEG C.If hot rolling start temperature is too low, cannot Ensure that austenite grain is coarse in the rolling in austenite recrystallization domain, the low-temperature flexibility of base material is possible to deteriorate.Hot rolling is opened thus The lower limit of beginning temperature is more preferably 930 DEG C or more, further preferably 950 DEG C or more.On the other hand, if hot rolling start temperature mistake Height, then the austenite grain after recrystallizing is coarse, and the low-temperature flexibility of base material is possible to deteriorate.The upper limit of hot rolling start temperature thus More preferably 1090 DEG C hereinafter, further preferably 1080 DEG C or less.

Reduction ratio from 950 DEG C to hot rolling end temp is preferably 40~80%.If from 950 DEG C to hot rolling end temp Reduction ratio is too low, then cannot ensure the strain imported into austenite crystal, the coarse grains after bainitic transformation, the low temperature of base material Toughness is possible to deteriorate.The lower limit of reduction ratio is more preferably 50% or more, further preferably 60% or more thus.Another party Face, if excessively high to the reduction ratio of hot rolling end temp from 950 DEG C, the strain into austenite crystal imports superfluous, hardenability drop It is low.The upper limit of reduction ratio is more preferably 77% hereinafter, further preferably 75% or less thus.

Hot rolling end temp is preferably 770~880 DEG C.If hot rolling end temp is too low, the strain into austenite crystal Import superfluous, hardenability reduction.The lower limit of hot rolling end temp is more preferably 790 DEG C or more, further preferably 800 DEG C thus More than.On the other hand, if hot rolling end temp is excessively high, the strain imported into austenite crystal, bainitic transformation be cannot ensure Coarse grains afterwards, the low-temperature flexibility of base material are possible to deteriorate.Thus the upper limit of hot rolling end temp be more preferably 860 DEG C with Under, further preferably 850 DEG C or less.

After hot rolling, acceleration cooling is preferably proceeded as follows.In addition, not necessarily by this term restriction.

The beginning of cooling temperature after hot rolling, preferably 730 DEG C or more.If being less than 730 DEG C, ferrite transformation is promoted Into ferrite is precipitated, therefore metal structure can not become bainite, there is the case where high-yield strength for being difficult to ensure base material.For The lower limit of this beginning of cooling temperature is more preferably 735 DEG C or more, further preferably 740 DEG C or more.The beginning of cooling temperature it is upper Limit is not particularly limited, but more preferably 860 DEG C hereinafter, further preferably 850 DEG C or less.

After hot rolling, acceleration cooling is preferably carried out with 10~50 DEG C/sec of average cooling rate immediately.Accelerate cooling Average cooling rate is preferably 10 DEG C/sec or more, so as to make non-transformed austenite mutually become bainite structure, prevents iron plain The precipitation of body moreover it is possible to improve the highest hardness of bainite is easy that yield strength is made to improve.Average cooling rate thus Lower limit is more preferably 13 DEG C/sec or more, further preferably 15 DEG C/sec or more.On the other hand, average cold higher than 50 DEG C/sec But under speed, although martensitic traoformation occurs for surface of steel plate neighborhood, the yield strength of steel plate rises, the hardness of surface of steel plate It significantly rises, the formability for being configured to steel pipe is easy deterioration, therefore the upper limit of average cooling rate is preferably 50 DEG C/sec or less. If considering the formability for being configured to steel pipe, the upper limit of average cooling rate is more preferably 45 DEG C/sec or less.

The cooling temperature that stops is preferably 370~550 DEG C.It is 370~550 DEG C by making the cooling temperature that stops, MA area occupation ratios It reduces, is easy to get the high-yield strength of 555MPa or more.Therefore the cooling lower limit for stopping temperature being more preferably 390 DEG C or more, Further preferably 400 DEG C or more.The cooling upper limit for stopping temperature being more preferably 540 DEG C hereinafter, further preferably 530 DEG C with Under.

Carry out after being cooled to 370~550 DEG C, if the common cooling for let cool etc. and be cooled to room temperature, can obtain To the non-quenched and tempered steel plate of the present invention.Specifically, average cooling rate at this moment, preferably approximately 0.1~5 DEG C/sec.

The plate thickness of steel plate of the present invention is not particularly limited, but in order to as the lower limit of line pipe, plate thickness be preferably 6mm with On, more preferably 10mm or more.On the other hand, from the cooling velocity for ensuring to need, from the perspective of inhibiting ferritic precipitation, The upper limit of plate thickness is preferably 32mm hereinafter, more preferably 30mm or less.

The non-quenched and tempered steel plate obtained as described so especially can be used as line-pipes and be effectively utilised.In addition, using The line pipe that the non-quenched and tempered steel plate of the present invention obtains reflects that the characteristic of non-quenched and tempered steel plate, the low-temperature flexibility and hardness of HAZ are special Property and yield strength are excellent.

The application is based on Japanese Patent Application No. 2015-237839 CLAIM OF PRIORITYs filed in 4 days December in 2015 Interests.The full content of the specification of Japanese Patent Application No. filed in 4 days December in 2015 2015-237839, For referring to and quoting in the application.

Embodiment

Hereinafter, enumerating embodiment further illustrates the present invention, but the present invention is not limited by following embodiments, can accorded with The range of aftermentioned objective can also be changed implementation before closing, these are all contained in the technical scope of the present invention.

Shown in melting following table 1 slab is used as at the steel grade A~X (surplus is iron and inevitable impurity) being grouped as Afterwards, it is heated with condition shown in following table 2, carries out hot rolling, then cooled down with condition shown in following table 2, manufacture plate thickness：20mm Steel plate.

In detail, in the present embodiment, it is 50% containing Ce, the 35Fe- that La is 20% used as REM 30REM-35Si alloys.In addition, in molten steel treatment process, REM and Ca are added again after carrying out deoxidation with Al and Zr.In addition REM It is added by the sequence of REM, Ca with Ca, the time that Ca additions are added to from REM is 4 minutes or more.In addition, 200 after Ca additions Solidification is set to finish and make slab within minute.

In addition, carrying out after being cooled to the cooling stopping temperature of table 2, is let cool and be cooled to room temperature.Being averaged at this moment is cold But generally 1 DEG C/sec of speed.

The measurement of the area occupation ratio of bainite

The test film of 20mm × 15mm × 15mm is cut from above-mentioned steel plate, the grinding section parallel with rolling direction is real Apply the corrosion of nitric acid ethyl alcohol.Thereafter, the tissue of 1/4 position of plate thickness t is observed using light microscope with 100 times, By image analysis, the area occupation ratio for setting bainite when metal structure is generally 100% is measured.Measurement is aggregated in 3 visuals field It carries out, acquires its average value.In the present embodiment, it for the remnant tissue other than above-mentioned bainite and aftermentioned MA, also carries out It is similarly observed with bainite.

The measurement of the area occupation ratio of MA

The test film of 20mm × 15mm × 15mm is cut from above-mentioned steel plate, the grinding section parallel with rolling direction is real Apply the corrosion of lepera reagents.Thereafter, it for the tissue of 1/4 position of plate thickness t, is seen with 1000 times using light microscope It examines, by image analysis, measures the area occupation ratio for setting MA when metal structure is generally 100%.Measurement be aggregated in 3 visuals field into Row, is averaged.

The measurement of the highest hardness of bainite

The test film that 20mm × 15mm × 15mm is cut from above-mentioned steel plate makes the section parallel with rolling direction expose. Thereafter, for the tissue of 1/4 position of plate thickness t, with the Vickers pyramid hardness testing machine of load 5gf (0.049N), in 100 μ m, 100 μ To measure at equal intervals at 20 points in the range of m.Wherein, using upper 3 points of average value as the highest hardness of bainite.

The measurement of yield strength

From above-mentioned steel plate so that the direction vertical with the rolling direction of steel plate is the lengthwise of test film, is advised based on API5L Lattice cut test film, and 0.5% yield strength is measured as yield strength.Yield strength is X80 grades of API specifications, i.e. 555MPa Above, 705MPa or less is qualified.

The evaluation of the low-temperature flexibility of welding heat affected zone (HAZ)

From the steel plate of No.1~24 of above-mentioned table 2 so that the direction vertical with the rolling direction of steel plate is test film Lengthwise and the test film for cutting 12mm × 32mm × 55mm, as reproducing thermal cycling test piece.For the reproduction thermal cycling test Piece applies the thermal cycle that the maximum heating temperature for the coarse-grain heat affected zone for simulating molten thread neighborhood is 1350 DEG C.In detail, Be heated to 1350 DEG C keep 5 seconds after, 800~500 DEG C temperature ranges place cooling in 30 seconds.Thereafter, it is advised with API5L standards Fixed method implements pendulum impact test, evaluates the low-temperature flexibility of HAZ.About the low-temperature flexibility of HAZ, with -10 DEG C of carry out pendulums Impact test, absorption can be that 27J or more is qualified.

The evaluation of the hardness property of welding heat affected zone (HAZ)

Same as the evaluation of the low-temperature flexibility of welding heat affected zone, from the steel plate of No.1~24 of above-mentioned table 2, extraction is again Existing thermal cycling test piece, applies thermal cycle.Implement Vickers hardness test, evaluates the hardness property of HAZ.The hardness of HAZ indicate with The peak of Vickers hardness when load 98N measures at 3.About the hardness property of HAZ, the hardness of HAZ is closed less than 225HV Lattice.

These results describe in table 2.In addition, bainite, the remnant tissue other than MA is entirely ferrite.

[table 1]

[table 2]

According to this this as a result, it is possible to be investigated as follows.

No.17~24 of table 2 are to use to meet steel grade Q~X given to this invention at the table 1 being grouped as, to meet The example of the manufacturing condition manufacture of No.17~24 of the table 2 of preferred important document specified in the present invention.It understands to obtain HAZ's Low-temperature flexibility and hardness property are good, and the steel plate of the high-yield strength with 555MPa or more.

In contrast, No.1~16 below, are unsatisfactory for a certain of important document given to this invention.

The No.1 of table 2, be used each element at be grouped as meet present invention provide that important document, but use Ceq The example of the steel grade A of big table 1, because Ceq is big, the maximum hardness of HAZ is high, therefore the low-temperature flexibility of HAZ is caused to reduce.

The No.2 of table 2 is to have used B amounts more, the example of the steel grade B of A values and the small table 1 of B values, because of the area of bainite Rate is low, and the highest hardness of bainite is low, so yield strength is low, because B amounts are more, the low-temperature flexibility of HAZ reduces.

The No.3 of table 2 is to have used B amounts and Ti amounts more, the example of the steel grade C of A values and the small table 1 of B values, because of B amounts and Ti Amount is more, so the low-temperature flexibility of HAZ reduces.In addition, although A values and B values are small, B is also compound to be added with higher than 0.0003% Mo, therefore the area occupation ratio of bainite, the highest hardness of bainite and yield strength rise.

The No.4 of table 2 is the example for the steel grade D for having used A values and the small table 1 of B values, because the area occupation ratio of bainite is low, shellfish The highest hardness of family name's body is low, so yield strength is lower.

The No.5 of table 2 is the example of the steel grade E for the table 1 for having used A values small, because the area occupation ratio of bainite is low, is bent Intensity is taken to be lower.

The No.6 of table 2 is the example of the steel grade F for the table 1 for having used B values small, although the bayesian with 80 area % or more Body, but because the highest hardness of bainite is low, yield strength is lower.

The No.7 of table 2 is to have used to be free of Mo, Cu, Ni, Cr and V, the example of the steel grade G of A values and the small table 1 of B values, because To be free of Mo, Cu, Ni, Cr and V, the area occupation ratio of bainite is low, and the highest hardness of bainite is low, so yield strength is low.

The No.8 of table 2 be using C amounts less, the example of the steel grade H of the small table 1 of B values because C amounts are few, bainite it is maximum firmly Spend it is low, so yield strength is lower.

The No.9 of table 2 be used Si amounts less, the example of the steel grade I of the small table 1 of A values because Si amounts are few, the face of bainite Product rate is low, so yield strength is lower.

The No.10 of table 2 is to have used Mn amounts few, the example of the steel grade J of A values and the small table 1 of B values, because Mn amounts are few, bayesian The area occupation ratio of body is low, and the highest hardness of bainite is low, so yield strength is lower.

The No.11 of table 2, be used Mn amounts and Nb amounts less, the example of the steel grade K of A values and the small table 1 of B values, because of Mn amounts Few with Nb amounts, the area occupation ratio of bainite is low, and the highest hardness of bainite is low, so yield strength is lower.

The No.12 of table 2 is to have used Nb amounts few, without Mo, Cu, Ni, Cr and V, the steel grade L's of A values and the small table 1 of B values Example is free of Mo, Cu, Ni, Cr and V because Nb amounts are few, and the area occupation ratio of bainite is low, and the highest hardness of bainite is low, so bending Intensity is taken to be lower.

The No.13 of table 2 is the example for the steel grade M for having used more Ni amounts, A values and the small table 1 of B values, and MA is more, the face of bainite Product rate is low, and yield strength is lower.

The No.14 of table 2 is to have used Cr amounts more, and the example of the steel grade N of A values and the small table 1 of B values, MA is more, the face of bainite Product rate is low, and the highest hardness of bainite is low, and yield strength is lower.

The No.15 of table 2, be used Mn amounts less, the example of the steel grade O for the table 1 that Cr amounts are more, A values and B values are small, Mn amounts are few, MA is more, and the area occupation ratio of bainite is low, and the highest hardness of bainite is low, and yield strength is lower.

The No.16 of table 2 is to have used V amounts more, and the example of the steel grade P of A values and the small table 1 of B values, MA is more, the face of bainite Product rate is low, and the highest hardness of bainite is low, and yield strength is lower.

Claims

1. the hardness of a kind of low-temperature flexibility deterioration inhibiting welding heat affected zone and welding heat affected zone has high yield strong The non-quenched and tempered steel plate of degree, which is characterized in that contained in terms of quality %

C：Higher than 0.04% and below 0.10%,

Si：0.15~0.50%,

Mn：1.20~2.50%,

P：Higher than 0% and below 0.020%,

S：Higher than 0% and below 0.0050%,

Nb：0.020~0.100%,

Ti：0.003~0.020%,

N：0.0010~0.0075%,

Zr：0.0001~0.0100%,

Ca：0.0005~0.0030%,

REM：0.0001~0.0050%,

Al：0.010~0.050% and

B：0.0003% or less and include 0%,

In addition, also containing from Mo：Higher than 0% and 0.30% hereinafter, Cu：Higher than 0% and 0.30% hereinafter, Ni：Higher than 0% And 0.30% hereinafter, Cr：Higher than 0% and 0.30% hereinafter, and V：The group constituted higher than 0% and below 0.050% Middle selection more than one, surplus is made of iron and inevitable impurity,

The Ceq of following formula (1) defined is less than 0.44,

The A values of following formula (2) defined are 2.50 or more, and

The B values of following formula (3) defined are 2.37 or more, and

In 1/4 position of the plate thickness of steel plate, the area occupation ratio of following metal structures meets

Bainite：80 area % or more, and

Island-like martensite：0 area % or more and 0.26 area % hereinafter,

The highest hardness of the bainite is 270HV or more,

Ceq=C+Mn/6+ (Cu+Ni)/15+ (Cr+Mo+V)/5 ... (1)

Value=1.15 A × Mn+2.20 × Mo+6.50 × Nb ... (2)

Value=1.20 B × Mn+0.50 × Ni+4.25 × Nb ... (3)

Wherein, C, Mn, Cu, Ni, Cr, Mo, V and Nb are indicated respectively in terms of quality %, and C, Mn, Cu, Ni, Cr, Mo, V and Nb's contains Amount.

2. non-quenched and tempered steel plate according to claim 1, is used for line pipe.