JP2730800B2 - Manufacturing method of ERW steel pipe with excellent fire resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is directed to a steel pipe used for manufacturing a structure. The steel pipe has a sufficient strength at the time of a fire and has excellent fire resistance even if the coating of a refractory material is simplified or omitted. And a method for producing the same.

[0002]

2. Description of the Related Art In recent years, in various fields dealing with steel materials,
Various demands have been increasing, such as improvement of use characteristics for improvement of competitiveness and reduction of manufacturing cost. Among them, in the field of construction, in particular, improvement of fire resistance characteristics is desired for improvement of safety of structures.

Hitherto, in a structure such as a steel frame structure, in order to ensure sufficient strength even in the event of a fire, a steel material is coated with a rock wool or the like so that the temperature of the steel material is not required to rise to 350 ° C. or more. Was. In recent years, the Building Standards Law has been revised, and it has become possible to simplify or omit the refractory coating according to the strength of steel at high temperatures. That is, if the steel material is 600
It is said that if it has a sufficient strength at a high temperature such as ℃ (2/3 or more of the normal yield strength at room temperature), the refractory coating can be omitted and bare use is possible.

The strength of steel materials at high temperatures has been well studied, and the developed materials have been standardized as steel for boilers or steel for pressure vessels. In addition, Tokubo Sho 5
As described in JP-A-1-15188, various improvements and
Development is ongoing. These are steel materials having high strength in long-time use such as tens of thousands or hundreds of thousands of hours at high temperature, that is, high creep strength.

[0005]

The refractory properties to be solved by the present invention are the strength within at most several hours at the time of a fire, and are completely different from the high-temperature strength which has long been the object of development. This is an important characteristic in the case of omitting the refractory coating in a structure such as a steel frame structure.
It is an object of the present invention to provide a steel pipe whose strength at ° C is significantly improved as compared with conventional steel.

[0006]

The inventors of the present invention have conducted a number of experiments and detailed studies to impart fire resistance to ERW steel pipes.
It has been found that the composite addition of o and Nb, the composite addition of Mo and V, and the composite addition of Mo, Nb and V are effective.
In other words, when the material is exposed to high temperatures, Mo carbides and Mo
And Nb, or a complex carbide of Mo and V, are finely dispersed and precipitated on dislocations introduced in the formation of the ERW steel pipe, thereby inhibiting the movement of the dislocation generated at a high temperature.

At that time, from the above Mo alone,
It was also found that the composite additive was more effective, because the composite addition promoted the precipitation of carbides and increased the absolute amount of precipitates.

The present invention has made it possible to manufacture a steel pipe having excellent fire resistance based on such knowledge. The gist of the present invention is that Mo is contained in an amount of 0.10 to 0.40% by weight%.
Less than 0.10 or 0.40% of Mo
And Nb: 0.010-0.15%, V:
A low-carbon steel containing one or two kinds of 0.010 to 0.30% is hot-rolled in a normal step, manufactured into an electric resistance welded steel pipe in a normal step, and then 200 to 600 ° C. as necessary. Characterized by tempering in the temperature range of This is a method for producing an electric resistance welded steel pipe having excellent fire resistance.

[0009]

In the present invention, the components of the electric resistance welded steel pipe are specified,
The tube is used as it is, and in some cases, the heat treatment after the tube is made to be about the temper has succeeded in improving the fire resistance.

Next, the components of the present invention, hot rolling, steel pipe production,
The tempering conditions will be described.

According to the method of the present invention, Mo: 0.10 or more and 0.40%
Low-carbon steel containing less than Mo: 0.10 or more and 0.40 or less
% : Nb: 0.010 to 0.15% and V: 0.01
Good results can be obtained by applying the present invention to a low carbon steel containing 0 to 0.30% of one or two kinds or a low carbon low alloy steel to which a special element is added. Other preferable component compositions include: C: 0.03 to 0.30% Si: 0.02 to 0.50% Mn: 0.20 to 2.00% Al: 0.001 to 0.100% N: Depending on the required properties of the low carbon steel or the strength steel containing 0.0005 to 0.0100% as a component, Cu: 2.0% or less Ni: 9.5% or less Cr: 5.5% or less Ti: 0.15 % Or less B: 0.0003% to 0.0030% Ca: 0.0080% or less One or more of these may be added.

As described above, Mo is indispensable for finely dispersing and precipitating as a carbide in ferrite when steel is exposed to a high temperature and inhibiting the movement of dislocation generated at a high temperature. 10% or more is added, but if the added amount is too large, the weldability is impaired, so the content is limited to less than 0.4% as an upper limit.

Nb is added in order to form a composite carbide with Mo, or Nb is useful for refining austenite grains and increasing the strength, and is added in an amount of 0.010% or more. The upper limit of the amount is 0.15%.

V, like Nb, is added in an amount of 0.010% or more to form a composite carbide with Mo. It is also useful for precipitation strengthening, but if it increases, the weldability is impaired. Therefore, the upper limit of the content is 0.3%.

As described above, in the present invention, the addition of Mo is indispensable, but when Nb or V is added in combination, the absolute value of the amount of carbide precipitation increases, and the fire resistance is further improved. I know.

Further, C, Si, M in the preferable component range are set.
n, Al, and N may be in a generally used component range. C is an element indispensable for securing the strength of the steel. Usually, 0.03% or more is added, but 0.30% If contained in excess of, the toughness of the steel material will be significantly deteriorated,
The range was set to 0.03 to 0.30%.

Si has the effect of improving the strength and ductility of the steel by the solid solution strengthening effect, and is required to be 0.02% or more. However, if it exceeds 0.50%, the toughness of the steel is deteriorated. Therefore, the range is 0.02-0.
50%.

Since Mn is an element necessary for strength, it is necessary to add 0.20 to Mn.
%, But the upper limit is set to 2.0% in order to ensure weldability and toughness.

Al is necessary for deoxidation at the steel making stage, and the lower limit is made 0.001%. However, if the content is too large, the absolute value of the inclusion itself increases, so the upper limit was made 0.10%.

If the content of N is too large, the toughness of the steel material is degraded. Therefore, the upper limit is set to 0.0100%, but the lower limit is set to 0.000% in consideration of the cost increase from the steelmaking capacity.
5%.

The components added for the purpose of increasing the strength are described below. First, Cu is useful for increasing the strength and improving the corrosion resistance. However, even if added over 2.0%, almost no increase in the strength is obtained. Therefore, the upper limit of the content is 2.
0%.

Ni is useful for improving low-temperature toughness, but its content is limited to 9.5% because it is an expensive element.

Cr is useful for increasing the strength and improving the corrosion resistance. However, the content is limited to 5.5% as the upper limit because the Cr content hinders the low-temperature toughness and weldability.

[0024] Ti is useful for refining austenite grains and is added. However, if it is increased, the weldability is impaired. Therefore, the upper limit of the content is 0.15%.

B has an effect of significantly increasing the hardenability of steel when added in a small amount. In order to effectively obtain this effect, it is necessary to add at least 0.0003%. However, an excessive addition generates a B compound and deteriorates toughness, so the upper limit is made 0.0030%.

[0026] Ca is useful for controlling the form of sulfide-based inclusions, but if it is increased, it forms inclusions in the steel and deteriorates the properties of the steel. Therefore, the upper limit of the content is 0.0080%. There are no particular restrictions on the hot rolling conditions. Depending on the required characteristics of the final product, the crystal grain size and the strength level according to the finish rolling conditions may be considered, and the strength level according to the winding conditions may be considered.

There are no particular restrictions on the production of steel pipes as long as they are ERW steel pipes. The requirements for ERW steel pipes are:
This is because this steel pipe manufacturing method can uniformly introduce a large amount of dislocations in the manufacturing process. That is, fine dispersion precipitation of Mo carbide or composite carbide of Mo and Nb or V for obtaining refractory properties occurs with the introduced dislocation as a nucleus, and if there is no dislocation, there is no nucleus for precipitation. As a result, finely dispersed precipitation of carbides cannot occur, and thus the refractory properties are not improved. It is for this reason that the method of manufacturing the steel pipe is specified for the ERW steel pipe.

By the way, depending on the type of steel, there is a case that the toughness is not good when formed into an electric resistance welded steel pipe, and a tempering treatment is required in order to improve the toughness. At this time, if the tempering temperature is too high, the dislocations disappear, and the precipitation nuclei of carbides disappear, and the refractory properties deteriorate.
Therefore, the upper limit was set to 600 ° C. However, when the tempering temperature is low and lower than 200 ° C., the effect of tempering hardly occurs, and the toughness may not be improved. Therefore, the lower limit is set to 200 ° C.

[0029]

EXAMPLES Table 1 shows the chemical composition of the test material, and Table 2 shows the size of the steel pipe, heat treatment conditions, and the mechanical properties of the obtained steel pipe. The numerical values in Table 1 are wt%, but Ca, B, N
Is shown in ppm.

[0030]

[Table 1]

[0031]

[Table 2]

The steel pipe No. shown in Table 2 was used. A1, B1, C
1, D1, H1, I1, J1, K1, M1, O1, P
1, Q1, R1, S1, T1, and V1 are examples of the present invention, and the high-temperature strength (YS6
00 / TSRT> 0.40) at the same time.

On the other hand, A2 does not have sufficient fire resistance because the heating temperature in the temper is too high.

B2 also does not have sufficient fire resistance because the tempering temperature is too high. E1 and F1 have low strength at high temperatures because Mo is not added.

[0035] H1 to J1 are Y since Mo is a single additive.
S600 / TSRT> 0.40, but the other material of the present invention is a composite additive of Mo and Nb or V,
YS600 / TSRT> 0.45 is satisfied. This is described in the remarks column of Table 2.

[0036]

As described in detail above, the present invention makes it possible to manufacture inexpensively a steel pipe having high strength of 40 kgf / mm ² or more and excellent in fireproof properties without using specially expensive alloying elements. The effect is great in industry.

Claims (4)

(57) [Claims] 1. Mo is 0.10 or more and 0.4 % by weight.
A method for producing an electric resistance welded steel pipe having excellent fire resistance, wherein low-carbon steel containing less than 0% is hot-rolled in an ordinary step to produce an electric resistance welded steel pipe in an ordinary step. 2. Mo is 0.10 to 0.4 % by weight.
Less than 0% , and Nb: 0.010 to 0.15%,
V: Low-carbon steel containing one or two kinds of 0.010 to 0.30% is hot-rolled in a normal process and manufactured into an electric resistance welded steel tube in a normal process, and is characterized by fire resistance. Method for producing ERW steel pipes with excellent quality. 3. Mo is 0.10 to 0.4 % by weight.
A low-carbon steel containing less than 0% is hot-rolled in a normal process, manufactured into an ERW pipe in a normal process, and then 200 to 6%.
A method for producing an electric resistance welded steel pipe having excellent fire resistance, characterized by tempering in a temperature range of 00 ° C. 4. Mo is 0.10 to 0.4 % by weight.
Less than 0% , and Nb: 0.010 to 0.15%,
V: Low carbon steel containing one or two kinds of 0.010 to 0.30% is hot-rolled in a usual process, manufactured into an electric resistance welded steel tube in a usual process, and then heated to a temperature of 200 to 600 ° C. A method for producing an electric resistance welded steel pipe having excellent fire resistance, characterized by tempering in a range.