CN110273109A - A kind of 450MPa grades of submerged pipeline roll of steel plate and preparation method thereof - Google Patents

Abstract

The invention discloses a 450MPa grade submarine pipeline steel plate coil with excellent mechanical properties and low cost and a preparation method thereof, comprising the following chemical components in weight percentage: C: 0.040%-0.060%, Si: 0.20%-0.40%, Mn : 1.40%～1.60%, Nb: 0.040%～0.060%, Ti: 0.010%～0.030%, Als: 0.020～0.040%, S≤0.0020%, P≤0.015%; the rest are Fe and unavoidable impurity elements. It contains very low carbon content and has very low sulfur and phosphorus contents. Under the TMCP process system, the controlled rolling and controlled cooling processes are adjusted to obtain a uniform ferrite + fine pearlite structure. The material has a grain size of 10-12, a band structure of 1.0, and low non-metallic inclusions. It has a yield strength higher than 450MPa, an elongation greater than 30%, and an impact energy greater than 300J at -20°C, with good toughness.

Description

A kind of 450MPa class submarine pipeline steel coil and its preparation method

technical field

The invention belongs to the technical field of preparation of submarine pipeline steel, and in particular relates to a 450MPa grade submarine pipeline steel coil and a preparation method thereof.

Background technique

my country's seabed oil and natural gas are widely distributed in the four sea areas of "East, South, Bohai, and Yellow River". With the increasing demand for energy, the exploration and development of seabed oil and gas resources have also been further strengthened. Support for oil and gas exploration and development was further strengthened. At the same time, in the 2018 national major project "High-end Equipment and New Materials", key researches were carried out on deep-sea oil and gas storage and transportation and pipelines. Various policies, etc. will surely promote subsea oil and gas exploration and construction and development of subsea pipelines.

Submarine pipelines are in harsh service environments such as low temperature, high pressure, surge, vortex induction, and strong corrosion. Submarine pipelines need to withstand large plastic deformation and crush resistance. Lower yield ratio, high strain hardening index, high uniform elongation, etc.

In the prior art, 450MPa steel plate coils for submarine pipelines are mostly produced by adding chromium, vanadium, nickel, etc., or increasing the thickness of the steel plate coils. The production cost of such steel plate coils is high and the mechanical properties are unstable.

Contents of the invention

In order to solve the above-mentioned technologies, the present invention provides a 450MPa class submarine pipeline steel coil with excellent mechanical properties and low cost and a preparation method thereof.

The technical scheme that the present invention takes is:

A 450MPa class submarine pipeline steel coil, comprising the following chemical components in weight percentage: C: 0.040%-0.060%, Si: 0.20%-0.40%, Mn: 1.40%-1.60%, Nb: 0.040%-0.060%, Ti : 0.010%～0.030%, Als: 0.020～0.040%, S≤0.0020%, P≤0.015%; the rest is Fe and unavoidable impurity elements.

Further, it is preferred to include the following chemical components in weight percentage: C: 0.044% to 0.051%, Si: 0.24% to 0.31%, Mn: 1.48% to 1.53%, Nb: 0.049% to 0.056%, Ti: 0.014% to 0.026%, Als: 0.021～0.034%, S≤0.0012%, P≤0.011%; the rest is Fe and unavoidable impurity elements.

The metallographic structure of the 450MPa submarine pipeline steel coil is acicular ferrite + pearlite, the grain size is 10.0-12.0, and the banded structure is ≤ 1.0.

The transverse mechanical properties of the 450MPa class submarine pipeline steel coil: Rt0.5: 503-520MPa, Rm: 607-623MPa, _A50 : 37.5%-42.5%; longitudinal mechanical properties: Rt0.5: 481-489MPa, Rm: 593~605MPa, A ₅₀ : 39%~42%; both transverse and longitudinal impact energy at -20°C are greater than 300J.

The present invention also provides a preparation method for the 450MPa-grade submarine pipeline steel coil, the preparation method comprising the following steps: pretreatment of molten iron, compound blowing at the top and bottom of the converter, alloy fine-tuning, refining in LF and RH furnaces, continuous casting of slabs, Heating, 2-stand rough rolling + 7-stand finish rolling, laminar cooling, coiling.

Further, molten iron pretreatment: control the molten iron [S] after desulfurization to ≤0.0020%, and the bright surface after slag removal ≥70%.

End point control of converter smelting: [C] ≤ 0.035%, [P] ≤ 0.010%, [S] ≤ 0.0100%; most alloys are added during the tapping process to make the composition of molten steel reach or approach the lower limit of internal control; do a good job of slag blocking operation to prevent falling Slag back to phosphorus.

Refining in LF furnace: Ladle top slag is fully reduced, the end point [S]≤0.0020%, and the content is adjusted to the target value or close to the target value.

Refining in RH furnace: adjust all components to the target value; vacuum treatment to make molten steel [H]≤1.5ppm.

In the slab continuous casting process, the quenching time of molten steel is not less than 20 minutes, the stopper is blown with argon at 4-6 NL/min, the casting speed is constant, the fluctuation range of the liquid level is controlled within ± 3 mm, and finally a slab with a thickness of 230 mm is cast.

After the step of continuous casting of slabs, a step of slow cooling of cast slabs is also included, and the step of slow cooling of cast slabs is stacked for more than 48 hours, preferably 50-55 hours.

In the heating step, the heating temperature is controlled at 1170-1210°C, and the soaking time is not less than 60 minutes.

In the 2-stand rough rolling + 7-stand finish rolling step, the rough rolling temperature is controlled at 1000-1060°C, the finish rolling temperature is controlled at 900-1000°C, and 7 four-roll CVC mills are used in the finish rolling stage Continuous rolling is carried out, the cumulative deformation is ≥60%, and the final rolling temperature is controlled at 830-870°C.

The laminar cooling method is post laminar cooling, the cooling rate is controlled at 20-30°C/s, the coiling temperature of the cooled steel plate is controlled at 500-600°C, and air-cooled to room temperature after coiling.

Further, the coiling temperature is preferably 558-572°C.

The present invention mainly adopts ultra-low C, low Si, low P, and low S in composition design. C: 0.04% to 0.06% is a necessary element to ensure strength. In order to ensure strength, the lower limit of C content must be guaranteed to be 0.04%, but C As the content increases, the toughness, weldability and corrosion resistance of the material will all decrease, so the upper limit is set at 0.06%. Mn is an effective element to ensure strength, but it is easy to segregate, and if the content is too high, it will affect the toughness and corrosion resistance. Therefore, the present invention considers that the content of Mn should be controlled at 1.40%-1.60%. P and S are harmful impurity elements in steel, which will induce segregation and increase the brittleness of the material. Therefore, the lower the content, the better.

The preferred Nb content of the present invention is 0.040% to 0.060%, preferably 0.049 to 0.056%. The addition of Nb can significantly increase the recrystallization temperature of the steel plate and expand the temperature range of the non-recrystallization zone, thereby enabling high temperature rolling and reducing the load on the rolling mill; At the same time, Nb can also form Nb (C, N) precipitates with C and N in the steel, thereby increasing the strength. If the Nb is too low, the expected strength target will not be achieved, and if the Nb is too high, the cost will be greatly increased. Increase.

The preferred Ti content of the present invention is 0.010% to 0.030%, preferably 0.014 to 0.026%. Adding Ti can refine the grains and improve the toughness of the steel, and Ti is beneficial to the grains in the heat-affected zone during welding. Control and improve the toughness of the heat-affected zone of the weld.

The content of AlS in the present invention is 0.020-0.040%, preferably 0.021-0.034%, mainly plays a role of deoxidation, reduces the oxygen content in the steel, forms AlN at the same time, and refines the crystal grains.

In the hot rolling process design of the present invention, the heating temperature is controlled at 1170-1210°C, and the soaking section holding time is not less than 60min. Excessive growth of austenite grains.

Then two-stage rolling is adopted. The first stage is rolling in the recrystallization zone. The rolling temperature is controlled at 1000-1060°C. Through repeated deformation and recrystallization, the austenite grains are significantly refined. Rolling in the recrystallization zone, the finish rolling temperature is controlled at 900-1000 ° C, is the stage of deformation and phase transformation at the same time, in this stage, the austenite grains are elongated, and slip bands and austenite grain boundaries are produced at the same time The increase and the appearance of slip bands provide favorable conditions for ferrite nucleation, and then fine-grained ferrite is obtained.

For thick-walled submarine pipeline steel, a higher cooling rate should be adopted, but the final cooling temperature should not be too low to prevent the appearance of island martensite. For this reason, the rapid cooling after rolling is set, the cooling rate is 20-30°C/s, cooled to 500-600°C, and coiled, which can reduce the precipitation of pro-eutectoid ferrite and pearlite, and make the austenite structure There is sufficient space for precipitation of acicular ferrite structure.

The invention discloses a seabed pipeline steel coil with excellent mechanical properties and low cost, which contains very low carbon content, and has extremely low sulfur content and phosphorus content. Under the TMCP process system, the controlled rolling and controlled cooling processes are adjusted to obtain a uniform acicular ferrite + pearlite structure. The material has a grain size of 10-12, a band structure of 1.0, and a low non-metallic structure. Inclusions make it have a yield strength higher than 450MPa, elongation greater than 30%, impact energy greater than 300J at -20°C, and good toughness.

Description of drawings

Fig. 1 is a metallographic structure diagram of a steel plate coil for a submarine pipeline in Example 1 of the present invention.

Detailed ways

The present invention will be described in detail below in conjunction with examples.

According to the chemical composition requirements provided by the present invention, molten iron pretreatment→converter steelmaking→alloy fine-tuning station→LF refining outside furnace→continuous casting process is adopted for smelting. After refining outside the LF furnace, the chemical composition in the steel meets the weight percentage (wt%): C: 0.040% ~ 0.060%, Si: 0.20% ~ 0.40%, Mn: 1.40% ~ 1.60%, Nb: 0.040% ~ 0.060% , Ti: 0.010% to 0.030%, Als: 0.020 to 0.040%, S≤0.0020%, P≤0.015%, and the rest are Fe and unavoidable impurity elements. The whole process of continuous casting is protected casting.

The chemical composition of each embodiment of the present invention and comparative example is shown in Table 1. Composition detection is carried out according to GB/T4336 "Carbon Steel and Medium and Low Alloy Steel Spark Source Atomic Emission Spectroscopic Analysis Method (conventional method)".

The chemical composition of each embodiment of the present invention in table 1

The rolling process adopts slab heating to 1160～1200℃→high pressure water descaling→2-stand rough rolling→7-stand finish rolling→laminar cooling→coiling, main rolling process parameters and tensile mechanical properties of test steel As shown in Table 2 and Table 3.

Table 2 main process parameters

Table 3 mechanical properties

The test results of the Charpy V-type impact energy of the test steel of the present invention are shown in Table 4.

The energy of impact of table 4 test steel of the present invention

The inspection results of non-metallic inclusions in the test steel of the present invention are shown in Table 5.

Table 5 The non-metallic inclusions of test steel of the present invention

In summary, according to the design range of steel chemical composition and rolling process control technology of the present invention, the performance of the steel in the example is significantly better than that in the comparative example: its transverse mechanical properties: Rt0.5: 503-520MPa, Rm: 607-623MPa , A ₅₀ : 37.5%～42.5%; Longitudinal mechanical properties: Rt0.5: 481～489MPa, Rm: 593～605MPa, A ₅₀ : 39%～42%; Transverse and longitudinal impact energy at -20°C is greater than 300J; finished product The mechanical properties are stable, the grain size is 10-12 grades, and the banded structure is ≤1.0 grade.

The above detailed description of a 450MPa class submarine pipeline steel coil and its preparation method with reference to the above examples is illustrative rather than restrictive, and several examples can be listed according to the limited scope, so without departing from the present invention Changes and modifications under the general concept should fall within the protection scope of the present invention.

Claims (10)

1. a kind of 450MPa grades of submerged pipeline roll of steel plate, which is characterized in that the chemical component including following weight percent: C: 0.040%~0.060%, Si:0.20%~0.40%, Mn:1.40%~1.60%, Nb:0.040%~0.060%, Ti: 0.010%~0.030%, Als:0.020~0.040%, S≤0.0020%, P≤0.015%；Remaining is for Fe and unavoidably Impurity element.

2. 450MPa grades of submerged pipeline roll of steel plate according to claim 1, which is characterized in that including following weight percent Chemical component: C:0.044%~0.051%, Si:0.24%~0.31%, Mn:1.48%~1.53%, Nb:0.049% ~0.056%, Ti:0.014%~0.026%, Als:0.021~0.034%, S≤0.0012%, P≤0.011%；Remaining For Fe and inevitable impurity element.

3. 450MPa grades of submerged pipeline roll of steel plate according to claim 1 or 2, which is characterized in that the sea 450MPa grades of The metallographic structure of bottom tube line roll of steel plate be acicular ferrite+pearlite, 10.0~12.0 grades of grain size, banded structure≤1.0 grade.

4. 450MPa grades of submerged pipeline roll of steel plate according to claim 1 or 2, which is characterized in that the sea 450MPa grades of The horizontal mechanical performance of bottom tube line roll of steel plate: Rt0.5:503~520MPa, Rm:607~623MPa, A₅₀: 37.5%~ 42.5%；Vertical mixing coefficient: Rt0.5:481~489MPa, Rm:593~605MPa, A₅₀: 39%~42%；It is horizontal at -20 DEG C Impact of collision function is all larger than 300J.

5. the preparation method of 450MPa grades of submerged pipeline roll of steel plate according to any one of claims 1-4, feature exist In the preparation method comprises the following steps: molten iron pretreatment, the fine tuning of converter top bottom blowing, alloy, LF and RH furnace essence Refining, heating ,+7 rack finish rolling of 2 rack roughing, section cooling, is batched sheet billet continuous casting.

6. preparation method according to claim 5, which is characterized in that in the sheet billet continuous casting technique, the molten steel calmness time Not less than 20min, 4~6NL/min of stopper Argon, permanent pulling rate operation, liquid fluctuating scope control is in ± 3mm.

7. preparation method according to claim 5, which is characterized in that further include slab slow cooling after the sheet billet continuous casting step Step, casting blank stacking slow cooling 48 hours or more.

8. preparation method according to claim 5, which is characterized in that in the heating stepses, heating and temperature control exists 1170~1210 DEG C, soaking zone soaking time is not less than 60min.

9. preparation method according to claim 5, which is characterized in that in+7 rack finish rolling step of 2 rack roughing, slightly Roll rolling temperature control at 1000~1060 DEG C, the finish rolling stage carries out tandem rolling using 7 frame high CVC mills, add up deflection >= 60%, finishing temperature control is at 830~870 DEG C.

10. preparation method according to claim 5, which is characterized in that the section cooling mode is back segment section cooling, Cooling velocity is controlled in 20~30 DEG C/s, is controlled coiler plate temperature after cooling at 500~600 DEG C, is air-cooled to room after batching Temperature.