Low-cost non-annealing cold-rolled heat-resistant steel strip and method for manufacturing same

Abstract

The application discloses a low-cost annealing-free cold-rolled heat-resistant steel strip and a preparation method thereof, and chemical component compositions and mass percentages thereof are as follows: C: 0.12-0.18%, Si: 0.20-0.35%, Mn: 0.30-0.45%, P: 0.015% or less, S: 0.010% or less, Cr: 0.80-0.90%, Mo: 0.40-0.48%, and the rest is iron and inevitable impurity elements. Process steps include: steelmaking, continuous casting, casting blank heating, wire rod rolling, post-rolling cooling and cold-rolled steel strip. The heat-resistant steel strip has the advantages of simple production process, low production cost, low strength of the cold-rolled base material, good plasticity, tensile strength of 620 Mpa or less and section shrinkage of 45% or more, and can be directly cold-rolled without annealing.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of alloy steel, and particularly relates to a low-cost annealing-free cold-rolled heat-resistant steel strip and a preparation method thereof. BACKGROUND

[0002] Heat-resistant steel refers to special steel with high strength and good corrosion resistance at high temperature. According to the use, the heat-resistant steel can be divided into heat-resistant steel and oxidation-resistant steel. The heat-resistant steel is usually used at a temperature of 450-900 DEG C, and is required to have good anti-creep, anti-breaking and oxidation resistance, and can bear periodic fatigue stress, and is used for manufacturing petroleum hydrogenation reactors, internal combustion engine gas valves, high-pressure boiler pipes, steam turbines, gas turbines and blades.

[0003] Structural members serving in high-temperature environment such as boiler pipe supports are usually made of cold-rolled heat-resistant steel strips. The base material of the cold-rolled heat-resistant steel strip is wire rod. From the whole processing process and use, the wire rod is required to have low strength and good plasticity to ensure that the wire rod is not cracked during cold drawing and cold rolling, and to meet the requirements of subsequent high-temperature service. In order to meet the above requirements, Cr, Mo and other heat strengthening alloy elements are usually added to the steel, which causes the steel to easily produce bainite and martensite hard phase structures, and it is difficult to directly cold roll. Therefore, high-temperature annealing is required before cold rolling. In addition, some enterprises use two-fire material process to produce, and the production cost is high, and the market competitiveness is poor. Therefore, it is urgent to develop a low-cost annealing-free cold-rolled heat-resistant steel strip which can be directly cold-rolled. SUMMARY

[0004] The technical problem to be solved by the application is to provide an annealing-free cold-rolled heat-resistant steel strip and a preparation method thereof. The production process is simple, the cost is low, the cold-rolled base material has low strength and good plasticity, the tensile strength is less than or equal to 620 MPa, the reduction of area is greater than or equal to 45%, the steel strip can be directly cold-rolled without annealing, the residual stress of the steel strip after cold rolling is low, the steel strip has the characteristics of high-temperature resistance, corrosion resistance and easy processing, and is suitable for high-temperature environment such as high-pressure boiler pipes and automobile exhaust pipes, and has a wide application prospect.

[0005] To solve the above technical problems, the technical scheme adopted by the application is as follows: a low-cost annealing-free cold-rolled heat-resistant steel strip, the chemical composition of the heat-resistant steel strip is as follows: C: 0.12-0.18%, Si: 0.20-0.35%, Mn: 0.30-0.45%, P≤0.015%, S≤0.010%, Cr: 0.80-0.90%, Mo: 0.40-0.48%, and the rest is iron and inevitable impurity elements.

[0006] The tensile strength of the heat-resistant steel strip is less than or equal to 620 MPa, the reduction of area is greater than or equal to 45%, and the steel strip can be directly cold-rolled without annealing. The cold-rolled steel strip has high-temperature resistance, high pressure resistance and corrosion resistance.

[0007] The heat-resistant steel strip disclosed by the application is mainly composed of ferrite and pearlite.

[0008] The application also provides a preparation method of the low-cost annealing-free cold-rolled heat-resistant steel strip.

[0009] The cold-rolled steel strip process is as follows: the steel strip is cold-rolled for 4-6 times, the pass reduction rate is 10-15%, and the annealing temperature is 650-720 DEG C after the cold rolling to obtain the low-cost annealing-free cold-rolled heat-resistant steel strip.

[0010] The heating temperature is 1120-1180 DEG C, and the heating time is 150-180 min.

[0011] The hot-rolled wire diameter is 12-20 mm.

[0012] The superheat control is 15-40 DEG C, the steel drawing speed is 1.5-2.0 m / min, the crystallizer electromagnetic stirring I = 360 ± 10 A, the end electric stirring I = 370 ± 10 A, and the cross-section size of the cast blank is 150*150 mm.

[0013] The design idea of the application is as follows:

[0014] C: Carbon has a significant solid solution strengthening effect, improves the strength of the steel, and can expand and stabilize austenite to improve the high temperature strength of the heat-resistant steel. Considering the easy processing performance, the C content of the application is 0.12-0.18%.

[0015] Si: Silicon is one of the deoxidizing elements in steel, has a strong solid solution strengthening effect, helps to form and stabilize ferrite, and can form a dense oxide film on the surface of the steel at high temperature to prevent the continuous oxidation of the steel, but too high Si content will reduce the plasticity of the steel. The Si content of the application is 0.20-0.35%.

[0016] Mn: Manganese improves the high temperature strength of the austenitic steel, but damages the oxidation resistance of the heat-resistant steel. In addition, manganese improves the hardenability of the steel, which is beneficial to the formation of martensite supercooled structure, in order to avoid the formation of martensite, the Mn content of the application is 0.30-0.45%.

[0017] Cr: A moderate carbide-forming element. Partial Cr replaces Fe to form alloy cementite, improving carbide stability, effectively preventing graphitization, and enhancing the steel's hot strength. Even after long-term operation, it maintains sufficiently high mechanical properties. At high temperatures, it forms a dense oxide film on the steel surface, preventing further oxidation. It is a key element in improving the oxidation resistance and high-temperature gas corrosion resistance of heat-resistant steel. The Cr content in this invention ranges from 0.80% to 0.90%.

[0018] Mo: Molybdenum exists in the solid solution and carbides of steel, providing solid solution strengthening and significantly improving the hardenability of steel. It can also increase the recrystallization temperature of steel and improve the creep strength of steel through solid solution strengthening. In low-alloy heat-resistant steels, Mo is the most important element affecting hot strength. Mo is easily volatilized and oxidized at high temperatures, and adding too much Mo to steel will adversely affect its high-temperature oxidation resistance. The Mo content in this invention ranges from 0.40% to 0.48%.

[0019] The beneficial effects of adopting the above technical solution are as follows: 1. This invention uses a low-C, low-Mn, and appropriate Cr and Mo heat-resistant steel element composition design, and a short-process design for direct continuous casting and heating rolling of small billets. This ensures that the cold-rolled steel strip material possesses high-temperature resistance and corrosion resistance while maintaining low production costs. 2. This invention employs a reasonable continuous casting process and heating process, providing a prerequisite for mitigating the martensitic and bainitic supercooled structure caused by Cr and Mo steel component segregation. Combined with reasonable controlled rolling and controlled cooling, the cold-rolled strip substrate obtains a fine ferrite and pearlite structure, reducing the strength of the heat-resistant steel material. It can be directly cold-rolled, omitting the pre-rolling annealing process and saving energy. 3. The reasonable cold rolling pass reduction rate and post-rolling annealing process designed in this invention reduce the residual stress of the cold-rolled heat-resistant steel strip, which is beneficial for further processing and use. 4. By adopting the above preparation method, the present invention obtains a substrate that can be directly cold-rolled, with a tensile strength ≤620Mpa, a reduction of area ≥45%, and low residual stress after cold rolling. The cold-rolled steel strip has the characteristics of high temperature resistance, corrosion resistance, easy processing, and low cost, and is suitable for use in high-temperature environments such as high-pressure boiler tubes and automobile exhaust pipes. Attached Figure Description

[0020] Figure 1 This is a metallographic diagram of the heat-resistant steel strip obtained in Example 1 of the present invention;

[0021] Figure 2 This is a metallographic diagram of the heat-resistant steel strip obtained in Example 2 of the present invention;

[0022] Figure 3 This is a metallographic diagram of the heat-resistant steel strip obtained in Example 3 of the present invention. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Example 1

[0024] A low-cost, anneal-free cold-rolled heat-resistant steel strip preparation method includes steelmaking, continuous casting, heating, wire rod rolling, cooling, and cold-rolling steel strip processes; wherein:

[0025] The chemical composition of the heat-resistant steel strip is as follows (by mass percentage): C: 0.12%, Si: 0.25%, Mn: 0.40%, P: 0.015%, S: 0.008%, Cr: 0.85%, Mo: 0.45%, with the remainder being iron and unavoidable impurities.

[0026] Continuous casting process: Smelt according to the above composition, and then continuously cast according to the following parameters, wherein the superheat of continuous casting is controlled at 15℃, the steel pulling speed is 1.5m / min, the electromagnetic stirring of the crystallizer is I=360A, the end electric stirring is I=380A, and the billet with a cross-sectional size of 150×150mm is continuously cast.

[0027] Heating process: The billet is heated to 1150℃ for 150 minutes;

[0028] Wire rod rolling and cooling process: After the billet is heated, it goes through rough rolling, intermediate rolling, finishing rolling, final rolling and wire drawing in sequence. After rolling, it reaches the required size. The final rolling temperature is 780℃, the wire drawing temperature is 880℃, the roller table inlet speed is 9m / min, the roller table increment is 0.8m / min, and the heat insulation cover and fans are all closed.

[0029] Cold-rolled steel strip process: The wire is cold-rolled 4 times with a reduction rate of 10% per pass, and then stress-relief annealing is performed at a temperature of 720°C to obtain the low-cost, anneal-free cold-rolled heat-resistant steel strip.

[0030] By employing the above preparation method, a base material suitable for direct cold rolling was obtained, exhibiting a tensile strength of 600 MPa, a reduction of area of ​​50%, and low residual stress and good plasticity after cold rolling. The microstructure of the hot-rolled base material is mainly ferrite plus pearlite, such as... Figure 1 As shown. Example 2

[0031] A low-cost, anneal-free cold-rolled heat-resistant steel strip and its preparation method include steelmaking, continuous casting, heating, wire rod rolling, cooling, and cold-rolling steel strip processes; wherein:

[0032] The chemical composition of the heat-resistant steel strip is as follows (by mass percentage): C: 0.15%, Si: 0.20%, Mn: 0.45%, P: 0.010%, S: 0.010%, Cr: 0.80%, Mo: 0.40%, with the remainder being iron and unavoidable impurity elements.

[0033] Continuous casting process: Smelt according to the above composition, and then continuously cast according to the following parameters, wherein the superheat of continuous casting is controlled at 25℃, the steel pulling speed is 2.0m / min, the electromagnetic stirring of the crystallizer is I=370A, the end electric stirring is I=360A, and the billet with a cross-sectional size of 150×150mm is continuously cast.

[0034] Heating process: The billet is heated to 1120℃ for 180 minutes;

[0035] Wire rod rolling and cooling process: After the billet is heated, it goes through rough rolling, intermediate rolling, finishing rolling, final rolling and wire drawing in sequence. After rolling, it reaches the required size. The final rolling temperature is 800℃, the wire drawing temperature is 850℃, the roller table inlet speed is 12m / min, the roller table increment is 0.8m / min, and the heat insulation cover and fans are all closed.

[0036] Cold-rolled steel strip process: The wire is cold-rolled 5 times with a reduction rate of 12% per pass, and then stress-relief annealing is performed at a temperature of 650°C to obtain the low-cost, anneal-free cold-rolled heat-resistant steel strip.

[0037] By employing the above preparation method, a base material suitable for direct cold rolling was obtained, exhibiting a tensile strength of 610 MPa, a reduction of area of ​​48%, and low residual stress and good plasticity after cold rolling. The microstructure of the hot-rolled base material is mainly ferrite plus pearlite, such as... Figure 2 As shown. Example 3

[0038] A low-cost, anneal-free cold-rolled heat-resistant steel strip and its preparation method include steelmaking, continuous casting, heating, wire rod rolling, cooling, and cold-rolling steel strip processes; wherein:

[0039] The chemical composition of the heat-resistant steel strip is as follows (mass percentage): C: 0.18%, Si: 0.35%, Mn: 0.45%, P: 0.011%, S: 0.009%, Cr: 0.90%, Mo: 0.48%, with the remainder being iron and unavoidable impurity elements.

[0040] Continuous casting process: Smelt according to the above composition, and then continuously cast according to the following parameters, wherein the superheat of continuous casting is controlled at 40℃, the steel pulling speed is 1.8m / min, the electromagnetic stirring of the crystallizer is I=350A, the end electric stirring is I=370A, and the billet with a cross-sectional size of 150×150mm is continuously cast.

[0041] Heating process: The billet is heated to 1180℃ for 160 minutes;

[0042] Wire rod rolling and cooling process: After the billet is heated, it goes through rough rolling, intermediate rolling, finishing rolling, final rolling and wire drawing in sequence. After rolling, it reaches the required size. The final rolling temperature is 820℃, the wire drawing temperature is 870℃, the roller table inlet speed is 11m / min, the roller table increment is 0.8m / min, and the heat insulation cover and fans are all closed.

[0043] Cold-rolled steel strip process: The wire is cold-rolled 6 times with a reduction rate of 15% per pass, and then stress-relief annealing is performed at a temperature of 680℃ to obtain the low-cost, anneal-free cold-rolled heat-resistant steel strip.

[0044] By employing the above preparation method, a base material suitable for direct cold rolling was obtained, exhibiting a tensile strength of 620 MPa, a reduction of area of ​​45%, and low residual stress and good plasticity after cold rolling. The microstructure of the hot-rolled base material is mainly ferrite plus pearlite, such as... Figure 3 As shown.

[0045] The above embodiments are only used to illustrate and not limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention without departing from the spirit and scope of the present invention. Any modifications or partial substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A low-cost, anneal-free, cold-rolled heat-resistant steel strip, characterized in that, The heat-resistant steel strip has the following chemical composition by mass percentage: C: 0.12–0.18%, Si: 0.20–0.35%, Mn: 0.30–0.45%, P≤0.015%, S≤0.010%, Cr: 0.80–0.90%, Mo: 0.40–0.48%, with the remainder being iron and unavoidable impurities. The heat-resistant steel strip is prepared by the following method: including steelmaking, continuous casting, heating, wire rod rolling, cooling, and... The cold-rolled steel strip process; the wire rod rolling and cooling process is as follows: the billet is rolled into wire rod, wherein the final rolling temperature is 780-820℃, the wire drawing temperature is 850-880℃, the roller table inlet speed is 9-12m / min, the roller table increment is 0.8m / min, and the heat insulation cover and fan are all turned off; the cold-rolled steel strip process is as follows: cold rolling 4-6 times, the reduction rate per pass is 10-15%, and stress-relief annealing is performed after cold rolling, with an annealing temperature of 650-720℃.

2. The low-cost, anneal-free, cold-rolled heat-resistant steel strip according to claim 1, characterized in that, The heat-resistant steel strip has a tensile strength ≤620MPa and a reduction of area ≥45%, and can be cold-rolled directly without annealing.

3. The low-cost, anneal-free cold-rolled heat-resistant steel strip according to claim 1, characterized in that, The microstructure of the hot-rolled substrate of the heat-resistant steel strip is mainly ferrite plus pearlite.

4. A method for preparing a low-cost, anneal-free cold-rolled heat-resistant steel strip according to any one of claims 1-3, characterized in that, The method includes steelmaking, continuous casting, heating, wire rod rolling, cooling, and cold-rolled steel strip processes. The wire rod rolling and cooling processes are as follows: the billet is rolled into wire rod, with a final rolling temperature of 780-820℃, a wire drawing temperature of 850-880℃, a roller table inlet speed of 9-12 m / min, and a roller table increment of 0.8 m / min. The heat insulation cover and fans are all turned off. The cold-rolled steel strip process is as follows: cold rolling for 4-6 passes, with a pass reduction rate of 10-15%, followed by stress-relief annealing at a temperature of 650-720℃.

5. The method for preparing a low-cost, anneal-free, cold-rolled heat-resistant steel strip according to claim 4, characterized in that, The heating process involves a heating temperature of 1120–1180°C and a heating time of 150–180 min.

6. The method for preparing a low-cost, anneal-free, cold-rolled heat-resistant steel strip according to claim 4, characterized in that, In the hot-rolled wire rod process, the diameter of the hot-rolled wire rod is 12-20 mm.

7. A method for preparing a low-cost, anneal-free, cold-rolled heat-resistant steel strip according to any one of claims 4-6, characterized in that, The superheat of the continuous casting process is controlled at 15–40°C, and the steel pulling speed is 1.5–2.0 m / min.

8. A method for preparing a low-cost, anneal-free cold-rolled heat-resistant steel strip according to any one of claims 4-6, characterized in that, The electromagnetic stirring of the crystallizer in the continuous casting process is I=360±10A, and the end electric stirring is I=370±10A.

9. A method for preparing a low-cost, anneal-free cold-rolled heat-resistant steel strip according to any one of claims 4-6, characterized in that, The cross-sectional dimensions of the billet in the continuous casting process are 150*150mm.

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