A 500MPa-grade economical high-strength ferritic stainless steel medium and thick plate and its preparation method

Abstract

The present invention discloses a 500MPa-grade economical high-strength ferritic stainless steel medium and thick plate and its preparation method. The invention relates to the field of high-strength stainless steel medium and thick plate production processes. The plate's chemical composition is as follows: C, Cr, Ni, Si, Mn, P, S, Ti, Nb, Als, and N; the remainder is Fe and unavoidable impurity elements. The preparation process includes raw material preparation, heating and phosphorus removal, rolling, quenching, and tempering heat treatment, thereby producing the 500MPa-grade economical high-strength ferritic stainless steel medium and thick plate. The plate, controlled by low-cost alloy composition design and production methods, achieves a yield strength exceeding 500MPa, and exhibits high elongation, good low-temperature impact toughness, and excellent corrosion resistance. The plate features a simple alloy composition, minimal process steps, ease of operation, and low production cost, making it widely applicable to coastal construction steel and offshore platforms.

Description

Technical Field

[0001] The invention belongs to the field of high-strength stainless steel medium and thick plate production technology, and relates to a 500MPa-grade economical high-strength ferritic stainless steel medium and thick plate and a preparation method thereof. Background Art

[0002] Stainless steel is widely used in various industries, including construction, shipbuilding, petroleum, chemical industry, national defense, and daily necessities, due to its corrosion resistance, high temperature resistance, wear resistance, and beautiful appearance. With the rapid development of industries such as marine engineering and bridge construction, the demand for high-strength, high-toughness, and high-corrosion-resistant stainless steel medium and thick plates is increasing.

[0003] Ferritic and austenitic stainless steels have low strength, with yield strengths generally only 200-300 MPa. Martensitic stainless steels are brittle due to their structural characteristics. Duplex stainless steels have complex heat treatment processes, high alloy content, and high production costs. Therefore, the development of high-strength, high-toughness, high-corrosion-resistant, and economical stainless steel medium and thick plates is an important development direction. Summary of the Invention

[0004] Purpose of the invention: The purpose of the present invention is to improve the strength of ferritic stainless steel through low-cost alloy composition design, microstructure regulation and production process control, and to provide a 500MPa grade economical high-strength ferritic stainless steel medium and thick plate and its preparation method with high elongation, good low-temperature impact toughness and excellent corrosion resistance.

[0005] Technical solution: The 500MPa-grade economical high-strength ferritic stainless steel medium and thick plate described in the present invention has the following chemical composition and mass percentage: C: 0.05-0.08%, Cr: 15.0-19.0%, Ni: 0.8-1.8%, Si: 0.2-0.6%, Mn: 0.5-0.8%, P≤0.015%, S≤0.003%, Ti: 0.10-0.20%, Nb: 0.010-0.020%; Als: 0.015-0.045%, N: 0.006-0.012%, and the rest are Fe and unavoidable impurity elements.

[0006] Furthermore, its chemical composition and mass percentage are as follows: C: 0.05%, Cr: 15.0%, Ni: 0.8%, Si: 0.2%, Mn: 0.5%, P: 0.010%, S: 0.001%, Ti: 0.10%, Nb: 0.010%; Als: 0.015%, N: 0.006%, and the rest are Fe and unavoidable impurity elements.

[0007] Furthermore, its chemical composition and mass percentage are as follows: C: 0.08%, Cr: 19.0%, Ni: 1.8%, Si: 0.6%, Mn: 0.8%, P: 0.015%, S: 0.003%, Ti: 0.20%, Nb: 0.020%; Als: 0.045%, N: 0.012%, and the rest are Fe and unavoidable impurity elements.

[0008] Furthermore, its chemical composition and mass percentage are as follows: C: 0.065%, Cr: 17.5%, Ni: 1.3%, Si: 0.4%, Mn: 0.65%, P: 0.012%, S: 0.002%, Ti: 0.15%, Nb: 0.015%; Als: 0.030%, N: 0.009%, and the rest are Fe and unavoidable impurity elements.

[0009] Furthermore, a method for preparing a 500MPa grade economical high-strength ferritic stainless steel medium and thick plate is provided, wherein the preparation process is as follows:

[0010] (1): Prepare raw materials;

[0011] (2): Heating and phosphorus removal process;

[0012] (3): rolling process;

[0013] (4): Quenching process;

[0014] (5): Tempering heat treatment process.

[0015] Furthermore, in step (1), the raw material is prepared as follows: the raw material is low-nickel chromium iron, and is smelted into a casting billet of the above composition through the production process of EAF-V0D-LF refining-continuous casting;

[0016] Among them, electromagnetic stirring and soft reduction technology are used in the continuous casting process.

[0017] Furthermore, in step (2), the heating process is specifically as follows: heating the ingot in a heating furnace to 1140-1200° C., with a total heating time of 1.0-1.6 mm / min;

[0018] The dephosphorization process specifically comprises: subjecting the heated ingot to high-pressure water dephosphorization, with the dephosphorization system pressure being ≥20 MPa.

[0019] Furthermore, in step (3), the rolling process is specifically: a two-stage rolling process is adopted, the rough rolling start temperature is 1060-1160°C, a large reduction rolling technology is adopted, and the reduction amount of each pass is ≥15%; the finishing rolling start temperature is 940-980°C, and the final rolling temperature is ≥920°C.

[0020] Furthermore, in step (4), the quenching process is specifically as follows: online quenching is performed immediately after rolling, using laminar cooling, a water inlet temperature of 900-1000°C, a water cooling rate of 5-20°C / s, a red-return temperature ≤200°C, and then air cooling to room temperature; if curvature occurs, straightening treatment is performed.

[0021] Furthermore, in step (5), the tempering heat treatment process is specifically: performing tempering heat treatment on the steel plate after online quenching or straightening, controlling the tempering temperature at 620-780°C and the holding time at 120-240 minutes; thereby producing a 500MPa grade economical high-strength ferritic stainless steel medium and thick plate.

[0022] Beneficial effects: Compared with the prior art, the present invention has the following features: 1. The present invention is based on Fe-Cr-Ni composition through alloy composition design, adopts low-nickel chromium iron smelting, contains 0.8-1.8% Ni, Ni is to expand the austenite phase region, can significantly improve low-temperature toughness, hardenability and strength; 2. The material strength is improved by solid solution strengthening by C and N elements, and at the same time, an appropriate amount of Ti and Nb stabilizing elements are added to make C / N and Ti / Nb undergo solid solution precipitation at high temperature, and precipitate a fine and dispersed Ti / Nb (C, N) second phase, which can serve as an equiaxed crystal heterogeneous nucleation core, promote nucleation, pin dislocations, and inhibit grain growth, thereby refining grains, improving strength and toughness, and inhibiting the precipitation of chromium carbonitrides, thereby improving intergranular corrosion performance; 3. The temperature control, rolling control and Cold technology regulates the ratio of α-ferrite, δ-ferrite and martensite phases to obtain the best match between strength and toughness; 4. The online quenching technology can effectively dissolve C and N, avoid the precipitation of harmful phases such as carbides, and effectively control grain growth. In addition, it can also replace the offline solution process, thereby reducing production procedures and saving production time and costs; 5. The stainless steel of the present invention combines the advantages of carbon structural steel to produce stainless steel medium and thick plates with a yield strength of ≥500Mpa, a tensile strength of ≥550Mpa, an elongation of ≥20%, and a longitudinal impact of -40℃ KV2≥55J. It has high strength, high elongation, good low-temperature impact toughness and excellent corrosion resistance. Compared with stainless steel of the same strength, it has less precious alloy content and low production cost, and can be widely used in coastal construction steel and offshore platforms and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the organization in Example 1 of the present invention. DETAILED DESCRIPTION

[0024] The 500MPa-grade economical high-strength ferritic stainless steel medium and thick plate described in the present invention has the following chemical composition and mass percentage: C: 0.05-0.08%, Cr: 15.0-19.0%, Ni: 0.8-1.8%, Si: 0.2-0.6%, Mn: 0.5-0.8%, P≤0.015%, S≤0.003%, Ti: 0.10-0.20%, Nb: 0.010-0.020%; Als: 0.015-0.045%, N: 0.006-0.012%, and the rest are Fe and unavoidable impurity elements.

[0025] Furthermore, its chemical composition and mass percentage are as follows: C: 0.05%, Cr: 15.0%, Ni: 0.8%, Si: 0.2%, Mn: 0.5%, P: 0.010%, S: 0.001%, Ti: 0.10%, Nb: 0.010%; Als: 0.015%, N: 0.006%, and the rest are Fe and unavoidable impurity elements.

[0026] Furthermore, its chemical composition and mass percentage are as follows: C: 0.08%, Cr: 19.0%, Ni: 1.8%, Si: 0.6%, Mn: 0.8%, P: 0.015%, S: 0.003%, Ti: 0.20%, Nb: 0.020%; Als: 0.045%, N: 0.012%, and the rest are Fe and unavoidable impurity elements.

[0027] Furthermore, its chemical composition and mass percentage are as follows: C: 0.065%, Cr: 17.5%, Ni: 1.3%, Si: 0.4%, Mn: 0.65%, P: 0.012%, S: 0.002%, Ti: 0.15%, Nb: 0.015%; Als: 0.030%, N: 0.009%, and the rest are Fe and unavoidable impurity elements.

[0028] Furthermore, a method for preparing a 500MPa grade economical high-strength ferritic stainless steel medium and thick plate is provided, wherein the preparation process is as follows:

[0029] (1): Preparation of raw materials: low nickel chromium iron is used as raw material, and the ingots with the above composition are smelted through the production process of EAF-V0D-LF refining-continuous casting, wherein electromagnetic stirring and soft reduction technology are used in the continuous casting process to improve the segregation and looseness defects of the ingots;

[0030] (2): Heating and dephosphorization process: heat the ingot in a heating furnace to 1140-1200°C, with a total heating time of 1.0-1.6 mm / min;

[0031] The heated ingot is subjected to high-pressure water dephosphorization. The dephosphorization system pressure is ≥20MPa to ensure that the surface iron oxide scale is completely dephosphorized in one step.

[0032] (3): Rolling process: adopt two-stage rolling process, the starting temperature of rough rolling is 1060~1160℃, and the large reduction rolling technology is adopted. The reduction of each pass is increased within the range allowed by the roller, and the reduction of each pass is ≥15%, so that the rolling force penetrates into the core and fully refines the structure; the starting temperature of finishing rolling is 940~980℃, and the final rolling temperature is ≥920℃;

[0033] (4): Quenching process: Online quenching is carried out immediately after rolling, using laminar cooling, water inlet temperature 900-1000℃, water cooling rate 5-20℃ / s, red-return temperature ≤200℃, and then air cooling to room temperature to avoid chromium carbide precipitation and grain growth; if curvature occurs, straightening treatment is carried out;

[0034] (5): Tempering heat treatment process: The steel plate after online quenching or straightening is then subjected to tempering heat treatment, with the tempering temperature controlled at 620-780°C and the holding time at 120-240 min; thereby obtaining 500 MPa grade economical high-strength ferritic stainless steel medium and thick plates.

[0035] The high-strength ferritic stainless steel medium and thick plate and the manufacturing method thereof of the present invention are further described below through specific embodiments:

[0036] Table 1 lists the chemical composition of the high-strength ferritic stainless steel medium and thick plates of Examples 1 to 6 (the remainder is Fe and unavoidable impurities). Steel plates of different specifications were produced according to the production process of EAF, V0D, LF refining, continuous casting, heating, rolling, online quenching, cooling, straightening, and tempering heat treatment. The specific process parameters are shown in Table 2. The mechanical properties of the steel plates of Examples 1 to 6 were tested, as shown in Table 3.

[0037] Table 1 Chemical composition of Examples 1-6 (%)

[0038]

[0039] Table 2 Process parameters of Examples 1-6

[0040]

[0041]

[0042] Table 3 Mechanical properties of Examples 1-6

[0043]

[0044] This high-strength ferritic stainless steel medium and thick plate is controlled through low-cost alloy composition design and production methods, with a yield strength of more than 500MPa, and has high elongation, good low-temperature impact toughness and excellent corrosion resistance. It has a simple alloy composition, few steps, easy operation and low production cost, and can be widely used in coastal construction steel and offshore platforms.

Claims

1. A 500MPa grade economical high-strength ferritic stainless steel medium and thick plate, characterized in that: Its chemical composition and mass percentage are as follows: C: 0.05-0.08%, Cr: 15.0-19.0%, Ni: 0.8-1.8%, Si: 0.2-0.6%, Mn: 0.5-0.8%, P≤0.015%, S≤0.003%, Ti: 0.10-0.20%, Nb: 0.010-0.020%; Als: 0.015-0.045%, N: 0.006-0.012%, the rest are Fe and unavoidable impurity elements; The specific process of its preparation method is as follows: (1): Prepare raw materials; (2): Heating and phosphorus removal process; (3): Rolling process: adopt two-stage rolling process, the starting temperature of rough rolling is 1060~1160℃, the large reduction rolling technology is adopted, and the reduction of each pass is ≥15%; the starting temperature of finishing rolling is 940~980℃, and the final rolling temperature is ≥920℃; (4): Quenching process: Online quenching is carried out immediately after rolling, using laminar cooling, water inlet temperature 900-1000℃, water cooling rate 5-20℃ / s, red-return temperature ≤200℃, and then air cooling to room temperature; if curvature occurs, straightening treatment is carried out; (5): Tempering heat treatment process: The steel plate after online quenching or straightening is subjected to tempering heat treatment, the tempering temperature is controlled at 620-780℃, and the holding time is 120-240min; thereby, 500MPa grade economical high-strength ferritic stainless steel medium and thick plates are produced.

2. The 500MPa grade economical high-strength ferritic stainless steel medium and thick plate according to claim 1, characterized in that: Its chemical composition and mass percentage are as follows: C: 0.05%, Cr: 15.0%, Ni: 0.8%, Si: 0.2%, Mn: 0.5%, P: 0.010%, S: 0.001%, Ti: 0.10%, Nb: 0.010%; Als: 0.015%, N: 0.006%, and the rest are Fe and inevitable impurity elements.

3. The 500MPa grade economical high-strength ferritic stainless steel medium and thick plate according to claim 1, characterized in that: Its chemical composition and mass percentage are as follows: C: 0.08%, Cr: 19.0%, Ni: 1.8%, Si: 0.6%, Mn: 0.8%, P: 0.015%, S ： 0.003%, Ti: 0.20%, Nb: 0.020%; Als: 0.045%, N: 0.012%, and the rest are Fe and inevitable impurity elements.

4. The 500MPa grade economical high-strength ferritic stainless steel medium and thick plate according to claim 1, characterized in that: Its chemical composition and mass percentage are as follows: C: 0.065%, Cr: 17.5%, Ni: 1.3%, Si: 0.4%, Mn: 0.65%, P: 0.012%, S: 0.002%, Ti: 0.15%, Nb: 0.015%; Als: 0.030%, N: 0.009%, and the rest are Fe and inevitable impurity elements.

5. The 500MPa grade economical high-strength ferritic stainless steel medium and thick plate according to claim 1, characterized in that: In step (1), the raw material is prepared as follows: low nickel chromium iron is used as the raw material and smelted into a casting billet of the above composition through the production process of EAF-V0D-LF refining-continuous casting; Among them, electromagnetic stirring and soft reduction technology are used in the continuous casting process.

6. The 500MPa grade economical high-strength ferritic stainless steel medium and thick plate according to claim 1, characterized in that: In step (2), the heating process is specifically as follows: heating the ingot in a heating furnace to 1140-1200° C., with a total heating time of 1.0-1.6 mm / min; The dephosphorization process specifically comprises: subjecting the heated ingot to high-pressure water dephosphorization, with the dephosphorization system pressure being ≥20 MPa.

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