WO2024088056A1 - Tmcp-produced low-cost q550d steel and production method therefor - Google Patents

Abstract

The present disclosure relates to the technical field of wide and thick plate metallurgy, and in particular to TMCP-produced low-cost Q550D steel and a production method therefor. In the present disclosure, a medium carbon design is used for components of a steel plate, so that the addition amount of an alloy is reduced while the strength is ensured; the reduction, temperature and cooling speed are accurately controlled during rolling and cooling, so that a heat treatment process is omitted; the obtained Q550D steel has 50-60% of bainite, 20-30% of acicular ferrite and 10-20% of pearlitic structure, has reasonable chemical composition and matrix structure combination, can achieve both high strength and excellent low-temperature impact toughness, and achieves low alloy costs; heat treatment is omitted during production, so that the manufacturing costs are further reduced, and the use and manufacturing requirements for large coal mining machines and engineering machinery can be met.

Description

A TMCP process for producing low-cost Q550D steel and its production method

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to a Chinese patent application with application number 202211336793.5 filed with the State Intellectual Property Office of China on October 28, 2022, entitled “A TMCP process for producing low-cost Q550D steel and its production method”, the entire contents of which are incorporated by reference into this application.

Technical Field

The present invention belongs to the technical field of wide and thick plate metallurgy, and specifically relates to a TMCP process for producing low-cost Q550D steel and a production method thereof.

Background technique

In recent years, high-strength steel for engineering machinery has been used more and more widely, and the demand has also increased accordingly. Among them, Q550D is suitable for manufacturing steel structures such as coal mine hydraulic supports, heavy vehicles, and engineering machinery. Coal mine machinery mainly includes roadheaders, coal mining machines, scraper conveyors, and hydraulic supports, commonly known as "three machines and one frame". Among them, hydraulic support equipment accounts for the highest proportion and is the largest equipment in all coal mining machinery products.

The 30-50mm Q550D high-strength steel currently produced domestically is mainly delivered through heat treatment, and requires the addition of precious Ni and Cu alloy elements, resulting in high production costs and long cycles.

Therefore, proposing a low-cost method for producing Q550D steel is of great significance to my country's coal machinery and engineering machinery manufacturing industries.

Summary of the invention

The present disclosure provides a Q550D steel comprising the following chemical components in percentage by mass:

0.13-0.16wt% C, 0.10-0.25wt% Si, 1.40-1.60wt% Mn, ≤0.015wt% P, ≤0.003wt% S, 0.020-0.035wt% Als, 0.030-0.060wt% Nb, 0.40-0.60wt% Cr, 0.10-0.20wt% Mo, ≤0.020wt% Ti, and 0.0010-0.0020wt% B, with the balance being Fe and residual elements.

Optionally, the steel is a steel plate with a thickness of 30 to 50 mm.

Optionally, the structure of the steel plate includes 50-60% bainite, 20-30% acicular ferrite and 10-20% pearlite.

The present disclosure also provides a low-cost Q550D steel, which is a steel plate with a thickness of 30 to 50 mm and contains the following chemical components in mass percentage:

0.13-0.16wt% C, 0.10-0.25wt% Si, 1.40-1.60wt% Mn, ≤0.015wt% P, ≤0.003wt% S, 0.020-0.035wt% Als, 0.030-0.060wt% Nb, 0.40-0.60wt% Cr, 0.10-0.20wt% Mo, ≤0.020wt% Ti, and 0.0010-0.0020wt% B, with the balance being Fe and residual elements; and,

The structure of the steel plate is 50-60% bainite + 20-30% acicular ferrite + 10-20% pearlite, and its yield strength is ≥550MPa, tensile strength is ≥670MPa, elongation is ≥17%, and longitudinal KV2 impact energy at -20°C is ≥100J.

The present disclosure also provides a method for producing Q550D steel using the TMCP process, the method comprising smelting, casting, heating, TMCP controlled rolling and controlled cooling, and stack cooling steps; wherein the TMCP controlled rolling and controlled cooling step comprises two stages: rough rolling and finish rolling;

The rough rolling stage meets the following requirements: at least 5 reduction passes with a rate of ≥15%, the thickness of the steel plate to be dried is 2 to 3 times the thickness of the finished steel plate, and the cumulative reduction rate is ≥65%;

The finishing rolling stage meets the following requirements: at least 6 reduction pass rates ≥ 10%, cumulative reduction rate ≥ 60%, and when the finished steel thickness is ≥ 30-40 mm, the finishing rolling start temperature is 770-790° C., the final rolling temperature is 760-780° C., the water entry temperature is 730±5° C., the cooling rate is controlled at 10-15° C./s, and the red-return temperature is 570±10° C.;

When the thickness of the finished steel is ≥40-50mm, the starting temperature of the finishing rolling is 760-780℃, the final rolling temperature is 750-770℃, the water entering temperature is 725±5℃, the cooling rate is controlled at 7-12℃/s, and the red-returning temperature is 550±10℃.

Optionally, the TMCP controlled rolling and controlled cooling step also includes relaxing or air cooling the steel plate before entering the water, and the relaxation or air cooling time is 20S-60S; optionally, the relaxation or air cooling time is 30S-40S.

Optionally, in the stack cooling step, slow cooling pit stack cooling is used, the stack cooling temperature is ≥400°C, and the stack cooling time is ≥48h.

The present disclosure also provides a production method for producing low-cost Q550D steel by TMCP process, comprising the following steps: smelting, casting, heating, TMCP controlled rolling and controlled cooling, and stack cooling;

The TMCP controlled rolling and controlled cooling process requires that the rough rolling should ensure at least 5 reduction passes with a rate of ≥15%, the steel thickness should be 2 to 3 times the thickness of the finished steel plate, and the cumulative reduction rate should be ≥65%. The finishing rolling should ensure at least 6 reduction passes with a rate of ≥10%, and the cumulative reduction rate should be ≥60%. The process requirements are: when the finished steel thickness is ≥30 to 40 mm, the finishing rolling start temperature is 770 to 790 ° C, the final rolling temperature is 760 to 780 ° C, the relaxation time is 30 s, the water entry temperature is 730 ± 5 ° C, the cooling rate is controlled at 10 to 15 ° C / s, and the red return temperature is 570 ± 10 ° C; when the finished steel thickness is ≥40 to 50 mm, the finishing rolling start temperature is 760 to 780 ° C, the final rolling temperature is 750 to 770 ° C, the relaxation time is 40 s, the water entry temperature is 725 ± 5 ° C, the cooling rate is controlled at 7 to 12 ° C / s, and the red return temperature is 550 ± 10 ° C;

The stack cooling process requires that the steel plate be directly placed in a slow cooling pit for stack cooling after straightening, with a stack cooling temperature ≥400°C and a stack cooling time ≥48h.

The present disclosure also provides Q550D steel prepared by the above method.

Optionally, the structure of the steel plate is 50-60% bainite+20-30% acicular ferrite+10-20% pearlite.

Optionally, the steel plate has a yield strength of ≥550MPa, a tensile strength of ≥670MPa, and an elongation of ≥17%, at -20°C Longitudinal KV2 impact energy ≥100J.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the structure of a steel plate obtained in an embodiment of the present disclosure.

FIG. 2 is a schematic diagram of a high-magnification inspection of the steel plate structure obtained in an embodiment of the present disclosure.

Detailed ways

In order to make the purpose, technical scheme and advantages of the embodiments of the present disclosure clearer, the technical scheme in the embodiments of the present disclosure will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

Definition of Terms:

As used herein, unless otherwise specified, Als used herein means acid-soluble aluminum.

The present disclosure provides a TMCP process for producing low-cost Q550D steel. The steel plate provided by the present disclosure has a reasonable combination of chemical components, low alloy cost, and excellent low-temperature impact toughness, and can meet actual production, processing and use requirements.

The present disclosure also provides a production method for producing low-cost Q550D steel using a TMCP process.

In some embodiments, the present disclosure provides a Q550D steel comprising the following chemical components in mass percentage:

0.13-0.16wt% C, 0.10-0.25wt% Si, 1.40-1.60wt% Mn, ≤0.015wt% P, ≤0.003wt% S, 0.020-0.035wt% Als, 0.030-0.060wt% Nb, 0.40-0.60wt% Cr, 0.10-0.20wt% Mo, ≤0.020wt% Ti, and 0.0010-0.0020wt% B, with the balance being Fe and residual elements.

The components disclosed in the present invention adopt a medium carbon design. Under the premise of ensuring strength, the amount of alloy added is reduced, and the hardenability of the steel plate is enhanced by Cr and B. Mo shifts the pearlite transformation line in the CCT curve to the right, reduces the formation of pearlite, and expands the cooling rate range for the formation of acicular ferrite; while Cr is conducive to obtaining a bainite structure at a low cooling rate. With the increase of Mo and Cr content, the driving force for pearlite nucleation has decreased to a certain extent. In addition, in addition to delaying the nucleation and growth of pearlite, Mo can also increase the bonding force between solid solution atoms and reduce the self-diffusion coefficient of iron, thereby delaying the γ-α transformation in the pearlite transformation, which is beneficial to the refinement of the structure and the improvement of precipitation strengthening and fine grain strengthening.

In some embodiments, the present disclosure further provides a Q550D steel, which is a steel plate with a thickness of 30 to 50 mm.

In some embodiments, the present disclosure further provides a Q550D steel, wherein the structure of the steel plate includes 50-60% bainite, 20-30% acicular ferrite, and 10-20% pearlite.

Among them, with the different components and processing technology of steel, various structures will appear in the steel, such as austenite, iron Ferrite, cementite, pearlite, upper bainite, lower bainite, granular bainite, carbide-free bainite, martensite, ledeburite, tempered troostite, tempered troostite, Widmanstätten structure, etc., these steel plate structures are all internal structures of metals and alloys observed by metallographic methods, and these metallographic structures are characterized by area, and their relative area determination is a conventional method in the art. In some embodiments, the present disclosure also provides a Q550D steel, which is a steel plate with a thickness of 30 to 50 mm, comprising the following chemical components in mass percentage:

0.13-0.16wt% C, 0.10-0.25wt% Si, 1.40-1.60wt% Mn, ≤0.015wt% P, ≤0.003wt% S, 0.020-0.035wt% Als, 0.030-0.060wt% Nb, 0.40-0.60wt% Cr, 0.10-0.20wt% Mo, ≤0.020wt% Ti, and 0.0010-0.0020wt% B, with the balance being Fe and residual elements; and,

The structure of the steel plate is 50-60% bainite + 20-30% acicular ferrite + 10-20% pearlite, and its yield strength is ≥550MPa, tensile strength is ≥670MPa, elongation is ≥17%, and longitudinal KV2 impact energy at -20°C is ≥100J.

In some embodiments, the present disclosure provides a TMCP process for producing low-cost Q550D steel and a production method thereof, wherein the steel plate has a thickness of 30 to 50 mm and contains the following chemical components in mass percentage (unit, wt%): 0.13 to 0.16 C, 0.10 to 0.25 Si, 1.40 to 1.60 Mn, ≤0.015 P, ≤0.003 S, 0.020 to 0.035 Als, 0.030 to 0.060 Nb, 0.40 to 0.60 Cr, 0.10 to 0.20 Mo, ≤0.020 Ti, and 0.0010 to 0.0020 B, with the remainder being Fe and residual elements.

The structure of the steel plate is 50-60% bainite + 20-30% acicular ferrite + 10-20% pearlite, and its yield strength is ≥550MPa, tensile strength is ≥670MPa, elongation is ≥17%, and longitudinal KV2 impact energy at -20°C is ≥100J.

In some embodiments, the present disclosure provides a method for producing Q550D steel using a TMCP process, the method comprising smelting, casting, heating, TMCP controlled rolling and controlled cooling, and stack cooling steps; wherein the TMCP controlled rolling and controlled cooling step comprises two stages of rough rolling and finishing rolling;

The rough rolling stage meets the following requirements: at least 5 reduction passes ≥ 15%, the steel thickness is 2 to 3 times the thickness of the finished steel plate, and the cumulative reduction rate is ≥ 65%

The finishing rolling stage meets the following requirements: at least 6 reduction pass rates ≥ 10%, cumulative reduction rate ≥ 60%, and when the finished steel thickness is ≥ 30-40 mm, the finishing rolling start temperature is 770-790° C., the final rolling temperature is 760-780° C., the water entry temperature is 730±5° C., the cooling rate is controlled at 10-15° C./s, and the red-return temperature is 570±10° C.;

When the thickness of the finished steel is ≥40-50mm, the starting temperature of the finishing rolling is 760-780℃, the final rolling temperature is 750-770℃, the water entering temperature is 725±5℃, the cooling rate is controlled at 7-12℃/s, and the red-returning temperature is 550±10℃.

Optionally, in the stack cooling step, slow cooling pit stack cooling is used, the stack cooling temperature is ≥400°C, and the stack cooling time is ≥48h.

Optionally, the TMCP controlled rolling and controlled cooling step also includes relaxing or air cooling the steel plate before entering the water, and the relaxation or air cooling time is 20S-60S; optionally, the relaxation or air cooling time is 30S-40S.

In some embodiments, the present disclosure provides a method for producing low-cost Q550D steel by TMCP process, comprising: The process includes the following steps: smelting, casting, heating, TMCP controlled rolling and controlled cooling, and pile cooling;

The TMCP controlled rolling and controlled cooling process requires that the rough rolling should ensure at least 5 reduction passes with a rate of ≥15%, the steel thickness should be 2 to 3 times the thickness of the finished steel plate, and the cumulative reduction rate should be ≥65%. The finishing rolling should ensure at least 6 reduction passes with a rate of ≥10%, and the cumulative reduction rate should be ≥60%. The process requirements are: when the finished steel thickness is ≥30 to 40 mm, the finishing rolling start temperature is 770 to 790 ° C, the final rolling temperature is 760 to 780 ° C, the relaxation time is 30 s, the water entry temperature is 730 ± 5 ° C, the cooling rate is controlled at 10 to 15 ° C / s, and the red return temperature is 570 ± 10 ° C; when the finished steel thickness is ≥40 to 50 mm, the finishing rolling start temperature is 760 to 780 ° C, the final rolling temperature is 750 to 770 ° C, the relaxation time is 40 s, the water entry temperature is 725 ± 5 ° C, the cooling rate is controlled at 7 to 12 ° C / s, and the red return temperature is 550 ± 10 ° C;

The stack cooling process requires that the steel plate be directly placed in a slow cooling pit for stack cooling after straightening, with a stack cooling temperature ≥400°C and a stack cooling time ≥48h.

The method disclosed in the present invention adopts the TMCP controlled rolling and controlled cooling process. In the rolling process, through large rough rolling, finishing rolling cumulative reduction rate, pass reduction rate, it is ensured that the steel plate obtains fine grains and uniform and refined structure, which is a key reason for ensuring the impact work. Secondly, acicular ferrite is a product of the medium temperature transformation process formed by isothermal transformation at medium temperature or continuous cooling at a medium cooling rate. During the finishing process, if the temperature is too high, grain boundary ferrite and intracrystalline equiaxed ferrite are formed. As the temperature decreases, the equiaxed ferrite gradually transforms into lath-shaped acicular ferrite. When the temperature is further reduced, bainite and ferrite are formed. Therefore, the finishing temperature must be accurately controlled.

In addition, the study found that the cooling rate affects the formation of acicular ferrite. If the cooling rate is too low, equiaxed ferrite and polygonal ferrite will be obtained; if the cooling rate is too high, bainite, ferrite, and even martensite will be obtained. Therefore, the red-return temperature and cooling rate must be accurately controlled to obtain more acicular ferrite and ensure that the impact energy of the steel plate meets the requirements.

The present disclosure provides a Q550D steel plate, which has a reasonable combination of chemical composition and matrix structure, can have both high strength and excellent low-temperature impact toughness, has low alloy cost, omits the heat treatment step in the production process, further reduces the manufacturing cost, and can meet the use and manufacturing of large coal mining machines and engineering machinery.

Example

This embodiment provides a Q550D steel with a thickness of 40 mm, including the following chemical components in mass percentage:

C: 0.15wt%, Si: 0.17wt%, Mn: 1.42wt%, P: 0.013wt%, S: 0.002wt%, Als: 0.025wt%, Nb: 0.043wt%, Mo: 0.16wt%, Cr: 0.52wt%, Ti: 0.016wt%, B: 0.0016wt%, and the balance is Fe and residual elements.

The production method includes:

Smelting: After KR stirring and desulfurization, the S content of the molten iron is 0.008wt%; the C content of the converter steel is 0.08wt% and the P content is 0.010wt%; the slag thickness at the converter is ≤16mm; the VD-determined [H] content is ≤1.0PPm.

Casting: The liquidus temperature of molten steel is 1518℃, and the temperature of the tundish is controlled in the range of 1530～1535℃.

Heating: The first heating temperature of the steel billet is 960°C, the second heating temperature is 1210°C, and the temperature of the soaking section is 1200°C. The heating time is 270 minutes.

Controlled rolling: Rough rolling with a steel thickness of 100 mm, finishing rolling at 780 ° C, final rolling at 765 ° C, and red-rolling at 560 ° C. The specific pass distribution, reduction amount, and reduction rate are shown in Table 1.

Stack cooling: The steel plate stack cooling temperature is 400℃ and the stack cooling time is 48h.

Example Performance Testing

The Q550D plate obtained in the embodiment is used as the test product. The chemical composition, mechanical properties test piece sampling position and sample preparation of the steel plate are tested according to the standard "GB/T2975". The low temperature impact toughness test is tested according to the standard "GB/T229", the tensile property test is tested according to the standard "GB/T228", and the bending property test is tested according to the standard "GB/T232". The test results are shown in Table 2 below:

It can be seen from Table 2 that the Q550D steel provided in the embodiments of the present disclosure has good strength properties and low-temperature impact properties.

The structure and high-magnification test results of the steel plate obtained in the embodiment are shown in Figures 1 and 2. It can be seen that the main structure is bainite (50-60%) + acicular ferrite (20-30%) + pearlite (10-20%).

Based on the above test results, it can be seen that the strength performance, impact toughness, microstructure ratio and other indicators of the Q500D steel plate provided in the embodiment of the present disclosure meet the manufacturing and use requirements of coal mining machinery and engineering machinery.

In addition, the surface inspection and internal flaw detection were carried out on the Q550D steel obtained in the example, and the qualified rate reached 100.00%.

In summary, the chemical composition, production process, and internal organization of the Q55D steel plate provided by the present disclosure are reasonable, and can have good mechanical properties and welding properties at the same time. Its production method meets the organizational production of the metallurgical industry and can It can reach the quality of Q550D steel and improve its performance.

The above description is only a preferred embodiment of the present disclosure and is not intended to limit the present disclosure. For those skilled in the art, the present disclosure may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present disclosure shall be included in the protection scope of the present disclosure.

Industrial Applicability

The present invention provides a Q550D steel and a production method thereof. The production method adopts the TMCP process. Through precise control of the reduction amount, temperature and cooling rate during rolling and cooling, the obtained Q550D steel has high strength and excellent low-temperature impact toughness, and has excellent industrial applicability.

Claims (9)

1. A Q550D steel, characterized in that the Q550D steel contains the following chemical components in mass percentage:

   0.13-0.16wt% C, 0.10-0.25wt% Si, 1.40-1.60wt% Mn, ≤0.015wt% P, ≤0.003wt% S, 0.020-0.035wt% Als, 0.030-0.060wt% Nb, 0.40-0.60wt% Cr, 0.10-0.20wt% Mo, ≤0.020wt% Ti, and 0.0010-0.0020wt% B, with the balance being Fe and residual elements.
2. The Q550D steel according to claim 1, wherein the steel is a steel plate with a thickness of 30 to 50 mm.
3. The Q550D steel according to claim 1, wherein the structure of the steel plate includes 50-60% bainite, 20-30% acicular ferrite and 10-20% pearlite.
4. A TMCP process for producing low-cost Q550D steel, characterized in that the steel plate has a thickness of 30 to 50 mm and contains the following chemical components in mass percentage:

   0.13-0.16wt% C, 0.10-0.25wt% Si, 1.40-1.60wt% Mn, ≤0.015wt% P, ≤0.003wt% S, 0.020-0.035wt% Als, 0.030-0.060wt% Nb, 0.40-0.60wt% Cr, 0.10-0.20wt% Mo, ≤0.020wt% Ti, and 0.0010-0.0020wt% B, with the balance being Fe and residual elements;

   The structure of the steel plate is 50-60% bainite + 20-30% acicular ferrite + 10-20% pearlite, and its yield strength is ≥550MPa, tensile strength is ≥670MPa, elongation is ≥17%, and longitudinal KV2 impact energy at -20°C is ≥100J.
5. A method for producing Q550D steel using TMCP process, characterized in that the method comprises smelting, casting, heating, TMCP controlled rolling and controlled cooling, and stack cooling steps;

   Wherein, the TMCP controlled rolling and controlled cooling step includes two stages: rough rolling and finish rolling;

   The rough rolling stage meets the following requirements: at least 5 reduction passes with a rate of ≥15%, the thickness of the steel plate to be dried is 2 to 3 times the thickness of the finished steel plate, and the cumulative reduction rate is ≥65%;

   The finishing rolling stage meets the following requirements: at least 6 reduction pass rates ≥ 10%, cumulative reduction rate ≥ 60%, and when the finished steel thickness is ≥ 30-40 mm, the finishing rolling start temperature is 770-790° C., the final rolling temperature is 760-780° C., the water entry temperature is 730±5° C., the cooling rate is controlled at 10-15° C./s, and the red-return temperature is 570±10° C.;

   When the thickness of the finished steel is ≥40-50mm, the starting temperature of the finishing rolling is 760-780℃, the final rolling temperature is 750-770℃, the water entering temperature is 725±5℃, the cooling rate is controlled at 7-12℃/s, and the red-returning temperature is 550±10℃.
6. The method according to claim 5, wherein in the stack cooling step, slow cooling pit stack cooling is used, the stack cooling temperature is ≥400°C, and the stack cooling time is ≥48h.
7. According to the method of claim 5 or 6, the TMCP controlled rolling and controlled cooling step further includes relaxing or air cooling the steel plate before entering the water, and the relaxation or air cooling time is 20S-60S; optionally, the relaxation or air cooling time is 30S-40S.
8. The method for producing low-cost Q550D steel by TMCP process according to any one of claims 1 to 4, characterized in that it comprises the following steps: smelting, casting, heating, TMCP controlled rolling and controlled cooling, and pile cooling;

   The TMCP controlled rolling and controlled cooling process requires that the rough rolling should ensure at least 5 reduction passes with a rate of ≥15%, the steel thickness should be 2 to 3 times the thickness of the finished steel plate, and the cumulative reduction rate should be ≥65%. The finishing rolling should ensure at least 6 reduction passes with a rate of ≥10%, and the cumulative reduction rate should be ≥60%. The process requirements are: when the finished steel thickness is ≥30 to 40 mm, the finishing rolling start temperature is 770 to 790 ° C, the final rolling temperature is 760 to 780 ° C, the relaxation time is 30 s, the water entry temperature is 730 ± 5 ° C, the cooling rate is controlled at 10 to 15 ° C / s, and the red return temperature is 570 ± 10 ° C; when the finished steel thickness is ≥40 to 50 mm, the finishing rolling start temperature is 760 to 780 ° C, the final rolling temperature is 750 to 770 ° C, the relaxation time is 40 s, the water entry temperature is 725 ± 5 ° C, the cooling rate is controlled at 7 to 12 ° C / s, and the red return temperature is 550 ± 10 ° C;

   The stack cooling process requires that the steel plate be directly placed in a slow cooling pit for stack cooling after straightening, with a stack cooling temperature ≥ 400°C and a stack cooling time ≥ 48h.
9. Q550D steel prepared according to the method described in any one of claims 5-8;

   Optionally, the structure of the steel plate is 50-60% bainite + 20-30% acicular ferrite + 10-20% pearlite;

   Optionally, the steel plate has a yield strength of ≥550MPa, a tensile strength of ≥670MPa, an elongation of ≥17%, and a longitudinal KV2 impact energy of ≥100J at -20°C.