Production method of low-cost NM600 steel plate

Abstract

A production method of a low-cost NM600 steel plate comprises the steps of smelting, continuous casting, heating, rolling, heat treatment and furnace rear cutting, and steel comprises the following chemical components in percentage by mass: 0.40%-0.42% of C, 0.10%-0.20% of Si, 0.50%-0.60% of Mn, less than or equal to 0.008% of P, less than or equal to 0.0015% of S, 0.75%-0.85% of Cr, 0.008%-0.015% of Ti, 0.030%-0.040% of V, 0.050%-0.070% of Alt, 0.0008%-0.0020% of B, less than or equal to 0.00010% of vacuum H, less than or equal to 0.00012% of tundish H, less than or equal to 0.0040% of N, less than or equal to 0.0015% of O and the balance According to the NM600 wear-resistant steel plate produced through the method, the thickness covers 10-40 mm, the surface Brinell hardness ranges from 570 HB to 640 HB, the yield strength is larger than or equal to 1700 MPa, the tensile strength is larger than or equal to 2200 MPa, and the elongation is larger than or equal to 7.5%.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy and relates to a production method of a low-cost NM600 steel plate. Background Art

[0002] Wear-resistant steel is widely used in various fields such as metallurgy, mining, building materials, and railways. It plays an important role in the key wear-prone parts of equipment such as mining dump trucks, coal mine scraper conveyors, bulldozers, excavators, mixers, and loaders. With the rapid development of modern industry, the problem of wear failure has become increasingly prominent. The service environment of wear-resistant materials is becoming increasingly harsh, and therefore they are required to have extremely high strength, hardness, and wear resistance to extend the service life of equipment, shorten the replacement cycle of components, and greatly improve operating time. Hardness is an important indicator for measuring the wear resistance of metal materials. In other words, the performance of wear-resistant steel is most intuitively distinguished by the hardness level. In recent years, China has made great progress in the research and development of low-grade wear-resistant steels such as NM360, NM400, NM450, and NM500 wear-resistant steels. However, the alloy content is generally high, which is not conducive to welding performance on the one hand and leads to increased production costs on the other.

[0003] Chinese patent CN119433371A discloses a low-alloy NM600 wear-resistant steel and its production method. The steel plate has a thickness range of 10 to 30 mm, but the steel plate has poor control over harmful elements such as P, S, N, and O, as well as hydrogen content that can cause hydrogen-induced cracking. Chinese patent CN119710447A discloses a high-strength, medium-thin wear-resistant steel plate NM600 and its production method. The steel plate has a thickness range of 2.0 to 12.0 mm, but the steel plate has insufficient control over harmful gas elements such as H, N, and O. The yield strength of the steel plate is ≥1200 MPa and the tensile strength is ≥1400 MPa, indicating insufficient strength.

[0004] Therefore, the development of a low-cost, high-wear-resistant 600HB high-strength wear-resistant steel is of great significance to the development of the engineering machinery industry. Summary of the Invention

[0005] The object of the present invention is to provide a low-cost production method of NM600 steel plate. The produced wear-resistant steel plate is of NM600 grade, with a steel plate thickness ranging from 10 to 40 mm, a surface hardness of 570 to 640 HBW, a yield strength ≥1700 MPa, a tensile strength ≥2200 MPa, and an elongation ≥7.5%.

[0006] The technical solution of the present invention: A low-cost NM600 steel plate production method, comprising a process flow of smelting-continuous casting-heating-rolling-heat treatment-furnace cutting, characterized in that the chemical composition of the steel is as follows by mass: C=0.40%-0.42%, Si=0.10%-0.20%, Mn=0.50%-0.60%, P≤0.008%, S≤0.0015%, Cr=0.75%-0.85%, Ti=0.008%-0.015%, V=0.030%-0.040%, Alt=0.050%-0.070%, B=0.0008%-0.0020%, H₂≤0.00010%, H₂≤0.00012%, N≤0.0040%, O≤0.0015%, and the remainder is Fe and unavoidable impurities; and key process steps include: (1) Smelting: The BOF-LF-RH production process is adopted. The molten iron is treated with desulfurization and dephosphorization. When the LF is discharged from the station, it is fed with 150m of pure calcium wire and then enters the RH furnace for vacuum treatment. The vacuum degree is ≤67Pa and the holding time is 25min. It is then put on the stage for soft blowing for 26-32min. After breaking the air, 150m of pure calcium wire is fed at one time. The gas of the molten steel measured at the station is H≤0.00010%, N≤0.0040%, and O≤0.0015%.

[0007] (2) Continuous casting: adopt full-process protective pouring, control the moisture content of protective slag and covering agent, tundish baking and cover the ingot with insulation cover for slow cooling and hydrogen expansion to ensure that the actual tundish control H is ≤ 0.00012%; the tundish overheating temperature is ≤ 20℃ for continuous casting furnace and ≤ 25℃ for open casting furnace. Dynamic light reduction technology is used in continuous casting to improve the internal quality of continuous casting ingot.

[0008] (3) Heating: preheating section temperature 680 ~ 830 ° C, heating section temperature 1120 ~ 1240 ° C, soaking section temperature 1170 ~ 1230 ° C; furnace time 230 ~ 250 min.

[0009] (4) Rolling: The finished steel plate has a thickness of 10 to 40 mm and adopts two-stage controlled rolling. The starting rolling temperature of rough rolling is ≤1040℃, the cumulative compression ratio of rough rolling is ≥2.6, the thickness of intermediate billet is 60 to 100 mm, the starting rolling temperature of finishing rolling is ≤950℃, and the cumulative compression ratio of finishing rolling is ≥2.5, of which the compression ratio of 10 mm steel plate is 6 and the compression ratio of 40 mm steel plate is 2.5.

[0010] (5) Heat treatment: quenching + low temperature tempering process is adopted.

[0011] Furthermore, in step (1) smelting, the molten iron is subjected to KR desulfurization treatment and smelted in a top-bottom combined-blowing converter, and the converter slag removal is combined with deep desulfurization treatment by a post-furnace slag skimming process.

[0012] Furthermore, in step (2) continuous casting, the ingot is covered with a heat-insulating cover and slowly cooled to 200±20°C before being loaded into the furnace.

[0013] Furthermore, step (5) heat treatment: quenching heating temperature 850-870°C, heating rate 1.6-2.2 min / mm, holding time 15-25 min, water cooling to room temperature; tempering heating temperature 150-170°C, heating rate 3.5-4.0 min / mm, holding time 10-25 min; after tempering, stacking and slowly cooling to room temperature.

[0014] Principle of the invention: The present invention effectively combines scientific alloy element ratios and reasonable rolling and heat treatment processes to ensure that the steel plate has excellent mechanical properties. The produced NM600 wear-resistant steel has the characteristics of low cost, high strength, high hardness, and high wear resistance. In terms of strengthening mechanism, it is mainly based on C and Mn elements, with the addition of Cr and B hardenability elements and the precipitation of V, Ti, and Al. The strength performance of the steel plate is improved by combining organizational strengthening and alloy strengthening; the grains are refined through reasonable rolling and heat treatment process regulations to improve the toughness, hardness and wear resistance of the steel plate. The design reasons for each main added element are as follows: C: Effectively improves the strength and hardness of steel, increases hardenability, and significantly increases the surface hardness of wear-resistant steel plates. However, excessive carbon content can adversely affect the steel's toughness, cold forming, and weldability. Based on these considerations, the carbon content in this invention is controlled within a range of 0.40% to 0.42%.

[0015] Mn: The most effective alloying element for improving hardenability. When dissolved in ferrite, it has a solid solution strengthening effect, improves the heat treatment properties of steel, refines pearlite grains, and increases the strength and hardness of steel. While adding a certain amount of manganese to steel is beneficial, the content should not be too high. This is because Mn is an element that easily segregates. During solidification, Mn causes the molten steel to aggregate at the end of solidification, forming central segregation, which leads to coarse cementite in the core of the steel plate, which is detrimental to the core's performance. Mn also lowers the martensite transformation temperature in the material. When Mn accumulates to a certain proportion in the segregation zone, high-hardness microstructures such as martensite and bainite are produced during post-weld cooling, significantly reducing toughness. Based on the above comprehensive considerations, the manganese content in the present invention is controlled at 0.50% to 0.60%.

[0016] Cr: One of the essential elements of wear-resistant steel, it improves hardenability, strengthens the matrix through solid solution, refines grains, and enhances steel's strength, hardness, and wear resistance. It also significantly improves steel's oxidation resistance and corrosion resistance. The Cr content in this invention is controlled at 0.75% to 1.15%.

[0017] The beneficial effects of the present invention are as follows: The NM600 wear-resistant steel produced by the method of the present invention has high strength, hardness, and excellent wear resistance. The mechanical properties are as follows: surface hardness 570-640 HBW, yield strength ≥1700 MPa, tensile strength ≥2200 MPa, and elongation ≥7.5%.

[0018] The main innovations and benefits of this invention are: 1) A low-alloy design, with a rationally designed C, Mn, and Cr alloy and no additions of precious alloys such as Mo and Ni, reduces costs. This, combined with a rigorous controlled rolling process and a quenching and low-temperature tempering heat treatment process to ensure the ultimate mechanical properties of the steel plate, results in the development of a low-cost, highly wear-resistant, high-grade 600HB wear-resistant steel. 2) The thickness ranges from 10 to 40 mm, further enhancing the service performance of the wear-resistant steel in heavy-duty applications such as mining machinery and engineering equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a metallographic photograph of the steel produced in Example 1.

[0020] Figure 2 This is a metallographic photograph of the steel produced in Example 2. DETAILED DESCRIPTION Example 1

[0021] A method for producing low-cost NM600 steel plate comprises smelting one furnace of NM600 wear-resistant steel and rolling the steel plate to a thickness of 10 mm. The chemical composition of the steel by weight is shown in Table 1, with the remainder being Fe and unavoidable impurities, and a CEV of 0.67. The method includes the following key process steps: (1) Smelting: The molten iron is smelted in a top-bottom combined blown converter. The molten iron is pre-desulfurized and dephosphorized by KR. When the LF leaves the station, it is fed with 150m pure calcium wire and then enters the RH furnace for vacuum treatment. The vacuum degree is ≤67Pa and the holding time is 25 minutes. The molten iron is then soft-blown on the stage for 26 minutes. After the vacuum is broken, 150m pure calcium wire is fed in one go.

[0022] (2) Continuous casting: full protection pouring is adopted, the tundish superheat is 17℃, dynamic light pressure is used to improve the internal quality (the low magnification results of the furnace: segregation C class 1.0, porosity 1.0, no internal cracks), the ingot is covered with a heat preservation cover and slowly cooled to 200±20℃ and then loaded into the furnace for rolling.

[0023] (3) Heating: preheating section temperature 690 ~ 810 ° C, heating section temperature 1125 ~ 1230 ° C, soaking section temperature 1160 ~ 1220 ° C, furnace time 238 min.

[0024] (4) Rolling: The finished steel plate thickness is 10 mm. Two-stage controlled rolling is adopted. The starting rolling temperature of rough rolling is 1040 °C, the thickness of intermediate billet is 60 mm, and the cumulative reduction ratio of rough rolling is 4.3; the starting rolling temperature of finishing rolling is 930 °C, and the cumulative reduction ratio of finishing rolling is 6. The rolling process parameters are detailed in Table 2.

[0025] (5) Heat treatment: quenching + low-temperature tempering process is adopted, quenching heating temperature is 862℃, heating rate is 1.6min / mm, holding time is 17min, and water cooling is performed to room temperature; tempering heating temperature is 164℃, heating rate is 3.7min / mm, and holding time is 14min; after tempering, the stack is slowly cooled to room temperature. Example 2

[0026] A method for producing low-cost NM600 steel plate comprises smelting one furnace of NM600 wear-resistant steel and rolling the steel plate to a thickness of 40 mm. The chemical composition of the steel by weight is shown in Table 1, with the remainder being Fe and unavoidable impurities, and a CEV of 0.67. The method includes the following key process steps: (1) Smelting: The molten iron is smelted in a top-bottom combined blown converter. The molten iron is pre-desulfurized and dephosphorized by KR. When the LF leaves the station, it is fed with 150m pure calcium wire and then enters the RH furnace for vacuum treatment. The vacuum degree is ≤67Pa and the holding time is 26 minutes. The molten iron is then soft-blown on the stage for 32 minutes. After the vacuum is broken, 150m pure calcium wire is fed in one go.

[0027] (2) Continuous casting: full protection pouring is adopted, the tundish superheat is 16℃, dynamic light pressure is used for continuous casting to improve the internal quality (the low magnification results of the furnace: segregation C class 1.5, porosity 1.0, no internal cracks), the ingot is covered with a heat preservation cover and slowly cooled to 200±20℃ and then loaded into the furnace for rolling.

[0028] (3) Heating: preheating section temperature 710 ~ 810 ° C, heating section temperature 1123 ~ 1232 ° C, soaking section temperature 1175 ~ 1230 ° C, furnace time 243 min.

[0029] (4) Rolling: The finished steel plate thickness is 40 mm. Two-stage controlled rolling is adopted. The starting rolling temperature of rough rolling is 1040 °C, the thickness of intermediate billet is 100 mm, and the cumulative reduction ratio of rough rolling is 2.6; the starting rolling temperature of finishing rolling is 850 °C, and the cumulative reduction ratio of finishing rolling is 2.5. The rolling process parameters are detailed in Table 2.

[0030] (5) Heat treatment: quenching + low-temperature tempering process is adopted, quenching heating temperature is 859℃, heating rate is 1.7min / mm, holding time is 19min, quenching water cooling to room temperature; tempering heating temperature is 162℃, heating rate is 3.8min / mm, holding time is 16min; after tempering, the stack is slowly cooled to room temperature.

[0031] The rolling process parameters of Example 1 and Example 2 are shown in Table 2, the heat treatment process parameters are shown in Table 3, and the mechanical properties are shown in Table 4; Figure 1 and Figure 2 .

[0032] Table 1 Chemical composition mass percentage (wt.%) .

[0033] Table 2 Rolling process parameters .

[0034] Table 3 Heat treatment process parameters .

[0035] Table 4 Mechanical properties test results of the examples .

Claims

1. A method for producing low-cost NM600 steel plate, comprising a process flow of smelting - continuous casting - heating - rolling - heat treatment - post-furnace cutting, characterized in that: The chemical composition of steel is as follows by mass: C = 0.40% ~ 0.42%, Si = 0.10% ~ 0.20%, Mn = 0.50% ~ 0.60%, P ≤ 0.008%, S ≤ 0.0015%, Cr = 0.75% ~ 0.85%, Ti = 0.008% ~ 0.015%, V = 0.030% ~ 0.040%, Alt = 0.050% ~ 0.070%, B = 0.0008% ~ 0.0020%, H ≤ 0.00010%, H ≤ 0.00012%, N ≤ 0.0040%, O ≤ 0.0015%, and the rest are Fe and unavoidable impurities; The key process steps include: (1) Smelting: The BOF-LF-RH production process is adopted. The molten iron is treated with desulfurization and dephosphorization. When the LF is discharged from the station, it is fed with 150m pure calcium wire. Then it enters the RH furnace for vacuum treatment. The vacuum degree is ≤67Pa and the holding time is 25 minutes. It is then soft-blown on the stage for 26-32 minutes. After breaking the vacuum, 150m pure calcium wire is fed in one go. The gas of the molten steel measured at the station is H≤0.00010%, N≤0.0040%, and O≤0.0015%. (2) Continuous casting: adopt full-process protection pouring, control the moisture content of protective slag and covering agent, tundish baking and cover the ingot with insulation cover to slow cooling and hydrogen expansion measures to ensure that the actual tundish control H is ≤ 0.00012%; the tundish overheating temperature is ≤ 20℃ for continuous casting furnace and ≤ 25℃ for open casting furnace. Dynamic soft reduction technology is used in continuous casting to improve the internal quality of continuous casting ingot; (3) Heating: preheating section temperature 680-830°C, heating section temperature 1120-1240°C, soaking section temperature 1170-1230°C, furnace time 230-250 min; (4) Rolling: The finished steel plate has a thickness of 10 to 40 mm and adopts two-stage controlled rolling. The starting rolling temperature of rough rolling is ≤1040°C, the cumulative compression ratio of rough rolling is ≥2.6, the thickness of intermediate billet is 60 to 100 mm, the starting rolling temperature of finishing rolling is ≤950°C, and the cumulative compression ratio of finishing rolling is ≥2.5, where the compression ratio of 10 mm steel plate is 6 and the compression ratio of 40 mm steel plate is 2.5; (5) Heat treatment: quenching + low temperature tempering process is adopted.

2. The method for producing a low-cost NM600 steel plate according to claim 1, characterized in that Step (1) smelting: the molten iron is subjected to KR desulfurization treatment and smelted in a top-bottom double-blown converter, and the converter slag removal is combined with deep desulfurization by the post-furnace slag removal process.

3. The method for producing a low-cost NM600 steel plate according to claim 1, characterized in that: Step (2) Continuous casting: The ingot is covered with a heat-insulating cover and slowly cooled to 200±20℃ before being loaded into the furnace.

4. The method for producing a low-cost NM600 steel plate according to claim 1, characterized in that: Step (5) heat treatment: quenching heating temperature 850-870°C, heating rate 1.6-2.2 min / mm, holding time 15-25 min, water cooling to room temperature; tempering heating temperature 150-170°C, heating rate 3.5-4.0 min / mm, holding time 10-25 min; after tempering, stacking and slowly cooling to room temperature.

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