A production method of NM400 wear-resistant steel plate

Abstract

A production method of NM400 wear-resistant steel plate, the chemical composition percentage of the steel is C = 0.14% - 0.15%, Si = 0.15% - 0.35%, Mn = 0.95% - 1.02%, P ≤ 0.012%, S ≤ 0.005%, Cr = 0.58% - 0.61%, Mo = 0.20% - 0.23%, Nb = 0.022% - 0.030%, Ti = 0.015% - 0.025%, Al = 0.020% - 0.050%, B = 0.0015% - 0.0025%, H ≤ 0.0002%, N ≤ 0.0060%, O ≤ 0.0015%, the rest are Fe and inevitable impurities, CEV ≤ 0.50%; the process steps include converter smelting, LF refining, vacuum degassing, continuous casting, heating, rolling, and heat treatment. The produced wear-resistant steel plate has a surface hardness of 370 - 440 HBW, a core hardness of 350 - 430 HBW, a yield strength ≥ 1000 MPa, a tensile strength ≥ 1200 MPa, an elongation rate ≥ 13%, meets the 8a diameter 180° cold bend, and the -40°C impact Akv ≥ 40 J.

Description

Technical Field

[0001] The present invention belongs to the field of metallurgical technology and relates to a production method of NM400 wear-resistant steel plates. Technical Background

[0002] NM400 wear-resistant steel is widely used in wear-resistant materials in various fields such as metallurgy, mining, building materials, and railways, and is mainly applied to the key worn parts of equipment such as mining dump trucks, coal mine scraper conveyors, bulldozers, excavators, mixers, and loaders. High wear resistance is required for these parts. The improvement of the hardness of the steel plate can effectively improve the wear resistance, especially the improvement of the core hardness, which can not only significantly improve the wear resistance but also extend the service life of the equipment. The performance of NM400 wear-resistant steel is usually required to have a surface hardness of 370 - 430 HBW and a tensile strength of ≥1200 MPa. Summary of the Invention

[0003] The purpose of the present invention is to provide a low carbon equivalent NM400 wear-resistant steel plate with guaranteed core hardness and its production method. The thickness specification of the produced wear-resistant steel plate is 8 - 30 mm, and it meets the requirements of high wear resistance and high impact toughness, with a surface hardness of 370 - 440 HBW, a core hardness of 350 - 430 HBW, a yield strength of ≥1000 MPa, a tensile strength of ≥1200 MPa, an elongation of ≥13%, meeting the 180° cold bend with a diameter of 8a, and an impact Akv of ≥40 J at -40°C.

[0004] The technical solution of the present invention:

[0005] A production method of NM400 wear-resistant steel plates, the chemical composition of the steel by weight percentage is C = 0.14% - 0.15%, Si = 0.15% - 0.35%, Mn = 0.95% - 1.02%, P ≤ 0.012%, S ≤ 0.005%, Cr = 0.58% - 0.61%, Mo = 0.20% - 0.23%, Nb = 0.022% - 0.030%, Ti = 0.015% - 0.025%, Al = 0.020% - 0.050%, B = 0.0015% - 0.0025%, H ≤ 0.0002%, N ≤ 0.0060%, O ≤ 0.0015%, and the rest is Fe and unavoidable impurities, CEV ≤ 0.50%; the key process steps include:

[0006] (1) Converter smelting: Top-bottom combined blown converter, control the tapping temperature at 1550 - 1600°C, the P content in the converter tapping is ≤0.010%, during the tapping process, add deoxidizers and alloys for deoxidation and alloying, and low-P alloys are used for the alloys to avoid the increase of P in the molten steel;

[0007] (2) Refining: After the large ladle of molten steel is heated up by power supply in the LF furnace, the chemical composition is precisely adjusted, and then it enters the RH furnace or VD furnace for vacuum treatment. When tapping, the gas content in the molten steel is measured as H≤0.0002%, N≤0.0060%, and O≤0.0015%.

[0008] (3) Continuous casting: The superheat of the tundish is 8 - 20°C. Dynamic soft reduction or heavy reduction technology is adopted in continuous casting to improve the internal quality of the continuous casting billet. The thickness dimension of the continuous casting billet is 180 - 300mm, and the width dimension is 1700 - 2500mm.

[0009] (4) Heating: The temperature of the preheating section is 650 - 900°C, the temperature of the heating section is 1100 - 1260°C, the temperature of the soaking section is 1150 - 1250°C, and the residence time in the furnace is 160 - 300min.

[0010] (5) Rolling: Two-stage controlled rolling is adopted. The rolling temperature in the roughing stage is 1150 - 980°C, the cumulative reduction ratio in roughing is ≥3.3, the thickness of the intermediate billet is 60 - 90mm, the rolling start temperature in finishing is 860 - 1020°C, the cumulative reduction ratio in finishing is ≥2.6, and the final rolling temperature in finishing is 800 - 880°C.

[0011] (6) Heat treatment: Quenching + tempering process is adopted. The quenching heating temperature is 870 - 900°C, the heating rate is 1.6 - 2.2min / mm, and the holding time is 10 - 30min; the tempering heating temperature is 190 - 220°C, the heating rate is 3.0 - 4.0min / mm, and the holding time is 10 - 35min.

[0012] The physical properties of the wear-resistant steel plate obtained by the above method are as follows: surface hardness 370 - 440HBW, core hardness 350 - 430HBW, yield strength ≥1000MPa, tensile strength ≥1200MPa, elongation ≥13%, meeting the 180° cold bend for a diameter of 8a, and the impact Akv at -40°C ≥40J.

[0013] Principle of the invention: The wear-resistant steel of the present invention has characteristics such as high strength, high toughness, and high wear resistance, and at the same time has good welding performance and forming performance.

[0014] The reasons for the design of the chemical composition of the steel of the present invention are described as follows:

[0015] By controlling the C range, the hardness range of the steel plate is ensured to meet the target requirements; by adding elements such as Mn, B, and a small amount of Si and Cr, Mo, the hardenability of the steel plate is improved to ensure uniform structure of the steel plate; by combining tissue strengthening and alloy strengthening, the strength performance of the steel plate is improved; by the precipitates of Nb, Ti, Al and a reasonable rolling and heat treatment process specification, the grain is refined to achieve the purpose of improving the strength, toughness and hardness; at the same time, P, S, H, N, O in the molten steel are strictly controlled. Through the effective combination of scientific alloy element ratio and reasonable rolling and heat treatment process in the present invention, with a lower CEV design, the steel plate has excellent mechanical properties, welding properties and processing properties.

[0016] The beneficial effects of the present invention: The wear-resistant steel produced by the method of the present invention has excellent strength and toughness, wear resistance, weldability and formability, and has the advantage of low carbon equivalent to ensure the hardness of the core. Its mechanical properties are as follows: surface hardness 370 - 440 HBW, core hardness 350 - 430 HBW, yield strength ≥1000 MPa, tensile strength ≥1200 MPa, elongation ≥13%, meeting the 180° cold bending of 8a diameter, -40 °C impact Akv ≥40 J. The steel plate produced by the method of the present invention can be used for wear-resistant parts and structural parts such as excavators, bulldozers, loaders, dump trucks, etc. Brief Description of the Drawings

[0017] Figure 1 It is the metallographic structure photo of the embodiment of the present invention. Detailed Embodiments

[0018] Example 1:

[0019] Smelt 1 furnace of wear-resistant steel and produce steel plates with specifications of 8 mm and 12 mm respectively. The chemical composition by weight percentage of the steel is shown in Table 1; it includes the following key process steps:

[0020] (1) Converter smelting: Adopt top-bottom combined blowing converter for smelting, tapping temperature 1576 °C, P content at the end of converter tapping is 0.010%, alloying is carried out during tapping, adding deoxidizers such as ferrosilicon aluminum and aluminum blocks, and adding alloys such as low-carbon ferrochrome, silicomanganese alloy, medium-carbon ferromanganese, medium-carbon ferroboron, and metallic manganese;

[0021] (2) Refining: Heat up in LF furnace and adjust the composition. After the composition adjustment is completed, heat up to 1619 °C and leave the station, enter the VD furnace for vacuum treatment, keep the vacuum time for 15 min, soft blow and stand still for 20 min after breaking the vacuum, and sample and detect H = 0.00012%, N = 0.0036%, O = 0.0010%;

[0022] (3) Continuous casting: The liquidus temperature of the molten steel is about 1516 °C, the tundish temperature is controlled at 1520 - 1529 °C, continuous casting adopts dynamic soft reduction, and the cross-section of the billet is thickness × width = 260 × 2070 mm;

[0023] (4) Heating: The heating regime is as follows: preheating section at 720°C, heating section at 1120 - 1260°C, soaking section at 1170 - 1240°C, slab discharging temperature at 1200 - 1230°C, residence time in the furnace 195 - 226 min;

[0024] (5) Rolling: For rolling 8 and 12 mm thick steel plates, two-stage controlled rolling is adopted, and the rolling process parameters are shown in Table 2;

[0025] (6) Heat treatment: Quenching heating temperature is 890°C, tempering temperature is 210°C, and the detailed heat treatment parameters are shown in Table 3.

[0026] Example 2:

[0027] Smelt one furnace of wear-resistant steel and produce steel plates with specifications of 16 mm and 18 mm respectively. The chemical composition by weight percentage of the steel is shown in Table 1; it includes the following key process steps:

[0028] (1) Converter smelting: Top-bottom combined blowing converter is used for smelting, tapping temperature is 1577°C, the P content at the end of converter tapping is 0.007%, alloying is carried out during tapping, and deoxidizers such as ferrosilicon aluminum and aluminum blocks are added, and alloys such as low-carbon ferrochromium, silicomanganese alloy, medium-carbon ferro-manganese, and medium-carbon ferro-boron are added;

[0029] (2) Refining: The LF furnace raises the temperature and adjusts the composition. After the composition adjustment is completed, the temperature is raised to 1634°C for tapping and entering the VD furnace for vacuum treatment. The vacuum holding time is 15 min, and after breaking the vacuum, soft blowing and static holding are carried out for 21 min. Sampling and testing show that H = 0.00015%, N = 0.0039%, O = 0.0011%;

[0030] (3) Continuous casting: The liquidus temperature of the molten steel is about 1516°C, the tundish temperature is controlled at 1525 - 1533°C, dynamic soft reduction is adopted for continuous casting, and the slab cross-section is thickness × width = 260 × 2070 mm;

[0031] (4) Heating: The heating regime is as follows: preheating section at 810°C, heating section at 1100 - 1250°C, soaking section at 1180 - 1230°C, slab discharging temperature at 1202 - 1225°C, residence time in the furnace 200 - 216 min;

[0032] (5) Rolling: For rolling 16 and 18 mm thick steel plates, two-stage controlled rolling is adopted, and the rolling process parameters are shown in Table 2;

[0033] (6) Heat treatment: Quenching heating temperature is 890°C, tempering temperature is 210°C, and the detailed heat treatment parameters are shown in Table 3.

[0034] Example 3:

[0035] Smelt 1 furnace of wear-resistant steel and produce steel plates with specifications of 20 mm and 25 mm respectively. The chemical composition of the steel by weight percentage is shown in Table 1; it includes the following key process steps:

[0036] (1) Converter smelting: Adopt top and bottom combined blowing converter for smelting, tapping temperature is 1565 °C, the P content at the end of tapping from the converter is 0.006%, alloying is carried out during tapping, adding deoxidizers such as ferrosilicon aluminum and aluminum blocks, and adding alloys such as low-carbon ferrochromium, silicomanganese alloy, medium-carbon ferro-manganese, and medium-carbon ferro-boron;

[0037] (2) Refining: The LF furnace heats up and adjusts the composition. After the composition adjustment is completed, it is heated up to 1613 °C and discharged from the station. Then it enters the VD furnace for vacuum treatment. The vacuum holding time is 18 min. After breaking the vacuum, it is softly blown and statically held for 25 min. Samples are taken for detection, and H = 0.00013%, N = 0.0032%, O = 0.0009%;

[0038] (3) Continuous casting: The liquidus temperature of the molten steel is about 1516 °C, the tundish temperature is controlled at 1529 - 1534 °C, dynamic soft reduction is adopted for continuous casting, and the cross-section of the billet is thickness × width = 260 × 2070 mm;

[0039] (4) Heating: The heating system is: preheating section at 850 °C, heating section at 1100 - 1250 °C, soaking section at 1170 - 1240 °C, the slab discharging temperature is 1198 - 1220 °C, and the time in the furnace is 190 - 210 min;

[0040] (5) Rolling: Roll steel plates with specifications of 20 and 25 mm, adopt two-stage controlled rolling, and the rolling process parameters are shown in Table 2;

[0041] (6) Heat treatment: The quenching heating temperature is 890 °C, and the tempering temperature is 210 °C. The detailed heat treatment parameters are shown in Table 3.

[0042] Example 4:

[0043] Smelt 1 furnace of wear-resistant steel and produce steel plates with a specification of 30 mm. The chemical composition of the steel by weight percentage is shown in Table 1; it includes the following key process steps:

[0044] (1) Converter smelting: Adopt top and bottom combined blowing converter for smelting, tapping temperature is 1586 °C, the P content at the end of tapping from the converter is 0.009%, alloying is carried out during tapping, adding deoxidizers such as ferrosilicon aluminum and aluminum blocks, and adding alloys such as low-carbon ferrochromium, silicomanganese alloy, medium-carbon ferro-manganese, and medium-carbon ferro-boron...

[0045] (2) Refining: The LF furnace heats up and adjusts the composition. After the composition adjustment is completed, it is heated up to 1618 °C and discharged from the station. Then it enters the VD furnace for vacuum treatment. The vacuum holding time is 15 min. After breaking the vacuum, it is softly blown and statically held for 20 min. Samples are taken for detection, and H = 0.00014%, N = 0.0036%, O = 0.0008%;

[0046] (3) Continuous casting: The liquidus temperature of the molten steel is about 1516 °C, the tundish temperature is controlled at 1523 - 1527 °C, dynamic soft reduction is adopted in continuous casting, and the cross-section of the billet is thickness × width = 260 × 2070 mm;

[0047] (4) Heating: The heating regime is as follows: preheating section at 820 °C, heating section at 1110 - 1250 °C, soaking section at 1180 - 1240 °C, the slab discharging temperature is 1200 - 1230 °C, and the residence time in the furnace is 200 - 226 min;

[0048] (5) Rolling: When rolling 30 mm thick steel plates, two-stage controlled rolling is adopted, and the rolling process parameters are shown in Table 2;

[0049] (6) Heat treatment: The quenching heating temperature is 890 °C, and the tempering temperature is 210 °C. The detailed heat treatment parameters are shown in Table 3.

[0050] The test results of the mechanical properties of the obtained steel plates are shown in Table 4.

[0051] Table 1 Chemical composition mass percentage (wt.%) of the examples

[0052] Embodiment C Si Mn P S AlT Cr Mo Nb Ti B CEV 1 0.15 0.20 0.96 0.010 0.0036 0.048 0.58 0.20 0.023 0.021 0.0017 0.47 2 0.14 0.20 0.99 0.009 0.0017 0.029 0.60 0.21 0.024 0.016 0.0014 0.47 3 0.14 0.22 0.97 0.009 0.0020 0.028 0.58 0.20 0.024 0.017 0.0016 0.46 4 0.14 0.20 0.95 0.010 0.0008 0.026 0.60 0.20 0.023 0.015 0.0016 0.46

[0053] Table 2 Rolling process parameters of the examples

[0054]

[0055] Table 3 Heat treatment process parameters of the examples

[0056]

[0057] Table 4 Test results of the mechanical properties of the examples

[0058]

[0059] In the above tables: The 8 mm impact is for the thinned specimen with dimensions 5 mm × 10 mm; the impact for ≥12 mm is for the standard specimen with dimensions 10 mm × 10 mm.

Claims

1. A production method of NM400 wear-resistant steel plate, characterized in that: The chemical composition of the steel is by weight percentage: C = 0.14% - 0.15%, Si = 0.15% - 0.35%, Mn = 0.95% - 1.02%, P ≤ 0.012%, S ≤ 0.005%, Cr = 0.58% - 0.61%, Mo = 0.20% - 0.23%, Nb = 0.022% - 0.030%, Ti = 0.015% - 0.025%, Al = 0.020% - 0.050%, B = 0.0015% - 0.0025%, H ≤ 0.0002%, N ≤ 0.0060%, O ≤ 0.0015%, the balance being Fe and unavoidable impurities, and CEV ≤ 0.50%; The key process steps include: (1) Converter smelting: Top and bottom combined blown converter, controlling the tapping temperature at 1560 - 1590 °C, P ≤ 0.010% for the converter tapping, adding deoxidizers and alloys during the tapping process for deoxidation and alloying, where low-P alloys are used for the alloys to avoid an increase in P in the molten steel; (2) Refining: After the molten steel in the tundish is heated by power supply in the LF furnace, the chemical composition is precisely adjusted, and then it enters the RH furnace or VD furnace for vacuum treatment. When leaving the station, the gas content in the molten steel is measured as H ≤ 0.0002%, N ≤ 0.0060%, O ≤ 0.0015%; (3) Continuous casting: The superheat of the tundish is 8 - 20 °C. The dynamic soft reduction or heavy reduction technology is adopted for continuous casting to improve the internal quality of the continuous casting billet. The thickness dimension of the continuous casting billet is 180 - 300 mm, and the width dimension is 1700 - 2500 mm; (4) Heating: The temperature of the preheating section is 650 - 900 °C, the temperature of the heating section is 1100 - 1260 °C, the temperature of the soaking section is 1150 - 1250 °C, and the residence time in the furnace is 160 - 300 min; (5) Rolling: Two-stage controlled rolling is adopted. The rolling temperature in the rough rolling is 1150 - 980 °C, the cumulative reduction ratio in the rough rolling is ≥ 2.5, the thickness of the intermediate billet is 60 - 90 mm, the starting rolling temperature in the finish rolling is 880 - 1040 °C, the cumulative reduction ratio in the finish rolling is ≥ 3, and the final rolling temperature in the finish rolling is 780 - 830 °C; (6) Heat treatment: The quenching + tempering process is adopted. The quenching heating temperature is 870 - 900 °C, the heating rate is 1.6 - 2.2 min / mm, the holding time is 10 - 30 min, and the quenching cooling rate is 20 - 40 °C / s; the tempering heating temperature is 190 - 220 °C, the heating rate is 3.0 - 4.0 min / mm, the holding time is 10 - 35 min. The surface hardness of the wear-resistant steel obtained is 370 - 440 HBW, the core hardness is 350 - 430 HBW, the yield strength is ≥ 1000 MPa, the tensile strength is ≥ 1200 MPa, the elongation is ≥ 13%, meeting the requirements of 180° cold bending with a diameter of 8a and Akv ≥ 40 J at - 40 °C.

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