A production method of a large-thickness high-toughness NM360 wear-resistant steel plate

Abstract

A production method of a large-thickness high-toughness NM360 wear-resistant steel plate, the chemical composition of the steel plate is as follows: C=0.15-0.17, Si=0.15-0.25, Mn=1.10-1.20, P≤0.008, S≤0.0015, Cr=0.60-0.70, Mo=0.4-0.45, Ni=1.15-1.3, Nb=0.025-0.030, V=0.045-0.050, Ti=0.014-0.020, Alt=0.030-0.060, B=0.0014-0.0020, Ce≥0.0010, H≤0.0015, N≤0.0040, O≤0.0012. The process steps include KR molten iron pretreatment, converter smelting, LF refining, RH vacuum degassing, continuous casting, heating, rolling and heat treatment. The thickness of the steel plate covers 80-120 mm, the surface and thickness section hardness is 330-380 HBW, the core / surface hardness is ≥0.90, the diameter of 6a is 180° cold bending, the impact Akv at-40 ℃ is ≥60 J, the impact Akv at-60 ℃ is ≥40 J, the strength and toughness performance is adapted, and the manufacturing performance of the steel plate cutting, cold forming and welding is excellent.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology and relates to a method for producing thick, high-toughness NM360 wear-resistant steel plates. technology

[0002] Wear-resistant steel is widely used in various fields such as metallurgy, mining, building materials, and railways, playing a crucial role in key wear-prone parts of equipment such as mining dump trucks, coal mine scraper conveyors, bulldozers, excavators, mixers, and loaders. However, in extreme industrial conditions, the demand for a combination of thick-walled wear-resistant steel and low-temperature impact toughness is becoming increasingly prominent, driven by the dual forces of the increasing size of heavy-duty equipment and low-temperature operations in cold regions. Regarding the demand for thickness, equipment in mining and construction machinery is shifting towards ultra-large sizes. A 100m³ mining excavator bucket needs to withstand the impact of thousands of tons of material. Traditional wear-resistant steel with a thickness of less than 50mm is prone to localized deformation or cracking due to insufficient thickness, necessitating the use of 60-100mm or even thicker wear-resistant steel plates to ensure structural stability through "thick section deformation resistance." Regarding the demand for low-temperature impact toughness, in cold regions such as Northeast China and Siberia, or in low-temperature operating scenarios such as cold chain logistics and polar engineering, equipment needs to operate in environments ranging from -20 to -60℃. Ordinary wear-resistant steel is prone to brittle fracture due to its low-temperature brittle impact energy being ≤20J. The demand for combined applications is currently concentrated in heavy-duty equipment in cold regions. For example, crusher liners in cold-region mines need to be 80mm thick to resist impact and have an impact energy of ≥27J at -40℃, while bucket blades in polar engineering machinery need to be 100mm thick to resist wear and have an impact energy of ≥35J at -40℃. These applications require wear-resistant steel to simultaneously possess uniform hardness across a thick section, a hardness difference of ≤50HBW across the entire thickness, and low-temperature toughness reserves.

[0003] In summary, the synergistic demand for greater thickness and high toughness under low-temperature impact is essentially an upgrade in the adaptability of industrial equipment to extreme working conditions, driving the development of wear-resistant steel from a single wear-resistant material to a multi-performance integration direction that combines wear resistance, impact resistance, and low-temperature toughness. Summary of the Invention

[0004] The purpose of this invention is to provide a method for producing thick, high-toughness NM360 wear-resistant steel plates, producing 80~120mm thick, high-toughness NM360 wear-resistant steel plates with a surface and thickness section hardness of 330~380HBW, a core / surface hardness ≥0.90, meeting the requirements of 6a diameter 180° cold bending, -40℃ impact Akv ≥60J, -60℃ impact Akv ≥40J, with good strength and toughness, and excellent manufacturing performance in steel plate cutting, cold forming and welding.

[0005] The technical solution of the present invention: A method for producing thick, high-toughness NM360 wear-resistant steel plates, wherein the chemical composition of the steel (by weight percentage) is C=0.15~0.17, Si=0.15~0.25, Mn=1.10~1.20, P≤0.008, S≤0.0015, Cr=0.60~0.70, Mo=0.4~0.45, Ni=1.15~1.3, Nb=0.025~0.030, V=0.045~0.050, Ti=0.014~0.020, Alt=0.030~0.060, B=0.0014~0.0020, Ce≥0.0010, H≤0.0015, N≤0.0040, O≤0.0012, with the remainder being Fe and unavoidable impurities; the key process steps include: (1) The KR-BOF-LF-RH-CC smelting process is adopted. The molten iron is subjected to deep desaturation and dephosphorization treatment. The vacuum degree of the RH furnace is ≤67Pa and the holding time is ≥20min. When the vacuum is maintained for 15~18min, 40~60kg of 30%Ce rare earth alloy and 80~100kg of silicon-calcium-barium alloy are added. After breaking the vacuum, soft blowing is performed for 20~25min. The gas in the tundish is measured to be H≤0.00015, N≤0.0040, and O≤0.0012. The superheat of the tundish is controlled at 5~14℃. After the billet is produced, it is stacked for slow cooling and hydrogen expansion. The stacking cooling time is ≥48h and the stacking temperature is ≤100℃.

[0006] (2) Billet heating: furnace temperature ≤1280℃, heating temperature 1200~1220℃, total furnace time 1.2~1.4min / mm×slab thickness mm.

[0007] (3) First stage rolling: the initial rolling temperature is ≥1050℃, the single pass reduction is 42~50mm; the final rolling temperature is ≥950℃, and the intermediate rolling thickness is the target rolling thickness +40~60mm.

[0008] (4) Second stage rolling: the initial rolling temperature is 870~900℃, the final rolling temperature is 790~830℃, the stacking is slow cooling within 2 hours after rolling, the stacking cooling time is ≥72h, and the unstacking temperature is ≤100℃.

[0009] (5) Heat treatment: Quenching + high temperature tempering process is adopted. The quenching temperature is 920~930℃ and the time is the thickness of the steel plate mm × (1.9~2.2) min / mm; the tempering temperature is 490~500℃ and the tempering time is the thickness of the steel plate mm × (2.0~2.2) min / mm until the plate is taken out of the furnace.

[0010] (6) Post-furnace cutting: The heat-treated steel plate is cut without preheating by flame cutting to obtain accurate dimensions.

[0011] Furthermore, the steel plate's chemical composition is designed to include rare earth element Ce, with a Ce content ≥ 0.0010%.

[0012] The steel plates produced by the above method have a thickness of 80-120mm, a surface and thickness section hardness of 330-380HBW, a core / surface hardness ≥0.90, meet the requirements of 6a diameter 180° cold bending, and have an impact Akv ≥60J at -40℃ and an impact Akv ≥40J at -60℃.

[0013] The main innovations of this invention are: 1) The alloying element is clearly added with Ce, which is required to be ≥0.0010%. Through rare earth treatment, large particle inclusions in the molten steel are reduced and refined.

[0014] 2) Strictly control the H content, with H in the intermediate package ≤ 0.00015, to reduce the amount of diffusible hydrogen and its accumulation, effectively preventing the occurrence of hydrogen-induced delayed cracks.

[0015] 3) The steel plate is subjected to high temperature and short time tempering treatment, with a furnace time coefficient of 2.0~2.2min / mm and a surface temperature of 490~500℃ when it is taken out of the furnace.

[0016] 4) Thickness ranges from 80 to 120 mm, surface and thickness section hardness is 330 to 380 HBW, core / surface hardness is ≥0.90, meets 6a diameter 180° cold bending, -40℃ impact Akv≥60J, -60℃ impact Akv≥40J, and has excellent comprehensive application performance.

[0017] 5) Enables preheating-free cutting of 80-120mm thick NM360 plates at ambient temperatures of 0-30℃, with a cutting speed of 100-250mm / min. After cutting, the cut edges are ground and then colored or subjected to magnetic particle testing within ≥48 hours, with no delayed crack defects.

[0018] The beneficial effects of this invention are as follows: The thick, high-toughness NM360 wear-resistant steel plate produced by the method of this invention adopts a process route of KR molten iron pretreatment + converter smelting + LF refining + RH vacuum degassing + continuous casting + billet heating + rolling + quenching and tempering, coupled with appropriate composition design, smelting and heat treatment processes. The process is simple and highly operable. During the smelting process, Ce rare earth alloys are added, and the contents of H, N, and O are strictly controlled. Combined with quenching + high-temperature short-time tempering processes, excellent microstructure and cross-sectional uniformity are obtained, meeting the synergistic requirements of thick NM360-grade wear-resistant steel and high toughness in low-temperature impact. This promotes the development of wear-resistant steel from "single wear resistance" to a multi-performance integration direction of "wear resistance + impact resistance + low-temperature toughness". Attached Figure Description

[0019] Figure 1 A photograph of the metallographic structure produced in Example 1.

[0020] Figure 2 Metallographic images of the tissue produced in Example 2. Detailed Implementation Example 1

[0021] A method for producing thick, high-toughness NM360 wear-resistant steel plates involves smelting one heat of NM360 wear-resistant steel and rolling it into an 80mm thick steel plate. The chemical composition (weight percentage) of the steel is shown in Table 1, with the remainder being Fe and unavoidable impurities. The method includes the following key process steps: (1) The KR-BOF-LF-RH-CC smelting process path is adopted. The vacuum degree of the RH furnace is 67 Pa and the holding time is 22 min. When the vacuum is maintained for 16 min, 50 kg of 30% Ce rare earth alloy and 80 kg of silicon-calcium-barium alloy are added. After breaking the vacuum, soft blowing is carried out for 20 min. The gas content of the molten steel is 0.00012%, N content is 0.0040%, and O content is 0.0012% when measured in the tundish. The superheat of the tundish is controlled at 6~11℃. After the billet is produced, it is stacked and slowly cooled to expand hydrogen. The stacking cooling time is 52 h and the stacking temperature is 96℃.

[0022] (2) Billet heating: furnace temperature 1273℃, heating temperature 1213℃, total furnace time 452min.

[0023] (3) First stage rolling: initial rolling temperature 1076℃, single pass reduction: 44~47mm; final rolling temperature 983℃, intermediate rolling thickness is the target rolling thickness 130mm.

[0024] (4) Second stage rolling: the initial rolling temperature is 884℃, the final rolling temperature is 811℃, the stacking is slow cooling within 2 hours after rolling, the stacking cooling time is 104 hours, and the unstacking temperature is 61℃.

[0025] (5) Heat treatment: Quenching + high temperature tempering process is adopted. The quenching temperature is 928℃ and the time is 165min; the tempering temperature is 496℃ and the tempering time is 166min until the furnace is opened.

[0026] (6) Post-furnace cutting: The steel plate after heat treatment is cut without preheating at an ambient temperature of 19℃ (cutting speed 240mm / min). The cutting time is 77h. The cut edge is ground and then colored or magnetic particle tested. There are no delayed crack defects.

[0027] Example 2 A method for producing thick, high-toughness NM360 wear-resistant steel plates involves smelting one heat of NM360 wear-resistant steel and rolling it into a 120mm thick steel plate. The chemical composition (weight percentage) of the steel is shown in Table 1, with the remainder being Fe and unavoidable impurities. The method includes the following key process steps: (1) The KR-BOF-LF-RH-CC smelting process path is adopted. The vacuum degree of the RH furnace is 67 Pa and the holding time is 24 min. When the vacuum is maintained for 18 min, 60 kg of 30% Ce rare earth alloy and 100 kg of silicon-calcium-barium alloy are added. After breaking the vacuum, soft blowing is carried out for 24 min. The tundish gas content is measured to be 0.00013% H, 0.0036% N, and 0.0009% O. The superheat of the tundish is controlled at 7~13℃. After the billet is produced, it is stacked for slow cooling and hydrogen expansion (stack cooling time is 61 h, and the stacking temperature is 87℃).

[0028] (2) Billet heating: furnace temperature 1278℃, heating temperature 1218℃, total furnace time 441min.

[0029] (3) First stage rolling: initial rolling temperature 1087℃, single pass reduction: 43~49mm; final rolling temperature 976℃, intermediate rolling thickness is the target rolling thickness 162mm.

[0030] (4) Second stage rolling: the initial rolling temperature is 872℃, the final rolling temperature is 808℃, the stacking is slow cooling within 2 hours after rolling, the stacking cooling time is 112 hours, and the stacking temperature is 72℃.

[0031] (5) Heat treatment: Quenching + high temperature tempering process is adopted. The quenching temperature is 922℃ and the time is 253min for the thickness of the steel plate; the tempering temperature is 498℃ and the tempering time is 248min until the plate is taken out of the furnace.

[0032] (6) Post-furnace cutting: The steel plate after heat treatment is cut without preheating at an ambient temperature of 14℃ (cutting speed 156mm / min). The cutting time is 124h. The cut edge is ground and then colored or magnetic particle tested. There are no delayed crack defects.

[0033] The rolling and heat treatment parameters produced in Examples 1 and 2 are shown in Tables 2 and 3, respectively, and the mechanical property test results are shown in Table 4. The metallographic structure of Example 1 is shown in Table 4. Figure 1 The metallographic structure in Example 2 is shown below. Figure 2 .

[0034] Table 1. Chemical composition by mass percentage (wt.) .

[0035] Table 2 Rolling process parameters .

[0036] Table 3 Heat treatment process parameters .

[0037] Table 4 Mechanical property test results .

Claims

1. A method for producing a thick, high-toughness NM360 wear-resistant steel plate, characterized in that: The chemical composition of the steel by weight percentage is C=0.15~0.17, Si=0.15~0.25, Mn=1.10~1.20, P≤0.008, S≤0.0015, Cr=0.60~0.70, Mo=0.4~0.45, Ni=1.15~1.3, Nb=0.025~0.030, V=0.045~0.050, Ti=0.014~0.020, Alt=0.030~0.060, B=0.0014~0.0020, Ce≥0.0010, H≤0.0015, N≤0.0040, O≤0.0012, with the remainder being Fe and unavoidable impurities; Key process steps include: (1) The KR-BOF-LF-RH-CC smelting process is adopted. The molten iron is subjected to deep desaturation and dephosphorization treatment. The vacuum degree of the RH furnace is ≤67Pa and the holding time is ≥20min. When the vacuum is maintained for 15~18min, 40~60kg of 30%Ce rare earth alloy and 80~100kg of silicon-calcium-barium alloy are added. After breaking the vacuum, soft blowing is performed for 20~25min. The gas content of the molten steel in the tundish is measured as H≤0.00015, N≤0.0040, and O≤0.0012. The superheat of the tundish is controlled at 5~14℃. After the billet is produced, it is stacked for slow cooling and hydrogen expansion. The stacking cooling time is ≥48h and the unstacking temperature is ≤100℃. (2) Billet heating: furnace temperature ≤1280℃, heating temperature 1200~1220℃, total furnace time 1.2~1.4min / mm×slab thickness mm; (3) First stage rolling: the initial rolling temperature is ≥1050℃, the single pass reduction is 42~50mm; the final rolling temperature is ≥950℃, and the intermediate rolling thickness is the target rolling thickness +40~60mm. (4) Second stage rolling: the initial rolling temperature is 870~900℃, the final rolling temperature is 790~830℃, the stacking is slow cooling within 2 hours after rolling, the stacking cooling time is ≥72 hours, and the unstacking temperature is ≤100℃. (5) Heat treatment: Quenching + high temperature tempering process is adopted. The quenching temperature is 920~930℃ and the time is the thickness of the steel plate mm × (1.9~2.2) min / mm; the tempering temperature is 490~500℃ and the tempering time is the thickness of the steel plate mm × (2.0~2.2) min / mm until the plate is taken out of the furnace. (6) Post-furnace cutting: The heat-treated steel plate is processed by flame cutting to obtain accurate dimensions.

2. The method for producing a thick, high-toughness NM360 wear-resistant steel plate according to claim 1, characterized in that: The steel plate is designed to contain rare earth element Ce, with a Ce content ≥ 0.0010%.

3. The method for producing a thick, high-toughness NM360 wear-resistant steel plate according to claim 1, characterized in that: The steel plates produced have a thickness of 80-120mm, a surface and thickness section hardness of 330-380HBW, a core / surface hardness ≥0.90, meet the requirements of 6a diameter 180° cold bending, and have an impact Akv ≥60J at -40℃ and an impact Akv ≥40J at -60℃.

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