CN111168192B - Hot cutting method for high-hardness wear-resistant steel plate with thickness of 50-80 mm - Google Patents
Hot cutting method for high-hardness wear-resistant steel plate with thickness of 50-80 mm Download PDFInfo
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- CN111168192B CN111168192B CN202010104720.8A CN202010104720A CN111168192B CN 111168192 B CN111168192 B CN 111168192B CN 202010104720 A CN202010104720 A CN 202010104720A CN 111168192 B CN111168192 B CN 111168192B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K28/00—Welding or cutting not covered by any of the preceding groups, e.g. electrolytic welding
- B23K28/02—Combined welding or cutting procedures or apparatus
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K10/00—Welding or cutting by means of a plasma
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K7/00—Cutting, scarfing, or desurfacing by applying flames
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K7/00—Cutting, scarfing, or desurfacing by applying flames
- B23K7/008—Preliminary treatment
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/84—Controlled slow cooling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/0081—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for slabs; for billets
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
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Abstract
The invention discloses a hot cutting method of a high-hardness wear-resistant steel plate with the thickness of 50-80 mm, which comprises the following steps: rapidly and slowly cooling the slab after the slab is rolled into a steel plate, wherein the slow cooling temperature is more than 550 ℃, and the slow cooling time is more than 50 hours; cutting the steel plate out of the slow cooling pit into an L-shaped steel plate with sample blocks at the corners, quickly stacking and cooling after cutting, wherein the stacking and cooling temperature is more than or equal to 120 ℃, the stacking and cooling time is more than or equal to 15 hours, and cooling to room temperature; carrying out quenching and low-temperature tempering heat treatment on the steel plate, wherein the tempering temperature is 180-220 ℃, and obtaining a high-hardness wear-resistant steel plate with a matrix structure of tempered martensite; and (3) after the steel plate is discharged from the furnace, controlling the cutting temperature of the steel plate to be more than or equal to 150 ℃, carrying out hot cutting separation on the connecting part of the steel plate and the corner sample block to obtain a finished steel plate and a detection sample block, rapidly stacking and cooling the finished steel plate at the stacking and cooling temperature of more than or equal to 120 ℃, and cooling to room temperature. The invention carries out the cutting in a rolling state, thereby thoroughly solving the problem of delayed edge cracking of the hot-cut thick high-hardness wear-resistant steel plate.
Description
Technical Field
The invention relates to the technical field of cutting of wear-resistant steel plates, in particular to a hot cutting method for a high-hardness wear-resistant steel plate with the thickness of 50-80 mm.
Background
The high-hardness wear-resistant steel plate (steel plate for short) provided by the invention refers to the wear-resistant steel plate with the surface Mohs hardness of more than or equal to 470HBW in the national standard GB/T24186-2009 high-strength wear-resistant steel plate for engineering machinery and the wear-resistant steel plate with the surface Mohs hardness of more than or equal to 470 HBW.
The wear-resistant steel plate is usually manufactured by adopting a quenching and tempering heat treatment process for obtaining high strength, the product is widely applied to various fields such as metallurgy, mines, building materials, electric power, railways, military affairs and the like, and the manufactured main parts comprise excavator bucket teeth, ball mill lining plates, crusher jaw plates, crushing walls, rolling mortar walls, fan mill impact plates, tractor track plates, railway turnouts and the like. Along with the rapid development of industries such as engineering machinery and the like in China, the demand for high-hardness wear-resistant steel plates with high strength and toughness, weldability and thickness is larger and larger, and the possibility of cracks after the steel plates are subjected to fixed-length hot cutting is higher and higher. For a high-hardness wear-resistant steel plate with the thickness of 50-80 mm, due to the fact that on-line shearing is difficult, hot cutting is the most economical at present, but the problem of hot cutting delayed cracks is caused (see fig. 1 and fig. 2), the delayed cracks are not generated during hot cutting, but are generated hours, days or weeks after the hot cutting is finished, and a good solution is not provided in the prior art. The delayed cracking of the steel plate causes large waste judgment amount, low yield and increased production cost, prolongs the delivery period of products, seriously influences the image of enterprises and reduces the product competitiveness.
Disclosure of Invention
In order to solve the technical problems, the invention aims to provide a hot cutting method of a high-hardness wear-resistant steel plate with the thickness of 50-80 mm, and thoroughly solves the problem of edge crack of the high-hardness wear-resistant steel plate with thicker hot cutting.
The purpose of the invention can be realized by the following technical scheme:
a hot cutting method for a high-hardness wear-resistant steel plate with the thickness of 50-80 mm comprises the following steps:
s1: preparing steel plate hot cutting: rolling the plate blank into a steel plate to obtain a ferrite and pearlite structure, and quickly and slowly cooling the steel plate at the slow cooling temperature of more than 550 ℃ for more than 50 hours;
s2: hot cutting of the steel plate: cutting the steel plate into L-shaped steel plates with sample blocks at the corners after the steel plate is taken out of the slow cooling pit, quickly cooling the steel plate in a heaping mode, wherein the heaping cooling temperature is more than or equal to 120 ℃, the heaping cooling time is more than or equal to 15 hours, and cooling the steel plate to room temperature;
s3: heat treatment after steel plate cutting: carrying out quenching and low-temperature tempering heat treatment on the steel plate, wherein the tempering temperature is 180-220 ℃, and obtaining a high-hardness wear-resistant steel plate with a matrix structure of tempered martensite;
s4: separating the steel plate from the corner sample block: and (3) after the steel plate is taken out of the furnace, the cutting temperature of the steel plate is not less than 150 ℃, the steel plate is thermally cut and separated from the connecting part of the corner sample block to obtain a finished steel plate and a detection sample block, the finished steel plate is rapidly cooled in a heaped mode, the temperature of the heaped cooling is not less than 120 ℃, and the steel plate is cooled to room temperature.
Furthermore, a cutting seam is arranged between the steel plate body of the L-shaped steel plate and the corner sample block, and the length of the cutting seam is 62.5% -75% of the length of the sample block.
Further, the cutting temperature of the steel plate in the step S2 is 200-300 ℃.
Further, the size of the corner sample piece of the steel plate in the step S2 is 200mm × 400 mm.
The invention relates to a thermal cutting delayed crack generation analysis:
according to the research of the applicant, the residual stress generated during the hot cutting and heat treatment process is found to be a direct cause of the crack of the thicker high hardness wear resistant steel plate. The high-hardness wear-resistant steel plate is generally subjected to quenching and low-temperature tempering to ensure the hardness, the tempered and discharged steel plate is a tempered martensite structure (see figure 3), the martensite structure is brittle, a cutting line is long, the steel plate has a rapid heating and quenching phenomenon, and a cutting surface and the vicinity generate larger phase change stress and structure stress due to martensite phase change and nonuniform structure. When the steel plate is subjected to hot cutting, combustion products of the steel plate are adsorbed on the steel plate under the action of residual stress (phase change stress, structural stress and thermal stress), along with the increase of the hydrogen content in the steel plate, the combustion products are concentrated at the defects such as dislocation, grain boundary, impurity atoms, inclusions, micro-cavities and the like in the steel plate, and when the hydrogen concentration reaches a critical value, the defects crack, and the cracks show typical stress crack characteristics. The high hardness wear resistant steel is not cracked during flame cutting, but is cracked hours, days or weeks after hot cutting, and is classified as hydrogen-induced delayed cracking. Before the steel plate is cut, if effective preheating and heat preservation measures after cutting are not taken, the heat input of the thicker steel plate during hot cutting is larger, the surface and the center of the cut steel plate are heated unevenly, and cooling after cutting is uneven, so that larger thermal stress can be generated. Quenching stress is the combination of quenching thermal stress, phase transformation stress and stress caused by different structures. The residual stress after quenching is the superposition of the above stress after heat treatment. The delayed crack is generated because the fine cracks existing in the core of the steel plate require a considerable time to be fused and expanded under the above residual stress during the stay process after cutting, and the fracture may occur when the size of the fine cracks reaches the fracture critical crack size. Meanwhile, because the size of the steel plate in the thickness direction is obviously smaller than that of the steel plate in other directions, cracks are formed in the thickness direction firstly and then are expanded in the rolling direction. Therefore, for a thicker and high-hardness wear-resistant steel plate, long-distance cutting in a martensite structure state is avoided on the premise of eliminating the residual stress of the steel plate as much as possible, and the problem of delayed cracks of hot cutting can be well solved.
The technical scheme of the invention has the general idea that: 1) the rolled steel plate is fed into a slow cooling pit for slow cooling before cutting, so that the residual stress in the steel is effectively reduced, hydrogen is discharged, the internal quality of the steel plate is improved, and the influence of the residual stress on cutting is reduced; 2) after the slow cooling time of the steel plate is more than 50 hours, the steel plate is cut to length after leaving the slow cooling pit, and the cutting is carried out in a rolling state that the matrix structure of the steel plate is ferrite and pearlite, so that cutting edge crack can not be generated; 3) the L-shaped steel plate with the sample blocks at the corners is cut, so that the sampling is convenient after the steel plate is subjected to heat treatment, the cutting amount is reduced, and cracks are prevented from being generated by long-distance cutting; 4) after the steel plate is cut, the steel plate is quickly cooled in a heaping mode, and the residual stress of hot cutting is reduced; 5) carrying out quenching and low-temperature tempering heat treatment on the steel plate, wherein the tempering temperature is 180-220 ℃, and obtaining a high-hardness wear-resistant steel plate with a matrix structure of tempered martensite; 6) and after the steel plate is taken out of the furnace, controlling the cutting temperature of the steel plate to be more than or equal to 150 ℃, and thermally cutting and separating the steel plate from the connecting part of the corner sample block, wherein cracks can not be generated due to small cutting amount and cold heaping.
The invention has the advantages that: the steel sheet is different from current finished product cutting, puts the cutting and goes on at rolling state, has effectively avoided long distance rapid heating and quenching cutting edge crack. The rolled steel plate is slowly cooled and subjected to hydrogen discharge, so that the residual stress in the steel can be effectively reduced, and the risk of cutting delayed edge cracking is reduced; the dump cooling measure can eliminate the residual stress in the steel; the steel plate is cut into an L-shaped steel plate with sample blocks at the corners, so that the sampling is convenient after the steel plate is subjected to heat treatment, the cutting amount is reduced, and cracks are prevented from being generated by long-distance cutting; carrying out quenching and low-temperature tempering heat treatment on the cut steel plate, wherein the tempering temperature is 180-220 ℃, and obtaining a high-hardness wear-resistant steel plate with a matrix structure of tempered martensite; after the steel plate is tempered and discharged out of the furnace, the steel plate is separated from the connecting part of the corner sample block by hot cutting, and cracks can not be generated due to less cutting amount and cold heaping, so that the problem of delayed edge cracking of the high-hardness wear-resistant steel plate with thicker hot cutting is thoroughly solved.
Drawings
Fig. 1 is a macro topography diagram of a delayed crack of a cut surface of a conventional NM500 wear-resistant steel plate from top to bottom.
FIG. 2 is a macro topography of a lateral delayed crack of a cut surface of a prior NM500 wear-resistant steel plate.
Fig. 3 is a diagram of a metallographic structure (magnified 500 times) of an NM500 wear-resistant steel plate after tempering.
FIG. 4 is a schematic top view of the high hardness wear-resistant steel plate of the present invention cut into an "L" shape in a rolled state.
FIG. 5 is a macroscopic topography diagram of the rolled head of the high-hardness wear-resistant steel plate of the invention, which is cut into an L shape.
FIG. 6 is a macro-topography diagram of the final state of the high-hardness wear-resistant steel plate after cutting.
FIG. 7 is a metallographic structure (magnified 500 times) of a high-hardness wear-resistant steel plate according to the present invention at a thickness of 1/4;
in the figure: A. a steel plate body; B. sample blocks; C. and (6) cutting the seam.
Detailed Description
The invention is further illustrated with reference to the following figures and examples. Referring to fig. 1 to 6, a hot cutting method of a high-hardness wear-resistant steel plate with a thickness of 50 to 80mm includes the following steps:
s1: preparing steel plate hot cutting: rolling the plate blank into a steel plate to obtain a ferrite and pearlite structure, and quickly and slowly cooling the steel plate at the slow cooling temperature of more than 550 ℃ for more than 50 hours;
s2: hot cutting of the steel plate: cutting the steel plate into L-shaped steel plates with sample blocks B at the corners after the steel plate is taken out of the slow cooling pit, quickly cooling the steel plates in a heaping mode, wherein the heaping temperature is more than or equal to 120 ℃, the heaping time is more than or equal to 15 hours, and cooling the steel plates to room temperature;
s3: heat treatment after steel plate cutting: carrying out quenching and low-temperature tempering heat treatment on the steel plate, wherein the tempering temperature is 180-220 ℃, and obtaining a high-hardness wear-resistant steel plate with a matrix structure of tempered martensite;
s4: separating the steel plate from the corner sample block B: and (3) after the steel plate is taken out of the furnace, the cutting temperature of the steel plate is not less than 150 ℃, the steel plate is thermally cut and separated from the connecting part of the corner sample block B to obtain a finished steel plate body A and a detection sample block B, the finished steel plate is rapidly cooled in a heaped mode, the temperature of the heaped cooling is not less than 120 ℃, and the steel plate is cooled to room temperature.
Furthermore, a cutting seam C is formed between the steel plate body A and the corner sample block B of the L-shaped steel plate, and the length of the cutting seam C is 62.5% -75% of the length of the sample block.
Further, the cutting temperature of the steel plate in the step S2 is 200-300 ℃.
Further, the size of the steel plate corner block B in the step S2 is 200mm × 400 mm.
The invention produces the wear-resistant steel plate with the thickness of 50-80 mm and the hardness of more than or equal to 470HBW, and the wear-resistant steel plate comprises the following chemical components in percentage by mass: c: 0.25 to 0.35%, Si: 0.10 to 0.50%, Mn: 0.80-1.35%, P: less than or equal to 0.015 percent, less than or equal to 0.005 percent of S, Cr: 0.70-1.00%, Ni: less than or equal to 1.00 percent, Mo: 0.10-0.30%, Ti: 0.010-0.020%, B: 0.0005-0.0060%, Als: 0.015 to 0.040%, Nb: 0.015 to 0.050% and the balance of Fe and inevitable impurities; the process flow is as follows: molten iron → converter → refining → continuous casting → heating by hot delivery → rolling → pit entering slow cooling → fixed length hot cutting → stacking cooling → quenching → tempering → cutting of corner sample block → temperature control stacking cooling of finished product → finishing and warehousing.
Example 1: the wear-resistant steel plate for NM 500-grade engineering machinery, which is produced by the embodiment and has the thickness of 50mm and the hardness of more than or equal to 500HBW, comprises the following components in percentage by weight: c: 0.28%, Si: 0.40%, Mn: 1.29%, Cr: 0.80%, Mo: 0.24%, Nb: 0.022%, Als: 0.031%, P: 0.014%, S: 0.003%, Ca: 0.0035%, Ni: 0.03%, Ti: 0.018%, B: 0.0021% and the balance of Fe and inevitable impurities, and the thickness of the slab is 250 mm. The ferrite and pearlite structure is obtained after the steel plate is rolled, the steel plate enters a slow cooling pit for slow cooling, the slow cooling starting temperature is 596 ℃, the slow cooling time is 51h, the residual stress in the steel can be effectively reduced, meanwhile, hydrogen is discharged, and the internal quality of the steel plate is improved. And (3) taking the steel plate out of the pit after pit cooling for 51h, lifting the steel plate to a cutting field, putting a cutting track on the steel plate, and simultaneously placing a flame cutting machine (adopting propane gas) on the cutting track to cut the steel plate to length so as to reduce the cutting length and the cutting time after tempering. When the steel plate is cut, measuring the temperature of the steel plate to be 245 ℃, cutting one corner of the head of the steel plate into an L shape with a sample block B, and particularly referring to fig. 4 and 5, measuring the temperature of the steel plate to be 172 ℃ after cutting, rapidly stacking and cooling the steel plate, and cooling the steel plate to room temperature after stacking and cooling the steel plate for 15 hours. The size of the sample block B should meet the performance detection requirement, and the size of the sample block B is a rectangle of 200mm multiplied by 400mm, so that the detection requirement of tensile, impact and hardness mechanical properties can be met. In order to further reduce the cutting amount between the finished steel plate and the sample block B and avoid cracks generated by cutting at the position, 300mm of cutting seam C with the length of 300mm is pre-cut between the steel plate body A and the corner sample block B in a rolling state, so that the connecting part (a dotted line part in figure 4) is kept to be 100mm long continuously, and the requirements of steel plate strip sample quenching and low-temperature tempering heat treatment are met. Quenching and low-temperature tempering are carried out on the steel plate, the quenching temperature is 900 ℃, the tempering temperature is 200 ℃, and the high-hardness wear-resistant steel plate with a matrix structure of tempered martensite is obtained, and is shown in detail in figure 7. And (3) after the steel plate is tempered and taken out of the furnace, hanging the steel plate to a cutting field, placing a cutting track on the steel plate, placing a plasma cutting machine on the cutting track to perform thermal cutting separation on the connecting part of the steel plate and the corner sample block B, cutting and taking a sample, wherein the cutting temperature of the steel plate is 154 ℃, obtaining a finished steel plate body A and a detection sample block B, rapidly stacking and cooling the finished steel plate, measuring the stacking and cooling temperature to 125 ℃, and cooling to room temperature. After 1-3 months, the surface quality of the cut end face is observed to be normal, and no cutting delay crack appears, which is shown in detail in figure 6. And (3) sampling hardness detection results: the upper table hardness is 521HBW, and the lower table hardness is 513 HBW.
Example 2: the NM 500-grade wear-resistant steel plate with the thickness of 80mm and the hardness of more than or equal to 470HBW produced by the embodiment comprises the following components in percentage by weight: c: 0.27%, Si: 0.38%, Mn: 1.25%, Cr: 0.78%, Mo: 0.23%, Nb: 0.030%, Als: 0.032%, P: 0.012%, S: 0.004%, Ca: 0.0032%, Ni: 0.02%, Ti: 0.016%, B: 0.0020% and the balance of Fe and inevitable impurities, and the thickness of the slab is 300 mm. And (3) obtaining ferrite and pearlite structures after rolling the steel plate, slowly cooling the steel plate in a slow cooling pit, wherein the slow cooling starting temperature is 620 ℃, slowly cooling the steel plate for 58 hours, then taking the steel plate out of the pit, hoisting the steel plate to a cutting site, putting a cutting rail on the steel plate, and simultaneously placing a flame cutting machine (adopting propane gas) on the cutting rail to cut the steel plate to length so as to reduce the cutting length and the cutting time after tempering. When the steel plate is cut, the temperature of the steel plate is 279 ℃ and one corner of the tail part of the steel plate is cut into an L shape with a sample block B, the detail is shown in figures 4 and 5, the temperature of the steel plate is 189 ℃ after the steel plate is cut, the steel plate is rapidly cooled in a heaping mode, and the steel plate is cooled to the room temperature after being cooled in the heaping mode for 18 hours. The sample block B is a rectangle with the size of 200mm wide multiplied by 400mm long, and can meet the detection requirements of tensile, impact and hardness mechanical properties. In order to further reduce the cutting amount between the finished steel plate and the sample block B and avoid cracks generated by cutting at the position, 250mm long cutting seams C are formed by pre-cutting 250mm between the steel plate body A and the corner sample block B in a rolling state, so that the connecting part (a dotted line part in figure 4) keeps 150mm long continuously, and the requirements of steel plate strip sample quenching and low-temperature tempering heat treatment are met. Quenching and low-temperature tempering are carried out on the steel plate, the quenching temperature is 905 ℃, the tempering temperature is 210 ℃, and the high-hardness wear-resistant steel plate with a matrix structure of tempered martensite is obtained, and is shown in detail in figure 7. Cutting and reserving a sample after the steel plate is tempered and discharged, hanging the steel plate to a cutting field, placing a cutting track on the steel plate, simultaneously thermally cutting and separating the connecting part of the steel plate and the corner sample block B by using a plasma cutting machine, wherein the cutting temperature of the steel plate is 162 ℃, obtaining a finished steel plate body A and a detection sample block B, rapidly stacking and cooling the finished steel plate, measuring the stacking and cooling temperature to be 123 ℃, and cooling to room temperature. And observing that the surface quality of the cut end face is normal after 1-3 months, and no cutting delay crack appears. And (3) sampling hardness detection results: the hardness of the upper table is 492HBW, and the hardness of the lower table is 489 HBW.
Example 3: the wear-resistant steel plate for NM 550-grade engineering machinery, which is produced by the embodiment and has the thickness of 70mm and the hardness of more than or equal to 530HBW, comprises the following components in percentage by weight: c: 0.32%, Si: 0.16%, Mn: 0.82%, Cr: 0.92%, Mo: 0.12%, Nb: 0.022%, Als: 0.031%, P: 0.013%, S: 0.002%, Ca: 0.0025%, Ni: 0.02%, Ti: 0.013%, B: 0.0017% of iron, the balance being Fe and inevitable impurities, the slab having a thickness of 250 mm. The ferrite and pearlite structure is obtained after the steel plate is rolled, the steel plate enters a slow cooling pit for slow cooling, the slow cooling starting temperature is 606 ℃, the slow cooling time is 54 hours, the residual stress in the steel can be effectively reduced, meanwhile, hydrogen is discharged, and the internal quality of the steel plate is improved. And (3) taking the steel plate out of the pit after the steel plate pit is cooled for 54h, lifting the steel plate to a cutting field, putting a cutting track on the steel plate, and simultaneously placing a flame cutting machine (adopting propane gas) on the cutting track to cut the steel plate to length so as to reduce the cutting length and the cutting time after tempering. When the steel plate is cut, the temperature of the steel plate is measured to be 235 ℃, one corner of the head of the steel plate is cut into an L shape with a sample block B, the detail is shown in figures 4 and 5, the temperature of the steel plate is measured to be 158 ℃ after the steel plate is cut, the steel plate is rapidly cooled in a heaping mode, and the steel plate is cooled to the room temperature after being cooled in the heaping mode for 17 hours. The size of the sample block B should meet the performance detection requirement, and the size of the sample block B is usually 200mm multiplied by 400mm, so that the tensile, impact and hardness mechanical performance detection requirement can be met. In order to further reduce the cutting amount between the finished steel plate and the sample block B and avoid cracks generated by cutting at the position, 280mm of cutting seam C with the length of 280mm is pre-cut between the steel plate body A and the corner sample block B in a rolling state, so that the connecting part (a dotted line part in figure 4) keeps the length of 120mm continuously, and the requirements of steel plate strip sample quenching and low-temperature tempering heat treatment are met. Quenching and low-temperature tempering are carried out on the steel plate, the quenching temperature is 902 ℃, the tempering temperature is 190 ℃, and the high-hardness wear-resistant steel plate with a matrix structure of tempered martensite is obtained, and is shown in figure 7 in detail. Cutting and reserving a sample after the steel plate is tempered and discharged, hanging the steel plate to a cutting field, placing a cutting track on the steel plate, simultaneously thermally cutting and separating the connecting part of the steel plate and the corner sample block B by using a plasma cutting machine, wherein the cutting temperature of the steel plate is 156 ℃ to obtain a finished steel plate body A and a detection sample block B, rapidly stacking and cooling the finished steel plate, measuring the stacking and cooling temperature to be 122 ℃, and cooling to room temperature. And observing that the surface quality of the cut end face is normal after 1-3 months, and no cutting delay crack appears. And (3) sampling hardness detection results: the upper table hardness was 548HBW, and the lower table hardness was 542 HBW.
Example 4: the wear-resistant steel plate for NM 600-grade engineering machinery, which is produced by the embodiment and has the thickness of 60mm and the hardness of more than or equal to 570HBW, comprises the following components in percentage by weight: c: 0.43%, Si: 0.43%, Mn: 1.22%, Cr: 0.95%, Mo: 0.26%, Ni: 0.86%, Als: 0.029%, P: 0.011%, S: 0.002%, Ca: 0.0022%, Ti: 0.017%, B: 0.0021% and the balance of Fe and inevitable impurities, and the thickness of the slab is 250 mm. The ferrite and pearlite structure is obtained after the steel plate is rolled, the steel plate enters a slow cooling pit for slow cooling, the slow cooling starting temperature is 613 ℃, the slow cooling time is 52h, the residual stress in the steel can be effectively reduced, meanwhile, hydrogen is discharged, and the internal quality of the steel plate is improved. And (3) taking the steel plate out of the pit after the steel plate pit is cooled for 52h, lifting the steel plate to a cutting field, putting a cutting track on the steel plate, and simultaneously placing a flame cutting machine (adopting propane gas) on the cutting track to cut the steel plate to length so as to reduce the cutting length and the cutting time after tempering. When the steel plate is cut, the temperature of the steel plate is measured to be 265 ℃, one corner of the head of the steel plate is cut into an L shape with a sample block B, the detail is shown in figures 4 and 5, the temperature of the steel plate is measured to be 188 ℃ after the steel plate is cut, the steel plate is rapidly cooled in a heaping mode, and the steel plate is cooled to the room temperature after being cooled in the heaping mode for 16 hours. The size of the sample block B should meet the performance detection requirement, and the size of the sample block B is usually 200mm multiplied by 400mm, so that the tensile, impact and hardness mechanical performance detection requirement can be met. In order to further reduce the cutting amount between the finished steel plate and the sample block B and avoid cracks generated by cutting at the position, 270mm of long cutting seam C is formed between the steel plate body A and the corner sample block B in a pre-cutting mode in a rolling state, so that the connecting part (a dotted line part in figure 4) is kept 130mm long and continuous, and the requirements of steel plate strip sample quenching and low-temperature tempering heat treatment are met. Quenching and low-temperature tempering are carried out on the steel plate, the quenching temperature is 908 ℃, the tempering temperature is 200 ℃, and the high-hardness wear-resistant steel plate with a matrix structure of tempered martensite is obtained, and is shown in detail in figure 7. Cutting and reserving a sample after the steel plate is tempered and discharged, hanging the steel plate to a cutting field, placing a cutting track on the steel plate, simultaneously thermally cutting and separating the connecting part of the steel plate and the corner sample block B by using a plasma cutting machine, wherein the cutting temperature of the steel plate is 152 ℃, obtaining a finished steel plate body A and a detection sample block B, rapidly stacking and cooling the finished steel plate, measuring the stacking and cooling temperature to be 126 ℃, and cooling to room temperature. And observing that the surface quality of the cut end face is normal after 1-3 months, and no cutting delay crack appears. And (3) sampling hardness detection results: the upper table hardness was 588HBW and the lower table hardness was 580 HBW.
Claims (4)
1. A hot cutting method for a high-hardness wear-resistant steel plate with the thickness of 50-80 mm is characterized by comprising the following steps:
s1: hot cutting preparation of the steel plate in a rolling state: rolling the plate blank into a steel plate to obtain a ferrite and pearlite structure, and quickly and slowly cooling the steel plate at the slow cooling temperature of more than 550 ℃ for more than 50 hours;
s2: hot cutting of the steel plate in a rolling state: cutting the steel plate into L-shaped steel plates with sample blocks at the corners after the steel plate is taken out of the slow cooling pit, quickly cooling the steel plate in a heaping mode, wherein the heaping cooling temperature is more than or equal to 120 ℃, the heaping cooling time is more than or equal to 15 hours, and cooling the steel plate to room temperature;
s3: heat treatment after cutting of the rolled steel sheet: carrying out quenching and low-temperature tempering heat treatment on the steel plate, wherein the tempering temperature is 180-220 ℃, and obtaining a high-hardness wear-resistant steel plate with a matrix structure of tempered martensite;
s4: separating the heat-treated steel plate from the corner sample block: and after the steel plate is taken out of the furnace through heat treatment, the cutting temperature of the steel plate is more than or equal to 150 ℃, the connecting part of the steel plate and the corner sample block is subjected to hot cutting and separation to obtain a finished steel plate and a detection sample block, the finished steel plate is rapidly cooled in a heaped mode, the temperature of the heaped cooling is more than or equal to 120 ℃, and the steel plate is cooled to room temperature.
2. The hot cutting method for the high-hardness wear-resistant steel plate with the thickness of 50-80 mm according to claim 1, wherein a cutting seam is formed between the steel plate body of the L-shaped steel plate and the corner sample block, and the length of the cutting seam is 62.5% -75% of the length of the sample block.
3. The hot cutting method for high-hardness wear-resistant steel plate with a thickness of 50-80 mm according to claim 1, wherein the cutting temperature of the steel plate in the step S2 is 200-300 ℃.
4. The method for hot cutting a high-hardness wear-resistant steel plate with a thickness of 50-80 mm as claimed in claim 1, wherein the size of the corner sample block of the steel plate in the step S2 is 200mm x 400 mm.
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