HB450-grade thick-specification wear-resistant steel plate without flame cutting delayed cracks and production method of HB450-grade thick-specification wear-resistant steel plate

Abstract

The invention relates to the technical field of HB450-grade thick-specification wear-resistant steel plates, in particular to a flame cutting delayed crack-free HB450-grade thick-specification wear-resistant steel plate and a production method thereof. The steel is composed of the following chemical components in percentage by weight: 0.18%-0.22% of C, 1.00%-1.10% of Si, 0.8%-1.0% of Mn, 0.015%-0.03% of Nb, 0.6%-0.70% of Cr, 0.06%-0.09% of Al, 0.0005%-0.0020% of B, more than or equal to 1.4% and less than or equal to 1.6% of Mn and Cr, and the balance of Fe and inevitable impurities. The production process flow comprises the steps of smelting, refining, slab continuous casting, casting blank heating and slow cooling, slab heating, controlled rolling, stacking and slow cooling, quenching and tempering heat treatment, flame cutting with temperature and slow cooling with hot water. The surface hardness is larger than or equal to HB450, the thickness ranges from 40 mm to 80 mm, the tensile strength is larger than or equal to 1250 MPa, the retained austenite content is 5%-7%, delayed cracks do not exist after fire cutting, the trimming hardness is larger than or equal to HB410, AKV at the temperature of-40 DEG C is larger than or equal to 40 J, and A is larger than or equal to 12%.

Description

Technical Field

[0001] The present invention relates to the technical field of HB450 grade thick specification wear-resistant steel plates, and specifically to a non-flame-cut delayed crack HB450 grade wear-resistant steel plate with a thickness specification of 40-80 mm and a production method thereof. Background Art

[0002] Compared with HB400, the wear resistance of HB450 grade low-alloy wear-resistant steel is increased by about 15% - 20%; it has better toughness than HB500 and is suitable for occasions with strong impact. Through scientific composition design and heat treatment process, HB450 achieves a balance among wear resistance, strength and toughness, and is one of the preferred materials in the field of engineering wear resistance.

[0003] Flame cutting is a common blanking method for wear-resistant steel plates, with low cost, high efficiency and wide application range. At present, delayed cracking often occurs after flame cutting of HB450 wear-resistant steel plates with a thickness specification of 40-80 mm, posing a safety hazard to production and use. The delayed crack in wear-resistant steel plate cutting is the result of embrittlement under the interaction of internal defects of the steel plate, hydrogen and cutting stress. The occurrence time of delayed cracks is uncertain. Usually, the steel plate will undergo brittle failure statically several hours or days after flame cutting, which is one of the common quality defects of wear-resistant steel plates and is extremely harmful. How to reduce the delayed fracture resistance after flame cutting of high-hardness thick specification wear-resistant plates has become an urgent problem to be solved by domestic and foreign steel mills and users.

[0004] Chinese patent document with publication number CN117344198A discloses "A production method of high and low temperature toughness NM450 wear-resistant steel plate". Although it is a high-toughness wear-resistant steel, the alloy is complex and the internal stress is large, and it cannot prevent cutting cracks in thick steel plates. Chinese patent document with publication number CN109072367A discloses "Wear-resistant steel plate and manufacturing method thereof". This steel plate has complex alloy composition, high cost and no anti-delayed crack ability. Summary of the Invention

[0005] In order to overcome the deficiencies of the prior art, the present invention provides a non-flame-cut delayed crack HB450 grade thick specification wear-resistant steel plate and a production method thereof, with moderate alloy composition, no delayed crack after flame cutting of the steel plate, and the surface hardness of the cut edge ≥ HB410.

[0006] In order to achieve the above object, the present invention is realized by adopting the following technical solutions:

[0007] A non-flame-cut delayed crack HB450 grade thick specification wear-resistant steel plate, without flame-cut delayed crack, surface hardness ≥ HB450, thickness 40-80 mm, tensile strength ≥ 1250 MPa, cut edge hardness ≥ HB410, -40 °C AKV ≥ 40 J, A ≥ 12%.

[0008] It is composed of chemical components with the following weight percentages: C: 0.18% - 0.22%, Si: 1.00% - 1.10%, Mn: 0.8% - 1.0%, Nb: 0.015 - 0.03%, Cr: 0.6% - 0.70%, Al: 0.06% - 0.09%, B: 0.0005% - 0.0020%, 1.4% ≤ Mn + Cr ≤ 1.6%, and the balance is Fe and inevitable impurities. Control of impurity elements: P ≤ 0.010%, S ≤ 0.002%, [N] ≤ 0.0040%, [H] ≤ 0.00010%, [O] ≤ 0.0010%, and the retained austenite content is 5% - 7%.

[0009] In the design of the chemical composition of the steel plate of the present invention:

[0010] C: In order to ensure that the surface of the steel plate has a hardness of HB450 after quenching, it can also improve the hardenability of thick - gauge steel plates and ensure uniform wear resistance along the thickness direction of the steel plate. At the same time, carbon can form carbides with Cr and precipitate, increasing wear resistance. If the carbon content is too high, the crack sensitivity after cutting increases. In order to ensure that the steel plate has high wear resistance and good resistance to delayed cracking, the C content in the present invention is controlled at 0.18% - 0.22%.

[0011] Si: The key element added in the present invention, it is a non - carbide - forming element. Its main function is to inhibit the precipitation of carbides, stabilize the retained austenite content in the steel. During flame cutting, the retained austenite acts as a hydrogen trap to inhibit the formation and propagation of delayed cracks. A certain amount of retained austenite is also beneficial to improving the toughness of the steel plate. However, when Si is excessive, the welding performance will decline. Therefore, the Si content in the present invention is controlled at 1.0% - 1.1%;

[0012] Mn: It has the effect of delaying the transformation of austenite to ferrite, promoting martensite transformation, and improving hardenability. However, it is easy to form center segregation, and there is a tendency to easily generate delayed cracks in the center of the steel plate thickness during flame cutting. Therefore, the Mn content in the present invention is controlled at 0.8% - 1.0%;

[0013] Nb: The most effective element for controlled rolling. During the two - stage rolling process, carbon and nitrogen compounds inhibit austenite recrystallization, refine austenite grains. After quenching, refined martensite lath bundles can be formed, and the refined martensite can effectively prevent the occurrence of delayed cracks in the steel plate cutting. However, if the Nb content is too high, excessive precipitation of carbon and nitrogen compounds will affect the steel plate's resistance to delayed cracking. Therefore, the addition amount of Nb in the present invention is 0.015% - 0.03%.

[0014] Al: An effective element for deoxidation and nitrogen fixation. Deoxidation can reduce oxide inclusions in steel and purify the steel quality. After deoxidation, nitrogen fixation can ensure that element B does not combine with N, giving full play to the role of B in improving hardenability. Excessive content will cause difficulties in casting and form a large amount of Al2O3 inclusions in the steel, which is likely to become the initiation source of delayed cracks after cutting. Therefore, in this invention, Al is 0.06% - 0.09%.

[0015] Cr: It has the function of reducing the critical cooling rate, promoting martensite transformation, and improving the hardenability of the steel plate. In addition, chromium is a strong carbide-forming element and can form various carbides in the steel to ensure the wear resistance of the steel plate. However, excessive addition of Cr will increase the crack sensitivity after thermal cutting. Therefore, in this invention, Cr is controlled at 0.60% - 0.70%. Since both Mn and Cr can improve hardenability, excessive addition will increase the risk of cracking after thermal cutting. To ensure that no delayed fracture occurs during the cutting of the steel plate, 1.4% ≤ Mn + Cr ≤ 1.6%.

[0016] B: Trace amounts of boron can inhibit the formation of proeutectoid ferrite and greatly improve hardenability. Boron has an effect only when its content is greater than 0.0005. When the B content is too high (≥0.0025%), it is likely to accumulate at the grain boundaries after thermal cutting, reducing the grain boundary binding energy and causing intergranular fracture in the heat-affected zone of thermal cutting under the action of residual stress. Therefore, in this invention, the addition amount of B is 0.0005% - 0.0020%.

[0017] Retained austenite and impurity elements: 5 - 7% of retained austenite near the cutting edge during flame cutting can act as a hydrogen trap to inhibit the propagation of delayed cracks, ensuring good crack arrest ability of the cutting edge of the steel plate. Excessive content of retained austenite will reduce the hardness and wear resistance of the steel plate. Impurity elements P, S, O, N, especially H, will act as crack initiation sources in the steel plate, significantly reducing the crack arrest ability of the steel plate and increasing the risk of forming delayed cracks after thermal cutting. Therefore, in this invention, to ensure good anti-delayed fracture performance, the impurity element P ≤ 0.012%, S ≤ 0.002%, [H] ≤ 0.00010%, [O] ≤ 0.0010%, [N] ≤ 0.0040%.

[0018] The production method of the above HB450 grade thick specification wear-resistant steel plate without thermal cutting delayed cracks has a production process flow of: smelting → refining → slab continuous casting → casting blank heating and slow cooling → slab heating → controlled rolling → stacking and slow cooling → quenching + tempering heat treatment → hot flame cutting with temperature → hot water slow cooling.

[0019] This production method specifically includes the following steps:

[0020] 1) Refining:

[0021] Control the RH degassing time, and the RH vacuum circulation time ≥ 18 min;

[0022] 2) Slab continuous casting:

[0023] The target superheat of the tundish ≤ 20°C; the center segregation of the slab is controlled below C1.0, and the inclusions A + B + C + D ≤ 3.0;

[0024] 3) Slab heating and slow cooling:

[0025] The slow cooling start temperature ≥ 450°C, heated at a heating rate ≤ 50°C / second to 600 - 650°C, held for 15 - 20 hours, then slowly cooled in the furnace to less than 400°C, and taken out of the furnace and air-cooled to room temperature;

[0026] 4) Slab heating:

[0027] The temperature of the heating soaking section is 1200 - 1250°C, and the soaking time is more than 2.5 hours;

[0028] 5) Controlled rolling:

[0029] Two-stage controlled rolling of rough rolling and finish rolling is adopted. The rolling start temperature in the rough rolling stage ≥ 1020°C, and the finish rolling temperature is controlled at ≥ 980°C; the finish rolling start temperature is 880 - 850°C, the finish rolling reduction rate ≥ 50%, and the finish rolling temperature is 800 - 850°C;

[0030] 6) Stacking slow cooling:

[0031] If the offline temperature of the hot-rolled steel plate ≥ 500°C, then stacking slow cooling is carried out, the holding time is greater than or equal to 34 hours, and after cooling to 350 - 400°C, it is air-cooled to room temperature;

[0032] If the offline temperature of the hot-rolled steel plate < 470°C, then high-temperature tempering is carried out. The tempering heating temperature is 650 - 700°C, the holding time is 120 - 150 min. After tempering, the steel plate is stacked and slowly cooled. The stacking time is greater than or equal to 24 hours, and after the unstacking temperature is 360 - 400°C, it is air-cooled to room temperature;

[0034] 7) Quenching + tempering heat treatment:

[0035] The quenching temperature is 870 - 900°C, and the holding time is 2 - 2.5 min / mm;

[0036] The tempering temperature is 200 - 230°C, and the low-temperature tempering holding time is 8 - 10 min / mm;

[0037] 8) Flame cutting with temperature maintained:

[0038] The temperature of the steel plate at the flame cutting position ≥ 100°C;

[0039] If the temperature is lower than 100°C, then preheat the cutting position. The preheat temperature is 130 - 180°C, and the preheat width is 100 mm on both sides of the cutting edge;

[0040] During hot cutting, perform slow cutting with a cutting speed ≤ 150 mm / min;

[0041] 9) Slow cooling in hot water

[0042] After the steel plate is cut, it is slowly cooled in a hot water pool. The cut steel plate is kept in water at a high temperature of 80 - 100 °C for more than 2 hours.

[0043] Furthermore, in step 2), during continuous casting, perform full-process protected casting to prevent hydrogen from entering the tundish.

[0044] Furthermore, in step 2), during continuous casting, use electromagnetic stirring or soft reduction to reduce central segregation.

[0045] Furthermore, in step 4), the thickness of the slab is 250 - 300 mm to ensure the reduction ratio.

[0046] Furthermore, in step 6), stack and slowly cool in a slow cooling pit, covering it for heat preservation.

[0047] Furthermore, in step 8), use a flame torch or an electronic heating pad to preheat the cutting position.

[0048] Compared with the prior art, the beneficial effects of the present invention are:

[0049] 1. The present invention uses Si to inhibit the precipitation of carbides. Si is a non-carbide forming element, and its main function is to inhibit the precipitation of carbides and stabilize the content of retained austenite in the steel. During flame cutting, retained austenite acts as a hydrogen trap to inhibit the formation and propagation of delayed cracks. A certain amount of retained austenite is also beneficial to improving the toughness of the steel plate. At the same time, control the contents of C, Mn, Nb, AL, Cr, and B to ensure that the steel plate has high wear resistance and good resistance to delayed cracks. During flame cutting, 5 - 7% of the retained austenite near the cutting edge acts as a hydrogen trap to inhibit the propagation of delayed cracks, which can ensure that the cutting edge of the steel plate has good crack arrest ability. Excessive content of retained austenite will reduce the hardness and wear resistance of the steel plate.

[0050] 2. Impurity elements, especially H, will act as crack initiation sources in the steel plate, significantly reducing the crack arrest ability of the steel plate and increasing the risk of delayed crack formation after hot cutting. To ensure good anti-delayed fracture performance, the present invention controls the impurity elements P ≤ 0.012%, S ≤ 0.002%, [H] ≤ 0.00010%, [O] ≤ 0.0010%, [N] ≤ 0.0040%.

[0051] 3. During the refining process of the present invention, the RH degassing time is controlled. Through long-time vacuum treatment, the molten steel can be controlled to have [N] ≤ 0.0040%, [O] ≤ 0.0010%, and [H] ≤ 0.00010%. The central segregation of the continuous casting billet is controlled below C1.0, and the inclusions A + B + C + D ≤ 3.0, thereby reducing the segregation and inclusions from becoming the initiation points of delayed cracks. The hydrogen content and the internal casting stress in the steel billet are removed by heating and slow cooling.

[0052] 4. During the heating of the steel billet of the present invention, the soaking time is greater than 2.5 hours. Through long-time high-temperature heating, the carbon and alloying elements in the center of the steel plate are fully diffused, further improving the central segregation. During rolling, two-stage controlled rolling of rough rolling and finish rolling is adopted to fully refine and homogenize the hot-rolled structure.

[0053] 5. After hot rolling, the steel plate of the present invention is taken offline and stacked in a slow-cooling pit for slow cooling or subjected to high-temperature tempering. By utilizing the different solubilities of hydrogen in steel at different temperatures, the hydrogen inside the thick-specification steel plate is removed by diffusion. At the same time, by equalizing the temperature of the steel plate, the internal stress of the steel plate is removed.

[0054] 6. The purpose of temperature-carrying and preheating cutting in the present invention is to reduce the temperature difference between the surface and the center of the cutting edge, reduce the thermal stress during cutting, and at the same time prevent the condensed water formed on the surface of the steel plate during cutting from entering the gas-cutting surface in an atomic state to form hydrogen-induced cracks.

[0055] 7. During the oxygen cutting of the present invention, slow cutting is adopted, and the cutting speed ≤ 150 mm / min to reduce the cutting thermal stress. After the steel plate is cut, it is slowly cooled in a hot water pool. Cooling in hot water can quickly make the temperature of the surface and the center of the cutting-edge steel plate consistent, reducing the thermal stress and tissue stress formed after cutting. At the same time, the rapid cooling of the cutting surface in hot water can also reduce the decrease in the surface hardness of the cutting surface and improve the wear resistance of the steel plate. After cutting, the steel plate is kept warm in water at a high temperature of 80 - 100 °C for more than 2 hours, which can fully homogenize the overall temperature of the steel plate, further reduce the cutting residual stress, and avoid the occurrence of delayed cracks.

[0056] In summary, the present invention adopts a new composition and process design for preventing delayed cracks during thermal cutting. The chemical composition of the steel plate is mainly characterized by medium carbon, high silicon, and niobium microalloying. After refining, continuous casting, controlled rolling, and heat treatment, a wear-resistant steel plate with low impurity content, uniform, fine martensite, and a certain amount of retained austenite structure is obtained, which can inhibit the formation and propagation of delayed cracks during thermal cutting. During thermal cutting, through the cutting process of cutting with temperature and slow cooling with hot water after cutting, the thermal stress and tissue stress formed during the cutting process of thick-specification steel plates are reduced, achieving the effect of no delayed cracks after cutting. By using the present invention, wear-resistant steel plates with a thickness specification of 40 - 80 mm and a surface Brinell hardness of 450 HB grade can be produced. The surface hardness of the steel plate is ≥ HB450, the thickness is 40 - 80 mm, the tensile strength is ≥ 1250 MPa, the retained austenite content is 5% - 7%, there are no delayed cracks after thermal cutting, the hardness of the cut edge is ≥ HB410, the -40°C AKV is ≥ 40 J, and A is ≥ 12%. Description of the Drawings

[0057] Figure 1 It is a coloring flaw detection diagram of the cutting surface of the 40 mm thick steel plate of the present invention after 48 hours of thermal cutting. Detailed Embodiments

[0058] The present invention discloses a wear-resistant steel plate with a thickness specification of HB450 grade without delayed cracks during thermal cutting and its production method. Those skilled in the art can draw on the content of this article and appropriately modify the process parameters to achieve it. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are all regarded as included in the present invention. The method and application of the present invention have been described through preferred embodiments, and those related can obviously make changes or appropriate changes and combinations to the methods and applications described in this article without departing from the content, spirit, and scope of the present invention to implement and apply the technology of the present invention.

[0059] A wear-resistant steel plate with a thickness specification of HB450 grade without delayed cracks during thermal cutting is composed of the following chemical components by weight percentage: C: 0.18% - 0.22%, Si: 1.00% - 1.10%, Mn: 0.8% - 1.0%, Nb: 0.015 - 0.03%, Cr: 0.6% - 0.70%, Al: 0.06% - 0.09%, B: 0.0005% - 0.0020%, 1.4% ≤ Mn + Cr ≤ 1.6%, and the balance is Fe and inevitable impurities.

[0060] Control of impurity elements in the wear-resistant steel plate: P ≤ 0.010%, S ≤ 0.002%, [N] ≤ 0.0040%, [H] ≤ 0.00010%, [O] ≤ 0.0010%, and the retained austenite content is 5% - 7%.

[0061] The production method of the above-mentioned non-fire cutting delayed crack HB450-grade thick-specification wear-resistant steel plate has a production process flow as follows: smelting → refining → slab continuous casting → casting blank heating and slow cooling → slab heating → controlled rolling → stacking slow cooling (tempering) → quenching + tempering heat treatment → flame cutting → hot water slow cooling.

[0062] Specifically as follows:

[0063] The production process flow of the present invention is: smelting → refining → slab continuous casting → casting blank heating and slow cooling → slab heating → controlled rolling → stacking slow cooling (tempering) → quenching + tempering heat treatment → flame with-temperature cutting → hot water slow cooling

[0064] 1. Smelting process:

[0065] During the refining of the present invention, the RH degassing time is controlled. The RH vacuum circulation time ≥ 18 min. Through long-time vacuum treatment, the molten steel [N] ≤ 0.0040%, [O] ≤ 0.0010%, [H] ≤ 0.00010% can be controlled.

[0066] For the continuous casting tundish of the present invention, the target superheat is controlled at ≤ 20 °C; full protection casting is carried out to prevent hydrogen from entering the tundish.

[0067] During continuous casting, electromagnetic stirring or soft reduction is adopted to reduce central segregation. The central segregation of the casting blank is controlled below C1.0, and the inclusions A + B + C + D ≤ 3.0, thereby reducing the segregation and inclusions from becoming the initiation points of delayed cracks.

[0068] After the slab continuous casting is taken off the production line, it needs to enter the slow cooling pit for heating and slow cooling. The slow cooling start temperature ≥ 450 °C, and it is heated to 600 - 650 °C at a heating rate of ≤ 50 °C / second. After keeping warm for 15 - 20 hours, it is slowly cooled in the furnace to less than 400 °C and then taken out of the furnace and air-cooled to room temperature. The purpose of heating and slow cooling is to remove the hydrogen content and casting internal stress in the steel billet.

[0069] 2. Rolling process:

[0070] The temperature of the heating soaking section is 1200 - 1250 °C, the thickness of the casting blank is 250 - 300 mm, and the soaking time is more than 2.5 hours. Through long-time high-temperature heating, the carbon and alloy elements in the center of the steel plate are fully diffused, further improving the central segregation.

[0071] During rolling, two-stage controlled rolling of rough rolling and finish rolling is adopted to fully refine and homogenize the hot-rolled structure. In the rough rolling stage, the rolling start temperature ≥ 1020 °C, and the finish rolling temperature is controlled at ≥ 980 °C; the finish rolling start temperature is 880 - 850 °C, and the finish rolling reduction rate ≥ 50%, aiming to refine the original austenite structure, and the finish rolling temperature is 800 - 850 °C.

[0072] 3. Post-rolling dehydrogenation process:

[0073] After hot rolling, the steel plate is taken offline and stacked in a slow cooling pit for slow cooling or subjected to high-temperature tempering. If the offline temperature of the hot-rolled steel plate is ≥500°C, it is stacked for slow cooling with a holding time of ≥34 hours, and then air-cooled to room temperature after reaching 350 - 400°C; if the offline temperature of the hot-rolled steel plate is <470°C, it is subjected to high-temperature tempering with a tempering heating temperature of 650 - 700°C and a holding time of 120 - 150 min. After tempering, the steel plate is stacked for slow cooling with a stacking time of ≥24 hours and air-cooled to room temperature after the unstacking temperature reaches 360 - 400°C.

[0074] After tempering, the steel plate is stacked for slow cooling with a stacking time of ≥24 hours and air-cooled to room temperature after the unstacking temperature reaches 350 - 400°C. The purpose of slow cooling in the slow cooling pit and slow cooling after high-temperature tempering is to utilize the different solubilities of hydrogen in steel at different temperatures, remove the hydrogen inside the thick-specification steel plate through diffusion, and at the same time remove the internal stress of the steel plate by equalizing the steel plate temperature.

[0075] The purpose of slow cooling in the slow cooling pit and slow cooling after high-temperature tempering is to utilize the different solubilities of hydrogen in steel at different temperatures, remove the hydrogen inside the thick-specification steel plate through diffusion, and at the same time remove the internal stress of the steel plate by equalizing the steel plate temperature.

[0076] 4. Heat treatment process:

[0077] The quenching temperature is 870 - 900°C with a holding time of 2 - 2.5 min / mm. The purpose of quenching is to obtain a hardness of HB450. The tempering temperature is 200 - 230°C, and the holding time for low-temperature tempering is 8 - 10 min / mm. The purpose is to remove the internal stress formed during quenching of the steel plate.

[0078] 5. Flame cutting process:

[0079] After low-temperature tempering heat treatment, the steel plate is flame-cut to size and sampled while still warm. It is required that the temperature of the steel plate at the flame-cutting position is ≥100°C. If the cutting temperature is lower than 100°C, the cutting position is preheated.

[0080] The preheating temperature is 130°C - 180°C, and the preheating width is 100 mm on both sides of the cutting edge. It can be carried out using a flame torch or an electronic heating pad. The purpose of warm and preheated cutting is to reduce the temperature difference between the surface and the core of the cutting edge, reduce the thermal stress during cutting, and at the same time prevent the condensed water formed on the surface of the steel plate during cutting from entering the gas-cutting surface in an atomic state to form hydrogen-induced cracks.

[0081] During flame cutting, slow cutting is carried out with a cutting speed ≤150 mm / min. The purpose of slow cutting is to reduce the cutting thermal stress. After the steel plate is cut, it is lifted into a hot water slow cooling pool by a crane for cooling. The temperature of the slow cooling water is 80 - 100°C, and the holding time in the water is >2 hours.

[0082] Cooling in hot water can quickly make the surface and core temperatures of the cutting-edge steel plate consistent, reducing the thermal stress and tissue stress formed after cutting. At the same time, the rapid cooling of the cutting surface in hot water can also reduce the decrease in the surface hardness of the cutting surface and improve the wear resistance of the steel plate. After cutting, the steel plate is kept in water at a high temperature of 80-100 °C for more than 2 hours, which can fully homogenize the overall temperature of the steel plate, further reduce the cutting residual stress, and avoid the occurrence of delayed cracks.

[0083] The steel plate produced by the above production method has no delayed cracks after flame cutting, the cutting-edge hardness ≥ HB410, the surface hardness ≥ HB450, the thickness is 40-80 mm, the tensile strength ≥ 1250 MPa, -40 °C AKV ≥ 40 J, and A ≥ 12%.

[0084]

Example

[0085] According to the chemical composition and production process of the present invention, the actual chemical composition of the steel grade of the present invention is shown in Table 1 during smelting, the smelting process is shown in Table 2, the actual rolling process parameters of the steel examples of the present invention are shown in Table 3, the dehydrogenation process parameters after rolling are shown in Table 4, the heat treatment process parameters are shown in Table 5, the physical property test results of the present invention are shown in Table 6, and the cutting process and delayed crack test results are shown in Table 7.

[0086] Table 1 Examples of the smelting composition of the steel grade of the present invention, Wt%

[0087] Serial number C Si Mn Nb Cr Al P S H 0 N Mn + Cr 1 0.18 1.10 1.0 0.025 0.60 0.075 0.008 0.002 0.000085 0.00010 0.0028 1.60 2 0.19 1.08 0.9 0.016 0.65 0.083 0.007 0.0015 0.000087 0.00092 0.0025 1.55 3 0.21 1.05 0.85 0.015 0.68 0.064 0.009 0.0013 0.000076 0.00075 0.0032 1.49 4 0.22 1.00 0.8 0.03 0.70 0.072 0.010 0.0016 0.000065 0.00066 0.0026 1.50

[0088] Table 2 Smelting process of the steel grade of the present invention

[0089]

[0090] Table 3 Actual rolling process parameters of the steel examples of the present invention

[0091]

[0092] Table 4 Dehydrogenation process parameters after rolling of the steel examples of the present invention

[0093]

[0094]

[0095] Table 5 Heat treatment process of the steel examples of the present invention

[0096]

[0097] Table 6 Mechanical properties of the steel examples of the present invention

[0098]

[0099] Table 7 Flame cutting process and crack inspection of the steel examples of the present invention

[0100]

[0101]

[0102] Figure 1 This is the coloring flaw detection diagram of the cutting surface of the 40-mm-thick steel plate of the present invention after 48 hours of oxy-fuel cutting. As Figure 1 shown, after 48 hours of slow cooling, the oxy-fuel cutting surface of the steel plate of the present invention was inspected for delayed cracks by the method of coloring flaw detection, and no delayed cracks were found. It can be seen that the steel plate of the present invention has good resistance to delayed cracks.

[0103] The present invention adopts new components and process designs for preventing oxy-fuel cutting delayed cracks. The chemical composition of the steel plate is mainly characterized by medium carbon, high silicon, and niobium microalloying. After refining, continuous casting, controlled rolling, and heat treatment, a wear-resistant steel plate with low impurity content, uniform, and fine martensite and a certain amount of retained austenite structure can be obtained, which can inhibit the formation and propagation of delayed cracks during oxy-fuel cutting. During oxy-fuel cutting, through the cutting process of cutting with temperature and hot water slow cooling after cutting, the thermal stress and tissue stress formed during the cutting process of thick-specification steel plates are reduced, and the effect of no delayed cracks after cutting is achieved. By using the present invention, wear-resistant steel plates with a thickness specification of 40-80 mm and a surface Brinell hardness of 450 HB grade can be produced. The surface hardness of the steel plate is ≥ HB450, the thickness is 40-80 mm, the tensile strength is ≥ 1250 MPa, the retained austenite content is 5%-7%, there are no delayed cracks after oxy-fuel cutting, the hardness of the cut edge is ≥ HB410, the AKV at -40 °C is ≥ 40 J, and A is ≥ 12%.

[0104] The above is only the preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered within the protection scope of the present invention.

Claims

1. A non-fire cutting delayed crack HB450 grade thick specification wear-resistant steel plate, characterized in that, The wear-resistant steel plate has no delayed crack after thermal cutting, the surface hardness is ≥ HB450, the thickness is 40 - 80 mm, and it consists of chemical components with the following weight percentages Composition: C: 0.18% - 0.22%, Si: 1.00% - 1.10%, Mn: 0.8% - 1.0%, Nb: 0.015 - 0.03%, Cr: 0.6% - 0.70%, Al: 0.06% - 0.09%, B: 0.0005% - 0.0020%, 1.4% ≤ Mn + Cr ≤ 1.6%, and the balance is Fe and inevitable impurities.

2. A thick - specification wear - resistant steel plate with no delayed crack after thermal cutting and HB450 level according to claim 1, characterized in that For the control of impurity elements in the wear - resistant steel plate: P ≤ 0.010%, S ≤ 0.002%, [N] ≤ 0.0040%, [H] ≤ 0.00010%, [O] ≤ 0.0010%, and the retained austenite content is 5% - 7%.

3. A thick - specification wear - resistant steel plate with no delayed crack after thermal cutting and HB450 level according to claim 1, characterized in that The tensile strength of the wear - resistant steel plate is ≥ 1250 MPa; the hardness of the cut edge is ≥ HB410.

4. A thick - specification wear - resistant steel plate with no delayed crack after thermal cutting and HB450 level according to claim 1, characterized in that The wear - resistant steel plate has - 40°C AKV ≥ 40 J; A ≥ 12%.

5. A production method of a fire-free cutting delayed crack HB450 grade thick specification wear-resistant steel plate as described in any one of claims 1-4, characterized in that, The production process flow is: smelting → refining → slab continuous casting → casting blank heating and slow cooling → slab heating → controlled rolling → stacking and slow cooling → quenching + tempering heat treatment → warm - cutting with flame → hot - water slow cooling; This production method specifically includes the following steps: 1) Refining: Control the RH degassing time, and the RH vacuum circulation time ≥ 18 min; 2) Slab continuous casting: The target superheat of the tundish ≤ 20°C; the center segregation of the casting blank is controlled below C1.0, and the inclusions A + B + C + D ≤ 3.0; 3) Casting blank heating and slow cooling: The slow - cooling start temperature ≥ 450°C, heated at a heating rate ≤ 50°C / s to 600 - 650°C, held for 15 - 20 hours, then slowly cooled in the furnace to less than 400°C, and taken out of the furnace and air - cooled to room temperature; 4) Slab heating: The heating soaking - section temperature is 1200 - 1250°C, and the soaking time is greater than 2.5 hours; 5) Controlled rolling: Two - stage controlled rolling of rough rolling and finish rolling is adopted. In the rough - rolling stage, the rolling start temperature ≥ 1020°C, and the finish - rolling temperature is controlled at ≥ 980°C; the finish - rolling start temperature is 880 - 850°C, the finish - rolling reduction rate ≥ 50%, and the finish - rolling temperature is 800 - 850°C; 6) Stacking and slow cooling: If the off - line temperature of the hot - rolled steel plate ≥ 500°C, then stacking and slow cooling is carried out, the heat - preservation time is greater than or equal to 34 hours, and after cooling to 350 - 400°C, it is air - cooled to room temperature; If the off - line temperature of the hot - rolled steel plate < 470°C, then high - temperature tempering is carried out, the tempering heating temperature is 650 - 700°C, the heat - preservation time is 120 - 150 min, after tempering, the steel plate is stacked and slowly cooled, the stacking time is greater than or equal to 24 hours, and after unstacking at 360 - 400°C, it is air - cooled to room temperature; 7) Quenching + tempering heat treatment: The quenching temperature is 870 - 900 °C, and the holding time is 2 - 2.5 min / mm; The tempering temperature is 200 - 230 °C, and the holding time for low-temperature tempering is 8 - 10 min / mm; 8) Flame cutting with temperature retention: The temperature of the steel plate at the flame cutting position is ≥100 °C; If the temperature is lower than 100 °C, preheat the cutting position. The preheating temperature is 130 - 180 °C, and the preheating width is 100 mm on both sides of the cutting edge; During flame cutting, perform slow cutting, and the cutting speed ≤150 mm / min; 9) Slow cooling in hot water After the steel plate is cut, it is slowly cooled in a hot water pool. The cut steel plate is held in water at a high temperature of 80 - 100 °C for more than 2 hours.

6. The production method of a thick-specification wear-resistant steel plate of HB450 grade without post-flame-cutting delayed crack according to claim 5, characterized in that In step 2), during continuous casting, perform whole-process protective casting to prevent hydrogen from entering the tundish.

7. The production method of a thick-specification wear-resistant steel plate of HB450 grade without post-flame-cutting delayed crack according to claim 5, characterized in that In step 2), during continuous casting, use electromagnetic stirring or soft reduction to reduce central segregation.

8. The production method of a thick-specification wear-resistant steel plate of HB450 grade without post-flame-cutting delayed crack according to claim 5, characterized in that In step 4), the thickness of the continuous casting billet is 250 - 300 mm.

9. The production method of a thick-specification wear-resistant steel plate of HB450 grade without post-flame-cutting delayed crack according to claim 5, characterized in that In step 6), stack and slowly cool in a slow cooling pit, and cover it for heat preservation.

10. The production method of a thick-specification wear-resistant steel plate of HB450 grade without post-flame-cutting delayed crack according to claim 5, characterized in that In step 8), use a flame torch or an electronic heating pad to preheat the cutting position.

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