High-hardness thick-specification flame cutting delayed crack-free high-wear-resistance steel plate and production method thereof

Abstract

The invention relates to the technical field of high-hardness thick-specification high-wear-resistance steel plates, in particular to a high-hardness 30-80mm thick-specification flame-cutting-delayed-crack-free high-wear-resistance steel plate and a production method thereof. New flame cutting delayed crack preventing components and process design are adopted, the chemical components of the steel plate are mainly characterized by medium carbon, high silicon and niobium microalloying, and the wear-resistant steel plate with low impurity content, uniform and fine martensite and a certain amount of retained austenite structures is obtained after refining, continuous casting, controlled rolling and heat treatment. And formation and expansion of delayed cracks during flame cutting can be inhibited. And during flame cutting, thermal stress and structural stress formed in the cutting process of the thick steel plate are reduced through the cutting process of cutting with temperature and slow cooling with hot water after cutting, and the effect of no delayed crack after cutting is achieved. The surface hardness is larger than or equal to HB500, the tensile strength is larger than or equal to 1350 MPa, AKV at-40 DEG C is larger than or equal to 30 J, A is larger than or equal to 10%, retained austenite is 4%-6%, delayed cracks do not exist after flame cutting, and the flame cutting edge hardness is larger than or equal to HB460.

Description

Technical Field

[0001] The present invention relates to the technical field of high-hardness thick-specification highly wear-resistant steel plates, and specifically to a high-hardness 30-80 mm thick-specification non-flame-cutting delayed crack highly wear-resistant steel plate and a production method thereof. Background Art

[0002] Low-alloy wear-resistant steels at the HB500 level have relatively high hardness, significantly improved wear resistance, certain impact resistance while maintaining high hardness, good toughness, weldability and fatigue resistance. With their high hardness and good toughness, they are widely used in the manufacture of wear-resistant components in multiple industries and are suitable for high-wear environments (such as mining machinery and crusher components).

[0003] Flame cutting is a commonly used blanking method for wear-resistant steel plates, with low cost, high efficiency and wide application range. Currently, for HB500 wear-resistant steel plates with a thickness specification of 30-80 mm, delayed cracking often occurs after flame cutting, posing potential safety hazards 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 CN114850618A discloses a "cutting method for reducing edge cracks of steel plates", which is a wear-resistant steel cutting method that requires the use of a double-flame gun for preheating and heat preservation, with a wide heat-affected zone and a large decrease in the hardness of the flame-cut edge. Chinese patent document with publication number CN111270042A discloses a "method for controlling hydrogen-induced cracks in high-carbon equivalent steel plates", and this steel plate cutting process is only applicable to high-carbon equivalent hot-rolled steel plates and is not applicable to wear-resistant steel plates delivered in the heat-treated state. Moreover, there is no effective slow cooling after cutting, resulting in high internal stress in the steel plate and easy cracking. Chinese patent document with publication number CN114147434A discloses a "method for improving the cutting quality of medium and high-carbon steel in ultra-thick plates", and this method can cut thick-specification steel plates, but the stress relief annealing heating temperature is too high, which will cause a decrease in the hardness of the wear-resistant steel and affect its wear resistance. Chinese patent document with publication number CN115369303A discloses a "preparation method for wear-resistant steel NM500", which is a high-toughness wear-resistant steel with complex alloys and high internal stress after online water cooling, and cannot prevent the cutting delayed cracks of thick steel plates. Chinese patent document with publication number CN109072367A discloses a "wear-resistant steel plate and a manufacturing method thereof", and this steel plate has complex alloy components, high cost and no ability to resist delayed cracks.

[0005] In summary, the existing HB500 wear-resistant steel plates disclosed in patent documents have at least the following defects and deficiencies: 1. There are delayed cracks; 2. It can only be cut in the hot-rolled state; 3. The internal stress is large; 4. The hardness of the oxy-cut edge decreases. Summary of the Invention

[0006] In order to overcome the deficiencies of the prior art, the present invention provides a high-hardness thick-specification non-oxy-cut delayed crack high-wear-resistant steel plate and its production method, with a surface hardness ≥ HB500, a tensile strength ≥ 1350 MPa, an AKV at -40°C ≥ 30 J, an elongation A ≥ 10%, a retained austenite content of 4 - 6%, no delayed cracks after oxy-cutting, and a hardness of the oxy-cut edge ≥ HB460.

[0007] To achieve the above object, the present invention is realized by adopting the following technical solutions:

[0008] A high-hardness thick-specification non-oxy-cut delayed crack high-wear-resistant steel plate, without oxy-cut delayed cracks, with a surface hardness ≥ HB500 and a thickness of 30 - 80 mm, is composed of chemical components with the following weight percentages:

[0009] C: 0.26% - 0.30%, Si: 0.80% - 0.95%, Mn: 0.6% - 0.8%, Nb: 0.015% - 0.03%, Cr: 0.70% - 0.80%, Al: 0.06% - 0.09%, B: 0.0005% - 0.0020%, 1.3% ≤ Mn + Cr ≤ 1.5%, and the balance is Fe and inevitable impurities.

[0010] 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 4% - 6%.

[0011] In the design of the steel plate composition of the present invention:

[0012] C: In order to ensure that the surface of the steel plate has a hardness of HB500 after quenching, it can also improve the hardenability of the thick-specification steel plate 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 cracks, the C content in the present invention is controlled at 0.26% - 0.30%.

[0013] Si: The key element added in this invention, which 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 there is too much Si, the surface quality and welding performance will decline. Therefore, the Si content in this invention is controlled at 0.8% - 0.95%.

[0014] Mn: It has the effect of delaying the transformation of austenite to ferrite, promoting martensite transformation, and improving hardenability. However, it is prone 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 this invention is controlled at 0.6% - 0.8%.

[0015] Nb: The most effective element for controlled rolling. During the two-stage rolling process, its 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 cracks. Therefore, the addition amount of Nb in this invention is 0.015% - 0.030%.

[0016] Al: An effective element for deoxidation and nitrogen fixation. Deoxidation can reduce oxide inclusions in the steel and purify the steel quality. After deoxidation, nitrogen fixation can ensure that element B does not combine with N, giving play to the role of B in improving hardenability. Excessive content will cause difficulties in casting and also form a large amount of Al2O3 inclusions in the steel, which are likely to become the initiation sources of delayed cracks after cutting. Therefore, in this invention, Al is 0.06% - 0.09%.

[0017] Cr: It has the effect 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 flame cutting. Therefore, in this invention, Cr is controlled at 0.70% - 0.80%. Since both Mn and Cr have the effect of improving hardenability, excessive addition will increase the cracking risk after flame cutting. To ensure that no delayed fracture occurs during the cutting of the steel plate, in this invention, 1.3% ≤ Mn + Cr ≤ 1.5%

[0018] 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 prone to enrichment at the grain boundaries after flame cutting, which will reduce the grain boundary binding energy and cause intergranular fracture in the heat affected zone of flame cutting under the action of residual stress. Therefore, the addition amount of B in this invention is 0.0005% - 0.0020%.

[0019] Retained austenite and impurity elements: 4-6% retained austenite near the cutting edge during flame cutting acts as a hydrogen trap to inhibit the propagation of delayed cracks, ensuring that the cutting edge of the steel plate has good crack arrest ability. Excessive retained austenite content 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 delayed crack formation after flame cutting. Therefore, in order to ensure good anti-delayed fracture performance, the impurity elements are controlled as follows: P≤0.012%, S≤0.002%, [H]≤0.00010%, [O]≤0.0010%, [N]≤0.0040%.

[0020] The surface hardness of the above wear-resistant steel plate is ≥HB500, the tensile strength is ≥1350MPa, the -40°C AKV is ≥30J, A≥10%, the retained austenite is 4-6%, there are no delayed cracks after flame cutting, and the hardness of the flame-cut edge is ≥HB460.

[0021] The production method of the above high-hardness thick-specification high-wear-resistant steel plate without flame-cutting delayed cracks has the following production process: smelting → refining → slab continuous casting → casting blank heating and slow cooling → slab heating → controlled rolling → stacking and slow cooling (tempering) → quenching + tempering heat treatment → flame cutting → hot water slow cooling.

[0022] The specific production method is as follows:

[0023] 1) Smelting:

[0024] ① During refining, control the RH degassing time, and the RH vacuum circulation time ≥18min;

[0025] ② During continuous casting, control the target superheat of the tundish at ≤20°C; control the center segregation of the casting blank below C1.0, and the inclusions A+B+C+D≤2.5;

[0026] ③ After the slab continuous casting is taken offline, perform heating and slow cooling. The slow cooling start temperature ≥450°C, heat up to 600-650°C at a heating rate of ≤50°C / second, hold for 15-20 hours, then slow cool with the furnace to less than 400°C, and take out of the furnace and air cool to room temperature;

[0027] 2) Rolling:

[0028] ① The temperature of the heating soaking section is 1200-1250°C, and the soaking time is greater than 2.5 hours;

[0029] ② Adopt two-stage controlled rolling in the rough rolling and finish rolling stages. 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;

[0030] 3) Post-rolling dehydrogenation:

[0031] ① If the off-line temperature of the hot-rolled steel plate is ≥ 450 °C, it shall be stacked and slowly cooled, with the heat preservation time being greater than or equal to 36 hours, and then air-cooled to room temperature after reaching 350 - 400 °C;

[0032] ② If the off-line temperature of the hot-rolled steel plate is < 450 °C, it shall be put into the heat treatment furnace for high-temperature tempering. The tempering heating temperature is 650 - 700 °C, and the heat preservation time is 90 - 150 min. After tempering, the steel plate shall be stacked and slowly cooled, with the stacking time being ≥ 28 hours, and then air-cooled to room temperature after the unstacking temperature reaches 350 - 400 °C;

[0033] 4) Heat treatment:

[0034] ① The quenching temperature is 850 - 880 °C, and the heat preservation time is 2 - 2.5 min / mm;

[0035] ② The tempering temperature is 180 - 220, and the low-temperature tempering heat preservation time is 8 - 10 min / mm;

[0036] 5) Flame cutting:

[0037] ① It is required that the temperature of the steel plate at the flame cutting position is ≥ 150 °C. If the temperature is lower than 150 °C, the cutting position shall be preheated, with the preheating temperature being 170 °C - 220 °C, and the preheating width being 100 mm on both sides of the cutting edge;

[0038] ② The cutting speed ≤ 130 mm / min;

[0039] ③ After the steel plate is cut, it is put into a hot water pool for slow cooling, with the slow cooling water temperature being 80 - 100 °C and the heat preservation in water being greater than 2 hours.

[0040] Furthermore, in step 1), during continuous casting, whole-process protective casting is carried out to prevent hydrogen from entering the tundish.

[0041] Furthermore, in step 1), electromagnetic stirring or soft reduction is adopted during continuous casting to reduce central segregation.

[0042] Furthermore, in step 2), the thickness of the continuous casting billet is 250 - 300 mm to ensure the reduction ratio.

[0043] Furthermore, in item ① of step 3), stacking and slow cooling in a slow cooling pit are adopted.

[0044] Furthermore, in step 5), a flame burning gun or an electronic heating pad is used to preheat the cutting position.

[0045] Compared with the prior art, the beneficial effects of the present invention are:

[0046] 1. The present invention utilizes 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, stabilize the content of retained austenite in the steel. During flame cutting, the retained austenite serves 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, the contents of C, Mn, Nb, AL, Cr, and B are controlled to ensure that the steel plate has high wear resistance and good resistance to delayed cracks. During flame cutting, 4-6% of the retained austenite near the cutting edge serves 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. 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%.

[0047] 2. During the refining of the present invention, the RH degassing time is controlled. Through long-time vacuum treatment, the content of [N] in the molten steel can be controlled ≤0.0040%, [O]≤0.0010%, and [H]≤0.00010%. The center segregation of the continuous casting billet is controlled below C1.0, and the inclusions A + B + C + D≤2.5, thereby reducing segregation, inclusions, and H from becoming the initiation points of delayed cracks. After the slab continuous casting is taken off the production line, it needs to be heated and slowly cooled in a slow cooling pit to further remove the hydrogen content and casting internal stress in the steel billet.

[0048] 3. During the heating of the steel billet of the present invention, the soaking time is greater than 2.5 hours. Through the long-time high-temperature heating of the steel billet, the carbon and alloy elements in the core of the steel billet are fully diffused, further improving the center segregation. During rolling, two-stage controlled rolling of rough rolling and finish rolling is adopted, aiming to fully refine and homogenize the hot-rolled structure.

[0049] 4. After the hot rolling of the steel plate of the present invention, it is taken off the production line and stacked and slowly cooled in a slow cooling pit or subjected to high-temperature tempering. The purpose of slow cooling in the slow cooling pit stack and slow cooling after high-temperature tempering is to utilize the different solubilities of hydrogen in the 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 balancing the steel plate temperature.

[0050] 5. After the low-temperature tempering heat treatment of the present invention, the steel plate is cut to size and sampled by flame cutting. It is required that the temperature of the steel plate at the flame cutting position is ≥150°C. If the cutting temperature is lower than 150°C, the cutting position is preheated. The required preheating temperature is 170°C - 220°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 cutting with temperature and preheating 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.

[0051] During oxygen cutting, the cutting speed ≤ 130 mm / min. The purpose of slow cutting is to reduce 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 surface and core temperatures of the cut-edge steel plate consistent, reducing the thermal stress and tissue stress formed after cutting. At the same time, 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.

[0052] In summary, the present invention adopts a new composition and process design to prevent delayed cracks during oxygen 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 can be obtained, which can inhibit the formation and propagation of delayed cracks during oxygen cutting. During oxygen cutting, through the cutting process of cutting with temperature and slow cooling in hot water after cutting, the thermal stress and tissue stress formed during the cutting of thick-specification steel plates are reduced, achieving the effect of no delayed cracks after cutting. Wear-resistant steel plates with a thickness of 30 - 80 mm and a surface Brinell hardness of HB500 level without delayed cracks during oxygen cutting can be produced. The surface hardness of the present invention is ≥ HB500, the tensile strength is ≥ 1350 MPa, the AKV at - 40 °C is ≥ 30 J, A is ≥ 10%, the retained austenite is 4 - 6%, there are no delayed cracks after oxygen cutting, and the hardness of the oxygen-cut edge is ≥ HB460. Description of the Drawings

[0053] Figure 1 It is a coloring flaw detection diagram of the cutting surface of the 40-mm-thick steel plate of the present invention 48 hours after oxygen cutting. Detailed Embodiments

[0054] The present invention discloses a high-hardness, thick-specification wear-resistant steel plate without delayed cracks during oxygen 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 considered to be 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 alterations and combinations to the methods and applications described herein without departing from the content, spirit, and scope of the present invention to implement and apply the technology of the present invention.

[0055] A high-hardness, thick-specification wear-resistant steel plate without delayed cracks during oxygen cutting, with a surface hardness ≥ HB500 and a thickness of 30 - 80 mm, is composed of the following chemical components in weight percentage:

[0056] C: 0.26% - 0.30%, Si: 0.80% - 0.95%, Mn: 0.6% - 0.8%, Nb: 0.015% - 0.03%, Cr: 0.70% - 0.80%, Al: 0.06% - 0.09%, B: 0.0005% - 0.0020%, 1.3% ≤ Mn + Cr ≤ 1.5%, the balance being Fe and unavoidable impurities.

[0057] Control of impurity elements in wear-resistant steel plates: P ≤ 0.010%, S ≤ 0.002%, [N] ≤ 0.0040%, [H] ≤ 0.00010%, [O] ≤ 0.0010%, and the retained austenite content is 4% - 6%.

[0058] The surface hardness of the above-mentioned wear-resistant steel plate is ≥ HB500, the tensile strength is ≥ 1350 MPa, -40°C AKV ≥ 30 J, A ≥ 10%, the retained austenite is 4 - 6%, there is no delayed crack after flame cutting, and the hardness of the flame-cut edge is ≥ HB460.

[0059] The production method of the above-mentioned HB500-grade thick-specification wear-resistant steel plate without delayed crack in flame cutting, and the production process flow is: smelting → refining → slab continuous casting → heating and slow cooling of the cast slab → heating of the slab → controlled rolling → stacking and slow cooling (tempering) → quenching + tempering heat treatment → flame cutting → hot water slow cooling.

[0060] Specifically, it includes the following steps:

[0061] 1) Smelting:

[0062] 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%, and [H] ≤ 0.00010% can be controlled.

[0063] Continuous casting: The target superheat of the tundish is controlled at ≤ 20°C; the whole process is protected from pouring to prevent hydrogen from entering the tundish; electromagnetic stirring or soft reduction is used during continuous casting to reduce central segregation.

[0064] It is required that the central segregation of the cast slab be controlled below C1.0, and the inclusions A + B + C + D ≤ 2.5, aiming to reduce segregation and inclusions from becoming the initiation points of delayed cracks.

[0065] After the slab continuous casting is off-line, the steel billet needs to enter the slow cooling pit for heating and slow cooling. It is required that the slow cooling start temperature ≥ 450°C, and it is heated to 600 - 650°C at a heating rate of ≤ 50°C / second. After holding for 15 - 20 hours, it is slowly cooled with 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: to remove the hydrogen content and casting internal stress in the steel billet.

[0066] 2) Rolling:

[0067] The heating soaking section temperature is 1200 - 1250°C, the slab thickness is 250 - 300 mm, and the soaking time is more than 2.5 hours. Through long-time high-temperature heating, the carbon and alloying elements in the core of the steel plate are fully diffused, further improving the center segregation.

[0068] During rolling, two-stage controlled rolling is adopted in the rough rolling and finish rolling stages, aiming 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, the finish rolling reduction rate ≥ 50%, and the finish rolling temperature is 800 - 850°C, aiming to refine the original austenite structure.

[0069] 3) Post-rolling dehydrogenation:

[0070] After hot rolling, the steel plate is taken offline and stacked in a slow cooling pit for slow cooling or sent to a heat treatment furnace for high-temperature tempering.

[0071] If the offline temperature ≥ 450°C, the slow cooling holding time in the slow cooling pit is greater than or equal to 24 hours, and after cooling to 350 - 400°C, it is air-cooled to room temperature.

[0072] If the offline temperature is lower than 450°C, it needs to be sent to a heat treatment furnace for high-temperature tempering. The tempering heating temperature is 650 - 700°C, and the holding time is 3 min / mm. After tempering, the steel plate is stacked for slow cooling. The stacking time is greater than or equal to 24 hours, and after the unstacking temperature reaches 350 - 400°C, it is air-cooled to room temperature.

[0073] The purpose of stacking the steel plate in the slow cooling pit for slow cooling or 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.

[0074] 4) Heat treatment:

[0075] ① The quenching temperature is 850 - 880°C, and the holding time is 2 - 2.5 min / mm;

[0076] ② The tempering temperature is 180 - 220, and the low-temperature tempering holding time is 8 - 10 min / mm;

[0077] The purpose of quenching is to obtain a hardness of HB500. The tempering temperature is 180 - 220°C, and the low-temperature tempering holding time is 8 - 10 min / mm, aiming to remove the internal stress formed during the quenching of the steel plate.

[0078] 5) Flame cutting:

[0079] After the low-temperature tempering heat treatment, the steel plate is cut to size and sampled with a flame while still warm. It is required that the temperature of the steel plate at the flame cutting position is ≥150°C. If the temperature is lower than 150°C, the cutting position is preheated, with the preheating temperature being 170°C - 220°C and the preheating width being 100 mm on both sides of the cutting edge. A flame torch or an electronic heating pad can be used. The purpose of cutting with the steel still warm and preheating 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.

[0080] During flame cutting, slow cutting should be carried out, with the cutting speed ≤130 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 pool by a crane for slow cooling. The temperature of the slow cooling water is 80 - 100°C, and the insulation time in the water is more than 2 hours. Cooling in hot water can quickly make the temperature of the surface and the core of the cutting edge of the steel plate reach the same, reduce the thermal stress and tissue stress formed after cutting. At the same time, 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.

[0081] After cutting, the steel plate is insulated 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.

[0082]

Example

[0083] According to the chemical composition and production process of the present invention, the actual chemical composition of the steel grade of the present invention during smelting is shown in Table 1, 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 post-rolling dehydrogenation process parameters are shown in Table 4, the heat treatment process parameters are shown in Table 5, the physical property test results of the physical objects of the present invention are shown in Table 6, and the cutting process and delayed crack test results are shown in Table 7.

[0084] Table 1 Examples of the smelting composition of the steel grade of the present invention, Wt%

[0085]

[0086] Table 2 The smelting process of the steel grade of the present invention

[0087]

[0088] Table 3 The actual rolling process parameters of the steel examples of the present invention

[0089]

[0090]

[0091] Table 4 The post-rolling dehydrogenation process parameters of the steel examples of the present invention

[0092]

[0093] Table 5 Heat treatment process of the steel examples of the present invention

[0094]

[0095] Table 6 Mechanical properties of the steel examples of the present invention

[0096]

[0097] Table 7 Thermal cutting process and crack inspection of the steel examples of the present invention

[0098]

[0099] Figure 1 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 thermal cutting, as Figure 1 shown. After 48 hours of slow cooling, the coloring flaw detection method is used to check the delayed crack situation on the thermal cutting surface of the steel plate of the present invention, and no delayed crack is found. It can be seen that the steel plate of the present invention has good resistance to delayed cracks.

[0100] The present invention adopts a new composition and process design to prevent thermal 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, 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 hot water slow cooling after cutting, the thermal stress and tissue stress formed during the cutting process of thick-gauge steel plates are reduced, and the effect of no delayed cracks after cutting is achieved. Wear-resistant steel plates with no thermal cutting delayed cracks with a thickness specification of 30-80 mm and a surface Brinell hardness of HB500 can be produced. The surface hardness of the present invention is ≥HB500, the tensile strength is ≥1350 MPa, the -40°C AKV is ≥30 J, A is ≥10%, the retained austenite is 4-6%, there are no delayed cracks after thermal cutting, and the hardness of the thermal cutting edge is ≥HB460.

[0101] 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 high-hardness, thick-specification non-flame-cut delayed crack high-wear-resistant steel plate, characterized in that, The wear-resistant steel plate has no delayed crack after thermal cutting, the surface hardness is ≥ HB500, the thickness is 30 - 80 mm, and it consists of chemical components with the following weight percentages as follows: C: 0.26% - 0.30%, Si: 0.80% - 0.95%, Mn: 0.6% - 0.8%, Nb: 0.015% - 0.03%, Cr: 0.70% - 0.80%, Al: 0.06% - 0.09%, B: 0.0005% - 0.0020%, 1.3% ≤ Mn + Cr ≤ 1.5%, and the balance is Fe and inevitable impurities.

2. A high-hardness thick-specification wear-resistant steel plate without delayed crack after thermal cutting according to claim 1, characterized in that 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 4% - 6%.

3. A high-hardness thick-specification wear-resistant steel plate without delayed crack after thermal cutting according to claim 1, characterized in that the tensile strength of the wear-resistant steel plate is ≥ 1350 MPa, the AKV at - 40 °C is ≥ 30 J, A ≥ 10%, and the hardness of the thermal cutting edge is ≥ HB460.

4. A production method of a high-hardness thick-specification non-flame-cut delayed-crack high-wear-resistant steel plate as described in any one of claims 1-3, characterized in that, The production process flow is: smelting → refining → slab continuous casting → heating and slow cooling of the casting blank → heating of the slab → controlled rolling → tempering → quenching + tempering heat treatment → flame cutting → hot water slow cooling; The specific production method is as follows: 1) Smelting: ① Control the RH degassing time during refining, and the RH vacuum circulation time is ≥ 18 min; ② During continuous casting, control the target superheat of the tundish at ≤ 20 °C; control the center segregation of the casting blank below C1.0, and the inclusions A + B + C + D ≤ 2.5; ③ After the slab continuous casting is taken offline, carry out heating and slow cooling. The slow cooling start temperature is ≥ 450 °C, heat it to 600 - 650 °C at a heating rate of ≤ 50 °C / s, keep it warm for 15 - 20 hours, then slow cool it in the furnace to less than 400 °C, and take it out of the furnace and air cool it to room temperature; 2) Rolling: ① The temperature of the heating soaking section is 1200 - 1250 °C, and the soaking time is more than 2.5 hours; ② Adopt two-stage controlled rolling in the rough rolling and finish rolling stages. The rolling start temperature in the rough rolling stage is ≥ 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 is ≥ 50%, and the finish rolling temperature is 800 - 850 °C; 3) Post-rolling dehydrogenation: ① If the offline temperature of the hot-rolled steel plate is ≥ 450 °C, then stack and slow cool it, and the heat preservation time is greater than or equal to 36 hours, and then air cool it to room temperature after reaching 350 - 400 °C; ② If the offline temperature of the hot-rolled steel plate is < 450 °C, then put it into the heat treatment furnace for high-temperature tempering. The tempering heating temperature is 650 - 700 °C, the heat preservation time is 90 - 150 min, and after tempering, the steel plate is stacked and slow cooled. The stacking time is ≥ 28 hours, and then air cool it to room temperature after the unstacking temperature reaches 350 - 400 °C; 4) Heat treatment: ① The quenching temperature is 850 - 880 °C, and the heat preservation time is 2 - 2.5 min / mm; ② The tempering temperature is 180 - 220, and the low-temperature tempering heat preservation time is 8 - 10 min / mm; 5) Flame cutting: ① The temperature of the steel plate at the flame cutting position ≥ 150 °C; If the temperature is lower than 150 °C, preheat the cutting position, with the preheating temperature being 170 °C - 220 °C and the preheating width being 100 mm on both sides of the cutting edge; ② The cutting speed ≤ 130 mm / min; ③ After the steel plate is cut, slow cooling is carried out in a hot water pool, with the slow cooling water temperature being 80 - 100 °C and the heat preservation in water being more than 2 hours.

5. The production method of a high - hardness thick - specification non - flame - cut delayed - crack high - wear - resistant steel plate according to claim 4, characterized in that, In step 1), during continuous casting, full - protection casting is carried out throughout the pouring process to prevent hydrogen from entering the tundish.

6. The production method of a high - hardness thick - specification non - flame - cut delayed - crack high - wear - resistant steel plate according to claim 4, characterized in that, In step 1), electromagnetic stirring or soft reduction is adopted during continuous casting to reduce central segregation.

7. The production method of a high - hardness thick - specification non - flame - cut delayed - crack high - wear - resistant steel plate according to claim 4, characterized in that, In step 2), the thickness of the continuous casting billet is 250 - 300 mm.

8. The production method of a high - hardness thick - specification non - flame - cut delayed - crack high - wear - resistant steel plate according to claim 4, characterized in that, In ① of step 3), slow cooling by stacking in a slow - cooling pit is adopted.

9. The production method of a high - hardness thick - specification non - flame - cut delayed - crack high - wear - resistant steel plate according to claim 4, characterized in that, In step 5), a flame torch or an electronic heating pad is used to preheat the cutting position.

Images