Hot-rolled pickled steel plate for saw blade and manufacturing method of hot-rolled pickled steel plate

Abstract

The invention discloses a hot-rolled pickled steel plate for a saw blade and a manufacturing method of the hot-rolled pickled steel plate. The technical problems that existing high-carbon and high-manganese steel with the thickness of 2.5-7.0 mm for the saw blade is prone to segregation, poor in structure uniformity and thick and large in pearlite structure are mainly solved. According to the technical scheme, the hot-rolled pickled steel plate for the saw blade comprises the following chemical components in percentage by weight: 0.75%-0.85% of C, 0.20%-0.50% of Si, 0.20%-0.50% of Mn, less than or equal to 0.020% of P, less than or equal to 0.005% of S, 0.01%-0.02% of Al, less than or equal to 0.0060% of N, 0.4%-0.8% of Cr, 0.18%-0.28% of V and the balance of Fe and inevitable impurity elements. The metallographic structure of the hot-rolled pickled steel plate is superfine pearlite with the interlamellar spacing of 0.4-0.8 mu m, and the hot-rolled pickled steel plate is used for production of circular saw webs, chain saws, frame saws and the like.

Description

Technical Field

[0001] The invention relates to steel for saw blades, in particular to a hot-rolled pickled steel plate for saw blades and a manufacturing method thereof, specifically, to a hot-rolled pickled steel plate with a thickness of 2.5 to 7.0 mm for circular saw blades and a manufacturing method thereof, belonging to the technical field of iron-based alloys. Background Art

[0002] Saw blade steel can be divided into wood saw, stone saw and metal saw according to the final use. In addition to excellent cutting performance and wear resistance, saw blade steel is also required to maintain a certain strength and hardness at high temperatures due to the rapid increase in temperature during high-speed rotary cutting. In the saw blade manufacturing process, the hot-rolled pickled steel plate for the saw blade is cold-rolled to the target thickness, and then quenched to form martensite to increase the hardness of the steel matrix; then tempered at 300-600℃. Tempering treatment releases phase change stress on the one hand, and on the other hand, tries to avoid the hardness drop caused by high temperature redness when the saw blade is cutting at high speed under working conditions, that is, to maintain excellent red hardness.

[0003] Existing saw blade steel generally adopts medium and high carbon steel, and adds microalloys of different components and contents to improve its hardenability and tempering stability. Existing steel grades include 30CrMo, 65Mn, and 75Cr1. Existing saw blade steel has the following problems: low C content, poor hardness and hardenability. Although it can be improved to a certain extent by adding alloys, the cost increases significantly. The above problems can be effectively solved by increasing the C and Mn contents, but at the same time, it is easy to cause organizational segregation and surface decarburization, which further affects the uniformity of hardenability. Therefore, how to maintain the optimal balance between cost and organizational and performance uniformity has always been the main technical problem faced by this type of steel.

[0004] Due to the high strength of steel used in saw blades, hot-rolled pickled steel plates for saw blades usually adopt a higher hot rolling coiling temperature during hot rolling production, which inevitably causes: 1) the pearlite of the hot-rolled steel plate is coarse, which is not conducive to the user's subsequent spheroidizing annealing; 2) the cooling speed of the head, tail and edge of the hot-rolled steel plate is fast, and the uniformity of the organization of the hot-rolled steel plate in the rolling direction and the plate width direction is poor; 3) with the increase of the coiling temperature of the hot-rolled steel plate, the iron oxide scale on the surface of the hot-rolled steel plate is obviously thickened, which increases the difficulty of pickling.

[0005] The Chinese patent application with application publication number CN102134681A discloses a steel for saw blade substrate and a manufacturing method thereof, which relates to a production method for a large-scale saw blade steel with a thickness of 7-9 mm and a diameter of 1800-2300 mm. The main components of the saw blade steel are C: 0.68-0.80%, Si: 0.10-0.50%, Mn: 0.50-1.00%, Cr: 0.30-0.70%, V: 0.03-0.15, the hot-rolled steel plate has a final rolling temperature of 870-950°C, a coiling temperature of 720-820°C, and a quenching hardness of 840°C HRC

[0006] 63-66.1, 500℃ tempering hardness HRC 42.5-45.6. The design has moderate C and Mn content, and adds trace amounts of Cr and V. The coiling temperature is 720-820℃, which is relatively high. The pearlite interlamellar spacing of the hot-rolled coil is greater than 1μm, and the pearlite is obviously coarse. After tempering at 500℃, the hardness is HRC 42.5-45.6, and the tempering hardness is low.

[0007] The Chinese patent application with application publication number CN1904119A discloses a stone cutting saw blade steel and a manufacturing method thereof, which relates to a production method for a large saw blade steel with a thickness of 10 mm and a diameter of more than 1000 mm. The saw blade steel mainly comprises C: 0.45-0.60%, Si: 0.10-0.60%, Mn 1.30-1.80%, V: 0.05-0.20, Cr: 0.15-0.30, N: 0.005-0.020%, and AL: 0.005-0.040%. The steel adopts a VN-strengthened component system, the hot-rolled steel plate has a final rolling temperature of more than 900°C, and a coiling temperature of more than 700°C; the hardness after quenching at 810-840°C and tempering at 410-440°C is HRC 43±2. This design has low C and high Mn, adds trace amounts of Cr and V, and uses N to strengthen. The coiling temperature is higher than 700℃, and the hardness after tempering at 410-440℃ is HRC 43±2. The hardness is lower if tempered at 500℃.

[0008] The Chinese patent application with application publication number CN104178691A discloses a high-strength metallurgical steel for saw blades and a manufacturing method thereof, which relates to a saw blade steel with main components of C: 0.30% to 0.60%, Si: 0.15% to 0.30%, Mn: 1.35% to 1.9%, V: 0.070% to 0.19%, Al: 0.025% to 0.055%, and a surface hardness of HRC 60±2 after quenching at 800 to 900°C; and a steel plate hardness of HRC 28 to 40 after tempering at 500 to 600°C. The design has low C, high Mn, and a trace amount of V added. The hardness after tempering at 500°C is HRC40, and the tempering hardness is low.

[0009] The Chinese patent application with application publication number CN106319378A discloses a steel for a large-diameter thin saw blade substrate and a manufacturing method thereof, which relates to a production method for a large-diameter saw blade steel with a thickness of 3 to 7 mm and a diameter greater than 1800 mm, mainly using Si deoxidation, thin slab continuous casting and rolling and ultra-fast cooling hot-rolled steel plate, with a composition of C: 0.72% to 0.95%, Si: 0.06% to 0.40%, Mn: 0.5% to 0.95%, Cr: 0.10% to 0.39%, V: 0.03% to 0.080%. The final rolling temperature is 900 to 980°C, the coiling temperature is 680 to 800°C, the quenching is 850 to 980°C, and the hardness of the steel plate after tempering at 350 to 500°C is HRC 49-54. The design has moderate C and Mn content, with trace amounts of Cr and V added. The coiling temperature is relatively high at 680-800°C, and the hardness after tempering at 500°C is HRC 49. Although the tempering hardness of this invention is relatively high, the final rolling and coiling temperatures are extremely high, the pearlite lamellar spacing of the hot-rolled coil is greater than 1μm, and the coarse pearlite is obviously not conducive to the subsequent user spheroidizing annealing. Summary of the invention

[0010] The purpose of the present invention is to provide a hot-rolled pickled steel plate for saw blades and a manufacturing method thereof, which mainly solves the technical problems that the existing high-carbon high-manganese steel with a thickness of 2.5 to 7.0 mm for saw blades is easy to segregate, has poor structural uniformity, and has coarse pearlite structure; the hot-rolled pickled steel plate of the present invention has a good spheroidization effect after annealing, and is convenient for cold rolling to obtain a cold-rolled steel plate with the thickness of a finished saw blade; the cold-rolled steel plate with the thickness of a finished saw blade has high hardness and high red hardness after quenching and tempering.

[0011] The technical idea of ​​the present invention is to adopt a medium C and low Mn design to reduce the problem of structural segregation that is prone to occur in existing high-carbon and high-manganese steels, and at the same time adopt a relatively low coiling temperature to avoid the difficulty of spheroidizing annealing caused by abnormally coarse pearlite; through the reasonable addition of Cr and V alloy elements, the hardness after quenching and tempering is significantly improved, the red hardness of the saw blade is improved, and then the service life and machinability of the saw blade are improved.

[0012] The technical solution adopted by the present invention is a hot-rolled pickled steel plate for saw blades, whose chemical composition weight percentage is: C: 0.75% ~ 0.85%, Si: 0.20% ~ 0.50%, Mn: 0.20% ~ 0.50%, P≤0.020%, S≤0.005%, Al: 0.01% ~ 0.02%, N≤0.0060%, Cr: 0.4% ~ 0.8%, V: 0.18% ~ 0.28%, and the balance is Fe and unavoidable impurity elements.

[0013] The metallographic structure of the hot-rolled pickled steel plate of the present invention is ultrafine pearlite with a sheet spacing of 0.4 to 0.8 μm, and the yield strength R of the hot-rolled pickled steel plate with a thickness of 2.5 to 7.0 mm is p0.2550~850MPa, tensile strength R m 900~1250MPa, elongation after fracture It is 13% to 25%.

[0014] The hot-rolled pickled steel plate of the present invention is annealed, cold-rolled to the thickness of a finished saw blade, quenched, tempered, and cut to obtain a finished saw blade; the quenching temperature is 880-900°C, the metallographic structure of the cold-rolled steel plate after quenching is needle-shaped martensite, and the hardness of the cold-rolled steel plate after quenching is 65-67HRC; the tempering temperature is 500°C, the tempering holding time is 20-40min, the metallographic structure of the cold-rolled steel plate after tempering is tempered sorbite, and the hardness of the cold-rolled steel plate after tempering is 45-47HRC.

[0015] The reasons why the chemical composition of the hot-rolled pickled steel plate for saw blades of the present invention is limited to the above range are as follows:

[0016] C: Carbon is the main element that affects the strength and hardness of steel plates after quenching. If the carbon content is low, the hardenability of the steel plate is poor, resulting in a low hardness of the saw blade after heat treatment. However, if the C content is too high, the surface decarburization tendency increases, the surface hardenability will be affected to a certain extent, and the anti-tempering stability will also decrease. Therefore, it is necessary to determine a reasonable C content range based on production feasibility and product use. The present invention sets C to 0.75% to 0.85%.

[0017] Si: It has a strong solid solution strengthening effect. At the same time, it can improve the hardenability of steel by significantly reducing the critical cooling rate of steel. However, high Si content will increase the brittleness of the steel plate, and it is easy to form iron silicate oxide scale on the surface of the steel plate during hot rolling, which increases the difficulty of pickling. Taking into account the product performance requirements and production and manufacturing process capabilities, the present invention sets Si to 0.20% to 0.50%.

[0018] Mn: Manganese is one of the most effective elements for improving hardenability and is also a solid solution strengthening element. At the same time, when properly matched with silicon, it can reduce the decarburization caused by silicon. However, too high a manganese content can easily cause slab segregation and affect the uniformity of the hot-rolled plate structure. This application adopts a low Mn design based on the existing C content, combined with the addition of microalloys, which can ensure hardenability and effectively avoid structural segregation. The present invention sets Mn to 0.20% to 0.50%.

[0019] S and P are impurity elements in steel. The lower the content, the better. Meanwhile, S is easy to form MnS in steel, which affects fatigue performance. Considering economy and feasibility, the present invention sets S≤0.005%; P≤0.020%.

[0020] Al: It is a strong oxidizing element, which can effectively reduce oxide inclusions in steel and purify steel. However, at the same time, the Al2O3 particles formed are large and have no plasticity. They are difficult to deform during processing and use, which causes stress concentration and has a certain impact on the fatigue strength of the saw blade. Taking into account the feasibility of production and product use requirements, the present invention sets Al to 0.01% to 0.02%.

[0021] N: It is easy to form fine nitrides with alloy elements in steel, which may precipitate again during tempering, resulting in a decrease in the toughness of the steel. Therefore, the present invention limits N to ≤ 0.0060%

[0022] Cr: It is an element that can significantly improve hardenability. At the same time, it is a strong carbide-forming element that can strongly prevent the diffusion of carbon in austenite, thereby reducing the diffusion coefficient of carbon and the tendency of decarburization. At the same time, during tempering, it can make the carbides in the steel small and uniform, effectively inhibiting the structural transformation during low-temperature tempering, so the tempering stability is good. However, too high a Cr content will increase the difficulty of hot rolling. Considering the feasibility of the product comprehensively, the present invention limits the Cr content to 0.4% to 0.8%.

[0023] V: It is a microalloying element for fine grain strengthening and precipitation strengthening, which can effectively improve the strength and hardness of steel plates. At the same time, it can precipitate VC and V (C, N) during medium and high temperature tempering to improve the tempering stability and strengthen the red hardness of saw blades. However, the V content cannot be too high, otherwise the strength of the steel plate will be too high, which will bring difficulties to hot rolling and pickling uncoiling. Taking the above into consideration, the present invention limits the V content to 0.18% to 0.28%.

[0024] A method for producing a hot-rolled pickled steel plate for saw blades, the method comprising:

[0025] The molten steel is continuously cast to obtain a continuous casting slab, wherein the chemical composition of the molten steel is as follows: C: 0.75% to 0.85%, Si: 0.20% to 0.50%, Mn: 0.20% to 0.50%, P≤0.020%, S≤0.005%, Al: 0.01% to 0.02%, N≤0.0060%, Cr: 0.4% to 0.8%, V: 0.18% to 0.28%, and the remainder is Fe and unavoidable impurity elements;

[0026] The continuous casting slab is heated in a heating furnace and then hot rolled. The continuous casting slab is fed into the heating furnace by hot charging and hot delivery. The temperature of the continuous casting slab into the heating furnace is ≥400°C. The excess air coefficient in the heating furnace is 0.95-1.00. The heating temperature of the continuous casting slab is 1200-1260°C and the heating time is 180-240min. The hot rolling is a two-stage rolling process. The rough rolling is 6 continuous rolling passes, which are rolled above the austenite recrystallization temperature. The rough rolling end temperature is 1000-1050°C. The thickness of the intermediate slab after rough rolling is 38-42mm. The finishing rolling is 7 continuous rolling passes, and the finishing temperature of the finishing rolling is 840-900°C. After finishing rolling, the thickness of the steel plate is 2.5-7.0mm. The laminar cooling adopts front-stage cooling, and the cooling rate is 5-8°C / s. The laminar cooling end temperature is 610-680°C. The hot-rolled steel coil is obtained when the coiling temperature is 600-670°C.

[0027] The hot rolled steel coil is slowly cooled after coiling, and the cooling rate of the hot rolled steel coil to 200°C is 5-9°C / h;

[0028] After the hot-rolled steel coil is unrolled, it is pickled, rinsed, dried and oiled by push-pull methods, and the finished hot-rolled pickled steel plate is obtained by coiling.

[0029] Through simulation calculation and experimental verification, the Ar3 point phase transition temperature of the steel composition system of the present invention is 740°C, and the hot rolling processes adopted in the present invention are all based on the composition system of the steel of the present invention and the phase transition point calculated by simulation experiments.

[0030] The reasons for the production process adopted by the present invention are as follows:

[0031] 1. Setting of the temperature of the continuous casting slab entering the heating furnace, the heating temperature of the continuous casting slab and the heating time

[0032] Since the steel of the present invention has high carbon and alloy content, rapid heating from a cold state will generate certain thermal stresses causing deformation or cracking of the continuous casting slab. Therefore, it is usually required that the continuous casting slab be cut and then put into the furnace in a hot state. The continuous casting slab is put into the heating furnace by hot charging and hot conveying. The temperature of the continuous casting slab entering the heating furnace is ≥400°C.

[0033] After the continuous casting slab enters the heating furnace, it gradually austenitizes as the temperature rises, which can significantly improve the various components and organizational segregation caused by the solidification process of the slab. Generally speaking, the higher the heating temperature and the longer the insulation time, the better the uniformity of the composition and organization. However, due to the high carbon content, the decarburization tendency will increase during the heating process, and the depth of the decarburization layer will increase accordingly, which is not conducive to the surface quality. Therefore, considering the cost and operability, the present invention sets the heating temperature of the continuous casting slab to 1200-1260°C and the heating time to 180-240min. In addition, the atmosphere in the heating furnace also has a certain influence on decarburization. This application sets the excess air coefficient to 0.95-1.00.

[0034] 2. Setting of finishing temperature, laminar cooling mode, laminar cooling speed, laminar cooling ending temperature and coiling temperature

[0035] The finishing temperature setting is generally to ensure that the entire slab is fully rolled in the austenite region to avoid mixed crystals caused by rolling in the two-phase region at the end of rolling. The setting of the post-rolling laminar cooling rate and coiling temperature mainly considers the final microstructure requirements of the steel plate, while taking into account the coiling capacity of the equipment.

[0036] For saw blade steel, due to its high strength, a coiling temperature higher than 700°C is usually used after hot rolling. However, according to research, under this high-temperature coiling process, the pearlite structure of the steel plate is abnormally coarse, and due to the high alloy content, there is also a certain degree of intergranular oxidation, which is not conducive to the fatigue resistance of this type of product. Therefore, although high-temperature coiling can reduce the difficulty of production, the appearance of such coarse structure and intergranular oxidation is obviously not conducive to the user's subsequent spheroidizing annealing and final processing and use. At the same time, the coiling temperature cannot be too low. On the one hand, the coiling capacity of the equipment should be considered. On the other hand, too low coiling temperature will cause the pearlite interlamellar spacing to be too small, the strength will increase, which is not conducive to subsequent processing. Therefore, considering the processing, use requirements and manufacturing feasibility of the final product, the present invention sets the finishing temperature of the finishing rolling to 840-900°C, the laminar cooling adopts the front-stage cooling control, the cooling rate is 5-8°C / S, the laminar cooling end temperature is 610-680°C; the coiling temperature is 600-670°C.

[0037] 3. Setting of cooling speed of hot rolled steel coil

[0038] The formulation of the cooling process for high carbon steel mainly considers the structural transformation and uniformity of the steel plate during the subsequent gradual cooling process after coiling. Studies have shown that when the cooling rate is ≤7°C / s, the proportion of ferrite increases, which may affect the hardenability. If the cooling rate is too fast, the spacing between pearlite lamellae will be refined, the strength will increase, and the plasticity will decrease. At the same time, too fast a cooling rate will also cause uneven internal structure of the steel coil to varying degrees, thereby increasing the internal stress and causing brittle fracture during pickling and uncoiling. Therefore, the cooling process set by the present invention requires cooling into a slow cooling wall or slow cooling hood as soon as possible after coiling, and the cooling rate of the hot-rolled steel coil to 200°C is 5 to 9°C / h.

[0039] 4. Setting of pickling process

[0040] This product adopts a push-pull pickling process. The specific pickling process can be set according to different production lines, with the standard being no obvious residual iron oxide scale.

[0041] The metallographic structure of the hot-rolled pickled steel plate produced by the method of the present invention is ultrafine pearlite with a sheet spacing of 0.4 to 0.8 μm, and the yield strength R of the hot-rolled pickled steel plate with a thickness of 2.5 to 7.0 mm is p0.2 550~850MPa, tensile strength Rm 900~1250MPa, elongation after fracture It is 13% to 25%.

[0042] The hot-rolled pickled steel plate produced by the method of the present invention is annealed, cold-rolled to the thickness of a finished saw blade, quenched, tempered, and cut to obtain a finished saw blade; the quenching temperature is 880-900°C, the metallographic structure of the cold-rolled steel plate after quenching is needle-shaped martensite, and the hardness of the cold-rolled steel plate after quenching is 65-67HRC; the tempering temperature is 500°C, the tempering holding time is 20-40min, the metallographic structure of the cold-rolled steel plate after tempering is tempered troostite, and the hardness of the cold-rolled steel plate after tempering is 45-47HRC.

[0043] Compared with the prior art, the present invention has the following positive effects: 1. The steel plate of the present invention adopts a medium C and low Mn (0.2% to 0.5%) design to avoid the structural segregation problem caused by the low C or high C and high Mn (above 1.3%) design commonly used in most existing processes to achieve quenching hardness. 2. The present invention adopts a relatively low coiling temperature of about 620°C to avoid the problem of abnormally coarse pearlite caused by the high coiling temperature of more than 700°C commonly used by similar products at present. The metallographic structure of the hot-rolled pickled steel plate is ultrafine pearlite with a sheet spacing of 0.4-0.8μm, which is beneficial to the user's spheroidizing annealing. 3. The steel plate of the present invention adds reasonable Cr and V alloy elements, and the hardness of the hot-rolled pickled steel plate is significantly improved after annealing, cold rolling to the thickness of the finished saw blade, quenching and tempering. After tempering at 500°C, the hardness of the cold-rolled steel plate is 45-47HRC. Compared with the prior art, the hardness of the cold-rolled steel plate is increased by more than 2HRC after tempering under the same conditions, thereby improving the red hardness of the saw blade and thus improving the service life of the saw blade. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a metallographic photograph of the hot-rolled pickled steel plate according to Example 3 of the present invention.

[0045] Figure 2 This is a metallographic structure photograph of a cold-rolled steel plate obtained by annealing, cold rolling to the thickness of a finished saw blade, and quenching the hot-rolled pickled steel plate in Example 3 of the present invention. The quenching temperature is 900°C.

[0046] Figure 3 This is a metallographic structure photograph of a cold-rolled steel plate obtained by annealing, cold rolling to the thickness of a finished saw blade, quenching, and quenching the hot-rolled pickled steel plate in Example 3 of the present invention. The quenching temperature is 900°C, the tempering temperature is 500°C, and the tempering holding time is 30 minutes. DETAILED DESCRIPTION

[0047] The present invention is further described below in conjunction with Examples 1-5, as shown in Tables 1-7.

[0048] Table 1 shows the chemical composition (by weight percentage) of the steel according to the embodiment of the present invention, with the remainder being Fe and unavoidable impurities.

[0049] Table 1 Chemical composition of the steel of the present invention, unit: weight percentage.

[0050]

[0051] The molten steel meeting the chemical composition requirements is obtained by converter smelting, the molten steel is treated with Ar blowing in the LF ladle refining furnace refining process, the RH furnace is used for vacuum cycle degassing and composition fine-tuning, and the molten steel is continuously cast under Ar blowing protection throughout the process to obtain continuous casting slabs with a thickness of 210-230mm, a width of 1000-1300mm and a length of 5000-8500mm.

[0052] The continuous casting slab is directly sent to the heating furnace for heating. The continuous casting slab is sent to the heating furnace by hot charging and hot delivery. The continuous casting slab is heated in the heating furnace and then hot rolled. The hot rolling is a two-stage rolling process. The rolling is controlled by the rough rolling and finishing rolling mills. After laminar cooling, the coiling is carried out. The laminar cooling adopts the front cooling to produce qualified hot rolled steel coils. The thickness of the hot rolled steel plate is 2.5-7.0mm. The heating furnace process control parameters are shown in Table 2; the hot rolling process control parameters are shown in Table 3.

[0053] Table 2 Process control parameters of the heating furnace in the embodiment of the present invention

[0054]

[0055]

[0056] Table 3 Hot rolling process control parameters of the embodiment of the present invention

[0057]

[0058] After coiling, the hot-rolled steel coil is transferred to the slow cooling hood for slow cooling. The hot-rolled steel coil slow cooling process control parameters are shown in Table 4.

[0059] Table 4 Control parameters of the slow cooling process of hot-rolled steel coil according to the embodiment of the present invention

[0060] Slow cooling parameters Temperature of slow cooling hood / ℃ Temperature out of slow cooling hood / ℃ Cooling speed / ℃ / h The present invention 550-600 100-200 5-9 Example 1 565 185 7.9 Example 2 580 165 6.8 Example 3 575 145 7.9 Example 4 585 175 8.4 Example 5 590 165 5.6

[0061] The hot-rolled pickled steel sheet obtained by the above method is shown in Figure 1 The metallographic structure of the hot-rolled pickled steel plate is ultrafine pearlite with a sheet spacing of 0.4 to 0.8 μm, and the yield strength R of the hot-rolled pickled steel plate with a thickness of 2.5 to 7.0 mm p0.2 550~850MPa, tensile strength R m 900~1250MPa, elongation after fracture It is 13% to 25%.

[0062] The hot-rolled pickled steel plate obtained by the present invention was subjected to a tensile test according to "GB / T228.1-2010 Tensile test of metallic materials Part 1: Room temperature test method", and its mechanical property parameters are shown in Table 5.

[0063] Table 5 Mechanical properties of hot-rolled pickled steel plates according to the present invention

[0064]

[0065] The hot-rolled pickled steel plate obtained by the present invention is annealed, cold-rolled to the thickness of a finished saw blade, quenched, tempered, and cut to obtain a finished saw blade; see Figure 2 The quenching temperature is 900℃. The metallographic structure of the cold-rolled steel sheet after quenching is acicular martensite. The hardness of the cold-rolled steel sheet after quenching is shown in Table 6; see Figure 3 The tempering temperature is 500℃, the tempering holding time is 30min, the metallographic structure of the cold-rolled steel plate after tempering is tempered troostite, and the hardness of the cold-rolled steel plate after tempering is shown in Table 7.

[0066] Table 6 Hardness parameters of cold-rolled steel sheets obtained by annealing, cold rolling and quenching of the steel sheets of the embodiment of the present invention

[0067] Performance Indicators Quenching temperature / ℃ Hardness of cold rolled steel plate after quenching / HRC The present invention 900 65-67 Example 1 900 66.5 Example 2 900 66.2 Example 3 900 66.4 Example 4 900 65.5 Example 5 900 66.8

[0068] Table 7 Hardness parameters of cold-rolled steel sheets obtained by annealing, cold rolling, quenching and tempering of the steel sheets of the embodiment of the present invention

[0069]

[0070] As shown in Table 7, after tempering at 500°C, the hardness of the cold-rolled steel plate is 45-47 HRC. Compared with the prior art, the hardness of the cold-rolled steel plate is increased by more than 2 HRC after tempering under the same conditions, which improves the red hardness of the saw blade and thus improves the service life of the saw blade.

[0071] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. A hot-rolled pickled steel plate for saw blades, wherein the chemical composition by weight is as follows: C: 0.75% to 0.85%, Si: 0.20% to 0.50%, Mn: 0.20% to 0.50%, P≤0.020%, S≤0.005%, Al: 0.01% to 0.02%, N≤0.0060%, Cr: 0.4% to 0.8%, V: 0.18% to 0.28%, the remainder being Fe and unavoidable impurity elements; the metallographic structure of the hot-rolled pickled steel plate is ultrafine pearlite with a sheet spacing of 0.4 to 0.8 μm, and the yield strength R of the hot-rolled pickled steel plate with a thickness of 2.5 to 7.0 mm p0.2 550~850MPa, tensile strength R m 900~1250MPa, elongation after fracture It is 13% to 25%.

2. The hot-rolled pickled steel plate for saw blades according to claim 1, characterized in that: The hot-rolled pickled steel plate is annealed, cold-rolled to the thickness of the finished saw blade, quenched, tempered, and cut to obtain a finished saw blade; the quenching temperature is 880-900°C, the metallographic structure of the cold-rolled steel plate after quenching is acicular martensite, and the hardness of the cold-rolled steel plate after quenching is 65-67HRC; the tempering temperature is 500°C, the tempering holding time is 20-40min, the metallographic structure of the cold-rolled steel plate after tempering is tempered troostite, and the hardness of the cold-rolled steel plate after tempering is 45-47HRC.

3. The method for manufacturing a hot-rolled pickled steel plate for saw blades according to claim 1, characterized in that: The following steps are involved: The molten steel is continuously cast to obtain a continuous casting slab, wherein the chemical composition of the molten steel is as follows: C: 0.75% to 0.85%, Si: 0.20% to 0.50%, Mn: 0.20% to 0.50%, P≤0.020%, S≤0.005%, Al: 0.01% to 0.02%, N≤0.0060%, Cr: 0.4% to 0.8%, V: 0.18% to 0.28%, and the remainder is Fe and unavoidable impurity elements; The continuous casting slab is heated in a heating furnace and then hot rolled. The continuous casting slab is fed into the heating furnace by hot charging and hot delivery. The temperature of the continuous casting slab into the heating furnace is ≥400°C. The excess air coefficient in the heating furnace is 0.95-1.

00. The heating temperature of the continuous casting slab is 1200-1260°C and the heating time is 180-240min. The hot rolling is a two-stage rolling process. The rough rolling is 6 continuous rolling passes, which are rolled above the austenite recrystallization temperature. The rough rolling end temperature is 1000-1050°C. The thickness of the intermediate slab after rough rolling is 38-42mm. The finishing rolling is 7 continuous rolling passes, and the finishing temperature of the finishing rolling is 840-900°C. After finishing rolling, the thickness of the steel plate is 2.5-7.0mm. The laminar cooling adopts front-stage cooling, and the cooling rate is 5-8°C / s. The laminar cooling end temperature is 610-680°C. The hot-rolled steel coil is obtained when the coiling temperature is 600-670°C. The hot rolled steel coil is slowly cooled after coiling, and the cooling rate of the hot rolled steel coil to 200°C is 5-9°C / h; after the hot rolled steel coil is uncoiled again, it is push-pull pickling, rinsing, drying, and oiling, and the finished hot rolled pickled steel plate is obtained by coiling.

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