Pickling-free cold-rolled steel for bimetal saw and manufacturing method of pickling-free cold-rolled steel

Abstract

The thickness of finished strip steel is smaller than or equal to 1 mm, and the finished strip steel comprises the following chemical components: 0.25% < = C < = 0.40%, 0.01% < = Si < = 0.3%, 0.5% < = Mn < = 1.5%, 3.0% < = Cr < = 5.0%, 0.5% < = Mo < = 1.6%, 0.5% < = Ni < = 1.0%, 0.01% < = Al < = 0.09%, 0.1% < = V < = 0.5%, 0.001% < = Re < = 0.02%, 0.004% < = N < = 0.010%, and Al / N < = 18, p < = 0.010%, S < = 0.010%; and the balance Fe and impurities. The produced metal saw back material does not need acid pickling, has no scale on the surface, and can be directly cold-rolled; the double-metal band saw blade back material prepared by the method is free of surface oxidation and decarburization layers, the surface roughness reaches 0.5-2.0 microns, the fatigue life of a real object reaches 36 hours or above, the double-metal band saw blade back material can replace imported steel for double-metal saw back materials, and localization of high-end double-metal band saw blade back materials is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of tool steel production, and particularly relates to a steel for the back material of a bimetal band saw for cutting metals with a 500 MPa level without pickling and its manufacturing method. Background Art

[0002] A band saw blade for cutting metals is generally composed of two metal materials, namely a back material and a tooth material, which are compounded through welding and heat treatment, so it is also called a bimetal band saw blade. With the development of China's basic manufacturing industry, the demand for bimetal band saw blade cutting tools is increasing. The market demand for bimetal band saw blades is growing at a high speed with an annual growth rate of 20%, and the future market development space will be even broader. The back material of the bimetal band saw blade is required to have high strength and high toughness, and the strength-toughness matching should be good; the tooth material is required to have high wear resistance and high red hardness. At present, the tooth material is generally processed from high-speed steel or cemented carbide materials, and the back material is generally processed from alloy steel materials with high strength, high toughness and high fatigue resistance. In order to improve the overall high wear resistance, high red hardness and high fatigue performance of the bimetal band saw blade, the materials of the tooth material and the back material are constantly updated. Among them, the back material has evolved from the initial spring steel to high-strength cutting tool steel and then to ultra-high-strength steel. The bimetal band saw blade can be used in combination with any type of band sawing machine and is suitable for almost all types of continuous metal sawing, such as structural steel, weathering steel, alloy steel, bearing steel, stainless steel, heat-resistant steel, aluminum alloy, die steel, etc.

[0003] The most common failure mode of the bimetal band saw blade is insufficient wear resistance at the tooth tip, and the fatigue performance of the back material is poor and it is easy to break the strip, which directly affects the sawing efficiency. The fatigue failure analysis results show that the fatigue fracture of the bimetal band saw blade is mainly related to the large thickness fluctuation of the back material strip steel, uneven strength and hardness. 65Mn steel is the most used spring steel for the back material of the saw blade, containing 0.62%-0.7% C, 0.9%-1.2% Mn. The cold-rolled and annealed yield strength is above 700 MPa. It has high strength and hardness but low toughness and plasticity. The pickling and cold rolling are difficult. The strip steel has large thickness fluctuation, large strength difference, uneven hardness, difficult forming, poor welding performance, and large tendency of cracking after welding. The heat treatment hardness is about 500 HV, the tensile strength is about 1500 MPa, the elongation is about 12%, and the impact energy is only below 10 J. It has high strength and hardness but low toughness and plasticity, resulting in poor fatigue performance and easy brittle fracture.

[0004] On the other hand, since the thickness of the back material of the bimetal saw blade for cutting metals is all below 1 mm, while the conventional thickness of the hot-rolled coil is above 2 mm, when using ordinary hot-rolled coil as the back material of the bimetal saw blade, it needs to go through multiple annealing and cold rolling processes before its thickness can reach below 1 mm. The surface of the raw material strip steel before cold rolling cannot have scale and needs pickling treatment, which causes environmental pollution. Moreover, the strength and hardness of the hot-rolled plate are uneven, and problems such as cold rolling cracking are likely to occur, seriously affecting the production efficiency.

[0005] In recent years, with the development of high-tech such as aerospace, a large number of high-hardness and high-temperature resistant metal materials have been developed. At the same time, higher requirements have been placed on the cutting performance of bimetallic band saw blades for cutting metal materials. Therefore, it is necessary to develop a bimetallic band saw back material steel with a thickness of less than 1 mm, no need for pickling, uniform strength and hardness, good processing formability, high strength and hardness after heat treatment, easy to weld, and high fatigue performance.

[0006] The Chinese invention patent with the authorization announcement number CN101358321B discloses a "HG20 backing steel for high-strength and toughness bimetallic band saw blades". Its chemical composition by weight (percentage) is: carbon 0.29-0.33, manganese 0.70-0.90, silicon 0.20-0.40, chromium 3.60-4.00, molybdenum: 1.20-1.40, vanadium 0.30-0.40, aluminum 0.04-0.08, phosphorus 0-0.02, sulfur 0-0.015, nitrogen 0-0.010, hydrogen: 0-0.0005, and the rest is iron and impurities. The process includes: EAF furnace smelting - LF refining - VD vacuum treatment - continuous casting steel billet - hot rolled steel strip - annealing - spheroidizing annealing - pickling - cold rolling - stripping into strip steel for backing. The product has the characteristics of high strength, high toughness, high fatigue resistance and low cost. However, the pickling and cold rolling processes are difficult to control, the hydrogen content is not suitable for converter smelting production, and the smelting includes three steps, with high smelting costs.

[0007] The Chinese invention patent with the authorization announcement number CN 104451421 B discloses "a high-strength and toughness bimetallic band saw blade backing steel and its preparation method", with chemical composition of C: 0.34-0.45%; Si: 0.20-0.40%; Mn: 0.70-0.90%; Cr: 3.30-3.60%; Ni: 0.50-0.70%; Mo: 0.90-1.20%; V: 0.30-0.40%; Nb: 0.08-0.20%; Al: 0.015-0.05%. In the production process, the annealing is heated to 780±5℃ at a rate of ≤100℃ / h, kept at this temperature for 1-4 hours, and then cooled to below 550℃ at a rate of ≤20℃ / h, then taken out of the furnace for air cooling, pickling and cold rolling, quenching and tempering and cold treatment in a heat treatment furnace or vacuum furnace under a protective atmosphere. After heat treatment, the yield strength is 1400MPa, the tensile strength is 1700MPa, and the elongation is more than 9%. To achieve the above properties, it is necessary to spheroidize annealing after hot rolling and then pickle and cold roll, which has a high production cost. In addition, the raw material strength of high carbon hot rolled plate is high, the pickling and cold rolling process is difficult to control, and the high Nb content is not suitable for converter smelting and continuous casting production.

[0008] The Chinese invention patent with the authorization announcement number CN109306432B discloses "A cold-rolled strip steel for the back material of a bimetal saw blade and its manufacturing method". The chemical composition is as follows: C 0.45% - 0.55%, Si 0.05% - 0.30%, Mn 0.6% - 1.0%, P ≤ 0.025%, S ≤ 0.010%, Cr 0.9% - 1.20%, V 0.08% - 0.15%, Ni 0.50% - 0.70%, Mo 0.90% - 1.20%, Al 0.05% - 0.10%, N 0.007% - 0.015%. The production process includes: soft annealing, pickling, full-hydrogen bell-type furnace spheroidizing annealing, cold rolling by a single-stand reversible cold rolling mill, abrasive cloth polishing by a polishing unit, full-hydrogen bell-type furnace annealing, and tempering to obtain the finished product; based on common steel production equipment, it solves problems such as surface decarburization and surface grain boundary oxidation, the sponge iron for annealing reduction is difficult to pickle, and poor flatness control, etc., and realizes high-quality and low-cost production. The average grain size of ferrite in the cold-rolled strip steel is 4 - 4.5 μm, the cementite size is below 0.3 μm, and the spheroidization rate is over 95%; the average hardness is 256 - 280 HV; there is no semi-decarburized layer and no grain boundary oxidation layer; the flatness in the width direction is not more than 0.5% of the width. Its process has many annealing times, resulting in high production costs; the product has poor low-temperature toughness and plasticity, requires pickling, is not environmentally friendly, and in addition, there is some unspheroidized pearlite in its structure, affecting toughness.

[0009] The Chinese invention patent with the authorization announcement number CN 109136746 B discloses "A steel strip for the back material of a bimetal band saw and its preparation method". The chemical composition in the steel is as follows: 0.29 ≤ C ≤ 0.33%; 0.20% ≤ Si ≤ 0.35%; 0.80% ≤ Mn ≤ 1.10%; 3.50 ≤ Cr ≤ 4.20%; 0.20% ≤ Ni ≤ 0.80%; 1.00% ≤ Mo ≤ 1.40%; 0.30% ≤ V ≤ 0.40%; 0% < P ≤ 0.02%; 0% < S ≤ 0.025%; the width is 327 mm - 410 mm. After pickling the surface scale with 7% - 17% hydrochloric acid aqueous solution, it undergoes two annealing and two cold rolling processes, with relatively high costs and pickling polluting the environment. The product has a tensile strength Rm of 850 - 900 MPa, an elongation rate A of 3.6 - 4.4%, a hardness of 210 - 262 HV, a surface oxidation decarburization of ≤ 0.02 μm, and a roughness of ≤ 0.5 μm. However, it requires multiple segmented annealing processes, with complex processes and great control difficulty, and there is still about 10% of non-spheroidized structure, resulting in low elongation rate, poor toughness and plasticity, and easy band breakage.

[0010] The steel for the back material of a bimetal band saw blade is a high-strength spring steel. When combined with a composite sawing tool prepared by special processing techniques such as high-speed tool steel or cemented carbide, it not only has excellent cutting performance but also good elasticity. During actual application, it has high cutting efficiency, high wear resistance, and good toughness, and is suitable for continuous sawing of most types of metals. The thickness of the back material of the bimetal band saw blade is generally less than 1 mm. All of the above technical solutions require an acid pickling and cold rolling process, which has high requirements for the surface quality of the steel plate used as the raw material. There should be no scale, and pickling treatment is required before cold rolling, which pollutes the environment. There are certain defects in the steel grades and production methods of the above technical solutions, and they cannot meet the requirements of high-end bimetal band saw blade back materials. Summary of the Invention

[0011] In view of the problems existing in the raw material steel for the back material of the bimetal band saw blade for cutting metals, such as poor ductility and plasticity, large thickness tolerance, uneven strength and hardness, and the need for pickling which is not environmentally friendly, the present invention provides a steel for bimetal saw without pickling cold rolling and its manufacturing method. The thickness of the produced metal saw back material does not exceed 1 mm, pickling is not required, there is no scale on the surface, and it can be directly cold rolled. After cold rolling, the carbide diameter in the steel is less than 0.2 μm, the spheroidization rate reaches 100%, the yield strength of the finished product is 500 - 600 MPa, the tensile strength is 700 - 800 MPa, the elongation rate is greater than 15%, the hardness is 85 - 95 HRB, there is no surface oxidation and decarburization layer, and the surface roughness reaches 0.5 - 2.0 μm. It can replace the imported steel for the back material of the bimetal saw and achieve the localization of high-end bimetal band saw blade back materials.

[0012] To achieve the above objectives, the present invention is realized by adopting the following technical solutions:

[0013] A steel for bimetal saw without pickling cold rolling, the thickness of the finished strip steel ≤ 1 mm, and the chemical composition by weight percentage is: 0.25% ≤ C ≤ 0.40%, 0.01% ≤ Si ≤ 0.3%, 0.5% ≤ Mn ≤ 1.5%, 3.0% ≤ Cr ≤ 5.0%, 0.5% ≤ Mo ≤ 1.6%, 0.5% ≤ Ni ≤ 1.0%, 0.01% ≤ Al ≤ 0.09%, 0.1% ≤ V ≤ 0.5%, 0.001% ≤ Re ≤ 0.02%, 0.004% ≤ N ≤ 0.010%, and 3 ≤ Al / N ≤ 18; P ≤ 0.010%, S ≤ 0.010%; the balance is Fe and unavoidable impurities.

[0014] The carbide diameter in the finished strip steel is less than 0.2 μm, and the spheroidization rate is 100%.

[0015] The yield strength of the finished strip steel is 500 - 600 MPa, the tensile strength is 700 - 800 MPa, the elongation rate is greater than 15%, the hardness is 85 - 95 HRB, there is no surface oxidation and decarburization layer, and the surface roughness is 0.5 - 2.0 μm; the thickness fluctuation value of the strip steel is within ±0.05 mm, the tensile strength difference of the same coil is ≤20 MPa, and the hardness difference of the same coil is ≤3 HRB.

[0016] A manufacturing method of steel for a pickling-free cold-rolled bimetal saw, comprising the following technological processes:

[0017] 1) Smelting and continuous casting:

[0018] Smelting includes converter smelting and LF electric furnace refining; before tapping from the converter, 0.2% ≤ C ≤ 0.3% in the molten steel; during the LF electric furnace refining process, control the sulfur content ≤ 0.010%, then add alloys to adjust the composition of the molten steel, and at the same time introduce nitrogen to adjust the N content in the molten steel to 0.004% - 0.010%;

[0019] Continuous casting adopts soft reduction and mold electromagnetic stirring, the electromagnetic stirring current intensity is 300 - 700 A, and the frequency is 2.2 - 2.9 Hz; the dynamic water volume of the mold is 80 - 160 L / min, use mold powder for casting, control the mold liquid level at 750 - 850 mm, and control the superheat at 20 - 30 °C; the continuous casting drawing speed is 0.8 - 1.4 m / min, the secondary cooling water volume is 0.15 - 0.35 L / kg, the surface temperature deviation of the casting blank is not more than 10 °C, and the equiaxed crystal ratio is above 50%;

[0020] 2) Slab treatment:

[0021] The slab is cooled slowly after being taken off the production line, kept warm at a temperature of 600 - 700 °C for more than 90 h, and hot delivered and hot charged into a walking beam reheating furnace for heating; the atmosphere in the walking beam reheating furnace is weakly oxidizing; the temperature of the preheating section is 500 - 600 °C, and the holding time is more than 60 min; the temperature of the first heating section is 900 - 1100 °C, and the holding time is more than 60 min; the temperature of the second heating section is 1200 - 1350 °C; the total time in the furnace is 3 - 4 h;

[0022] 3) Hot rolling:

[0023] High-pressure water descaling is adopted before rough rolling and finish rolling, and the high-pressure water pressure is not less than 30 MPa;

[0024] Rough rolling adopts 3 passes of reverse rolling, the reduction rate of each pass is 10% - 15%, the rough rolling temperature is 1000 - 1250 °C, and the rolling temperature difference of each pass for the whole length of the steel strip is ≤20 °C;

[0025] The finish rolling is carried out by 7-pass continuous rolling. The reduction rate for each of the first two passes is 25% - 40%. The finish rolling temperature is 1000 - 1100°C. Edge heating devices are installed on both sides of the steel plate, with a compensation heating temperature of 35 - 45°C, a heating width of not less than 50 mm, and the rolling temperature difference for each pass along the entire length of the steel strip ≤ 10°C;

[0026] 4) Cooling:

[0027] After the steel plate exits the finish rolling mill, it enters laminar flow cooling, with a cooling rate of 10 - 50°C / s; the cooling rate difference in the width direction at the same position ≤ 1°C / s; it is coiled when cooled to 500 - 700°C, and then slowly cooled to below 200°C at a cooling rate of 20 - 30°C / h to obtain a uniform and fine mixed structure of martensite and ferrite;

[0028] 5) Softening treatment:

[0029] The steel coil is softened by a fully hydrogen bell-type annealing furnace, heated to 700 - 800°C and held for 20 - 30 h. A segmented cooling rate control process is adopted. First, it is cooled at a cooling rate of 20 - 30°C / h to 600 - 650°C, then cooled at a cooling rate of 10 - 20°C / h to below 300°C, and finally air-cooled to room temperature;

[0030] 6) Surface treatment:

[0031] The steel coil after softening treatment is straightened and leveled by a straightening machine with a straightening force greater than 600 MPa, and then sandblasted;

[0032] 7) Cold rolling:

[0033] The steel coil without scale after surface treatment is rolled more than 3 passes by a multi-roll reversible cold rolling mill, with a rolling temperature not lower than 10°C and a reduction per pass of 0.2 - 0.8 mm;

[0034] 8) Annealing treatment:

[0035] The cold-rolled steel coil is annealed by a fully hydrogen bell-type annealing furnace. First, it is heated to 750 - 800°C and held for 15 - 20 h, then cooled at a cooling rate of 30 - 50°C / h to 550 - 600°C, then cooled at a cooling rate of 10 - 20°C / h to 300°C, and finally water-cooled by a cooling hood to below 100°C and then air-cooled;

[0036] 9) Strip heat treatment:

[0037] The strip continuous heat treatment process is adopted, with a water spray quenching heating temperature of 830 - 860°C, a tempering temperature of 350 - 450°C, and a threading speed of 10 - 15 m / h.

[0038] During the continuous casting process, a vertical-bending arc continuous caster is used for pouring. The arc radius of the vertical-bending arc continuous caster is not less than 5 m, and the thickness of the cast slab is 170 - 250 mm.

[0039] During the surface treatment process, a 9-roll straightener is used for straightening and leveling. During sandblasting, the distances from the upper nozzle and the lower nozzle to the upper and lower surfaces of the corresponding steel plate are 50 - 200 mm, the sandblasting pressure is 100 - 200 MPa, the threading speed is 5 - 20 m / min, the water temperature is 10 - 50 °C, and the sand particle size is 0.5 - 2.0 mm.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0041] 1) Alloying such as Cr-Mo-Ni-V-Re is adopted, and at the same time, process parameters such as the heating temperature of the cast slab, the descaling pressure of rough and finish rolling, the rolling temperature, the rolling reduction ratio, the coiling temperature, the softening treatment temperature and time, the cooling rate, the surface sandblasting pressure and speed are controlled. Pickling is not required before cold rolling, and a uniform fine spheroidized structure can be obtained. The carbide diameter is below 0.2 μm, and the spheroidization rate reaches 100%;

[0042] 2) The yield strength of the finished product is 500 - 600 MPa, the tensile strength is 700 - 800 MPa, the elongation is greater than 15%, the hardness is 85 - 95 HRB, and there is no surface oxidation and decarburization layer; the surface roughness is 0.5 - 2.0 μm; not only the comprehensive performance is good, but also the surface quality is high;

[0043] 3) The thickness fluctuation of the strip steel is within ±0.05 mm, the tensile strength difference of the same coil is ≤20 MPa, and the hardness difference of the same coil is ≤3 HRB.

[0044] 4) After heat treatment, the hardness is above 50 HRC, the hardness difference is ≤±0.5 HRC, the fatigue life reaches more than 36 h (simulating actual application, idling under tension), the wear-resistant life is extended by more than 1.5 times, the wear-resistant life is extended by more than 0.5 times, and the service life is significantly improved;

[0045] 5) The strip steel manufactured by the present invention can replace the steel used for the back material of imported bimetallic band saw blades, realizing the localization of the back material of high-end bimetallic band saw blades. Description of the Drawings

[0046] Figure 1 It is the microstructure morphology diagram after heat treatment of the pickling-free cold-rolled bimetallic saw steel described in the present invention. Detailed Embodiments

[0047] The steel for non-pickling cold-rolled bimetal saw described in the present invention has a finished strip thickness of ≤ 1 mm. The chemical composition by weight percentage is: 0.25% ≤ C ≤ 0.40%, 0.01% ≤ Si ≤ 0.3%, 0.5% ≤ Mn ≤ 1.5%, 3.0% ≤ Cr ≤ 5.0%, 0.5% ≤ Mo ≤ 1.6%, 0.5% ≤ Ni ≤ 1.0%, 0.01% ≤ Al ≤ 0.09%, 0.1% ≤ V ≤ 0.5%, 0.001% ≤ Re ≤ 0.02%, 0.004% ≤ N ≤ 0.010%, and 3 ≤ Al / N ≤ 18; P ≤ 0.010%, S ≤ 0.010%; the balance is Fe and unavoidable impurities.

[0048] The carbide diameter in the finished strip steel is below 0.2 μm, and the spheroidization rate is 100% (as Figure 1 shown).

[0049] The yield strength of the finished strip steel is 500 - 600 MPa, the tensile strength is 700 - 800 MPa, the elongation is greater than 15%, the hardness is 85 - 95 HRB, there is no surface oxidation and decarburization layer, and the surface roughness is 0.5 - 2.0 μm; the thickness fluctuation value of the strip steel is within ±0.05 mm, the tensile strength difference of the same coil is ≤ 20 MPa, and the hardness difference of the same coil is ≤ 3 HRB.

[0050] The manufacturing method of the steel for non-pickling cold-rolled bimetal saw described in the present invention includes the following technological processes:

[0051] 1) Smelting and continuous casting:

[0052] Smelting includes converter smelting and LF electric furnace refining; before tapping from the converter, 0.2% ≤ C ≤ 0.3% in the molten steel; during the LF electric furnace refining process, control the sulfur content ≤ 0.010%, then add alloys to adjust the molten steel composition, and at the same time introduce nitrogen to adjust the N content in the molten steel to 0.004% - 0.010%;

[0053] Continuous casting adopts soft reduction and mold electromagnetic stirring. The electromagnetic stirring current intensity is 300 - 700 A, and the frequency is 2.2 - 2.9 Hz; the dynamic water volume of the mold is 80 - 160 L / min, use mold powder for casting, control the mold liquid level at 750 - 850 mm, and control the superheat at 20 - 30 °C; the continuous casting casting speed is 0.8 - 1.4 m / min, the secondary cooling water volume is 0.15 - 0.35 L / kg, the surface temperature deviation of the casting billet is not more than 10 °C, and the equiaxed crystal ratio is above 50%;

[0054] 2) Billet treatment:

[0055] The continuous casting billet is taken offline for slow cooling, heat-preserved at a temperature of 600 - 700°C for more than 90 hours, and then hot-charged and hot-transported to a walking beam reheating furnace for heating. The atmosphere inside the walking beam reheating furnace is a weakly oxidizing atmosphere. The temperature of the preheating section is 500 - 600°C, and the heat-preserving time is more than 60 minutes. The temperature of the first heating section is 900 - 1100°C, and the heat-preserving time is more than 60 minutes. The temperature of the second heating section is 1200 - 1350°C. The total time in the furnace is 3 - 4 hours.

[0056] 3) Hot rolling:

[0057] High-pressure water descaling is adopted before both rough rolling and finish rolling, and the pressure of the high-pressure water is not less than 30 MPa.

[0058] Rough rolling adopts 3 passes of reverse rolling, with the reduction rate per pass being 10% - 15%. The rough rolling temperature is 1000 - 1250°C, and the temperature difference per pass of rolling along the full length of the steel strip is ≤20°C.

[0059] Finish rolling adopts 7 passes of continuous rolling. The reduction rate per pass of the first two passes is 25% - 40%. The finish rolling temperature is 1000 - 1100°C. Edge heating devices are arranged on both sides of the steel plate, with the compensation heating temperature being 35 - 45°C, the heating width being not less than 50 mm, and the temperature difference per pass of rolling along the full length of the steel strip being ≤10°C.

[0060] 4) Cooling:

[0061] After the steel plate exits the finish rolling mill, it enters laminar flow cooling, with the cooling rate being 10 - 50°C / s. The cooling rate difference in the width direction at the same position is ≤1°C / s. It is coiled when cooled to 500 - 700°C, and then slowly cooled to below 200°C at a cooling rate of 20 - 30°C / h to obtain a uniform and fine mixed structure of martensite and ferrite.

[0062] 5) Softening treatment:

[0063] The steel coil is softened by a fully hydrogen bell-type annealing furnace, heated to 700 - 800°C and heat-preserved for 20 - 30 hours. A segmented control cooling rate process is adopted. First, it is cooled to 600 - 650°C at a cooling rate of 20 - 30°C / h, then cooled to below 300°C at a cooling rate of 10 - 20°C / h, and finally air-cooled to room temperature.

[0064] 6) Surface treatment:

[0065] The steel coil after softening treatment is straightened and leveled by a straightening machine with a straightening force greater than 600 MPa, and then sandblasted.

[0066] 7) Cold rolling:

[0067] The steel coil without scale after surface treatment is rolled more than 3 passes by a multi-roll reversible cold rolling mill, with the rolling temperature not lower than 10°C and the reduction per pass being 0.2 - 0.8 mm.

[0068] 8) Annealing treatment:

[0069] The cold-rolled steel coil is annealed in a full-hydrogen bell-type annealing furnace. First, it is heated to 750 - 800 °C and held for 15 - 20 h, then cooled at a cooling rate of 30 - 50 °C / h to 550 - 600 °C, then cooled at a cooling rate of 10 - 20 °C / h to 300 °C, and finally water-cooled by a cooling hood to below 100 °C and then air-cooled.

[0070] 9) Strip heat treatment:

[0071] The strip continuous heat treatment process is adopted. The heating temperature for water spray quenching is 830 - 860 °C, the tempering temperature is 350 - 450 °C, and the threading speed is 10 - 15 m / h.

[0072] During the continuous casting process described above, a vertical-bending arc continuous caster is used for pouring. The arc radius of the vertical-bending arc continuous caster is not less than 5 m, and the thickness of the casting blank is 170 - 250 mm.

[0073] During the surface treatment process described above, a 9-roll straightening machine is used for straightening and leveling. During sandblasting, the distances from the upper nozzle and the lower nozzle to the upper and lower surfaces of the corresponding steel plate are 50 - 200 mm, the sandblasting pressure is 100 - 200 MPa, the threading speed is 5 - 20 m / min, the water temperature is 10 - 50 °C, and the sand grain size is 0.5 - 2.0 mm.

[0074] The action mechanisms of the alloying elements (by weight percentage) in the pickling-free cold-rolled bimetal saw steel described in the present invention are as follows:

[0075] C: 0.25% - 0.40%;

[0076] C is the main solid solution strengthening element in the steel. And in the present invention, sufficient C is required to react with Re to form rare earth carbides to inhibit surface oxidation and decarburization and improve the fatigue performance of the bimetal band saw back material. At the same time, it is ensured that the generated surface scale is sparse and is easily removed completely during EPS sandblasting, ensuring that the surface roughness is within the range of 3.0 - 5.0 μm. If the C content is lower than 0.25%, it is difficult to ensure the hardness of the steel plate after heat treatment; if the C content is higher than 0.40%, the strength is too high, which will deteriorate the toughness and plasticity of the steel after heat treatment, resulting in easy breakage of the bimetal band saw. Therefore, the C content in the present invention is controlled at 0.25% - 0.40%.

[0077] Mn: 0.50% - 1.5%;

[0078] Mn is relatively inexpensive and is a good deoxidizer and desulfurizer, and is an essential element for ensuring the strength and toughness of steel. Manganese and iron can form a solid solution infinitely to form a solid solution, thereby increasing hardness and strength, and having a relatively small impact on plasticity. Mn combines with S to form MnS, which can avoid the thermal cracking caused by the formation of FeS at the grain boundaries and affect the hot formability of steel. At the same time, Mn is also a good deoxidizer and can increase hardenability. When the Mn content in steel is low, it cannot meet the requirements of high strength and hardness. When the Mn content is too high, it will lead to serious segregation, affect the welding performance and formability, and increase production costs. Considering factors such as cost and performance requirements, the Mn content in the present invention is controlled at 0.50% - 1.5%.

[0079] Si: 0.01% - 0.3%;

[0080] Si is one of the common elements in steel and is used as a reducing agent and deoxidizer during steelmaking. Si is a ferrite-forming element and a non-carbide-forming element. When Si is dissolved in ferrite, it can improve the hardenability and tempering resistance of steel, increase strength and hardness, improve wear resistance, significantly increase the elastic limit, yield strength and yield ratio, and at the same time increase the fatigue strength and extend the service life of steel. When the Si content exceeds 0.3%, the steel surface is prone to decarburization oxidation, seriously affecting the fatigue performance. A Si content of 0.01% - 0.3% can ensure that a loose scale is formed on the steel surface, which is easy to remove during EPS sandblasting treatment, and then a steel coil with a surface roughness of 3.0 - 5.0 μm can be obtained.

[0081] Mo: 0.5% - 1.6%;

[0082] Mo can refine the grains of steel, improve hardenability and hot strength properties, and maintain sufficient strength and creep resistance at high temperatures. In saw blade steel, it can improve red hardness, inhibit temper brittleness, and also increase the A3 and A1 temperatures, move the GS line to the upper left, and at the same time molybdenum is a medium-strength carbide-forming element.

[0083] Cr: 3.0% - 5.0%;

[0084] Chromium is a medium-strength carbide-forming element. After adding Cr in the present invention, it forms a composite carbide with Re, which can inhibit microsegregation and reduce banded structure. Chromium can also increase the A3 and A1 temperatures, move the GS line to the upper left, slow down the decomposition of A, improve hardenability, improve the oxidation resistance and corrosion resistance of steel, improve tempering stability, and at the same time increase hardness and wear resistance.

[0085] V: 0.1% - 0.5%;

[0086] Solution annealing at high temperature can improve the hardenability of steel. The formed VC is a carbide with high melting point, high hardness and high dispersion degree, which is an element that strongly improves wear resistance. V and Re form complex carbides, which can reduce decarburization sensitivity, inhibit intergranular oxidation, improve the surface quality of steel, and ensure that the surface roughness reaches 3.0 - 5.0 μm.

[0087] Ni: 0.5% - 1.0%;

[0088] Nickel has a solution strengthening effect, can improve hardenability and the strength of steel, while maintaining good plasticity and toughness. Nickel has a high corrosion resistance to acids and alkalis and has rust and heat resistance at high temperatures. In this invention, the main function of Ni is to inhibit the formation of pearlite to obtain martensite structure, while inhibiting microsegregation, ensuring uniform structure and reducing banded structure.

[0089] N: 0.004% - 0.010%;

[0090] Generally, N is considered a harmful element, and the lower the N content in steel, the better. This invention adopts a composition design containing N. During refining, nitrogen is introduced to make the N content in steel above 0.004%, and 3 ≤ Al / N ≤ 18 is controlled. The purpose is to form fine and dispersed carbides of N with Al and V with a size ≤ 30 μm, refine the martensite lath structure, inhibit microsegregation, obtain a fine and uniform structure, and reduce banded structure.

[0091] P ≤ 0.010%, S ≤ 0.010%;

[0092] Both P and S are inevitable harmful impurities in steel. Their presence will seriously deteriorate the toughness of steel. Therefore, measures should be taken to reduce the contents of P and S in steel as much as possible. In this invention, the P content is limited to P ≤ 0.010%. The combined action of P and Ni can improve the corrosion resistance during the operation of the bimetal band saw with coolant, and at the same time reduce segregation. The maximum S content in this invention is controlled at 0.010% to reduce the formation of MnS.

[0093] Al: 0.01% - 0.09%;

[0094] Al is used as a deoxidizer and nitrogen fixer during steelmaking, which can refine grains, inhibit the aging of steel, improve the toughness of steel at low temperatures, especially can reduce the brittle transition temperature of steel; Al is a non-carbide forming element, can improve the oxidation resistance of steel, inhibit surface oxidation and decarburization, and improve surface quality. When adding Al in this invention, 0.004 - 0.010% of N should also be added, and 3 ≤ Al / N ≤ 18 is controlled to form AlN with a size ≤ 30 μm and fine and dispersed distribution, refine the hot-rolled martensite structure, inhibit microsegregation, make the structure uniform, and reduce banded structure.

[0095] Re: 0.001% - 0.02%;

[0096] As a microalloying element, Re forms complex carbides with Cr and V, which can inhibit microsegregation and reduce banded structure. At the same time, it refines grains, improves the fluidity of molten steel, improves the surface finish of the steel, eliminates the anisotropy of the structure, ensures that the surface roughness reaches 3.0 - 5.0 μm, and extends the service life of the bimetal band saw.

[0097] For the manufacturing method of the steel for pickling-free cold-rolled bimetal saws of the present invention, the action mechanisms of each process are as follows:

[0098] The present invention adopts the process of "converter smelting + LF electric furnace refining" without RH vacuum treatment; before tapping from the converter, the carbon content in the molten steel is controlled at 0.2% ≤ C ≤ 0.3% to ensure uniform carbon content in the continuous casting billet and no macrosegregation; LF electric furnace refining is adopted, after controlling the sulfur content ≤ 0.010%, other alloys such as RE are added, and at the same time nitrogen is introduced to adjust the N content in the molten steel, change the composition, quantity and morphology of non-metallic inclusions, accelerate the flow of molten steel, promote the full floating of inclusions, improve the steel purity (the various non-metallic inclusions in the finished strip steel do not exceed grade 1.5), and improve the surface finish of the strip steel and eliminate the anisotropy of the structure.

[0099] In the continuous casting process of the present invention, the method of "soft reduction + mold electromagnetic stirring" is adopted. The electromagnetic stirring current intensity is 300 - 700 A and the frequency is 2.2 - 2.9 Hz. The dynamic water volume of the mold is 80 - 160 L / min, and the special mold powder for casting is used. The mold liquid level is controlled at 750 - 850 mm, the superheat degree of the first furnace of each casting heat is 30 - 40 °C, and the superheat degree of other furnace heats is 20 °C - 30 °C to control inclusions and segregation. The continuous casting drawing speed is controlled at 0.8 - 1.4 m / min, and the secondary cooling water volume is 0.15 - 0.35 L / kg to ensure that the surface temperature deviation of the continuous casting billet is not greater than 10 °C, the cooling rate of the continuous casting billet is uniform, the structure is uniform, the strength difference of the strip steel in the same coil after rolling is ≤ 50 MPa, the hardness difference of the same coil is ≤ 5 HRB, the equiaxed crystal ratio reaches more than 50%, and the microsegregation of the alloy liquid at the end of the columnar crystal is controlled.

[0100] The continuous casting billet is slowly cooled offline and kept warm at 600 - 700 °C for more than 90 hours to reduce the surface temperature difference of the continuous casting billet and relieve microsegregation. The walking beam reheating furnace adopts a weakly oxidizing atmosphere, the preheating section temperature is 500 - 600 °C, the holding time is more than 60 minutes, the first heating section temperature is 900 - 1100 °C, the holding time is more than 60 minutes, the second heating section temperature is 1200 - 1350 °C, and the total time in the furnace is 3 - 4 hours to ensure the surface quality of the continuous casting billet and avoid oxidation decarburization.

[0101] High-pressure water descaling is adopted before rough rolling and finish rolling. The pressure of the high-pressure water is not less than 30 MPa to ensure the surface quality of the steel plate. Three passes of reverse rolling are used in rough rolling, and the reduction rate per pass is 10% - 15%. The rough rolling temperature is 1000 - 1250 °C, ensuring that the temperature difference per pass of rolling along the entire length of the steel strip is ≤ 20 °C, and the microstructure and properties are uniform. The reduction rate per pass for the first two passes of finish rolling is 25% - 40%, and the finish rolling temperature is 1000 - 1100 °C. The final rolling temperature is relatively high, aiming to control the length of martensite lath bundles at 20 - 30 μm, and the banded structure not exceeding grade 3, which is helpful for the spheroidization of carbides during subsequent softening treatment. Edge heating devices are used on both sides of the steel plate, with a compensation heating temperature of 35 - 45 °C, a width of not less than 50 mm, the temperature difference per pass of rolling along the entire length of the steel strip is ≤ 10 °C, and the microstructure and properties are uniform; the thickness fluctuation of the steel strip is ≤ 0.04 mm, the convexity is ≤ 40 μm, the difference in tensile strength within the same coil is ≤ 40 MPa, and the difference in hardness within the same coil is ≤ 4 HRC.

[0102] After the steel plate exits the finish rolling mill, it enters laminar flow cooling. The cooling rate is 10 - 50 °C / s for uniform cooling, and the cooling rate difference in the width direction at the same position is ≤ 1 °C / s, ensuring uniform microstructure and properties of the same plate. It is coiled after cooling to 500 - 700 °C and slowly cooled to below 200 °C at a cooling rate of 3 - 10 °C / h, obtaining a uniform and fine mixed structure of martensite and ferrite, with the length of lath bundles at 20 - 30 μm and the banded structure not exceeding grade 3, which is helpful for the spheroidization of carbides during subsequent softening treatment.

[0103] The steel coil is softened by full-hydrogen batch annealing furnace, ensuring a reducing atmosphere inside the batch annealing furnace to avoid severe oxidation and decarburization of the steel plate at high temperatures. It is heated to 700 - 800 °C and held for 20 - 30 hours to fully diffuse alloying elements such as carbon, chromium, and nickel in the lath martensite structure, and at the same time promote the formation of a loose scale layer on the surface oxide layer, which is beneficial for removal by shot blasting. It is cooled to 600 - 650 °C at a cooling rate of 20 - 30 °C / h to form a ferrite matrix and fine carbide precipitation particles, and then cooled to below 300 °C at a cooling rate of 10 - 20 °C / h. At this time, the fine carbides spheroidize and grow, and are evenly distributed in a dispersed state. A relatively fast cooling rate of 20 - 30 °C / h is adopted above 600 °C, which is helpful for carbide nucleation, ensuring that the carbides are uniform and fine, with a final size below 0.2 μm and a spheroidization rate reaching 100%. A cooling rate exceeding 30 °C / h is likely to form plate-like carbides, and a cooling rate below 20 °C / h is likely to cause the growth of carbides. A relatively slow cooling rate of 10 - 20 °C / h is adopted below 550 °C, aiming to inhibit the formation of plate-like carbides and other structures such as bainite and martensite. A cooling rate below 10 °C / h results in poor surface quality, incomplete removal of scale during shot blasting, too high surface roughness value, and poor cold rolling performance.

[0104] The coiled steel after softening treatment is leveled by a 9-roll straightening machine with a straightening force greater than 600 MPa to ensure a flat sheet shape. The distance between the upper and lower nozzles and the steel plate surface is 50 - 200 mm, the sandblasting pressure is 100 - 200 MPa, the threading speed is 5 - 20 m / min, the water temperature is 10 - 50 °C, and the sand grain size is 0.5 - 2.0 mm. Ensure that the scale is completely removed during sandblasting treatment, the surface quality reaches the FB higher level, the surface roughness is 0.5 - 2.0 μm, and there is no intergranular oxidation on the surface.

[0105] The coiled steel after surface treatment is rolled by a multi-roll reversible cold rolling mill. The rolling temperature is not lower than 10 °C, and the reduction per pass is 0.2 - 0.8 mm. When the rolling temperature is too low, the strip is prone to breakage and cracking. If the reduction per pass is too large, the rolling load will be large, the thickness will be unstable, the tolerance will be large, and the convexity will be large. Rolling with a large reduction per pass (0.2 - 0.8 mm) in multiple passes helps to improve the spheroidization rate, reduce the strength, improve the rolling stability, ensure that the thickness fluctuation is within ±0.05 mm, the tensile strength difference of the same coil is ≤20 MPa, and the hardness difference of the same coil is ≤3 HRB.

[0106] The coiled steel is annealed in a full-hydrogen bell-type annealing furnace, heated to 750 °C - 800 °C and held for 15 - 20 hours. The temperature of the whole coil is uniform, which is beneficial to the uniform distribution of carbides. It is cooled at a cooling rate of 30 - 50 °C / h to 550 - 600 °C, aiming to control the growth of carbides; then it is cooled at a cooling rate of 10 - 20 °C / h to 300 °C and water-cooled by the cooling hood to inhibit the formation of martensite and bainite. After water-cooling by the cooling hood to below 100 °C, it is air-cooled to ensure no oxidation and decarburization on the surface.

[0107] The strip continuous heat treatment process is adopted. The heating temperature of water spray quenching is 830 - 860 °C, the tempering temperature is 350 - 450 °C, and the threading speed is 10 - 15 m / h. Ensure that the hardness of the finished product is above 50 HRC, the hardness difference of the same strip does not exceed 1 HRC, and the fatigue life is above 36 h.

[0108] To more intuitively illustrate the present invention, the implementation mode of the present invention will be further described in combination with the embodiments. The following embodiments are only the preferred specific implementation modes of the present invention, but the protection scope of the present invention is not limited thereto. Any technical solutions that can be obviously obtained by those skilled in the art within the technical scope disclosed by the present invention, including simple changes or equivalent replacements, are within the protection scope of the present invention.

[0109]

Embodiment

[0110] The chemical components in the steel of each embodiment are shown in Table 1, the smelting continuous casting process parameters are shown in Table 2, the billet treatment process parameters are shown in Table 3, the hot rolling - cooling process parameters are shown in Table 4, the softening treatment - surface treatment process parameters are shown in Table 5, the cold rolling - annealing treatment process parameters are shown in Table 6, and the steel plate structure and properties are shown in Table 7.

[0111] Table 1 Chemical composition in steel, wt%

[0112] Example C Si Mn P S Ni Cr V Mo Al Re N Al / N 1 0.26 0.06 0.8 0.006 0.009 0.8 4.23 0.26 0.83 0.032 0.018 0.0064 5.00 2 0.37 0.2 1.02 0.002 0.005 0.56 3.32 0.42 1.24 0.04 0.006 0.004 10.00 3 0.39 0.23 0.88 0.005 0.003 0.78 5 0.39 0.93 0.09 0.017 0.0056 16.07 4 0.32 0.01 1.2 0.006 0.004 0.89 4.73 0.15 0.56 0.056 0.002 0.0078 7.18 5 0.28 0.19 0.63 0.003 0.005 0.66 3 0.22 0.89 0.083 0.009 0.01 8.30 6 0.32 0.21 1.35 0.008 0.01 0.93 3.59 0.47 1.32 0.069 0.018 0.008 8.63 7 0.34 0.3 1.28 0.004 0.005 0.83 4.99 0.34 1.6 0.088 0.011 0.0052 16.92 8 0.31 0.18 0.98 0.006 0.002 1 3.78 0.45 0.61 0.018 0.012 0.006 3.00 9 0.25 0.25 1.16 0.005 0.008 0.68 4.36 0.35 0.9 0.026 0.005 0.0072 3.61 10 0.33 0.14 1.5 0.009 0.004 0.89 4.82 0.14 1.36 0.038 0.01 0.0084 4.52 11 0.27 0.1 0.79 0.002 0.006 0.63 4.59 0.29 0.5 0.072 0.02 0.0098 7.35 12 0.26 0.29 0.82 0.004 0.008 0.73 4.88 0.32 0.83 0.068 0.016 0.0062 10.97 13 0.32 0.03 1.32 0.006 0.002 0.94 3.65 0.39 0.74 0.015 0.001 0.0048 3.13 14 0.3 0.27 0.72 0.01 0.007 0.5 4.32 0.46 1.28 0.062 0.004 0.0082 7.56 15 0.4 0.24 1.48 0.002 0.001 0.86 3.56 0.48 1.05 0.028 0.006 0.0091 3.08 Comparative Example 0.65 0.25 0.6 0.004 0.008 0 0 0 - 0 0 0 -

[0113] Table 2 Process parameters of smelting and continuous casting

[0114]

[0115]

[0116] Table 3 Process parameters of billet treatment

[0117]

[0118] Table 4 Hot rolling - cooling process parameters

[0119]

[0120]

[0121] Table 5 Softening treatment - surface treatment process parameters

[0122]

[0123] Table 6 Cold rolling - annealing process parameters

[0124]

[0125]

[0126] Table 7 Microstructure and properties of steel plate

[0127]

[0128] As described above, it is only the preferred specific embodiment 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, making equivalent substitutions or changes, shall be covered by the protection scope of the present invention.

Claims

1. A pickling-free cold-rolled bimetallic saw steel, characterized in that: The thickness of the finished strip steel is ≤1mm, and the chemical composition is calculated by weight percentage: 0.25%≤C≤0.40%, 0.01%≤Si≤0.3%, 0.5%≤Mn≤1.5%, 3.0%≤Cr≤5.0%, 0.5%≤Mo≤1.6%, 0.5%≤Ni≤1.0%, 0.01%≤Al≤0.09%, 0.1%≤V≤0.5%, 0.001%≤Re≤0.02%, 0.004%≤N≤0.010%, and 3≤Al / N≤18; P≤0.010%, S≤0.010%; the balance is Fe and unavoidable impurities.

2. The pickling-free cold-rolled bimetallic saw steel according to claim 1, characterized in that: The carbide diameter in the finished strip is below 0.3μm and the spheroidization rate is 100%.

3. The pickling-free cold-rolled bimetallic saw steel according to claim 1, characterized in that: The yield strength of the finished strip steel is 500-600MPa, the tensile strength is 700-800MPa, the elongation is greater than 15%, the hardness is 85-95HRB, there is no surface oxidation and decarburization layer, and the surface roughness is 0.5-2.0μm; the strip steel thickness fluctuation value is within ±0.05mm, the tensile strength difference of the same roll is ≤20MPa, and the hardness difference of the same roll is ≤3HRB.

4. A method for manufacturing pickling-free cold-rolled bimetallic saw steel according to any one of claims 1 to 3, characterized in that: The process includes the following: 1) Smelting and continuous casting: The smelting includes converter smelting and LF electric furnace refining; 0.2%≤C≤0.3% in the molten steel before the converter is tapped; during the LF electric furnace refining process, the sulfur content is controlled to be ≤0.010%, and then alloys are added to adjust the composition of the molten steel, and nitrogen is introduced to adjust the N content in the molten steel to 0.004%~0.010%; Continuous casting adopts light pressure reduction and crystallizer electromagnetic stirring, the electromagnetic stirring current intensity is 300-700A, the frequency is 2.2-2.9Hz; the dynamic water volume of the crystallizer is 80-160L / min, the crystallizer protective slag is used for casting, the crystallizer liquid level is controlled at 750-850mm, and the superheat is controlled at 20-30℃; the continuous casting speed is 0.8-1.4m / min, the secondary cooling water volume is 0.15-0.35L / kg, the surface temperature deviation of the ingot is not more than 10℃, and the equiaxed crystal rate is above 50%; 2) Ingot processing: The ingot is slowly cooled down after it leaves the production line, and kept at 600-700℃ for more than 90h, and then hot-transferred and heated into a walking beam heating furnace; the walking beam heating furnace is in a weak oxidizing atmosphere; the temperature of the preheating section is 500-600℃, and the holding time is more than 60min; the temperature of the first heating section is 900-1100℃, and the holding time is more than 60min; the temperature of the second heating section is 1200-1350℃; the total time in the furnace is 3-4h; 3) Hot rolling: High-pressure water is used for descaling before rough rolling and finish rolling, and the pressure of high-pressure water is not less than 30MPa; The reduction rate of each rough rolling pass is 10% to 15%, the rough rolling temperature is 1000 to 1250°C, and the temperature difference of each rolling pass over the entire length of the steel strip is ≤20°C; Finish rolling adopts 7-pass continuous rolling, the reduction rate of each of the first two passes is 25% to 40%, the finishing temperature is 1000 to 1100°C, edge heating devices are set on both sides of the steel plate, the compensation heating temperature is 35 to 45°C, the heating width is not less than 50mm, and the temperature difference of each rolling pass of the full length of the steel strip is ≤10°C; 4) Cooling: After the steel plate leaves the finishing mill, it enters laminar cooling with a cooling rate of 10-50℃ / s; the cooling rate difference in the same position in the bandwidth direction is ≤1℃ / s; it is coiled when cooled to 500-700℃, and then slowly cooled to below 200℃ at a cooling rate of 20-30℃ / h to obtain a uniform and fine mixed structure of martensite and ferrite; 5) Softening treatment: The steel coil is softened in a full hydrogen bell annealing furnace, heated to 700-800℃ and kept warm for 20-30h, and then cooled to 600-650℃ at a cooling rate of 20-30℃ / h, and then cooled to below 300℃ at a cooling rate of 10-20℃ / h, and finally air-cooled to room temperature. 6) Surface treatment: After softening, the steel coil is straightened and leveled by a straightening machine with a straightening force greater than 600MPa, and then sandblasted; 7) Cold rolling: The steel coil without iron oxide scale after surface treatment is rolled for more than 3 times by a multi-roller reversible cold rolling mill, with a rolling temperature of not less than 10°C and a reduction of 0.2 to 0.8 mm per pass; 8) Annealing treatment: The cold-rolled steel coil is annealed in a full hydrogen hood annealing furnace, first heated to 750-800℃ and kept for 15-20h, then cooled to 550-600℃ at a cooling rate of 30-50℃ / h, then cooled to 300℃ at a cooling rate of 10-20℃ / h, and finally cooled to below 100℃ by water using a cooling hood and then air-cooled; 9) Strip heat treatment: A continuous heat treatment process for strip steel is adopted, with a water mist quenching heating temperature of 830-860°C, a tempering temperature of 350-450°C, and a strip threading speed of 10-15m / h.

5. The method for manufacturing pickling-free cold-rolled bimetallic saw steel according to claim 4, characterized in that: In the continuous casting process, a vertical bending arc continuous casting machine is used for casting, the arc radius of the vertical bending arc continuous casting machine is not less than 5m, and the thickness of the casting billet is 170-250mm.

6. The method for manufacturing pickling-free cold-rolled bimetallic saw steel according to claim 4, characterized in that: During the surface treatment process, a 9-roll straightening machine is used for straightening and leveling; during sandblasting, the distance between the upper nozzle and the lower nozzle and the upper and lower surfaces of the corresponding steel plate is 50-200 mm, the sandblasting pressure is 100-200 MPa, the belt threading speed is 5-20 m / min, the water temperature is 10-50° C., and the sand particle size is 0.5-2.0 mm.

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