A steel for scrap steel shearing machine blades and its preparation method

Abstract

This invention provides a steel for scrap steel shearing machine blades and its preparation method, belonging to the field of ultra-high strength steel technology. It comprises the following elements by mass percentage: C: 0.3–0.45%, Cr: 4.0–6.0%, Mo: 1.0–2.0%, V: 0.4–0.6%, W: 1.0–3.0%, Si: 0.1–0.3%, Mn: 0.1–0.6%, P: ≤0.02%, S ≤0.02%, with the balance being Fe and unavoidable impurities. The low Si and V content in this invention improves the impact toughness of the steel, significantly enhancing the performance of scrap steel shearing machine blades under heavy loads, reducing spalling and fracture, and lowering the probability of abnormal failure; the addition of W promotes the precipitation of Mn phases in the steel. 23 C6 transforms into finer, more dispersed M6C, while M6C exhibits a spherical, uniform distribution within the steel, significantly improving the steel's wear resistance and high-temperature performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ultra-high strength steel, and particularly relates to a steel for blades of a scrap steel shearing machine and a preparation method thereof. BACKGROUND

[0002] With the increase of steel reserves, the amount of scrap steel resources has been increasing, and steel production will inevitably move towards low emission and environmentally friendly production, and the scrap steel processing industry will play an increasingly important role in this process. Scrap steel processing not only effectively reduces environmental pollution and shares resources, but also provides a solid foundation and sustainability for the development of the steel industry. Therefore, the development prospect of scrap steel processing equipment is very broad.

[0003] The scrap steel shearing machines commonly used in the industry currently include alligator shears, gantry shears and hawk beak shears, and the gantry shears are currently mainly used as scrap steel shearing equipment in large quantities. The gantry shears are driven by hydraulic pressure, and the shearing force is 500-2000t, and as the scrap steel processing capacity continues to increase, the gantry shears gradually develop towards higher load and larger scale, and therefore higher requirements are put forward for the performance of the steel for blades of the scrap steel shearing machine.

[0004] The working environment of the blades of the scrap steel shearing machine is very harsh, the shearing blades not only have to withstand a large friction force in work, but also have to withstand a large impact force in the moment of contacting the sheared components, and have to withstand the thermal effect generated by friction and impact in the shearing process, and are very easy to fail. Currently, the steel for blades of the gantry shears mainly selects three kinds of H13, 1.2767 and 55SiCrA, and there is no special steel grade, and the service life is still far from the expectation, and therefore it is necessary to develop a special steel grade for blades of the scrap steel shearing machine with high impact toughness, high wear resistance and excellent high-temperature performance. SUMMARY

[0005] In view of this, the present application aims to provide a steel for blades of a scrap steel shearing machine and a preparation method thereof. The steel for blades of the scrap steel shearing machine provided by the present application has high impact toughness, high wear resistance and excellent high-temperature performance.

[0006] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0007] The present application provides a steel for blades of a scrap steel shearing machine, which comprises the following elements in mass percentage: C: 0.3-0.45%, Cr: 4.0-6.0%, Mo: 1.0-2.0%, V: 0.4-0.6%, W: 1.0-3.0%, Si: 0.1-0.3%, Mn: 0.1-0.6%, P: ≤0.02%, S≤0.02%, and the balance is Fe and inevitable impurities.

[0008] Preferably, the annealed microstructure of the steel used for scrap steel shearing machine blades consists of a ferrite matrix with spherical secondary carbides uniformly distributed on it, the average particle size of which is 0.2–0.8 μm. The tempered microstructure of the steel used for scrap steel shearing machine blades after tempering at 585–600℃ includes lath-shaped tempered martensite and retained austenite, the precipitates appearing as fine spherical or rod-shaped particles, the average size of which is 0.1–0.3 μm, the grain size grade being 7–8, and the average grain size being 18–25 μm.

[0009] Preferably, the steel used for the scrap steel shearing machine blades has a fully austenitic temperature range of 1040℃ to 1400℃.

[0010] Preferably, the steel used for the scrap steel shearing machine blades has a hardness ≥47HRC after tempering at 585-600℃, an impact energy of ≥29J with a V-notch, a tensile strength ≥1600MPa, and a reduction of area ≥50%.

[0011] This invention also provides a method for preparing the steel for scrap steel shearing machine blades as described in the above technical solution, comprising the following steps:

[0012] Iron, chromium, tungsten and molybdenum are mixed and then subjected to a first smelting process to obtain a first molten material;

[0013] The first molten material is mixed with graphite and then refined and deoxidized to obtain a refined material;

[0014] The refined material is mixed with silicon, manganese and vanadium in sequence and then smelted a second time, and then cast into ingots to obtain ingots;

[0015] The ingot is coated with a decarburized refractory coating and then subjected to homogenization treatment, forging, normalizing treatment, isothermal spheroidizing annealing treatment, solution treatment and tempering heat treatment in sequence to obtain the steel for scrap steel shearing machine blades.

[0016] Preferably, the homogenization treatment temperature is 1200-1250℃, the holding time is 8-10h, and the heating rate to the homogenization treatment temperature is 3-5℃ / min.

[0017] Preferably, the normalizing temperature is 950±10℃, the holding time is 1~3h, and the heating rate to the normalizing temperature is 3~5℃ / min.

[0018] Preferably, the isothermal spheroidizing annealing includes the following process: heating to 860±10℃ at a heating rate of 3-5℃ / min and holding for 2 hours, then cooling to 740±10℃ and holding for 4 hours, then cooling to 500±20℃ and air cooling to room temperature.

[0019] Preferably, the solution treatment temperature is 1010–1030°C, and the holding time is 30–45 min.

[0020] Preferably, the tempering heat treatment includes the following process: holding at 585-600°C for 2 hours and then cooling to room temperature, followed by holding at 585-600°C for another 2 hours, and then cooling to room temperature.

[0021] This invention provides a steel for scrap steel shearing machine blades, comprising the following elements by mass percentage: C: 0.3-0.45%, Cr: 4.0-6.0%, Mo: 1.0-2.0%, V: 0.4-0.6%, W: 1.0-3.0%, Si: 0.1-0.3%, Mn: 0.1-0.6%, P: ≤0.02%, S≤0.02%, with the balance being Fe and unavoidable impurities.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] The scrap steel shear blades of this invention have low Si and V content. Compared to conventional steel with a Si content of 1% and a V content of 0.9% by mass, the reduced Si and V content improves the impact toughness of the steel, resulting in significantly improved performance of the scrap steel shear blades under heavy loads, reduced spalling and fracture, and lower probability of abnormal failure. The invention also incorporates W, which promotes the transformation of precipitated phases in the steel from M... 23 The C6 steel transforms into the finer and more dispersed M6C, while the M6C is uniformly distributed in a spherical pattern within the steel. This greatly improves the steel's wear resistance and high-temperature performance, thus extending the service life of scrap steel shearing machine blades.

[0024] The present invention also provides a method for preparing steel for scrap steel shearing machine blades as described in the above technical solution. By adding a normalizing treatment process after forging, the grain size of the forging is refined, segregation is reduced, secondary carbides are eliminated from precipitating in a network, the cracking tendency of the forging is reduced, and the comprehensive mechanical properties of the steel (including impact toughness and tensile properties) are improved, providing a uniform microstructure for subsequent isothermal spheroidizing annealing.

[0025] The scrap steel for shearing blades of this invention achieves fine grain strengthening, precipitation strengthening, and solid solution strengthening through reasonable composition design and preparation process. The final product is a scrap steel for shearing blades with a tempered hardness higher than 47 HRC, an impact energy higher than 29 J with an open V-notch, a tensile strength higher than 1600 MPa, a reduction of area higher than 50%, and excellent wear resistance and high temperature performance. Furthermore, it maintains a low cost while improving various properties, and the preparation process is simple and easy to industrialize. Attached Figure Description

[0026] Figure 1Thermodynamic equilibrium phase diagram of the alloy composition in Example 1 of this invention;

[0027] Figure 2 The metallographic structure of the alloy system in the spheroidized annealed state in Example 1 of this invention;

[0028] Figure 3 The metallographic structure of the alloy system in the spheroidized annealed state in Example 2 of this invention;

[0029] Figure 4 This is the spheroidized annealed metallographic structure of the alloy system in Comparative Example 1 of this invention;

[0030] Figure 5 The tempered metallographic structure of the alloy system in Example 1 of this invention;

[0031] Figure 6 The tempered metallographic structure of the alloy system in Example 2 of this invention;

[0032] Figure 7 This is the tempered metallographic structure of the alloy system in Comparative Example 1 of this invention;

[0033] Figure 8 The impact fracture morphology of Embodiment 1 of the present invention;

[0034] Figure 9 The impact fracture morphology of Embodiment 2 of the present invention;

[0035] Figure 10 This is the impact fracture morphology of Comparative Example 1 of the present invention;

[0036] Figure 11 The tensile stress-strain curve of Embodiment 1 of the present invention;

[0037] Figure 12 The tensile stress-strain curve is shown in Embodiment 2 of the present invention.

[0038] Figure 13 This is the tensile stress-strain curve of Comparative Example 1 of the present invention;

[0039] Figure 14 The tensile fracture morphology of Embodiment 1 of the present invention;

[0040] Figure 15 The tensile fracture morphology of Embodiment 2 of the present invention;

[0041] Figure 16 This is the tensile fracture morphology of Comparative Example 1 of the present invention;

[0042] Figure 17 The dynamic friction coefficient curve of Embodiment 1 of the present invention is obtained by grinding against Si3N4 ceramic balls under a load of 100N.

[0043] Figure 18The dynamic friction coefficient curve of Embodiment 2 of the present invention is obtained by grinding against Si3N4 ceramic balls under a load of 100N.

[0044] Figure 19 The curve of dynamic friction coefficient of Comparative Example 1 of the present invention is shown when it is polished against a Si3N4 ceramic ball under a load of 100N. Detailed Implementation

[0045] This invention provides a steel for scrap steel shearing machine blades, comprising the following elements by mass percentage: C: 0.3-0.45%, Cr: 4.0-6.0%, Mo: 1.0-2.0%, V: 0.4-0.6%, W: 1.0-3.0%, Si: 0.1-0.3%, Mn: 0.1-0.6%, P: ≤0.02%, S≤0.02%, with the balance being Fe and unavoidable impurities.

[0046] The preferred mass percentage of carbon (C) in the steel used for scrap steel shearing machine blades provided by this invention is 0.35-0.37%. The role of C is to form a solid solution structure, which increases the strength of the steel, and to form a carbide structure, which increases the hardness and wear resistance of the steel.

[0047] The preferred mass percentage of Cr in the steel for scrap steel shearing machine blades provided by this invention is 4.96-5.35%. The role of Cr is to improve the wear resistance, high temperature strength, hot hardness, toughness and hardenability of the steel. At the same time, its dissolution into the matrix will significantly improve the corrosion resistance of the steel.

[0048] The preferred mass percentage of Mo in the steel for scrap steel shearing machine blades provided by this invention is 1.19-1.55%. The role of Mo is to achieve solid solution strengthening, and the resulting carbides can significantly improve the strength and toughness of the steel.

[0049] The preferred mass percentage of W in the steel for scrap shearing machine blades provided by this invention is 1.89–1.98%. The addition of W in this invention promotes the precipitation of M phases in the steel. 23 The C6 steel transforms into the finer and more dispersed M6C, while the M6C is uniformly distributed in a spherical pattern within the steel. This greatly improves the steel's wear resistance and high-temperature performance, thus extending the service life of scrap steel shearing machine blades.

[0050] The preferred mass percentage of V in the steel used for scrap steel shearing machine blades provided by this invention is 0.54–0.55%.

[0051] The preferred mass percentage of Si in the steel used for scrap steel shearing machine blades provided by this invention is 0.19–0.24%.

[0052] The scrap steel shear blades of this invention have low Si and V content. Compared with conventional steel, which has a Si content of 1% and a V content of 0.9% by mass, the reduced Si and V content improves the impact toughness of the steel. This significantly improves the performance of the scrap steel shear blades under heavy loads, reduces spalling and breakage, and lowers the probability of abnormal failure.

[0053] The preferred mass percentage of Mn in the steel for scrap steel shearing machine blades provided by this invention is 0.35-0.45%. The presence of Mn in the steel can change the properties and shape of the oxides formed during solidification. At the same time, it has a strong affinity for S, which can prevent the formation of low-melting-point sulfides FeS at the grain boundaries, and instead allow it to exist as MnS with a certain degree of plasticity, thereby eliminating the harmful effects of sulfur, improving the hot working properties of the steel, and also achieving solid solution strengthening and improving the hardenability of the steel.

[0054] In this invention, the annealed microstructure of the steel used for scrap steel shearing machine blades is preferably a ferrite matrix with spherical secondary carbides uniformly distributed on it, and the average particle size of the spherical secondary carbides is preferably 0.2-0.8 μm; the tempered microstructure of the steel used for scrap steel shearing machine blades after tempering at 585-600℃ preferably includes lath-shaped tempered martensite and retained austenite, the precipitates are preferably fine spherical or rod-shaped, the average size of the spherical precipitates is preferably 0.1-0.3 μm, the grain size level is preferably 7-8, and the average grain size is preferably 18-25 μm.

[0055] In this invention, the fully austenitic temperature range of the steel used for the scrap steel shearing machine blades is preferably 1040℃~1400℃.

[0056] In this invention, the steel used for the scrap steel shearing machine blades preferably has a hardness of ≥47HRC after tempering at 585-600℃, a V-notch impact energy of ≥29J, a tensile strength of ≥1600MPa, and a reduction of area of ​​≥50%.

[0057] This invention also provides a method for preparing the steel for scrap steel shearing machine blades as described in the above technical solution, comprising the following steps:

[0058] Iron, chromium, tungsten and molybdenum are mixed and then subjected to a first smelting process to obtain a first molten material;

[0059] The first molten material is mixed with graphite and then refined and deoxidized to obtain a refined material;

[0060] The refined material is mixed with silicon, manganese and vanadium in sequence and then smelted a second time, and then cast into ingots to obtain ingots;

[0061] The ingot is coated with a decarburized refractory coating and then subjected to homogenization treatment, forging, normalizing treatment, isothermal spheroidizing annealing treatment, solution treatment and tempering heat treatment in sequence to obtain the steel for scrap steel shearing machine blades.

[0062] Unless otherwise specified, all raw materials used in this invention are commercially available products in the field.

[0063] The present invention involves mixing iron, chromium, tungsten and molybdenum and then performing a first smelting to obtain a first molten material.

[0064] In this invention, the iron is preferably industrial pure iron.

[0065] Before the first smelting, the present invention preferably adds industrial pure iron, metallic chromium, metallic tungsten, and metallic molybdenum into the smelting furnace, turns on the vacuum pump to draw a vacuum, and then applies electricity to melt the furnace charge. After the furnace charge begins to melt, the vacuum pump is turned off and argon gas is introduced until the furnace charge is completely melted, thus obtaining the first molten material.

[0066] In this invention, the first melting is preferably carried out in a vacuum induction furnace.

[0067] In this invention, the vacuum level is preferably below 3 Pa, and the argon gas is preferably introduced to a total pressure of 40000 Pa inside the furnace.

[0068] The present invention does not impose any special limitations on the specific parameters of the first melting process, as long as complete melting is guaranteed.

[0069] After obtaining the first molten material, the present invention mixes the first molten material with graphite for refining and deoxidation to obtain a refined material.

[0070] In this invention, the refining is preferably vacuum refining, the refining temperature is preferably 1540±20℃, more preferably 1540~1543℃, and the holding time is preferably 30min. The function of the refining is carbon deoxidation.

[0071] In this invention, the mixture is preferably vacuumed again to below 20 Pa for vacuum refining.

[0072] In this invention, after the refining is completed, it is preferable to introduce argon gas again and add metallic aluminum for deoxidation, and the deoxidation time is preferably 5 minutes.

[0073] In this invention, the deoxidation process preferably includes a slag removal process, wherein the slag removal is preferably the process of cutting off the head and tail.

[0074] In this invention, argon gas is preferably introduced into the furnace to a total pressure of 40,000 Pa.

[0075] After obtaining the refined material, the present invention mixes the refined material with silicon, manganese and vanadium in sequence and then performs a second smelting, and then casts it into ingots to obtain ingots.

[0076] In this invention, the reason for mixing silicon, manganese and vanadium in sequence is: silicon is added first for further deoxidation to prevent vanadium from being oxidized.

[0077] In this invention, the temperature of the second melting is preferably 1540±20℃, more preferably 1545~1550℃. This invention does not have a special limitation on the time of the second melting, as long as it can ensure complete melting.

[0078] In this invention, the casting temperature is preferably 1540±20℃, more preferably 1545~1550℃.

[0079] The feeding sequence in this invention is required, and the materials are melted in layers from top to bottom, which involves processes such as deoxidation, so they cannot be added all at once.

[0080] After obtaining the ingot, the present invention coats the ingot with a decarburized refractory coating and then performs homogenization treatment, forging, normalizing treatment, isothermal spheroidizing annealing treatment, solution treatment and tempering heat treatment in sequence to obtain the steel for scrap steel shearing machine blades.

[0081] The present invention preferably involves cutting off the head shrinkage cavity and tail of the ingot before coating it with the decarburized refractory coating.

[0082] In this invention, the function of the decarburized refractory coating is to prevent surface decarburization. This invention does not have any special limitations on the type or amount of the decarburized refractory coating, as long as it can completely cover the ingot.

[0083] In this invention, the homogenization treatment temperature is preferably 1200-1250℃, the holding time is preferably 8-10h, the heating rate to the homogenization treatment temperature is preferably 3-5℃ / min, and the heating is preferably carried out in the furnace.

[0084] After homogenization, the present invention preferably further includes cooling to room temperature. Cooling to room temperature preferably includes the following steps: first cooling to 900±20°C with the furnace, more preferably 890~910°C, and then air cooling to room temperature.

[0085] In this invention, the material cooled to room temperature is preferably heated in a furnace to 1200±20°C for forging, and more preferably to 1180~1210°C.

[0086] In this invention, after homogenization treatment and before forging, it is preferable to perform three-stage bending and three-stage pulling to eliminate defects such as porosity and segregation, transform large dendrites and columnar crystals into fine equiaxed crystals, increase the amount of deformation, and improve the forging effect.

[0087] In this invention, the final forging temperature is preferably 950±20℃, more preferably 950~954℃, the total forging ratio is preferably not less than 4, and after forging into bars, they are preferably placed in a sand pile to cool slowly to room temperature.

[0088] In this invention, the normalizing temperature is preferably 950±10℃, more preferably 950~960℃, the holding time is preferably 1~3h, the heating rate to the normalizing temperature is preferably 3~5℃ / min, and the heating is preferably furnace heating. The function of the normalizing treatment is to eliminate the network carbides precipitated during forging and improve the impact toughness of the steel.

[0089] After the normalizing treatment is completed, the present invention preferably further includes air cooling to room temperature.

[0090] In this invention, the isothermal spheroidizing annealing preferably includes the following process: heating to 860±10℃ (more preferably 860~864℃) at a heating rate of 3~5℃ / min and holding for 2 hours, then cooling to 740±10℃ (more preferably 740~745℃) and holding for 4 hours, then cooling to 500±20℃ and air-cooling to room temperature. In this invention, the heating is preferably furnace heating, and the purpose of the isothermal spheroidizing annealing is to improve the machinability of the steel, facilitate processing and forming, eliminate residual stress, and provide a good microstructure for subsequent quenching.

[0091] In this invention, the temperature of the solution treatment is preferably 1010-1030℃, more preferably 1020℃, and the holding time is preferably 30-45 min. The function of the solution treatment is to strengthen the solution.

[0092] After the solution treatment is completed, the present invention preferably further includes quenching to room temperature, wherein the purpose of quenching is to transform the supercooled austenite into martensite.

[0093] In this invention, the quenching is preferably performed using oil cooling.

[0094] In this invention, the tempering heat treatment preferably includes the following process: holding at 585-600°C (more preferably 595°C) for 2 hours and then cooling to room temperature, followed by holding at 585-600°C (more preferably 595°C) for another 2 hours, and then cooling to room temperature. The purpose of the tempering heat treatment is to eliminate residual stress in the quenched steel, reduce the brittleness of the steel, and improve the toughness and plasticity of the steel.

[0095] After the tempering heat treatment is completed, the present invention preferably further includes cooling to room temperature, wherein the cooling is preferably air cooling.

[0096] To further illustrate the present invention, the steel for scrap steel shearing machine blades and its preparation method provided by the present invention are described in detail below with reference to examples, but these should not be construed as limiting the scope of protection of the present invention.

[0097] Example 1

[0098] A type of steel for scrap steel shearing machine blades, the chemical composition of which, by mass percentage, is: Fe-0.35C-5.35Cr-1.19Mo-0.54V-1.98W-0.19Si-0.45Mn (wt.%).

[0099] The method for preparing the steel used in the scrap steel shearing machine blades includes the following steps:

[0100] Step 1, Smelting: According to the steel composition ratio for scrap steel shearing machine blades, add industrial pure iron, metallic chromium, metallic tungsten, and metallic molybdenum into the smelting furnace. Turn on the vacuum pump to create a vacuum, controlling the vacuum degree below 3 Pa. After the furnace charge begins to melt, introduce argon gas until the total pressure inside the furnace reaches 40000 Pa. After the furnace charge has completely melted, add graphite and evacuate the furnace again to below 20 Pa. Hold the vacuum for 30 minutes for vacuum refining at a refining temperature of 1540℃.

[0101] After vacuum decarburization and deoxidation refining, argon gas is introduced into the furnace until the total pressure is 40,000 Pa. Then, aluminum is added and timed for 5 minutes. Silicon, manganese and vanadium are added in sequence. The melting temperature is 1545℃. After complete melting, the casting temperature is controlled at 1545℃.

[0102] Step 2, Casting Treatment: After removing the shrinkage cavities at the head and tail of the ingot, evenly apply an anti-decarburization refractory coating, then heat the ingot in the furnace to 1250℃ and hold for 10 hours for high-temperature homogenization treatment at a heating rate of 5℃ / min. After the homogenization holding period, cool it in the furnace to 900℃ and remove it for air cooling to room temperature.

[0103] Step 3, Forging: The high-temperature homogenized ingot is heated to 1210℃ in the furnace, and then forged into bars after three forgings and three drawings. The final forging temperature is 950℃. After forging, the bars are placed in a sand pile to cool slowly to room temperature.

[0104] Step 4, Post-forging heat treatment: The forged bar is heated in the furnace to 950℃ and held for 2 hours for normalizing treatment at a heating rate of 4℃ / min. After normalizing, it is removed and air-cooled to room temperature. Then, it is heated in the furnace to 860℃ and held for 2 hours, then slowly cooled in the furnace to 740℃ and held for 4 hours for isothermal spheroidizing annealing treatment. After slowly cooling in the furnace to 500℃, it is air-cooled to room temperature. Then, the steel is instantaneously heated to 1020℃ and held for 30 minutes for solution treatment. It is then oil-quenched to room temperature. Finally, the quenched steel is instantaneously heated to 585℃ and held for 2 hours, then removed and air-cooled to room temperature. Then, the steel is instantaneously heated to 585℃ again and held for 2 hours, then removed and air-cooled to room temperature.

[0105] The thermodynamic equilibrium phase diagram of the alloy composition of the steel used for scrap steel shearing blades prepared in this embodiment is as follows: Figure 1 spheroidized annealed microstructure such asFigure 2 As shown, the tempered microstructure is as follows Figure 5 As shown, the grain size is grade 8; the impact fracture morphology is as follows. Figure 8 The tensile stress-strain curve is as follows Figure 11 The tensile fracture morphology is as follows Figure 14 Mechanical property analysis revealed that the steel used for scrap steel shearing machine blades has a hardness of 48.9 HRC, a tensile strength of 1618.5 MPa, a reduction of area of ​​54%, and an impact energy of 30.7 J with a V-notch. Under a load of 100 N, the average coefficient of friction when rubbing against a 9.525 mm diameter Si3N4 ceramic ball is 0.54 (stroke 10 mm, frequency 2 Hz). Figure 17 The dynamic friction coefficient curve of Embodiment 1 of the present invention is obtained by grinding against Si3N4 ceramic balls under a load of 100N.

[0106] Example 2

[0107] A type of steel for scrap steel shearing machine blades, the chemical composition of which, by mass percentage, is: Fe-0.37C-4.96Cr-1.55Mo-0.55V-1.89W-0.24Si-0.35Mn (wt.%).

[0108] The method for preparing the steel used in the scrap steel shearing machine blades includes the following steps:

[0109] Step 1, Smelting: According to the steel composition ratio for scrap steel shearing machine blades, add industrial pure iron, metallic chromium, metallic tungsten, and metallic molybdenum into the smelting furnace. Turn on the vacuum pump to create a vacuum, controlling the vacuum degree below 3 Pa. After the furnace charge begins to melt, introduce argon gas until the total pressure inside the furnace reaches 40000 Pa. After the furnace charge has completely melted, add graphite and evacuate the furnace again to below 20 Pa. Hold the vacuum for 30 minutes for vacuum refining at a refining temperature of 1543℃.

[0110] After vacuum decarburization and deoxidation refining, argon gas is introduced into the furnace until the total pressure is 40,000 Pa. Then, aluminum is added and timed for 5 minutes. Silicon, manganese and vanadium are added in sequence. The melting temperature is 1550℃. After complete melting, the casting temperature is controlled at 1550℃.

[0111] Step 2, Casting Treatment: After removing the shrinkage cavities at the head and tail of the ingot, evenly apply an anti-decarburization refractory coating, then heat the ingot in the furnace to 1250℃ and hold for 8 hours for high-temperature homogenization treatment at a heating rate of 3℃ / min. After the homogenization holding is completed, cool it in the furnace to 890℃ and remove it, then air cool it to room temperature.

[0112] Step 3, Forging: The high-temperature homogenized ingot is heated to 1180℃ in the furnace, and then forged into bars after three forgings and three drawings. The final forging temperature is 954℃. After forging, the bars are placed in a sand pile to cool slowly to room temperature.

[0113] Step 4, Post-forging heat treatment: The forged bar is heated in the furnace to 960℃ and held for 2 hours for normalizing treatment at a heating rate of 5℃ / min. After normalizing, it is removed and air-cooled to room temperature. Then, it is heated in the furnace to 864℃ and held for 2 hours, then slowly cooled in the furnace to 745℃ and held for 4 hours for isothermal spheroidizing annealing treatment. After slowly cooling in the furnace to 500℃, it is air-cooled to room temperature. Then, the steel is instantaneously heated to 1020℃ and held for 30 minutes for solution treatment. It is then oil-quenched to room temperature. Finally, the quenched steel is instantaneously heated to 595℃ and held for 2 hours, then removed and air-cooled to room temperature. Then, the steel is instantaneously heated to 595℃ again and held for 2 hours before being removed and air-cooled to room temperature.

[0114] The spheroidized annealed metallographic structure of the scrap steel shearing blade prepared in this embodiment is as follows: Figure 3 As shown, the tempered microstructure is as follows Figure 6 As shown; the grain size of the steel used for scrap shearing machine blades is grade 8, and the impact fracture morphology is as follows. Figure 9 The tensile stress-strain curve is as follows Figure 12 The tensile fracture morphology is as follows Figure 15 Mechanical property analysis revealed a hardness of 48.1 HRC, a tensile strength of 1630.2 MPa, a reduction of area of ​​56%, and an impact energy of 31.5 J with a V-notch. Under a load of 100 N, the average coefficient of friction when rubbed against a 9.525 mm diameter Si3N4 ceramic ball was 0.60 (stroke 10 mm, frequency 2 Hz). Figure 18 The dynamic friction coefficient curve of Embodiment 2 of the present invention is obtained by grinding against Si3N4 ceramic balls under a load of 100N.

[0115] Comparative Example 1

[0116] The ultra-high strength steel, which did not adopt the design concept of low Si and low V with increased W and post-forging normalizing treatment, has the following chemical composition by mass percentage: Fe-0.39C-5.29Cr-1.27Mo-0.90V-0.95Si-0.45Mn (wt.%).

[0117] The method for preparing the steel used in the scrap steel shearing machine blades includes the following steps:

[0118] Step 1, Smelting: According to the steel composition ratio for scrap steel shearing machine blades, add industrial pure iron, metallic chromium, metallic tungsten, and metallic molybdenum into the smelting furnace. Turn on the vacuum pump to create a vacuum, controlling the vacuum degree below 3 Pa. After the furnace charge begins to melt, introduce argon gas until the total pressure inside the furnace reaches 40,000 Pa. After the furnace charge has completely melted, add graphite and evacuate the furnace again to below 20 Pa. Hold the vacuum for 30 minutes for vacuum refining at a refining temperature of 1537℃.

[0119] After vacuum decarburization and deoxidation refining, argon gas is introduced into the furnace until the total pressure is 40,000 Pa. Then, aluminum is added and timed for 5 minutes. Silicon, manganese and vanadium are added in sequence. The melting temperature is 1545℃. After complete melting, the casting temperature is controlled at 1549℃.

[0120] Step 2, Casting Treatment: After removing the shrinkage cavities at the head and tail of the ingot, and evenly applying an anti-decarburization refractory coating, the ingot is heated in the furnace to 1250℃ and held for 8 hours for high-temperature homogenization treatment at a heating rate of 5℃ / min. After the homogenization holding is completed, the ingot is cooled in the furnace to 900℃ and then removed and air-cooled to room temperature.

[0121] Step 3, Forging: The high-temperature homogenized ingot is heated to 1200℃ in the furnace, and then forged into bars after three forgings and three drawings. The final forging temperature is 951℃. After forging, the bars are placed in a sand pile to cool slowly to room temperature.

[0122] Step 4, Post-forging heat treatment: Heat the forged bar in the furnace to 870℃ and hold for 2 hours. Slowly cool it in the furnace to 750℃ and hold for 4 hours for isothermal spheroidizing annealing. Slowly cool it in the furnace to 500℃ and then air cool it to room temperature. Then, instantaneously heat the steel to 1030℃ and hold for 30 minutes for solution treatment. Oil quench it to room temperature. Finally, instantaneously heat the quenched steel to 585℃ and hold for 2 hours. Remove it and air cool it to room temperature. Then, instantaneously heat the steel to 585℃ again and hold for 2 hours before removing it and air cooling it to room temperature.

[0123] The annealed microstructure of the scrap steel shearing blade prepared in this embodiment is as follows: Figure 4 As shown, the tempered microstructure is as follows Figure 7 As shown, the grain size is grade 8; the impact fracture morphology is as follows. Figure 10 The tensile stress-strain curve is as follows Figure 13 The tensile fracture morphology is as follows Figure 16 Mechanical property analysis revealed that the steel used for scrap steel shearing machine blades has a hardness of 48.5 HRC, a tensile strength of 1558.3 ​​MPa, a reduction of area of ​​44%, and an impact energy of 18.6 J with a V-notch. Under a load of 100 N, the average coefficient of friction when rubbing against a 9.525 mm diameter Si3N4 ceramic ball is 0.70 (stroke 10 mm, frequency 2 Hz). Figure 19 The curve of dynamic friction coefficient of Comparative Example 1 of the present invention is shown when it is polished against a Si3N4 ceramic ball under a load of 100N.

[0124] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A steel for scrap shear blades, characterized by, Comprise the following mass percentage of elements: C: 0.35~0.37%, Cr: 4.96~5.35%, Mo: 1.19~1.55%, V: 0.54~0.55%, W: 1.89~1.98%, Si: 0.19~0.24%, Mn: 0.35~0.45%, P: ≤0.02%, S ≤0.02%, the balance of Fe and inevitable impurities; The annealed microstructure of the scrap shearing machine blade steel is that globular secondary carbides are uniformly distributed on a ferrite matrix, and the average particle size of the globular secondary carbides is 0.2~0.8μm; the microstructure of the scrap shearing machine blade steel after tempering at 585~600℃ includes lath-shaped tempered martensite and residual austenite, and the precipitates are in the form of fine globular or rod-shaped, the average size of the globular precipitates is 0.1~0.3μm, the grain size level is 7~8, and the average grain size is 18~25μm; The preparation method of the scrap shearing machine blade steel comprises the following steps: mixing iron, chromium, tungsten and molybdenum and then performing first smelting to obtain first molten material; mixing the first molten material with graphite and then performing refining and deoxidation to obtain refined material; mixing the refined material with silicon, manganese and vanadium in sequence and then performing second smelting, and then casting into ingot to obtain cast ingot; coating the cast ingot with decarburization refractory coating and then performing homogenization treatment, forging, normalizing treatment, isothermal spheroidizing annealing treatment, solid solution treatment and tempering heat treatment in sequence to obtain the scrap shearing machine blade steel; the temperature of the normalizing treatment is 950±10℃, and the holding time is 1~3h; the temperature of the solid solution treatment is 1010~1030℃, and the holding time is 30~45min.

2. A scrap shear blade steel according to claim 1 characterised in that, The full austenite range of the scrap shearing machine blade steel is 1040℃~1400℃.

3. The scrap shear blade steel of claim 1, characterized by, After tempering at 585~600℃, the hardness of the scrap shearing machine blade steel is ≥47HRC, the V-notch impact energy is ≥29J, the tensile strength is ≥1600MPa, and the reduction of area is ≥50%.

4. Method for the production of a steel for scrap shears blades according to any one of claims 1 to 3, characterized in that, The preparation method comprises the following steps: mixing iron, chromium, tungsten and molybdenum and then performing first smelting to obtain first molten material; mixing the first molten material with graphite and then performing refining and deoxidation to obtain refined material; mixing the refined material with silicon, manganese and vanadium in sequence and then performing second smelting, and then casting into ingot to obtain cast ingot; coating the cast ingot with decarburization refractory coating and then performing homogenization treatment, forging, normalizing treatment, isothermal spheroidizing annealing treatment, solid solution treatment and tempering heat treatment in sequence to obtain the scrap shearing machine blade steel; the temperature of the normalizing treatment is 950±10℃, and the holding time is 1~3h; the temperature of the solid solution treatment is 1010~1030℃, and the holding time is 30~45min.

5. The preparation method according to claim 4, characterized in that, The temperature of the homogenization treatment is 1200~1250℃, the holding time is 8~10h, and the heating rate for heating to the temperature of the homogenization treatment is 3~5℃ / min.

6. The preparation method according to claim 4, characterized in that, The heating rate for heating to the temperature of the normalizing treatment is 3~5℃ / min.

7. The preparation method according to claim 4, characterized in that, The isothermal spheroidizing annealing comprises the following processes: heating at a heating rate of 3-5 ℃ / min to 860±10 ℃ and holding for 2 h, then cooling to 740±10 ℃ and holding for 4 h, cooling to 500±20 ℃ and then air cooling to room temperature.

8. The preparation method according to claim 4, characterized in that, The tempering heat treatment comprises the following processes: holding at 585-600 ℃ for 2 h, cooling to room temperature, then holding at 585-600 ℃ for 2 h again, and then cooling to room temperature.

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