Low-cost high-plasticity alloy steel wire rod for sorbite tool and manufacturing method thereof

Abstract

The invention discloses an alloy steel wire rod for a low-cost high-plasticity sorbite tool and a manufacturing method of the alloy steel wire rod. The alloy steel wire rod comprises the following chemical components in percentage by mass: 0.55-0.61% of C, 1.25-1.60% of Si, 0.60-0.80% of Mn, 0.60-0.80% of Cr, less than or equal to 0.35% of Ni, less than or equal to 0.35% of Cu, less than or equal to 0.025% of P, less than or equal to 0.020% of S and the balance of Fe and inevitable impurities. The manufacturing method comprises the steps of steel billet smelting, continuous casting, heating, controlled rolling and controlled cooling, wherein a soft reduction process is adopted for continuous casting, the initial rolling temperature is controlled to be 900-980 DEG C, the high-pressure water descaling pressure is larger than or equal to 19 MPa, the final rolling temperature is 780-840 DEG C, the spinning temperature is 780-840 DEG C, and cooling is conducted through an air cooling roller bed. The steel wire rod is free of precious metal and low in cost, the hardness of a finished product reaches 58-61 HRC, and the product requirement is met.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, and in particular to a low-cost and high-plasticity alloy steel wire rod for troostite tools and a manufacturing method thereof. Background Art

[0002] Alloy tool steel is widely used in manufacturing products such as sockets, extension rods, hexagonal wrenches and electric screwdriver bits. Sockets and extension rods are produced using 50BV30 wire, which is ground and chrome-plated after forming, and has high surface quality requirements. Hexagonal wrenches and screwdriver bits can be produced using SAE6150 and S2 wire according to the hardness requirements of the finished product.

[0003] In order to meet the high hardness, high toughness and high wear resistance requirements of hexagonal wrenches and screwdriver bits, SAE6150 and S2 are added with one or more alloy elements of 0.7-1.2% Cr, 0.40-0.50% Mo, and 0.15-0.25% V on the basis of medium carbon steel products. Cr can increase the hardenability and hardness of steel, vanadium can improve the hardness, wear resistance and toughness of steel by forming carbonitrides, and fine dispersed vanadium carbonitride can significantly improve the wear resistance of steel; molybdenum can improve the hardenability and tempering stability of steel, thereby improving the strength and toughness of steel; hardware tool steel often adds a combination of CrV, CrMo and other alloy elements to ensure its quality stability.

[0004] Due to the addition of a certain amount of alloy, the hot rolled structure contains a large amount of martensite / bainite structure, with high hardness and poor deformation ability, and needs to be spheroidized annealed before use. The current hot rolled wire rod production process is: continuous casting billet-heating-rolling-controlled cooling-coiling and packaging; the tool production process is: hot rolled wire rod-spheroidized annealing-surface treatment-drawing-(bending)-quenching and tempering.

[0005] At present, the patents related to wire rods for tool steel mainly optimize the composition design by optimizing the addition amount of different alloy contents, or optimize the organizational performance by optimizing the production process. Specifically:

[0006] In terms of composition design: Patent application number CN105149878A and CN103436687A add 0.40-0.60% Mo element; Patent application number CN111690801A adds 0.010-0.025% Nb to ensure the hardness of the finished product. Patent application number CN113528937A considers that adding CrV and CrMo multi-alloy structure can ensure stable quality, but there is excess quality, so V and Mo addition are cancelled, and hardenability is improved by adding 0.0005-0.0035% B, and the surface hardness of the finished product is 55-57HRC.

[0007] Process optimization: Patent application number CN109517968A adds 0.15-0.25% V and 0.40-0.50% Mo, and obtains troostite structure through large coil + insulation tunnel method, but slow cooling rate will aggravate surface decarburization and reduce tool surface hardness and wear resistance. Patent application number CN114134399A adds 0.30-0.70% Mo and 0.15-0.25% V, adopts post-rolling water bath + insulation tunnel method, uses water bath to quickly cool to bainite zone, avoids decarburization caused by high temperature slow cooling, and finally obtains bainite structure.

[0008] From the perspective of the patents that have been published so far, one method is to ensure performance by adjusting and optimizing alloy elements, but adjusting alloy elements alone will reduce the hardness after quenching and tempering, and cannot meet the 58HRC hardness requirement. Another method is an innovative post-rolling controlled cooling process, which mainly adds tunnel-type insulation and slow cooling equipment to eliminate or reduce the proportion of martensite in the structure to prevent brittle fracture during the storage and transportation of wire rods. However, for the medium-carbon component system, the addition of alloy elements will inevitably produce a certain amount of quenched structure, so spheroidizing annealing treatment is required before use, otherwise the uneven stress distribution during the drawing process will lead to bending and fracture or bending of the workpiece after quenching and tempering. Summary of the invention

[0009] In order to solve the problems raised in the above background technology, the present invention provides a low-cost and high-plasticity alloy steel wire rod for troostite tools and a manufacturing method thereof.

[0010] To achieve the above-mentioned purpose, the present invention provides the following technical solution: a low-cost and high-plasticity alloy steel wire rod for troostite tools, wherein the chemical composition of the low-cost and high-plasticity alloy steel wire rod for troostite tools comprises, by mass percentage: C: 0.55-0.61%, Si: 1.25-1.60%, Mn: 0.60-0.80%, Cr: 0.60-0.80%, Ni: ≤0.35, Cu: ≤0.35, P: ≤0.025, S: ≤0.020, and the rest are Fe and unavoidable impurities.

[0011] A method for manufacturing a low-cost, high-plasticity troostite tool alloy steel wire rod, the method comprising the following steps in sequence:

[0012] S1, billet smelting, qualified molten iron is subjected to converter smelting and LF furnace refining treatment;

[0013] S2: continuous casting, casting the above molten steel, the continuous casting process adopts a light reduction process, reasonably selects the reduction position and distributes the reduction amount, improves the macrostructure of the ingot, avoids the generation of reduction cracks, and performs surface quality inspection and grinding treatment on the continuous casting ingot;

[0014] S3: Billet heating: The continuous casting billet that has been confirmed by surface quality inspection is heated. In view of the fact that high Si steel is prone to decarburization, the residual oxygen content of the heating furnace is controlled to be ≤3% during the heating process to alleviate the decarburization of the continuous casting billet surface; the temperature of the high temperature section of the heating furnace is controlled to be 1000-1080℃, and the continuous casting billet heating time in the furnace is ≤120min;

[0015] S4: Controlled rolling and controlled cooling. The heated continuous casting billet is subjected to controlled rolling and controlled cooling. The starting rolling temperature is controlled at 900℃-980℃, the high-pressure water descaling pressure is ≥19MPa, the final rolling temperature is 780℃-840℃, and the wire-spinning temperature is 780℃-840℃. After the wire is spun, it is laid flat on the air-cooled roller. The wire rod density is controlled by adjusting the roller speed. At the same time, the number and frequency of fan opening are adjusted according to different specifications. The cooling rate and phase change are controlled in combination with the number of insulation hood openings. The target hood temperature is 670±10℃, so as to obtain a highly plastic troostite structure.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] No V, Mo and other precious micro-alloying elements are added. To ensure the hardness of the finished product after quenching, the content of Si, Cr and Mn elements in the steel is increased, which can reduce the production cost. At the same time, the influence of Si, Cr and Mn elements on the hardenability is weaker than that of V and Mo elements, which is conducive to the control of the microstructure after rolling.

[0018] The continuous casting process adopts a light reduction process, which can optimize the segregation of the continuous casting billet. The segregation index is reduced from about 1.15 to ≤1.08, avoiding the elements from gathering in the center and forming a quenched structure in the center of the wire rod.

[0019] The rolling process adopts controlled rolling and controlled cooling technology. The low temperature final rolling at 780℃-840℃ can reduce the degree of recovery and recrystallization. Retaining part of the rolling distortion can increase the instability of the high temperature structure, and the controlled cooling process is used to decompose the austenite structure. At the same time, 670℃ is the sorbite phase transition temperature. The hood insulation can obtain a hot-rolled structure dominated by sorbite, improve plasticity, and realize the annealing-free drawing processing of the wire rod.

[0020] The wire rod produced by this patent undergoes descaling and surface drawing pretreatment - drawing - blanking - bending - quenching and tempering post-treatment, and the hardness of the finished wrench is 58-61HRC. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the core structure of the wire rod in Example 1;

[0022] Figure 2 This is a schematic diagram of the core structure of the wire rod in Example 2;

[0023] Figure 3 This is a schematic diagram of the core structure of the wire rod in Example 3;

[0024] Figure 4 This is a schematic diagram of the core structure of the wire rod of comparative example 1. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] Example 1

[0027] A low-cost high-plasticity alloy steel wire rod for troostite tools. The chemical composition of the low-cost high-plasticity alloy steel wire rod for troostite tools includes, by mass percentage, C: 0.61%, Si: 1.35%, Mn: 0.68%, Cr: 0.70%, Ni: 0.010%, Cu: 0.008%, P: 0.008%, S: 0.004%, and the rest is Fe and unavoidable impurities.

[0028] The method for manufacturing the above-mentioned low-cost high-plasticity troostite tool alloy steel wire rod comprises the following steps in sequence:

[0029] S1, billet smelting, qualified molten iron is subjected to converter smelting and LF furnace refining treatment;

[0030] S2: continuous casting, casting the above molten steel, the continuous casting process adopts a light reduction process, reasonably selects the reduction position and distributes the reduction amount, improves the macrostructure of the ingot, avoids the generation of reduction cracks, and performs surface quality inspection and grinding treatment on the continuous casting ingot;

[0031] S3: Billet heating: The continuous casting billet that has been confirmed by surface quality inspection is heated. In view of the fact that high Si steel is prone to decarburization, the residual oxygen content of the heating furnace is controlled to be ≤3% during the heating process to alleviate the decarburization of the continuous casting billet surface; the temperature of the high temperature section of the heating furnace is controlled to be 1056℃, and the continuous casting billet is heated in the furnace for 114 minutes;

[0032] S4: controlled rolling and controlled cooling. The heated continuous casting billet is subjected to controlled rolling and controlled cooling. The starting rolling temperature is controlled at 900°C, the high-pressure water descaling pressure is 21MPa, the final rolling temperature is 786°C, the φ15mm wire rod is rolled, and the wire-spinning temperature is 800°C. After the wire rod is spun, it is laid flat on the air-cooled roller. The 1st and 2nd fans are turned on to blow-cool the wire rod. After cooling to 675°C, it is slowly cooled in the heat preservation cover to obtain a high-plasticity troostite structure.

[0033] The hot rolled wire rod structure is sorbite + a small amount of ferrite, the sorbite ratio is 892%, the tensile strength is 1045MPa, and the area reduction is 50%. The hot rolled wire rod is subjected to tempering treatment after pickling, phosphorus saponification, drawing, and blanking by the user, and the hardness of the finished product is 60-61HRC.

[0034] Example 2

[0035] A low-cost high-plasticity alloy steel wire rod for troostite tools. The chemical composition of the low-cost high-plasticity alloy steel wire rod for troostite tools includes, by mass percentage, C: 0.59%, Si: 1.58%, Mn: 0.70%, Cr: 0.72%, Ni: 0.010%, Cu: 0.009%, P: 0.009%, S: 0.005%, and the rest is Fe and unavoidable impurities.

[0036] The method for manufacturing the above-mentioned low-cost high-plasticity troostite tool alloy steel wire rod comprises the following steps in sequence:

[0037] S1, billet smelting, qualified molten iron is subjected to converter smelting and LF furnace refining treatment;

[0038] S2: continuous casting, casting the above molten steel, the continuous casting process adopts a light reduction process, reasonably selects the reduction position and distributes the reduction amount, improves the macrostructure of the ingot, avoids the generation of reduction cracks, and performs surface quality inspection and grinding treatment on the continuous casting ingot;

[0039] S3: Billet heating: The continuous casting billet that has been confirmed by surface quality inspection is heated. In view of the fact that high Si steel is prone to decarburization, the residual oxygen content of the heating furnace is controlled to be ≤3% during the heating process to alleviate the decarburization of the continuous casting billet surface; the temperature of the high temperature section of the heating furnace is controlled to be 1072℃, and the continuous casting billet is heated in the furnace for 110 minutes;

[0040] S4: controlled rolling and controlled cooling. The heated continuous casting billet is subjected to controlled rolling and controlled cooling. The starting rolling temperature is controlled at 950°C, the high-pressure water descaling pressure is 20MPa, the final rolling temperature is 802°C, the φ12mm wire rod is rolled, and the wire-spinning temperature is 785°C. After the wire rod is spun, it is laid flat on the air-cooled roller. The 1st and 2nd fans are turned on to blow-cool the wire rod. After cooling to 680°C, it is slowly cooled in the heat preservation cover to obtain a high-plasticity troostite structure.

[0041] The hot rolled wire rod structure is sorbite + a small amount of ferrite, the sorbite ratio is 90%, the tensile strength is 1068MPa, and the area reduction is 53%. The hot rolled wire rod is treated by the user after pickling, phosphorus saponification, drawing, and cutting, and the hardness of the finished product is 59-60HRC.

[0042] Example 3

[0043] A low-cost high-plasticity alloy steel wire rod for troostite tools. The chemical composition of the low-cost high-plasticity alloy steel wire rod for troostite tools includes, by mass percentage, C: 0.55%, Si: 1.45%, Mn: 0.75%, Cr: 0.69%, Ni: 0.011%, Cu: 0.009%, P: 0.013%, S: 0.004%, and the rest is Fe and unavoidable impurities.

[0044] The method for manufacturing the above-mentioned low-cost high-plasticity troostite tool alloy steel wire rod comprises the following steps in sequence:

[0045] S1, billet smelting, qualified molten iron is subjected to converter smelting and LF furnace refining treatment;

[0046] S2: continuous casting, casting the above molten steel, the continuous casting process adopts a light reduction process, reasonably selects the reduction position and distributes the reduction amount, improves the macrostructure of the ingot, avoids the generation of reduction cracks, and performs surface quality inspection and grinding treatment on the continuous casting ingot;

[0047] S3: Billet heating: The continuous casting billet that has been confirmed by surface quality inspection is heated. In view of the fact that high Si steel is prone to decarburization, the residual oxygen content of the heating furnace is controlled to be ≤3% during the heating process to alleviate the decarburization of the continuous casting billet surface; the temperature of the high temperature section of the heating furnace is controlled to be 1060℃, and the continuous casting billet is heated in the furnace for 118min;

[0048] S4: Controlled rolling and controlled cooling. The heated continuous casting billet is subjected to controlled rolling and controlled cooling. The starting rolling temperature is controlled at 980°C, the high-pressure water descaling pressure is 19MPa, the final rolling temperature is 823°C, the φ5.5mm specification wire rod is rolled, and the wire-spinning temperature is 796°C. After the wire rod is spun, it is laid flat on the air-cooled roller. The 1st and 2nd fans are turned on to blow-cool the wire rod. After cooling to 668°C, it is slowly cooled in the heat preservation cover to obtain a high-plasticity troostite structure.

[0049] The hot rolled wire rod structure is sorbite + a small amount of ferrite, the sorbite ratio is 92%, the tensile strength is 1074MPa, and the area reduction is 55%. The hot rolled wire rod is subjected to tempering treatment after pickling, phosphorus saponification, drawing, and blanking by the user, and the hardness of the finished product is 58-60HRC.

[0050] Comparative Example 1

[0051] The tool alloy steel in this comparative example includes, by mass percentage, the following: C: 0.55%, Si: 1.45%, Mn: 0.75%, Cr: 0.69%, Ni: 0.011%, Cu: 0.009%, P: 0.013%, S: 0.004%, and the rest is Fe and unavoidable impurities.

[0052] After the above components are ground, the qualified continuous casting billet is heated to a heating temperature of 1060°C and a furnace time of 112 minutes. After the billet is taken out of the furnace, it is descaled by high-pressure water, the final rolling temperature is 887°C, and the φ5.5mm specification wire rod is rolled at a wire-spinning temperature of 882°C. After the wire-spinning, natural slow cooling is adopted, and finally 84% sorbite + 14% ferrite structure + 2% bainite / martensite structure is obtained, the wire rod tensile strength is 1092MPa, and the area reduction rate is 44%. The hot-rolled wire rod is subjected to a quenching and tempering treatment after the user's pickling, phosphorus saponification, drawing, and blanking. The hardness of the finished product is 58-60HRC, and it breaks 5-8 times / ton during the drawing process.

[0053] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A low-cost, high-plasticity troostite tool alloy steel wire rod, characterized in that: Measured in percentage by mass, the chemical composition of the low-cost, high-plasticity troostite tool alloy steel wire rod includes: C: 0.55-0.61%, Si: 1.25-1.60%, Mn: 0.60-0.80%, Cr: 0.60-0.80%, Ni: ≤0.35, Cu: ≤0.35, P: ≤0.025, S: ≤0.020, and the rest is Fe and unavoidable impurities.

2. A method for manufacturing a low-cost, high-plasticity troostite tool alloy steel wire rod, characterized in that: The method comprises the following steps in sequence: S1, billet smelting, qualified molten iron is subjected to converter smelting and LF furnace refining treatment; S2: continuous casting, casting the above molten steel, the continuous casting process adopts a light reduction process, reasonably selects the reduction position and distributes the reduction amount, improves the macrostructure of the ingot, avoids the generation of reduction cracks, and performs surface quality inspection and grinding treatment on the continuous casting ingot; S3: Billet heating: The continuous casting billet that has been confirmed by surface quality inspection is heated. In view of the fact that high Si steel is prone to decarburization, the residual oxygen content of the heating furnace is controlled to be ≤3% during the heating process to alleviate the decarburization of the continuous casting billet surface; the temperature of the high temperature section of the heating furnace is controlled to be 1000-1080℃, and the continuous casting billet heating time in the furnace is ≤120min; S4: Controlled rolling and controlled cooling. The heated continuous casting billet is subjected to controlled rolling and controlled cooling. The starting rolling temperature is controlled at 900℃-980℃, the high-pressure water descaling pressure is ≥19MPa, the final rolling temperature is 780℃-840℃, and the wire-spinning temperature is 780℃-840℃. After the wire is spun, it is laid flat on the air-cooled roller. The wire rod density is controlled by adjusting the roller speed. At the same time, the number and frequency of fan opening are adjusted according to different specifications. The cooling rate and phase change are controlled in combination with the number of insulation hood openings. The target hood temperature is 670±10℃, so as to obtain a highly plastic troostite structure.

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