Processing technology of high-hardness wear-resistant steel guide rail

Abstract

The invention discloses a processing technology of a high-hardness wear-resistant steel guide rail, relates to the technical field of alloy tool steel heat treatment, and aims to solve the problems of insufficient wear resistance, large heat treatment deformation, high cracking risk and non-uniform cooling in the production process of the high-hardness wear-resistant steel guide rail in the prior art. The invention provides a high-hardness wear-resistant steel guide rail prepared from 9Mn2CrWV steel, and a processing technology comprising preheating, austenitizing treatment, oil cooling (including heat straightening), primary tempering, deep cooling, secondary tempering and post-treatment. According to the process, by strictly controlling the temperature, the time and the medium of each stage, the hardness, the wear resistance and the structure uniformity of the guide rail are effectively improved, meanwhile, the risks of deformation and cracking are remarkably reduced, and green and environment-friendly production is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of heat treatment of alloy tool steel, in particular to a processing technology for high-hardness wear-resistant steel guide rails. Background Art

[0002] As a key moving component in precision machinery, the performance of guide rails directly impacts the equipment's accuracy, operating efficiency, and service life. High hardness and wear resistance are the most fundamental and crucial performance requirements for steel guide rails. Traditional steel guide rail materials, such as bearing steels like S55C and GCr15, while relatively low-cost and easy to process, often exhibit shortcomings such as insufficient wear resistance and susceptibility to wear when subjected to the harsh conditions of high loads, high precision, or long-term operation. This makes it difficult to meet the longevity and high efficiency requirements of modern industry.

[0003] To improve the wear resistance of guide rails, existing technologies often use surface heat treatment (such as induction hardening and flame hardening) or surface strengthening (such as hard chrome plating). However, these methods have certain limitations: while surface heat treatment can increase surface hardness, it can lead to poor core microstructure properties and a high risk of heat treatment deformation and cracking. While hard chrome plating provides good wear resistance, it poses environmental concerns (including chromium contamination) and the coating is prone to flaking, making it difficult to guarantee a long service life.

[0004] To meet the above challenges, the use of high-performance alloy tool steel to manufacture guide rails has become an inevitable trend. 9Mn2CrWV steel is an alloy tool steel with excellent comprehensive performance. Its high content of carbon, manganese, chromium, tungsten, vanadium and other alloying elements gives it excellent hardness, wear resistance, red hardness and good hardenability. However, during the heat treatment process, high-performance alloy steels such as 9Mn2CrWV steel are more likely to produce internal stress due to their high alloying element content, showing the characteristics of easy deformation and cracking. Especially in the production of large-sized or special-shaped guide rails, the traditional box-type resistance furnace heating method may cause a large temperature difference between the inside and outside of the workpiece and uneven heating, which in turn causes serious quenching deformation and even cracking. In addition, although the traditional oil quenching has a relatively mild cooling rate, for guide rails that require high uniformity, there may still be problems with uneven cooling, and oil quenching has fire risks and serious environmental pollution problems.

[0005] In view of the problems of insufficient wear resistance of guide rails, large deformation during heat treatment, high risk of cracking, uneven cooling and environmental pollution in the existing technology, there is an urgent need for a processing technology that can fully exert the excellent performance of 9Mn2CrWV steel, effectively control deformation and cracking during heat treatment, and take into account environmental protection requirements. Summary of the Invention

[0006] In order to solve the above problems, that is, to solve the problems raised by the above background technology, the present invention proposes a processing technology for high-hardness wear-resistant steel guide rails, which strictly controls the temperature and time nodes of heat treatment, including the following steps: S1, preheating: placing the workpiece in an air furnace to heat up, and when the temperature rises to 500-550℃, keep it warm for 60-80s / mm; S2, austenitizing treatment: moving the workpiece to a salt furnace to heat up, and when the temperature reaches 790-810℃, keep it warm for 30-50s / mm; S3, oil cooling: after reaching the austenitizing temperature, immerse the workpiece in quenching oil with an oil temperature of 65-70℃ to cool it, and when the workpiece cools to 150℃, Remove from the oil and perform heat straightening; S4, primary tempering: subject the workpiece after heat straightening to the first tempering treatment, the tempering temperature is 180-200℃, and the temperature is kept at this temperature for 2-3 hours; S5, deep cooling: place the workpiece after the primary tempering in a deep cooling device, use liquid nitrogen as the refrigerant to reduce the temperature of the workpiece to -70℃ to -80℃, and keep it at this temperature for 1-3 hours; S6, secondary tempering: subject the workpiece after the deep cooling treatment to the second tempering treatment, the tempering temperature is 160-180℃, and the temperature is kept at this temperature for 1.5-2.5 hours; S7, post-processing: subject the workpiece after the secondary tempering to rough grinding, aging, fine grinding and packaging in sequence to finally obtain the steel guide rail.

[0007] The present invention is further configured as follows: the guide rail is made of 9Mn2CrWV steel, and the chemical composition of the 9Mn2CrWV steel is as follows by mass percentage: C: 0.85%-0.95%, Mn: 1.5%-2.5%, Cr: 1.5%-2.5%, W: 0.5%-1.5%, V: 0.1%-1.5%, P≤0.025%, S≤0.025%, and the balance is Fe and unavoidable impurities.

[0008] The beneficial technical effects of this invention are as follows: 1. Significantly improved wear resistance and uniform hardness: The 9Mn2CrWV steel used in this invention, with its optimized chemical composition (particularly precise control of alloying elements such as Mn, Cr, W, and V) and multi-stage heat treatment process (including cryogenic treatment), significantly improves the surface hardness, hardenability, and tempering stability of the guide rail. This gives the guide rail excellent wear resistance and uniform mechanical properties, far exceeding those of traditional materials such as S55C and GCr15, and meeting national standards.

[0009] 2. Effectively Control Deformation and Cracking: This invention effectively mitigates thermal and structural stresses within the workpiece during quenching through precise temperature control during heat treatment and timely thermal straightening during oil cooling. In particular, the application of cryogenic treatment further stabilizes the structure and reduces residual stress, significantly reducing the risk of deformation and cracking in large and special-shaped guide rails, significantly improving yield, and reducing finishing allowances and production costs.

[0010] 3. Uniform and Refined Microstructure: By precisely controlling heat treatment parameters, particularly the austenitization process and cooling rate, and employing cryogenic treatment, the guide rails produced by this invention achieve a finer, more uniform martensitic structure. Furthermore, a rational alloying element ratio and heat treatment process improve inclusion morphology, intergranular toughness, and fatigue resistance, enabling the guide rails to maintain high precision and a long service life even under extreme operating conditions.

[0011] 4. Low defective rate and high economic benefits: This process flow's refined control of each link (from preheating to post-processing) effectively avoids common defects in production (such as quenching cracks, excessive deformation, uneven hardness, etc.), significantly reduces the defective rate, improves production efficiency and economic benefits, and demonstrates excellent production technology level. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The quenching process curve of 9Mn2CrWV steel is shown. DETAILED DESCRIPTION

[0013] Please refer to the attached Figure 1 It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0014] s / mm refers to the time that the workpiece needs to be kept warm at this temperature for each millimeter of thickness or cross-sectional diameter. The purpose is to make the temperature inside the workpiece uniform and ensure sufficient preheating.

[0015] The material of the high-hardness wear-resistant steel guide rail used in the present invention is 9Mn2CrWV steel. The chemical composition of this steel has been carefully designed to ensure its high hardness, high wear resistance and excellent comprehensive mechanical properties.

[0016] The chemical composition and functions of 9Mn2CrWV steel are as follows: Carbon (C): A key element essential for ensuring high hardness and strength in steel. In 9Mn2CrWV steel, the carbon content is typically controlled between 0.85% and 0.95%. This range aims to optimize carbide distribution while maintaining high hardness, avoiding excessive carbon content that can lead to increased carbide inhomogeneity, resulting in brittleness or reduced processability.

[0017] Manganese (Mn): A key element in improving the hardenability of steel, it significantly increases austenite stability, ensures martensite formation during quenching, and compensates for the strength loss caused by reduced carbon content. Manganese also effectively improves the material's wear resistance. In this invention, the manganese content is typically controlled within a relatively high range of 1.5%-2.5% to maximize its contribution to hardenability and wear resistance.

[0018] Chromium (Cr): The content of this steel is typically controlled at 1.5%-2.5%, preferably 2%. Chromium is a medium carbide-forming element that dissolves almost entirely into the austenite during quenching, significantly improving the steel's hardenability and ensuring uniform hardness across the entire cross-section of large workpieces. Chromium carbides (such as Cr23C6) also enhance the stability and hardness of the matrix. Chromium also improves the steel's resistance to oxidation, decarburization, and corrosion.

[0019] Tungsten (W): One of the key elements contributing to the red hardness of alloy steels. A strong carbide former, tungsten can form a variety of high-hardness carbides (such as WC and W2C), primarily as (Fe, W)6C carbides. These undissolved carbides significantly enhance the steel's wear resistance. Furthermore, some tungsten dissolves in the solid solution, providing solid-solution strengthening. In 9Mn2CrWV steel, the tungsten content is typically controlled between 0.5% and 1.5%.

[0020] Vanadium (V): It is also a strong carbide former, particularly forming stable VC. During tempering, VC disperses and precipitates as fine particles, creating a secondary hardening effect on the alloy steel, even more potent than that of tungsten. Vanadium's dispersion hardening significantly improves the alloy's wear resistance. In 9Mn2CrWV steel, the vanadium content is typically controlled between 0.1% and 1.5%.

[0021] Phosphorus (P) and sulfur (S): As harmful impurity elements in steel, their content should be reduced as much as possible. Usually, P is controlled to be ≤ 0.025% and S is controlled to be ≤ 0.025% to reduce defects such as segregation and inclusions and improve the toughness and purity of the steel.

[0022] Example 1: Prepare a high-hardness wear-resistant steel guide rail with a specification of 200mmx50mmx1000mm (length).

[0023] S1. Preheating: Place the guide rail workpiece in an air furnace. Raise the temperature to 530°C at a rate of 20°C / min and keep it at 530°C for 4 hours to ensure uniform temperature inside the workpiece.

[0024] S2. Austenitization: Move the preheated workpiece into a salt furnace. Raise the temperature to 790°C at a rate of 15°C / min and hold at 790°C for 2 hours to ensure full and uniform austenitization.

[0025] S3. Oil cooling: After reaching the austenitizing temperature, quickly immerse the workpiece in a special quenching oil at a temperature of 70°C. When the center temperature of the workpiece drops to 150°C (measured using a thermocouple), immediately remove the workpiece from the oil and perform thermal straightening in a heat-insulating fixture to correct any minor deformation.

[0026] S4. Primary tempering: Place the workpiece after heat straightening in a tempering furnace and keep it at 190℃ for 2h to release some of the quenching stress and prepare for subsequent deep freezing treatment.

[0027] S5. Cryogenic cooling: The workpiece after primary tempering is transferred to a cryogenic device. Liquid nitrogen is used as the cooling medium to reduce the workpiece temperature to -75°C and keep it at -75°C for 2 hours to promote the transformation of retained austenite and improve the hardness and toughness of the material.

[0028] S6. Secondary Tempering: The workpiece after cryogenic treatment is subjected to a second tempering at 170°C for 2 hours to further stabilize the structure, eliminate the stress generated during the cryogenic process, and further improve the toughness of the material.

[0029] S7, post-processing: Rough grinding: Roughly grind the workpiece to remove surface oxide scale and a small amount of deformation layer in preparation for fine machining.

[0030] Aging: Keep the workpiece at 110℃ for 3h for aging treatment to further stabilize the structure and release residual stress.

[0031] Fine grinding: High-precision fine grinding of the workpiece to achieve the final size and surface roughness requirements.

[0032] Packaging: The finished guide rails are packaged to prevent rust and collision.

[0033] Figure 1 The temperature-time relationship from preheating to secondary tempering is schematically shown.

[0034] X-axis: time; Y axis: temperature; Curve 1: preheating curve (500-550℃ insulation); Curve 2: austenitizing treatment curve (790-810℃ holding); Curve 3: Oil cooling curve (to 150°C, including thermal straightening); Curve 4: primary tempering curve (180-200℃ insulation); Curve 5: Deep cooling curve (-70℃ to -80℃ insulation); Curve 6: secondary tempering curve (160-180℃ holding); Curve 7: Post-processing (coarse grinding, aging, fine grinding, packaging).

[0035] The 9Mn2CrWV steel guide rail and its processing technology disclosed in the present invention can significantly improve the hardness, wear resistance and structural uniformity of the guide rail through a refined heat treatment process, especially optimized austenitization, oil cooling (with hot straightening), primary tempering, cryogenic treatment and secondary tempering, and effectively solve the problems of deformation and cracking existing in traditional processes.

[0036] In actual production, the temperature, holding time, and cooling rate of each step need to be fine-tuned based on the specific size and shape of the workpiece and the equipment conditions. The embodiments of the present invention are illustrative only and not restrictive. The scope set forth in the claims encompasses various feasible variations.

[0037] The present invention is not limited to the specific embodiments described herein, but may be modified in various ways without departing from the spirit and scope of the present invention. Those skilled in the art may make various equivalent substitutions or improvements to the present invention based on actual circumstances, and such substitutions or improvements shall fall within the scope of protection of the claims of the present invention.

[0038] The term "comprise" or any other similar term is intended to cover non-exclusive inclusion, such that a process, article, or apparatus / device that comprises a list of elements includes not only those elements but also other elements not expressly listed or inherent to such process, article, or apparatus / device.

[0039] Thus far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present invention.

Claims

1. A processing technology for high-hardness wear-resistant steel guide rails, characterized by: Strictly control the temperature and time nodes of heat treatment, including the following steps: S1. Preheating: Place the workpiece in an air furnace to heat it up. When the temperature reaches 500-550℃, keep it warm for 60-80s / mm. S2. Austenitizing treatment: Move the workpiece into the salt furnace to heat it up. When the temperature reaches 790-810℃, keep it warm for 30-50s / mm; S3, oil cooling: After reaching the austenitizing temperature, immerse the workpiece in quenching oil at an oil temperature of 65-70 ° C to cool it. When the workpiece cools to 150 ° C, take it out of the oil for hot straightening; S4. Primary tempering: The workpiece after heat straightening is subjected to the first tempering treatment at a tempering temperature of 180-200°C for 2-3 hours; S5. Cryogenic cooling: Place the workpiece after primary tempering in a cryogenic device and use liquid nitrogen as the refrigeration medium to reduce the temperature of the workpiece to -70°C to -80°C and keep it warm for 1-3 hours; S6. Secondary tempering: The workpiece after cryogenic treatment is subjected to a second tempering treatment at a tempering temperature of 160-180°C for 1.5-2.5 hours; S7. Post-processing: The workpiece after secondary tempering is subjected to rough grinding, aging, fine grinding and packaging in sequence to finally obtain the steel guide rail.

2. A high-hardness, wear-resistant steel guide rail prepared according to the processing technology of claim 1, characterized in that: The guide rail is made of 9Mn2CrWV steel, and the chemical composition of the 9Mn2CrWV steel is as follows by mass percentage: C: 0.85%-0.95%, Mn: 1.5%-2.5%, Cr: 1.5%-2.5%, W: 0.5%-1.5%, V: 0.1%-1.5%, P≤0.025%, S≤0.025%, and the balance is Fe and unavoidable impurities.

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