Application of Vacuum Heat Treatment Technology in Forging Industry

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As an advanced heat treatment production technology, vacuum heat treatment technology has a development history of more than 40 years in my country. It is widely used in various materials and has many advantages such as no oxidation, good surface quality, small deformation, and no pollution. This article focuses on the typical applications of vacuum heat treatment technology in the forging industry, including vacuum quenching of H13 die steel (oil quenching, high pressure gas quenching, gas oil quenching). Finally, this article puts forward the application prospect of vacuum heat treatment technology in forging industry.

1. Introduction to Vacuum Heat Treatment Technology

Products and parts processed by vacuum heat treatment technology have the advantages of no oxidation, no decarburization, degassing, degreasing, good surface quality, small deformation, and excellent comprehensive mechanical properties. At the same time, vacuum heat treatment equipment also has the outstanding advantages of pollution-free, pollution-free, and high degree of automation, so vacuum heat treatment technology is widely used in the production of various precision product parts. It can be said that vacuum heat treatment has become the main symbol of the current advanced heat treatment production technology.

The basic research of vacuum heat treatment technology in my country began in the 1970s, and then experienced the process of technology introduction, digestion and absorption and independent development. In the 1990s, with the rapid development of aviation, aerospace and other defense industries and machinery manufacturing industries, vacuum heat treatment technology and equipment were popularized. At present, the main products of vacuum heat treatment furnaces in my country are vacuum oil quenching furnaces, vacuum high pressure gas quenching furnaces, vacuum tempering furnaces, vacuum brazing furnaces, vacuum sintering furnaces, vacuum low pressure carburizing furnaces, vacuum nitriding furnaces and vacuum heat treatment continuous production lines.

Vacuum heat treatment technology is widely used in various materials, including ordinary carbon steel, alloy steel, die steel, stainless steel, heat-resistant steel, high temperature alloy, titanium alloy, magnetic alloy, elastic alloy, copper alloy and high-purity aluminum foil. These materials are widely used in industries such as metallurgy, machinery, chemicals, electronics, automobiles, and aerospace.

Forging is the basic industry of the equipment manufacturing industry. In mechanical equipment, forging products account for a high proportion, such as almost all key parts of automobiles (crankshafts, connecting rods, camshafts, half shafts, transmission gears, etc.), and key load-bearing components of aircraft (frames and beams in the aircraft body). , Landing gear, joints, etc.; engine discs, shafts, rings, etc.), nearly half of the parts and components of hydraulic and pump machinery. Almost all of the molds and forging products used to produce these forgings have to undergo heat treatment. Or to improve the formability of the material, or to enhance the mechanical properties and surface quality of parts. As an advanced heat treatment technology, vacuum heat treatment can not only provide quality assurance for many high-quality forging products, but also solve the problem of large energy consumption and environmental pollution in traditional heat treatment. The following is a detailed introduction to several typical applications of vacuum heat treatment technology in the forging industry.

2. Vacuum Quenching of H13 Die Steel

H13 die steel is widely used in hot forging dies, hot extrusion and die casting dies. In order to obtain a bright surface, high strength and high toughness, and reduce cooling stress and distortion, H13 die steels of different sizes and technical requirements often adopt different treatment processes: vacuum oil quenching, vacuum high pressure gas quenching, vacuum oil Compound quenching.

(1) General heat treatment process

The general heat treatment process of H13 die steel is two preheating—austenitizing temperature heating—quenching—twice high temperature tempering. In the preheating stage, the temperature must be increased slowly, the preheating speed of 0～650℃ should be less than 220℃/h, and the preheating speed of 650～850℃ should be less than 165℃/h; the heating phase should be heated as fast as possible to austenitize The temperature is 1030℃; in the quenching stage, the cooling rate should be greater than 28℃/min to avoid pearlite transformation, reduce secondary carbides and bainite as much as possible, and ensure that the deformation is small.

(2) Different quenching methods

1) Vacuum oil quenching

Compared with vacuum oil quenching, vacuum oil quenching can achieve a faster cooling rate, so it is easy to obtain bright surface, high strength and high toughness performance, so most domestic mold steels still use oil quenching technology. For H13 die steel, when the effective size is less than 100mm, the microstructure after oil quenching is only martensite, and there is basically no secondary carbide precipitation, and it has good impact toughness. However, due to the excessive cooling rate, there are also problems of large distortion and high risk of quenching cracking.

2) Vacuum high pressure gas quenching

In order to solve the problem of large oil quenching distortion of H13 die steel and out of tolerance in size, and to achieve the requirements of clean production, more and more vacuum high-pressure gas quenching technology is used in China. However, the cooling rate of high-pressure gas quenching is affected by the size of the mold and the amount of furnace installed. It is possible to obtain a martensite + secondary carbide structure, or it may obtain a martensite + secondary carbide + bainite structure. Both secondary carbides and bainite will reduce the impact toughness of the material. Therefore, in actual production, the atmospheric quenching pressure should be increased as much as possible to increase the airflow cooling rate to avoid these undesirable structures.

3) Vacuum oil compound quenching

In order to take into account the technical requirements of reducing deformation and high strength and toughness, H13 mold steel more uses the process of first inflating and pre-cooling and then oil quenching, which can meet the heat treatment technical requirements of most molds. In addition, the Beijing Institute of Mechanical and Electrical Technology has developed a vacuum oil compound quenching process that uses high-pressure gas quenching in the high temperature zone (1030°C to 540°C) and oil quenching in the low temperature zone (540°C to room temperature) to obtain martensite + two Subcarbide + a small amount of bainite structure, better mold performance. This process is the new trend of H13 die steel heat treatment.

Vacuum low-pressure carburizing technology and high-pressure gas quenching technology are typical green technologies in the heat treatment industry. They have the characteristics of energy saving, environmental protection, and clean production, and are worthy of promotion. The forging industry is facing industrial upgrading, precision forging technology is constantly developing, and the demand for precision heat treatment of various forging products is increasing. As a means of precision heat treatment, vacuum heat treatment technology can effectively reduce thermal stress and structural stress, thereby reducing distortion . It is believed that the application of vacuum heat treatment technology in the forging industry will become more and more extensive, and the combination and development of vacuum heat treatment and forging technology is bound to greatly enhance the level of my country’s advanced manufacturing technology.

Shanghai Geheng Vacuum Technology Co., Ltd. is a vacuum heat treatment furnace manufacturer with many years of experience in design, manufacturing and production. It mainly produces true air quenching furnaces, double chamber vacuum oil quenching furnaces, vacuum annealing furnaces, vacuum tempering furnaces, and other vacuum furnaces.