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Automobile vacuum carburizing gear steel

Most automobile transmission gears are made of alloy carburized steel, which is one of the most widely used alloy structural steels for automobiles.

Due to the differences in resources and industrial development experience in different countries, the steel grades used by countries and even major factories are not exactly the same. However, due to the large production volume of automobiles, reducing the cost of its parts while stably meeting the service performance requirements is an important condition for obtaining a competitive advantage in the market. Therefore, using cheap steel and reducing manufacturing costs are common goals. To this end, the world’s major automobile companies are paying attention to research and development of low-cost steel grades and manufacturing technologies. The steel for automobile gears in various countries is in the transitional stage of development from resource-based and experience-based to scientific and international. Countries are gradually developing from low-alloy CrMo steel and CrMn steel with similar compositions to low-carbon micro-alloyed steel with low price, which is mainly based on ensuring hardenability, making full use of alloy resources in scrap steel, and does not strictly require alloy type and content.

Vacuum carburized gear steel is one of the main structural steels for automobiles. The development of its material technology directly affects the overall technical level of automobile manufacturing, especially the manufacturing level of important structures such as gearboxes and drive axles.

Vacuum carburized gear steel is one of the key materials for automobiles with high requirements. Its metallurgical quality not only directly affects the technical and economic indicators such as vehicle life and energy consumption, but also is crucial to meet the requirements of automobile safety, comfort and environmental protection. The vacuum carburized gear steel for automobiles is developed on the basis of carburized structural steel, which mainly include Cr series, MrCr series, CrMo series, Ni-CrMo series, NiCr series, etc. ISO/R683- 11 Recommended standards include 13 alloy carburized gear steel grade 31.

At present, the focus of designing vacuum carburized gear steels in various countries in the world is different, but they basically follow the following technical requirements:

(1) Sufficient hardenability of the core and good hardenability of the infiltrating layer to ensure that the supercooled austenite decomposition products appear in the infiltrating layer and the core during the vacuum carburizing and quenching of the gear;

(2) The deformation of the gear after vacuum carburizing and quenching is small, which eliminates or reduces the grinding process of the gear, and reduces the energy consumption of production and the noise when the vehicle is running.

(3) Good formability, including thermoplastic deformation forming, cold plastic deformation forming and cutting forming, low energy consumption, high precision, and low mold and tool loss.

(4) Good vacuum heat treatability, including blank normalizing (or annealing) and crystal-producing vacuum carburizing and quenching, reduces energy consumption and shortens production cycle under the premise of ensuring the required performance and fiber structure.

Under normal production and use conditions, the main failure modes of vacuum carburized gears are bending fatigue fracture and tooth surface contact fatigue damage. The research shows that the bending fatigue resistance of carburized gear increases with the increase of strength, and also with the increase of residual compressive stress, the reduction of the size and number of inclusions and the content of impurities in the steel, and the uniform and fine fiber structure and grains. The main factors affecting these parameters are the metallurgical quality of the steel and the carburizing, quenching, and tempering processes, rather than the type and quantity of alloying elements contained in the steel. Therefore, high purity, narrow hardenability and fine grain size are still the main directions for the development of automobile carburized gear steel.

With the increasingly intensified competition in the automobile market, the development of steel for auto parts should be to ensure the service life of parts stably and reliably.

On the premise, strive to reduce costs, including the price of steel and processing costs. For this reason, carburized steel will be developed in the direction of low-priced low-alloy steel and micro-alloy steel, so as to use cheap multi-component iron alloys and alloying elements in scrap steel, and use multi-component and small-scale alloying methods to ensure that certain hardenability requirements are met. Rather than the content of a certain alloying element as a standard. As economical steel types, MrCr steel and MrCrB steel have very broad development prospects. Adding B to MrCr steel can improve the hardenability of the material, strengthen the grain boundary, and can also meet the requirements of the gears with larger modules for the hardenability of automobiles. It may become the main steel grade to replace MrCr Ti steel in the future.

As a high-strength gear steel, CrMo steel has high hardenability, and can obtain a low-carbon martensitic structure with good strength and toughness in the core of large-modulus gears. The application of CrMo steel in commercial vehicles will become better and better. The addition of Ni element to CrMo steel can improve the plasticity and toughness of gears, especially the toughness of the carburized layer, and also improve the hardenability of the steel, which will be the development direction of heavy-duty gear steel; Oxygen content and improving the purity of steel will greatly increase the fatigue life of gears. Therefore, the development of high-purity gear steel is also one of the development directions of gear steel. There are also narrow hardenability belt gear steel and free-cutting gear steel will also be the direction of development.

Selection of vacuum carburizing equipment: The RVC series vacuum carburizing furnace produced by SIMUWU is a high-quality product for the vacuum carburizing process of tools and molds. Good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum carburizing process. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.