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Low alloy wear-resistant steel and its vacuum heat treatment process

Wear is one of the main forms of workpiece failure, and it generally exists in various application fields of steel materials. While catastrophic failures due to wear are rare, industrial economic losses due to wear causing workpieces to fail are quite staggering. The proportion of energy consumption due to wear is as high as 1/2 in the world every year, and 80% of materials fail due to unreliable applications caused by wear. Although the wear of metal materials will not directly cause serious consequences, the industrial economic loss caused by the wear and tear of the workpiece failure is particularly serious.

Wear-resistant steel is a general term for steel materials with excellent wear resistance, and it is also the material with the largest amount of wear-resistant materials today. In addition to traditional austenitic manganese steel, modified high manganese steel, and medium manganese steel, wear-resistant steel can be divided into low-carbon, medium-carbon, medium-high carbon, and high-carbon alloy wear-resistant steel according to the amount of carbon; It can be divided into low-alloy, medium-alloy and high-alloy wear-resistant steel; according to the structure type, it can be divided into austenite, bainite, and martensitic wear-resistant steel. Low-alloy wear-resistant steel is a low-alloy steel used in conditions where wear is the main failure mode, and its cost is relatively low. Therefore, research and development of low-alloy steel with good wear resistance or wear reduction performance and excellent comprehensive mechanical properties Wear-resistant steel, saving energy and reducing consumption.

Microstructure and properties of low alloy wear-resistant steel

The hardened structure in low alloy wear-resistant steel mainly includes martensite (including lath martensite and sheet martensite), bainite (upper and lower bainite), retained austenite and undissolved carbide things etc. Low-alloy high-strength wear-resistant steel can obtain the composite structure of lath martensite and retained austenite through alloy element control and vacuum quenching + vacuum tempering; through isothermal treatment or continuous cooling, lower bainite or bainite can be obtained , The composite structure of martensite, its wear resistance is higher than that of simple martensite.

The hardness and wear resistance of low-alloy wear-resistant steel are its main performance indicators. At the same time, it is also required to have certain plasticity, toughness and brittle fracture resistance, high strain fatigue strength, and good processing performance.

Vacuum heat treatment process of low alloy wear-resistant steel

Low-alloy high-strength wear-resistant steel is usually alloyed with chromium, nickel, molybdenum and other elements, and then vacuum quenched and vacuum tempered to obtain lath martensite and a small amount of retained austenite distributed between the laths.
High-strength wear-resistant steel products have inherent properties such as high hardness, high toughness, and high strength, so as to achieve the purpose of “high wear resistance, easy processing, and cost reduction”.

The production of NM450 high-strength wear-resistant steel plates in steel mills mostly adopts the heat treatment process of quenching + low temperature tempering. The NM450 steel is kept at 900°C for 30 minutes, water-cooled to room temperature quenching process, and then tempered. After low-temperature tempering at 200°C~350°C, the segregation of NM450 has not been completely eliminated, but its structure has become more and more uniform. also decreased. Tempering temperature has a great influence on the hardness of NM450 steel. With the increase of tempering temperature, the hardness of NM450 decreases. With the prolongation of tempering time, the structure of NM450 steel does not change much, but the hardness is not obvious. Decline. Ma Heng et al. used ordinary NM450 steel. On the premise of ensuring the strengthening of microalloy elements, they adopted controlled rolling and air cooling after rolling. ℃, keep warm for 25 minutes to eliminate quenching stress, reduce brittleness, and obtain martensite + retained austenite + acicular bainite structure, and the content of bainite gradually increases from the surface to the center, the size increases, and the distribution is more uniform , so as to achieve the best overall performance.