The total amount of alloy of low alloy wear-resistant cast steel is less than 5%, and the total amount of alloy of medium alloy wear-resistant cast steel is less than 10%. On the basis of Si and Mn, low and medium alloy wear-resistant cast steel is superior to high manganese steel in strength and hardness (up to more than 50HRC). Rare earth and boron are also added to some wear-resistant steels in China, which improves the hardenability, microstructure, mechanical properties and wear resistance of the steel. Compared with other wear-resistant cast steels, the grades of low alloy wear-resistant cast steels are more complex because of the variety of alloy elements that can be added. However, generally speaking, the smelting process is easy to master, and the heat treatment process is relatively simple, generally quenching + tempering, which has great advantages in production. If the composition heat treatment process can be designed according to the specific working conditions and ensure the production stability, its application effect is better than that of other steel grades. Multi element low and medium alloy wear-resistant cast steel mainly includes martensitic wear-resistant cast steel and bainitic Martian multiphase wear-resistant cast steel.
(1) Martensitic wear resistant cast steel
Low alloy martensitic wear-resistant cast steel is obtained by “quenching + tempering”, which is divided into water cooling, air cooling and oil cooling. The commonly used water-cooled martensitic cast steels in China are zg30crnimo, ZG30CrMnSiMo, zg30mn2si, and the main brands of water quenched martensite abroad are 4330M, 300m, 333200, etc. Generally, its carbon content is 0.2% – 0.35%. After water quenching and low-temperature tempering, lath tempered martensite can be obtained. Under the condition of ensuring sufficient toughness, the hardness of 50HRC can be obtained. In recent years, with the optimization ofand heat treatment process, the hardness of martensitic cast steel with 0.3% carbon can be increased to 52hrc. The bremsstrahlung AK of 30crmn2si inoculated with RE can be increased from 20-60j to 100J before inoculation and modification. Typical air-cooled martensitic cast steels include Si Mn Cr Mo system and Si Mn Cr Ni Mo system. The preferred composition of air-cooled martensite is 0.4% – 0.6% C, 0.7% – 1.0% Si, 1.3% – 1.5% Mn, 0.5% – 0.6% M0, 0.7% – 0.9% CR. The hardness of air-cooled martensitic cast steel with carbon content of 0.4% can reach 46hrc and AK can reach 16J. Air cooled martensitic cast steel has high carbon content and alloy content, slow cooling rate, easy to produce mixed microstructure of martensite and bainite, and long production cycle. Oil cooled martensitic cast steel can avoid water-cooled cracking. The main grades of oil-cooled martensitic cast steel in China are zg40crnimo, 42cr2si2mnmo, etc. among them, 42cr2si2mnmore can reach 57hrc when it is oil quenched at 930 ° C / s and tempered at 250 ° C / s.
(2) Bainite Martian multiphase wear resistant cast steel
Bainitic martensitic wear-resistant cast steel can be divided into Austempered High Silicon bainitic cast steel and air-cooled bainitic cast steel according to different ways of obtaining. The chemical composition of Austempered bainitic cast steel is mainly: 0.5% – L.L% C, 2.3% – 4.0% Si, 0.3% – 0.6% Mn, 0.2% – 0.4% M0, P < 0.04%, s < 0.04%, an appropriate amount of RE, heat preservation for a certain time after austenitizing, and at a lower temperature (240-400 ° C / s) After isothermal salt bath quenching, the hardness can reach 50HRC and the toughness AK can reach 30J, which has good strength and toughness. Air cooled bainite cast steel obtains bainite through air cooling, mainly including medium and high carbon Mo system and Mn-B series. The Si Mn Mo medium carbon Mo bainite cast steel developed by Kang Mo Kuang of Northwest University of technology has good strength, toughness and wear resistance. Fang Hongsheng of Tsinghua University found that when the Mn content reaches a certain value, the isothermal transformation curve of undercooled austenite can show an obvious “harbor” and separate the C curve up and down. The combination of Mn and B makes the incubation period of high temperature transformation significantly longer than that of medium temperature transformation, so as to obtain Mn-B air-cooled bainite.