Manganese steel, as a large category of wear-resistant steel, mainly includes ordinary high manganese steel and modified high manganese steel. Modified high manganese steel includes modified medium manganese steel and ultra-high manganese steel. There are three ways to improve the application range of manganese steel. One is the re alloying of high manganese steel to increase the yield strength and make it have greater deformation resistance; The second is to change the manganese carbon ratio of high manganese steel and reduce the stability of austenite, so that it can induce martensitic transformation under small induced stress and obtain higher surface hardness; The third is the improvement of production process, such as fine grain strengthening, precipitation hardening, explosion hardening, etc. The above measures have expanded the rational application range of high manganese steel.
High manganese steel refers to alloy steel with manganese content of more than 10%. Austenitic high manganese steel was first discovered by R.A. Hadfield in 1882. It is characterized by low cost and excellent performance. It has been used as wear-resistant material in mining, building materials, metallurgy, energy, railway and other machinery for a long time. Its as cast structure is composed of austenite, carbide and pearlite.
When the amount of carbides is large, they are often distributed in a network on the grain boundary and have great brittleness, so they need solution treatment to be used. Generally, in order to reduce or eliminate carbides, high manganese steel is heated and insulated. Single phase austenite structure is obtained after austenitization of high manganese steel. After water bremsstrahlung treatment, the austenite structure can be maintained at room temperature. At this time, high manganese steel has good initial strength. When austenitic high manganese steel is subjected to impact load, plastic deformation occurs on the metal surface. After deformation strengthening, there is obvious work hardening in the deformed layer, and the surface hardness is greatly improved. It can reach 300-400hb under low impact load and 500-800hb under high impact load. With different impact loads, the depth of case hardening layer can reach 10-20mm. The higher the hardness of the hardened layer, the stronger the impact abrasive wear resistance. High strength steel has excellent wear resistance under the condition of high impact abrasive wear. It is often used in the manufacture of mechanical equipment such as mines, building materials and thermal power. It is precisely because of the excellent wear resistance of high manganese steel based on work hardening that its use is limited. Therefore, in order to expand the application range of high manganese steel, it must be modified.
In recent years, the research progress on alloying mechanism and application of high manganese steel has been reported. The main trend of alloying research on high manganese steel is to obtain dispersed carbide particles on its austenitic matrix by adding CR, Mo, V, Ti, rare earth and other alloy elements to the traditional high manganese steel and carrying out modification treatment, so as to improve the wear resistance of the material, That is, obtaining carbide particles that can produce the second phase strengthening mechanism through alloying is one of the effective ways to improve the wear resistance of traditional high manganese steel. In addition, the strengthening of austenitic matrix by alloying elements and then enhancing its deformation hardening ability is also an important reason to improve the wear resistance of alloyed high manganese steel.
In the 1970s, there were high manganese steel and as cast high manganese steel with alloying elements Mo and Cr abroad. Domestic research on high manganese steel focuses on adding CR, Mo, V, Ti, Nb and other alloy elements for second phase strengthening to improve its yield strength. The structure of as cast high manganese steel is generally austenite plus carbide. After heating the as cast structure to the temperature of austenite zone and holding and solid solution for a period of time, the carbide can be dissolved to obtain a single austenite. After being impacted, it will undergo surface hardening. Under strong impact, the hardness can rise from 200hb to about 500hb. However, the wear hardness of high manganese steel under some working conditions is only 240-350hb, because the high manganese steel has not been fully work hardened in the process of use, so it is very not wear-resistant. Coupled with the low yield strength of high manganese steel, it is easy to deform in work. For example, the use of high manganese steel has been gradually reduced in the United States and Japan. The United States adds 1.5% – 2.5% Cr to high manganese steel to produce standard cast high manganese steel with grade C; Add 0.9% – 1.2% or 1.8% – 2.1% Mo to produce standard cast high manganese steel with grades of E-L and E-2. ASTM a 1281a128m － 93 standard for austenitic manganese steel castings.
In Japan, 1.5% – 2.5% Cr is added to ordinary high manganese steel to produce standard cast high manganese steel with the brand of scmnhl, and 2.0% – 3.0% Cr and 0.4% – 0.7% v are added to produce standard cast high manganese steel with the brand of scmnh21. Japanese high manganese steel casting standard jisgs131-91.