Development of high wear resistance and high chromium cast steel liner

The ball mill for cement industry mainly uses two kinds of wear-resistant products, namely grinding ball and lining plate. In China, the metal materials consumed due to wear are more than 2 million tons, of which the lining plate materials account for about 11%. Therefore, it is of great economic value to improve the service life of lining plate

High manganese steel refers to alloy steel with manganese content of more than 10%. The manganese content of high manganese steel used for ball mill lining is generally 10% – 15%, and the carbon content is generally 0.90% – 1.50%. The as cast structure of high manganese steel is usually composed of austenite, carbide and pearlite, and sometimes contains a small amount of phosphorus eutectic. When the number of carbides is large, it often appears on the grain boundary as a network. Therefore, the high manganese steel with as cast structure is brittle, It needs heat treatment before it can be used. The usual heat treatment method is solution treatment, i.e. heating the steel to 1050 ℃ ~ 1100 ℃, heat preservation to eliminate as cast structure, obtaining single-phase austenite structure, then water quenching, and keeping it to normal temperature. After heat treatment, the strength, plasticity and toughness of the steel are greatly improved

The normal austenite structure of high manganese steel is soft and not wear-resistant. The premise of its wear-resistance is that the austenite structure is subjected to a large impact load, which causes plastic deformation on the metal surface. After deformation, there is obvious work hardening phenomenon in the deformation layer, and the surface hardness is greatly improved. Under low impact load, Hb 300-400 can be achieved; under high impact load, Hb can be achieved 500-800. Different impact load, different surface hardening layer depth, up to 10 mm-20 mm. The hardened layer with high hardness can resist the abrasion of impact abrasive. Under the condition of strong impact abrasive wear, high manganese steel has excellent anti-wear performance, so it is often used as wear-resistant parts in mining, building materials, thermal power and other mechanical equipment. But under the condition of low impact, the work hardening effect is not obvious, High manganese steel can not give full play to its wear resistance

The first generation of cement ball mill liner material is made of high manganese steel. Under the working condition of cement ball mill, the impact force of high manganese steel liner is not large enough, the working hardening is not obvious, the plasticity is too high, the wear resistance is insufficient, and the wear is serious. The market investigation shows that most of the small and medium-sized cement plants in China still use the traditional high manganese steel liner, the economic and environmental benefits are low

The Ni hard cast iron developed in 1930s is the second generation of lining material. Ni hard cast iron is a kind of white cast iron with 5% Ni and 3% Cr added. The pearlite matrix of non alloy white cast iron is replaced by martensite and retained austenite to form a martensitic white cast iron. Because the hard carbide exists on the hard matrix, it is not easy to yield, The wear resistance of the cast iron has been greatly improved. However, the microstructure of the cast iron is very brittle and easy to crack because of the carbide up to 50%

In order to reduce the brittleness of Ni hard cast iron, the third generation of wear-resistant material, high chromium cast iron, has been developed internationally since 1970s. Chromium white cast iron is still the mainstream of wear-resistant cast iron at home and abroad. Cr15, Cr20 and Cr26 series of high chromium wear-resistant cast iron have been mass produced and applied in the United States, Japan and China

The important difference of microstructure between high chromium cast iron and Ni hard cast iron lies in the difference of carbide morphology and hardness. Ni hard cast iron forms continuous network carbide Fe3C. When CR accounts for more than 12%, intermittent block chromium carbide Cr7C3 is formed. Cr7C3 is harder than Fe3C, so its wear resistance is stronger. Carbide morphology changes from continuous network to block, greatly improving toughness. Compared with high manganese steel, high chromium cast iron has better wear resistance, The wear resistance is greatly improved, but due to its high carbon content, its toughness is insufficient, and the high chromium cast iron lining plate is easy to crack in use.