The characteristics of heat treatment process for high chromium cast iron grinding balls
For example, it is a reasonable and feasible heat treatment process of grinding ball to save energy, equipment, field, good quenching effect, less investment, and big output by using the residual heat after forging, rolling and casting. According to incomplete statistics, the steel and iron balls produced by this process now have an annual output of nearly 600,000 tons and should be vigorously promoted. The hardness of 50N 120mm high chromium ball is HRC 58-62, N. The impact value is 3.9 ~ 6.7 j / CRNZ. METALLOGRAPHIC STRUCTURE: from the surface to the heart are fine needle martensite + carbide. The ball is distinguished by its high hardness and initial cost. As far as its comprehensive economic benefit is concerned, its application in cement industry is successful. It is not suitable to use black metallurgy mine concentrator. The treatment of iron ore is mostly wet grinding, and the friction coefficient between high chromium balls is small.
Taking 80mm as an example, the impact value is about 2.94 j / cm 2, the Rockwell hardness is less than 28-32 and the core hardness is less than 15 in 0-5 mm. 20, commonly known as ordinary cast iron white iron. The fracture surface of the ball is silvery white, the metallographic structure is ledeburite-pearlite, the core is grey-black, the metallographic structure is iron chain + pearlite. The typical common cast iron balls are all cast pig iron of national standard, cast 14-cast 18, 80mm iron balls were once l 3 mm white fracture. The toughness of cast iron ball was improved by adding 30h ~ 5% scrap. If on the basis of casting 14-cast 1880 %, adding 20% iron, the white layer of iron ball fracture is 3-7 mm. The cooling rate is too fast, then the general body for the white mouth. The low-grade iron ball has low hardness and poor toughness. After putting into use, the breakage rate is as high as Loclo-25clo. Grinding ball residual roundness is not good, more gravel-like. It is used for lattice mill, 30 clo-40% of the total ball-throwing volume, and 5%-8% of the grinding efficiency of overflow mill. Even so, some large and medium-sized iron concentrators are still in use.
In the field of alloyed iron balls, medium manganese rare earth magnesium ductile iron balls, meet the technical requirements of GB 3180-82, and low chromium balls. In recent years, a new medium grade iron ball-natural multi-element low alloy quenched iron ball (called quencher ball for short) was introduced On this basis, according to the ball size to adjust the chemical composition, and quenching, tempering heat treatment. There are more than 20 kinds of gold elements in quenching balls, most of which are inherent in Sinter used to smelt pig iron. Therefore, compared with high chromium ball, low chromium ball, medium manganese rare-earth magnesium ductile iron ball, the quenched ball has lower production cost, but its properties can be compared with low chromium ball and all kinds of medium manganese ball. The microstructure of the Matrix is martensite (70qo-75%) + phosphorus eutectic + carbide + sorbite. Impact toughness, value 49-78J / C Ding 12, hardness value according to the size of the ball, can meet the requirements of users. There are 12 series in Dashihe concentrator of Shougang Mining Company. All the two-stage ball mills have been changed to use this kind of Quencher Ball Compared with common cast iron ball without heat treatment, it can reduce consumption by 35% ~ 40 %. It is a promising medium-grade iron ball.