The service life of the liner depends on the hardness of the wear-resistant layer of high chromium cast iron, and the hardness of high chromium cast iron must be improved by heat treatment. The austenitizing temperature in the destabilization heat treatment process and the cooling rate in the air flotation process are very important to the hardness of the high chromium cast iron layer of the final composite sample.
Generally, the austenitizing temperature of high chromium cast iron ranges from 850 ° C to 1100 ° C. the parameter selection shall be determined according to the wear resistance and toughness requirements of lining plate castings. The decisive factor of performance is the carbon content of high chromium cast iron in high-temperature austenite matrix. At the beginning, the hardness of martensite increases with the increase of carbon content dissolved in austenite, but when the carbon content exceeds 0.6%, The carbon content in the matrix is supersaturated and tends to be stable. At low temperature, it is difficult to transform into martensite, the hardness decreases, and the residual austenite increases. However, due to the influence of chromium, the best hardness of high chromium cast iron is that the carbon content in the matrix can be as high as 1.1%, the hardness is 66hrc, the carbide accounts for 20%, and the rest are martensite.
Secondary carbide precipitated from austenite plays a dominant role in the transformation characteristics of high chromium cast iron. It occurs not only in the austenitizing process, but also in the air extraction process. In the continuous cooling process, controlling the destabilization during heat treatment is actually controlling the phase transformation of the casting during the continuous cooling process. However, the cooling rate must be controlled by referring to the austenitizing temperature. When high chromium cast iron is treated at 1000 ° C, carbon has high solubility and stability in austenite. When equilibrium is reached, only a small amount of secondary carbides are precipitated from austenite. When it is cooled to room temperature, part of austenite is transformed into martensite, and the rest of austenite remains. Under this condition, The smaller the cooling rate, the more secondary carbides precipitated, the smaller the retained austenite, and thus the higher the hardness. When the austenite temperature is 920 ° C, due to the low solubility of carbon in austenite, more secondary carbides will precipitate when the heat preservation reaches equilibrium. At this time, the content of carbon and chromium in austenite is low, showing de steady state, and all of them can be transformed into martensite at cooling room temperature. In this case, if the cooling process is slow, further secondary carbides will precipitate, The transformation of austenite with low carbon content into martensite with low carbon content makes the hardness of high chromium cast iron not higher after heat treatment.
To sum up, moderate quenching temperature and too large or too small cooling rate will reduce the hardness of the material. Only by matching the quenching temperature and cooling rate can we obtain the highest hardness and ensure the best wear resistance of high chromium cast iron. Therefore, when studying and selecting the austenitic temperature, considering that the cr/c ratio is 7.3, the austenitic temperature is determined to be 1000 ° C. the appropriate cooling rate is specified according to the quenching temperature. According to the hardness test results, the heat treatment process parameters of the composite style selected in the test are very correct.