The lining plate of cone crusher is a large casting. Combined with the requirements of industrial application, the performance requirements and microstructure design results of Bei Ma multiphase wear-resistant cast steel, the basic heat treatment process of “quenching + tempering” will be adopted for the experimental steel, so as to achieve the multiphase organization with high strength, hardness and considerable bremsstrahlung. In this chapter, taking the quenching and insulation process, quenching process and tempering process of experimental steel as the main starting point, the effects of heat treatment process parameters on the microstructure and mechanical properties of bainite Martian duplex wear-resistant cast steel are studied, and the best heat treatment process of bainite Martian duplex wear-resistant cast steel is obtained.
(1) With the increase of quenching and holding temperature, the comprehensive mechanical properties of the experimental steel first increased, reached the best at 900 ° C, then decreased, and the properties decreased significantly at 1000 ° C. The reason is that the experimental steel first needs sufficient temperature for complete austenitization, and then the quenching and holding temperature directly affects the austenite grain size, strip bundle size and strip block width, and reduces the mechanical properties. However, the sensitivity of strip width to the change of original austenite grain size is not strong, so this effect is amplified at 1000 ° C.
(2) With the increase of quenching cooling rate, the strength and hardness of the experimental steel increase and the toughness decreases. The quenching medium seriously affects the content of bainite and martensite in the structure. In the microstructure dominated by martensite, Mn, s, C and Si compounds at the grain boundary seriously damage the toughness. On the contrary, in the microstructure dominated by bainite, large angle grain boundary and Y203 precipitates are beneficial to the initial toughness.
(3) Due to high density dislocation winding and fine lath structure, the nano hardness of martensite is very high. The nano hardness of bainite is lower due to lower density dislocations and wider laths. The nano hardness of bainite martensite interface is between them, and its substructure is characterized by martensitic twins between bainite laths.
(4) In the tempering temperature range of 250-600 ° C, the experimental steel shows two valley values at 350 ° C and 500 ° C, corresponding to the first and second types of tempering brittleness respectively, which should be avoided in the design of process parameters. When tempering above 500 ° C, the hardness decreases obviously, and the microstructure also changes from tempered martensite to tempered sorbite. Therefore, the experimental steel should be tempered at low temperature.
(5) In conclusion, in order to obtain a good strength toughness fit, the optimal heat treatment process of bainitic Martian multiphase wear-resistant cast steel under laboratory conditions is 900 ° cx2h air cooling or furnace cooling + 300 ° cx2h.