High-chromium Cast Ball Heat Treatment Process Research (1)
(Aluminium corporation of China zhongzhou branch, Jiaozuo 454174, China)
Abstract： High chromium cast iron is considered to be the best of the anti-wear properties and has a good toughness of the material, So in this cast iron abroad used widely. For years the ball from high chromium cast in the research and production of experience, To make high chromium cast ball has excellent performance, The key is to have the suitable heat treatment process, And the formulation of appropriate heat treatment process is depends on the correct grasp composition, Quenching temperature, The cooling speed and organization, the relationship between the performance. In this paper the experimental research of the system, In this paper the experimental research of the system, For high chromium cast ball formulating appropriate heat treatment process to provide reliable basis.
Key words： high-chromium cast ball; component; quenching temperature; cooling rate
Cast grinding balls are solidified in high chromium cast iron to form (CR, Fe)7C3 type carbides, which are discontinuous in the structure, so they have much better toughness than ordinary white iron. In addition, the microhardness of (CR, Fe)7C3 is much higher than that of (Fe, CR)3C carbides in common white iron, and it exceeds the hardest abrasive material commonly encountered in abrasive wear, I, so (CR, Fe)7C3 itself has a very high anti-wear effect. The problem is (CR, Fe)7C3 is isolated in the metal matrix; to give full play to its anti-wear role, it must have a hard matrix for support so that in the wear process does not break, break. This means that the Metal Matrix largely determines the wear resistance of high chromium cast iron.
1.Effect of carbon content on properties of high chrome cast iron and composition design of cast ball
The hardness of Martensite is closely related to its carbon content. As shown in Fig. 1, the hardness of Martensite increases with the increase of carbon content, especially in low carbon content. In general, the presence of alloying elements has little effect on the martensite hardness in steel. The effect of carbon content on Martensite’s hardness is mainly due to the solid solution caused by the interaction between Saturated Carbon Atoms and crystal defects in Martensite.
The main reasons for the poor toughness and plasticity of High Carbon Lamellar martensite are:
- the degree of supersaturation of carbon in Martensite, C/A ≥1, serious lattice distortion, and large residual stress;
- The substructure of Lamellar Martensite is mainly twinning. The toughness and plasticity of low carbon Lath martensite are quite good; the main reasons are: 1) Carbon Saturation in Martensite is small, C/A ≈1, lattice distortion is slight, and residual stress is small; 2)The substructures in Lath martensite are mainly dislocations.
The medium temperature deformation heat treatment can refine the martensite structure, increase the dislocation density in Martensite, promote carbide precipitation along dislocations, reduce the carbon content of Austenite, reduce the relative amount of twin Martensite, thus improve the strength and toughness of the high chromium cast ball.
The chemical composition w (%) of the designed high chromium cast ball is: 2.5 C, 16Cr, 0.8 Si, 1.5 Mn, 0.8 W, ≤0.05 S, ≤0.05 P.