| The microstructure and mechanical properties of liquid-liquid and solid-liquid composite casting hammer with high chromium cast iron and carbon steel are studied by heat treatment test, hardness test, impact-toughness test, optical microscope (OM), X-ray diffraction (XRD) and scanning electronic microscope(SEM), and the production testing of hammer has been conducted in the mine. The results show that the hardness of high chromium cast iron increases with the increasing of chromium content. The hardness of KmTBCr26NiMo (Cr26), KmTBCr22NiMo (Cr22) and KmTBCr18NiMo (Crl8) is HRC55, HRC49and HRC38respectively. The hardness of high chromium cast iron is within563～642HV and the hardness of eutectic carbide is within1220.0～2226.OHV after normalizing heat treatment. The hardness of M7C3carbide in cross-section is higher than that in longitudinal section.The microstructure of Crl8, Cr22and Cr26mainly consists of tempered martensite, eutectic carbide and residual austenite after normalizing and tempering at200℃for2h. The lath M7C3eutectic carbide discontinuously distributed in the tempered martensite of Cr18. The carbide is M7C3which likes lath or daisy independently distributing in the matrix as a hexagonal rod and its cross-section is hexagonal.The three-stage heat treatment of950℃for2h,820℃for4h and720℃for4h and then furnace cooling to room temperature and the two-stage heat treatment of1050℃for4h and720℃for10h and then furnace cooling to room temperature have a good softening effect on the hardness of Cr22decreasing from HRC49to HRC40. However, the softening effect becomes weak with increasing of Cr content and they have almost no effect on the hardness of Cr26.After normalizing at980℃～1040℃, Cr22possesses high hardness and after normalizing at980℃for0.5h and tempering at200℃for4h, Cr22has a good combination with hardness of62.5HRC and impact toughness of6J/cm2. The microstructure mainly consists of martensite, eutectic carbides, secondary carbides and residual austenite. The fracture mechanism of impact specimen is cleavage and quasi-cleavage fracture.For the solid-liquid composite casting hammer materials, the network ferrites are distributed in the boundary in carbon steel near the interface and for the carbon diffusion from cast iron to carbon steel in high temperature. The proportion of pearlite increases in carbon steel. Due to the diffusion of Cr and C elements, the hardness distribution in the interface of the liquid-liquid composite casting hammer is more smoother than that in the interface of the solid-liquid composite casting hammer. The results of the mining production testing show that high chromium cast iron-carbon steel composite casting hammer has a longer service life than high manganese steel hammer and also has a fairly high cast performance. |
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