Manual Failure Analysis of Large Water Mill Castings

In the process of heat treatment, special attention should be paid to protecting the surface of the cavity from oxidation, erosion, decarbonization or carburization. If the surface carbon content is too high, it will increase the retained austenite and make it difficult or impossible to polish at all. When quenching and cooling, a moderate cooling medium should be used to avoid deformation and cracking. Delayed cooling quenching can be used. Fire or hot bath quenching or air cooling. Free cutting Pre-hardening steel can avoid quenching deformation; maraging steel or high-quality low-alloy aging steel can control aging deformation rate within 0.05%; Stress removal between roughing and finishing and before high finishing can eliminate deformation caused by residual stress; reasonable heat treatment process can be adopted to obtain die steel. Stable structure can avoid the deformation caused by the transformation of structure; steel with small coefficient of thermal expansion can reduce the deformation caused by thermal expansion and cold contraction. Tempering of die should be sufficient, tempering temperature should be higher than working temperature, so as to avoid the tempering transformation of die while working, and thus the structure stress appears on the surface of die cavity.

Of course, the heat treatment of large water grinder processing dies includes preparatory heat treatment, the main purpose of which is to prepare the structure for the final heat treatment of dies.The key to heat treatment is the selection of heating temperature (to ensure the full bath of carbides or the full solid solution of alloy elements), the selection of cooling speed or isothermal temperature (to ensure the uniform distribution of carbides precipitated, to obtain appropriate cutting hardness), such as normalizing, high temperature tempering, and so on. Spheroidizing annealing, quenching and tempering, etc. also include final heat treatment, such as quenching, tempering, surface strengthening, etc.