HEAT TREATMENT METHOD FOR SOUNDNESS AND STABILITY OF HIGH C -HIGH CR -(V)TYPE TOOL STEEL MOLD BY IMPROVING MICRO STRUCTURE,HARDNESS AND RESIDUAL STRESS OF ELECTRO SPARK MACHINING AFFECTED LAYER

摘要

The present invention relates to a technical field of manufacturing a mold, which has a mold processing means divided into milling machining and electrospark machining. The electrospark machining is used to process an inside surface and a complex shape, which is a difficult to be processed by the milling machining, and is the final one of the mold manufacturing processes which consecutively include cutting a mold material, tempering for reinforcing the strength of a mold, tempering heat-treatment, and electrospark machining. The principle of the electrospark machining is to melt and form a mold by generating electric discharge (spark) between an electrode and the mold in a metalworking fluid, which makes the structure and hardness of the mold be changed by a melting coagulation layer and a re-tempering layer in accordance with the melting coagulation of the surface of the mold; and therefore an affected layer generating residual stress is formed, which causes the cracking, underfill, deformation, and damage to the mold being in use. Accordingly, the structures of the melting coagulation layer and the re-tempering layer, and the hardness and the residual stress of a mold are required to be improved. The heat treatment method comprises: primarily, tempering and heat-treating an electro spark-machined mold at the high temperatures of a conversion point or less to facilitate the conversion of a residual austenite structure into a martensite structure, lower hardness, relieve residual stress; and secondly, tempering and heat-treating the mold at relatively low temperatures to facilitate the conversion of the residual austenite structure into the martensite structure, stabilize the martensite structure generated in the primary treatment, secure wear resistance and the hardness of toughness, and facilitate the release of residual stress; thereby providing soundness and stability to a mold by preventing the cracking, underfill, deformation, and damage to the mold being in use.