Mold preparatory heat treatment mainly includes annealing, normalizing and quenching and tempering. The main purpose is to eliminate residual structural defects of the blank, facilitate subsequent cold and hot processing, and improve performance and service life. There are always various defects in using traditional equipment for heat treatment. Now, more and more manufacturers are using IGBT medium frequency induction heating equipment for heat treatment, and the results are very good.
(1) The purpose of normalizing is to eliminate the residual carbide network of carbon tool steel and alloy tool steel and refine the uneven flake pearlite. The normalizing temperature is approximately 800-920℃.
(2) The purpose of stress relief annealing is to eliminate residual stress before mold quenching or finishing, or to avoid naphthalene-like fractures that occur during rework and quenching of high-speed steel. Its temperature is mostly 630-700°C.
(3) The purpose of spheroidizing annealing is to obtain satisfactory processability and prepare the structure for quenching. The spheroidized annealing structure has a significant impact on the strength, toughness, distortion, cracking tendency, wear resistance, and fracture toughness after final heat treatment.
The spheroidization temperature is preferably 20-50°C above Ac1. To avoid remaining original flaky carbides or new flaky and angular carbides during the annealing process, many undissolved fine carbide particles should be retained as the crystallization core of spheroidization to ensure that the spheroidization process can be accelerated and Form a uniform spheroid. The isothermal temperature and holding time of spheroidization annealing should be selected so that no flakes or mixed structures of flakes and balls appear, and there is a suitable spheroidization speed range.
(4) The purpose of quenching and tempering is to obtain fine pearlite and ultra-fine carbides, eliminate carbide networks and bands, eliminate residual stress after processing, improve the structure, facilitate machining, prevent quenching cracking and reduce quenching distortion.
The quenching and tempering process of cold work mold steel can adopt a process of quenching at conventional heating temperature and then tempering at 640-680°C high temperature. The hardness after tempering by IGBT medium frequency induction heating equipment is generally ≤229HBS.
The heat treatment process is a key factor affecting the quality of the workpiece's heat treatment. Therefore, it is very important to understand and master the heat treatment process of the workpiece. Today’s article briefly introduces the preparatory heat treatment process of the mold. I hope it can be helpful to your work.
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