1. Low temperature spheroidizing annealing
Low temperature spheroidizing annealing is to heat the workpiece to below the eutectoid transformation temperature Acl for heat preservation, and then slowly cool down to obtain the heat treatment method of the spheroidization structure. When the temperature of 45 steel forgings is close to 724 ℃, long-term heat preservation is required In this stage, the flaky spheroids will be transformed into spherical pearlites, the hardness of which is within 145HB, and its strength and toughness are better, which lays the foundation for cold extrusion.
2. Quenching
The quenching of 45 steel is to heat the steel to a temperature above Ac3 (hypoeutectoid steel) or Ac1 (hypereutectoid steel), and put it in various cooling media after heat preservation (V cold should be greater than V Lin) to obtain Martensite organization. Because 45 steel has relatively poor austenite stability, it is necessary to quickly quench and cool it after heating in order to obtain a high-hardness martensite structure. 45 steel has good thermal conductivity. When quenching, it can be directly heated to the furnace without preheating. The temperature is selected according to the relevant technical requirements of the workpiece. Generally, the heating temperature is controlled between 860°C and 820°C.
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