Heat treatment process of cold-drawn seamless steel tube: annealing and normalizing. The main differences between annealing and normalizing of cold-drawn seamless steel tube: 1. The cooling speed of normalizing is slightly faster than annealing, the degree of undercooling is larger 2. The microstructure obtained after normalizing is finer, and the strength and hardness are higher than annealing. Selection of annealing and normalizing:
1. Low carbon steel with carbon content less than 0.25% is usually normalized instead of annealing. Because the faster cooling speed can prevent the free tertiary cementite from precipitating along the grain boundary of low carbon steel, thus improving the cold deformation performance of stamping parts; normalizing can improve the hardness of steel and the cutting performance of low carbon steel; normalizing can refine grains and improve the strength of cold-drawn seamless steel tube without other heat treatment processes.
2. Medium-carbon steel with carbon content between 0.25% and 0.5% can also be normalized instead of annealing. Although the hardness of cold-drawn seamless steel pipe approaching the upper limit of carbon content is higher after normalizing, it can still be machined, and the normalizing cost is low and the productivity is high.
3. Steel with carbon content between 0.5% and 0.75% is difficult to be machined because of its high carbon content and its hardness after normalizing is significantly higher than that after annealing. Therefore, complete annealing is generally used to reduce hardness and improve machinability.
４、 含碳量＞ 0.75％的高碳钢或工具冷拔无缝钢管一般均采用球化退火作为预备热处理，如有网状二次渗碳体存在，则应先进行正火消除。退火是将工件加热到适当温度，保持一定时间，然后缓慢冷却的热处理工艺。缓冷是退火的主要特点，退火件一般随炉冷却至550℃以下时出炉空冷。退火是应用非常广泛的热处理，在工模具或机械零件等的制造过程中，经常作为预备热处理安排在铸锻焊之后，切削（粗）加工之前，用以消除前一道工序所带来的某些缺陷，并为随后的工序做好准备。
4. Spheroidizing annealing is generally used as the preparatory heat treatment for high carbon steel or cold-drawn seamless steel pipes with carbon content of more than 0.75%. If there are reticulated secondary cementite, normalizing should be carried out first. Annealing is a heat treatment process in which the workpiece is heated to an appropriate temperature for a certain period of time and then slowly cooled. Slow cooling is the main feature of annealing. The annealed parts are generally cooled with the furnace to below 550 (?) Annealing is a widely used heat treatment. In the manufacturing process of dies, dies and mechanical parts, it is often arranged as a preparatory heat treatment after casting, forging and welding, before cutting (rough) to eliminate some defects caused by the previous process and prepare for the subsequent process.
The purpose of annealing is: (1) to reduce the hardness of materials to facilitate cutting; (2) to eliminate various stresses and prevent deformation of parts; and (3) to refine coarse grains and improve internal structure in preparation for final heat treatment.
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