1.Why are cast metal sheet ingots hot-rolled first instead of being cold-rolled?
Because of cold rolling is to use hot rolled steel coils as the raw material, after acid pickling to remove oxide skin for cold rolling, the finished product is hard roll, because of cold work hardening caused by deformation of continuous cold rolling hard roll strength, increase hardness, toughness and plastic index decreased, so the stamping performance will deteriorate, can only be used for simple deformation of the parts
2.What type of heat treatment is given to the rolled metal sheet after hot and
“warm” rolling? What is its purpose?
轧钢的热处理的类型？轧钢热处理的目的？
Heat treatment of the main types are annealing, normalizing, quenching and tempering, solution treatment and aging treatment, cold treatment, chemical treatment, etc.
Annealing：
The steel is heated to a certain temperature and heat preservation for a period of time, and then make it slowly cooling, called annealing. Steel annealing is a heat the steel to the phase change or part of the phase change temperature, slow cooling after heat preservation heat treatment method. The purpose of annealing is to eliminate tissue defects, improve the organization make composition uniformity and fine grains, increase mechanical properties of the steel, reduce residual stress; Can decrease the hardness at the same time, improve the plasticity and toughness, improve machinability. So before annealing in order to eliminate and improve both the legacy of tissue defects and internal stress, and to prepare for the follow-up process, so the annealing is belong to the intermediate heat treatment, also called heat treatment in advance Normalizing：
Normalizing is heated to above the critical temperature of steel, to all into homogeneous austenitic steel, heat treatment and natural cooling in air. It can eliminate hypereutectoid steel mesh cementite, for hyposteel normalizing can refine crystal lattice, improve comprehensive mechanical properties, low requirements for the parts use the normalized instead of the annealing process is more economic.
Quenching:
Quenching is the steel is heated to above the critical temperature, heat preservation for a period of time, then quickly into the quenching medium, the temperature plummeted, rapid cooling at greater than the critical cooling rate of speed, which is mainly composed of martensite and unbalanced heat treatment method of the organization. Can increase strength and hardness of the steel quenching, but to reduce its plasticity. That is commonly used in quenching hardening agent are: water, oil, caustic soda, and salt solution, etc
