The heat treatment of steel generally includes quenching, tempering and annealing. The heat treatment of steel affects the properties of metal materials.
1、Quenching: Quenching is to heat the steel to 800-900 degrees, keep it for a certain time, and then rapidly cool it in water or oil, which can improve the hardness and wear resistance of the steel, but increase the brittleness of the steel.
The cooling rate determines the quenching effect. The faster the cooling, the higher the hardness and wear resistance of the steel, but the greater the brittleness. The quenching property of steel increases with the increase of carbon content. The steel with carbon content below 0.2% can hardly be quenched and hardened.
When the pipe is welded with the flange, the heat near the weld is equivalent to quenching, which may cause hardening. However, low carbon steel with carbon content less than 0.2% will not be hardened by quenching, which is one of the reasons why low carbon steel has good weldability.
2. Tempering: The quenched steel is hard and brittle, and it also generates internal stress. In order to reduce this hard brittleness and eliminate internal stress, the quenched steel is usually heated to below 550 ° C, and then cooled after heat preservation to improve the toughness and plasticity of the steel and meet the requirements for use.
3. Annealing: In order to reduce the hardness and improve the plasticity of the steel, facilitate processing, or eliminate the hard brittleness and internal stress generated during cooling and welding, the steel can be heated to 800-900 degrees, and slowly cooled after heat preservation to meet the requirements for use. For example, white iron annealed at 900-1100 degrees can reduce the hardness and brittleness and obtain the malleability.
Post time: Nov-24-2022