Heat treatment of cold finished
Cold finished pressure-receiving elements, when the amount of deformation during forming is large, cause significant cold work hardening, which increases the strength and hardness of the material, reduces plasticity and toughness, and also generates large internal stress. In order to restore the mechanical properties of the material, the residual machining stress is eliminated or reduced, and if necessary, the cold formed or warm formed pressure member should be heat treated.
Whether the cold finished pressure-receiving element needs to be heat-treated depends mainly on the degree of cold working deformation and the conditions of use of the pressure-receiving element. Generally, the deformation rate is used as an index for measuring the degree of deformation of cold working, and the pressure-receiving element for cold-formed steel sheet is used, and the control index of the deformation rate and other control conditions are as follows.
1) Deformation rate of cold finished compression components
The deformation rate of the steel sheet is calculated as follows:
Uniaxial stretching (such as barrel forming): deformation rate (%) = 50δ (1-Rf/Ro) / Rf
Biaxial stretching (such as head molding): deformation rate (%) = 75 δ (1-Rf / Ro) / Rf
Where: δ - sheet thickness
Rf - the mid-radius after forming
Ro - the mid-surface radius before forming (Ro is infinite for flat plates)
2) Compressed components using cold finished of steel sheets
When one of the following conditions is met and the deformation rate exceeds a certain range, the corresponding heat treatment should be performed after the formation to restore the properties of the material.
For carbon steel and low alloy steel, the thickness before forming is greater than 16mm;
For carbon steel and low alloy steel, the amount of thinning after forming is more than 10%;
For carbon steel, low alloy steel, the material is required to be tested for impact.