Indeformability
By indeformability we understand the tendency to retain certain dimensional stability after tempering.
If residual stress after or during sudden cooling are higher the elongation limit of the steel, the parts will twist and change dimensions, causing plastic deformation.
| Internal stress has three causes: |
| Residual stress from part machining. |
| Thermal stress from thermal contraction. |
| Changing stress due to the increase of volume existing between Austenite and the changing product (Martensite). |
Residual stress due to machining is not inherent to the steel and can be eliminated by a stress relief treatment before tempering.
However, thermal and changing stresses in similar tempering conditions do depend on the steel.
Steels with a lower austenization temperature for tempering and a lower critical speed, i.e. those more temperable, are less deformable.
Besides, other factors affect indeformability, such as elongation limit at elevated temperatures, heat conductivity and dilation, and other metallurgical factors related to the manufacturing process of steel, such as micro and macroscopic homogeneity, etc.
