Volume 8, Issue 3 (March 2011)
Correlation Between Chemical Composition of Steel, Optimal Hardened Layer, and Optimal Residual Stress Distribution
A method for optimizing the chemical composition of steels to obtain optimal residual stress distribution throughout the section of a steel part is proposed, which is based on the analytical equation for the calculation of ideal critical diameter (DI). The advantage of this method consists of the opportunity to calculate the ideal critical size for a variety of geometries on the basis of their respective continuos-cooling transformation (CCT) diagrams. Detailed discussions are provided relating to the optimal depth of the hardened layer, which provides high surface compressive residual stresses and minimal tensile stresses in the core. It is also shown that the ratio of the DI to the diameter of the part with an optimal residual stress distribution should be the same, that is, DI/Dopt=const with steel parts of varying sizes. This relationship can be used for the development of new technologies for large-sized parts based on the results obtained for small parts. The service life of steel parts increases after intensive quenching due to the formation of high surface compressive residual stresses and improved mechanical properties. During intensive quenching, the effect of additional strengthening (super strengthening) of the material is observed, which is connected with the intensification of cooling process within the martensite range.