抄録
The microstructural factors affecting the yield strength of Mn-Cr-B spring steel ausformed at a comparatively low temperature in the stable phase of austenite and tempered at temperatures of 400°-600°C were investigated by Conrad's method.
The higher yield strength was obtained by this ausforming, but the ductility dropped slightly. The yield strength of the ausformed specimens increased almost linearly with the degree of deformation.
The results of the two-step replica microscopy indicated that relatively large carbides were located preferentially at the martensite boundaries in the conventionally heat-treated specimens, but in the ausformed steel smaller carbides precipitated in a much more uniform and random morphology. Therefore, the mean-free path of carbide was smaller in the ausformed steel than in the conventionally processed specimen.
It has been shown by the structural analysis that the major increase of yield strength by ausforming is attributable to the increase of dislocation density and the contribution of carbide dispersion is relatively small.
