Fine Grain Resistance of Steel 20NiMoCr6-5+Nb (Material No. 1.6757) during Case Hardening depending on Cold Massive Forming∗

Abstract

Abstract Cold massive forming of steel has been used for over 100 years to reduce mechanical finishing for cost reasons. A systematic investigation regarding the austenitic grain coarsening in the following heat treatment steps during the application treatment of e. g. gear steels could not be found, only indications of sporadic qualitative failures. The material 20NiMoCr6-5+Nb for gear shafts was subjected to a simulating treatment for the investigation of cold massive forming. No significant coarse grain growth was observed. Because the degree of cold massive forming at the individual shaft sections was not known, oblique samples were taken from the same bar steel lot, with which degrees of forming could be carried out steplessly from ∊ = 0 to 50 % on a press. After simulation of a high temperature carburization from 990 °C to 1050 °C, no significant coarse grain growth could be observed, only a uniform increase of the grain size index G with increasing temperature at the same holding time. In order to gain further knowledge in the field of modern manufacturing processes on the subject, newly available computer programs should to be used to simulate the production of components from case hardened steels from steel production to the ready to install part and to identify weak points.