Fine blanking of pre-hardened high manganese steel to investigate the sheared surface hardening and part quality

Abstract

Abstract. Fine blanking is a highly productive process for manufacturing of high accuracy sheet metal parts with functional surfaces. The specific process characteristic leads to high forming in the shear zone and an associated strain hardening of the sheared functional surfaces. Utilization of the process-immanent sheared surface hardening can reduce time and resources of downstream heat treatment processes such as case hardening. High Manganese Steels (HMnS) are characterized by a high strain hardening capacity due to the deformation mechanisms of twinning and transformation induced plasticity occurring during forming. As a result of high tensile strengths, HMnS are suitable as lightweight materials, but often exhibit a relatively low yield strength in terms of structural design features. One approach for increasing the strength values without changing the alloy design is a forming-induced strain hardening of the semi-finished sheet metal by means of upsetting. Therefore, this paper deals with an experimental investigation of the influence of pre-hardening on the blanked part properties during fine blanking of HMnS X40MnCrAlV19-2 LY (1.7401). For this purpose, sheet blanks were strain hardened by means of flat coining and subsequently fine blanked with an analog geometry representing tribologically stressed functional surfaces. Relevant functional surfaces were then analyzed by means of microhardness measurements with regard to the sheared surface hardening as well as characterized in terms of the quality-determining attributes die roll and clean-shear area. Due to the deformation mechanism of twinning, fine blanking of pre-hardened HMnS resulted in a combination of process-immanent high sheared surface hardening and increased yield strength with simultaneous optimal functional surface quality.