부산대학교 도서관

A novel approach of high‐voltage low‐current energy input is applied for hardening of plain carbon eutectoid steel. Initial fine lamellar pearlitic structure disintegrates into four characteristic regions: lamellar pearlite often containing nucleated cementite spheroids (Region‐I), fragmented cementite lamella in α‐ferrite matrix (Region‐II), submicroscopic cementite particles/clusters dispersed in α‐ferrite matrix (Region‐III), and supersaturated α‐ferrite (Region‐IV). At a particular applied voltage, structural refinement and matrix supersaturation (evolving martensite) progress concomitantly up to 5 min, followed by a reverse trend of coarsening and degeneration of martensite. The refinement effect and martensite‐peak‐broadening effect are augmented with increasing voltage up to 75 kV at which the highest hardness (429 HV) of the steel is achieved with treatment duration of 5 min. While primary hardening effect arises from the martensite region of stratified plate morphology (Region‐IV), a secondary effect of hardening is resulted from the region containing dispersed submicroscopic cementite particles/clusters in α‐ferrite matrix (Region‐III). In addition, in the specimen exhibiting maximum hardening effect (at 75 kV, 5 min), as a unique feature, nanosized cementite particles also appear in Region‐IV being dispersed in martensite matrix so as to provide further effect of dispersion hardening along with martensitic hardening. [ABSTRACT FROM AUTHOR]