Adhesion behavior in sliding test of austenitic stainless steel on VC coated by TRD process

บทคัดย่อ

Austenitic stainless steel is prone to adhere to tool steels which are used as forming tools. This causes difficulties in the formation of stainless steels. Hard coating on forming tools is a method to diminish adhesion problems. In this work, adhesive behavior of stainless steel was tested against VC coated by thermo-reactive deposition and diffusion (TRD) process. Sliding wear test was conducted under unlubricated condition at room temperature by a ring-on-disc tester. AISI 304 was used as a ring for sliding couple with VC coating layer. DC 53 steel was used as a disc on which VC with a thickness of 7 microns was coated in molten borax salt bath under ambient atmosphere. Normal load and sliding velocity in sliding test were varied in the range of 120 – 320N and 0.716 – 2.148 m/s, respectively. The wear track was investigated by optical microscope and scanning electron microscope (SEM). The chemical composition of the ring surface was identified by X-ray energy dispersive spectroscopy (EDS). It was found that weight loss of the ring increased gradually with increasing normal load from 120N to 220N; it then increased abruptly until the load reached 320N. The EDS analysis of the ring surface for a load of 320N showed that the ring surface contained higher oxygen content than that without wear testing. This implies that oxide of Cr and Fe on the ring surface contributed to adhesion, resulting in higher weight loss for a load of 320N. In the case of sliding velocity, the weight loss of SS ring increased from a velocity of 0.716 m/s to 1.432 m/s; it then seemed to remain constant with increasing sliding velocity. The thick Cr-oxide layer which formed on the stainless steel surface during sliding test might have prevented adhesion.