Effects of Plasma cutting on surface integrity of mild steel

Abstract

Persistent fatigue failure observed in vibrating screen side plates motivated this investigation to determine the effects of plasma cutting on the surface integrity and hence fatigue performance of mild steel plates. Fatigue crack initiation and propagation was reported to have occurred in a number of vibrating screen side plates in which bolt holes had been produced using plasma cutting. This cutting technique had been introduced to reduce bolt hole production times thus replacing the traditional hole drilling technique previously used. This inadvertently modified the surface conditions of the material. Since fatigue is largely a surface phenomenon due to a number of factors such as stress concentration and surface roughness, fatigue strength was unintentionally compromised. A proper assessment is always required to test the effect of new processing techniques on service performance before implementation. Although full scale fatigue testing is too expensive, low cost surface integrity tests can be conducted to assess the impact of the new technique on anticipated fatigue performance. Experimental assessments done on the plasma-cut mild steel plate using microstructure and micro-hardness testing techniques revealed clear evidence of material hardening. Since increased hardening implies increased notch sensitivity, it was therefore concluded that plasma cutting has the effect of reducing the fatigue strength of mild steel components hence the observed fatigue failures in vibrating screen side plates.