A STUDY OF THE EFFECT OF ANNEALING HEAT TREATMENT ON THE FATIGUE PROPERTIES OF 0.17%C HSLA STEELS: A STATISTICAL APPROACH

Abstract

The present study investigated the effect of annealing heat treatment on the fatigue properties of

0.17%C of HSLA steels using a statistical approach. The Carbon equivalent (CE) was first

calculated to determine the ideal starting point for annealing which is 840oC from the Iron Carbon

phase diagram. The steel samples were then exposed to multi-régimes of annealing temperatures

namely; 840 oC, 870 oC, 900oC, 930oC, 960oC and 990oC at 30oC interval they were then soaked

for 30 minutes. Some of the samples were thereafter machined into fatigue samples before being

subjected to fatigue test. Quantitative metallography was also carried to examine its micro

structure; results showed that for the steel under study, higher annealing temperature improved

the fatigue properties significantly. Highest number of cycles being recorded at 3.9 Ⅹ 103 and 1.3

X 103 at 321.3 MPa and 1606.57 MPa stress levels for samples annealed at 990 oC, this is followed

closely by samples annealed at 960 oC which had 3.5 X 103 and 0.8 X 103 number of cycles at the

same stress levels before failure. The control had the least number of cycles of about 0.9 X 103 and

0.1 X 103 at the same stress levels, and, standard deviation of 5.960 and a mean of 26.881 which

shows that annealing greatly improved the fatigue life of the steel. The implemented software

(ANOVA) test confirmed the results at 95% confidence which further showed that there was

significant difference amid the annealing parameters and, it shows promising results.