Examination of the effect of tin particles and grain size on the charpy impact transition temperature in steels

Abstract

The toughness of ferritic steels is influenced by the grain size distribution, second phase, precipitates and coarse inclusions. In this work an examination of the effect of coarse TiN particles (> 0.5 \(\mu\)m) and ferrite grain size on the Charpy impact transition temperature in high strength low alloyed steels has been carried out. Steels with high (up to 0.045 wt %) Ti content, have been heattreated and furnace cooled to obtain a ferrite-pearlite microstructure with different ferrite grain sizes. Coarse TiN particle size and ferrite grain size distributions have been measured and Charpy impact testing has been carried out. Scanning electron microscopy (SEM) analysis was used to measure the grain boundary carbide thickness and for fractographic analysis to determine if the coarse TiN particles are acting as cleavage initiation sites. The Charpy ductile-brittle transition temperatures (DBTT) have been predicted using standard literature equations, and compared to the measured values. It has been found that there was no significant effect of the coarse TiN particles on shifting the Charpy impact DBTT with the DBTT values being adequately predicted by literature equation across the ferrite grain size range from 5 – 27 \(\mu\)m.