Effect of sulfur on the fractographic characteristics of failure for low-carbon low-alloy steel

Abstract

1. An increase in hot-rolled ferrite-pearlite steel 09G2 of sulfur content from 0.007 to 0.040 wt.%, causing an increase in the volume fraction of sulfide inclusions ((0.37...2.12)·10−3) with an almost constant size, leads to an increase by approximately a factor of two in the brittle zones of fractures of the proportion of intercrystalline failure due to segregation of sulfur along ferrite and pearlite grain boundaries, and by a factor of two to ten in the proportion of pitting failure connected with formation of pits at large MnS particle inclusions. The degree of the effect of sulfide inclusions on the proportion of pitting failure increases with a reduction in test temperature from −20 to −60°C. 2. In the transition temperature range (Ttest=−20°C) an increase in the steel of sulfide volume fraction (by a factor of 5.5) does not markedly affect the nature of leading TC microcrack distribution at the tip of a large microcrack: they propagate predominantly counter to a brittle macrocrack. The effect of sulfide inclusions on the nature of leading microcrack distribution becomes marked with a reduction in test temperature to −60°C when the proportion of pitting failure in the brittle fractures of specimens of test steel containing 0.007–0.040 wt.% sulfur differs by a factor of ten due to a marked increase in the proportion of counter leading TC microcracks in the steel with an increase in sulfur content. 3. A tendency is detected towards an increase in ferrite grain size with an increase in sulfur content from 0.007 to 0.040 wt.% in steel 09G2. An increase in volume fraction of sulfides (0.37...2.12)·10−3 does not affect the frequency of TC microcrack generation in ferrite grains.