Abstract
Several 0·4C–Cr–Mo–Ni steels with different sulphur and calcium levels have been studied to determine the effect of the morphology of non-metallic inclusions on the Charpy 2 mm V-notch (CVN) impact properties of quenched and tempered low alloy structural steels. Stringy MnS inclusions which existed in the steel containing sulphur at a commercial level produced a marked anisotropy in Charpy impact properties. The fine elliptical MnS inclusions, which precipitated in steel with a low sulphur content (0·002 wt-%) tempered at 473 K, had a detrimental effect on the upper shelf energy (USE), ductile to brittle transition energy (DBTE), and ductile to brittle transition temperature (DBTT) in a CVN impact test. However, when this desulphurised steel (0·002 wt-%) was tempered at 923 K or the steel was desulphurised to a very low sulphur level (0·0008 wt-%), a beneficial effect on the isotropy of the CVN impact properties was found. Fine particle inclusions which appeared in the calcium treated steel, coupled with a low sulphur content, dramatically improved the isotropy regarding the USE, DBTE, and DBTT for both tempering conditions, whereas two cluster types of composite inclusion which were associated with the calcium treated steel containing sulphur at a commercial level had a detrimental effect on the isotropy regarding the CVN impact properties.
MST/3083
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