THE INFLUENCE OF SEGREGATION ON HIC IN PRESSURE VESSEL STEELS

摘要

The influence of the composition, microstructure, hardness and geometry of segregation bands on HIC was studied using composite specimens of a low carbon hot rolled steel containing a segregation zone in the form of an artificial segregation band The artificial segregation band (ASB) compositions were chosen to study the influence of segregation intensity at different base manganese and phosphorus levels. Testing was done in NACE solution, Extensive cracking occurred within the ASB when the manganese content reached a level of about 2.0% irrespective of the level of the other elements Two base levels of phosphorus were examined, 0.015 and 0 005%. At a lower manganese level of 1.4% the lower phosphorus content caused a large improvement in HIC performance. The most important factor influencing HIC was the microstructure (and related hardness) of the segregation band which in hot rolled or normalised steels is influenced mainly by the manganese segregation. Thus the probability of HIC failure can be reduced by reducing the manganese content where possible to the order of 0.8% maximum. It is also advantageous to reduce the phosphorus content to a low level of around 0.005% Other effective procedures for minimising the influence of segregation on HIC include tempering after normalising and quenching and tempering.