A Novel Concept of High Cu, Low Mn, Environmentally-Friendly Weathering Steels

Abstract

A novel concept of hot shortness control on copper containing weathering steels is proposed. The weathering effect of copper addition in steels and its improvement in the mechanical and impact properties by age hardening are well known. Again, it is also very well know the problem of cracks on hot processing of those steels, caused by liquid copper segregation, the “hot shortness”. Hot shortness is the main problem of commercial producing of copper containing steels because of the increase of cost production caused by cracks the Ni addition to prevent them. Recent research found that copper segregates surrounding MnS inclusions in the steel, worsening the copper segregation caused by the preferential oxidation of iron on the hot processing of copper containing steels, which is the traditional cause of the “hot shortness”. The same results also show that copper additionally precipitates as CuS in the bulk of the steel. This work points that the “hot shortness” can then be prevented by reducing the Mn in the steel, rather than by the expensive Ni addition. Reducing Mn means reduction of inclusions of MnS sites for copper segregation in the steel. Residual sulphur can therefore be trapped by the copper as finer CuS precipitates, so copper is then dissolved in the bulk of the steel rather than segregated. This paper introduces an alternative solution for the problem of the “hot shortness” by partially or fully replacing the Mn by Cu in those steels. It is then proposed a novel concept of low Mn, or Mn free, Cu containing weathering steels in which Cu replaces Mn in trapping the S. That new steel opens the possibility to a cheaper and easier controls of the “hot shortness” so the copper contamination from scraps become a technological benefit because of its age hardening and weathering effect on steels. The recycling of highly copper contaminated scraps is another important environmental advantage. The conclusion of this work is that the current results introduces a new technology of cheaper copper containing low Mn, or Mn free, high strength, environmentally-friendly weathering steels with high potential market for different welded on shore and offshore specifications.