On the Cu precipitation behavior in thermo-mechanically embrittlement processed low copper reactor pressure vessel model steel

Cu precipitation behavior in 30% pre-deformed reactor pressure vessel model steel has been investigated during thermal ageing. In this work, a thermo-mechanical treatment based embrittlement process, including high temperature quenching, pre-deformation and thermal ageing, has been applied to a low-Cu (0.17 wt.%) RPV model steel to produce Cu-rich precipitates. Ultrafine Cu-rich precipitates were observed by transmission electron microscope (TEM) and energy dispersive X-ray microanalysis following this embrittlement process. Moreover, differential scanning calorimetry was used to study the structure transformation of Cu precipitates during long-term thermal ageing. It is noted that for dilute Cu containing steel, high temperature quenching and pre-deformation was found to promote the production of high density of vacancies in calculation, which may facilitate the formation of the fine Cu-rich precipitation. As a result, it leads to a significant hardness peak in the initial stage of thermal ageing. The results were discussed to link with the thermo-mechanical embrittlement process, which provides a method for studying the Cu-rich precipitates formation mechanism in steels containing less concentration of impurity Cu.

► Cu-rich precipitation was found in a low-Cu RPV steel with 0.17 wt.% Cu. ► A thermo-mechanical embrittlement process has been developed in this study. ► DSC results reveal the transformation of bcc to 9R. ► Embrittlement process is a good way to study CRPs formation in dilute Cu alloys.