Effect of Deformation Sequence and Coiling Conditions on Precipitation Strengthening in High Ti-Nb-Microalloyed Steels

In this work, multipass torsion tests followed by coiling simulations under different conditions have been performed with a reference Nb (0.03 pct) and a high Ti (0.1 pct)-Nb-microalloyed (0.03 pct) steel. In the case of the high Ti steel, estimated yield strengths close to or over 700 MPa were obtained for some of the conditions researched. However, a very significant effect of previous austenite grain size and strain accumulation on precipitation strengthening has also been observed. As a result, depending on deformation sequence and final cooling conditions, the coiling simulation temperatures that lead to the highest mechanical strength varied from 600 degrees C to 500 degrees C. The effect of increasing strain accumulation was mainly related to higher phase transformation temperatures, which led to a lower driving force for precipitation and higher microalloying element diffusivity, resulting in the formation of less and coarser precipitates.

Automated summary

In this study, multipass torsion tests and coiling simulations were conducted on high titanium and microalloyed steel. The effects of austenite grain size and strain accumulation on precipitation strengthening were observed, leading to different coiling simulation temperatures for the highest mechanical strength.