experimental study of the effect of hot rolling parameters on the critical temperatures of api x70 pipeline steel

the critical temperatures of a thermomechanical process have a great importance for the final microstructure and mechanical properties of high strength low alloy steels. in this study, the average scheduling was used to determine the critical temperatures of api x70 steel. this steel is extensively used in iran for large diameter, high-pressure gas transportation pipelines as well as the oil transmission networks. the critical temperatures in various conditions including different strains, strain rates (from 0.1 to 1 s-1) and rolling interpass times were determined and the effects of these parameters on no-recrystallization critical temperature (tnr) was investigated. the results showed that tnr decreased with an increase in the strain and strain rate. in addition, it was observed that tnr increased with a decrease in the interpass time. a good agreement was found between the results of this research with those of existing empirical relations and those of similar steel. with regard to the lack of experimental data, the results obtained in the present study can be used for production of api x70 steel in iran.