en گروه مکانیکی و شکل دادن Mechanical Performance and Formability of Materials Research Paper Research Paper <p style="text-align: justify;"><span style="color: rgb(0, 0, 0);"><span new="" sakkal="" style="line-height: 150%; font-family: ;" times="">Till now, different constitutive models have been applied to model the hot deformation flow curves of different materials. In this research, the hot deformation flow stress of API X65 pipeline steel was modeled using the power law equation with strain dependent constants. The results was compared with the results of the other previously examined constitutive equations including the </span><span new="" style="line-height: 150%; font-family: ;" times="">Arrhenius equation, the equation with the peak stress, peak strain and four constants and the equation developed based on a power function of Zener-Hollomon parameter and a third order polynomial function of strain power a constant number</span><span new="" sakkal="" style="line-height: 150%; font-family: ;" times="">.</span><span new="" sakkal="" style="line-height: 150%; font-family: ;" times=""> </span><span new="" sakkal="" style="line-height: 150%; font-family: ;" times="">Root mean square error (RMSE) criterion was used to assess</span><span new="" sakkal="" style="line-height: 150%; font-family: ;" times=""> </span><span new="" sakkal="" style="line-height: 150%; font-family: ;" times="">the performance of the understudied models. It was observed that the power law equation with strain dependent constants has a better performance (lower RMSE) than that of the other understudied constitutive equations except for the equation with the peak stress, peak strain and four constants. The overall results can be used for the mathematical simulation of hot deformation processes</span></span></p> Constitutive equations, Hot deformation processes, Power law equation, API X65 pipeline steel. 45 53 http://ijmse.iust.ac.ir/browse.php?a_code=A-10-1043-1&slc_lang=en&sid=1 M. Rakhshkhorshid m_rakhshkhorshid@yahoo.com 180031947532846004119 180031947532846004119 Yes Department of Mechanical Engineering, Birjand University of Technology, POBOX 97175-569, Birjand, Iran