Effect Of Temperature an‎d Strain Rate On Hot-Working Behavior an‎d Microstructure Of Stainless Steel 17-7PH

5/11/2019 12:00:00 AM

The stainless precipitated hardened semi austenitic 17-7PH steel, with a bi-phase microstructure (austenite-δ ferrite) has a wide application in military, aerospace, chemical, oil and petrochemical industries. There are some statistical deficiencies in observing the thermo-mechanical behavior of 17-7PH steel as well as its flow curves. Regarding the aforementioned case, in this study, hot press tests were performed in a temperature range of 950 – 1100 0C and strain range of 0.001-1 S-1 until the strain value of 0.6 is reached. Analyzing the flow curves of 17-7PH alloy, after correction too friction and the generated heat during deformation revealed that the flow stress is severally sensetive to temperature and strain rate changes. So that by increasing temperature and decreasing strain rate resulted to a decrease in flow stress. Also to investigate the microstructural evolution during hot deformation, hot press tests were performed until strain values of 0.15, 0.30 and 0.45 are reached at 950 and 1050 0C, utelizing strain rates of 0.001 and 1 S-1. microstructureal evaluations were performed by optical microscope. These observations showed that the dominant deformation mechanism was continuous dynamic recrystallization (CDR). Furthermore the hot deformation tests were performed in this study to investigate the stress dependency of strain rate to temperature. By calculating the constants of the principal equations, the sinus-hyperbolic equation was found to be operative in this study. This equation presents a good approximation of flow stress of 17-7PH alloy in high values of Z. The alloy process charts were also drawn in this study, focusing on changes of energy consumption efficiency and strain rate. These charts proove the deformation stability of 17-7PH alloy under various test conditions. Regarding the resultsobtained from this chart, temperature range of 1050 -1100 0C was suggested as the appropriate condition for hot-working process. Finally, energy consumption efficiency map at different temperature conditions ranging from 1050 to 1100 0C and strain rates (below S-1) was suggested as appropriate hot-working conditions.