Flow Curve Analysis of 17-4 PH Stainless Steel under Hot Compression Test

Abstract

The hot compression behavior of a 17-4 PH stainless steel (AISI 630) has been investigated at temperatures of 950°C to 1150°C and strain rates of 10 À3 to 10 s À1 . Glass powder in the Rastegaev reservoirs of the specimen was used as a lubricant material. A step-by-step procedure for data analysis in the hot compression test was given. The work hardening rate analysis was performed to reveal if dynamic recrystallization (DRX) occurred. Many samples exhibited typical DRX stress-strain curves with a single peak stress followed by a gradual fall toward the steady-state stress. At low Zener-Hollomon (Z) parameter, this material showed a new DRX flow behavior, which was called multiple transient steady state (MTSS). At high Z, as a result of adiabatic deformation heating, a drop in flow stress was observed. The general constitutive equations were used to determine the hot working constants of this material. Moreover, after a critical discussion, the deformation activation energy of 17-4 PH stainless steel was determined as 337 kJ/mol.

Hot deformation behavior, dynamic recrystallization, and physically-based constitutive modeling of plain carbon steels

“…This condition was also observed in a stainless steel alloy and subsequently was named as multiple transient steady state (MTSS) behavior [2,3]. This implies that the MTSS behavior might be a general flow behavior.…”

“…Due to the low stacking fault energy of austenite, the kinetics of DRV is slow and hence the DRX process normally occurs during hot forming of steels, which initiates at a critical strain (ε c ). Generally, three types of DRX flow curves have been proposed: single peak [1], multiple transient steady state (MTSS) [2,3], and cyclic [4,5] behaviors, which are dependent on the level of flow stress (deformation temperature and strain rate) and initial grain size [6]. The understanding of the hot deformation behavior together with the constitutive relations describing material flow is a prerequisite for large-scale production in the industry.…”

Hot Deformation and Dynamic Recrystallization of 17-4 PH Stainless Steel

“…This condition may be considered as a transition state between single and multiple peak behaviors and it was called the multiple transient steady state (MTSS) behavior. 8) As shown in Fig. 5(b), there may be an overlap between the end of a given cycle and the onset of the subsequent cycle of DRX.…”

“…Cylindrical samples with diameter of 5 mm and height of 10 mm were used as hot compression specimens, which had the Rastegaev design 8) to hold glass powder as a lubricant material at the contact surface of anvils and specimen. A Baehr DIL-805 deformation dilatometer was used for hot compression test.…”

“…7) Hot deformation processing such as forging for this steel is conducted in the temperature range of stability of austenite phase. 8) Due to the low stacking fault energy of austenite in the 17-4 PH stainless steel, the major restoration process during hot deformation is dynamic recrystallization (DRX). In our literature survey, there was not found any © 2013 ISIJ information on DRX microstructures of this important engineering alloy.…”