Constitutive Characteristics, Microstructure, and Texture Evolution of As-Cast 42CrMo Alloy in Nonisothermal Multipass Compression

Fangcheng Qin,Huiping Qi,Haiquan Qi,Zhengbing Meng,Chongyu Liu,Gianfranco Palumbo

doi:10.1155/2021/6638505

Abstract

The nonisothermal multipass deformation behavior of as-cast 42CrMo alloy was studied with declining temperature, constant pass strain, varying strain rate, and interval time. The stresses are used to develop the constitutive model. As the finishing temperature increases from 990°C to 1070°C, the stress decreases gradually and the softening effect increases, which results in a large grain size and inhomogeneous microstructure. The low angle grain boundaries transform into high angle grain boundaries through absorbing dislocations. The noticeable stress softening in a high strain rate is attributed to the thermal softening, dynamic recovery, and dynamic recrystallization. The thermal softening is no longer considered to be the main interpass softening mechanism at a low strain rate. The interval time has a negligible effect on the stress, but the significant changes in grain size and texture component are caused by the interpass softening. The average grain size is approximately 40 μm, and the distorted grain boundaries and small fine grains are found in the interval times of 0.5–5 s, implying the dynamic recovery and grain growth. The near {001}<110> and {110}<112> orientation exerts an important influence on the grain refinement.

Highlights

42CrMo alloy is widely used in the production of ring components such as bearing and flange due to the high strength, excellent fracture toughness, and abrasive resistance [1, 2]. e 42CrMo ring parts are manufactured by the radial-axial hot ring rolling (RAHRR). e RAHRR is a complex process with the characteristics of nonisothermal, multipass, and accumulative deformation and so forth. e wall thickness of ring blank is gradually reduced with a progressively narrowing gap between the driven roll and mandrel. e height is controlled by feeding the upper axial roll towards the lower axial roll [3]. e continuous expansion in diameter and shape in cross section is produced
For industry multipass processing, the nonisothermal process is always undergone with gradually declining temperature [4, 13]. e interaction between hardening and softening effects of as-cast 42CrMo alloy in RAHRR presents the complicated microstructure and texture evolution. e microstructure and texture are affected by the discontinuous characteristics in deformation intervals during multipass rolling [14,15,16]. e grain refinement and size distribution are closely related to the texture evolution. e softening behavior under interpass deformation results in some distinct differences when compared with that under single-pass continuous compression. us, it is critical to clarify the mechanisms of stress softening and grain refinement in discontinuous multipass compression first
The nonisothermal multipass compression of as-cast 42CrMo ally was performed on a Gleeble-3500 thermal simulator, and the effects of finishing temperature, strain rate, and interval time on the stress, microstructure, and texture were studied. e corresponding constitutive model was established. e softening behavior and microstructure evolution mechanism were clarified in detail by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) techniques. e results will provide new insights for the microstructure control and parameter optimization in RAHRR

Summary

Introduction

E effects of temperature and interval time on the microstructure of as-cast 42CrMo alloy were clarified using interrupted isothermal compression [12]. The nonisothermal multipass compression of as-cast 42CrMo ally was performed on a Gleeble-3500 thermal simulator, and the effects of finishing temperature, strain rate, and interval time on the stress, microstructure, and texture were studied.

Results

Conclusion