Plastic Instability in Medium-Carbon Tempered Martensite Steel.

Hai Qiu,Rintaro Ueji,Yuuji Kimura,Tadanobu Inoue

doi:10.3390/ma14164609

Hai Qiu, Rintaro Ueji + Show 2 more

Open Access

https://doi.org/10.3390/ma14164609

Copy DOI

Journal: Materials	Publication Date: Aug 17, 2021
Citations: 1	License type: CC BY 4.0

Affiliation: National Institute for Materials Science

Abstract

Inhomogeneous plastic deformation damages the surface quality of a product in the metal forming process. Therefore, it is necessary to investigate the plastic instability of a metal. Tempered martensite is a common microstructure of medium-carbon steel. Plastic instability (Lüders phenomenon, Portevin-Le Châtelier phenomenon) in this phase was investigated by a uniaxial tension test performed at room temperature. The formation and propagation of a plastic band were analyzed via two-dimensional digital image correlation, and the strain and strain-rate fields were experimentally evaluated. The results obtained are as follows: (1) there was no clear yield plateau on the stress–strain curve; (2) Lüders phenomenon was present, but the Portevin-Le Châtelier phenomenon was not found; (3) in the Lüders deformation process, local strain distribution in tempered martensite is more complicated than that in ferrite.

Highlights

Plastic instability occurs in the deformation process of some crystalline materials in the form of single or multiple plastic bands
The plastic instability occurring in the former period is referred to as the Lüders phenomenon, and that in the latter period is the Portevin-Le Châtelier (PLC) phenomenon
The PLC effect is strongly influenced by the temperature [21] and strain rate [22]

Summary

Introduction

Plastic instability occurs in the deformation process of some crystalline materials in the form of single or multiple plastic bands. Portevin and Le Châtelier [3] found that plastic localization existed in a certain range of a plastic deformation process in aluminum-based alloys and low-carbon steels. Their results showed that plastic instability could take place in the elastic-to-plastic transition region and during the process of plastic deformation. The evolution of strain and strain rate in the tempered martensite of medium-carbon steel in a tension test was analyzed via digital image correlation (DIC), and the possibility of the occurrence of plastic instability was investigated by the obtained experimental results

Experimental Methods

Macroscopic Stress–Strain Curves

Plastic Instability