Improvement of Strength and Impact Toughness for Cold-Worked Austenitic Stainless Steels Using a Surface-Cracking Technique

Kwangyoon Kim,Se-Hun Kwon,Hyunmyung Kim,Dong-Ha Lim,Hyoung-Seok Moon,Jong Jeon,Jaeho Jang,Hyoung Kim,Byung Kim,Minha Park

doi:10.3390/met8110932

Abstract

For cryogenic applications, materials must be cautiously selected because of a drastic degradation in the mechanical properties of materials when they are exposed to very low temperatures. We have developed a new technique using a cold-working and surface-cracking process to overcome such degradation of mechanical properties at low temperatures. This technique intentionally induced surface-cracks in cold-worked austenitic stainless steels and resulted in a significant increase in both strength and fracture at low temperatures. According to the microstructure observations, dissipation of the crack propagation energy with surface-cracks enhanced the impact toughness, showing a ductile fracture mode in even the cryogenic temperature region. In particular, we obtained the high strength and toughness materials by a surface-cracking technique at 5% cold-worked specimen with surface-cracks.

Highlights

The study of very low temperature environments in terms of cryogenics is one field in which the materials play a major part in desirable performances in severe conditions
We have developed a new technique using a cold-working and surface-cracking process to increase the strength and toughness at the same time
After the cold-working process, the microstructure was changed from austenite single phase to dual phases which consisted of austenite

Summary

Introduction

The study of very low temperature environments in terms of cryogenics is one field in which the materials play a major part in desirable performances in severe conditions. Austenitic steels with face centered cubic (FCC) structures such as stainless steels [9], Al alloys [10], Ni alloys [11], and Ti alloys [12] are used as low temperature materials because they have high impact toughness at low temperatures [13,14,15]. These alloys with FCC structure have excellent mechanical properties at low temperatures, brittle fracture may occur in welds and rectangular structures due to the stress concentration [16]. It is Metals 2018, 8, 932; doi:10.3390/met8110932 www.mdpi.com/journal/metals

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