Warm stretch-formability of 0.2%C- 1.5%Si-(1.5-5.0)%Mn TRIP-aided steels

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Warm stretch-formability of 0.2%C- 1.5%Si-(1.5-5.0)%Mn TRIP-aided steels

Journal Title: Archives of Materials Science and Engineering - Year 2016, Vol 80, Issue 1

Abstract

Purpose: Warm stretch-formability of 0.2%C-1.5%Si-(1.5-5.0)%Mn transformation-induced plasticity (TRIP)-aided sheet steels with annealed martensite matrix was investigated for automotive applications. Additionally, the warm stretch-formability was related with the retained austenite characteristics.Design/methodology/approach: This study was aimed to enhance the stretch-formability by warm forming which stabilizes mechanically a large amount of metastable retained austenite in the steels.Findings: The warm stretch-formability increased with an increase in Mn content. The stretch-formability of 5% Mn steel was improved by warm forming at peak temperatures of 150-300°C, which was the same level as that of 0.2%C-1.5%Si-1.5%Mn0.05%Nb TRIP-aided martensitic steel. The superior warm stretch-formability was caused by a large amount of mechanically stabilized retained austenite which suppresses considerably void initiation and growth at interface between matrix and transformed martensite. Higher peak temperatures for the stretch-formability than that for the total elongation was associated with high mean normal stress on stretch-forming.Research limitations/implications: The effect of warm forming on the stretch-formability is smaller than that on the ductility.Practical implications: Investigation results can be easily applied to industrial technology.Originality/value: This paper presents an important result which the stretch-formability of 5% Mn TRIP-aided steel is mainly improved by stabilizing of retained austenite with low stacking fault energy. On the forming, only strain-induced α’-martensite transformation takes place and suppresses the void growth. The strain-induced bainite transformation never occurs during forming in 5% Mn steel, differing from conventional 1.5% Mn TRIP-aided steel.

Authors and Affiliations

K. Sugimoto, H. Tanino, J. Kobayashi

Keywords

Medium Mn TRIP-aided steel stretch-formability Warm forming Retained austenite Mechanical stability strain-induced martensite transformation

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EP ID EP189756
DOI 10.5604/18972764.1229612
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