Impact of intercritical annealing temperature and strain state on mechanical stability of retained austenite in medium Mn steel

The present investigation was made to study the effect of Al on the microstructure and mechanical properties of hot-rolled medium-Mn TRIP steel (abbreviated as Al-TRIP). As a contrast, a Si-added medium-Mn TRIP steel (abbreviated as Si-TRIP) was also studied. Addition Al in medium-Mn steel can raise Ac3 temperature, which will restrain austenite transformation and expand the two-phase region, promoting Mn and C elements enriched in austenite. In-depth microstructure and mechanical properties analysis were carried out for the hot-rolled Al-TRIP and Si-TRIP steels in this study. The microstructure was characterized by scanning electron microscope (SEM) and electron probe microanalyzer (EPMA). Volume fraction of retained austenite was measured by D/max2400 X-ray diffractometer (XRD). A dual-phase microstructure consisting of ultra-fine grained intercritical ferrite (IF) and lath-like retained austenite (RA) with high mechanical stability was obtained after annealing at 630°C for 2h for Al-TRIP steel. As prolonging the intercritical annealing time, the stability of RA decreased primarily due to the increase of grain size. The tensile test results indicated that the Al-TRIP steel possessed a better combination of tensile strength and elongation compared to Si-TRIP steel. Excellent mechanical properties with yield strength of 790MPa, tensile strength of 1050MPa, total elongation of 35% and UTS×TEL of 39GPa·% was obtained for the Al-TRIP steel.

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Study on the Mechanical Stability of Retained Austenite in Cold-Rolled Medium-Mn Steel

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.936.1283 ◽

2014 ◽

Vol 936 ◽

pp. 1283-1289

Author(s):

Jun Hu ◽

Wen Quan Cao ◽

Jie Shi ◽

Han Dong

Keyword(s):

Mechanical Properties ◽

Retained Austenite ◽

Mechanical Stability ◽

Volume Fraction ◽

Residual Austenite ◽

Tensile Tests ◽

Medium Mn Steel ◽

Cold Rolled ◽

Mn Steel ◽

High Mechanical Stability

The mechanical stability of the retained austenite in the cold-rolled medium-Mn steel was studied. Tensile tests were carried out to measure the mechanical properties of the annealed steel. Scanning electron microscopy was applied to characterize the microstructure evolution during the tensile process; X-ray diffraction analysis was used to determine the residual austenite content in the deformed steel. It was found that the volume fraction of retained austenite gradually decreases with strain .The value of the stability coefficient of retained austenite k was small in the test steel, which indicated high mechanical stability of retained austenite. Due to TRIP effect, the high mechanical stability of the retained austenite strongly delays the onset of necking, which resulted in good comprehensive mechanical properties with ultrahigh strength and plasticity.

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The Effects of Intercritical Annealing Temperature and Initial Microstructure on the Stability of Retained Austenite in a 0.1C-6Mn Steel

Materials Science Forum ◽

10.4028/www.scientific.net/msf.879.1847 ◽

2016 ◽

Vol 879 ◽

pp. 1847-1852 ◽

Cited By ~ 2

Author(s):

Katharina Steineder ◽

Daniel Krizan ◽

Reinhold Schneider ◽

Coline Beal ◽

Christof Sommitsch

Keyword(s):

Mechanical Properties ◽

Retained Austenite ◽

Annealing Temperature ◽

Intercritical Annealing ◽

Strong Dependence ◽

Tensile Tests ◽

Initial Microstructure ◽

Intercritical Annealing Temperature ◽

Batch Annealing ◽

The Stability

The effects of the intercritical annealing temperature and initial microstructure on the stability of retained austenite were investigated for a 0.1C-6Mn (wt-%) steel. Medium-Mn transformation-induced plasticity (TRIP) steels exhibit a strong dependence of their mechanical properties on the variation of intercritical annealing temperature. This behavior is strongly linked to the amount and stability of the retained austenite. Thus, interrupted tensile tests were used to examine the effect of annealing temperature on the stabilization of the retained austenite. Detailed microstructural investigations were employed to elaborate the effects of its chemical and mechanical stabilization. Furthermore, the final microstructure was varied by applying the batch annealing step to an initial non-deformed and deformed microstructure respectively. Retained austenite stability along with resulting mechanical properties of the investigated medium-Mn TRIP steel was significantly influenced as the amount and morphology of the respective phases altered as a consequence of both initial microstructure and applied intercritical annealing temperature.

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