Enhancement of elongation by retained austenite in intercritical annealed 0.4C-1.5Si-0.8Mn steel.

Abstract

SynopsisAn excellent combination of elongation over 30 % and high strength about 100 kgf/mm2 is achieved in processing of a 0.4C-1.5Si-0.8Mn steel by intercritical annealing, rapid cooling into bainite transformation temperature to soak several minutes. This combination is caused by transformation induced plasticity of retained austenite. Sufficient amount of stable austenite is a requisite for the good ductility. For the rapid cooling after annealing, the soaking temperature for the best combination of strength and ductility is immediately above Aci. On the other hand, a delay before rapid cooling provides good properties if the soaking temperature is near Ac3 and the subsequent cooling is performed at a lower rate before pearlite transformation; in this case the critical cooling rate is reduced. These phenomena are discussed in terms of the growth of ferrite and the diffusion of alloying elements inclusive of Mn during slow cooling.

Enhanced Low-Temperature Tensile Properties of Fe-14Cr-(4^|^sim;9)Ni Weld Metal by Retained Austenite

“…This research confirms that SIMT can effectively enhance the uniform elongation and strength-ductility balance (Ref [1][2][3][4][5][6][7][8][9][10]. By utilizing this benefit, TRIP steels have been developed.…”

Effects of Copper Addition on Mechanical Properties of 0.15C-1.5Mn-1.5Si TRIP-aided Multiphase Cold-rolled Steel Sheets.

“…Mo-Ka characteristic ray was used, and the volume fraction of retained austenite, V g , was calculated from the integrated intensity of ferrite and austenite peaks using the following Eq. (1), 12,13) V g ϭ1.4I g /(I g ϩ1.4I g ) ........................ (1) where I g and I a are the average integrated intensity obtained at 220 g and 311 g peaks and that obtained at 211 a peak, respectively. The average lattice constant, a 0 , of retained austenite was calculated from the following Eq.…”

“…In the meantime, the ECOCu steel shows higher yield strength than the ECO-0 steel, implying that some other mechanism is working in increasing yield strength, since the effect of increasing the retained austenite volume fraction is negligible in the increase of yield strength in TRIP-aided multiphase steels. 1,3,4,15) It is generally known that the copper addition leads to the effect of precipitation strengthening as fine e-copper particles are precipitated in ferrite grains. 17) In this study, the micro-hardness of ferrite grain of both steels isothermally aged for 3 min at 430°C was measured using nano-indentation tester with the load of 1 g. The hardness value of the ECO-0 was Hv 200 and that of the ECO-Cu was Hv 243.…”

Microstructure and Mechanical Properties of a TRIP-Aided Martensitic Steel

“…In the past decade, some advanced high-strength and ultrahigh-strength sheet steels (AHSS and AUHSS, respectively) such as transformation-induced plasticity (TRIP) [1] -aided sheet steel [2][3][4][5][6][7][8][9][10][11], quench and partitioning steel [12,13], and twinning-induced plasticity (TWIP) steel [14] have been developed in order to reduce the weight and improve the impact safety of automobiles. General ultrahigh-strength TRIP-aided steels such as TRIP-aided bainitic ferrite (TBF) steel are produced by an isothermal transformation (IT) process at a temperature above the martensite-start temperature (M s ) or at a temperature between M s and the martensitefinish temperature (M f ) [6].…”