Fracture Toughness of Advanced TRIP-Aided Martensitic Steels

Abstract

The effects of microalloying on the fracture toughness of 0.2%C1.5%Si1.5%Mn 0.05%Nb (mass%) transformation-induced plasticity-aided steel with a lath-martensite structure matrix were investigated. When 0.002% B or 1.0% Cr was added to the base steel, the steel achieved a fracture toughness that was as high as that of 18%Ni maraging steel. Based on our results, the high fracture toughness was essentially caused by (i) a matrix with a softened lath-martensite structure, low carbide content and low carbon concentration; (ii) the effective plastic relaxation of localized stress concentration by the strain-induced transformation of metastable retained austenite of about 3 vol% in the martensite-austenite constituent or phase.

Cold Formability of 22SiMnCrB TRIP-aided Martensitic Sheet Steel

“…A variety of third-generation advanced high-strength steels (AHSSs) such as a TRIP-aided bainitic ferrite steel (Sugimoto et al, 2000), medium Mn-TRIP steel (Aydin et al 2013), quenching and partitioning steel (Speer et al, 2004), and quenching-partitioning-tempering steel (Zhong et al, 2009) have been generated with the purpose of developing automobiles with improved crash safety while maintaining a low weight. More recently, Sugimoto et al (2010b) have developed a novel ultrahigh-strength TRIPaided sheet steel, called TM steel, based on a wide-lath martensite structure matrix and a complex secondary phase consisting of narrow-lath martensite and metastable retained austenite. This is achieved through isothermally holding the steel at a lower martensite-finish temperature (M f ) after austenitizing.…”

Low and Medium Carbon Advanced High-Strength Forging Steels for Automotive Applications

“…TM steel can be produced by IT process at T IT lower than M f immediately after hot-forging of austenite, as well as direct quenching to room temperature (Figure 4) [12][13][14][15][16]. If the T IT is near room temperature or direct quenching to room temperature is conducted, partitioning at T P lower than M S is added.…”

“…(II) Second generation AHSS: twinning-induced plasticity (TWIP) high Mn steels [7][8][9][10]. (III) Third generation AHSS: TRIP-aided steels with bainitic ferrite, bainitic ferrite-martensite, and martensite matrix structures (TBF, TBM, and TM steels, respectively) [11][12][13][14][15][16], quench and partitioning (Q&P) steels [7,8,[17][18][19], nanostructured bainitic (Nano-B) steels (or carbide free bainitic steels) [3,4,7,8,[20][21][22][23], dual-phase type and martensite type medium Mn (M-Mn) steels [7,8,[24][25][26], and maraging-TRIP steels [7,27].…”

“…Low and medium carbon TBF [8,11,12], TBM [11][12][13][14][15], and TM steels [12][13][14][15][16] are produced by a similar heat-treatment process to low and medium carbon Q&P, Nano-B, and martensite type M-Mn steels, except Q&P steel subjected to a two-step Q&P process. For the TBF, TBM, and TM steels, isothermal transformation (IT) processes at temperature (T IT ) above the martensite-start temperature (M S ) [11,12], between M S and the martensite-finish temperature (M f ) [11][12][13][14][15] and lower than M f are conducted after austenitizing or annealing [12][13][14][15][16], respectively. Recently, low and medium carbon TBF [28][29][30] and Q&P steels [31] were applied to the automotive body and seats because their steels possess a superior combination of tensile strength and cold formability.…”

Microstructure and Mechanical Properties of Ultrahigh-Strength TRIP-aided Steels

“…TEl 30 GPa % 5-10%Mn-TRIP [33][34][35][36][37][38][39][40][41] TPF 980 1960 MPa TBF 42-51 TBM 52-57 TM [58][59][60][61][62][63][64][65][66][67][68][69][70] Quenching & Partitioning Q&P 28,[71][72][73][74][75][76][77][78][79][80][81] Maraging TRIP TRIP [82][83][84] 22MnB5 85…”