Retained Austenite Characteristics and Tensile Properties in a TRIP Type Bainitic Sheet Steel.

Sugimoto, Koh‐ichi; Iida, Tsutomu; Sakaguchi, Jyunya; Kashima, Takahiro

doi:10.2355/isijinternational.40.902

Cited by 233 publications

(137 citation statements)

References 18 publications

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“…5. 36) The decrease in yield strength with increasing cooling rate, as observed in Fig. 6, can be related to the lower content of pearlite, the presence of low strength ferrite, and some austenite in agreement with results reported by other investigators.…”

Section: Mechanical Properties 421 Influence Of Reheating Temperatsupporting

confidence: 81%

Impact Toughness and Tensile Properties Improvement through Microstructure Control in Hot Forged Nb-V Microalloyed Steel

et al. 2005

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The influence of thermomechanical processing parameters such as reheating temperature, deformation temperature, deformation percent and cooling rate on achieving high impact toughness properties was studied in a Nb-V microalloyed steel to be used as forged parts in automotive applications. 15 mm long and 65 mm diameter billets were forged using a 20 MN mechanical press. Tensile and Charpy impact tests specimens were machined out of the central part of the forged billets. The microstructure of the specimens was examined for each experimental condition using optical microscopy. Phase identification and distribution was studied using X-ray diffraction and orientation image microscopy techniques. The results indicate that, increasing the reheating temperature above the dissolution temperature of (Nb)(C, N) improved the impact energy values. By increasing the cooling rate from 0.3 to 3°C/s both tensile strength and impact toughness were improved. High elongation percent was also observed on samples reheated at higher temperature and/or cooled with the higher cooling rates. The obtained mechanical properties were related to the characteristics of microstructural components including acicular ferrite, retained austenite, pearlite and ferrite.The interrelationship between thermomechanical processing parameters, microstructure development, and final mechanical properties were identified and optimized forging conditions to obtain high impact energy (Ͼ30 J) microalloyed forge steels were determined.KEY WORDS: microalloy steel; mechanical properties; acicular ferrite; forging.The growth of ferrite plates results in carbon enrichment of the remaining austenite, which may remain untransformed or transform to martensite, bainite or interlath carbides. Upon the application of strain, the untransformed austenite is converted to martensite, which would increase strain hardening and residual compressive stresses bringing higher resistance to necking and crack arrest properties, respectively. 24) In the acicular ferrite microstructure, refining the ferrite lath size, eliminating pearlite, minimizing the development of interlath carbides, and control of the amount and distribution of retained austenite are critical for the achievement of optimum strength and toughness properties. 7,9,25) In the present article the influence of thermomechanical process parameters on the above mentioned microstructural characteristics particularly with regard to the formation of acicular ferrite and the resultant mechanical properties of a Nb-V microalloyed steel is investigated. The overall objective of the study was the development of a forging process to produce high strength-high toughness (tensile strength Ͼ850 Mpa, impact energy at room temperature Ͼ30 J) microalloyed forged automotive safety parts such as axles, hubs and steering parts. Material and Experimental ProceduresThe material used in this investigation was a Nb-V microalloyed steel produced in an electric arc furnace equipped with semi-automatic charging system and oxy-gas burners. Sec...

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Section: Mechanical Properties 421 Influence Of Reheating Temperatsupporting

confidence: 81%

Impact Toughness and Tensile Properties Improvement through Microstructure Control in Hot Forged Nb-V Microalloyed Steel

et al. 2005

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“…It is important that the steels A-E do not contain any cementite in the bainitic ferrite lath structure, differing from the conventional structural steels such as SCM steels, as previously reported. [1,4] Figure 6(a) shows the variations in an initial volume fraction and carbon concentration of retained austenite as a function of hardenability factor in steels A-E. It is found that the carbon concentration decreases with increasing hardenability.…”

Section: Methodsmentioning

confidence: 99%

“…Advanced C-Si-Mn high-strength transformation-induced plasticity (TRIP)-aided steel with bainitic ferrite structure matrix (TRIP-aided bainitic ferrite steel; TBF steel) [1][2][3][4] possesses a good combination of tensile strength and stretch-flangeability. So, commercial TBF steels with tensile strength of 980-1180 MPa are applied to some automotive members in Japan.…”

Section: Introductionmentioning

confidence: 99%

Notch-Fatigue Properties of Advanced TRIP-Aided Bainitic Ferrite Steels

Yoshikawa

Kobayashi

Sugimoto

2012

Metall Mater Trans A

Self Cite

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To develop a transformation-induced plasticity (TRIP)-aided bainitic ferrite steel (TBF steel) with high hardenability for a common rail of the next generation diesel engine, 0.2%C-1.5%Si-1.5%Mn-0.05%Nb TBF steels with different content of Cr, Mo and Ni were produced. And, notch-fatigue strength of the TBF steels was investigated and was related to the microstructural and retained austenite characteristics. If Cr, Mo and/or Ni were added to the base steel, the steels achieved extremely higher notch-fatigue limits and lower notch-sensitivity than base TBF steel and the conventional structural steels. This was mainly associated with (i) carbide-free and fine bainitic ferrite lath structure matrix without pro-eutectoid ferrite, (ii) a large amount of fine metastable retained austenite and (iii) blocky martensite phase including retained austenite, which may suppress a fatigue crack initiation and propagation.

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“…Microstructures are generally formed by a bainitic ferrite matrix with or without carbides, depending on the alloying elements and the isothermal holding time, and retained austenite, in the form of thin films or martensite-austenite (MA) islands. [7][8][9][10][11][12][13] The isothermally obtained phase product is generally called bainite. While the bainitic ferrite is free of carbides in upper bainite, lower bainitic ferrite can contain a fine dispersion of plate-like carbides, depending on the silicon content.…”

Section: Introductionmentioning

confidence: 99%

Effect of Prior Athermal Martensite on the Isothermal Transformation Kinetics Below M s in a Low-C High-Si Steel

Navarro-López

Sietsma

Santofimia

2015

Metall Mater Trans A

106

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A. NAVARRO-LÓ PEZ, J. SIETSMA, and M.J. SANTOFIMIA Thermomechanical processing of Advanced Multiphase High Strength Steels often includes isothermal treatments around the martensite start temperature (M s ). It has been reported that the presence of martensite formed prior to these isothermal treatments accelerates the kinetics of the subsequent transformation. This kinetic effect is commonly attributed to the creation of potential nucleation sites at martensite-austenite interfaces. The aim of this study is to determine qualitatively and quantitatively the effect of a small volume fraction of martensite on the nucleation kinetics of the subsequent transformation. For this purpose, dilatometry experiments were performed at different temperatures above and below the M s temperature for athermal martensite in a low-carbon high-silicon steel. Microstructural analysis led to the identification of the isothermal decomposition product formed above and below M s as bainitic ferrite. The analysis of the transformation processes demonstrated that the initial stage of formation of bainitic ferrite at heat treatments below M s is at least two orders of magnitude faster than above M s due to the presence of martensite.

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Retained Austenite Characteristics and Tensile Properties in a TRIP Type Bainitic Sheet Steel.

Cited by 233 publications

References 18 publications

Impact Toughness and Tensile Properties Improvement through Microstructure Control in Hot Forged Nb-V Microalloyed Steel

Impact Toughness and Tensile Properties Improvement through Microstructure Control in Hot Forged Nb-V Microalloyed Steel

Notch-Fatigue Properties of Advanced TRIP-Aided Bainitic Ferrite Steels

Effect of Prior Athermal Martensite on the Isothermal Transformation Kinetics Below M s in a Low-C High-Si Steel

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