Effects of the Addition of Cr, Mo and Ni on the Microstructure and Retained Austenite Characteristics of 0.2% C^|^ndash;Si^|^ndash;Mn^|^ndash;Nb Ultrahigh-strength TRIP-aided Bainitic Ferrite Steels

Kobayashi, Junya; Ina, Daiki; Yoshikawa, Nobuo; Sugimoto, Koh‐ichi

doi:10.2355/isijinternational.52.1894

Cited by 40 publications

(28 citation statements)

References 16 publications

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“…The authors' previous study [18] also reported that Cr addition improves the comprehensive property of the steel austempered at 350 • C. However, the present study finds that at a lower transformation temperature (400 • C), Cr addition increases the comprehensive property of the steel, whereas Cr addition decreases the comprehensive property of the steel at higher transformation temperatures (430 • C and 450 • C). The difference between the previous result [18,27,28] and the present result may be because the austempering temperatures used in previous studies are relatively lower. In addition, the effect of Cr on bainitic transformation was not studied in references [27,28].…”

Section: Dilatationcontrasting

confidence: 93%

“…The difference between the previous result [18,27,28] and the present result may be because the austempering temperatures used in previous studies are relatively lower. In addition, the effect of Cr on bainitic transformation was not studied in references [27,28]. The authors' previous study [18] reported that Cr addition increases the amount of isothermal bainitic transformation at 350 • C, because high temperature ferritic transformation occurs in Cr-free steel and consumes some untransformed austenite before austempering, whereas no ferritic transformation occurs in Cr-added steel.…”

Section: Dilatationcontrasting

confidence: 93%

“…However, isothermal treatment is not studied in their studies. Sugimoto and his co-workers [27,28] investigated the effects of alloying elements (Cr, Mo, Ni, etc.) on the microstructure, the retained austenite, and the mechanical properties of bainitic steels treated by austempering.…”

Section: Dilatationmentioning

confidence: 99%

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Bainitic Transformation and Properties of Low Carbon Carbide-Free Bainitic Steels with Cr Addition

Zhou

Tian

et al. 2017

Metals

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Two low carbon carbide-free bainitic steels (with and without Cr addition) were designed, and each steel was treated by two kinds of heat treatment procedure (austempering and continuous cooling). The effects of Cr addition on bainitic transformation, microstructure, and properties of low carbon bainitic steels were investigated by dilatometry, metallography, X-ray diffraction, and a tensile test. The results show that Cr addition hinders the isothermal bainitic transformation, and this effect is more significant at higher transformation temperatures. In addition, Cr addition increases the tensile strength and elongation simultaneously for austempering treatment at a lower temperature. However, when the austempering temperature is higher, the strength increases and the elongation obviously decreases by Cr addition, resulting in the decrease in the product of tensile strength and elongation. Meanwhile, the austempering temperature should be lower in Cr-added steel than that in Cr-free steel in order to obtain better comprehensive properties. Moreover, for the continuous cooling treatment in the present study, the product of tensile strength and elongation significantly decreases with Cr addition due to more amounts of martensite.

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Section: Dilatationcontrasting

confidence: 93%

Section: Dilatationcontrasting

confidence: 93%

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Bainitic Transformation and Properties of Low Carbon Carbide-Free Bainitic Steels with Cr Addition

Zhou

Tian

et al. 2017

Metals

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“…On further increasing cooling rate to 110 Ks -1 , the Bs increased again up to 631 °C. It corresponds to observations by other researchers [33,35]. Bs and martensite transformation start temperature Ks -1 .…”

Section: Continuous Cooling Transformation Diagrammentioning

confidence: 99%

Microstructures and mechanical properties of TRIP steel produced by strip casting simulated in the laboratory

Xiong

Kostryzhev

Saleh

et al. 2016

Materials Science and Engineering: A

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Conventional transformation induced plasticity (TRIP) steel (0.17C-1.52Si-1.61Mn-0.03Al, wt%) was produced via strip casting technology simulated in the laboratory. Effects of holding temperature, holding time and cooling rate on ferrite formation were studied via analysis of the continuous cooling transformation diagram obtained here. A typical microstructure for conventional TRIP steels consisting of ~ 0.55 fraction of polygonal ferrite with bainite, retained austenite and martensite was obtained. However, coarse prior austenite grain size of ~80 μm led to large polygonal ferrite grain size of ~17 μm, coarse second phase regions of ~21 μm size, small amount of retained austenite (0.02-0.045) and the presence of Widmanstätten ferrite. Optimisation of the microstructure-property relationship was reached via a variation in the isothermal bainite transformation temperature. The highest retained austenite fraction of 0.045±0.003 with medium carbon content of 1.23±0.01 wt% was obtained after holding at 400 °C, resulting in the highest ultimate tensile strength of 590±35 MPa and largest total elongation of 0.27±0.05. The presence of TRIP effect in the studied steel was revealed through the analysis of strain hardening exponent and modified Crussard-Jaoul model. Effect of processing parameters on retained austenite retention and stress-strain behaviour was discussed. Conventional transformation induced plasticity (TRIP) steel (0.17C-1.52Si-1.61Mn-0.03Al, wt. %) was produced via strip casting technology simulated in the laboratory. Effects of holding temperature, holding time and cooling rate on ferrite formation were studied via analysis of the continuous cooling transformation diagram obtained here. A typical microstructure for conventional TRIP steels consisting of ~ 0.55 fraction of polygonal ferrite with bainite, retained austenite and martensite was obtained. However, coarse prior austenite grain size of ~ 80 μm led to large polygonal ferrite grain size of ~ 17 μm, coarse second phase regions of ~ 21 μm size, small amount of retained austenite (0.02 -0.045) and the presence of Widmanstätten ferrite. Optimisation of the microstructure-property relationship was reached via a variation in the isothermal bainite transformation temperature. The highest retained austenite fraction of 0.045±0.003 with medium carbon content of 1.23±0.01 wt. % was obtained after holding at 400 °C, resulting in the highest ultimate tensile strength of 590±35 MPa and largest total elongation of 0.27±0.05. The presence of TRIP effect in the studied steel was revealed through the analysis of strain hardening exponent and modified Crussard -Jaoul model. Effect of processing parameters on retained austenite retention and stress-strain behaviour was discussed.

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“…TBF steel is produced by an isothermal transformation (IT) process at temperatures higher than the martensite transformation-start temperature (Ms) (when the matrix structure is bainitic ferrite) or between Ms and the martensite transformation-finish temperature (Mf) temperature (when the matrix structure is a mixture of bainitic ferrite and martensite) after austenitizing. 2,3) Q&P steel is fabricated by first quenching the steel at a temperature below Ms after austenitizing and then by partitioning (P) at a temperature higher than Ms (the matrix structure is the same mixture of bainitic ferrite and martensite as in the case of TBF steel). [4][5][6] In order to increase the strength of TBF steel, Sugimoto et al recently developed a C-Si-Mn "TRIP-aided martensitic" (TM) steel with a wide lath-martensite structure and a narrow lath-martensite/metastable austenite-retained complex phase (MA-like phase).…”

Section: Introductionmentioning

confidence: 99%

Effects of Microalloying on Stretch-flangeability of Ultrahigh-strength TRIP-aided Martensitic Steel Sheets

2014

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The effects of Cr, Mo, and Ni addition on the microstructure and stretch-flangeability of a 0.2%C-1.5%Si-1.5%Mn-0.05%Nb (mass%) transformation-induced plasticity (TRIP)-aided martensitic steel sheet produced by an isothermal transformation process at a temperature below martensite transformation-finish temperatures were investigated in order to develop third-generation steel sheet for automobiles requiring high hardenability. When 0.5% or 1.0% Cr was added to the base steel, a tensile strength of 1.5 GPa and a hole-expanding ratio of 40% was attained. On the other hand, the addition of Cr-Mo or Cr-Mo-Ni had a minimal influence on stretch-flangeability and stretch-formability, although it increased the yield and tensile strengths as compared to the base steel. The good balance of the Cr-bearing steel was mainly caused by a suitable combination of (1) volume fraction and (2) interparticle path of a finely dispersed martensiteaustenite complex phase, which suppressed void initiation at the matrix/complex-phase interface on holepunching and void coalescence or crack extension on hole-expanding.

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Effects of the Addition of Cr, Mo and Ni on the Microstructure and Retained Austenite Characteristics of 0.2% C^|^ndash;Si^|^ndash;Mn^|^ndash;Nb Ultrahigh-strength TRIP-aided Bainitic Ferrite Steels

Cited by 40 publications

References 16 publications

Bainitic Transformation and Properties of Low Carbon Carbide-Free Bainitic Steels with Cr Addition

Bainitic Transformation and Properties of Low Carbon Carbide-Free Bainitic Steels with Cr Addition

Microstructures and mechanical properties of TRIP steel produced by strip casting simulated in the laboratory

Effects of Microalloying on Stretch-flangeability of Ultrahigh-strength TRIP-aided Martensitic Steel Sheets

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