Effects of Hot-Forging Process on Combination of Strength and Toughness in Ultra High-Strength TRIP-Aided Martensitic Steels

Recently developed ultra high-strength low alloy transformation-induced plasticity (TRIP)-aided steel with martensitic lath structure matrix or "TRIP-aided Martensitic steel; TM steel" possesses a high impact toughness. In this study, to apply the TM steel to some hot-forging parts, the effects of hot-forging on microstructure, retained austenite characteristics, tensile properties and toughness in the TM steels with chemical composition of 0.3-0.4%C, 1.5%Si, 1.5%Mn, 0.002%B, 0.02Ti, 0.05Nb (mass%) were investigated. The hot forging brought on an excellent combinations of tensile strength of 1500-2000 MPa or 0.2% offset proof stress of 1200-1560 MPa and Charpy impact absorbed value of 35-80 J/cm2 when partitioned at 250-350°C after quenching in oil. The combinations exceeded so much those of the conventional quench and tempering structural steels. From examinations of microstructure and retained austenite characteristics, it was found that the excellent combinations are mainly caused by (i) refined and uniform martensitic lath structure matrix with a small amount of carbide, (ii) increasing narrow martensite with high dislocation density and (iii) the increased stability of retained austenite, resulting from the FQP process.

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Hot Forging of Ultra High-Strength TRIP-Aided Steel

Materials Science Forum ◽

10.4028/www.scientific.net/msf.638-642.3074 ◽

2010 ◽

Vol 638-642 ◽

pp. 3074-3079 ◽

Cited By ~ 11

Author(s):

Kohichi Sugimoto ◽

Shohei Sato ◽

Goro Arai

Keyword(s):

Retained Austenite ◽

Mechanical Stability ◽

Hot Forging ◽

Bainitic Ferrite ◽

Charpy Impact ◽

High Strength ◽

Ferrite Matrix ◽

Isothermal Transformation ◽

Mixed Structure ◽

High Toughness

Ultra high-strength TRIP-aided steel consisting of bainitic ferrite matrix and interlath retained austenite films (TBF steel) possesses high toughness and fatigue strength, as well as high resistance against hydrogen embrittlement. In this study, to improve further these mechanical properties, the effects of hot forging and subsequent isothermal transformation holding process (FIT process) on microstructure, retained austenite characteristics, tensile properties and toughness of the TBF steel with chemical composition of 0.4%C, 1.5%Si, 1.5%Mn, 0.5%Cr, 0.2%Mo, 0.05%Nb and 0.5%Al (mass%) were investigated. The FIT process brought on an excellent combination of tensile strength of 1350-1550 MPa and Charpy impact absorbed value of 100-110 J/cm2 in the developed TBF steel, exceeding so much that of SCM440 steel. The excellent combination was mainly caused by (i) refined mixed structure of bainitic ferrite and retained austenite and (ii) the increased mechanical stability of retained austenite due to the FIT process.

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Toward the Development of AHSS for Wear Resistant Applications

Materials Science Forum ◽

10.4028/www.scientific.net/msf.941.568 ◽

2018 ◽

Vol 941 ◽

pp. 568-573 ◽

Cited By ~ 1

Author(s):

Preston Wolfram ◽

Christina Hensley ◽

Ronald Youngblood ◽

Rachael Stewart ◽

Emmanuel de Moor ◽

...

Keyword(s):

Wear Resistance ◽

Retained Austenite ◽

Process Development ◽

High Strength ◽

Advanced High Strength Steel ◽

Wear Resistant ◽

Transformation Induced Plasticity ◽

Enhance Wear Resistance ◽

Improve Wear Resistance ◽

Strength And Ductility

Advanced High Strength Steel (AHSS) developments have largely focused on automotive applications using metallurgical approaches to develop retained austenite-containing microstructures in a variety of new steels, using the transformation-induced plasticity (TRIP) effect to achieve better combinations of strength and ductility. These efforts have been extended in recent studies to explore the potential to improve wear resistance, using metastable retained austenite to enhance wear resistance for earth-moving and other applications. This paper provides selected highlights of the authors’ efforts to develop wear resistant steels using AHSS processing approaches. Some attractive product/process development opportunities are identified, and it appears that martensite-austenite microstructures produced using “quenching and partitioning” exhibit increased wear resistance.

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Quantitative Description of External Force Induced Phase Transformation in Silicon–Manganese (Si–Mn) Transformation Induced Plasticity (TRIP) Steels

Materials ◽

10.3390/ma12223781 ◽

2019 ◽

Vol 12 (22) ◽

pp. 3781

Author(s):

Zhongping He ◽

Huachu Liu ◽

Zhenyu Zhu ◽

Weisen Zheng ◽

Yanlin He ◽

...

Keyword(s):

Phase Transformation ◽

Carbon Steel ◽

Trip Steel ◽

Retained Austenite ◽

Low Carbon Steel ◽

High Strength ◽

High Plasticity ◽

Low Carbon ◽

Transformation Induced Plasticity ◽

Trip Steels

Transformation Induced Plasticity (TRIP) steels with silicon–manganese (Si–Mn) as the main element have attracted a lot of attention and great interest from steel companies due to their low price, high strength, and high plasticity. Retained austenite is of primary importance as the source of high strength and high plasticity in Si–Mn TRIP steels. In this work, the cold rolled sheets of Si–Mn low carbon steel were treated with TRIP and Dual Phase (DP) treatment respectively. Then, the microstructure and composition of the Si–Mn low carbon steel were observed and tested. The static tensile test of TRIP steel and DP steel was carried out by a CMT5305 electronic universal testing machine. The self-built true stress–strain curve model of TRIP steel was verified. The simulation results were in good agreement with the experimental results. In addition, the phase transformation energy of retained austenite and the work borne by austenite in the sample during static stretching were calculated. The work done by austenite was 14.5 J, which was negligible compared with the total work of 217.8 J. The phase transformation energy absorption of retained austenite in the sample was 9.12 J. The role of retained austenite in TRIP steel is the absorption of excess energy at the key place where the fracture will occur, thereby increasing the elongation, so that the ferrite and bainite in the TRIP steel can absorb energy for a longer time and withstand more energy.

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Stability of Retained Austenite in High-Strength Martensitic Steels with Low Ms Temperature

MANUFACTURING TECHNOLOGY ◽

10.21062/ujep/x.2017/a/1213-2489/mt/17/4/428 ◽

2017 ◽

Vol 17 (4) ◽

pp. 428-433 ◽

Cited By ~ 6

Author(s):

Dagmar Bublíková ◽

Bohuslav Mašek ◽

Ivan Vorel ◽

Štěpán Jeníček

Keyword(s):

Retained Austenite ◽

High Strength ◽

Martensitic Steels

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Transformation Induced Plasticity (TRIP) Effect Used in Forming of Carbon CMnSi Steel

Materials Science Forum ◽

10.4028/www.scientific.net/msf.500-501.461 ◽

2005 ◽

Vol 500-501 ◽

pp. 461-470 ◽

Cited By ~ 1

Author(s):

Jiří Kliber ◽

Bohuslav Mašek ◽

Ondrej Zacek ◽

H. Staňková

Keyword(s):

Continuous Casting ◽

Hot Rolling ◽

Retained Austenite ◽

Volume Fraction ◽

Thermomechanical Processing ◽

High Strength ◽

Ferrite Matrix ◽

Transformation Induced Plasticity ◽

Trip Steels ◽

Forming Temperature

Transformation induced plasticity (TRIP) steel combines high strength and high ductility that makes it particularly suitable for forming. Martensite within a ferrite matrix is usually obtained either by continuous casting of slabs followed by hot rolling (which is the fastest method, hence the most economical one, producing, however, relatively thick products) or by the continuous casting of slabs followed by hot rolling, cold rolling and annealing (the method used for thin products). High cooling rates, low coiling temperatures and low reduction during hot deformation were generally found to suppress the formation of polygonal ferrite and promote the presence of retained austenite. This paper focuses on development and modifications of two CMnSi-based TRIP steels with 0,23 % C;1,4 % Mn; 1,9 % Si; ( 0,08 % Nb) by means of laboratory thermomechanical processing. Description of experimental devices for the analysis of transformation plasticity under tensioncompression loading is given. Experiments were carried out on the simulator for thermaldeformation cycles SMITWELD and TANDEM was used for thermomechanical processing on the laboratory rolling mill. The maximum volume fraction of retained austenite and the resulting optimum combination of tensile strength and ductility were achieved in testing heats. Special attention was paid to volume fraction changes of single phases and to changes in morphology of phases. The results suggest that rather short isothermal bainite transformation times are sufficient to obtain TRIP microstructure. The influence of parameters of thermomechanical processing such as the amount of strain, forming temperature and austenitization time and temperature on microstructures of TRIP steels were evaluated.

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Modeling of Lath Martensitic Microstructures and Failure Evolution in Steel Alloys

Journal of Engineering Materials and Technology ◽

10.1115/1.3183780 ◽

2009 ◽

Vol 131 (4) ◽

Cited By ~ 6

Author(s):

T. M. Hatem ◽

M. A. Zikry

Keyword(s):

Dislocation Density ◽

Retained Austenite ◽

High Strength ◽

Martensitic Steels ◽

Steel Alloys ◽

Failure Evolution ◽

Sharp Crack ◽

Void Interaction ◽

Finite Element Formulations ◽

Crack Tip Blunting

A multiple-slip dislocation-density-based crystalline formulation, specialized finite-element formulations, and Voronoi tessellations adapted to martensitic orientations were used to investigate dislocation-density activities and crack tip blunting in high strength martensitic steels. The formulation is based on accounting for variant morphologies and orientations, retained austenite, and initial dislocations densities that are uniquely inherent to martensitic microstructures. The effects of variant distributions and arrangements are investigated for different crack and void interaction distributions and arrangements. The analysis indicates that for certain orientations related to specific variant block arrangements, which correspond to random low angle orientations, cracks can be blunted by dislocation-density activities along transgranular planes. For other variant block arrangements, which correspond to random high angle orientations, sharp crack growth can occur due to dislocation activities along intergranular planes.

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Microstructure and Mechanical Properties of Cold-Rolled TRIP Steel Sheets

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.266.280 ◽

2011 ◽

Vol 266 ◽

pp. 280-283 ◽

Cited By ~ 1

Author(s):

Cai Nian Jing ◽

Xiao Hui Chen ◽

Ming Gang Wang ◽

Qi Zhong Tian ◽

Zuo Cheng Wang

Keyword(s):

Retained Austenite ◽

High Strength ◽

Transformation Induced Plasticity ◽

Trip Steels ◽

Multiphase Microstructure ◽

Steel Sheets ◽

High Strength Level ◽

Cold Rolled ◽

Level 2 ◽

Strength And Ductility

Transformation induced plasticity (TRIP) steels have complex multiphase microstructure composed of ferrite, bainite and retained austenite [1]. These metastable retained austenite can transforms into martensite during plastic deformation, which generates a TRIP effect resulting in excellent combination of high strength and ductility even at high strength level [2-5]. For this reason, the TRIP-aided steel sheets are suitable to fabricate automobile parts, as they can offer excellent formability without sacrifice the strength and safety requirement of the steel sheets. As a result, the development of TRIP-aided steels has been a very important issue in the automobile field.

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Effect of Cooling Rate below Ms Temperature on Hydrogen Embrittlement of TRIP-Aided Martensitic Steels

Materials Science Forum ◽

10.4028/www.scientific.net/msf.1016.654 ◽

2021 ◽

Vol 1016 ◽

pp. 654-659

Author(s):

Naoya Kakefuda ◽

Shintaro Aizawa ◽

Ryo Sakata ◽

Junya Kobayashi ◽

Goroh Itoh ◽

...

Keyword(s):

Hydrogen Embrittlement ◽

Cooling Rate ◽

Trip Steel ◽

Retained Austenite ◽

Volume Fraction ◽

High Strength ◽

Martensitic Steels ◽

The Matrix ◽

Embrittlement Resistance ◽

Hydrogen Embrittlement Resistance

Low alloy TRIP steel is expected to be applied to automobile bodies because of its high strength, high ductility, and excellent impact properties and press formability. It has been reported that the low alloy TRIP steel of hydrogen embrittlement resistance is improved by utilizing the hydrogen storage characteristics of highly stable retained austenite. Therefore, for the purpose of increasing the volume fraction of retained austenite, it was produced at various cooling rates below the martensite transformation start temperature. As a result, the volume fraction of retained austenite increased, and then the effect of hydrogen embrittlement decreased. The matrix phase and retained austenite is refined with decrees of the cooling rate. It is considered that the size and surface area of the retained austenite also affected the improvement of hydrogen embrittlement resistance.

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