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

2017 ◽  
Vol 17 (4) ◽  
pp. 428-433 ◽  
Author(s):  
Dagmar Bublíková ◽  
Bohuslav Mašek ◽  
Ivan Vorel ◽  
Štěpán Jeníček
Keyword(s):  
Retained Austenite ◽  
High Strength ◽  
Martensitic Steels

Modeling of Lath Martensitic Microstructures and Failure Evolution in Steel Alloys

2009 ◽  
Vol 131 (4) ◽  
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.

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

2011 ◽  
Vol 409 ◽  
pp. 696-701 ◽  
Author(s):  
Junya Kobayashi ◽  
Koh Ichi Sugimoto ◽  
Goro Arai
Keyword(s):  
Retained Austenite ◽  
Hot Forging ◽  
Charpy Impact ◽  
High Strength ◽  
Martensitic Steels ◽  
Structure Matrix ◽  
Transformation Induced Plasticity ◽  
Lath Structure ◽  
Martensitic Lath ◽  
Hot Forging Process

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.

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

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.

scholarly journals Microstructure and Retained Austenite Characteristics of Ultra High-strength TRIP-aided Martensitic Steels

2012 ◽  
Vol 52 (6) ◽  
pp. 1124-1129 ◽  
Author(s):  
Junya Kobayashi ◽  
Sung-Moo Song ◽  
Koh-ichi Sugimoto
Keyword(s):  
Retained Austenite ◽  
High Strength ◽  
Martensitic Steels

scholarly journals Effects of Alloying Elements Addition on Delayed Fracture Properties of Ultra High-Strength TRIP-Aided Martensitic Steels

Metals ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 6 ◽  
Author(s):  
Tomohiko Hojo ◽  
Junya Kobayashi ◽  
Koh-ichi Sugimoto ◽  
Akihiko Nagasaka ◽  
Eiji Akiyama
Keyword(s):  
Hydrogen Embrittlement ◽  
Retained Austenite ◽  
Hydrogen Diffusion ◽  
High Strength ◽  
Alloying Elements ◽  
Bending Test ◽  
Hydrogen Trapping ◽  
Martensitic Steels ◽  
Diffusible Hydrogen ◽  
Martensite Matrix

To develop ultra high-strength cold stamping steels for automobile frame parts, the effects of alloying elements on hydrogen embrittlement properties of ultra high-strength low alloy transformation induced plasticity (TRIP)-aided steels with a martensite matrix (TM steels) were investigated using the four-point bending test and conventional strain rate tensile test (CSRT). Hydrogen embrittlement properties of the TM steels were improved by the alloying addition. Particularly, 1.0 mass% chromium added TM steel indicated excellent hydrogen embrittlement resistance. This effect was attributed to (1) the decrease in the diffusible hydrogen concentration at the uniform and fine prior austenite grain and packet, block, and lath boundaries; (2) the suppression of hydrogen trapping at martensite matrix/cementite interfaces owing to the suppression of precipitation of cementite at the coarse martensite lath matrix; and (3) the suppression of the hydrogen diffusion to the crack initiation sites owing to the high stability of retained austenite because of the existence of retained austenite in a large amount of the martensite–austenite constituent (M–A) phase in the TM steels containing 1.0 mass% chromium.

Retained austenite-induced fire-resistance of a 690 MPa high strength steel

2021 ◽  
Vol 291 ◽  
pp. 129448
Author(s):  
L.J. Wei ◽  
X.M. Ji ◽  
Y.S. Yu ◽  
R.D.K. Misra ◽  
P.C. Liu ◽  
...  
Keyword(s):  
Fire Resistance ◽  
High Strength Steel ◽  
Retained Austenite ◽  
High Strength

scholarly journals Heat Treatment Design for a QP Steel: Effect of Partitioning Temperature

Metals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 1136
Author(s):  
Marcel Carpio ◽  
Jessica Calvo ◽  
Omar García ◽  
Juan Pablo Pedraza ◽  
José María Cabrera
Keyword(s):  
Retained Austenite ◽  
High Strength Steels ◽  
High Strength ◽  
Tensile Tests ◽  
Quenching Temperature ◽  
Advanced High Strength Steels ◽  
New Family ◽  
Automotive Parts ◽  
Fresh Martensite ◽  
Industry Needs

Designing a new family of advanced high-strength steels (AHSSs) to develop automotive parts that cover early industry needs is the aim of many investigations. One of the candidates in the 3rd family of AHSS are the quenching and partitioning (QP) steels. These steels display an excellent relationship between strength and formability, making them able to fulfill the requirements of safety, while reducing automobile weight to enhance the performance during service. The main attribute of QP steels is the TRIP effect that retained austenite possesses, which allows a significant energy absorption during deformation. The present study is focused on evaluating some process parameters, especially the partitioning temperature, in the microstructures and mechanical properties attained during a QP process. An experimental steel (0.2C-3.5Mn-1.5Si (wt%)) was selected and heated according to the theoretical optimum quenching temperature. For this purpose, heat treatments in a quenching dilatometry and further microstructural and mechanical characterization were carried out by SEM, XRD, EBSD, and hardness and tensile tests, respectively. The samples showed a significant increment in the retained austenite at an increasing partitioning temperature, but with strong penalization on the final ductility due to the large amount of fresh martensite obtained as well.

scholarly journals Carbon Redistribution and Microstructural Evolution Study during Two-Stage Quenching and Partitioning Process of High-Strength Steels by Modeling

Materials ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2302 ◽  
Author(s):  
Yilin Wang ◽  
Huicheng Geng ◽  
Bin Zhu ◽  
Zijian Wang ◽  
Yisheng Zhang
Keyword(s):  
Retained Austenite ◽  
Volume Fraction ◽  
High Strength Steels ◽  
High Strength ◽  
Simulation Method ◽  
Low Carbon ◽  
Two Stage ◽  
Quenching And Partitioning ◽  
Carbon Redistribution ◽  
Carbon Martensite

The application of the quenching and partitioning (Q-P) process on advanced high-strength steels improves part ductility significantly with little decrease in strength. Moreover, the mechanical properties of high-strength steels can be further enhanced by the stepping-quenching-partitioning (S-Q-P) process. In this study, a two-stage quenching and partitioning (two-stage Q-P) process originating from the S-Q-P process of an advanced high-strength steel 30CrMnSi2Nb was analyzed by the simulation method, which consisted of two quenching processes and two partitioning processes. The carbon redistribution, interface migration, and phase transition during the two-stage Q-P process were investigated with different temperatures and partitioning times. The final microstructure of the material formed after the two-stage Q-P process was studied, as well as the volume fraction of the retained austenite. The simulation results indicate that a special microstructure can be obtained by appropriate parameters of the two-stage Q-P process. A mixed microstructure, characterized by alternating distribution of low carbon martensite laths, small-sized low-carbon martensite plates, retained austenite and high-carbon martensite plates, can be obtained. In addition, a peak value of the volume fraction of the stable retained austenite after the final quenching is obtained with proper partitioning time.

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