Research on Microstructure Evolution Laws of Ultrafine Grained Metastable Automobile Steel

2013 ◽  
Vol 423-426 ◽  
pp. 281-285
Author(s):  
Ji Guang Li ◽  
Hai Liang Huang ◽  
Shang Wu Zeng ◽  
Jia Li Cao ◽  
Tie Jun Wang
Keyword(s):  
Microstructure Evolution ◽  
Retained Austenite ◽  
Large Fraction ◽  
Lath Martensite ◽  
High Strength ◽  
Ultrafine Grain ◽  
High Plasticity ◽  
Ultrafine Grained ◽  
The Matrix ◽  
Evolution Laws

The microstructure evolution laws of ultrafine grained metastable automobile steels was studied in this paper by laser confocal scanning microscope, EBSD, XRD and TEM. Results showed that, the matrix organizations of hot-rolled steel were lath martensite and deformation ferrite, and there were a little of retained austenite film and lath between the lath martensite. After heat treatment, the matrix organizations of steel were ultrafine ferrite and retained austenite. The retained austenite transformed into martensite and ε-martensitic in the deformation process, and the strength and plasticity of steel were improved. A lot of retained austenite were obtained in the annealing process. The TRIP effects by the large fraction of metastable austenite and the ultrafine grain size add to the test steel with high strength and high plasticity.

scholarly journals Heterogeneous lamella structure unites ultrafine-grain strength with coarse-grain ductility

2015 ◽  
Vol 112 (47) ◽  
pp. 14501-14505 ◽  
Author(s):  
Xiaolei Wu ◽  
Muxin Yang ◽  
Fuping Yuan ◽  
Guilin Wu ◽  
Yujie Wei ◽  
...  
Keyword(s):  
Large Scale ◽  
Low Cost ◽  
High Strength ◽  
Back Stress ◽  
Coarse Grained ◽  
Ultrafine Grain ◽  
Asymmetric Rolling ◽  
Dislocation Hardening ◽  
Ultrafine Grained ◽  
Lamella Structure

Grain refinement can make conventional metals several times stronger, but this comes at dramatic loss of ductility. Here we report a heterogeneous lamella structure in Ti produced by asymmetric rolling and partial recrystallization that can produce an unprecedented property combination: as strong as ultrafine-grained metal and at the same time as ductile as conventional coarse-grained metal. It also has higher strain hardening than coarse-grained Ti, which was hitherto believed impossible. The heterogeneous lamella structure is characterized with soft micrograined lamellae embedded in hard ultrafine-grained lamella matrix. The unusual high strength is obtained with the assistance of high back stress developed from heterogeneous yielding, whereas the high ductility is attributed to back-stress hardening and dislocation hardening. The process discovered here is amenable to large-scale industrial production at low cost, and might be applicable to other metal systems.

Studying the Effect of Manganese Content on TRIP Advanced High Strength Steel

2019 ◽  
Vol 950 ◽  
pp. 50-54 ◽  
Author(s):  
Ahmed El-Sherbiny ◽  
Ahmed Y. Shash ◽  
Mohamed Kamal El-Fawkhry ◽  
Tarek M. El-Hossainy ◽  
Taha Mattar
Keyword(s):  
High Strength Steel ◽  
Retained Austenite ◽  
Manganese Content ◽  
High Strength ◽  
Uniaxial Tensile ◽  
Strain Hardening Exponent ◽  
Uniaxial Tensile Test ◽  
Advanced High Strength Steel ◽  
High Manganese ◽  
The Matrix

TRIP effect containing steel was well reputed by its high mechanical properties among the 1st generation of Advanced High Strength Steel. High Silicon content was well established as an inhibitor for cementite precipitation at para-equilibrium condition. However, the effect of manganese as a powerful stabilizer for retained austenite was not much studied in TRIP-Steel. Thereby, the effect of high manganese content on the TRIP containing steel is studied in this research. As been observed from OM, and XRD results, it was found that as long as increasing Manganese content, the fraction of retained austenite increases. No doubt that enrichment of retained austenite throughout the matrix, beers a great impact on the plastic deformation character of the investigated steels, which was proved by using a uniaxial tensile test and determining the strain hardening exponent.

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

Materials ◽  
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.

scholarly journals The Mechanism of High-Strength Quenching-Partitioning-Tempering Martensitic Steel at Elevated Temperatures

Crystals ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 94 ◽  
Author(s):  
Ke Zhang ◽  
Maoyuan Zhu ◽  
Bitong Lan ◽  
Ping Liu ◽  
Wei Li ◽  
...  
Keyword(s):  
Retained Austenite ◽  
Elevated Temperatures ◽  
Martensitic Steel ◽  
Lath Martensite ◽  
Temperature Stability ◽  
High Strength ◽  
High Temperature Stability ◽  
High Deformation ◽  
Heat Treated ◽  
The Relationship

High-strength medium-carbon martensitic steel was heat treated through a quenching-partitioning-tempering (Q-P-T) treatment. Both the mechanism for improved ductility and the high temperature stability of austenite were investigated. The Q-P-T martensitic steel showed good products of strength and elongation (PSE) at various deformation temperatures ranging within 25–350 °C. The optimum PSE value (>57,738 MPa%) was achieved at 200 °C. The microstructure of the Q-P-T steel is constituted of laths martensite with dislocations, retained austenite located within lath martensite and small niobium carbides (NbC), and/or transitional ε-carbides that precipitated in the lath martensite. The good ductility can be mainly attributed to the laminar-like austenite that remained within the lath-martensite. The austenite can effectively enhance ductility through the effect of dislocation absorption by the retained austenite and through transformation-induced plasticity. The relationship between the microstructures and mechanical properties was investigated at high deformation temperatures.

Synthesis of high-strength W–Ta ultrafine-grain composites

2008 ◽  
Vol 23 (1) ◽  
pp. 133-139 ◽  
Author(s):  
R.T. Ott ◽  
X.Y. Yang ◽  
D.E. Guyer ◽  
S. Chauhan ◽  
D.J. Sordelet
Keyword(s):  
High Strength ◽  
High Energy ◽  
High Temperature Phase ◽  
High Yield ◽  
Ultrafine Grain ◽  
Temperature Phase ◽  
Composite Powders ◽  
Ultrafine Grained ◽  
Submicron Scale ◽  
The Individual

Bulk samples of an ultrafine-grained tungsten–tantalum composite alloy have been synthesized by consolidating mechanically milled composite powders. The grain growth during densification is limited due to the submicron-scale layering of the individual metals in the composite particles and the relatively low sintering temperature (1300 °C). The ultrafine microstructure of the high-density (∼99% theoretical density) samples leads to a high yield stress of ∼3 GPa under quasi-static uniaxial compression. A tendency for Ta-rich solid-solution formation during densification was observed, and the high-temperature phase equilibria in the composite powders were examined further using high-energy x-ray diffraction at temperatures up to 1300 °C.

Microstructure Evolution of Mg-10Gd-2Y-0.5Zn-0.3Zr Alloy during Isothermal Forging Process

2014 ◽  
Vol 783-786 ◽  
pp. 485-490
Author(s):  
De Bin Shan ◽  
X.Z. Han ◽  
Wen Chen Xu
Keyword(s):  
Microstructure Evolution ◽  
Ageing Time ◽  
High Strength ◽  
Aged Alloy ◽  
Secondary Phases ◽  
Obvious Effect ◽  
Isothermal Forging ◽  
Forging Process ◽  
The Matrix ◽  
Peak Aged

The isothermal forging process of a bracket and its microstructure evolution of Mg-10Gd-2Y-0.5Zn-0.3Zr alloy have been investigated in the present study. The results show that the bracket with thin-web and high-rib is well formed through modifying corners and adding an active damping block into male die. Amounts of lamellae and particles distribute uniformly on the matrix after the isothermal forging process and ageing process. The isothermal forging process has an obvious effect on the precipitation behaviour of secondary phases, while it did not change the grain size greatly. With the increase of ageing time, more secondary phases precipitate from α-Mg matrix until 60h. The optimal ultimate tensile strength and elongation of the peak-aged alloy are 382MPa and 4.03%, respectively. The combined effects of LPO and β′ phases contribute to the high strength of the peak-aged alloy.

Effects of Heat Treatment on Microstructure of High-Strength Manganese-Silicon Steels

2017 ◽  
Vol 270 ◽  
pp. 239-245
Author(s):  
Dagmar Bublíková ◽  
Štěpán Jeníček ◽  
Kateřina Opatová ◽  
Bohuslav Mašek
Keyword(s):  
Heat Treatment ◽  
Cooling Rate ◽  
Microstructure Evolution ◽  
Retained Austenite ◽  
Volume Fraction ◽  
High Strength ◽  
Quenching And Partitioning ◽  
Alloying Additions ◽  
New Procedures ◽  
Strength And Ductility

Today’s advanced steels are required to possess high strength and ductility. This can be accomplished by producing appropriate microstructures with a certain volume fraction of retained austenite. The resulting microstructure depends on material’s heat treatment and alloying. High ultimate strengths and sufficient elongation levels can be obtained by various methods, including quenching and partitioning (Q&P process). The present paper introduces new procedures aimed at simplifying this process with the use of material-technological modelling. Three experimental steels have been made and cast for this investigation, whose main alloying additions were manganese, silicon, chromium, molybdenum and nickel. The purpose of manganese addition was to depress the Ms and Mf temperatures. The Q&P process was carried out in a thermomechanical simulator for better and easier control. The heat treatment parameters were varied between the sequences and their effect on microstructure evolution was evaluated. They included the cooling rate, partitioning temperature and time at partitioning temperature. Microstructures including martensite with strength levels of more than 2000 MPa and elongation of 10–15 % were obtained.

Microstructure Evolution during Warm Deformation of Low Carbon Steel with Dispersed Cementite

2007 ◽  
Vol 558-559 ◽  
pp. 505-510 ◽  
Author(s):  
J. Gallego ◽  
Alberto Moreira Jorge ◽  
O. Balancin
Keyword(s):  
Microstructure Evolution ◽  
Large Strain ◽  
Cell Structure ◽  
Lath Martensite ◽  
Low Carbon Steel ◽  
Testing Temperature ◽  
Equivalent Strain ◽  
Low Carbon ◽  
Ultrafine Grained ◽  
Ebsd Technique

The microstructure evolution and mechanical behavior during large strain of a 0.16%CMn steel has been investigated by warm torsion tests. These experiments were carried out at 685 °C at equivalent strain rate of 0.1 s-1. The initial microstructure composed of a martensite matrix with uniformly dispersed fine cementite particles was attained by quenching and tempering. The microstructure evolution during tempering and straining was performed through interrupted tests. As the material was reheated to testing temperature, well-defined cell structure was created and subgrains within lath martensite were observed by TEM; strong recovery took place, decreasing the dislocation density. After 1 hour at the test temperature and without straining, EBSD technique showed the formation of new grains. The flow stress curves measured had a peculiar shape: rapid work hardening to a hump, followed by an extensive flow-softening region. 65% of the boundaries observed in the sample strained to ε = 1.0 were high angle grain boundaries. After straining to ε = 5.0, average ferrite grain size close to 1.5 1m was found, suggesting that dynamic recrystallization took place. Also, two sets of cementite particles were observed: large particles aligned with straining direction and smaller particles more uniformly dispersed. The fragmentation or grain subdivision that occurred during reheating and tempering time was essential for the formation of ultrafine grained microstructure.

Investigation of Possible Mechanisms for Developing Long Steel Products with Ultrafine Grained Microstructure

2014 ◽  
Vol 783-786 ◽  
pp. 744-749
Author(s):  
Claudio Guarnaschelli ◽  
Ilaria Salvatori ◽  
Tommaso Coppola
Keyword(s):  
Process Parameters ◽  
Hot Rolling ◽  
High Strength ◽  
Ultrafine Grain ◽  
Rolling Mills ◽  
Size Refinement ◽  
Ultrafine Grained ◽  
Austenite Recrystallization ◽  
Environmentally Friendly Process ◽  
New Generation

The obtainment of ultrafine grain microstructures, by the application of process parameters which are potentially feasible under industrial conditions, is attractive to develop a new generation of low alloy steel (Ultrafine Grain Steel, UFG) characterized by high strength and toughness, good cold/warm formability, environmentally-friendly process. The ferrite grain size refinement beyond existing levels by means of hot rolling mills, without requiring drastic plant changes, can be achieved by lowering the rolling temperature down to the range Ae3 - Ar3 in the finishing stands. In this temperature range different metallurgical mechanisms may take place. Austenite recrystallization is slower and there is a greater chance of obtaining non-recrystallized deformed austenite (pancake), which after phase transformation will give finer ferrite (Heavy Gamma Deformation). Or, in alternative, Deformation Induced Ferrite Transformation can occur especially in C-Mn steels, promoting the formation of ultrafine ferrite grains (DIFT). Most of the existing studies on UFG steel focus on flat products. In this paper the mechanisms to be exploited for producing UFG long products are identified and examined on different low and medium carbon non-alloyed steels, as the common grades used for fastener applications. In particular, Heavy Gamma Deformation and DIFT are investigated through laboratory tests aimed at determining the process parameters affecting the two mechanisms in different ranges of chemical composition. On the basis of the results found, some basic concepts for industrialization on modern hot rolling mills will be given.

scholarly journals Effect of the Deformation Degree on the Microstructure Evolution of an Austenite Reverted Transformation-Annealed Medium Manganese Steel

Metals ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 887 ◽  
Author(s):  
Caiyi Liu ◽  
Yan Peng ◽  
Ling Kong ◽  
Yanqiang Wang
Keyword(s):  
Electron Microscopy ◽  
Grain Size ◽  
Microstructure Evolution ◽  
Retained Austenite ◽  
Lath Martensite ◽  
Annealing Process ◽  
Reverse Transformation ◽  
Manganese Steel ◽  
Deformation Degree ◽  
Medium Manganese Steel

An Fe-0.15C-1.2Si-5Mn-0.09Nb-0.08V-0.07Mo (wt.%) medium manganese steel that was subjected to a novel austenite reverted transformation (ART) annealing process. This paper is based on the conventional ART annealing process, and a deformation and ART annealing process is proposed. The influence of the deformation degree on the microstructure and grain size of the medium manganese steel was determined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). The results show that the deformation had a great effect on the microstructure evolution and grain size. The microstructure of the medium manganese steel after the deformation and ART annealing process was consistent with the theory of austenite reverse transformation, i.e., the martensite reverse transformation into austenite occurred during the deformation and ART annealing process. The final microstructure was a mixture of martensite and austenite. As the deformation degree increases, the martensite gradually refines, and carbides precipitate in the lath martensite. The retained austenite is gradually transformed from very large to small and is distributed between the martensite laths. The results show that when deformation occurs in the austenite region, a small deformation can obtain more retained austenite.

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