An Appraisal of Direct Quenching for the Development and Processing of Novel Super-High Strength Steels

2016 ◽  
Vol 879 ◽  
pp. 1819-1827 ◽  
Author(s):  
Mahesh C. Somani ◽  
Jaakko I. Hannula ◽  
Antti J. Kaijalainen ◽  
Devesh K. Misra ◽  
David A. Porter
Keyword(s):  
Linear Regression Analysis ◽  
High Strength Steels ◽  
High Strength ◽  
Processing Route ◽  
Low Carbon ◽  
Martensitic Steels ◽  
Quenching And Partitioning ◽  
Direct Quenching ◽  
Bainitic Steels ◽  
Novel Processing

Recent interests in developing novel super-high strength steels have led to extensive research efforts in direct quenching with or without tempering (DQ, DQT) or combined with partitioning (DQP). Both strip and plate products have been targeted for different applications. For boron-microalloyed DQ/DQT steels, the ASTM A255 approach for predicting the hardenability was considered inapplicable. Fresh attempts were made to develop new hardenability models through non-linear regression analysis by dynamically varying both the boron factor and multiplying factors of most elements in the alloy factor. Based on the recent concept of quenching and partitioning (Q&P), a novel processing route comprising thermomechanical rolling followed by direct quenching and partitioning (TMR-DQP) has been established for the development of ultra-high strength structural steels with yield strengths ≈1100 MPa combined with good uniform and total elongations and impact toughness. Examples of recent advances made in DQ processing and associated challenges, such as those related to the bendability of low carbon martensitic-bainitic steels and influence of boron on the toughness of Nb-bearing martensitic steels are presented.

The Multiphase Micro- and Nanostructures of 0.2 and 0.4 C Direct-Quenched and Partitioned Steels

2021 ◽  
Vol 1016 ◽  
pp. 1097-1102
Author(s):  
Sakari Pallaspuro ◽  
Ilkka Miettunen ◽  
S. Assa Aravindh ◽  
Sumit Ghosh ◽  
Wei Cao ◽  
...  
Keyword(s):  
Density Functional ◽  
High Strength Steels ◽  
High Strength ◽  
Density Functional Theory Calculations ◽  
Processing Route ◽  
Slow Cooling ◽  
Quenching And Partitioning ◽  
Main Research ◽  
Direct Quenching ◽  
Advanced High Strength Steels

Quenching and partitioning produces advanced high-strength steels that utilise transformation-induced plasticity for improved strength and deformability. Microstructures of these steels consist mainly of tempered martensite and carbon-enriched retained austenite. A novel processing route of direct-quenching and partitioning (DQP) facilitates carbon partitioning from supersaturated martensite to untransformed austenite directly from the quench-stop temperature in a decelerated cooling that simulates slow cooling of a coiled strip. A major advantage of DQP steels is that they keep both the costs and emissions down by inexpensive alloying and energy-efficient processing. In this study, we investigate the microstructures of 0.2C and 0.4C laboratory hot-rolled DQP steels with comparison to a direct-quenched variant with high-resolution transmission electron microscopy as the main research technique. We show that the structures of DQP steels have frequent nanotwinned regions and can contain three different crystal structures with characteristic length scales ranging from few nm to ~200 nm. This is in remarkable contrast to the traditional lath-martensitic microstructure of the as-quenched material. Density functional theory calculations provide further insight into these findings with the calculated results of energetics, and show that carbon helps in stabilising the newly found omega phase. These results give further insight to the aspects that must be considered when assessing their effect on essential mechanical properties like strain hardening and toughness.

Innovation and Processing of Novel Tough Ductile Ultra-High Strength Steels through TMR-DQP Processing Route

2014 ◽  
Vol 783-786 ◽  
pp. 1009-1014 ◽  
Author(s):  
Mahesh C. Somani ◽  
David A. Porter ◽  
L. Pentti Karjalainen ◽  
Pasi Suikkanen ◽  
R.D.K. Misra
Keyword(s):  
Mechanical Properties ◽  
Physical Simulation ◽  
High Strength Steels ◽  
High Strength ◽  
Structural Steels ◽  
Processing Route ◽  
Quenching And Partitioning ◽  
Direct Quenching ◽  
Thermomechanical Rolling ◽  
Ultra High Strength Steels

Based on the recent concept of quenching and partitioning (Q&P), a novel TMR-DQP (thermomechanical rolling followed by direct quenching and partitioning) processing route has been established for the development of ultra-high strength structural steels with yield strengths ≈1100 MPa combined with good uniform and total elongations and impact toughness. Suitable compositions were designed based on high silicon and/or aluminium contents with or without small additions of Nb, Mo or Ni. The DQP parameters were established with the aid of physical simulation on a Gleeble simulator. Finally, the TMR-DQP processing route was designed for trials on a laboratory rolling mill. Metallographic studies showed that the desired martensite-austenite microstructures were achieved thus providing the targeted mechanical properties. The advantage of strained austenite in refining the martensite packets/blocks was clearly evident. No adverse effect of prolonged partitioning simulating the coiling stage has been noticed suggesting new possibilities for strip and plate products. Promising results in respect of microstructures and mechanical properties indicate that there are possibilities for developing tough ductile structural steels through the TMR-DQP route.

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.

Local texture analysis of structure non-uniformity in low carbon high-strength steel after direct quenching

2020 ◽  
pp. 9-16
Author(s):  
A. A. Zisman ◽  
N. Yu. Zolotorevsky ◽  
S. N. Petrov ◽  
E. I. Khlusova ◽  
E. A. Yashina
Keyword(s):  
High Strength Steels ◽  
High Strength ◽  
Careful Analysis ◽  
Structural Features ◽  
Low Carbon ◽  
Orientation Data ◽  
Direct Quenching ◽  
Finish Rolling ◽  
Subsequent Quenching ◽  
Rolling Stage

The direct quenching of high-strength steels after hot rolling, which enables discard of the reheating operation, is economically efficient but necessitates a careful analysis of corresponding structural features. In particular, this treatment sometimes results in extended domains of coarse bainite decreasing the fracture toughness of steel. To reveal dependence of such effects on ausforming conditions, local textures of the parent γ-phase have been reconstructed from EBSD orientation data with allowance for the inter-phase orientation relationship. According to the obtained results, the unfavorable structural non-uniformity appears in the direct quenching due to excessive work hardening of austenite at the finish rolling stage; however, the structure and properties of steel can be improved by the reheating and subsequent quenching.

scholarly journals Hot Straining and Quenching and Partitioning of a TRIP-Assisted Steel: Microstructural Characterization and Mechanical Properties

2018 ◽  
Vol 941 ◽  
pp. 704-710
Author(s):  
Edwan Anderson Ariza ◽  
Jonathan Poplawsky ◽  
Wei Guo ◽  
André Paulo Tschiptschin
Keyword(s):  
Mechanical Properties ◽  
High Strength Steels ◽  
High Strength ◽  
Microstructural Characterization ◽  
Atom Probe ◽  
Carbon Partitioning ◽  
Carbon Accumulation ◽  
Processing Route ◽  
Carbide Formation ◽  
Quenching And Partitioning

Advanced high strength steels (AHSS), with yield strengths over 300 MPa and tensile strengths exceeding 600 MPa, are becoming more noticeable in vehicle manufacturing. A novel processing route of a TRIP-assisted steel was developed. Characterization and modelling techniques were used to establish correlations between processing, microstructure and mechanical properties. Quenching and partitioning (Q&P) and a novel process of hot straining (HS) and Q&P (HSQ&P) treatments have been applied to a TRIP-assisted steel in a Gleeble ®3S50 thermo-mechanical simulator. The heat treatments involved intercritical annealing at 800 oC and a two-step Q&P heat treatment with a partitioning time of 100 s at 400 oC. The effects of high-temperature isothermal deformation on the carbon enrichment of austenite, carbide formation and the strain-induced transformation to ferrite (SIT) mechanism were investigated. Carbon partitioning from supersaturated martensite into austenite and carbide precipitation were confirmed by means of atom probe tomography (APT). Austenite carbon enrichment was clearly observed in all specimens, and in the HSQ&P samples it was slightly greater than in Q&P, suggesting an additional carbon partitioning to austenite from ferrite formed by the SIT phenomenon. By APT, the carbon accumulation at austenite/martensite interface was clearly observed. The newly developed combined process is promising as the transformation induced plasticity can contribute to the formability and energy absorption, contributing to fill the gap of the third generation of high-strength steels.

Low Temperature Precipitation in Nb-Added Si- and Si-Free Bainitic Steels

2012 ◽  
Vol 706-709 ◽  
pp. 2384-2389 ◽  
Author(s):  
Ian Zuazo ◽  
Sebastian Cobo
Keyword(s):  
High Strength Steels ◽  
High Strength ◽  
Atom Probe ◽  
Carbon Steels ◽  
Peak Hardness ◽  
Low Carbon ◽  
Steel Strips ◽  
Bainitic Steels ◽  
Transmission Electron ◽  
Precipitation Phenomena

Precipitation strengthening by fine Nb-rich particles represents an important element on the design of low carbon high strength steels. This is typically obtained on steel strips by thermal holding at temperatures above 600°C following the austenite to ferrite transformation. These conditions are beneficial to obtain a large precipitation of small Nb-rich precipitates. On the other hand, precipitation at lower temperatures, in a phase already hard, such as bainite, has been scarcely studied. In this work, the precipitation phenomena occurring during isothermal treatments following the austenite to bainite transformation at 450°C are investigated. For this purpose, two Nb-alloyed low carbon steels with and without silicon are studied and the evolution of the microstructure is determined by the use of transmission electron microscopy and followed by hardness measurements. The presence of a hardness peak is not detected until long isothermal times (150h). Preliminary atom probe tomography (APT) characterization provides insight on the possible presence of fine NbC precipitates at the peak hardness treatment. A comparison with a Nb-free alloy indicates a significant hardening effect of niobium on the bainitic structure.

The Complexity of the Microstructural Changes during the Partitioning Step of the Quenching and Partitioning Process in Low Carbon Steels

2010 ◽  
Vol 638-642 ◽  
pp. 3485-3490 ◽  
Author(s):  
Maria Jesus Santofimia ◽  
Lie Zhao ◽  
Yoshiki Takahama ◽  
Jilt Sietsma
Keyword(s):  
Heat Treatment ◽  
High Strength Steels ◽  
Carbon Diffusion ◽  
Carbon Steels ◽  
Carbon Accumulation ◽  
Isothermal Treatment ◽  
Low Carbon ◽  
Martensitic Steels ◽  
Microstructural Changes ◽  
Quenching And Partitioning

The quenching and partitioning (Q&P) process is a novel heat treatment for the development of advanced high strength steels that is raising an elevated interest by steel makers and steel researchers around the world. The reason is that reported results on mechanical properties, showing promising levels of forming and strength, are proving this new type of steel as a serious competitor of TRIP, DP and martensitic steels. The Q&P heat treatment consists of an initial partial or full austenitisation, followed by a quench to form a controlled amount of martensite and an isothermal treatment to partition the carbon from the martensite to the austenite. Although the path of the heat treatment is simple, the investigations have shown that the evolution of the microstructure during the application of the Q&P process is rather complicated. Processes occurring during the partitioning step, such as the migration of the interfaces, the carbon accumulation near the austenite interfaces and the carbon diffusion through ferrite, have strong effects on the resulting microstructure. In this work, the most important microstructural changes found during the application and simulation of the partitioning step of the Q&P process are analysed and discussed. Procedures to control the microstructure development in the application of the Q&P process are proposed.

scholarly journals Comprehensive Analysis of the Microstructure and Mechanical Properties of Friction-Stir-Welded Low-Carbon High-Strength Steels with Tensile Strengths Ranging from 590 MPa to 1.5 GPa

2021 ◽  
Vol 11 (12) ◽  
pp. 5728
Author(s):  
HyeonJeong You ◽  
Minjung Kang ◽  
Sung Yi ◽  
Soongkeun Hyun ◽  
Cheolhee Kim
Keyword(s):  
Mechanical Properties ◽  
Tensile Test ◽  
Joint Strength ◽  
Solid Phase ◽  
Welding Process ◽  
High Strength Steels ◽  
High Strength ◽  
Low Carbon ◽  
Friction Stir ◽  
Welding Processes

High-strength steels are being increasingly employed in the automotive industry, requiring efficient welding processes. This study analyzed the materials and mechanical properties of high-strength automotive steels with strengths ranging from 590 MPa to 1500 MPa, subjected to friction stir welding (FSW), which is a solid-phase welding process. The high-strength steels were hardened by a high fraction of martensite, and the welds were composed of a recrystallized zone (RZ), a partially recrystallized zone (PRZ), a tempered zone (TZ), and an unaffected base metal (BM). The RZ exhibited a higher hardness than the BM and was fully martensitic when the BM strength was 980 MPa or higher. When the BM strength was 780 MPa or higher, the PRZ and TZ softened owing to tempered martensitic formation and were the fracture locations in the tensile test, whereas BM fracture occurred in the tensile test of the 590 MPa steel weld. The joint strength, determined by the hardness and width of the softened zone, increased and then saturated with an increase in the BM strength. From the results, we can conclude that the thermal history and size of the PRZ and TZ should be controlled to enhance the joint strength of automotive steels.

scholarly journals Materials for Automotive Lightweighting

2019 ◽  
Vol 49 (1) ◽  
pp. 327-359 ◽  
Author(s):  
Alan Taub ◽  
Emmanuel De Moor ◽  
Alan Luo ◽  
David K. Matlock ◽  
John G. Speer ◽  
...  
Keyword(s):  
Galvanic Corrosion ◽  
Low Carbon Steel ◽  
High Strength Steels ◽  
High Strength ◽  
Low Carbon ◽  
New Materials ◽  
Specific Strength ◽  
Advanced High Strength Steels ◽  
Strength And Stiffness ◽  
The Cost

Reducing the weight of automobiles is a major contributor to increased fuel economy. The baseline materials for vehicle construction, low-carbon steel and cast iron, are being replaced by materials with higher specific strength and stiffness: advanced high-strength steels, aluminum, magnesium, and polymer composites. The key challenge is to reduce the cost of manufacturing structures with these new materials. Maximizing the weight reduction requires optimized designs utilizing multimaterials in various forms. This use of mixed materials presents additional challenges in joining and preventing galvanic corrosion.

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