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 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.

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.

Bendability and Microstructure of Direct Quenched Optim® 960QC

2014 ◽  
Vol 783-786 ◽  
pp. 818-824 ◽  
Author(s):  
Vili Kesti ◽  
A. Kaijalainen ◽  
A. Väisänen ◽  
A. Järvenpää ◽  
A. Määttä ◽  
...  
Keyword(s):  
Material Handling ◽  
High Strength Steels ◽  
High Strength ◽  
Total Elongation ◽  
Roll Forming ◽  
Direct Quenching ◽  
Thermomechanical Rolling ◽  
Ultra High Strength Steels ◽  
End Use ◽  
Save Energy

Use of ultra-high-strength steels (UHSS) in weight critical constructions is an effective way to save energy and minimize carbon footprint in the end use. On the other hand, the demands for reducing manufacturing costs and energy consumption of the steelmaker are increasing. This has led to development of energy efficient direct quenching (DQ) steelmaking process as an alternative to the conventional quenched and tempered or thermomechanical rolling and accelerate cooled processes. Ruukki has employed thermomechanical rolling and direct quenching process (TM + DQ) for a novel type of ultra-high-strength strip and plate steels since 2001. Advantages of the ultra-high-strength level (>900MPa) can be fully utilized only if fabricated properties are on a sufficient level. Bending is one of the most important workshop processes and a good bendability is essential for a structural steel. Hence, the metallurgy and bendability of Ruukki ́s TM + DQ strip steel Optim® 960QC have been investigated closely. It was found that by optimizing process parameters and chemical composition, a good combination of strength and ductility can be achieved by a modification of martensitic-bainitic microstructure. Despite of smaller total elongation, the bendability of Optim® 960QC is at least on the same level as on conventionally manufactured 960MPa steels. However, it is important to pay special attention to bending process (tool parameters, springback, bending force, material handling) when bending UHSS. It was also found that the bendability of Optim® 960QC can be significantly enhanced by local laser heat treatments or roll forming.

Application of Quenching-Partitioning-Tempering Process in Hot Rolled Plate Fabrication

2010 ◽  
Vol 654-656 ◽  
pp. 82-85 ◽  
Author(s):  
Shu Zhou ◽  
Ying Wang ◽  
Nai Lu Chen ◽  
Yong Hua Rong ◽  
Jian Feng Gu
Keyword(s):  
Mechanical Properties ◽  
Retained Austenite ◽  
High Strength Steels ◽  
High Strength ◽  
Significant Fraction ◽  
Rolled Plate ◽  
Quenching And Partitioning ◽  
Good Ductility ◽  
Hot Rolled ◽  
Rolled Plates

The quenching-partitioning-tempering (Q-P-T) process, based on the quenching and partitioning (Q&P) treatment, has been proposed for producing high strength steels containing significant fraction of film-like retained austenite and controlled amount of fine martensite laths. In this study, a set of Q-P-T processes for C-Mn-Si-Ni-Nb hot rolled plates are designed and realized. The steels with Q-P-T processes present a combination of high strength and relatively good ductility. The origin of such mechanical properties is revealed by microstructure characterization.

scholarly journals USE OF MULTI-PHASE TRIP STEEL FOR PRESS-HARDENING TECHNOLOGY

2019 ◽  
Vol 25 (2) ◽  
pp. 101 ◽  
Author(s):  
Hana Jirková ◽  
Kateřina Opatová ◽  
Štěpán Jeníček ◽  
Jiří Vrtáček ◽  
Ludmila Kučerová ◽  
...  
Keyword(s):  
Trip Steel ◽  
Physical Simulation ◽  
Isothermal Holding ◽  
High Strength Steels ◽  
High Strength ◽  
Press Hardening ◽  
Passenger Safety ◽  
Ultra High Strength Steels ◽  
New Treatments ◽  
Multi Phase

<p class="AMSmaintext">Development of high strength or even ultra-high strength steels is mainly driven by the automotive industry which strives to reduce the weight of individual parts, fuel consumption, and CO<sub>2</sub> emissions. Another important factor is to improve passenger safety. In order to achieve the required mechanical properties, it is necessary to use suitable heat treatment in addition to an appropriate alloying strategy. The main problem of these types of treatments is the isothermal holding step. For TRIP steels, the holding temperature lies in the field of bainitic transformation. These isothermal holds are economically demanding to perform in industrial conditions. Therefore new treatments without isothermal holds, which are possible to integrate directly into the production process, are searched. One way to produce high-strength sheet is the press-hardening technology. Physical simulation based on data from a real-world press-hardening process was tested on CMnSi TRIP steel. Mixed martensitic-bainitic structures with ferrite and retained austenite (RA) were obtained, having tensile strengths in excess of 1000 MPa.</p>

Mechanical properties and microstructural evaluation of the heat-affected zone in ultra-high strength steels

2020 ◽  
Vol 157 ◽  
pp. 107072
Author(s):  
Mohsen Amraei ◽  
Shahriar Afkhami ◽  
Vahid Javaheri ◽  
Jari Larkiola ◽  
Tuomas Skriko ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Heat Affected Zone ◽  
High Strength Steels ◽  
High Strength ◽  
Microstructural Evaluation ◽  
Ultra High Strength Steels

Physical Simulation for Evaluating Heat-Affected Zone Toughness of High and Ultra-High Strength Steels

2013 ◽  
Vol 762 ◽  
pp. 711-716 ◽  
Author(s):  
Risto O. Laitinen ◽  
David A. Porter ◽  
L. Pentti Karjalainen ◽  
Pasi Leiviskä ◽  
Jukka Kömi
Keyword(s):  
Heat Affected Zone ◽  
Heat Input ◽  
Physical Simulation ◽  
Energy Requirement ◽  
High Strength Steels ◽  
High Strength ◽  
Coarse Grained ◽  
Test Results ◽  
Ultra High Strength Steels ◽  
The Impact

Physical simulation of the most critical sub-zones of the heat-affected zone is a useful tool for the evaluation of the toughness of welded joints in high-strength and ultra-high-strength steels. In two high-strength offshore steels with the yield strength of 500 MPa, the coarse grained, intercritical and intercritically reheated coarse grained zones were simulated using the cooling times from 800 to 500 °C (t8/5) 5 s and 30 s. Impact and CTOD tests as well as microstructural investigations were carried out in order to evaluate the weldability of the steels without the need for expensive welding tests. The test results showed that the intercritically reheated coarse grained zone with the longer cooling time t8/5=30 s was the most critical sub-zone in the HAZ due to the M-A constituents and coarse ferritic-bainitic microstructure. In 6 mm thick ultra-high-strength steel Optim 960 QC, the coarse grained and intercritically reheated coarse grained zones were simulated using the cooling times t8/5 of 5, 10, 15 and 20s and the intercritical zone using the cooling times t8/5 of 5 and 10 s in order to select the suitable heat input for welding. The impact test results from the simulated zones fulfilled the impact energy requirement of 14 J (5x10 mm specimen) at -40 °C for the cooling times, t8/5, from 5 to 15 s, which correspond to the heat input range 0.4-0.7 kJ/mm (for a 6 mm thickness).

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