New Frontiers in Physical Metallurgy of Steels: On-Demand Oral Presentations
Sponsored by: AIST: MPPA Committee, TMS Steels Committee
Program Organizers: Matthias Militzer, University of British Columbia; Pello Uranga, CEIT and TECNUN (University of Navarra); Jonah Klemm-Toole, Colorado School of Mines; Amy Clarke, Los Alamos National Laboratory; Amit Behera, QuesTek Innovations LLC
Friday 8:00 AM
October 22, 2021
Room: On-Demand Room 8
Location: MS&T On Demand
Invited
New Approach to Producing High Alloy Steels: Hatem Zurob1; Zachary Detweiler2; Daniel Bullard2; 1McMaster University; 2Arcanum Alloys
Surface Optimized Diffusion Alloys (SODA) allow for late-stage customization of steel products. In this process a steel sheet is coated with a slurry which contains the desired alloying additions. The coated steel sheet is then batch annealed to alloy the substrate surface. This has the potential to revolutionize steel production because it eliminates the need for the specialized infrastructure needed for making steels with high additions of elements such as Cr, Mn and Si. In addition, because the alloying additions are introduced after cold-rolling, it is possible to avoid rolling issues associated with certain alloying additions. Most importantly, the new compositionally graded steels produced in this way allow new combinations of properties that could not be achieved using homogenous materials. In this presentation, the use of SODA to produce corrosion resistant medium-Mn steel sheet is discussed.
Invited
Nanoscale Investigation of Austenite/ferrite Interfaces in Medium Carbon Fe-Mn-C Steels at Different Inter-critical Temperatures: Olha Nakonechna1; Fredric Danoix2; Helena Zapolsky2; Didier Huin3; Nicolas Charbonnier3; Lionel Germain4; Mohamed Gouné5; 1University of Rouen Normandy; 2CNRS/GPM; 3ArcelorMittal research SA; 4Université de Lorraine; 5Université de Bordeaux
The austenite-to-ferrite phase transformation plays a critical role in tailoring the final steel microstructure during the processing of advanced high-strength steels (AHSS), such as Dual-Phase steels. It has long been realized that the interaction between the alloying elements and the migrating transformation interface directly affects the kinetics of ferrite growth and can be critical for a profound understanding of the austenite-to-ferrite phase transformation mechanism. The transformation rate may also depend on the interface's ability to dissipate free energy due to its crystallographic nature. Therefore, in this paper, the atomic scale redistribution of the alloying elements across the austenite-ferrite interface in a model Fe-C-Mn steels are investigated. Different alpha/gamma interfaces corresponding to various experimental conditions were selectively analyzed. The profiles of both C and Mn through the transformation interface were discussed on the basis of the existing interfacial models for ferrite transformation in steels.
Austenite Decomposition during Hot-strip Rolling of Microalloyed Low-carbon Steel: Wing Shan Tam1; Matthias Militzer1; 1The University of British Columbia
To achieve the desired hot band microstructures and required mechanical properties during hot-strip rolling, precise control of the cooling path through the runout table is critical. In this study, the austenite decomposition kinetics during continuous cooling of two microalloyed low-carbon steels have been investigated. Austenite grain growth, deformation and austenite decomposition tests were performed using a Gleeble 3500 thermomechanical simulator. The influence of processing parameters including austenite grain size, cooling rate and retained strain on transformation kinetics and the transformation products under no-recrystallized rolling conditions were evaluated through dilatometry, microstructure characterization and hardness testing. A microstructure model describing these metallurgical phenomena has been proposed that is applicable to industrially relevant runout table cooling strategies.
Austenite Decomposition in the Coarse Grain Heat Affected Zone of X80 Line Pipe Steel: Sabyasachi Roy1; Matthias Militzer1; Warren Poole1; 1The University of British Columbia
Welding of steels results in microstructure changes in the heat affected zone (HAZ). The coarse grain HAZ (CGHAZ) experience temperature close to the melting point and is regarded as a potential region of failure. In the present work, continuous cooling austenite decomposition has been studied for three different line pipe steels subjected to conditions relevant for the CGHAZ. An increase in carbon content from 0.035wt% to 0.061wt% leads to a decrease in transformation temperature of up to 50°C, whereas a chromium increase from 0.023wt% to 0.24wt% resulted in approximately 10°C decrease in transformation temperatures. Microstructure characterization and hardness testing confirmed that lower transformation temperatures are associated with finer bainitic microstructures and higher hardness values. Based on the experimental results a phenomenological model has been proposed to predict the transformation kinetics, microstructure and hardness as a function of cooling rate and steel chemistry in terms of C and Cr content.
Nano-precipitation and Resultant Surface Hardening by Nitriding of Ferrous Alloys: Goro Miyamoto1; Tadashi Furuhara1; 1Tohoku University
Nitriding treatment is commonly used to increase surface hardness for improvement of fatigue strength and wear resistance. In the nitriding of ferrous alloys containing strong nitride forming element (M), surface hardening occurs by precipitation of fine nitrides. The present authors directly observed that surface hardening in the nitriding of Ti or V-added specimens occurs not by the precipitation of stable alloy nitrides but of meta-stable mono-layer M-nitrogen(N) clusters by means of high resolution transmission electron microscopy. On the other hand, clustering was not observed in Al-added specimens, meanwhile in nitriding of Fe-Al-(V, Ti) alloys, formation of V-N or Ti-N clusters in the early stage of nitriding induces nucleation of fine AlN particles, which results in significant surface hardening. This indicates pre-cursor solute clustering can be used to control precipitation reaction in ferrous alloys.
Microstructure and Toughness Correlation in High Strength Q&T Boron Steels Microalloyed with Nb and Mo: Irati Zurutuza1; Nerea Isasti1; Eric Detemple2; Volker Schwinn2; Hardy Mohrbacher3; Pello Uranga1; 1CEIT and TECNUN (University of Navarra); 2Dillinger Hüttenwerke; 3NiobelCon bvba
Suitable combination between alloy concept and processing is required for meeting the challenging market requirements for high strength steels produced by Direct Quenching (DQ) and tempering treatments. Even though the synergetic effect on tensile property improvement by combining boron and microalloying elements (Nb, Mo and Nb+Mo) is well-known, the impact of different microstructural aspects on Charpy impact toughness remains unclear. In the current presentation, the contribution of different microstructural aspects on toughness is evaluated, after DQ and tempering laboratory tests. Martensite unit size and dislocation density quantification was performed using EBSD. The detrimental effect of microstructural heterogeneity and carbides is also quantified. Additionally, an approach for impact transition temperature prediction is proposed for tempered martensite. Unit size refinement is shown to be the most effective mechanism for controlling simultaneously strength and toughness. The results suggest that Mo-B alloying concept shows the best yield strength-toughness balance.
Simulation of the Nitriding and Ferritic Nitrocarburizing (FNC) Processes: Mei Yang1; Haoxing You1; Richard Sisson1; 1Worcester Ploytechnic Institute
Nitriding and FNC are surface treatments that improve the wear and corrosion resistance of a wide variety of steels and cast irons. During nitriding nitrogen is absorbed to form a compound layer and a hardened diffusion zone. In the FNC process nitrogen and carbon are concomitantly absorbed. The FNC proceeds much faster than the nitriding due to the thermodynamic interactions of nitrogen and carbon in the alloy. In the present work, a physics-based software model is being developed to predict the nitriding and FNC performance of steels with tempered martensitic microstructure. The composition of the compound layer is predicted using computational thermodynamics to develop alloy specific nitriding potential KN and carburizing potential KC phase diagrams. The thickness of the compound layer is predicted using parabolic kinetics. The diffusion in the tempered martensite case is modeled using diffusion with a reaction. These model predictions are compared with experimental results.
Relationship between Fatigue Strength and Microstructure of Carburized Steel Tempered at Different Temperature: Takuya Kita1; Kazumasa Yasuda1; Junya Asaoka1; Goro Miyamoto2; Tadashi Furuhara2; 1Denso Corporation; 2Tohoku University
The relationship between fatigue strength and microstructure of carburized SCM415 steel tempered at 120-350℃ for 1h is evaluated with rotating bending fatigue test pieces. When tempering temperature is above 180 ℃, fatigue strength as well as hardness decreases with increasing temperature. On the other hand, when tempering temperature is below 180 ℃, the fatigue strength decreases at lower temperature in spite of the increase in hardness. The amount of carbide precipitation increases and the dislocation density decreases with increasing tempering temperature, which leads to softening. Fracture surface analysis of the specimens underwent fatigue tests revealed that crack initiated at the prior austenite grain boundary at the tempering below 180 ℃. This is probably due to the stress concentration on the grain boundary caused by the high intragranular hardness or the decrease in the grain boundary strength caused by solute segregation and carbide precipitation at the grain boundary.
Tribological Characterization of Silicon Stainless Steel Alloys: Prince Setia1; K Thomas Tharian2; T Venkateswaran2; Sudhanshu Shekhar Singh1; Shashank Shekhar1; 1Indian Institute of Technology Kanpur; 2Indian Space Research Organization
The present work investigates the effect of silicon content (2-6 wt.%) on the wear characteristics of stainless steel alloys using the ball-on-disc test. Wear experiments were carried out for fixed time interval with varying loads (20-40 N). Microstructural characterization of the worn samples was carried out using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Raman spectroscopy. The wear behavior was quantified in terms of wear volume, which was obtained from optical profilometry. With an increase in the load, the wear volume was found to increase. Furthermore, at all loads, 6 wt.% Si alloy exhibited the highest wear resistance as compared to the other alloys. The wear behavior of the alloys has been correlated with the microstructure and will be discussed.