Advanced High Strength Steels IV: Session IV
Sponsored by: TMS Structural Materials Division, TMS: Steels Committee
Program Organizers: Ana Araujo, Vesuvius USA; Mary O'Brien, Los Alamos National Laboratory; Tilmann Hickel, Bam Federal Institute For Materials Research And Testing; Amy Clarke, Los Alamos National Laboratory; Kester Clarke, Los Alamos National Laboratory; C. Tasan, Massachusetts Institute of Technology; MingXin Huang, University of Hong Kong
Wednesday 2:00 PM
February 26, 2020
Room: Balboa
Location: Marriott Marquis Hotel
Session Chair: Mary O'Brien, Colorado School of Mines; Hung-Wei Yen, National Taiwan University
2:00 PM
Effect of Si on Microstructure and Mechanical Properties of FeMnAlC Lightweight Steels: Zhangwei Wang1; Wenjun Lu1; Junyang He1; Dirk Ponge1; Dierk Raabe1; Zhiming Li1; 1Max-Planck-Institut für Eisenforschung
We systematically investigated the influence of Si on the microstructural evolution and mechanical properties of Fe-30Mn-9Al-1.2C-xSi (x=0-2 wt. %) lightweight steels under the as-homogenized state. With the increase of Si content from 0 to 2 wt. %, the average sizes of κ-carbides in the austenite matrix increase from ~1 nm to ~12 nm. In addition, particle-shaped κ_0-carbide and α-ferrite are formed at grain boundaries in the steel with 2 wt. % Si. The growth of κ-carbide in grain interior further causes a strong precipitate strengthening effect, leading to the increase of yield strength from ~450 MPa to ~900 MPa. The primary deformation mechanism is the formation of slip bands in all the three steels, which involves the shear of κ-carbides upon straining. The present study provides valuable insights into the design of lightweight steels via the addition of lightweight elements.
2:20 PM
Understanding the Effect of Nickel on the Microstructure of Low Density FeMnAl Steels: Laura Bartlett1; Michael Piston1; Ronald O'Malley1; Krista Limmer2; Daniel Field2; 1Missouri University of Science & Technology; 2CC DEVCOM Army Research Laboratory
Additions of nickel to high manganese and aluminum low density steels have been shown to greatly increase strength by forming hard intermetallic B2 precipitants within the austenite matrix. In this study the effects of nickel additions between 5 and 8wt.% were investigated as a function of thermomechanical processing in a Fe-20Mn-9Al-0.9C steel. Increasing the amount of nickel from 5 to 8% produced a higher density and a finer distribution of nano-sized B2 within the austenitic matrix after hot rolling and subsequent annealing at 950°C. Electron microscopy confirmed that these precipitants were consistent with B2-type NiAl. Increasing the annealing temperature from 950 to 1050°C, greatly coarsened B2 precipitation on grain boundaries as well as matrix B2. Therefore, the size and morphology of these precipitants must be carefully controlled by using an appropriate thermomechanical processing and annealing approach to avoid a deleterious reduction in ductility and toughness.
2:40 PM
Low-Density Steels: Microstructure Evolution and Tensile Behavior in Novel FE-MN-AL-C Steels: Tomas Scuseria1; Kelcey Garza2; Dean Pierce3; Amrinder Gill2; Erik Pavlina2; Jerry Arnold2; Amy Clarke1; Kester Clarke1; Omar Garcia4; Fred Fletcher5; 1Colorado School of Mines; 2AK Steel; 3Oak Ridge National Laboratory; 4Ternium; 5Arcelor Mittal
Low-density steels with high specific strength are an ideal path to energy savings and improved performance in advanced high strength steels for the transportation sector. Aluminum additions (3-12 wt%) to medium-Mn, low-C sheet steels provide direct mass savings, in addition to control over duplex ferrite-austenite microstructures and intermetallic precipitation such as κ-carbides. These Fe-Mn-Al-C steels have shown excellent strength-ductility combinations with density reductions beyond 10% compared to conventional Advanced High Strength Steels (AHSS). Experimental Fe-Mn-Al-C grades, including alloy additions such as Ni, Cu, Cr, and Si, were hot rolled into sheets and investigated. The effects of alloying content and various heat treatments on microstructure evolution and work hardening behavior, including Transformation Induced Plasticity and Twinning Induced Plasticity (TRIP/TWIP) effects were studied. Dilatometry and x-ray diffraction provided insight into critical temperatures and the stability of austenite and carbide phases.
3:00 PM
Improvement of Hydrogen Induced Cracking Resistance by Tempering of an X65 Pipeline Steel for Sour Service: Mary O'Brien1; Kip Findley1; 1Colorado School of Mines
Hydrogen induced cracking (HIC) occurs in steel pipelines during sour service due to elevated levels of hydrogen sulfide. In this investigation, an X65 steel was accelerated cooled to produce a granular bainitic microstructure and then charged with hydrogen by exposing steel samples to a high ppm hydrogen sulfide gas environment without an externally applied stress. Several of the as-received samples were also tempered for 40 minutes at 300, 400, 500, and 600°C. All tempering treatments improved HIC resistance, but the 400°C sample was the least effective in doing so. Mechanical properties such as hardness and UTS do not trend with HIC resistance, contrary to beliefs informing industrial selections of steels for sour service. The results are discussed in the context of microstructural features present at the various tempering temperatures.
3:20 PM
Effect of Composition on Properties of Age-hardenable Fe-Mn-Al-C Alloys: Krista Limmer1; Daniel Field1; Laura Bartlett2; Katherine Sebeck3; 1CCDC Army Research Laboratory; 2Missouri S&T; 3CCDC Ground Vehicle Systems Center
A series of Fe-Mn-Al-C alloys were evaluated in order to determine the effect of composition variation on resulting properties. Whereas past studies have examined the sensitivity of mechanical properties to changing a single element in the composition in these alloys, this study evaluated covariance of the major elements: Mn, Al, and C. In this study, a series of ingots were prepared according to a two-factor design of experiments that were all expected to be age hardenable through precipitation of kappa-carbide. Aging kinetics and mechanical properties will be discussed in terms of microstructure. Complimentary CALPHAD modeling results and challenges in accurate composition evaluation will also be discussed.
3:40 PM Break
4:00 PM Cancelled
Effect of Alloying on Adhesive Strength of Interfaces Between Matrix and Transition Metal Carbide and Nitride Precipitates in Austenitic Steels: First-principles Approach: Oleg Kontsevoi1; Gregory Olson1; 1Northwestern University
Controlled precipitation of carbides and nitrides is one of fundamental approaches in the design of high performance steels. We investigate effect of macro-alloying (Ni, Cr) and micro-alloying (Mn, Cu, Mo, Nb) elements on interfacial adhesion between nano-scale sized transition metal carbide and nitride precipitates M[C,N] (M=Ti,V,Mo,Nb,W,Ta) and matrix in the design of precipitation-strengthened austenitic steels. First-principles density functional theory calculations with the highly-precise FLAPW method were employed to study the interfacial adhesion strength relevant to the optimization of steel grain refining dispersions for resistance to microvoid-driven shear localization in ductile fracture. Binary, ternary and quaternary precipitate phases mixed on both metal and non-metal sublattice were considered. It was determined that Cr alloying strengthens the interface bonding, whereas Ni notably reduces the interface strength. Correlation between the electronic band filling effects and strengthening effect of alloying additions to fcc Fe was established, and the role of interfacial segregation is investigated.
4:20 PM
Development of Hot-rolled TRIP Steel: Hung-Wei Yen1; 1National Taiwan University
This work demonstrates the roles of hot-rolling processes in microstructure and mechanical properties in Fe-0.21C-2.04Mn-1.04Si-1.10Al-0.064Nb-0.2Mo (in wt.%) alloy. Two strong and ductile transformation-induced plasticity steels (UTS 980 MPa x EL 25 % and UTS 1180 MPa x EL 20%) with distinguishable stress-strain behaviors were developed. Dynamic ferrite and granular bainite respectively were applied into these two steels. Nano/microstructures, strengthening mechanisms, and behaviors of transformation-induced plasticity in two steels were elucidated based on investigations of electron backscattering diffraction, transmission electron microscopy, and X-ray diffraction. The metallurgical principles can be applied to fabricate new transformation-induced plasticity steels directly by hot-rolling processes.
4:40 PM
TRIP-Maraging Nanolaminate Stainless Steel: Hyunseok Oh1; Shaolou Wei1; Jaclyn Leigh Cann1; Cemal Cem Tasan1; 1Massachusetts Institute of Technology
Engineering the reverted nanoscale austenite dispersed in a martensitic matrix has been known as a promising way to increase ductility and toughness without sacrificing strength in advanced high strength steels (AHSS). Recently a new medium-manganese steel, which combines transformation induced plasticity (TRIP) and maraging effects, simultaneously with nanolaminate structure, was reported to have exceptional fatigue resistance. Here we propose that such effects can be achieved in Cr containing stainless steel series by a proper simple thermomechanical treatment. The steel has full martensite structure at the as-quenched state, and partly reverted nanoscale austenite with nanolaminate structure after aging treatment. The formation of nanoprecipitates within the martensite matrix was also triggered during the aging treatment. Depending on the aging temperature, deformation mode of the reverted austenite changes from twin induced plasticity to TRIP. The TRIP-maraging Nanolaminate stainless steel thus creates an attractive pathway for simultaneously increasing ductility and toughness without sacrificing strength.
5:00 PM
Multi-scale Modeling of Hydrogen Embrittlement in High-strength Steels: Tarek Hatem1; 1The British University in Egypt
Steel is the most used metal in industry today with a range of applications that include energy, transportation and construction. One outstanding technological problem yet to be solved is the localization and failure of steel alloys due to hydrogen-embrittlement (HE). Hydrogen atoms affect the dislocation core, materials cohesion, and vacancies clustering causing the material capacity for plastic deformation to decrease. Better predictive models of the hydrogen effect in steel structure shall enable new engineered class of materials that is HE resistant. Such predictive models must account for the multi-scale nature of failure while simultaneously incorporating the effect of hydrogen and steel microstructure. Therefore, the current research work developed reliable multiscale computational models that incorporate hydrogen effects in different scales (i.e. nano, micro and macro). These models and experiments will be able to capture materials behavior. The developed framework accounts for long and short-range defects evolution and their interaction with hydrogen.