Advances in Ferrous Metallurgy: HSLA Steel and Advances in Characterization Techniques
Sponsored by: AIST Metallurgy — Processing, Products & Applications Technology Committee
Program Organizers: Siddhartha Biswas, Big River Steel; Daniel Baker, LIFT; Lijia Zhao, Northeastern University
Monday 8:00 AM
October 10, 2022
Room: 406
Location: David L. Lawrence Convention Center
Session Chair: Siddhartha Biswas, Big River Steel
8:00 AM
A Rapid CCT Predictor for Low Alloys Steels and its Application to Compositionally Heterogeneous Material: Joshua Collins1; Ed Pickering2; 1The University of Manchester; 2University of Manchester
It is well understood that alloy processing has a direct impact on steel performance. By manipulating transformation kinetics, alloy behaviour can be modified to produce unique properties unlike those predicted under equilibrium. It is this relationship that grants the ability, and the ambition, to model steel behaviour and predict the performance of processed components. A model for predicting the continuous cooling transformation (CCT) behaviour of low alloy steels has been developed using modified semi-empirical equations by Kirkaldy and Venugopalan. The model is unique in that it considers the effects of carbon partitioning on subsequent transformations, allowing it to predict characteristic CCT behaviours, like martensite suppression, that are not considered in other models. The accuracy of the model has been determined through comparisons with experimental dilatometry data. Once validated, the model can then be used to predict the microstructure and performance of steel components.
8:20 AM
Adapting HSLA-100 to Thick-Section Forgings: Joshua Mueller1; Virginia Euser1; Joshem Gibson1; Mark Royer2; 1Los Alamos National Laboratory; 2Lehigh Heavy Forge Corporation
HSLA-100 is a naval steel that was developed to exhibit exceptional combinations of strength and toughness while maintaining good weldability without post-weld heat treatment. Originally developed as a plate steel grade, there is interest in adapting HSLA-100 to thick-section forgings. The work presented here investigates the amenability of HSLA-100 to forgings, and highlights successes and challenges associated with production of high-strength, high-toughness forgings relative to plate. Mechanical property results, including uniaxial tensile and Charpy V-notch, for various heat treatments are presented. Variation in mechanical properties in thick-section forgings are discussed and tied to through-thickness changes in microstructural evolution. Finally, potential alloy modifications are introduced that intend to remedy challenges associated with adapting HSLA-100 to thick-section forgings. Experimental trials suggest that HSLA-100 forgings can meet marginally reduced strength-toughness targets with the original HSLA-100 composition; however, with judicious alloy modifications, thick-section forgings may achieve properties comparable to plate.
8:40 AM
Characterization of Ductility Limiting Precipitation at High Temperatures in HSLA steels: Alyssa Stubbers1; John Balk1; 1University of Kentucky
Precipitation above 950°C is a major ductility limiting factor in HSLA steel and poses concerns about quality and safety of steel during continuous casting processes. To study this phenomena, continuous casting simulation took place in a Gleeble 3500 followed by a detailed SAXS analysis of quenched microstructures. This analysis of precipitation characteristics and high temperature material properties will indicate how precipitation influences microstructure development and it limits ductility at high temperatures. A range of alloys containing Nb, V, N, and Ti were examined to evaluate various precipitate species and their development during high temperature processes in order to better understand how precipitate sizes and distributions can alter ductility behavior.
9:00 AM
Further Analysis of the Relationship between Precipitate Formation and a Loss of Hot Ductility in Two Microalloyed Steels: Paul Estermann1; Viorel-Sergiu Ilie2; Jakob Six2; Ernst Kozeschnik1; 1Technische Universität Wien; 2Voestalpine Stahl GmbH
Several technical alloys experience an isolated area of lower deformability at elevated temperatures, which usually falls between 600 °C and 1000 °C for steels. This second ductility minimum can lead to severe problems. Because of the overlapping and interacting nature of influences, this problem is still of interest to the industry as well as the academia. Nitride and carbide precipitates, which can form at elevated temperatures are known to have an effect on the material. The precipitates can hinder the movement of dislocations as well as the sliding and growth of grain boundaries and they can act as nucleation sites for pores. One issue, which keeps coming up in hot ductility tests regarding the right flank is dynamic recrystallisation, which is often disregarded because of the low strain. In this presentation, the relationship between the right flank of the ductility minimum, precipitates and dynamic recrystallisation is investigated.
9:20 AM
Evaluation of Martensite Transformation Temperatures Using Magnetometry: Nicholas Jones1; Paul Lambert1; Jin-Hyeong Yoo1; Suok-Min Na1; Charles Fisher1; 1Naval Surface Warfare Center, Carderock Division
Martensite start and finish temperatures are two critical parameters needed to define the processing variables for steels. Magnetization measurements have been used herein as a method to determine these structural phase transformation temperatures. Eight compositions of steel having published martensite start temperatures ranging from -130 °C to +30 °C were synthesized via vacuum arc melting. After a high-temperature homogenization heat treatment, samples were extracted and room-temperature magnetic hysteresis loops were measured before and after a temperature cycle to cryogenic temperatures under constant applied field. Samples showed pronounced increases in magnetization as temperature decreased due to irreversible martensitic transformation, and eventually magnetization plateaued below the sample’s martensite finish temperature. In addition to the measured martensite start and finish temperatures and general characterization of the samples, the choice of applied magnetic field strength will be discussed, to ensure that the transformation is being appropriately characterized.
9:40 AM
Rigorous, Machine-Learning based Classification of Steel Microstructures Using EBSD: Michael Hjelmstad1; Pat Trimby1; 1Oxford Instruments
In many high-performance steels, the key physical properties are closely related to the fraction and distribution of different phases, including martensite, ferrite and austenite, as well as the microstructural constituent bainite. Although electron backscatter diffraction (EBSD) can discriminate austenite from other phases based on crystallographic differences, the separation of bainite, martensite and ferrite is much more challenging as all 3 can be reliably indexed using a body-centered cubic (BCC) structure.Here we introduce a technique utilizing machine learning to classify EBSD datasets. Using a combination of diffraction pattern quality, grain-based, and plastic strain measurements coupled with a system training process, the BCC-based phases can be differentiated quickly and reproducibly. We will show how this approach can be used to separate the constituent phases of the microstructure in a range of advanced steels, including dual-phase and highly heterogeneous structural steels.
10:00 AM Break
10:15 AM
Stereological Analysis for Microstructure Quantification in Advanced High Strength Steels: Brian Lin1; Narayan Pottore1; Sriram Sadagopan1; Jiahao Cheng2; Xiaohua Hu2; 1ArcelorMittal Global R&D; 2Oak Ridge National Laboratory
The microstructure statistics of two industrially produced advanced high strength quench and partition sheet steels was analyzed by stereology. Planes in the rolling, transverse, and normal direction through the thickness were characterized by both SEM and EBSD. Grain properties, such as size and shape, for different phases, including ferrite, martensite, and retained austenite were quantified. In the intercritically annealed quench and partition steel, the ferrite features were pancaked in comparison to the martensite and retained austenite. In comparison, in the supercritical annealed quench and partition steel, the prior austenite grains were mostly equiaxed. These microstructure statistics were collected with interest of synthetically constructing statistically representative volumes, which can be later used in computational models to predict deformation behaviors.
10:35 AM
In-situ Laser Confocal Microscopic Analysis of Phase Transformations in Cr-Ni-Mo and Cr-Mo High-strength Steels Coupled with Dilatometric Study: Viraj Ashok Athavale1; Rogerio Antao Cardoso1; Katelyn Kiser1; Mario Buchely1; Laura Bartlett1; Ronald O'Malley1; 1Missouri University of Science and Technology
Consequent to interdendritic segregation during solidification, chemical composition gradients in steels affect localized variations in phase transformation temperatures. Commercial software used to predict transformation temperatures does not necessarily account for such alterations. In this study, the predicted transformation temperatures were studied experimentally, utilizing high-temperature Laser Scanning Confocal Microscopy (LSCM) and Quenching Deformation Dilatometer (QDL) for two steel grades. Upon heating the specimens sufficiently above liquidus temperature, their melting-solidification behavior and solid-state phase transformation were recorded and analyzed. Secondary dendrite arm spacing (SDAS) measurements allowed for assessing the degree of interdendritic segregation. Dilatometric studies produced the austenite-to-martensite transformation temperature under different cooling rates. The findings yielded by both approaches were compared with a view to overlaying data to thermodynamic models and exploring the constituent variations in phase transformation temperature stemming from interdendritic segregation.
10:55 AM
Effect of Leaching Process Variables on the Reaction Kinetics of Pyrite Using Surface Response Methodology: Hilary Rutto1; Tumisang Seodigeng1; 1Vaal University of Technology
Acid mine drainage (AMD) is one of the leading water pollutants in many countries with mining activities. AMD is caused by the oxidation of pyrite and other metal sulphides. When these metals get exposed to moisture and oxygen, leaching occurs, discharging sulphate and Iron. A mathematical model was developed to correlate the leaching rate constant to reaction variables: temperature, hydrogen peroxide concentration, solid to liquid ratio, and stirring speed using a Central Composite Design (CCD). The iron pyrite before and after leaching was characterized using Fourier Transform Infrared Spectra (FTIR) analysis, X-Ray diffraction (XRD) and scanning electron microscope (SEM) were used to characterize before and after leaching. It was found that the leaching rate decreases with an increased solid to liquid ratio, temperature, stirring speed, and acid concentration. The leaching kinetics followed the shrinking core model with the product layer diffusion model as the rate-limiting step.
11:15 AM
Modelling of Accelerated Runout Table Cooling of Thicker Gauge Steel Products: Shixin Zhou1; Ali Doustahadi1; Vladan Prodanovic1; Matthias Militzer1; 1University of British Columbia
Accelerated cooling on the run-out table has become a key technology to manufacture TMCP steels, both hot rolled plates and strips. The application of power cooling units with increased heat extraction capacities enables efficient production of advanced high-performance steels with reduced alloying levels. Here, a challenge for thicker gauge products are resulting microstructure through-thickness gradients. Systematic pilot-scale simulations of ROT cooling have been conducted with the goal to develop a mechanistic heat transfer model that can be combined with austenite decomposition models.Heat transfer models accounting for the role of process parameters were built based on representative boiling curves obtained from systematic power unit cooling experiments with moving plates. An austenite decomposition model which accounts for the latent heat of phase transformation was coupled with the heat transfer model to predict the effect of plate thickness on the through-thickness final ferrite grain size for selected low carbon steels.
11:35 AM
Dielectric Behavior of Steel and Its Application in Structural Self-powering: Deborah Chung1; Xiang Xi1; 1State University of New York Buffalo
Dielectric behavior refers to electric polarization behavior. This behavior is well-known for nonconductors, but is only emerging for conductors. The polarization results in capacitance, which comprises capacitances in series. The associated material property is the permittivity. The polarization also results in a voltage that impedes conduction. The polarization is due to the interaction of a small fraction of the free electrons with the atoms. Although the capacitance is low, the permittivity is high, as high as 1,000,000, as shown for low carbon steel and stainless steel. Cold work enhances the permittivity, due to the microstructural effect of the cold work and the microstructure affecting the abundance of sites for the electron-atom interaction. Another aspect of the dielectric behavior is electret (permanent electric dipole) behavior without poling. The electret gives a DC voltage, which increases with the dimensions, potentially allowing steel structures to provide energy through capacitance discharge, i.e., structural self-powering.