Phase Transformations and Microstructural Evolution: Ferrous Alloys
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Phase Transformations Committee
Program Organizers: Rongpei Shi, Harbin Institute of Technology; Yipeng Gao, Jilin University; Fadi Abdeljawad, Lehigh University; Bharat Gwalani, North Carolina State Universtiy; Qi An, Iowa State University; Eric Lass, University of Tennessee-Knoxville; Huajing Song, Los Alamos National Laboratory
Tuesday 2:00 PM
March 16, 2021
Room: RM 57
Location: TMS2021 Virtual
Session Chair: HuaJing Song, Los Alamos National Lab
2:00 PM
Solute Partitioning during the Double Soaking Heat Treatment of Medium Manganese Steels: Alexandra Glover1; Emmanuel De Moor2; John Speer2; 1Los Alamos National Laboratory; 2Colorado School of Mines
Double soaking is a novel two-step heat treatment for medium manganese steels which produces microstructures of martensite and austenite. First, the primary intercritical annealing treatment is applied resulting in primary austenite nucleation and growth, with solute partitioning into austenite. Next, the secondary soaking treatment is applied at an (intercritical) annealing temperature, replacing some fraction of the remaining ferrite with austenite, termed secondary austenite. Upon quenching, secondary austenite is expected to transform to martensite, while significant fractions of primary austenite are retained. During the secondary soaking treatment redistribution of carbon, and potentially manganese, between microstructural constituents is expected. This work will present experimental results concerning austenite growth during the secondary soaking treatment, along with corresponding changes in solute concentration profiles. Microstructural evolution during the secondary soaking treatment is characterized using a combination of transmission Kikuchi diffraction (TKD), scanning transmission electron microscopy (STEM) energy dispersive X ray spectroscopy (EDS), and DICTRA simulations.
2:20 PM
Cementite Formation in Ferritic Steels:Ffirst-principles Based AtomisticSsimulations.: Oceane Buggenhoudt1; Chu-Chun Fu1; Thomas Schuler1; Jean-Luc Béchade1; 1CEA, Université Paris Saclay
Mechanisms of carbon diffusion and agglomeration play a central role in the nucleation process of cementite in α-Fe. However, so far, these properties are poorly known. To address these features, we first identified a precursor of cementite which consists in an ordered structure composed of Fe atoms in quasi-bcc lattice sites and C atoms occupying octahedral sites. Then, we investigated the early stage of cementite nucleation. A set of interaction energies and migration barriers for C interstitials in an α-Fe matrix with different local C concentration are calculated using density functional theory (DFT). Then, we parametrized effective interaction and diffusion models, and performed atomic Monte Carlo simulations. Finally, we studied the diffusion in cementite. We determined the migration barriers of a C interstitial via DFT and the corresponding diffusion coefficients via the computation of transport coefficients. The predicted diffusion coefficients are in good agreement with available experimental data.
2:40 PM
Effect of Cold Rolling on PhaseTtransformations in 2202 Lean Duplex Stainless Steel: Frederic Danoix1; Sophie Cazottes2; Raphaele Danoix3; Dimitri Rolland2; Sarata Cissé4; Véronique Massardier2; 1CNRS; 2INSA Lyon; 3CNRS - Univ Rouen Normandie; 4INDUSTEEL
The effect of plastic deformation on thermal ageing of a lean 2202 duplex stainless steel at intermediate temperatures (280-450°C) was studied by a combination of atom probe tomography and thermoelectric power. In non-deformed condition, spinodal decomposition of ferrite is shown to be the main ageing process, with an activation energy of 206kJ/mol. With plastic deformation, ageing proceeds faster, while austenite partly transforms to martensite. If residual austenite remains unaffected, both ferrite and martensite decompose. The spinal decomposition kinetics of ferrite is shown to increase with the deformation rate. Martensite also decomposes at 450°C, with precipitation of various phases, including chromium nitrides, G-phase and copper rich particles. The Fe-Cr rich martensite is also shown to decompose, but through a nucleation and growth mechanism, due to a decrease of Cr content in the matrix.
3:00 PM
Phase Instability and Formation of Radiation-induced BCC-phases in Austenitic Stainless Steel after Long Term Neutron Exposure: Diana Merezhko1; Mikhail Merezhko1; Maxim Gussev2; Thomas Rosseel2; Oleg Maksimkin1; Francis Garner3; 1Institute of Nuclear Physics; 2Oak Ridge National Laboratory; 3Radiation Effects Consulting
Accumulation of radiation-induced ferrite is a well-known phenomenon; however, it was not recognized as a potential issue until recently. BCC-phases, which may consist of Cr-rich ferrite or Fe-rich ferrite or both, being brittle after irradiation, may affect corrosion behavior in water coolant. This work analyzes available experimental datasets showing the accumulation of a significant amount of ferritic phase (3-4vol.% and more) after high-dose neutron irradiation. The data are derived from the BN-350 and BOR-60 SFR and also include several ion-irradiation experiments. The research considers Western (304 and 316) and Russian (12Cr18Ni10Ti, an analog of 321) austenitic steels (AustSS) irradiated to 0.3–125 dpa at temperatures of 280-420°C and dose rates of 0.25-60.2dpa/year. Experimental observations suggest that radiation-induced ferrite in AustSS forms a specific layered structure along grain boundaries, leading to reduced fracture toughness. Precipitates located near the grain boundaries may be also prone to corrosive attack in the high-temperature water.
3:20 PM
Applicability of Deep Cryogenic Treatment in Emerging Industries: Patricia Jovicevic-Klug1; Matic Jovicevic-Klug1; Bojan Podgornik1; 1Institute of Metals and Technology
In recent years, cryogenic treatment has been applied to improve properties of the steels in various industries. A common type of cryogenics is deep cryogenic treatment (DCT), where steel is subjected to temperatures below -160 °C. DCT has been reported to change properties of steels such as corrosion and wear resistance, hardness, toughness, better machinability etc. In addition to the beneficial changing of properties, DCT allows also replacement of 2-3 cycles of tempering, which reduces production costs. This study had taken under consideration a group of selected steels (under same DCT conditions), which are commonly used in various industries. Selected groups of steel were systematically investigated for the influence of DCT on their microstructural, mechanical, and tribological properties. The study provides systematic data of DCT influence on the properties of selected steels, showing that DCT is evidently an effective method for enhancing properties of materials used for industrial applications.
3:40 PM
Austempered Microstructures for Bearing Applications: Scott Hyde1; 1The Timken Company
Traditional bearing microstructures primarily consist of a martensitic structure formed using a high carbon alloy or a case hardening process. More recently, bearings have been manufactured with bainitic microstructures using a process known as austempering. Unlike the athermal transformation process by which martensite forms, bainite is produced from an isothermal transformation process. This cost-effective isothermal transformation process leads to improved heat treat part growth and distortion characteristics, while still providing excellent rolling contact fatigue performance. Using a combination of athermal martensitic and isothermal bainitic transformation processes, enhancements to bearing performance and processing can be achieved. Presented in this paper are multiple methods of heat-treating high carbon bearing steels, associated microstructures produced, component growth and distortion characteristics and demonstrated bearing performance improvement.