Quenching and Partitioning of Martensite and Other Advancements in Steels: Poster Session
Program Organizers: Emmanuel De Moor, Colorado School of Mines

Tuesday 5:30 PM
July 11, 2017
Room: Crystal Ballroom A
Location: Hyatt Regency Chicago

P2-54: Carbide Precipitation during Tempering of Martensite in Fe-C-Si and Fe-C-Mn-Si Alloys with Varying Si Levels: Monika Krugla1; S.Erik Offerman2; Jilt Sietsma2; David Hanlon3; 1Tata Steel R&D/TU Delft; 2Delft University of Technology; 3Tata Steel R&D
    The effect of silicon on the carbide precipitation kinetics during tempering of martensite in steel is not adequately understood. The discussion is still ongoing about the actual mechanism of carbide precipitation in steel that is alloyed with silicon. The data that is published in the literature is ambiguous regarding the solubility of silicon in cementite. This is partly due to the differences in the compositions of the alloys used in various studies. In order to investigate the solubility of silicon in cementite and transition carbides (ε and η), we use set of Fe-C-Mn-Si model alloys, containing various levels of silicon and two Mn-levels. Additionally, we analyse the influence of the Si/Mn-ratio and the counteracting effects of Mn and Si on the precipitation process in martensite during the tempering process in Fe-C-Mn-Si alloys.

P2-55: Effect of Pre-quenching Martensite on the Kinetics of Subsequent Isothermal Bainitic Transformation and Mechanical Properties of GCr15 Bearing Steel: Xiaohui Lu1; Wei Li2; Lin Hua1; Xuejun Jin2; 1Wuhan university of Technology; 2Shanghai Jiao Tong University
    The effect of pre-quenching martensite on the kinetics of subsequent isothermal bainitic transformation of GCr15 bearing steel has been studied by DIL850 thermal dilatometer by heating to 850℃ austenitizing temperature for 30min then pre-quenching at different temperatures (220℃, 200℃ 180℃) slightly below Ms temperature and isothermal treatment at 240℃. Dilatometry experimental results show that the pre-quenched martensite can accelerate subsequent isothermal bainitic transformation and exist an optimum pre-quenched temperature. Meanwhile, the improvement of strength-toughness were achieved due to the martensite-bainitic(MB) duplex microstructures. The pre-quenching at 200℃ can obtain the greatest acceleration effect for subsequent isothermal bainitic transformation and the optimum combination of strength and toughness.The competition between dislocation promote bainite nucleate and carbon partitioning retard bainite transformation due to pre-quenching martensite is also discussed.

P2-56: In-situ Neutron Diffraction Study on Microstructure Evolution during Thermo-mechanical Processing of Medium Manganese Steel: Yoshihiko Nakamura1; Akinobu Shibata1; Wu Gong2; Stefanus Harjo3; Takuro Kawasaki3; Nobuhiro Tsuji1; 1Kyoto University; 2Elements Strategy Initiative for Structural Materials; 3Japan Atomic Energy Agency
     Advanced high strength steels (AHSS), which manage both high strength and good ductility, have been investigated actively. Recently, medium Mn steels containing 3~7wt.% Mn have been received much attention as a new class of AHSS. It is reported that medium Mn steels achieve good balance of strength and ductility due to transformation induced plasticity (TRIP) effect of retained austenite. To obtain retained austenite, medium Mn steels are often subjected to thermo-mechanical processing. However, microstructure evolution during thermo-mechanical processing is still unclear. The present study investigated microstructure evolution of medium Mn steel (Fe-5Mn-2Si-0.1C) during thermo-mechanical processing by in-situ neutron diffraction analysis.We found that hot compression during thermo-mechanical processing assisted reverse transformation from martensite to austenite significantly. Moreover, we found that about 10% of austenite was retained after thermo-mechanical processing. The mechanism of austenite reverse transformation and TRIP effect of the medium Mn steel will be presented.

P2-57: Quenching and Partitioning in δ-ferrite Containing Steels: Eustaquio Baeta1; Ramon Botelho1; Monica Magalh„es1; Leonardo Araujo2; Andersan Paula1; Luiz Paulo Brandao1; 1Instituto Militar de Engenharia; 2Universidade Federal do Rio de Janeiro
    δ-TRIP steels are promissory new alloys which the TRIP effect and high elongation and strength can be achieved due the presence of stable δ-ferrite at room temperature. These steels have high aluminum content, which assists the partition of carbon to austenite. Once the development of theses alloys is recent, there is a lack of knowledge about the formation of the martensite. A study of quenching and partitioning heat treatment in these alloys is proposed to create microstructures containing carbon-enriched retained austenite, martensite and δ-ferrite. A computational method can be used to predict the final microstructure in steels with δ-ferrite stabilized by aluminum and niobium, estimate δ-ferrite and austenite fraction in the intercritical heat treatment, carbon concentration prior to quenching, and quenching temperature, aiming the maximum of retained austenite and martensite. Preliminary results indicate that quenching and partitioning can lead to according microstructures for the 3rd generation of AHSS steels.