Quenching and Partitioning of Martensite and Other Advancements in Steels: Session 1
Program Organizers: Emmanuel De Moor, Colorado School of Mines

Monday 10:40 AM
July 10, 2017
Room: Comiskey
Location: Hyatt Regency Chicago

Session Chair: Emmanuel De Moor, Colorado School of Mines

10:40 AM  Invited
Quenching and Partitioning: Science and Technology Update: John Speer1; Emmanuel De Moor1; David Matlock1; Kip Findley1; Amy Clarke1; 1Colorado School of Mines
    The quenching and partitioning (Q&P) concept was developed as a means to utilize carbon in as-quenched martensite to stabilize retained austenite and thereby enhance the mechanical properties. This contribution will provide an overview of background, and an update of advancements made in understanding important aspects of physical metallurgy and microstructure development, which have led to interest in implementing Q&P as a route for producing commercial high strength steels in volume. Initial industrialization has focused on automotive sheet steels, and substantial activity is now underway to meet aggressive near-term targets for vehicle “lightweighting” using Q&P steels or other novel approaches to generate microstructures with enhanced austenite fractions. Recent fundamental studies in the authors’ laboratories have examined a variety of alloying effects, and deeper exploration of the partitioning/tempering reactions.

11:20 AM  
Quenching and Partitioning Process – from Microstructural Developments to Technical Applications: Bohuslav Mašek1; Martin Wagner2; Hana Jirková1; Ivan Vorel1; 1University of West Bohemia; 2Chemnitz University of Technology
    Integration of the Q&P process into manufacturing chains that comprise heat treatments or thermomechanical treatments can change the existing perspective on the use of martensite in steels: New findings from research into the microstructures of AHSS steels treated by Q&P suggest that martensitic microstructures in steels are not always brittle. In fact, Q&P-processed steels pave the way for a range of engineering applications in which strengths of 2000 MPa and elongation levels of more than 10 % can be achieved at low costs, and with simple alloying strategies. In this contribution, we present results on the microstructures and mechanical properties of Q&P-processed steels on two length scales: Micro-pillar experiments provide information on the surprisingly ductile nature of small martensitic volumes; macroscopic mechanical testing, microscopy and X-ray diffraction of a CMnSiCr steel demonstrates how different Q&P processing routes affect mechanical, technological and utility properties relevant to innovative engineering applications.

11:35 AM  
The Morphology of Lath Martensite: A New Perspective: Anton Muehlemann1; Konstantinos Koumatos2; 1University of Oxford; 2Gran Sasso Science Institute
    A mathematical framework is proposed to predict the features of the (5 5 7) lath transformation in low-carbon steels based on energy minimisation. This theory generates a one-parameter family of possible habit plane normals and a selection mechanism then identifies the (5 5 7) normals as those arising from a deformation with small atomic movement and maximal compatibility. While the calculations bear some resemblance to those of double shear theories, the assumptions and conclusions are different. Interestingly, the predicted microstructure morphology resembles that of plate martensite, in the sense that a type of twinning mechanism is involved. Independent experiments by P. Zhang et al in early 2016 seem to support this hypothesis.

11:50 AM  
In situ Investigations of Partitioning Mechanisms in Q&P Steels by Synchrotron Diffraction Experiments: Sébastien Allain1; Guillaume Geandier1; Mohamed Gouné2; Samy Aoued2; Frédéric Danoix3; Michel Soler4; 1Institut Jean Lamour; 2ICMCB; 3GPM; 4Arcelormittal Maizières Research SA
     The Q&P treatment on a high C TRIP steel (Fe-0.3C-2.5 Mn-1.5Si-0.8Cr in wt.%) has been studied by the means of in situ X-Ray diffraction experiments using a synchrotron source. The experiments have been carried out on the ESRF-ID15B line (powder diffraction configuration in transmission). The high energy monochromatic beam (E = 87 keV) enables high acquisition rates (10 Hz) adapted to study ‘real time’ processes on bulk samples. The results support the concurrent bainite transformation and carbon diffusion from martensite to austenite as the main mechanisms of austenite enrichment during partitioning step. Nevertheless, large fraction of carbon remains trapped in martensite laths (segregations on dislocations, carbides) in the final microstructure. The in situ experiments permit also to measure internal stresses and plastic deformations of the phases. High residual tensile stresses in retained austenite at room temperature have been reported in particular due to thermal eigenstrains between phases during final cooling.