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Kahkonen J.,Colorado School of Mines | Pierce D.T.,Colorado School of Mines | Speer J.G.,Colorado School of Mines | de Moor E.,Colorado School of Mines | And 4 more authors.
JOM | Year: 2015

The effect of partitioning parameters on mechanical properties and carbon partitioning in quenching and partitioning (Q&P)-treated C-1.5Mn-1.5Si steels was studied using 0.3 wt.% and 0.4 wt.% carbon compositions. Fully austenitized specimens were quenched to a fixed quenching temperature followed by partitioning at 400°C and 450°C for varying times. In most cases, increasing the partitioning temperature decreased UTS and increased TE, and both UTS and TE decreased with increasing partitioning times. Similar ultimate tensile strength levels were obtained for the 0.3C alloy partitioned at 400°C and the 0.4C alloy partitioned at 450°C. Increasing alloy carbon content increased retained austenite fractions. Mössbauer effect spectroscopy results were used to investigate carbon redistribution after Q&P processing in the 0.4C alloy. © 2015 The Minerals, Metals & Materials Society Source

Araujo A.L.,Colorado School of Mines | Speer J.G.,Colorado School of Mines | Thomas G.A.,AK Steel Research | De Moor E.,Colorado School of Mines
Materials Science and Technology Conference and Exhibition 2015, MS and T 2015 | Year: 2015

The effects of microalloying elements on hot-rolled quenching and partitioning (Q&P) steels have not been extensively studied and offer an important avenue for future product enhancement. For the present study, a base steel composition of 0.2C-2.0Mn-1.5Si (wt pet) was selected. Three other alloys were produced with an addition of microalloying elements, two with varying levels of niobium (0.021 and 0.044 wt pet) and one with a vanadium addition (0.060 wt pet). Thermomechanical simulations of hot-strip mill processing were conducted for each of the steel alloys in a Gleeble® 3500 via hot torsion with varying coiling temperatures. The volume percent and morphology of the retained austenite were characterized using EBSD. Microstructure and hardness were evaluated as a function of both microalloy elements and coiling temperature. Nb and V microalloying additions appeared to increase the retained austenite fraction for a coiling temperature of 375 °C, the temperature usually associated with the peak austenite amount. Copyright © 2015 MS&T15®. Source

Thomas G.A.,AK Steel Research | Danoix F.,Colorado School of Mines | Speer J.G.,University of Rouen | Thompson S.W.,Colorado School of Mines | Cuvilly F.,Colorado School of Mines
ISIJ International | Year: 2014

Quenched and Partitioned (Q&P) steels have been shown in previous literature to exhibit attractive mechanical properties due to austenite and martensite present in the microstructure. However, questions have remained regarding the mechanisms at work during the partition step. In this work, x-ray diffraction and atom probe tomography were utilized to gain insights into phenomena that occur (such as carbon partitioning from martensite to austenite, carbon atom clustering/dislocation trapping, and carbide formation). Evidence of all of these mechanisms was observed.. © 2014 ISIJ. Source

Thomas G.A.,AK Steel Research | Speer J.G.,AK Steel Research
Materials Science and Technology (United Kingdom) | Year: 2014

The quenching and partitioning (Q&P) process for heat treatment of steel has previously been shown yield to good combinations of strength and ductility owing to the presence of martensite and austenite. Interface mobility has been discussed in previous literature, mostly related to local driving forces. The present work considers the migration of the martensite/austenite interface in two steels (containing CMnSiMo or CNiSiMo). Experimental data show clear evidence of interface migration in the CMnSiMo steel during partitioning treatments at temperatures between 200 and 400uC for times ranging from 30 to 1000 s; conversely, the interface in the CNiSiMo steel was stationary during the same partitioning treatments. The different behaviours observed are considered in the context of differences in interface mobility and driving forces, and it appears that interface crystallography differences could influence the partitioning behaviour of Q&P steels. © 2014 Institute of Materials, Minerals and Mining. Source

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