Microstructure Evolution and Competitive Reactions during Quenching and Partitioning of a Model Fe–C–Mn–Si Alloy

The mechanisms behind the carbon enrichment of austenite during quenching and partitioning are still a matter of debate. This work investigates the microstructural evolution during the quenching and partitioning of a model Fe–C–Mn–Si alloy by means of in situ high energy X-ray diffraction (HEXRD) atom probe tomography, and image analysis. The ultra-fast time-resolved quantitative information about phase transformations coupled with image analysis highlights the formation of carbide-free BCT bainite, which is formed within a very short range during the reheating and partitioning step. Its transformation rate, which is a better indicator than the intrinsic volume fraction, depends on the quenching temperature (QT). It is shown to decrease with decreasing QT, from 45% at QT = 260 °C to 20% at QT = 200 °C. As a consequence, a significant part of the carbon enrichment observed in austenite can be attributed to bainite transformation. Furthermore, a large part of carbon was shown to be trapped into martensite. Both the formation of Fe2.6C iron carbides and the segregation of carbon on lath boundaries in martensite were highlighted by atom probe tomography. The energy for carbon segregation was determined to be 0.20 eV, and the carbon concentration on the lath boundaries was obtained to be around 25 at %. Therefore, the carbon enrichment of austenite is the result of competitive reactions such as carbon partitioning from martensite, bainite transformation, and carbon trapping in martensite.

[1]  S. Godet,et al.  Into the quenching & partitioning of a 0.2C steel: An in-situ synchrotron study , 2019, Materials Science and Engineering: A.

[2]  M. Herbig,et al.  Formation of eta carbide in ferrous martensite by room temperature aging , 2018, Acta Materialia.

[3]  S. Allain,et al.  In Situ Investigation of the Iron Carbide Precipitation Process in a Fe-C-Mn-Si Q&P Steel , 2018, Materials.

[4]  J. Speer,et al.  Microstructural evolution during quenching and partitioning of 0.2C-1.5Mn-1.3Si steels with Cr or Ni additions , 2018, Acta Materialia.

[5]  Gregory Inacio Da Rosa.  Mécanismes et conséquences de la ségrégation du bore aux joints de grains austénitiques dans les aciers à très haute résistance. , 2018 .

[6]  A. A. Mirzoev,et al.  Thermodynamic analysis of the formation of tetragonal bainite in steels , 2017, Physics of Metals and Metallography.

[7]  J. Sietsma,et al.  Characterization of bainitic/martensitic structures formed in isothermal treatments below the M s temperature , 2017 .

[8]  S. Allain,et al.  In-situ investigation of quenching and partitioning by High Energy X-Ray Diffraction experiments , 2017 .

[9]  J. Speer,et al.  Quantitative investigation into the influence of temperature on carbide and austenite evolution during partitioning of a quenched and partitioned steel , 2016 .

[10]  P. Maugis,et al.  A methodology for the measurement of the interfacial excess of solute at a grain boundary , 2016 .

[11]  Wei Li,et al.  Investigation of carbon segregation during low temperature tempering in a medium carbon steel , 2016 .

[12]  S. Ringer,et al.  Low temperature bainitic ferrite: Evidence of carbon super-saturation and tetragonality , 2015 .

[13]  J. Speer,et al.  Characterization of transition carbides in quench and partitioned steel microstructures by Mössbauer spectroscopy and complementary techniques , 2015 .

[14]  D. Raabe,et al.  Carbon partitioning during quenching and partitioning heat treatment accompanied by carbide precipitation , 2015 .

[15]  L. Kestens,et al.  Effect of fresh martensite on the stability of retained austenite in quenching and partitioning steel , 2014 .

[16]  G. Krauss,et al.  Atomic and nanoscale chemical and structural changes in quenched and tempered 4340 steel , 2014 .

[17]  H. Bhadeshia,et al.  Experimental evidence for non-cubic bainitic ferrite , 2013 .

[18]  O. Bouaziz,et al.  Unambiguous carbon partitioning from martensite to austenite in Fe-C-Ni alloys during quenching and partitioning , 2013 .

[19]  H. Bhadeshia,et al.  Solubility of carbon in tetragonal ferrite in equilibrium with austenite , 2013 .

[20]  M. Santofimia,et al.  Temperature dependence of carbon supersaturation of ferrite in bainitic steels , 2012 .

[21]  S. V. Bohemen.  Bainite and martensite start temperature calculated with exponential carbon dependence , 2012 .

[22]  T. Hirsch,et al.  In situ X-Ray Diffraction Analysis of Carbon Partitioning During Quenching of Low Carbon Steel , 2012, Metallurgical and Materials Transactions A.

[23]  F. Hu,et al.  Nanostructured high-carbon dual-phase steels , 2011 .

[24]  J. Sietsma,et al.  Overview of Mechanisms Involved During the Quenching and Partitioning Process in Steels , 2011 .

[25]  A. Clarke,et al.  Examination of carbon partitioning into austenite during tempering of bainite , 2010 .

[26]  M. Santofimia,et al.  New Experimental Evidence on the Incomplete Transformation Phenomenon in Steel. , 2009 .

[27]  C. Becquart,et al.  Dislocation interaction with C in α-Fe: A comparison between atomic simulations and elasticity theory , 2008, 0809.1520.

[28]  D. Matlock,et al.  Carbon partitioning to austenite from martensite or bainite during the quench and partition (Q&P) process: A critical assessment , 2008 .

[29]  A. Kneissl,et al.  Ätztechniken für die Phasencharakterisierung von niedriglegierten Dual-Phasen- und TRIP-Stählen , 2006 .

[30]  D. Matlock,et al.  Partitioning of carbon from supersaturated plates of ferrite, with application to steel processing and fundamentals of the bainite transformation , 2004 .

[31]  O. Bouaziz,et al.  A Model for the Prediction of Microstructure and Mechanical Properties in Cold Rolled and Annealed TRIP Steels , 2003 .

[32]  D. Matlock,et al.  Carbon partitioning into austenite after martensite transformation , 2003 .

[33]  Morris Cohen,et al.  Structural changes and strengthening in the strain tempering of martensite , 1970 .

[34]  H. Rietveld.  A profile refinement method for nuclear and magnetic structures , 1969 .

[35]  A. Cochardt,et al.  Interaction between dislocations and interstitial atoms in body-centered cubic metals , 1955 .

[36]  C. Zener.  Theory of Strain Interaction of Solute Atoms , 1948 .