Materials Science and Engineering A 437 (2006) 114–119 Retained austenite stability investigation in TRIP steel using neutron diffraction J. Zrn´ ık a,b,∗ , O. Mur´ ansky c , P. Luk´ aˇ s c , Z. Nov ´ y a , P. Sittner d , P. Horˇ nak b a Comtes FHT, Lobezska E981, 326 00 Pilsen, Czech Republic b Technical University of Koˇ sice, Letna 9, 040 01 Koˇ sice, Slovak Republic c Institute of Nuclear Physics, 250 68 Reˇ z near Prague, Czech Republic d Institute of Physics, ASCR, Na Slovance 2, 18221 Prague Czech Republic Received 12 September 2005; received in revised form 15 April 2006; accepted 15 April 2006 Abstract In situ neutron diffraction experiment was employed for monitoring of conditioned austenite transformation to ferrite, and also for the retained austenite stability evaluation during subsequent mechanical loading. The progress in the austenite decomposition to ferrite is monitored at different transformation temperatures. The relevant information on the course of the transformation is extracted from neutron diffraction spectra. The useful information was also obtained on the retained austenite stability in the TRIP steel during mechanical testing. The in situ neutron diffraction experi- ments were conducted at two different diffractometers to assess the reliability of the neutron diffraction technique at monitoring the transformation of the retained austenite during room temperature tensile testing. In both experiments the neutron investigation was focused on the volume fraction quantification of the retained austenite as well as on internal stresses rising in structure phases due to the retained austenite transformation. © 2006 Elsevier B.V. All rights reserved. Keywords: TRIP steel; Austenite conditioning; Neutron diffraction; Austenite transformation; Stress; Strain 1. Introduction The considerable research effort has been invested in devel- oping high-strength steels with the necessary good formability mainly for applications in the automotive industry. The new high strength TRIP-aided steels seem to be a promising solution for such cold formable steels. The transformation induced plastic- ity (TRIP) effect has been observed in high alloy metastable austenitic steels as well as in low alloy multiphase steels [1,2]. In the last decade, this idea has been further developed and TRIP steels have constituted a new category of structural steels. The TRIP steels are multiphase steels with the ferrite, bainite and retained austenite phases found in the structure [3,4]. An attractive combination of the high strength and ductility results from the interaction of individual structural constituents. The high tensile strength arises from a martensitic transforma- tion of the metastable retained austenite induced by the external stress [5,6]. Mechanical properties of multiphase steels can be ∗ Corresponding author. Tel.: +420 377 327427; fax: +420 377 422224. E-mail address: jzrnik@comtesfht.cz (J. Zrn´ ık). tailored according to demands of the foreseen application by varying parameters such as the type, volume fraction, morphol- ogy, size and distribution of the individual structural phases. The investigation has confirmed that important effect of forming conditions on structure development may result from austenite conditioning and bainite transformation [7–9]. The proper evaluation of the volume fraction of the phases, and of the retained austenite especially, is essential to modify the properties of the TRIP steel. Nowadays, most frequently used methods include X-ray diffraction, neutron diffraction, optical and electron microscopy (TEM, SEM) combined with image analyses, M ¨ ossbauer spectroscopy, dilatometry, and magnetiza- tion measurings [10–12]. In the present work, the neutron diffraction method applied in situ upon the thermomechanical (TM) processing has been used to monitor the austenite to ferrite isothermal transformation at different temperatures, and to determine the transformation temperature for the experimental TRIP steel. The transforma- tion characteristics were analyzed with respect to the ferrite volume fraction. The effective transformation temperature was suggested. With respect to transformation results, the austenite conditioning process and temperature–time schedule to produce 0921-5093/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2006.04.067