TY - JOUR

T1 - In situ analysis of the effect of high heating rates and initial microstructure on the formation and homogeneity of austenite

AU - Eggbauer, Annika

AU - Lukas, Marina

AU - Ressel, Gerald

AU - Prevedel, Petri

AU - Mendez Martin, Francisca

AU - Keckes, Jozef

AU - Stark, Andreas

AU - Ebner, Reinhold

PY - 2019/3/22

Y1 - 2019/3/22

N2 - Decreasing processing time of a quench and temper heat treatment is of high interest for industry due to the possibility of cost reduction. One option to reduce processing time is to shorten the austenitizing cycle by applying high heating rates and minimum holding times. However, due to the high heating rates, the analysis of their influences on the formation kinetics of austenite and its crystallographic parameters is challenging. Thus, this work concentrates on the in situ analysis of the austenitization process by means of high-energy X-ray diffraction to study a range of heating rates applied to ferritic–pearlitic and soft annealed initial microstructures. The transformation kinetics from ferrite/pearlite and soft annealed state to austenite, the cementite dissolution behavior and the homogeneity of the freshly formed austenite were analyzed. The results indicate three distinct steps of austenite formation independent of initial microstructure and heating rate: (1) nucleation of carbon-rich austenite at cementite–ferrite interfaces, (2) growth of austenite phase fraction accompanied by a reduction of the carbon content, until reaching the mean carbon content of the steel, followed by growth of the austenite grain size, (3) regarding austenite homogeneity, the combination of austenitization temperature and initial microstructure are the main influencing factors.

AB - Decreasing processing time of a quench and temper heat treatment is of high interest for industry due to the possibility of cost reduction. One option to reduce processing time is to shorten the austenitizing cycle by applying high heating rates and minimum holding times. However, due to the high heating rates, the analysis of their influences on the formation kinetics of austenite and its crystallographic parameters is challenging. Thus, this work concentrates on the in situ analysis of the austenitization process by means of high-energy X-ray diffraction to study a range of heating rates applied to ferritic–pearlitic and soft annealed initial microstructures. The transformation kinetics from ferrite/pearlite and soft annealed state to austenite, the cementite dissolution behavior and the homogeneity of the freshly formed austenite were analyzed. The results indicate three distinct steps of austenite formation independent of initial microstructure and heating rate: (1) nucleation of carbon-rich austenite at cementite–ferrite interfaces, (2) growth of austenite phase fraction accompanied by a reduction of the carbon content, until reaching the mean carbon content of the steel, followed by growth of the austenite grain size, (3) regarding austenite homogeneity, the combination of austenitization temperature and initial microstructure are the main influencing factors.

UR - http://www.scopus.com/inward/record.url?scp=85063565982&partnerID=8YFLogxK

U2 - 10.1007/s10853-019-03527-3

DO - 10.1007/s10853-019-03527-3

M3 - Article

VL - 54.2019

SP - 9197

EP - 9212

JO - Journal of materials science

JF - Journal of materials science

SN - 0022-2461

IS - 12

ER -