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| Influence of Nb micro-alloying on austenite nucleation and growth in high speed railway wheels steel |
| WU Si1,2，LI Xiu-cheng1，ZHANG Juan1，SHANG Cheng-jia1 |
1. School of Materials Science and Engineering， University of Science and Technology Beijing， Beijing 100083
2. Metals and Chemistry Research Institute， China Academy of Railway Sciences， Beijing 100081， China |
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Abstract In allusion to high speed railway steel wheel， this papaer studied the influence of Nb micro-alloying on reverse transformation of ferrite and pearlite mocro-structure， whose precursor is ferrite and pearlite. The results indicated that the reverse transformation of ferrite and pearlite was controlled by carbon atomic diffusion. The austenite preferentially nucleated at the interface of α/Fe3C in pearlite and grew up faster in parallel with the direction of pearlite lamellae than perpendicular to that. The Nb micro-alloyed medium carbon steel with refined pearlite colonies could increase the nucleation rate of austenite and obtain smaller size austenite grains . The crystal mixture temperature of wheel steel with Nb is 80 ℃ higher than that without Nb. Nb micro-alloying could expand the temperature range of austenite reheat. Thermal-Calc calculation and TEM observation indicated that Nb existed in the form of precipitates in railway wheel steels. Precipitation pinning contributes to refine the austenite grain and postpone crystal mixture is the main mechanism of Nb-alloying in railway wheel steels.
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Received: 04 August 2014
Published: 06 July 2015
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2015, Vol. 50 
