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| EFFECT OF Ti AND Nb MICRO–ALLOYING ON THE MICROSTRUCTURE OF THE ULTRA–PURIFIED 11%Cr FERRITE STAINLESS STEELS |
| LIU Jing, LUO Xinghong, HU Xiaoqiang, LIU Shi |
| Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 |
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Cite this article:
LIU Jing LUO Xinghong HU Xiaoqiang LIU Shi. EFFECT OF Ti AND Nb MICRO–ALLOYING ON THE MICROSTRUCTURE OF THE ULTRA–PURIFIED 11%Cr FERRITE STAINLESS STEELS. Acta Metall Sin, 2011, 47(6): 688-696.
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Abstract Ultra–purified ferrite stainless steels (UP–FSS) are widely used in the fields of automobile, household appliances etc. Much better performance than conventional ferrite stainless steels is obtained by minimizing the interstitial elements level in UP–FSS. However, some negative effects, such as degradation of the formability and ridging–resistance, are also brought by purifying the steels, which lead to abnormally growth of the columnar grains. Moreover, the grains in heat affected zone (HAZ) are apt to coarsen during welding process. One of the effective ways to resolve such problems is to increase the equiaxial grain ratio in as–cast microstructure and refine the grain size. Micro–alloying of steels with strong carbide and nitride former, such as Ti and Nb, is a way to do that. In this work, the effects of Ti and Nb micro–alloying on the as–cast, as–rolled, and HAZ microstructures of the ultrapurified 11%Cr ferrite stainless steels with different interstitial element levels were investigated by both experimental research and thermodynamic calculation. The results indicated that the effect of Ti and Nb micro–alloying was better when the content of C and N in the steel was 0.0163%, which showed the minimum grain size in as–cast, as–rolled, and HAZ microstructures, and the equiaxial grain ratio in as–cast microstructure was evidently improved as well. It was found by calculation that, with increasing of C and N content and addition of Ti and Nb to the steels, the solid–liquid two–phase region was broadened. This was beneficial to increase the undercooling in front of the liquid–solid interface and the probability of heterogeneous nucleation, and consequently, increase the equiaxial grain ratio and decrease te mean grain size in as–cast microstructure. On the other hand, with addition of Ti and increase of N conent, TiN type particles might precipitate in olid–liquid two–phase regio, which was helpful for promoting the heterogeneous nucleation of δ ferrite.
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Received: 24 January 2011
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| Fund: Supported by National Natural Science Foundation of China (No.50734002) |
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