Effect of Solid Solution Elements on Solubility Products of Carbides and Nitrides in Ferrite: Thermodynamic Calculations
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pct Mn loga KTiN ¼ 5:41 T 32 þ ½wt pct Ni T 12; 799 þ 0:05½wt pct Mn loga KNbN ¼ 5:51 T 13 þ ½wt pct Ni T
XUAN-WEI LEI, XUE-HUI ZHANG, and TONG-XIANG LIANG are with the School of Materials Science and Engineering, Jiangxi University of Science and Technology, Ganzhou 341000, P.R. China. Contact e-mails: [email protected]; [email protected] DA-YONG LI is with the Bohai Shipyard Group Co., Ltd., Huludao 125000, P.R. China. Manuscript submitted August 16, 2018. Article published online April 12, 2019 2978—VOLUME 50A, JUNE 2019
10; 615 loga KVN ¼ 4:94 T 85 þ 0:05 þ ½wt pct Mn T 49 ½wt pct Ni þ 0:03 þ T
https://doi.org/10.1007/s11661-019-05188-y The Minerals, Metals & Materials Society and ASM International 2019
I.
INTRODUCTION
HEAT treatments, including annealing and tempering, are very effective and boastful techniques to improve the comprehensive mechanical properties of microalloyed steels. Besides microstructure, the formed precipitate in these processes is also one important component that affects its performance. The fraction of precipitates is a significant parameter in quantitatively analyzing the role of precipitates in improving mechanical properties. The deduced solubility product of carbide or nitride in pure ferrite by former researchers are commonly used to estimate its fraction.[1,2] A general consensus is that solubility products of carbide and nitride in pure ferrite are intensely small and solid solution alloy elements have a minor effect on the solubility products. Thus, even in a relatively high solid solution alloy steel, the solubility product of carbide or nitride in pure ferrite can be used to approximate the fraction of its precipitates.[3,4] However, the reasonableness of this approach has not been evaluated and systematic investigations on the effect of solid solution elements on solubility products of carbides and nitrides in ferrite have not been carried out. In addition, nearly no exact solubility product expressions of carbide and nitride in ferrite containing solid solution elements have been reported in references. METALLURGICAL AND MATERIALS TRANSACTIONS A
In this article, thermodynamic calculations are adopted to develop solubility products of titanium, niobium, vanadium carbide, and nitride in pure ferrite and to evaluate the effect of solid solution elements on solubility products of these carbides and nitrides. The calculation results are compared with previous studies to show their reliability. Thus, a reference of solubility products of these carbides and nitrides in ferrite containing solid solution elements can be obtained from this work.
II. THERMODYNAMIC CALCULATIONS TO EVALUATE SOLUBILITY PRODUCT OF FCC BINARY COMPOUND IN FERRITE Consider the Fe-X1-X2-…-M-N system consisting of two components: a-Fe based solid solution (ferrite) and fcc structure compound. Thermodynamic calculations are based on several assumptions: 1.
2.
3. 4.
Both Gibbs energies of ferrite and compound can be described by the two-sublattice model. Fe, Xi, and M atoms fill in
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