Mechanisem of reduction of subcutaneous cracking susceptibility in niobium-containing steel by nitrogen fixation with titanium microalloying
ZHENG Wan1,2, KOU Jin-rong1,2, LI Lie-jun3, WANG Guan4, WAN Xiang4, LIU Chen-sheng4
1. The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, Hubei, China; 2. Hubei Provincial Key Laboratory for New Processes of Ironmaking and Steelmaking, Wuhan University of Science and Technology, Wuhan 430081, Hubei, China; 3. National Engineering Research Center for Near Net Forming of Metal Materials, South China University of Technology, Guangzhou 510000, Guangdong, China; 4. Guangdong Shaogang Songshan Co., Ltd., Shaoguan 512000, Guangdong, China
Abstract：Reducing the crack sensitivity of Nb containing low alloy steel slabs is a necessary condition of the advanced process of hot delivery and hot charging of steel slabs with lower fuel consumption and emission reduction. The grain size number and precipitate characteristics of Nb bearing low alloy steel slab with different titanium content were comparative studied by ultra-high temperature confocal laser scanning microscope (HT-CLSM) and transmission electron microscope (TEM),in order to reveal the mechanism of reducing the crack sensitivity of Nb containing low alloy steel by nitrogen fixation with titanium alloying. Thermodynamic calculations and TEM results of precipitates in Nb containing low alloy steel slabs show that increasing the titanium content (from 0.010% to 0.023%) enhances the precipitation temperature of titanium nitride particles (more than 1 400 ℃), which reduces the grain size of the steel by about 44% (from grade 4 to grade 6.5) by pinning the austenite grain boundaries, resulting in a significant reduction in the crack susceptibility of the high-temperature cast billets. The preferential precipitation titanium nitride particles can fixing nitrogen element to reduce the precipitation temperature of niobium-carbon nitride and aluminum nitride, and act as a heterogeneous nucleation core of nitride precipitates of niobium and aluminum to inhibit their precipitation at the grain boundary,which reduces the risk of grain boundary embrittlement of the Nb bearing low alloy steel. Modulation of nitride precipitate behavior by nitrogen fixation with titanium microalloying and grain refinement of the Nb bearing low alloy steel effectively reduced the width and depth of the third embrittlement temperature groove and increased the high temperature tensile strength by 21.3%-27.5% of niobium-containing steels, resulting in reduction of the incidence of subcutaneous cracking in cast billets by more than 80%. Controlling the titanium content in the range of 0.015% to 0.020% niobium-containing low-alloy steels can effectively avoid grain-boundary chain precipitation of precipitates leading to rolling cracks of hot charged cast billets.
郑万, 寇锦荣, 李烈军, 王冠, 万翔, 刘辰生. 微钛固氮降低含铌钢皮下裂纹敏感性的机理[J]. 钢铁, 2022, 57(8): 94-102.
ZHENG Wan, KOU Jin-rong, LI Lie-jun, WANG Guan, WAN Xiang, LIU Chen-sheng. Mechanisem of reduction of subcutaneous cracking susceptibility in niobium-containing steel by nitrogen fixation with titanium microalloying[J]. Iron and Steel, 2022, 57(8): 94-102.
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2022, Vol. 57 
