Unexpected Effect of Nb Addition as a Microalloying Element on Mechanical Properties of δ-TRIP Steels  

作　　者：Sajad Gholami SHIRI Seyed Ahmad Jenabali JAHROMI Yahya PALIZDAR Majid BELBASI 

机构地区：[1]Department of Materials Science & Engineering, School of Engineering, Shiraz University, Shiraz 115019, Iran [2]Nanotechnology and Advanced Materials Department, Materials and Energy Research Center, Karaj 128747, Iran [3]Department of Materials Engineering, Islamic Azad University Central Tehran Branch, Tehran 009821, Iran

出　　处：《Journal of Iron and Steel Research International》2016年第9期988-996,共9页

基　　金：Sponsored by Iran National Science Foundation(94016117)

摘　　要：The concept of microalloying was applied to the δ-TRIP （transformation-induced plasticity） steel to inves- tigate the feasibility of increasing the mechanical properties and understanding the effect of microalloying on the morphology and structure of the steel. A hot rolled δ-TRIP steel with three different contents of Nb （0, 0.03, 0.07 mass%） was subjected to the microstructural and mechanical examination. The high Al and Si concentration in these steels guaranteed the presence of the considerable δ-ferrite phase in the microstructure after the casting and the subsequent hot rolling. The obtained results showed that Nb dramatically affects the microstructure the dynamic re- covery and recrystallization behavior, as well as the grain shape and thus the stability of austenite after the thermo- mechanical process of hot rolling. The results also revealed an unexpected effect of Nb on the mechanical properties. The addition of Nb to the δ-TRIP steel led to a significant decrease in the ultimate strength （from 1144 to 917 MPa） and an increase in ductility （from 24% to 28%）. These unconventional results could be explained by the change in the steel microstructure. The work-hardening＇behaviors of all samples exhibit three stages of the work-hardening rate evolution. At the stage 2, the work-hardening rate of the studied steels increased, being attributed to the TRIP effect and the transformation of austenite to martensite.The concept of microalloying was applied to the δ-TRIP （transformation-induced plasticity） steel to inves- tigate the feasibility of increasing the mechanical properties and understanding the effect of microalloying on the morphology and structure of the steel. A hot rolled δ-TRIP steel with three different contents of Nb （0, 0.03, 0.07 mass%） was subjected to the microstructural and mechanical examination. The high Al and Si concentration in these steels guaranteed the presence of the considerable δ-ferrite phase in the microstructure after the casting and the subsequent hot rolling. The obtained results showed that Nb dramatically affects the microstructure the dynamic re- covery and recrystallization behavior, as well as the grain shape and thus the stability of austenite after the thermo- mechanical process of hot rolling. The results also revealed an unexpected effect of Nb on the mechanical properties. The addition of Nb to the δ-TRIP steel led to a significant decrease in the ultimate strength （from 1144 to 917 MPa） and an increase in ductility （from 24% to 28%）. These unconventional results could be explained by the change in the steel microstructure. The work-hardening＇behaviors of all samples exhibit three stages of the work-hardening rate evolution. At the stage 2, the work-hardening rate of the studied steels increased, being attributed to the TRIP effect and the transformation of austenite to martensite.

关 键 词：δ-TRIP steel Nb microalloying high Al steel mechanical property WORK-HARDENING 

分 类 号：TG142.1[一般工业技术—材料科学与工程]