Effect of V Addition on Microstructure and Mechanical Properties in C–Mn–Si Steels after Quenching and Partitioning Processes

Gong-Ting Zhang,Zhi-Wang Zheng,Di Tang,Zheng-Zhi Zhao,Bo-Wei Sun,Lin Li,Na-Qiong Zhu

doi:10.3390/met11081306

Abstract

Three C-Si-Mn Q&P steels with different V addition after one-step and two-step quenching and partitioning (Q&P) processes were investigated by means of optical microstructure observation, X-ray diffraction (XRD) measurement, transmission electron microscopy (TEM) characterization and particle size distribution (PSD) analysis. The effect of V addition on strength and ductility of the steels was elucidated by comparative analysis on the microstructure and mechanical properties as functions of partitioning time and temperature. For one-step Q&P treatment, the mechanical properties were mainly controlled by the tempering behavior of martensite during partitioning. V addition was helpful to mitigate the deterioration of mechanical properties by precipitation strengthening and grain refinement strengthening. For two-step Q&P treatment, the satisfying plasticity was attributed to the transformation-induced plasticity (TRIP) effect of retained austenite maintaining the high work hardening rate at high strain regime. The higher volume fraction of retained austenite with high stability resulted from the refined microstructure and the promoted carbon partitioning for the steel with 0.16 wt% V addition. However, the carbon consumption due to the formation of VC carbides led to the strength reduction of tempered martensite.

Highlights

Quenching and partitioning (Q&P) steel provides excellent mechanical properties required for automotive applications [1,2,3,4]
The Q&P heat-treatment consists of fully austenizing or intercritical annealing followed by quenching below Ms temperature and partitioning at the same quenching temperature or at a higher temperature [5,6]
V-added Transformation-Induced Plasticity (TRIP) steels were reported to obtain a good combination of strength and elongation [11,12,13]

Summary

Introduction

Quenching and partitioning (Q&P) steel provides excellent mechanical properties required for automotive applications [1,2,3,4]. The strong carbide forming elements like V, Nb, and Ti have been added into the Q&P steels to improve the mechanical properties. In Q&P steels [7,8,9,10], V addition can increase the strength and work hardening exponent by VC carbides precipitating in ferrite and martensite. A fewer difference in the strength of ferrite with VC precipitation and tempered soften martensite can obtain a better plasticity. V-added Transformation-Induced Plasticity (TRIP) steels were reported to obtain a good combination of strength and elongation [11,12,13]. The V-alloying can increase both strength and ductility of medium Mn steel simultaneously

Methods

Results

Conclusion