Microstructure and Mechanical Properties of Low- and Medium-Carbon Si-Rich Low-Alloy Steels Processed by Austemping after Intercritical Annealing.

Xin Jia,Ting Zhao,Yuefeng Wang,Tiansheng Wang,Lin Wang,Xiaowen Sun

doi:10.3390/ma15031178

Abstract

In the present paper, the designed thermomechanical process was applied to prepare ferrite/bainite multiphase microstructures in Si-rich low-alloy steel with a carbon content of 0.33 wt.% (0.33C) and 0.21 wt.% (0.21C). The microstructures were analyzed by scanning electron microscope, transmission electron microscope, and electron backscatter diffraction, and the mechanical properties (tensile and impact properties) were tested. The results showed that, on the premise of obtaining 15 vol.% ferrite in both steels, the ferrite grains in the 0.33C steel were polygonal with an average grain size of 2.2 μm, recrystallized more completely. However, the ferrite grains in the 0.21C steel were mainly long strip-shaped with a width of 2–4 μm, and the recrystallization degree was poor. In addition, upon increasing the austempering temperature, bainite ferrite laths were formed in the 0.33C steel, and the thickness was in the range of 81–123 nm. The morphology of bainite ferrite in the 0.21C steel gradually changed from lath to granular. Upon increasing the austempering temperature, the tensile strength and yield strength of both steels increased and the elongation decreased slightly. The impact energy of the two steels showed different trends upon increasing the austempering temperature, in which the impact energy of the 0.33C steel increased, while that of the 0.21C steel decreased. This is due to the difference size of the martensite-austenite constituents in the two steels.

Highlights

Published: 3 February 2022With the rapid development of modern industry, higher requirements are put forward for the properties of materials [1,2]
In the previous work [22], we designed a novel process route, that is, the tempered troostite microstructure was subjected to 40% cold-rolling deformation, intercritical annealing + austempering treatment was performed to obtain ultrafine-grain ferrite/lowtemperature bainite microstructure, and both strength and toughness were improved
The low- and medium-C steels used in this study were smelted in a vacuum induction furnace and cast into ingot with a diameter of 180 mm

Summary

Introduction

With the rapid development of modern industry, higher requirements are put forward for the properties of materials [1,2]. In the previous work [22], we designed a novel process route, that is, the tempered troostite microstructure was subjected to 40% cold-rolling deformation, intercritical annealing + austempering treatment was performed to obtain ultrafine-grain ferrite/lowtemperature bainite microstructure, and both strength and toughness were improved. Alloying elements, such as Ni and W, were added to the steel, which increased the cost. The difference of microstructures between the two steels under the same process design was studied, and the relationship between microstructures and mechanical properties was briefly analyzed

Materials and Experimental Methods

Microstructures

Tensile Properties

Impact Properties

Fractographs of Impacted Samples

Conclusions