Journal of University of Science and Technology Beijing
Volume 13, Number 6, December 2006, Page 1
Corresponding author: Zhengzhi Zhao, E-mail: zhaozhengzhi@sina.com
Microstructure and mechanical properties of automobile
beam steels produced by EAF-CSP process
Zhengzhi Zhao, Yonglin Kang, and Hao Yu
Materials Science and Engineering School, University of Science and Technology Beijing, Beijing 100083, China
(Received 2006-02-12)
Abstract: The microstructure, mechanical properties and misorientation of automobile beam steels produced by EAF-CSP process
were studied using optical microscopy (OM) and electron back scattered diffraction (EBSD). It shows that the microstructure of
strips is mainly polygonal ferrite, the average grain size is about 5-8 m. The electron back scattered diffraction (EBSD) results show
that grain boundaries in ferrite are basically high angle grain boundaries without remarkable preferred orientation. Hot strips of au-
tomobile beam steels possess a good combination of strength and plasticity because of its fine microstructure and low quantity of
impurities.
Key words: CSP; microstructure; mechanical property; electron back scattered diffraction
[This work was financially supported by the National Natural Science Foundation of China (No. 50334010).]
1. Introduction
Compact strip production (CSP) is an advanced
manufacturing technology of the present steel world,
which produces hot strip using a short product line
owning science, technology and engineering. Since
the first CSP steel plant was commissioned at Nucor
in 1989, 39 production mills with 54 strands have
been established in the world. There are distinct dif-
ferences between CSP and conventional processes in
slab casting, reheat schedule, rolling process, delivery
speed on the runout table and so on
[1], especially in
thermal history such as the CSP technology with
thermal history, while conventional technology with
* thermal history [2]. Accompanying the
manufacture of hot strips by the CSP technology, nu-
merous metallurgical problems have to be reconsi-
dered. So much attention has been paid to microstruc-
ture features and its evolution, precipitation behavior
etc. [3-6].
In the urgent global situation of energy, natural re-
source and environment protection, lightening auto-
mobile bodies is required from the viewpoint of sav-
ing energy that contributes to ameliorating the eco-
logical problem. A used method of doing this is the
application of high strength steel sheets to automobile
bodies. Automobile beam steel is mainly made into
cross beam, longitudinal beam and other structures.
Accompanying the rapid development of automobile
industry, there is a wide foreground for high strength
automobile beam steel sheets with high elongation,
excellent formability, impact toughness, weldability
and so on.
Guangzhou Zhujiang Iron and Steel Co. Ltd (Zhu-
jiang Steel) is the first CSP plant in China. Up to now,
Zhujiang Steel has made much more technical
achievements than expected. The plant always focuses
on constantly increasing the range products with con-
tinual improvement, at the same time, in strip quality.
In this article, the microstructure, mechanical proper-
ties and misorientation of automobile beam steels de-
veloped and produced in Zhujiang Steel were investi-
gated using optical microscope and electron back
scattered diffraction.
2. Material and experimental procedure
The chemical composition of an automobile beam
steel produced by the CSP process is (wt%): C, 0.172;
Si, 0.33; Mn, 1.19; P, 0.015; S, 0.003; Cu, 0.11; Al
t
,
0.034; balance iron. Table 1 gives a summary of the
processing conditions for CSP to produce hot strips.
Tensile tests were performed using a universal ma-
terial testing machine at room temperature. In this