Materials Chemistry and Physics 117 (2009) 257–261
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Materials Chemistry and Physics
journal homepage: www.elsevier.com/locate/matchemphys
Effect of carbon content on microstructural characteristics of the
hypereutectic Fe–Cr–C claddings
Chia-Ming Chang
a
, Chi-Ming Lin
a
, Chih-Chun Hsieh
a
, Jie-Hao Chen
a
,
Chih-Ming Fan
b
, Weite Wu
a,∗
a
Department of Materials Science and Engineering, National Chung Hsing University, 250 Kuo-Kuang Rd., Taichung, Taiwan
b
Kuang Tai Metal Industrial Co., Ltd., 8 Lu-Ke Third Rd., Lujhu Township, Kaohsiung, Taiwan
article info
Article history:
Received 3 November 2008
Received in revised form 29 April 2009
Accepted 28 May 2009
Keywords:
Carbide
Welding
Microstructure
Hardness
abstract
The hypereutectic Fe–Cr–C claddings with different C contents were deposited on ASTM A36 steel sub-
strates by flux cored arc welding (FCAW) to investigate that the effect of C content on microstructural
characteristics. The results showed that the microstructure of hypereutectic Fe–Cr–C claddings con-
sisted of primary proeutectic (Cr,Fe)
7
C
3
and the austenite plus (Cr,Fe)
7
C
3
eutectic. Proeutectic carbides
undergone to several microstructural changes in response to higher carbon content in the cladding.
The morphologies of proeutectic (Cr,Fe)
7
C
3
carbides changed from blade-like to rod-like with hexagonal
cross section. The amounts of proeutectic (Cr,Fe)
7
C
3
carbides increased with increase of the C contents.
The nucleation sites of proeutectic (Cr,Fe)
7
C
3
carbides increased under high undercooling condition.
Hence, the latent heat of solidification can be released by formed proeutectic (Cr,Fe)
7
C
3
carbides and
then the growth of proeutectic (Cr,Fe)
7
C
3
carbides were suppressed. Consequently, it showed a maxi-
mum hardness value (about HRC 62) when the amount of proeutectic (Cr,Fe)
7
C
3
carbides exceeded 86%.
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
Fe–Cr–C alloys are used in severe abrasive conditions, so the
superior abrasion resistance is necessary. The excellent abrasive
wear resistance results from high volume fraction of carbides and
the toughness of the matrix also contribute to the wear resis-
tance [1]. The investigations of Fe–Cr–C alloy microstructures have
shown that these types of materials have hypoeutectic, eutec-
tic, and hypereutectic structures [2].M
7
C
3
primary carbides form
in large amounts at higher carbon concentration. The coating
microstructure consists of primarily solidified chromium-carbides
of the M
7
C
3
-type, which are embedded in the eutectic [3,4]. Earlier
research on Fe–Cr–C alloys produced with conventional tech-
niques has revealed the formation of microstructures comprising
-ferrite and complex carbides, such as M
3
C, M
7
C
3
and M
23
C
6
,
depending on the alloy composition [4,5].M
7
C
3
primary car-
bides formed when the carbon content is 2–5 wt.% and chromium
content is 18–30wt.%. This kind of hard material can be repre-
sented by high chromium white cast iron which has high hardness
M
7
C
3
(about 1600 Hv) [6–8]. Cr
7
C
3
is well known for its excel-
∗
Corresponding author.
E-mail address: wwu@nchu.edu.tw (W. Wu).
lent combination of high hardness, excellent wear resistance as
well as good corrosion and oxidation resistance, so it has been
widely used as the reinforcing phase in the composite coatings
[9–12].
Most researches focus on that the solidification behavior,
microstructural characteristics (such as hypoeutectic, eutectic,
and hypereutectic), and mechanical properties of Fe–Cr–C sys-
tem. However, there are few investigations about morphology of
primary carbide in Fe–Cr–C system. Therefore, the relationship
between the morphology of primary carbide and the carbon con-
tent of hypereutectic Fe–Cr–C claddings was investigated in this
study.
2. Experimental procedures
The base metals (100 mm × 80 mm × 10mm) for the welding surface were pre-
pared from ASTM A36 steel plates. Before welding, these specimens were ground
and cleaned with acetone. In order to get the claddings with different carbon con-
tents and their chemical composition must fall down in hypereutectic area, different
amounts of graphite (7, 10 and 13wt.%), the constant chromium powder (40wt.%),
and ferrosilicon (2 wt.%), ferromanganese (5 wt.%) were added into flux cored wire.
The addition of ferrosilicon and ferromanganese were used to reduce the oxygen of
claddings.
Bead-on-plate with oscillate flux cored arc welding was utilized to deposited
the claddings. Fig. 1 shows the schematic diagram of the welding method. Table 1
presents the range of welding conditions used in this research.
0254-0584/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.matchemphys.2009.05.052