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!" SACM 645 !"#$%&' 104 (2010) 19-23
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Effects of Gas Nitriding on the Corrosion Properties of
SACM 645 Steel
*
L. H. ChiuF. S. ChenS. H. Yeh
Received 3 November 2009; received in revised form 5 March 2010; accepted 16 March 2010
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Abstract
This research is to study the effect of the
nitrided case produced by gas nitriding processes
on the corrosion resistance properties of the JIS
SACM 645 steel. In gas nitriding, the effect of
different substrate hardness and nitriding holding
time was compared. Treated specimens were
characterized by means of microstructural
analysis, microhardness measurements, X-ray
diffraction analysis, glow discharge spectrometer
analysis and electrochemical tests in NaCl
1
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aerated solutions. The hardness of surface
layers of the nitrided specimens was in the
range between 1000-1100 HV0.1, and the phases
of the nitrided case were consisted of Fe 2-3 N
and Fe4N, that can increase corrosion resistance
of JIS SACM 645 steel.
Keywords: S A C M 6 4 5 , G a s n i t r i d i n g ,
Corrosion resistance, Polarization
curve
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645 !"#$%&'()*+,-./
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Table. 1 Chemical composition (wt%) of JIS SACM
645 steel.
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2.1 !
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!"#$%&'()*+,-. (GDS)
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wt%
C
Si
Mn
Cr
Mo
Al
SACM 645
0.48
0.22
0.53
1.66
0.16
1.01
Table. 2 Nomenclatures of specimens and treatments.
X-TMS
XC-GNY
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0.15418 nm) !"#$%&'()* 20°
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WE
RE
CE
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500
Sample
Case depth (µm)
450
400
350
300
250
3.5% NaCl Solution
200
0
Fig. 1 Schematic diagram of the flat cell used for
polarization corrosion test, WE: working
electrode, RE: reference electrode, CE: counter
electrode.
(a)
(b)
(c)
(d)
Fig. 2 Micrographs of SACM 645 specimens nitrided
at given processing conditions, (a) 30C-GN12,
(b) 30C-GN24, (c) 30C-GN48 and (d) 30CGN96.
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20
40
60
80
Nitriding time (hr)
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Fig. 3 Case depth of specimens at different nitriding
time.
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3.3 XRD 530°C ~ 21 ~
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: Fe2O3
30C-GN12
30C-GN24
30C-GN48
30C-GN96
800
: Fe4N
: Fe3N
:M
Substrate
200 µm
Intensity
Hardness (Hv0.1)
1000
600
110 µm
30 µm
400
200
Substrate
200 400 600 800 1000 1200 1400
Distance from surface (µm)
Fig. 4 The microhardness profile of specimens
nitrided at given conditions.
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40
60
80
2θ (Degree)
100
Fig. 5 XRD patterns of substrate and gas nitrided
layers at 530°C × 48 h.
12
10
Concentration (at%)
0
N
8
6
4
O
2
0
0
10 20 30 40 50 60 70 80 90 100
Depth (µm)
Fig. 6 The element concentration profile analysis for
the SACM 645 specimens nitrided at 530°C ×
48 h.
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Potential (Volts)
1.0
0.5
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GN48
30-TMS
GN24
30C-GN12
30C-GN24 GN12
GN96
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30C-GN96
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0
30-TMS
-0.5
-1.0 –9
10
10–8
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Current Density (A/cm2)
10–3
10–2
Fig. 7 Potential dynamic curves of SACM 645 specimens nitrided at given processing conditions.
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!"
1. ! !"#$% !"#$%&'
!"#$ 62 (1999) pp. 49-77.
2. ! !"#$% !"#$%&'
(2) !"# 63 (1999) pp. 63-71.
3. !"#!$%&!'()!*+,-./
65 (2000) pp. 17-28.
4. !"#$%! 13(2) (1981) pp. 21-33.
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