Materials Transactions, Vol. 52, No. 8 (2011) pp. 1709 to 1712
#2011 The Japan Institute of Metals
RAPID PUBLICATION
Interface Characteristic and Properties of Stainless Steel/HSLA Steel
Clad Plate by Vacuum Rolling Cladding
Guangming Xie* , Zongan Luo, Guanglei Wang, Liang Li and Guodong Wang
The State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, P. R. China
304 austenite stainless steel plate and HSLA steel plate were subjected to vacuum rolling cladding (VRC). The microstructure
characteristic and properties of the clad interface were investigated in detail. During the VRC process, the clad interface was held at a high
vacuum all the time, resulting in significantly decreased oxidation at the interface. A small amount of very fine oxide particles (diameter <
0:5 mm) can be found at the clad interface, and no obvious defects were observed. The remarkable diffusion of Ni and Cr elements led to the
formation of a transition zone with high hardness. The shear strength of the clad interface was as high as 487 MPa, and the fracture occurred at
the HSLA steel near the transition zone. No cracks were found at the clad interface after the 180 bending tests with both outside and inside
manners. [doi:10.2320/matertrans.M2011127]
(Received April 25, 2011; Accepted May 30, 2011; Published July 13, 2011)
Keywords: vacuum rolling cladding, clad plate, interface, microstructure, mechanical properties
1.
Introduction
Stainless steel clad plates are widely used in chemical and
nuclear industries in order to take advantage of the corrosionresistant and reduce the cost. The stainless steel clad plate
was fabricated by cladding a stainless steel on the surface
of the high strength low alloy (HSLA) steel.1) Recently,
explosive cladding,2,3) rolling cladding4,5) and weld overlay
cladding6–9) have been used to produce the clad plates.
Explosive cladding is a widely applied technique to produce
the clad plates, especially for the metals with dissimilar
melting points. However, the explosive clad plate has bad
flatness, and a hot rolling process is usually needed to
improve the flatness quality.2,3) The clad plate with good
flatness can be fabricated by rolling cladding, but it is difficult
to control the interface oxidation, resulting in the significantly reduced bonding strength.
Vacuum rolling cladding (VRC) was invented at Japan’s
Kawasaki Heavy Ind. Ltd. in 1981.10) Figure 1 shows the
concept of VRC. Two metal plates are surface-treated and
made up into a built-up slab and the electron beam welding
(EBW) was performed at the four sides (Figs. 1(a) and (b)).
The built-up slab is hot-rolled to produce a clad plate
(Fig. 1(c)). The surface treatment removes the scale and
other foreign matter, and the EBW ensures the high vacuum
in the built-up slab and avoids interface oxidation during
heating and hot rolling. During the VRC, by severe rolling
deformation at the high vacuum and high temperature,
sound metallurgical bonding of the two metals was achieved
at the clad interface. Recently, another rolling cladding
method under a vacuum atmosphere was reported
widely.11,12) Compared to the VRC, both heating and rolling
processes of two metal plates were conducted in a vacuum
chamber with the high vacuum. However, the large clad
plate is difficult to produce by this method and the rolling
capability of rolling mill, i.e., the rolling reduction rate,
is also limited due to the small chamber volume. The
Ti/stainless steel clad plate and aluminum alloy/stainless
*Corresponding
author, E-mail: xiegm@ral.neu.edu.cn
Fig. 1 Schematic presentation of the VRC process for stainless steel/
HSLA steel clad plate: (a) Surface treatment and stacking, (b) EBW and
heating, and (c) hot rolling.
steel clad plate were obtained by this method,11,12) but no
studies on the HSLA steel/stainless steel clad plate were
reported.
Currently, there are few investigations on the VRC. In
2004, JFE Steel Corporation reported the commercial
production of the stainless steel clad plate by VRC, but no
detailed microstructure characteristic of the clad interface
was investigated.13,14) In our previous work, clad plate of two
same carbon steel plates was achieved by VRC and exhibited
sound mechanical properties.15) In this study, we investigated
on the correlation between the interface microstructure and
the mechanical properties of the clad plate of 304 stainless
steel and HSLA steel by VRC.
2.
Experimental Procedure
304 austenite stainless steel and HSLA steel plates with
dimension of 200 mm 100 mm 10 mm and 200 mm 100 mm 50 mm, respectively, were clad by VRC. The
chemical compositions of the 304 stainless steel and the
HSLA steel are given in Table 1. The surfaces of stainless
steel and HSLA steel were machined by the milling machine
to reveal the fresh metal surface. EBW was performed at a
welding current of 30 mA, a welding voltage of 80 kV and
a welding speed of 200 mm/min with vacuum degree of
1 10 2 Pa. Hot rolling was carried out after soaking the
built-up slab at 1200 C for 60 min. The thickness of the clad
plate was reduced from 60 mm (10+50) down to 12 mm
(2+10) after 4 passes hot rolling with a reduction ratio of
24% in each pass.
1710
G. Xie, Z. Luo, G. Wang, L. Li and G. Wang
Table 1
Elements
C
Si
Mn
Chemical composition of 304 stainless steel and HSLA steel (mass%).
P
S
Cr
Ni
Al
Cu
Ti
Nb
V
Fe
Stainless steel
0.06
0.26
1.73
0.003
0.003
19.2
9.8
—
—
—
—
—
Bal.
HSLA steel
0.05
0.36
1.45
0.005
0.004
0.15
0.21
0.029
0.29
0.017
0.037
0.0026
Bal.
The clad interface sample was etched with a solution of
5 mL nitric acid and 95 mL ethanol. Microstructural features
were characterized by scanning electron microscopy (SEM)
and transmission electron microscopy (TEM), equipped with
energy dispersive spectroscopy (EDS). Element distribution
analysis was carried out on a JEOL-8530 electron probe
microscopic analyzer (EPMA). The Vickers hardness tests
were performed on a Future Tech-type Vickers hardness
machine with a 100 g load for 13 s. The bend and shear
specimens were machined perpendicular to the rolling
direction with a gauge length of 150 mm, gauge width of
10 mm and gauge thickness of 8 mm (2+6). The shear tests
were accorded with the ASTM standard.16) The bend and
shear tests were carried out using an Instron-type universal
testing machine at a strain rate of 1 10 3 s 1 .
3.
Results and Discussion
Figure 2(a) shows the cross-sectional structural photograph of the stainless steel/HSLA steel clad plate. Relatively
flat clad interface was achieved in the clad plate, which was
different from the wave-like explosive clad interface originated from the concentrated plastic deformation in the
localized contact zone.2,3) From the magnified view of the
clad interface shown in Fig. 2(b), a small amount of very fine
particles (diameter < 0:5 mm) were distributed at the clad
interface, and the typical TEM morphology of the fine
particle was shown in Fig. 2(c). A transition zone about 5 mm
in width was observed between the stainless steel and HSLA
steel from the contrast differences, and no obvious defects
were observed at the interface. By comparison, many distinct
defects were observed at the interface of the clad plate by
explosive cladding and weld overlay cladding, resulting in
significantly decreased bonding properties.2,6) Rao et al.3)
reported that the un-bonded zone exceeded 20 mm, and melt
pocket (10 mm) were found at the interface of the explosive
304 stainless steel clad plate. For the weld overlay clad
procedure, various defects such as blow, pin hole and
entrapped slag were easily formed at the clad interface.6)
Certainly, interface defects have a significant effect on the
interface bonding of the clad plate.
Figure 3(a) shows the EDS result by TEM of the fine
particle shown in Figs. 2(b) and (c). Besides the matrix
elements of Fe and Cr, very high content of Mn, Si and O
elements were clearly detected on the fine particle. Therefore,
the fine particles are more probably oxides according to the
results of Masahiroe et al.17) They indicated that the Mn-Si-O
oxide was easily formed on the surface of steel containing Si
and Mn elements due to the selection oxidation. For the conventional hot rolling cladding technique, however, the clad
metals significantly reacted with the atmospheric oxygen,
resulting in the formation of an obvious oxide film at the clad
interface during heating.4) Morizono et al.18) reported that the
Fig. 2 Micrographs of the clad interface of stainless steel/HSLA steel
clad plate: (a) SEM backscattered electron image of clad interface,
(b) magnified view of clad interface, and (c) TEM image of fine particle
near clad interface.
Fig. 3
EDS results of (a) fine particle, and (b) transition zone.
high temperature exposure led to obvious interface oxidation
in explosive welded titanium/430 ferritic stainless steel clad
plate. In this study, though the high vacuum technique
was used during the VRC process, the micro-oxidation still
existed at the clad interface. Firstly, few Fe-O oxides might
be formed at the surface of plates during the surface-treating
(Fig. 1(a)). Then, the easily oxidized elements of Mn, Si
would react with the O element in the Fe-O oxides during the
VRC, producing the Mn-Si-O oxide particles. Simultaneously, the severe plastic deformation by hot rolling made
these oxide particles broken and dispersed near the clad
interface shown in Fig. 2(b), reducing the size of the oxide
particles. Therefore, the fine particles near the clad interface
should be the Mn-Si-O oxides, but the influence of the oxide
particles on the mechanical properties should be very little
due to the fine size and the limited amount.
Interface Characteristic and Properties of Stainless Steel/HSLA Steel Clad Plate by Vacuum Rolling Cladding
1711
Table 2 Vickers hardness of clad plate.
Position
Stainless steel
HSLA steel
Transition zone
Vickers Hardness, Hv
204
135
381
Fig. 6 Macrographs of the clad plate after bending test: (a) stainless steel
faces outward to bend, and (b) stainless steel faces inward to bend.
Fig. 4
Element distribution maps of the clad interface by EPMA.
Fig. 7 (a) Failure location and (b) fracture surface morphology of the clad
interface after shear test.
Fig. 5 Line analyses of Ni and Cr elements at the clad plates by EPMA (the
analysis line is shown in Fig. 4(a)).
According to the EDS result shown in Fig. 3(b), the
transition zone consisted of Cr, Mn, Fe, Ni and C elements,
and exhibited a transitional chemical composition between
that of the stainless steel and HSLA steel shown in Table 1. A
high concentration gradient of Cr and Ni elements existed at
the interface zone between the stainless steel and HSLA steel
during the VRC process, thereby resulting in the remarkable
diffusion of Cr and Ni elements. Therefore, the formation of
the transition zone with 5 mm width (Fig. 2(b)) was related
with the element diffusion. Figures 4 and 5 show the map and
line distributions of Ni and Cr elements characterized by
EPMA. It is clear that Ni and Cr elements diffused from
stainless steel to the HSLA steel, and this would lead to the
movement of the CCT curve to the right side and decreasing
of critical cooling rate of martensite formation. Therefore,
some austenite phase transformed to martensite phase under
the air cooling during VRC process. Li et al.19) indicated that
martensite formed in the transition zone of arc welded 308
austenite stainless steel/HSLA steel due to the diffusion of Cr
and Ni elements. Similarly, fine martensite phase was also
found by Tosto et al.7) in the interface of the weld overlay
clad 316 stainless steel and mild steel. In this study, the
transition zone exhibited a high Vicker’s hardness value
(381 Hv), which was much higher than that of the stainless
steel and HSLA steel (Table 2). Therefore, the martensite
structure should very probably form at the transition zone
during the VRC process according to the similar microstructure and hardness value to those reported by Li et al.19)
Detailed microstructural examinations and discussion about
the martensite structure in the transition zone will be
presented elsewhere.
From Figs. 4 and 5, it was observed that Cr and Ni
elements diffused significantly from the stainless steel side to
the HSLA steel side with the diffusion distances of 13 mm
and 8 mm, respectively. Diffusion coefficients of Ni and Cr
in -Fe at the rolling temperature of 1180 C were calculated
to be approximately 5:7 10 11 and 4:6 10 11 cm2 /s,
respectively.20) Although Ni has a little higher diffusion
coefficient, the diffusion distance of Ni was lower than that of
Cr. This should be attributed to the obviously different
concentration gradients for Cr and Ni, which are 128 times
and 47 times, respectively.
Figure 6 shows the specimens of the clad plates after
bending test. No crack was observed in the clad interface
after bended to 180 in both outside and inside bend tests,
which was in accord with the ASTM standard.16) The shear
strength of the clad interface reached to a relatively high
value of 487 MPa, which was much higher than 140 MPa of
stainless steel clad plate in the ASTM standard and exceeded
the shear strength of the stainless steel clad plate (380 MPa)
by VRC, reported by JFE Steel Corporation.14) The failure
location and fractural surface morphology after shear tests
were presented in Fig. 7. The fracture occurred in the HSLA
steel and the fracture surface consisted of the predominant
1712
G. Xie, Z. Luo, G. Wang, L. Li and G. Wang
fine dimple rupture. Though martensite phase is a brittle
phase, we think that only few fine martensite phases formed
at the transition zone according to the study of Tosto et al.7)
In this case, the transition zone may be strengthened by the
few fine martensite phase. Therefore, the ductile fracture
showing fine dimples occurred at the HSLA steel side with
the lowest hardness near the transition zone. Kacar et al.2)
reported that during explosive clad of 316L stainless steel/
HSLA steel, the shear strength of 380 MPa was obtained due
to the occurrence of the melt zone. Rao et al.3) indicated that
the shear strength of the stainless steel/HSLA steel clad plate
by explosive cladding and hot rolling was 384 MPa and some
rubbed fracture features with a bamboo-like appearance
were observed. The low shear strength was attributed to the
interface oxidation during hot rolling. Therefore, the interface microstructure characteristic plays an important role in
the mechanical properties of the clad plate. In this study,
under the combination of high vacuum, high temperature and
high rolling deformation, significantly reduced interface
oxidation was achieved and no obvious defects were found at
the clad interface, resulting in the sound metallurgical
bonding. Anyhow, obtaining a defect-free clad interface is
the key for obtaining the high-property clad plate in any
cladding processes.
4.
Conclusions
The sound 304 austenite stainless steel/HSLA steel clad
plate was successfully fabricated by vacuum rolling cladding.
A small amount of fine oxide particles were found at the clad
interface. The transition zone was formed by the diffusion of
Ni and Cr. Excellent mechanical properties were achieved in
the stainless steel clad plate. No crack was observed at the
clad interface after bended to 180 with both inside and
outside manners. Shear strength of the clad plate reached to
487 MPa, and the obvious ductile fracture occurred in the
HSLA steel with lowest hardness near the transition zone.
Acknowledgements
This work was supported by the Fundamental Research
Funds for the Chinese Central Universities N090307003.
REFERENCES
1) I. F. Lancester: Metallurgy of Welding, (Chapman&Hall, 1984)
pp. 286–289.
2) R. Kacar and M. Acarer: Mater. Sci. Eng. A 363 (2003) 290–296.
3) N. V. Rao, D. S. Sarma, S. Nagarjuna and G. M. Reddy: Mater. Sci.
Techol. 25 (2009) 1387–1396.
4) H. Y. Wu, S. Lee and J. Y. Wang: J. Mater. Process. Technol. 75 (1998)
173–179.
5) X. K. Peng, G. Heness and W. Y. Yeung: J. Mater. Sci. 34 (1999) 277–
281.
6) N. V. Rao, G. M. Reddy and S. Nagarjuna: Mater. Design 32 (2011)
2496–2506.
7) S. Tosto, F. Nenci and H. Jiandong: J. Mater. Sci. 29 (1994) 5852–
5858.
8) P. K. Ghosh, P. C. Gupta, M. Breazu and P. K. Gupta: Trans. Japan Inst.
Metals 28 (1987) 579–584.
9) T. Ishda: J. Mater. Sci. 26 (1991) 6431–6435.
10) Y. Toshio: Patent Abstracts of Japan, Publication Number: 56-011189.
11) K. Takayuki, M. Masakazu, N. Kazumasa, K. Mitsuaki and H.
Masahiro: J. JWS. 22 (2004) 300–308 (in Japanese).
12) J. C. Yan, D. S. Zhao, C. W. Wang, L. Y. Wang, Y. Wang and S. Q.
Yang: Mater. Sci. Technol. 25 (2009) 914–918.
13) S. Nishida, T. Matsuoka and T. Wada: JFE Technical Report 5 (2005)
1–9.
14) http://www.jfe-steel.co.jp/en/products/plate/05-koucyo.html.
15) G. M. Xie, Z. A. Luo, H. G. Wang, G. D. Wang and L. J. Wang: Adv.
Mater. Res. 324 (2010) 97–101.
16) ASTM, Designation A 263-09.
17) N. Masahiro, H. Ikuro, K. Shinji, K. Manabu and O. Yoshinobu: Tetsu
To Hagane 92 (2006) 378–384.
18) Y. Morizono, M. Nishida, A. Chiba and K. Imamura: J. Iron Steel Inst.
Jpn. 85 (1999) 340–345.
19) G. F. Li, E. A. Charles and J. Congleton: Corros. Sci. 43 (2001) 1963–
1983.
20) K. E. Rhelning: Steel and Its Heat Treatment, 2nd ed, (London
Butterworths, 1984) pp. 25–26.