Note: Descriptions are shown in the official language in which they were submitted.
~L~LS~
-- 1 --
METHOD FOR PRODUCING CLAD STEEL PLATE
The present invention relates generally to a method
for producing a clad steel plate and more particularly to a
method for producing a clad steel plate of a high bonding
strength in a high yield rate.
Clad steel plates have been hereto~ore used widely in
various fields. Recently, however, there arose a strony
demand particularly for such clad steel plates having a high
bonding strength and a very high quality.
Among various methods for producing clad steel plates
used heretofore, the most typical methods utilized in industrial
scales are cold pressure cladding, hot pressure cladding, and
explosion cladding. In any of these conventional methods,
however, a poor bond between the backing steel and the cladding
metal was frequently caused b~ oxidation of these materials
in the contact surfaces, resulting in a decrease in the yield
rate of the products.
In order to obtain a better bond between the backing
steel and the cladding metal in the conventional hot pressure
welding process, various means as described below were used:
a. The backing steel and the cladding metal were
welded together along the entire contact lines between their
peripheral edges into a slab and any air remaining between
the contact surfaces was exhausted through a vent hole provided
in a portion o~ the contact lines using a vacuum pump;
b. The backing steel and the cladding metal were
superposed within a vacuum chamber and welded along the entire
.~.
1~518~L13
. .,
contact lines betewen their peripheral edges by an electron
beam; and
c. A space was intentionally proviaed between the
backing steel and the cladding metal into which an inert gas
such as argon was sealed, and then the inert gas was exhausted
from the space through a vent hole during the hot rolling
process.
In any of these means, however, it was difficult to
exhaust the air from between the contact surfaces to some
practically effective extent, and the backing steel and the
cladding metal were oxidized in their contact suraces during
heating by a small quantity of t~e air still remaining between
the contact surfaces, resulting in that scales which were
formed therein pre~ented the formation of a satisfactory
metallurgica~ bond therebetween and such insufficient metall-
urgical bond would appear as a defect in ultrasonic inspection~
The poor bond used to readily appear particularly in the
neighborhood of the securely welded contact lines between the
peripheral edges of the slab and presents a serious problem
in the yield rate of the ultrasonic inspection.
In an alternative means actually practised, for the
purpose of preventing a decrease in a shear strength of clad
interface, a metal such as nickel was plated onto the contact
surface of either one of the backing steel and the cladding
metal and the plated metal was diffused along the contact
surfaces of both the backing steel and the cladding metal to
form a strong bonding alloy layer. This alternative means,
however, had disadvantages of the increase of production cost
~l~l S~
and inability of complete prevention of oxidation in the
contact surfaces.
Accordingly, an object of the present invention is to
provide a method for producing a clad steel plate of a high
bonding strength in a high yield rate.
The method for producing a clad steel plate according
to the present invention comprises the steps of cleaning a
contact surface of each of a backing steel and a cladding
metal, superposing the backing steel and the cladding metal
a ,, ,~"~e, ~ ecli~f~
with~t~w~ layer interposed between the contact surfaces
of the backing steel and the cladding metal, welding the
backing steel and the cladding metal together along contact
lines therebetween to form a composite slab leavlng at least
one portion of the contact lines unwelded as a vent hole for
~ orce
air, applying a light reduction~ to the composite slab to
exhaust any air remaining between the contact surfaces through
the ~ent hole, close the vent hole of the reduced composite
slab by welding to isolate the contact surfaces from the
external atmosphere, charging the welded composite slab into
a heating furnace and heating it to a rolling temperature,
and hot-rolling the heated composite slab.
", ~er~n ecf,~
TheAmodium layer may be a metallic foil or a metallic
plating layer. The metallic plating layer may be provided
on one or both of the backing steel and the cladding metal.
The metallic foil may be used in one or more kinds.
The insufficient bond which results in the decrease
of the yield rate of products is caused mostly by oxidation
8~3
-- 4 --
in the contact surfaces. In the method according to the
present invention, it is made possihle to prevent the oxida~
tion in the contact surfaces during the hot rolling and,
accordingly, to sharply increase the bonding yield rate
because the final welding is performed after the air is
exhausted from between the contact suraces to bring them
into a tight contac~. with each other.
Further, in the method according to the present invention,
7~ ~ i,, 7~ ~ ~ e 6~ e
the ~ layer provided between the backing steel and the
cladding metal is diffused in both of them during the hot
rolling to thereby form a strong metallurigical bond there- `
between and to prevent carbon migration occuring ~rom the
backing steel to the cladding metal.
In the case ~here the metallic foil is used as the
e~ ~, e6~i~ f c
15 ~ layer, one or more kinds of the metallic foils are laid
on the backing steel, on top of which the cladding metal is
superposed. This requires no special equipment therefor and,
accordingly, no initial cost. Since there is no limitation
in the size of the welded composite slab the cost per unit
weight of the slab is considerably low. It is quite easy to
make the metallic foil thicker in contrast to the fact that
it is difficult to make the plating layer thicker. Accordingly,
by providing a metallic foil of a greater thickness it becomes
easier to prevent the carbon migration occurring from the
backing steel to th~ cladding metal, with which the embrittle-
ment of the interface can be prevented and to roll the slab
with a high workability in the hot rolling to thereby reduce
sharply the cost per unit weight of the slab. Further, in
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-- 5
view of the purchasing and handling costs of the metallic
foil which are far lower than in the metallic platlng layer,
the use of the metallic foil in the method according to the
present invention has made it possible to make the composite
slab at the cost equivalent to several percent of the cost
by the metallic plating process.
Heretofore, it has been commonly considered that a
metallic foil interposed between the backing steel and the
cladding metal would move freely between the contact surfaces
of them during the hot rolling and would not roll uniformly
with them. However, the inventors have experimentally
discovered that the diffusion of the constituents of the
metallic foil which had begun in both the backing steel and
the cladding metal during the heating penetrates deeper into
them with the progress of the hot rolling, whereby the backing
steel and the cladding metal are rolled well in one body,
resulting in the uniform rolling of the metallic foil.
Heretofore, further, it has also been commonly considered
that the metallic foil was prevented from rolling to a
sufficiently small thickness by the inclusions unexceptionally
present in the foils. However, the inventors have experiment-
ally discovered also that the metallic foil can be rolled
into the sufficiently small thickness on the order of 4 ~m
without breaking between the backing steel and the cladding
metal.
In the producing method according to the present invention,
the ultrasonic inspection yield rate of the hot-rolled clad
steel plates is sharply increased from the order of 70 - 80%
1~L5~8~3
-- 6
in the conventional producing method to the order of 95 -
100%.
In production of clad steel plates in the method
similar to that of the present invention without using the
medium layer, the ultrasonic inspection yield rate of the
hot-rolled plates can be fairly increased in some cases.
Without the medium layer, however, the backing steel and the
cladding metal generally diffuses in each other across the
interface to form an alloy layer there, which alloy layer is,
in most cases, fragile and brittle. Such a fragile alloy
layer formed along the interface will be easily broken in
the succeeding bending and/or welding process to make the
cladding metal separable from the backing steel and be detected
as a defect in ultrasonic inspection, resulting in a decrease
in the yield rate of the final products.
Generally, in widely used stainless steel clad steel
f f~r ", ec~
! produced without the ~ m layer, the diffusion produced
a martensite layer along the interface, a cemented layer on
the stainless steel side and a decarburized layer on the
backing steel side. Any of these layers were fragile and easily
crac~ed inthe succeeding working processes, thus presenting
a serious defect in ultrasonic inspection.
In some special cases of such combination of metals
that will not make a fragile alloy layer by diffusion between
the backing steel and the cladding metal (for example, nickel
", fér~ ~e f~/~f ~
clad steel), the ~ layer is not always necessary. Further,
a metal plate can well be used as the medium layer providing
equivalent effects as the metallic foil and the metallic
-- 7
plating layer.
The invention will be better understood from the
following description taken in connection with the accompanying
drawings in which:
Fig. 1 is a block diagram illustrating steps of the
method according to the present invention;
Figs. 2A and 2B are schematic illustrations of the
welding step of the method according to the present invention;
Fig. 3 is a graph showing the results of measurement
of a clad steel plates obtained by an example of practice of
the method according to the present invention by an electron
probe micro analyzer (E.P.M.A.);
Fig. 4 i5 a microstructure of a section of a steel plate
of Fig. 3;
Fig. 5 is a graph showing the results of E.P.M.A.
measurement of a clad steel plate obtained by another example
of practice of the method according to the present invention;
Fig. 6 is a microstructure of a section of a steel plate
of Fig.~
Fig. 7 is a graph showing the results of E.P.M.A.
measurement of a clad steel plate obtained by a further example
of practice of the method according to the present invention;
and
~5 Fig. 8 is a microstructure of a section of a steel plate
of Fig. 7.
The method for producing a clad steel plate according
~5~8~3
-- 8 --
to the present invention will now be described in detail with
reference to Fig. 1. In the first step 1 of the method
according to the present invention, the backing steel and the
cladding metal are cleaned in their contact surfaces. In the
succeeding second step 2, the backing steel and the cladding
e r ~ 4 ~
metal are superposed with ~-~U}ua~ layer interposed between
their contact surfaces. In the third step 3, the superposed
backing steel and the cladding metal are welded together along
the contact lines in their peripheral edges leaving at least
a portion of the contact lines unwelded as vent holes, to
form a composite slab. In the fourth step 4, the composite
~O~'C~
slab is subjected to a light reduction~ to exhaust any air
remaining between the contact surfaces through the vent holes.
In the fifth step 5, ~he vent holes of the slab after the
light reduction are closed by welding. In the sixth step 6,
the composite slab which has been welded along the entire
contact lines is charged into a heating furnace and heated to
a rolling temperature. Finally in the seventh step 7, the
heated composite slab is hot-rolled into a clad steel plate.
In the first step 1, the cleaning of the contact surfaces
of the backing steel and the cladding metal is performed by
any conventional means such as machining and/or grinding.
In the second step 2, the medium layer is formed either by
plating a metal or by laying a metallic foil.
In the case o~ the metal plating, a layer of the metal
plating is formed on one or both of the backing steel and thP
cladding metal each of which is cleaned in the contact surface.
The metal to be plated is preferably nickel or pure iron.
~ias~ ~
- 9 -
In the case of the metallic foil la~ing, one or more
kinds of metallic foils are laid on the cleaned contact
surface of the backing steel or the cladding metal, and then
the cladding metal or the backing steel is superposed on the
metallic foils with its contact surface downward. The foil
is preferably of such metals as titanium, aluminum, nickel,
chromium, and pure iron in the thickness of 20 - 200 ~m.
In the third step, the welding of the superposed
backing steel and the cladding metal along the edge of their
contact surfaces is performed by any conventional means such
as arc welding. In this step, the one or more vent holes
are formed by welding the backing steel and the cladding metal
to~ether along the contact lines between them leaving a
portion unwelded at the center of the bottom edge of the
slab tas shown in Fig. 2A) or more portions unwelded one at
the center of the bottom edge and a few in the lateral edges
(as shown in Fig. 2B). In Figs. 2A and 2B, designated general-
ly by the reference numeral 10 is the slab, in which the
reference numeral 11 denotes weld beads, 12 denotes the vent
holes, and 13 denotes the direction of advancement of the
rolling or pressing.
~ ~rc~ ~5 9~ c~ieG~
In the fourth step 4, the light reduction~ the slab
~Ls_pa~4~ed by either of a common rolling mill or press
machine without heating the slab.
In the sixth step 6, the slab is charged into a common
heating furnace, in which it is heated to an ordinary rolling
temperature of the cladding me-tal (for example, in the case
of stainless steel clad steel, to 1000 - 1250C).
-- 10 --
In the seventh step 7, the heated slab is rolled by
a common hot rolling mill into the clad steel plate.
Specific examples of the practice of the method according
to the present invention will now be described.
Ex~mple 1
(1) Backing Steel
Name: Welding Structural Steel Plate
(JIS~G3106 SM 41)
Chemical composition (wt %):
¦ C ~ Si ¦ Mn ¦ Fe
¦0.20 ¦ 0.30 ¦ 0.80 ~ nder¦
Size (mm): length 1500 x width 1000
. x thickness 77
(2) Cladding Metal
Name: Cupro-Nickel Plate
Chemical composition (wt ~):
¦ Cu 1 Ni
~ 90 10
Size (mm): length 1500 x width 1000
x thickness 17.5
~3) Medium Layer: Nickel Foil of thickness of 56 ~m
(4) Producing Condition
The backing steel and the cladding metal were finished
in the contact surfaces by grinding, superposed with the nickel
foil interposed between their opposed contact surfaces, welded
together along the contact lines in the peripheral edges into
a composite slab leaving a portion of 100 mm in length at the
Y center of the bottom edge of the slab along the contact line
unwelded as a vent hole, cold rolled unaer a light reduction~
1~ 5~
--11--
1 into the o~iginal total -thickness of the backiny steel and
the cladding metal, 94.5 mm, so as to exhaust any air
remaining between the contact surfaces through the vent hole,
supplementally welded to close the air vent into the slab
oE the thickness of 94.5 mm, and heated to the temperature
of 1000C and then hot-rolled into the clad steel plate of
the overall thickness of 13.5 mm, in which the thlckness
of the cladding metal, the backing steel and the nickel
foil were 2.5 mm, 11.0 mm and 8 ~m, respectively.
(5) Clad Steel Plate
The ultrasonic inspection of the clad steel plate
thus produced resulted in the yield rate as high as almost
100%. This shows that the air remaining between the contact
surfaces was entirely exhausted by the cold rolling and,
accordingly, the dèfect in bonding due to o~idation in
the contact surfaces was perfectly prevented.
Then, the state of diffusion in the area of bonding
between the backing steel and the cladding metal was inspected
by an electron probe micro analyzer (E.P.M.A.). The results
of the inspections are shown in Fig. 3, and the microstructure
of a section of the clad steel plate is shown in ~ig. 4.
-As seen from Figs. 3 and 4, the nickel o~ the foil
interposed as the intermediate layer was diused satisfac-
torily bvth in the backing steel and in the clad~ing metal to
produce a strong metallurgical bond therebetween.
Fillet weld tests perormed on this clad steel
plate showed that the metallurgical bond thus produced was
so strong that it was not detached from the interface by a
~5~8~l8
- 12 -
welding strain.
Example 2
-
The backing steel, the cladding metal and the metallic
foil were same as in Example 1. A composite slab was formed
in the same manner as in Example 1, and any air remaining
between the contact surfaces was exhausted through the vent
hole by cold pressing. Thereafter, the composite slab was
formed into a clad steel plate in th~ same manner as in Example
1, in which the cladding metal, the backing steel and the
metallic foil had the thickness of 2.5 mm, 11 mm and 8 ~m,
respectively. Ultrasonic inspections of the clad steel plate
thus produced showed the yield rate of almost 100~, as in
Example 1.
Example 3
~1) Backing Steel
Name: Welding Structural Steel Plate
(JIS SM 41)
Chemical composition (wt%):
C Si .Mn Fe
0.20 0.30 0.80 Remainder
Size (mm): length 1500 x width 1000
x thickness 56
~2) Cladding Metal
Name: Stainless Steel Plate
(SUS 316L)
Chemical composition (wt%):
¦ C ¦ Si ¦ Mn ¦ Ni lCr ¦ Mo ¦ Fe
¦0.02 ¦ 0.70 ¦ 1.60¦ 13 ¦17 ¦2.5 ¦ Remainder¦
Size (mm): length 1500 x width 1000
x thickness 21
~ s~
- 13 -
~ ~e ~7 e6~
(3) ~k~ff~ Layer: Nickel Foil of thickness of 56 ~m
(4) Producing Condition
A composite slab was formed in the same condition
as in E~ample 1. The slab was heated to 1200C and then
hot-rolled into a clad steel plate having the overall thick-
ness of 11 mm, in which the thicknesses of the cladding
me-tal, the backing steel and the metallic foil were 3 mm,
8 mm and 8 ~m, respectively.
The results of E.P.M.A. inspections and the micro-
photograph of a section of the clad steel plate thus producedare shown in Figs. 5 and 6, respectively. As seen from Figs~
5 and 6, the nickel of the foil interposed as the~ ~
layer was diffused satisfactorily both in the backing steel
and in the cladding metal to produce a strong metallurgical
bond therebetween. Fillet weld tests performed on this clad
steel plate showed that the metallurgical bond thus produced
was so strong that it was not detached from the interface by
a ~elding strain. Further, it was confirmed that the severe
cementation from the backing steel into the cladding metal was
perfectly prevented in this area by the nickel foil interposed
therebetween.
E~ample 4
(l) Backing Steel: Same as in Example 3.
(2) Cladding Metal
Name: Cupro-Nickel Plate
Chemical composition (wt%)o
¦ CU ~ Ni
1 90 1 10 1
115~
- 14 -
Size (mm): length 1500 x width 1000
x thickness 21
~ f ~7~ e J~ o,
(3) ~ ~ layer: Nickel Plating of thickness of 28 ~m
.~
~:~ (4) Producing Condition
After a nickel plating layer of the thickness of 28 ~m
was formed on the contact surface of the cladding metal, a
composite slab was formed in the same condition as in Example 1.
The slab was heated to 1000C and then hot-rolled into a clad
steel plate of the overall thickness of 11 mm, in which the
thicknesses of the cladding metal, the backing steel and the
nickel plating layer were 3 mm, 8 mm and 4 ~m, respectively,
Ultrasonic inspections of this clad steel plate resulted
in the yield r~te of almost 100%. This shows that a very
small quantity of air remaining between the contact surfaces
was completely exhausted through the vent hole by the cold
rolling step and the insufficient bonding due to oxidation in
the contact surfaces was perfectly preventedO
The results of E.P.M.A. inspections and the micro-
photograph of a section of the clad steel plate thus produced
are shown in Figs. 7 and 8, respectively. As seen from Figs.
7 and 8, the nickel component of the medium layer was diffused
satisfactorily both in the backing steel and in the cladding
metal to produce a strong metallurgica~ bond therebetween.
Further, fillet weld tests performed on this clad steel plate
showed that the metallurgical bond thus produced.was so strong
that it was not detached from the interface by a welding strain.
While we have described and illustrated certain preferred
practices of the present invention, it is to be distinctly
understood that the invention is not limited thereto bu-t may
181~3
- 15 -
be otherwise variously practic~d within the scope of the
appended claims.
