Method for manufacture titanium clad steel plate

A method for manufacturing titanium clad steel plate by forming a slab assembly having an alloy steel substrate, a titanium metal or alloy cladding on said substrate and a Ni-Cr alloy foil or film having opposed surfaces between said alloy steel and said cladding. The Ni-Cr alloy foil or film has one surface in surface contact with the cladding and the opposed surface in surface contact with the alloy steel substrate. The Ni-Cr alloy contains 32.5 to 40 wt. % Cr and 55 to 65 wt. % Ni. The slab assembly is heated at a temperature of 850.degree. to 1010.degree. C. The heated slab assembly is hot rolled with a reduction ratio of 30% or more to form the titanium clad steel plate.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method for manufacturing titanium or 
titanium alloy clad steel plate. 
2. Description of the Prior Art 
A clad metal plate is manufactured by laminating two metal plates or more 
and joining the laminated metal plates to each other. This clad metal 
plate is excellent in corrosion resistance, wear resistance and heat 
resistance, and has a high strength. Therefore, the clad metal plate is 
widely used as an inexpensive material. 
As the methods for manufacturing clad metal plate, an explosion bonding 
process, a surfacing process and a rolling process are pointed out. The 
rolling process, which can manufacture the clad metal plate of large area 
with high efficiency and at low cost, is most generally used. 
In the rolling process, surfaces of cladding metals and a base metal, at 
which the cladding metals are bonded to the base metal, are cleaned, and 
the cladding metals and the base metal are laminated and hot-rolled or 
warm-rolled, by which the cladding metals are metallurgically bonded to 
the base metal. In this method, stainless steel as the cladding metal and 
carbon steel, low alloy steel and high alloy steel as the base metals are 
used. 
However, when the rolling process is applied to the manufacture of a 
titanium clad steel plate, wherein titanium or titanium alloy is used as 
the cladding metal, it is extremely difficult to obtain a good joining 
property because there are problems as shown below. 
When titanium or titanium alloy and alloy steel are laminated, uniformly 
heated at a predetermined temperature, and hot-rolled or warm-rolled, a 
brittle Ti-Fe intermetallic compound is generated on cladding surfaces by 
interdiffusion of titanium and iron. This brittle Ti-Fe intermetallic 
compound greatly decreases the shearing strength of the cladding surfaces. 
As a method for preventing the intermetallic compound from being generated, 
a method, wherein a thin film or a foil of Mo, Nb or V which does not 
generate the intermetallic compound with titanium is employed as an insert 
material, has been proposed. The insert material is inserted between the 
base material and the cladding metal. 
There are, however, two problems in the method for using the film or the 
foil of Mo, Nb or V. The first problem is that the manufacturing cost 
increases greatly because Mo, Nb and V are very expensive. The second 
problem is that since the insert material lacks ductility, the insert 
material breaks during rolling. Due to those problems, this method is not 
put to practical use. 
Two sorts of insert materials which are manufactured on an experimental 
basis are pointed out. Plating and foil of Cu, Ni or Cr are disclosed in a 
journal "Metal" vol. 32, No. 20. A Japanese Patent Publication Laid Open 
No. 124483/85 discloses foil of stainless steel of ferrite and martensite. 
However, sufficient cladding strength cannot be obtained by those insert 
materials. 
When the explosion bonding process is used instead of the rolling process, 
the Ti-Fe intermetallic compound is not generated since the cladding metal 
is bonded to the base material not metallurgically, but mechanically. In 
this method, a comparatively good cladding property can be obtained. 
However, since the explosion bonding process is limited to cladding of the 
cladding metals to the base metal of large area, it is difficult to use 
this process widely. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a method for 
manufacturing titanium clad steel plates excellent in cladding property. 
To attain the aforementioned object, the present invention provides a 
method for manufacturing titanium clad steel plate comprising the steps 
of: 
inserting Ni-Cr alloy material containing 32.5 to 40 wt. % Cr and 55 to 65 
wt. % Ni between alloy steel material and titanium material, a slab 
assembly having alloy steel material, titanium material and Ni-Cr alloy 
material inserted between alloy steel material and titanium material being 
formed; 
heating said slab assembly at a temperature of 850 to 1010.degree. C.; and 
hot-rolling said heated slab assembly with a reduction ratio of 30% or 
more. 
The above objects and other objects and advantages of the present invention 
will become apparent from the detailed description which follows, taken in 
conjunction with the appended drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
When the titanium clad steel plate is manufactured, the brittle Ti-Fe 
intermetallic compound is generated on cladding surface of titanium and 
alloy steel due to the interdiffusion of atoms of titanium and iron. It is 
important in formation of good rolling cladding surfaces to limit the 
generation of the brittle Ti-Fe intermetallic compound. 
The present inventors selected various sorts of insert materials to be 
inserted into between the cladding materials of titanium or titanium alloy 
and the base material of alloy steel, and manufactured titanium clad steel 
plate by hot-rolling with the use of said insert materials. The cladding 
property of the titanium clad steel plate obtained was analyzed. As a 
result, the present inventors found that the good cladding property could 
be obtained by selecting the insert materials, the heating temperature and 
the reduction ratio during the hot rolling. 
That is, in the present invention, titanium clad steel plate excellent in 
the cladding strength is manufactured by inserting Ni-Cr alloy between the 
cladding metals of titanium or titanium alloy and the base metal of alloy 
steel and hot-rolling the cladding metals and the base alloy with the 
Ni-Cr alloy between them at a temperature of 850.degree. to 1010.degree. 
C. with the reduction ratio of 30% or more. 
The insert material can be any of a thin sheet, a foil, a plating film 
formed on a base material, or a flame coating film formed on a base 
material. Carbon steel, low alloy steel and various stainless steels are 
generically referred to as alloy steel. The alloy composition of titanium 
alloy is specifically not limited. 
FIG. 1 is a sectional view illustrating a slab assembly of titanium clad 
steel plate of the present invention. A slab assembly is made by 
laminating one obtained by inserting an insert material 2a between a base 
metal 1a and a cladding metal 3 and the other obtained by inserting an 
insert material 2b between a base metal 1b and a cladding metal 3. 
Spacer material 4 is incorporated into the outer edge spaces between the 
base material 1a and 1b, between which the insert material 2a, the 
cladding metal 3 and the insert material 2b are put. Surfaces, at which 
the base materials 1a and 1b contact the spacer 4, are tightly sealed by 
welding. Air remaining in voids inside the slab assembly is exhausted by a 
vacuum pump. After the slab has been temporarily assembled, the outer edge 
spaces can be sealed by an electron beam welding in a vacuum chamber. 
Since the air remaining in the voids inside the slab assembly is removed 
by means of the vacuum pump, or the outer edge spaces are welded in the 
vacuum chamber, the generation of titanium oxides or nitride between the 
insert materials 2a or 2b and the cladding metal can be suppressed. 
The insert material is Ni-Cr alloy. Ni-Cr alloy containing 32.5 to 40 wt. % 
Cr and 55 to 65 wt. % Ni is preferred. 
When Cr content is below 32.5 wt. %, a brittle Ti (Ni, Cr).sub.3 is formed 
at the boundary between the cladding metal 3 of titanium or titanium alloy 
and the insert materials 2a or 2b, which decreases the cladding strength. 
When the Cr content exceeds 40 wt. %, a brittle .delta.-phase is formed at 
the boundary of the base material of alloy steel and the insert materials 
2a or 2b, which decreases the cladding strength. The Cr content of 32.5 to 
35 wt. % is preferred. 
When Ni content is below 55 wt. %, a brittle TiCr.sub.2 is formed at the 
boundary of the cladding material of titanium or titanium alloy and the 
insert materials 2a or 2b, which decreases the cladding strength. When the 
Ni content exceeds 65 wt. %, the brittle Ti (Ni,Cr).sub.3 is formed as in 
the case where the Cr content is below 32.5 wt. %, which decreases the 
cladding strength. 
The content of Ni and Cr is important for the insert materials. Even though 
the insert materials contain impurities such as Fe of less than 10 wt. %, 
the insert materials do not lose their effect. 
The temperature for heating the slab assembly during the hot rolling is 
desired to be from 850.degree. to 1010.degree. C. The reduction ratio is 
desired to be 30% or more. When the heating temperature exceeds 
1010.degree. C., although the content of the insert materials 2a and 2b is 
limited to the aforementioned range, the brittle Ti (Ni,Cr).sub.3 is 
formed at the boundary of the cladding materials 3 of titanium or titanium 
alloy and the insert materials 2a or 2b during the rolling and during the 
successive cooling after the rolling, which decreases the cladding 
strength. When the heating temperature is below 850.degree. C. residual 
stress is generated in the finishing rolled plate by the hot rolling, 
which decreases the cladding strength. 
When the reduction ratio is below 30%, the plastic deformation necessary 
for cladding cannot be obtained without depending on the content of the 
insert materials 2a or 2b. That is, the plastic deformation cannot be 
obtained at the boundary of the cladding materials of titanium or titanium 
alloy and the insert materials 2a or 2b and at the boundary of the insert 
materials 2a or 2b and the alloy steel as the base metal 1. Accordingly, a 
sufficient cladding strength cannot be obtained. The reduction ratio has 
no specific upper limit. However, the range of 30 to 80% is preferred. 
EXAMPLE 
An example of the present invention will now be described with specific 
reference to the appended drawings. In the drawings, reference numerals 1a 
and 1b denote base metals, 2a and 2b insert materials, 3 a cladding metal, 
4 a steel, and 5 a separating compound of alumina. The base metals 1a and 
1b each were of steel, 50 mm in thickness, 200 mm in breadth and 250 mm in 
length. Cladding surfaces were subjected to milling. A pure titanium plate 
and an alloy plate of Ti-6% Al-4% V were used as the cladding metals 3. 
These plates each were of 10 mm in thickness, 140 mm in breadth and 190 mm 
in length. Cladding surfaces were subjected to milling. 
The influence of the Cr content and the Ni content on the joining property 
was studied by varying the Cr content in the range of 10 to 60 wt. % and 
the Ni content in the range of 30 to 80 wt. %. The thicknesses of the 
insert materials 2a and 2b each were 0.1 mm. As the insert materials 2a 
and 2b, a foil, a plating film formed on the surface or a flame coating 
film formed on the surface of the base metal were used. A slab assembly 
was constituted by interposing the insert materials 2a and 2b between the 
base metals 1a, 1b and the cladding materials 3. The slab assembly 
constituted in this way was of 120 mm in thickness. Air inside the slab 
was exhausted and the pressure inside the slab was reduced to 10.sup.-1 
Torr. 
After the slab assembly had been heated at a temperature of 800.degree. to 
1050.degree. C., the slab assembly was hot-rolled to be of a predetermined 
thickness in the range of 24 to 100 mm. After the hot rolling of the slab 
assembly, the slab assembly was cooled, and clad steel plates were made by 
separating the clad steel 1a-2a-3 from the clad steel 1b-2b-3. 
To examine the joining property of the clad steel plates, test pieces were 
taken from the aforementioned hot-rolled steel plates, and the shearing 
strength of the test pieces were examined. The manufacturing conditions 
and the joining property are shown in Table 1. The shearing strength of 
the test pieces in Test Nos. 1 to 10 were from 25.6 to 29.9 kgf/mm.sup.2. 
As against those, the shearing strength of the control test pieces were 
only from 4.2 to 13.9 kgf/mm.sup.2. In the Example of the present 
invention, a titanium clad steel plate having a shearing strength 25 
kgf/mm.sup.2 or more was manufactured. 
TABLE 1 
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Manufacturing conditions and joining property 
Composition of 
Insert Materials 
(wt. %) Heating Reduc- 
Shearing 
#Total 
Shapes of 
Tempera- 
tion Strength 
of Insert ture Ratio (kgf/ 
Nos. Ni Cr Others 
Materials 
(.degree.C.) 
(%) mm.sup.2) 
______________________________________ 
Examples of the Present Invention 
1 65 32.5 2.5 Foil 950 80 29.5 
2 60 32.5 7.5 Foil 950 80 29.9 
3 60 35 5 Foil 950 80 28.1 
4 55 35 10 Foil 950 80 29.0 
5 60 35 5 Flame 950 80 27.6 
Coating 
6 60 35 5 Plating 
950 80 28.3 
7 60 35 5 Foil 1010 80 25.6 
8 60 35 5 Foil 850 80 27.1 
9 60 35 5 Foil 950 30 25.9 
10 60 35 5 Foil 950 50 28.6 
Controls 
11 80 10 10 Foil 950 80 7.1 
12 70 20 10 Foil 950 80 8.4 
13 50 40 10 Foil 950 80 9.1 
14 30 60 10 Foil 950 80 6.5 
15 60 35 5 Foil 1020 80 11.3 
16 60 35 5 Foil 825 80 13.9 
17 60 35 5 Foil 950 25 4.2 
18 Low Carbon Foil 950 80 11.5 
Steel Containing 
0.005% C 
______________________________________ 
#Fe and inevitable impurities