JPH08276283A - Manufacture of titanium clad steel sheet - Google Patents

Abstract

PURPOSE: To manufacture a titanium clad steel sheet having a high joining strength at a low cost. CONSTITUTION: In the manufacture of a titanium clad steel sheet by in the hot rolling, an assembling slab for rolling is heated to 900-1,100 deg.C, then subjected to hot rolling by a total draft of >=10 at <=750 deg.C, or subjected to hot rolling at >=850 deg.C and <750 deg.C, then immediately cooled at a cooling rate of >=2 deg.C/sec. The cooling of >=2 deg.C/sec may be replaced with being left for cooling assuming the finish thickness of the slab is <=20mm. The mass production of a titanium clad steel sheet can be achieved by using the existing hot rolling equipment for steel. The total draft is large to drastically improve the yield and joining strength, thereby obtaining the objective titanium clad steel sheet with a high joining strength at low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a titanium clad steel plate.

[0002]

2. Description of the Related Art A clad material is obtained by joining dissimilar metals in layers, and is attracting attention as a material having excellent characteristics possessed by each metal. In particular,
Titanium clad steel is a material that combines the excellent strength, thermal conductivity and weldability of steel with the high corrosion resistance of titanium.
It is being applied to members that require high strength and corrosion resistance, such as those for chemical plants and marine anticorrosion.

At present, titanium clad steel plates are roughly classified into the explosive deposition method and the rolling method.

The explosive welding method uses the energy of explosion to join titanium and steel, and in addition to the large restrictions on the size and shape of the joining material, the place where the joining work is carried out is also greatly restricted. Therefore, it is not suitable for mass production, and it is difficult to manufacture an inexpensive titanium clad steel plate by the explosion deposition method.

In the rolling method, the conventional rolling equipment can be used, the plate thickness is limited, and the productivity is relatively high. Therefore, the rolling method is an advantageous manufacturing method as compared with the explosive deposition method. Can be said. However, since it is hot rolling, it is highly possible that a fragile Ti-Fe-based intermetallic compound or TiC carbide is formed at the joining interface between titanium and steel. Due to the formation of this intermetallic compound or carbide, There is concern that interface strength and corrosion resistance will be significantly reduced.

Until now, Ti-
For the formation of Fe-based intermetallic compounds and TiC carbide,
Fe-Ti and Ti-C depending on rolling joining temperature and intermediate material
Various efforts have been made from the viewpoint of preventing mutual diffusion of.

For example, a method in which a thin steel sheet having a carbon content of 0.03% or less is interposed between titanium and steel as an intermediate material (JP-A-62-158584, JP-A-63-56).
370), a 0.01% or less steel and nickel thin plate (see JP-A-5-8059), or a copper and nickel thin plate (see JP-A-60-170586). Has been proposed.

[0008] Also, without using an intermediate material, a method in which specific rolling conditions, that is, a rolling heating temperature is set to 800 to 850 ° C and a rolling end temperature is set to 700 ° C or more (Japanese Patent Laid-Open No. 56-1).
No. 63005) or a method of heating at 850 to 900 ° C., rolling at a reduction ratio of 2 or more, heat treatment at 650 to 950 ° C., and then hot rolling at a reduction ratio of 1.1 to 5 ( JP-A-60-213378), and 75
A method of performing a first rolling with a reduction ratio of 3 or more in a temperature range of 0 to 950 ° C., starting cooling at a cooling rate of 2 ° C./sec or more within 2 minutes from the first rolling, and cooling to 500 ° C. or less ( Japanese Patent Publication No. 6-61629) or a method in which the rolling pass interval at 750 ° C. or higher is set within 30 seconds (Japanese Patent Laid-Open No. 4-62).
No. 123883), etc. have been proposed.

[0009]

However, when the titanium clad steel plate, especially the thin plate thereof, is manufactured by the existing hot rolling equipment for steel by applying the above method, there are the following problems.

For example, in the existing hot rolling equipment for steel, a steel material slab is heated to a high temperature of 1000 ° C. or more and a continuous rolling mill is used to produce a large amount of thin steel sheets at a low cost by a high pressure reduction ratio of 10 or more. It can be manufactured. However, when this equipment and method is applied to the production of titanium clad steel sheet, the method using the intermediate material described above has a large reduction ratio by rolling, so that the intermediate material, the base material (steel), and the composite material (titanium) are rolled during rolling. ) And the difference in deformation resistance, the intermediate material is cut and the steel and titanium come into direct contact with each other to form a Ti-Fe intermetallic compound or TiC carbide at the interface, thereby obtaining stable and high bonding strength. Is difficult.

The method using no intermediate material disclosed in Japanese Patent Laid-Open No. 56-163005 described above has a low hot rolling heating temperature condition. Therefore, the existing hot rolling for steel requiring heating at 1000 ° C. or higher is required. It is difficult to apply the equipment. In the method of intermediately using the heat treatment as disclosed in JP-A-60-213378, the production efficiency is lowered and the cost of the clad steel plate is increased.

As disclosed in Japanese Patent Application Laid-Open No. 4-123883, in the method of simply determining only the pass interval of rolling at 750 ° C. or higher, the bonding area due to the new surface is small when the reduction ratio is small, so that high bonding strength is obtained. I can't get it. Also,
When rolling is finished at a high temperature (900 ° C or higher),
Since the temperature at the end of rolling is high even at the interface where no intermetallic compound is formed at the joint interface during rolling, an intermetallic compound is produced at the interface during cooling.

Therefore, high bonding strength cannot be obtained.

In order to prevent the formation of intermetallic compounds at the interface during this cooling, as shown in the above-mentioned Japanese Patent Publication No. 6-61629, within 2 minutes from the start of rolling, 2 ° C./second or more and 500 ° C. The method of cooling to the following is effective. However, according to this method, the length of the rolling coil becomes extremely long when a large amount of inexpensive clad steel is to be produced by the existing hot rolling equipment for steel. Moreover, when the assembly slab for rolling is heated to a high temperature of 900 to 1100 ° C. and continuously rolled,
The temperature of the slab after the final finish rolling becomes about 800 ° C., and it is impossible to cool this to 500 ° C. or less within 2 minutes from the start of rolling at a cooling rate of 2 ° C./sec or more.
Titanium clad steel sheet cannot be manufactured.

The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to produce a titanium clad steel sheet having stable and high joint strength in a large amount by using existing hot rolling equipment for steel. , To provide a method that can be manufactured at low cost.

[0016]

The gist of the present invention resides in the following methods (1) and (2) for producing a titanium clad steel sheet.

(1) Manufacture of a titanium clad steel plate in which a steel assembly is used as a base material and titanium or a titanium alloy is used as a laminating material, and an assembled slab for rolling is assembled by welding the base material and the laminating material by hot rolling. A method for producing a titanium clad steel sheet, which comprises heating an assembling slab for rolling to 900 to 1100 ° C., then hot rolling at a total reduction ratio of 10 or more, and ending rolling at 750 ° C. or less.

(2) Manufacture of a titanium clad steel plate in which a steel assembly is used as a base material and titanium or a titanium alloy is used as a composite material, and the assembly slab for rolling is assembled by welding the base material and the composite material by hot rolling. In the method, the assembly slab for rolling is heated to 900 to 1100 ° C., and then hot rolled at a total reduction ratio of 10 or more to 880 ° C. or less and 750 ° C.
A method for producing a titanium clad steel sheet, wherein rolling is completed in the super temperature range and immediately cooled at a cooling rate of 2 ° C / sec or more.

In the above methods (1) and (2),
The base material is preferably a low carbon steel having a carbon content of 0.3 mass% or less.

Further, in the above method (2), when the thickness of the finishing slab is 20 mm or less, cooling after completion of rolling can be replaced with standing cooling.

The inventors of the present invention used the existing hot rolling equipment for steel to raise the temperature higher than the temperature suitable for joining titanium and steel.
At the time of heating the assembly slab for rolling to a temperature of 00 ° C or higher to manufacture the titanium-clad steel plate with high efficiency, in order to solve the above-mentioned problems, the joining interface of the titanium-clad steel plate The formation and growth of intermetallic compounds and carbides were investigated. As a result, the heating temperature of the assembly slab for rolling is set to 900 to 1100 ° C., the total rolling reduction ratio of hot rolling is set to 10 or more, and the rolling is finished at a temperature of 750 ° C. or lower, or a temperature of 880 ° C. or lower and 750 ° C. or higher. By ending the rolling in the zone and immediately cooling at a cooling rate of 2 ° C / sec or more, the intermetallic compounds and carbides formed at the joint interface between titanium and steel during rolling are destroyed, and the thickness affects the joint strength. The new surface of titanium and steel newly formed by plastic deformation during rolling forms a bond between titanium and steel and suppresses the growth of intermetallic compounds and carbides on this new surface. The present invention has been accomplished on the basis of the finding that a titanium clad steel sheet that can be manufactured and has a high bonding strength can be obtained.

[0022]

First, an example of the method of assembling the rolling slab which is the object of the method of the present invention will be described with reference to FIG.

FIG. 1 is a view showing a cross section of a rolling slab after assembly. FIG. 1 (a) is an asymmetric type slab, and FIG. 1 (b) is the same.
Is for a target slab.

As shown in FIG. 1 (a), in the asymmetric type slab, spacers (steel) are provided on the base material (steel) 1 on all four sides.
5 and 6, the mating material (titanium) 2 is arranged in the center,
The release agent 4 is applied to the surface of the laminated material (titanium) 2, the entire surfaces of the spacers (steel) 5, 6 and the release agent 4 are covered with the dummy material (steel) 3, and then assembled by welding.

As shown in FIG. 1 (b), in the case of a symmetrical slab, the base material (steel) 1 and the laminated material (titanium) 2 are symmetrical (upper and lower in the figure) with respect to the release agent 4, Two pieces of mating material (titanium) within the thickness of spacers (steel) 5 and 6
It arrange | positions so that 2 and 2 and the release agent 4 may enter, and it assembles by welding. In this case, no dummy material is used.

Furthermore, in any case, no intermediate material is interposed on the joint surface between the base material (steel) and the laminated material (titanium). However, the joint surface is cleaned by a usual method such as grinding.

As the composite material 2, titanium or a titanium alloy (for example, Ti-8 mass% Mn, Ti-3 mass% Cr) is used.
Etc.), Al ₂ O ₃ as the release agent 4, and the dummy material 3
As the spacers 5 and 6, the same steel material as the base material may be used. The base material may be any carbon steel as long as it is carbon steel, but from the viewpoint of suppressing the formation of TiC carbides at the joint interface, a material having a low C content is preferable, and a low content of 0.3 mass% C or less. It is preferable to use carbon steel.

In the method of the present invention, the rolling slab assembled as described above is heated to a temperature of 900 to 1100 ° C., continuously rolled at a total reduction ratio of 10 or more, and rolled at a temperature of 750 ° C. or less. Or 880 ℃ or less, 750 ℃
This is a continuous rolling method in which rolling is finished in the super temperature range and immediately cooled at a cooling rate of 2 ° C./sec or more. This makes it possible to obtain a titanium clad steel plate with high bonding strength.

The reason for the above limitation will be described below.

<< Heating Temperature of Rolling Slab >> In order to use the existing hot rolling equipment for steel as it is for the production of titanium clad steel plate, from the viewpoint of the power of the rolling mill, the assembly slab for rolling is heated to 900 ° C. or higher. There is a need to. That is, if the heating temperature of the rolling slab is less than 900 ° C., rolling with a total reduction ratio of 10 or more cannot be performed. On the other hand, when the heating temperature of the assembly slab for rolling exceeds 1100 ° C., titanium and steel undergo a eutectic reaction to melt and melt the first slab during continuous rolling.
After pass rolling, a molten alloy layer of both is formed at the interface between titanium and steel, and a large amount of Ti—Fe based intermetallic compound is generated at the joint interface, so that the joint strength is significantly reduced. Therefore, the heating temperature of the rolling slab is 900 to 1100 ° C.
And

<< Total Reduction Ratio >> In the method of the present invention, the plastic deformation during rolling destroys a film that impairs the bonding property such as an oxide film on the bonding surface between titanium and steel, and the metal formed during rolling. The intermetallic compounds and carbides are destroyed to form new surfaces positively, and the new surfaces are joined together. However, if the total reduction ratio is less than 10, the newly formed surface is small and the bonding area is small, so that the desired interfacial bonding strength cannot be obtained. Therefore, the total reduction ratio is 10 or more.

The upper limit of the total reduction ratio is not particularly limited, and the higher the better. However, the upper limit thereof is determined by the power of the rolling mill and the assembly strength of the assembly slab for rolling (that the welded part of this slab does not separate during rolling), so it may be appropriately determined within the range where continuous reduction is possible. . As a desirable rolling reduction condition, the rolling reduction per pass and the total number of rolling passes are preferably about 10 to 20% and about 6 to 20 passes, respectively.

The "total reduction ratio" and the "reduction ratio" are values defined by the following formulas, where "T" is the slab thickness before rolling and "t" is the slab thickness after rolling. .

Total reduction ratio = T / t Reduction ratio (%) = {(T-t) / T} × 100 << Temperature of rolling and cooling >> Titanium or a titanium alloy is heated from about α phase at about 900 ° C. It transforms into the β phase and changes from a hexagonal system with a high atomic packing rate to a cubic crystal structure with a low atomic packing rate. The diffusion rate of Fe in α-titanium is about 1/1 of the diffusion rate in β-titanium.
0 and slow. Therefore, when rolling is performed in the α phase temperature range of titanium or titanium alloy that constitutes the assembled slab, α-
It is possible to suppress the formation of a Ti—Fe based intermetallic compound at the joint interface between titanium and steel, and to obtain a stable and high joint strength at the interface. However, this effect cannot be obtained stably when the finishing end temperature exceeds 880 ° C., so the finishing end temperature is 880 ° C. or less, preferably 750 ° C.
It must be below ℃.

That is, the finishing temperature is 880 ° C.
Even if the temperature is less than 750 ° C., if the temperature is higher than 750 ° C. and then left to cool from that temperature to room temperature after finish rolling, diffusion of Fe at the interface between titanium and steel proceeds, and a new interface is formed at the interface including the newly formed bonding interface. Ti-Fe-based intermetallic compound is formed, and the joint strength at the interface decreases. However, the rolling end temperature was 7
If the temperature is 50 ° C. or lower, the diffusion rate of Fe in titanium in the temperature range of 750 ° C. or lower is extremely slow (diffusion distance is 1 μm or less). Therefore, even if an intermetallic compound is formed at the interface, the bonding strength is low. It is possible to prevent the bonding strength from being lowered without affecting. Further, when rolling is finished in a temperature range of 880 ° C. or lower and higher than 750 ° C., if cooling is performed at a cooling rate of 2 ° C./sec or more immediately after the rolling is finished,
Almost no new Ti-Fe-based intermetallic compound is formed at the interface including the newly-formed bonding interface, and even if it is formed, it does not affect the bonding strength and prevents the bonding strength from decreasing. it can.

Therefore, in the present invention, the rolling end temperature is set to 750.
It was decided to immediately cool at a cooling rate of 2 ° C./sec or more after the completion of rolling at ° C. or less, or 880 ° C. or less, or more than 750 ° C.

The upper limit of the cooling rate is not particularly limited. That is, if the cooling rate is 2 ° C./second or more, the above effect can be obtained. However, in order to obtain a cooling rate of more than 20 ° C./second, it is necessary to use a forced cooling means such as water cooling, which increases equipment costs. Therefore, it is economical to set it to 20 ° C./second or less.

Further, the cooling rate of the steel sheet after the rolling is greatly influenced by the thickness of the slab to be finished, and if the thickness of the finishing slab after the rolling is large, it becomes difficult to lower the temperature.
In order to secure the cooling rate of 2 ° C./second or more, it is necessary to adopt a special forced cooling means such as water cooling. However, when the thickness of the finished slab is set to 20 mm or less, the cooling rate of 2 ° C./second or more can be secured by ordinary cooling. Therefore, in the present invention (the invention of (2) above), by setting the thickness of the finishing slab to 20 mm or less, a cooling rate of 2 ° C./second or more is ensured without using a forced cooling device or the like. Good.

In the method of the present invention, the atmosphere for assembling the rolling slab by welding is not particularly limited, but a sufficiently high joint strength can be obtained even when the assembly is performed by welding in the atmosphere. However, it is needless to say that the welding and assembling may be performed in a vacuum, because higher joining strength can be obtained when the welding and assembling is performed in a vacuum.

[0040]

[Example] C having a thickness of 80 mm and 160 mm as a base material:
0.3mass% low carbon steel, plate thickness 20mm as a laminated material
And 40 mm pure titanium (JIS-H4600, 1 type),
Using a low carbon steel similar to the base steel having a plate thickness of 30 mm and 60 mm as a dummy material, two types of asymmetric rolling slabs having a total thickness of 130 mm and 160 mm shown in FIG.
Assembled by welding. Also, as the base material, the plate thickness is 60 mm and 1
Using 20 mm of low carbon steel having the same composition as above, and using pure titanium having a plate thickness of 15 mm and 30 mm and having the same composition as described above, there are two types of total thicknesses of 150 mm and 300 mm.
The symmetrical rolling slab shown in (b) was assembled by welding.

Prior to assembly, the joint surfaces of the base material and the laminated material were each finished by mechanical grinding.

Al ₂ O ₃ is applied as a release agent,
As the spacer, the same low carbon steel as the base material and the dummy material was used. Furthermore, No. 1-4, No. 12-15, N
Nos. 26 to 30 and Nos. 35 to 38 were assembled in a vacuum (degree of vacuum: 10 ^-2 torr), and others were assembled in the atmosphere.

Then, in accordance with the rolling conditions shown in Tables 1 and 2, the existing hot rolling equipment for steel was used to finish various thicknesses shown in Tables 1 and 2, and the obtained titanium clad steel sheet was JIS-formed. A shear test piece was sampled according to Z0601, and the shear strength was measured and evaluated. The results are also shown in Tables 1 and 2.

[0044]

[Table 1]

[0045]

[Table 2]

As shown in Tables 1 and 2, when the heating temperature of the slab is over 1100 ° C (No. 12, 31), when the final finishing finish temperature is over 880 ° C (No. 13, 3).
2) When the total reduction ratio is less than 10 (No. 14, 17, 3)
3, 36), if the cooling rate is less than 2 ° C / sec (No. 1)
5, 16, 19, 34, 35, 38) and when the cooling end temperature is higher than 750 ° C. (No. 18, 37), the shear strength is 150 N / mm ² or less and the joint strength is low. On the other hand, in the case of the present invention (No. 1-11, 20-3
In 0), a shear strength of 200 N / mm ² or more was obtained, and a titanium clad steel sheet having a high joint strength of 30% or more compared to the comparative example was obtained.

[0047]

Industrial Applicability According to the method of the present invention, it is possible to achieve mass production of titanium clad steel sheet using existing hot rolling equipment for steel. In the method of the present invention, the total reduction ratio is large,
The yield and bonding strength are greatly improved. Therefore, the obtained titanium clad steel plate has low bonding cost and high bonding strength.

[Brief description of drawings]

FIG. 1 is a view showing a cross section after assembly of a rolling slab, wherein FIG. 1 (a) is an asymmetric type assembly slab and FIG. 1 (b) is a symmetrical type assembly slab.

[Explanation of symbols]

1: base material (steel), 2: laminated material (titanium or titanium alloy), 3: dummy material, 4: release agent, 5,
6: Spacer.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number for FI Technical indication C21D 8/02 9270-4K C21D 8/02 Z 9/00 9352-4K 9/00 Z

Claims (3)

[Claims] 1. A method for producing a titanium clad steel sheet, wherein a steel material is used as a base material, titanium or a titanium alloy is used as a laminated material, and an assembled slab for rolling, which is assembled by welding the base material and the laminated material, is joined by hot rolling. After heating the rolling slab to 900 to 1100 ° C., the total rolling ratio is 10
A method for producing a titanium clad steel sheet, which is characterized in that hot rolling is performed as described above and rolling is completed at 750 ° C. or lower. 2. A method for producing a titanium clad steel plate, wherein a steel material is used as a base material, titanium or a titanium alloy is used as a laminated material, and an assembled slab for rolling, which is assembled by welding the base material and the laminated material, is joined by hot rolling. After heating the rolling slab to 900 to 1100 ° C., the total rolling ratio is 10
A method for producing a titanium clad steel sheet, characterized in that hot rolling is performed as described above, the rolling is finished in a temperature range of 880 ° C. or less and 750 ° C. or more, and immediately cooled at a cooling rate of 2 ° C./second or more. 3. The method for producing a titanium clad steel sheet according to claim 2, wherein the thickness of the finished slab is set to 20 mm or less instead of cooling at a cooling rate of 2 ° C./second or more.