JP2642235B2 - Manufacturing method of titanium clad steel with high bonding strength - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a rolled clad steel sheet of titanium and a titanium alloy having high bonding strength.

[Prior art] There are two methods for producing titanium clad steel, the explosion method and the rolling method, and the former explosion method has great limitations in terms of product dimensions, dimensional accuracy, productivity, and the like. Recently, the latter rolling method has been impressed. This rolling method generally comprises the steps of <cleaning of mating surfaces>-<welding and assembly of chlorad material>-<evacuation and sealing>-<heating>-<hot working>. There is a disadvantage that the bonding strength is inferior. The cause is that brittle intermetallic compounds are easily generated between titanium and steel, and carbon in the steel sheet diffuses to the titanium side to generate titanium carbide,
It has been known to reduce the peel strength at the interface.

As a countermeasure, a method of providing nickel or the like as an insert material between titanium and a steel sheet for the purpose of suppressing generation of an intermetallic compound (for example, Japanese Patent Publication No. 53-10347), In order to suppress the formation of titanium, in addition to the above-mentioned method of using nickel as an insert material, a method of using ultra-low carbon steel having a low carbon content as a base material (for example, JP-A-56-122681) or A method of decarburizing the mating side of the material (for example, JP-A-59-220292), or a method of using a steel to which a strong carbide-forming element such as Ti is added in order to fix carbon in the steel in advance ( JP-A-56-122681) has been proposed.

[Problems to be Solved by the Invention] However, even if the formation of titanium carbide at the joint interface can be suppressed by these methods, Ti and Fe, or Ni and Ti when nickel foil or the like is used as an insert material.
It is difficult to suppress the formation of a trace amount of each of the intermetallic compounds and the formation of an extremely thin layer, and the cause of the deterioration of the bonding strength cannot be sufficiently eliminated yet.

[Means for Solving the Problems] The present invention examines various effects of hot rolling conditions and heat treatment conditions in order to suppress generation of such an intermetallic compound that causes deterioration of bonding strength. The formation of the intermetallic compound is suppressed, and the heat treatment conditions under which the intermetallic compound can be reduced and eliminated in the subsequent cooling step are found.

That is, in the present invention, a steel material as a base material is evacuated to a gap surface of a titanium material as a bonding material, and then subjected to hot working.
After hot-rolling within the temperature range described above, cooling is performed at a cooling rate of 50 ° C / min or more to a temperature of 600 ° C or less, and then 300 to 58 ° C.
An object of the present invention is to provide a method for producing a titanium-clad steel having a high bonding strength, wherein the method is heated and held in a temperature range of 0 ° C. for 0.5 to 24 hours.

[Function] Here, the steel type of the steel material as the base material is not particularly limited, and any of high-alloy steel such as ordinary steel or stainless steel may be used, but the steel component, particularly the steel component of the steel surface layer, is as described above. From the viewpoint of suppressing the formation of titanium carbide, C (Ti
It is desirable that the amount of so-called free carbon which does not form a stable carbide such as C) be small. From this viewpoint, when using a steel having a high C content such as a high carbon steel sheet as the steel base,
It is desirable to apply a surface decarburization treatment or to insert an insert material such as a pure iron plate between the steel base material and the titanium material. The type of titanium as the joining material is not particularly limited, and either pure titanium or alloyed titanium can be used.

The steel base material and the titanium material are assembled by a known method, and the inside is evacuated and then sealed. For example, in the case of three layers of a discarded material, a titanium material and a steel substrate, or four layers of a steel substrate, a titanium material, a titanium material, and a steel substrate, an assembly material is formed. In the case of a layer, a patch plate is applied between the end faces of the steel base material on both outer surfaces, the ends are welded, and then the inside of the assembly is evacuated via a pipe or the like, and then sealed. The material to be discarded is preferably made of the same material as the base material from the viewpoint of thermal expansion and the like. In the case of three layers, between the discarded material and the titanium material, in the case of four layers, the alumina is previously placed between the titanium materials. A release material such as a powder is provided. In addition, a spacer or the like is inserted at the end between the steel base material and the titanium material (a step may be provided on the backing material) to prevent direct contact between the two materials and prevent the useless metal during heating before hot rolling. FIG. 1 is a cross-sectional view illustrating an example of an assembling material in the case of four layers in which it is desirable to suppress generation of a compound. In FIG. 1, 1 is a steel substrate, 2 is a titanium material, 3 is a backing plate, 4 is a release material, 5 is a spacer,
6 is an exhaust pipe and 7 is a welded end.

Next, the assembled material thus manufactured is subjected to hot rolling to join the steel base material and the titanium material.

Here, in the present invention, after being subjected to hot rolling within a temperature range of 950 to 700 ° C, 600 ° C at a cooling rate of 50 ° C / min or more.
One feature is to cool to the following temperature. The purpose is to suppress the formation of intermetallic compounds as much as possible and to facilitate the interdiffusion of iron and titanium atoms. That is, if the hot rolling temperature exceeds 950 ° C., the formation of intermetallic compounds becomes remarkable, while if the temperature is less than 700 ° C., mutual diffusion of iron and titanium metal atoms at the bonding interface hardly occurs, and there is a possibility that an uncompressed portion may occur. It depends.

Further, if the cooling rate after the hot rolling until cooling to a temperature of 600 ° C. or less is less than 50 ° C./min, the intermetallic compound is enlarged at the joining interface and the joining strength is deteriorated. The upper limit of the cooling rate is not particularly limited, but if the cooling rate is increased, the workability is deteriorated depending on the components of the steel base material and the like. The reason for cooling above a certain cooling temperature until the temperature is below 600 ° C is 600
The formation behavior of intermetallic compounds differs from
This is due to the finding that intermetallic compounds have a unique tendency to decay and disappear at temperatures below ℃
At a temperature of not more than ° C., the cooling rate does not need to be particularly high, and natural cooling is sufficient.

Another important feature of the present invention is that after cooling under such conditions,
The purpose is to maintain the temperature in the temperature range of 300 to 580 ° C for 30 minutes or more. There are two methods for this heating and holding. One is to cool to a temperature of 600 ° C or less at a cooling rate of 50 ° C / min or more, then cool to room temperature by natural cooling, etc., then reheat and heat and hold. Others include a method of heating and holding during cooling from 600 ° C. to room temperature, in other words, a stepwise cooling treatment.

Such a heat-holding treatment is a very important component of the present invention, and is based on the following findings. That is,
Observation of the bonding interface by transmission electron microscopy revealed that the main inhibitor of the bonding strength was an intermetallic compound (Ti ₂ Fe, TiFe, etc.) with a thickness of several hundred mm formed at the interface. Five
It was found that the heat treatment at about 00 ° C. tended to disappear. There is still some unclear reason for this,
It is considered that this may be due to the absorption of Fe of the intermetallic compound into the β-Ti phase having a large amount of Fe solid solution.

In any case, such a heat-holding section treatment has made it possible to provide a titanium-clad steel sheet having unprecedented bonding strength. The reason for setting the heating and holding temperature to 300 to 580 ° C is
At a high temperature exceeding 580 ° C., an intermetallic compound tends to be generated, and at a low temperature below 300 ° C., it takes a long time for the intermetallic compound to disappear. The heating time is 0.5
If the time is less than the time, the improvement contribution of the bonding strength is small, and if the time exceeds 24 hours, the improvement effect is saturated.

After the heating and holding treatment, the material is cooled, the ends are cut, the assembled material after rolling is disassembled, the discarded material and the patch material are removed, and the clad material is taken out.

EXAMPLES Next, the effects of the present invention will be described in detail with reference to examples.

Steel composition as steel base material is C: 0.001, Si: 0.01, Mn: 0.3, P: 0.0
Ultra low carbon T with 70mm thickness, 1, S: 0.01, Ti: 0.2 (wt%)
i Additive steel, pure titanium material with a thickness of 30 mm (JISH4
600, 1 type), stack in the order of steel substrate, laminated material, laminated material and steel substrate (alumina-based release material is applied to the facing surfaces of the laminated material), and the same steel type as the steel substrate on the end surface Then, the end portion was sealed and welded, and then a suction pipe communicating with the inside was attached thereto, and the vacuum was set to 10 ⁻² Torr, followed by welding and sealing.

Next, a titanium-clad steel sheet having a thickness of 5 mm was produced under the 11 types of hot rolling and heat treatment conditions shown in Table 1, and the T peel strength and the shear peel strength were measured. 2 and 3 are longitudinal sectional views showing test pieces used for measuring the T peel strength and the shear peel strength, respectively.
Is a steel plate, 9 is a titanium plate, 10 is a vertical slit, and 11 is a width direction slit.

That is, T peel strength is 100 mm long and 25 mm wide at one end of a vertically split slit 10 (1 mm wide) with a depth of 25 mm in the length direction.
Is provided on the steel plate 8 side along the joining interface, and the steel plate 8 and the titanium plate 9 separated by the slit 10 are each bent outwardly at right angles into a T-shape, and a 50 mm /
It was measured by a method of pulling at a speed of one minute and peeling off the joint, and the load was indicated as it was. On the other hand, the shear peel strength is 10
Two 1-mm-wide slits 11 with a width of 1 mm are placed in the center of the test specimen with a width of 0 mm and a width of 25 mm approximately 2 m along the entire length of the test specimen in the width direction.
Cut at intervals of m from the titanium side and the steel plate side to the depth reaching the bonding interface, gripping both ends of the test piece at a tensile speed of 10 mm / min, pulling, and peeling off the bonding interface between the two slits It was measured and the load was divided by the peeled area (50 mm ² ) and indicated. The results of these measurements are
Also shown in the table.

As is clear from the evaluation results in Table 1, it is clear that according to the present invention, a titanium clad steel having higher bonding strength can be manufactured as compared with the comparative example.

[Effects of the Invention] The titanium-clad steel sheet according to the present invention has remarkably superior bonding strength, especially T-peel strength, as compared with conventional materials, and is reliable when used in offshore structures, chemical plants, various vehicles or building materials. It is highly efficient and has a great advantage in the related industrial fields.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating the configuration of an assembly material before hot rolling,
FIG. 2 and FIG. 3 are longitudinal sectional views of test pieces used for measuring T peel strength and shear peel strength, respectively. DESCRIPTION OF SYMBOLS 1 ... Steel base material 2 ... Titanium material 3 ... Patch material 4 ... Peeling material 5 ... Sparser 6 ... Exhaust pipe 7 ... Welded end 8 ... Steel plate 9 ... Titanium plate 10 ... Vertical slit 11 ... Width slit

Claims (1)

(57) [Claims] (1) A method for producing titanium clad steel by a so-called vacuum hot working method in which a gap between a steel material as a base material and a titanium material as a bonding material is evacuated and then subjected to hot working. After hot rolling within the temperature range of ~ 700 ° C, 50 ° C
A method for producing a titanium-clad steel having high bonding strength, comprising cooling to a temperature of 600 ° C. or lower at a cooling rate of not less than / min and then heating and maintaining the temperature within a temperature range of 300 to 580 ° C. for 0.5 to 24 hours.