JPH0623424B2 - Method for manufacturing Ti thin plate - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a Ti thin plate for processing, and more specifically to a Ti thin plate surface which is difficult to be scratched during secondary processing and has scratch resistance. The present invention relates to a method for producing a Ti thin plate having excellent properties.

In the present specification, as a secondary processed product of the Ti thin plate, for example, a pipe used as a condenser of a heat exchanger will be described as an example, but the Ti thin plate of the present invention is used as a material for manufacturing such a pipe. Is not limited to the use as.

[Prior Art] Ti thin plate for processing (hereinafter sometimes simply referred to as Ti plate)
Often concerns the surface accuracy of secondary processed products,
Therefore, the Ti plate is required to meet strict requirements regarding surface scratch resistance. Therefore, when manufacturing such a scratch-resistant Ti plate, when rolling the Ti plate using a bright roll with a very small roll roughness, degreasing and cleaning are performed to completely remove surface oil and dirt. And then under vacuum or inert gas atmosphere 600-800
A method in which annealing is performed at ℃ is generally adopted, and finally, a Ti plate having a smooth surface was obtained. The Ti plate thus obtained is slit into a hoop having a desired width according to the purpose of processing and is secondarily processed. For example, when a condenser tube for a heat exchanger is manufactured, a pipe is manufactured and welded by a pipe forming line such as a roll forming method to obtain a product. The welding in this case is generally TIG welding, but it is necessary that the Ti surface is completely free of water and dirt in order to efficiently perform the welding of the thin Ti pipe. For this reason, pipe making has conventionally been performed under completely dry conditions without using any lubricant. However, when roll forming is carried out without using a lubricant, the surface is likely to have a flaw, and a pipe-forming flaw easily occurs. For this reason, instead of using a normal iron roll as a forming roll, using a special copper alloy roll or a fluororesin coating roll, or devising the shape of the forming roll so that local mold contact does not occur, Alternatively, attempts have been made to adjust the pass line so that the strain applied to the Ti plate between the forming roll stands does not change extremely.

[Problems to be Solved by the Invention] However, Ti is an extremely active metal by nature, and when metal friction is applied, seizure easily occurs and the surface is easily scratched. Therefore, there is a problem that the flaw cannot be completely prevented by the above-mentioned conversion of the roll material and the devising of the processing method, and the equipment cost of the roll and the like increases and the product price rises. The present invention has been made in view of such a situation, and is excellent in pipe-forming flaw resistance in secondary processing such as pipe forming, and is capable of suppressing an increase in secondary processing cost. It is intended to provide a manufacturing method.

[Means for Solving the Problems] In the present invention, a Ti thin plate obtained by cold rolling a Ti material using a roll having a surface roughness Ra of 0.6 μm or more has a surface oil deposition amount of 10 mg / The gist is to anneal in a non-oxidizing atmosphere under a condition of m ² or more.

[Operation] The present inventors have conducted various studies and studies for the purpose of improving the scratch resistance in secondary processing of Ti plate such as pipe forming. As a result, in order to obtain a smooth and flawless Ti plate, if the rolling lubricating oil, which was conventionally completely removed by alkali degreasing, trichlene degreasing, etc. after rolling, is annealed with some remaining, a thin Ti plate surface is obtained. It was found that a surface hardened layer was formed. Therefore, the composition of this surface hardened layer was examined.

FIG. 4 shows the relationship between the seizure resistance and surface enrichment elements. As is clear from the figure, it was found that the carbon concentration on the plate surface was high in the Ti plate having excellent scratch resistance. Therefore, the surface analysis was performed by infrared spectroscopic analysis on the assumption that the surface hardened layer was TiC. FIG. 5 (A) shows the analysis result of the surface hardened layer, and FIG. 5 (B) shows the analysis result of the TiC powder.
From this result, it is estimated that the surface-hardened layer contains TiC as a main component. That is, after rolling the Ti material, annealing is performed in a state where the rolling lubricating oil remains, and a thermochemical reaction is generated between the active carbon atoms or hydrocarbons generated by the thermal decomposition of the lubricating oil and the surface of the Ti sheet, It is intended to form a surface hardened layer of TiC on the surface. TiC like this
After repeated experiments and research on forming a surface-hardened layer to improve the resistance to pipe flaws, cold rolling should be performed using a rolling roll with a rough surface when rolling Ti material. I found out. That is, if the surface roughness of the rolling roll is rough, the surface of the Ti plate becomes uneven, and as a result, the reaction interface with the C component during annealing expands, and a strong surface-hardened layer is formed. FIG. 1 (A) is a partial cross-sectional view of the Ti plate formed in this way, 1 is a Ti plate, 2 is a surface hardened layer, and FIG. 1 (B) is an uneven surface. Ti if not
It is a board partial sectional view. Further, in this case, the amount of Ti fine powder generated by rolling increases, and the amount of adhesion to the surface of the Ti plate increases. This Ti fine powder is mixed with rolling lubricant to obtain T
Since it adheres to the i-plate surface, it contributes to increase the reaction interface for the C component. Furthermore, since the surface of the Ti plate has irregularities, when the Ti plate is molded, the molding roll comes into point contact with only the microscopic protrusions of high hardness on the surface of the Ti plate, so the contact area between the molding roll and the Ti plate is large. Is smaller, and the risk of seizure / scratch is significantly reduced.

In order to determine the range of the surface roughness and the oil adhesion amount of the rolling roll for forming such a surface hardened layer, the roll diameter: 16
Several kinds of Ti thin plates were manufactured using rolling rolls having various roll roughnesses of 5 ^mmφ and beef tallow emulsion oil as a rolling lubricating oil, and used to manufacture condenser tubes for heat exchangers. First, the oil content of lubricating oil is 10 mg / m
It was investigated the relationship flaw with resistance due to surface roughness and pipe forming roll about what was prepared as a ^2. As for the flaw resistance, the ratio of the length of the flaw in the outer circumferential direction to the outer circumferential length of the tube is defined as the flaw width ratio However, it was calculated by the formula of D: outer diameter of pipe W: length of flaw in outer peripheral direction of pipe. Then, the degree of the flaw width ratio was divided into the pipe-making flaw ranks shown in Table 1 to perform product evaluation. ◎, ○, □, and × in the evaluation column indicate the following respectively.

⊚: Excellent ∘: Excellent □: Good ×: Poor The higher the rank, the better.
The same applies to the table and Fig. 3).

FIG. 2 shows the relationship between the roll surface roughness and the pipe-making flaw rank.

Next, the relationship between the surface roughness of the roll of the condenser tube for the heat exchanger, the oil adhesion amount, and the pipe forming flaw rank was investigated under the same manufacturing conditions as described above except that the oil adhesion amount of the lubricating oil was variously changed. Results are shown in FIG.

From the results shown in FIGS. 2 and 3, the rolling roll has a surface roughness R
It was found that it is necessary to use a: 0.6 μm or more. The rougher the surface roughness, the better the resistance to flaws in pipe making. However, if Ra exceeds 2.0 μm, the roughness of the plate surface increases, and the load during rolling tends to increase. Therefore, the surface roughness Ra is preferably 2.0 μm or less. When the surface roughness Ra of the rolling roll is 0.6 to 2.0 μm, the surface roughness Ra of the Ti plate after rolling is 0.3 to 1.0 μm.
m.

Also, as shown in FIG. 3, the amount of lubricating oil adhered to form a surface-hardened layer sufficient to impart pipe-forming flaw resistance is 1
It was found to be 0 mg / m ² or more. Resistance to pipe flaws increases in proportion to the amount of oil attached. However, if the amount of oil adhered is too large, the annealing furnace is likely to be contaminated, free carbon remains on the Ti plate surface, and there are problems such as coloring and adhesion failure after annealing, so 50 mg / m ² or less Is preferred. Such adjustment of the amount of oil adhered may be performed by washing with warm water spray or the like, but it is also possible to perform complete degreasing with an alkali or the like and then re-apply a predetermined amount of lubricating oil.

Examples will be described below, but the present invention is not limited to the following examples, and it is within the technical scope of the present invention to appropriately change the design in view of the gist of the preceding and the following.

[Example] Example 1 A condenser tube for a heat exchanger was manufactured using a Ti plate obtained by rolling and annealing a Ti material, and the pipe-forming flaw property was evaluated. Table 2 shows manufacturing conditions and evaluation results. The second
In the table, a and b in the lubricating oil column, a and b in the annealing condition column, and A, B, C, and D in the degreasing condition column have the following meanings.

Lubricating oil; A ... Beef tallow system 3% emulsion oil (particle size 3 μm or less) B ... Beef tallow system 2.5% emulsion oil (saponification value 172 mgK
OH / g) Annealing conditions; a ... Vacuum annealing 700 ° C x 5 hours b ... Vacuum annealing 690 ° C x 5 hours Degreasing conditions; A ... Warm water spray cleaning (incomplete degreasing) B ... Complete alkaline degreasing and re-coating oil C ... Rolling As it is D ... Complete alkaline degreasing The results of Table 2 are examined below.

No. 1, which is an embodiment of the present invention. In all of 1 to 5, excellent pipe flaw evaluation was obtained, and the flaw resistance was extremely good. No. For No. 5, the amount of oil adhered was 50 mg because the amount of oil adhered by hot water spray washing was not adjusted.
/ m ^2, and as a result, the weldability was slightly poor. On the other hand, No.
No. 6 was subjected to complete alkaline degreasing after rolling. 7
Since the surface roughness of the rolling roll was small, No.
In Nos. 8 and 9, the surface roughness of the rolling roll was small, and after the rolling, complete alkali degreasing was performed, so that the required surface hardened layer could not be obtained and good scratch resistance could not be obtained.

[Effects of the Invention] According to the method of the present invention, it is possible to inexpensively manufacture a Ti thin plate exhibiting excellent scratch resistance in secondary processing such as pipe making.

[Brief description of drawings]

Figures 1 (A) and (B) are partially enlarged cross-sectional views of a Ti sheet with a surface-hardened layer, Figure 2 shows the relationship between the surface roughness of rolling rolls and pipe flaw rank, and Figure 3 shows rolling. Fig. 4 is a diagram showing the relationship between the roll surface roughness, the amount of oil attached, and the pipe manufacturing flaw rank. Fig. 4 is a diagram showing the relationship between seizure resistance and surface enrichment elements, Fig. 5 (A),
(B) is a diagram showing an infrared spectroscopic analysis result. 1 ... Ti plate, 2 ... Surface hardening layer

Claims (1)

[Claims] 1. A T obtained by cold rolling a Ti material using a roll having a surface roughness Ra of 0.6 μm or more.
A method for producing a Ti thin plate, which comprises annealing the i thin plate in a non-oxidizing atmosphere under conditions where the amount of oil attached to the surface is 10 mg / m ² or more.