JPH0741292B2 - Titanium seamless pipe manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a hot manufacturing method for a seamless pipe made of industrial pure titanium or α-type or α + β-type titanium alloy.

[Conventional technology]

Titanium is classified into industrial pure titanium and α type, α + β type, and β type titanium alloys. As α-type titanium alloy, Ti-
There are 0.8Ni-0.3Mo, Ti-5Al-2.5Sn, Ti-0.15Pd, etc., and as an alloy of α + β type titanium, Ti-3Al-2.5V, T
i-6Al-4V, Ti-6Al-6V-2Sn, Ti-6Al-2Sn-4Zr-6
Mo, Ti-6Al-2Sn-4Zr-2Mo, Ti-8Al-1Mo-1V and the like.

These titaniums are lightweight and have high corrosion resistance, and their seamless pipes are particularly applied to chemical plants and hydraulic pipes for aircraft.

By the way, conventionally, a hot pipe manufacturing method such as an extrusion method and a tilt rolling method is well known as a method for manufacturing a seamless metal tube.

One of the extrusion methods is a method called Eugene Sejournet method. This is a method of hot extruding into a tubular shape using a glass lubricant.

The tilt rolling method is a method in which a solid billet is hot-punched with a tilt roll mill. Then, the obtained hollow shell is further hot rolled by a roll mill such as a plug mill, sizer, reducer or the like to reduce the diameter to a predetermined size.

Since titanium is inherently poor in hot workability, the former Eugene Sejournet extrusion method is exclusively used for the production of titanium seamless pipes.

The latter inclined rolling method has a high production efficiency and is advantageous in terms of production cost, but there is no example applied to the production of a titanium seamless pipe.

[Problems to be solved by the invention]

By the way, titanium is active and easily seized, and the skin after extrusion is deteriorated even if the former extrusion method by the Eugene Sejour method is used, and it is necessary to grind the inner and outer surfaces of the extruded tube. In addition, the extrusion method has a low manufacturing efficiency and requires pre-processing such as drilling a billet. Therefore, the yield is poor and the manufacturing cost is inevitably increased.

When the latter high-efficiency inclined rolling method is applied to the production of titanium seamless pipes, the processing speed is high, and the unevenness of the structure occurs due to partial temperature rise. A needle-like structure or a processed structure remains, which causes a fatal problem of reducing ductility of the product.

In view of such a situation, the present invention provides a method for producing a titanium seamless tube which guarantees good ductility comparable to or exceeding the extrusion method by the Eugene Sejournet method by a highly efficient inclined rolling method. With the goal.

[Means for solving problems]

According to the investigation by the present inventors, when the inclined rolling method is applied to the production of the titanium seamless pipe, it is found that the metal structure of the pipe is greatly affected by the outlet material temperature of the final rolling mill (for example, sizer or reducer). did.

Figure 2 shows the transformation temperatures of pure titanium and titanium alloy, V, Mo,
FIG. 3 is a state diagram schematically showing the relationship with the amounts of β-phase stabilizing elements such as Fe, Cr and Mn. According to the figure, as the β-phase stabilizing element increases, the temperature at which the β-phase changes to the α + β phase, that is, β
It is shown that the transus line is lowered.

The stable temperature range for pure titanium and titanium alloys is below the β transus line. When titanium has a high temperature above the β transus line, it becomes a β single phase, and when processed or annealed in this temperature range, a coarse needle-like structure is generated, which may impair the ductility of the product. Therefore, strip rolling is performed at a temperature of β transus or less.

However, when pure titanium or titanium alloy is rolled into a tubular shape like the inclined rolling method and undergoes large deformation strain in a three-dimensional state, if the material exits the final rolling mill at a temperature of β transus or more and β transus + 50 ° C or less. Although the needle-like structure was generated, it became clear that the structure became fine and did not adversely affect the product quality. Further, if the outlet temperature of the final rolling mill is in the temperature range of 200 ° C. or higher and β transus or lower, a fine equiaxed structure can be maintained. Therefore, in order to prevent crystal coarsening when introducing the inclined rolling method and to secure ductility, it is necessary to control the outlet temperature of the final rolling mill in the inclined rolling method to 200 ° C or higher and β transus + 50 ° C or lower. Become.

On the other hand, in the inclined rolling method, nonuniformity of the structure inevitably occurs due to partial temperature rise, but in order to eliminate this, it is also effective to anneal at a temperature of 500 ° C or higher and β transus or lower after rolling. Became clear.

By controlling the outlet temperature of the final rolling mill and annealing after rolling, it becomes possible to manufacture a titanium seamless pipe by a highly efficient inclined rolling method without causing a decrease in ductility.

The present invention has been made on the basis of such knowledge, and in producing a pure titanium or α type or α + β type titanium alloy seamless pipe by a tilt rolling method, as shown in FIG.
Final rolling mill outlet temperature 200 ℃ or more, β transus + 50 ℃
The following is a summary of a method for producing a titanium seamless tube, which is annealed at a temperature of 500 ° C. or more and β transus or less after rolling.

Here, the final rolling mill refers to a rolling mill located at the final stage of the inclined rolling line, and usually corresponds to a constant diameter rolling mill, a sizer called a reduction rolling mill, and a reducer.

[Action]

In the method of the present invention, the final rolling mill outlet temperature is set to 200 ° C. or higher and β transus + 50 ° C. or lower because cracks occur during processing of the product when the temperature is less than 200 ° C., and after final rolling after β transus + 50 ° C. This is because the acicular structure becomes coarse during cooling and the ductility of the product cannot be recovered even if annealing is performed after rolling.

Further, the annealing temperature after rolling is set to 500 ° C. or higher and β transus or less, the non-uniformity of the structure is not eliminated at less than 500 ° C., and a coarse needle-like structure is generated if annealing is performed above β transus, This is because the ductility of the product decreases.

〔Example〕

To clarify the effect of the present invention, four types of comparative tests were conducted. The materials, processing steps and performance tests in each comparative test are summarized in Table 1.

Comparative Test I A material equivalent to ASTM Gd III was used in a comparative test with respect to pure titanium for industrial use, and its β transus was 915 ° C. In the slant rolling process, a solid round billet is hot-punched into a 110mmφ × 12mmt raw tube with a rolling mill, heated in a reheating furnace and finished with a stretch reducer to 60.5mmφ × 12mmt. I decided. After that, annealing is applied, and the annealed tube is internally and externally cut by 0.5 mm for descaling, and the product dimension is 60 m.
It was set to mφ × 11 mm t. The obtained products were investigated for flatness and uniformity of structure. In the flatness test, the product was sandwiched between parallel jigs and compressed to a height of 20 mm to check for cracks.
The homogeneity of the metal structure was judged by observing the macro structure and the distribution deviation (20 or more) of Vickers hardness.

Table 2 shows the test results by correlating the exit temperature of the stretch reducer, which is the final rolling mill in tilt rolling, with the annealing temperature.

In No. 1 to 5, the reducer outlet temperature is β transus (915
℃) + 50 ° C, and the performance test results show that cracks occurred in the flatness test and ductility was reduced due to coarsening of the structure, and the overall evaluation is poor.

Nos. 6 to 14 are cases in which both the reducer outlet temperature and the annealing temperature are within the temperature range of the present invention, and the flatness and the nonuniformity of the structure are good.

Nos. 15 to 20 are cases in which the annealing temperature exceeds β transus, the structure is coarsened, and cracks are generated in the flatness test.

Nos. 18 to 20 are cases in which the annealing temperature is less than 500 ° C., and the nonuniformity of the structure caused by hot rolling has not been eliminated.

Nos. 21 to 25 are cases in which the reducer outlet temperature is less than 200 ° C., cracks occurred in the flatness test, and the cracks generated during hot working also remained.

Comparative test II In a comparative test with respect to α type titanium alloy, Ti-5Al-2.5Sn was used, and β transus was 1040 ° C. In the inclined rolling process, a 110 mmφ × 12 mm t raw tube manufactured by a punching machine and a drawing rolling machine was finished by a stretch reducer to 60.5 mm t × 12 mm t. After that, it is annealed and 60
A product of mmφ × 11 mm t was obtained.

Table 3 shows the results when the same test as the comparative test I was performed on the obtained product in correspondence with the reducer outlet temperature and the annealing temperature.

For No. 1 to 5, the reducer outlet temperature is β transus (1040
℃) + 50 ℃ is exceeded, causing a crack in the flatness test and coarsening of the structure, and the overall evaluation is poor.

In Nos. 6 to 14, both the reducer outlet temperature and the annealing temperature were within the temperature range of the present invention, and therefore, good results were obtained in both the flatness test and the uniform structure.

In Nos. 15 to 17, since the annealing temperature exceeded β transus, the structure was coarsened and cracks were generated in the flattening test.

Since No. 18 to 20 have an annealing temperature of less than 500 ° C, the nonuniformity of the structure has not been resolved.

In Nos. 21 to 25, the reducer outlet temperature was out of the range of less than 200 ° C., so cracking occurred in the flatness test and cracking occurred during hot working.

Comparative Test III This is a test on a Ti-6Al-4V alloy (β Transus 980 ° C.), which is a typical α + β type titanium alloy. In the inclined rolling process, the solid round billet is pierce-rolled and stretch-rolled with 11
After making a tube of 0 mm t × 9 mm t, this tube was heated in a reheating furnace and finished with a stretch reducer to 69.5 mm φ × 8.5 mm t. After that, annealing was performed, and further, internal and external cutting for descaling was performed to obtain a product of 69 mmφ × 7.5 mm t. As a flatness test on the obtained product, sandwich the product between parallel jigs,
It was compressed to a height of 23 mm and examined for cracks. The evaluation of the heterogeneity of the structure is the same as Test No. II. The test results are shown in Table 4 in correspondence with the reducer outlet temperature and the annealing temperature.

In No. 1 to 5, the reducer outlet temperature is β transus (980
(° C) + 50 ° C, flat cracking occurs due to a decrease in ductility regardless of the annealing temperature, coarsening of the structure also occurs, and the overall evaluation is poor.

In Nos. 6 to 14, both the reducer outlet temperature and the annealing temperature were within the range of the present invention, and good results were obtained in both flatness and structural uniformity.

In Nos. 15 to 17, the annealing temperature exceeded β transus, so cracking occurred in the flatness test.

Since No. 18 to 20 have an annealing temperature of less than 500 ° C, the nonuniformity of the structure has not been resolved.

In Nos. 21 to 25, the reducer outlet temperature is less than 200 ° C, so the ductility is insufficient and cracks occur in the flatness test.
The rolled material itself was cracked and void flaws were generated inside the material.

Comparative test IV In the test against industrial pure titanium, ASTM Gd IV equivalent material was used as industrial pure titanium, and its β transus was 950
℃. In the inclined rolling process, a solid round billet was made into a tube of 191 mmφ × 15 mm t by a piercing rolling machine and a stretching rolling machine, and this tube was heated in a reworking furnace, and a sizer of 174.5 mmφ was used as a final rolling machine. It is supposed to be finished to × 15mm t.

After annealing, the pipe is internally and externally cut by 0.5 m for descaling.
The product dimensions were set to 174 mmφ x 14 mm t. The flatness test for the obtained product is performed by sandwiching the product between parallel jigs.
It was supposed to be compressed to a height of mm.

The test results are shown in Table 5 in correspondence with the sizer outlet temperature and the annealing temperature.

For No. 1 to 5, the sizer outlet temperature is β transus (950 ° C)
This is the case where the temperature exceeds + 50 ° C, and cracks have occurred in the flatness test regardless of the annealing temperature.

Since Nos. 6 to 14 have the sizer outlet temperature and the annealing temperature both within the scope of the present invention, the flatness and the nonuniformity of the structure have good results.

In Nos. 15 to 17, since the annealing temperature exceeded β transus, the structure was coarsened and cracks were generated in the flatness test.

Since No. 18 to 20 have an annealing temperature of less than 500 ° C., the nonuniformity of the structure caused by hot rolling remains without being eliminated, and the uniformity of the structure is poor.

Since Nos. 21 to 25 had a sizer outlet temperature of less than 200 ° C, cracking occurred in the flattening test, and the cracking generated during hot working also remained.

〔The invention's effect〕

As described above, according to the present invention, the outlet material temperature in the final rolling mill such as reducer and sizer is set to 200 ° C to β transus + 5
By maintaining the temperature at 0 ° C and further annealing after rolling between 500 ° C and β transus, it is possible to manufacture a seamless pipe by the inclined rolling method of pure titanium and titanium alloy with excellent ductility and structure uniformity. It is a thing.

As a result, the yield from the material billet to the product is
81-85%, which is a significant improvement compared to 50-70% in the case of the hot extruded pipe by the conventional Eugene Sejournet method, and the effect of significantly reducing the pipe manufacturing cost together with the improvement of the pipe manufacturing speed Is obtained.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a heat treatment process after tilt rolling of the present invention, and FIG. 2 is a state diagram schematically showing the relationship between transformation temperature and β-phase stabilizing element amount.

Claims (1)

[Claims] 1. When manufacturing a seamless pipe made of pure titanium or α type or α + β type titanium alloy by a tilt rolling method, the outlet temperature of the final rolling mill is set to 200 ° C. or higher and β transus + 50 ° C. or lower, and further 500 after rolling. A method for producing a titanium seamless pipe, which comprises performing annealing at a temperature of ℃ or more and β transus or less.