JPH06292906A - Manufacture of bar and wire rod of titanium and titanium alloy - Google Patents

Abstract

PURPOSE:To produce a bar and wire rod excellent in surface properties at a high efficiency by heating a titanium rolling stock, rolling it with a skew rolling mill and rolling it with a caliber rolling mill after reheating. CONSTITUTION:The rolling stock of titanium and titanium alloy is heated in a heating stage, rolled at a specific reduction of area in accordance with a heating temp. with the skew rolling mill, reheated or kept at a certain temp. with a heating device and rolled with the caliber rolling mill. In such a manner, the bar and wire rod of titanium and titanium alloy are manufactured. The reduction of area in the skew rolling is determined in the range that satisfies a formula I. In the formula I, the reduction of area (%) is expressed by R and the heating temp. ( deg.C) is expressed by T. In this way, even about a cast ingot which has not been utilized in the past, the direct rolling of the same can be carried out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to heating and rolling of raw materials when hot working titanium and titanium alloys into bars and wires.

[0002]

2. Description of the Related Art Titanium and titanium alloys have excellent corrosion resistance and high specific strength. Therefore, rods and wire rods formed by processing them can be used in a variety of aircraft members, seawater ropes, eyeglass frames, and the like. Used in applications.

Usually, rods and wires made of titanium and titanium alloys are produced by a process of slab-casting or forging a cast ingot into a billet and rolling the billet in a group of continuous rolling mills having a hole type roll. There is. However, in the group of continuous rolling mills having this hole type roll, it is impossible to directly process a cast ingot having poor hot workability, and even in the case of a lump or forged billet, surface cracks are generated during the groove type rolling. There is a problem that occurs.

Therefore, a method has been reported in which a multi-pass process is performed under a light pressure using an inclined rolling mill to prevent cracking. For example, Japanese Examined Patent Publication No. 4-13041 discloses a method for producing a product having a good surface quality by hot working a rolling material of a titanium alloy only by tilt rolling. However, the processing by the inclined rolling mill has a slow rolling speed because it has many passes under light pressure. Therefore, if the temperature of the material is remarkably lowered during rolling and the cross-section reduction rate is high, cracking is likely to occur due to the temperature reduction even in inclined rolling. Further, in the same publication, it is shown that the inclined rolling mills are arranged in series and the inclined rolling is continuously performed. However, due to the temperature decrease during the inclined rolling and the residual processing strain during rolling, the inclined rolling is performed at the subsequent stage. Surface cracks are likely to occur. Moreover, since the rolling speed is low, the productivity is extremely low.

[0005]

DISCLOSURE OF THE INVENTION The present invention relates to the production of titanium and titanium alloy rods, wires and the like by combining the steps of heating, tilt rolling, reheating and hole rolling, and is excellent in surface quality and the like. Another object is to provide a manufacturing method with high production efficiency.

[0006]

DISCLOSURE OF THE INVENTION The present inventors have made various studies on the quality of surface cracks and the like and the manufacturing process when hot-working titanium and titanium alloys into rods, wires and the like. As a result, first, if the surface layer part is processed with multiple passes under light pressure at a cross-sectional reduction rate that corresponds to the heating temperature predetermined by the type and history of the rolling material using an inclined rolling mill, surface cracking due to the coarse structure of the rolling material It is possible to prevent the above, and further after the inclined rolling, reheat to compensate for the temperature drop during the inclined rolling, recrystallize the processed layer of the surface layer part, and then subject it to hole rolling to obtain excellent surface quality. It has been discovered that titanium and titanium alloy rods and wire rods can be manufactured, and the following means realize a manufacturing method with excellent quality such as surface properties and high production efficiency.

(1) Titanium and titanium alloy rolling materials are heated in a heating process, then rolled by an inclined rolling mill at a predetermined cross-section reduction rate corresponding to the heating temperature, and then reheated or retained by a heating device. Then, it is rolled by a hole rolling mill.

(2) Forging of titanium or a slab of billet is used as a rolling material, and the cross-section reduction rate of inclined rolling is as follows.
Set to the range that satisfies the formula.

10 ≦ R ≦ 0.5 ((T + 273) / 100)) ² (1) R: cross-section reduction rate (%) T: heating temperature (° C) (3) A forged or slab billet is used, and the cross-section reduction rate of tilt rolling is set within a range that satisfies the following formula (2).

10 ≦ R ≦ 0.4 ((T + 273) / 100)) ² ··· (2) R: Reduction rate of cross section (%) T: Heating temperature (° C) (4) Casting of rolling material into titanium As an ingot, the cross-section reduction rate of tilt rolling is set within the range that satisfies the following formula (3).

10 ≦ R ≦ 0.4 ((T + 273) / 100)) ² (3) R: cross-section reduction rate (%) T: heating temperature (° C.) (5) A casting ingot is used, and the cross-section reduction rate of inclined rolling is set within a range that satisfies the following expression (4).

10 ≦ R ≦ 0.3 ((T + 273) / 100)) ² (4) R: cross-section reduction rate (%) T: heating temperature (° C.) (6) reheating after tilt rolling The temperature or holding temperature is limited within the range of 600 ° C to 950 ° C for titanium and 700 ° C to 1250 ° C for titanium alloy, respectively.

[0013]

In constructing a series of manufacturing processes such as heating-gradient rolling-reheating-pore rolling of a rolling material, the present inventors firstly set the rolling material and the gradient rolling conditions, particularly the heating temperature and the cross-section reduction rate. I investigated the relationship. That is, since the hot workability differs depending on the type of rolling material and the manufacturing process (history) up to that point, the preferable inclined rolling conditions also differ. Therefore, the rolling materials are titanium and Ti-6Al.
A titanium alloy represented by a -4V alloy is used, and the history of each is a cast ingot and a slab,
These were heated to various temperatures and rolled with an inclined rolling mill while varying the cross-section reduction rate, and the surface properties of the rolled material were observed.

As a result, it has been found that the upper limit of the area reduction rate can be limited under the condition that surface cracking does not occur in the inclined rolling. Further, it has been found that rolling can be performed without defects such as surface cracks at a predetermined cross-section reduction rate according to the rolling material and heating temperature. The condition is that when the rolled material is forged or slabbed, titanium with relatively good hot workability is represented by the above formula (1), high strength and poor hot workability.
It has been found that the titanium alloy such as i-6Al-4V is represented by the formula (2). Further, when the rolled material is an ingot, the hot workability is inferior to that of the slab material due to the coarse casting structure, so the condition is the above formula (3) for titanium,
It was found that the titanium alloy is represented by the above formula (4).

On the other hand, the lower the cross-section reduction rate, the better the surface properties of the rolled material, but the lower limit is determined by the following two reasons. That is, it was found that if a recrystallized layer having a depth of 5 mm or more is formed in the material surface layer portion during reheating after tilt rolling, surface cracks can be prevented during post-rolling rolling, so the material surface layer portion can be prevented. It is necessary to impart the work strain necessary for producing a recrystallized layer of 5 mm or more to the material at the time of tilt rolling, and it is therefore necessary to limit the lower limit of the cross-section reduction rate. Further, from the viewpoint of productivity, it is desirable that the cross-section reduction rate at the time of tilt rolling be equal to or higher than the cross-section reduction rate of the hole rolling.

As a result of examining the work strain distribution in the surface layer portion of the rolling material in the tilt rolling, a relatively high work strain is applied particularly to the surface layer in the tilt rolling. Therefore, if the area reduction rate is 10% or more, the depth of the surface layer portion is large. It was found that the processing strain necessary for recrystallization is locally applied to the region of 5 mm or more. And this processing strain amount is not so much influenced by the kind of material and the heating temperature. Further, from the viewpoint of productivity, the cross-section reduction rate in the rough stage of ordinary hole rolling is about 10% or more, and therefore the cross-section reduction rate of at least 10% is also required for inclined rolling. For the above reasons, it is desirable to set the lower limit of the area reduction rate to 10%.

Further, the lower limit of the heating temperature range during tilt rolling is 6 for titanium in view of the hot workability of the material.
The temperature is preferably 00 ° C or higher, and 700 ° C or higher for a titanium alloy.
Further, although the hot workability is improved at a high temperature, an oxide layer is remarkably generated, which may have an adverse effect. Therefore, the upper limit is preferably 950 ° C. for titanium and 1250 ° C. for a titanium alloy.

The range of appropriate conditions for tilt rolling determined from the above viewpoints is shown in FIGS. 1 and 2. FIG. 1 shows the heating temperature and the cross-section reduction rate when the rolled material is a forged or agglomerated material and FIG. 2 shows the case where the rolled material is an ingot.

In the one-pass rolling of the inclined rolling mill, since the cross-section reduction rate is limited as described above, a product such as a wire rod cannot be manufactured. Further, even if the inclined rolling mills are arranged in series, the productivity is low and not practical because the rolling speed is slow. Therefore,
The combination of hole rolling as a post-process of the inclined rolling mill was studied. As a result, if the grooved rolling is arranged immediately after the inclined rolling, there is a problem that the surface crack is likely to occur during the grooved rolling due to the surface temperature decrease during the inclined rolling and the processing strain during the inclined rolling. It turned out to be. And
It was concluded that the problem could be solved by providing a reheating step immediately after the inclined rolling and then performing a groove rolling after the reheating.

That is, the purpose of the reheating is to prevent the occurrence of surface cracks in the post-step groove rolling. In order to prevent the occurrence of surface cracks in groove rolling, first, in order to compensate for the surface temperature drop in the inclined rolling process, from the viewpoint of hot workability, 600 ° C. or higher for titanium and 700 ° C. for titanium alloys.
It is necessary to heat above ℃. Furthermore, it has been found that it is necessary to finely recrystallize the surface layer of the material in order to remove the processing strain at the time of tilt rolling and further improve the workability. Therefore, as a result of studying the conditions under which surface cracking does not occur in the grooved rolling, a depth of 5 mm in the surface layer portion was observed during reheating after tilt rolling.
It was concluded that if the above-mentioned recrystallized layer is formed, it can be rolled in the post-step hole rolling without surface cracking.

Therefore, in order to recrystallize the surface layer of the material, the cross-sectional reduction rate is 10% so as to meet the above conditions.
Titanium and Ti-6A subjected to the above-described inclined rolling
The tilt-rolled material of the 1-4V alloy was reheated, and the depth from the surface of the recrystallized layer in the surface layer portion after heating was examined. as a result,
As for titanium, which was reheated to 600 ° C. or higher, a recrystallized layer of 5 mm or more was observed as shown in FIG. Similarly, in the case of a titanium alloy, a recrystallized layer of 5 mm or more was observed in the case of reheating to 700 ° C. or higher. Further, the upper limit of the reheating temperature is preferably 950 ° C. or lower for titanium and 1250 ° C. or lower for titanium alloy, similarly to the heating at the time of tilt rolling of the rolling material. Therefore, the reheating temperature range for titanium is 600 ° C.
To 950 ° C, and for titanium alloys 700 ° C to 125 ° C
Set to 0 ° C. In addition, the reheating device arranged between the inclined rolling mill and the hole rolling mill may be either induction heating or combustion atmosphere heating as the type, and the heating time is necessary for the rolled material to reach a predetermined temperature. However, it is preferable that the time is at least 1 minute or more. If the temperature of the material to be rolled after tilt rolling is 600 ° C. for titanium and 700 ° C. or more for titanium alloy, instead of reheating, hold the temperature of the material to be rolled. The holding time in this case is preferably 1 minute or more, as in the case of reheating.

The material reheated under the above-mentioned conditions can be directly used for the post-rolling rolling process, and the cross-sectional reduction rate in the rolling rolling in that case is not particularly limited.

[0023]

[Examples] Using a JIS class 2 titanium material, a slab of various titanium alloys and a rolling material round billet (outer diameter: 178 mm) of a cast ingot, each step of heating-gradient rolling-reheating-pore rolling is sequentially performed. Then, the surface texture of the rolled material was observed. That is, rolling material of titanium or titanium alloy,
In the heating process, it is heated to a predetermined temperature, then it is inclined rolled at a predetermined cross-section reduction rate, then reheated or held at a predetermined temperature with a heating device (the temperature is kept constant), then with a hole rolling mill. After rolling, the surface properties of the rolled material were observed.

In the inclined rolling mill used here, three cone type rolls having a roll diameter on the inlet side of the rolled material larger than that on the outlet side are connected to the pass line of the rolled material. It rotates with the roll housing around the center. One roll of this inclined rolling mill and rolled material are shown in FIG. The reheating device used was a combustion atmosphere heating system.

The test conditions of the examples and the results of the test are shown in Tables 1 and 2 below. From this result, it can be understood that the rod and wire processed by the method of the present invention have excellent surface quality.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

As described above, according to the present invention, it is possible to produce rods and wires having excellent surface properties with high efficiency. Further, a cast ingot that has not been conventionally available can be directly rolled in the present invention.

[Brief description of drawings]

FIG. 1 is a map showing an appropriate heating range and an appropriate range of area reduction rate during forging of titanium and titanium alloy or inclined rolling of a slab of billet.

FIG. 2 is a map showing an appropriate heating range and an appropriate range of cross-section reduction rate during tilt rolling of a cast ingot of titanium and a titanium alloy.

FIG. 3 is a map showing the relationship between the reheating temperature and the recrystallization layer depth after tilt rolling of titanium and titanium alloys.

FIG. 4 is a front view showing one roll of an inclined rolling mill and a rolled material.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yumitsu Yamamoto 3434 Shimada, Shinjuku Nippon Steel Co., Ltd. Inside the Komatsu Works (72) Inventor Yoshitaka Nakamura 3434 Shimada, Shinjuku Nippon Steel Co., Ltd. Inside the Shoko Works (72) Inventor Toyotoko Sano 3434 Shimada, Shinjuku City Shin-Nippon Steel Co., Ltd. Inside the Shoko Works (72) Inventor Kyotaro Tengoh 3434 Shimada Shinjuku, Nippon Steel Co., Ltd. Inside the Shoko Ironworks

Claims (6)

[Claims] 1. A rolling material of titanium and titanium alloy is heated in a heating step, then rolled by an inclined rolling mill at a predetermined cross-section reduction rate corresponding to the heating temperature, and then reheated or retained by a heating device. Then, a method for producing titanium and titanium alloy rods and wire rods, which is followed by rolling with a hole rolling mill. 2. The production of titanium and titanium alloy rods and wire rods according to claim 1, wherein the rolling material is a forged titanium or slab billet, and the cross-section reduction rate of inclined rolling is set in a range satisfying the following equation. Method. 10 ≦ R ≦ 0.5 ((T + 273) / 100)) ² R: Cross-section reduction rate (%) T: Heating temperature (° C) 3. The titanium or titanium alloy rod or wire rod according to claim 1, wherein the rolling material is a titanium alloy forged or slab billet, and the cross-section reduction rate of inclined rolling is set in a range satisfying the following formula. Production method. 10 ≦ R ≦ 0.4 ((T + 273) / 100)) ² R: Cross-section reduction rate (%) T: Heating temperature (° C) 4. The method for producing titanium and titanium alloy rods and wires according to claim 1, wherein the rolling material is a cast ingot of titanium, and the cross-section reduction rate of inclined rolling is set in a range satisfying the following formula. 10 ≦ R ≦ 0.4 ((T + 273) / 100)) ² R: Cross-section reduction rate (%) T: Heating temperature (° C) 5. The method for producing titanium and titanium alloy rods and wires according to claim 1, wherein the rolling material is a cast ingot of titanium alloy, and the cross-section reduction rate of inclined rolling is set in a range satisfying the following formula. 10 ≦ R ≦ 0.3 ((T + 273) / 100)) ² R: Cross-section reduction rate (%) T: Heating temperature (° C) 6. The reheating temperature or holding temperature after tilt rolling is set within the range of 600 ° C. to 950 ° C. for titanium and 700 ° C. to 1250 ° C. for titanium alloy, respectively. 1, claim 2, claim 3,
A method for manufacturing the titanium and titanium alloy rods and wires according to claim 4 or claim 5.