CN112718909B - Short-flow preparation method of Ti-Al-Nb-Zr-Mo alloy seamless pipe - Google Patents

Abstract

The invention provides a short-process preparation method for Ti-Al-Nb-Zr-Mo alloy seamless pipes, which is characterized by including the following steps: 1) preparing materials, 2) mixing and briquetting, 3) placing the materials in In the EB furnace of the electron beam gun, 4) Ti-Al-Nb-Zr-Mo alloy round ingot is obtained by vacuum melting, 5) centering holes are drilled at both ends of the ingot, and the two-roller cross-rolling machine is used for cross-rolling and perforation, 6) three-way Continuous rolling by roller rolling mill, 7) heating and sizing to obtain seamless pipes, 8) annealing treatment to obtain Ti‑Al‑Nb‑Zr‑Mo alloy seamless pipes. The obtained pipe has uniform composition and structure, few high and low density inclusions, high purity, short process flow, and better mechanical properties than the existing technical level. The comprehensive yield rate is increased to about 85%, and the production cost is reduced by 20 to 30%. It has obvious advantages. market application prospects.

Description

A short-process preparation method of Ti-Al-Nb-Zr-Mo alloy seamless pipe

Technical field

The invention relates to a short-process preparation method of Ti-Al-Nb-Zr-Mo alloy seamless pipe and belongs to the technical field of non-ferrous metal rolling.

Background technique

Ti-6Al-3Nb-2Zr-1Mo titanium alloy (ie TA31 titanium alloy) not only has low density, high specific strength, good plasticity and corrosion resistance, but also has high fracture toughness, stress corrosion fracture toughness, impact toughness and Weldability, etc., especially its outstanding resistance to seawater and marine atmospheric corrosion, it is an excellent lightweight structural material suitable for oil well pipes, sea pipeline systems, heat exchangers and other components. After being processed into seamless pipes, it has broad application prospects in the fields of offshore oil drilling platforms, marine engineering equipment, ships, submarines, deep submersibles and offshore facilities.

The process flow of preparing TA31 titanium alloy seamless pipes using the existing technology is as follows: first, mix titanium sponge with alloy raw materials, press and weld them into electrodes, and then smelt them into round shapes in a vacuum consumable electric arc furnace (VAR) 2 to 3 times. The round ingot is then forged, then drilled, extruded or cross-rolled and pierced, and finally through rolling, drawing, spinning and other processes to prepare TA31 titanium alloy seamless pipes of different specifications and uses. Obviously, the existing technology has shortcomings such as long process flow, low overall yield, and difficulty in obtaining ultra-long pipes. As a result, the cost of TA31 titanium alloy seamless pipes remains high and its application is greatly restricted. Therefore, it is necessary to improve the existing technology.

Contents of the invention

In order to overcome the above-mentioned shortcomings of the existing TA31 titanium alloy seamless pipe preparation method, the present invention provides a short-process preparation method of Ti-Al-Nb-Zr-Mo alloy seamless pipe, which is characterized by including the following steps:

(1) Prepare materials according to the following mass ratio:

Aluminum niobium alloy 5.7～6.3wt.%

Aluminum beans 4.05～4.77wt.%

Zirconium sponge 1.5～2.5wt.%

Aluminum-molybdenum alloy 1.5～1.7wt.%

Titanium sponge balance

The sum of the above components is 100 wt.%;

(2) After mixing the materials prepared in step (1), take an appropriate amount of the mixture as bulk material, and press the remaining mixture into blocks, dry them at 100-120°C for 5-6 hours, and then cool them with the furnace to obtain briquettes. material;

(3) Place the bulk material from step (2) in the cooling bed of an EB furnace equipped with seven electron guns, and then place an appropriate amount of briquettes from step (2) into the feeding area of the EB furnace;

(4) When the vacuum degree is 1.8×10 ^-3 ~ 3.5×10 ^-3 torr, turn on the No. 1 to 5 electron guns to melt the bulk materials in the cooling bed, and control the voltage of the No. 1 to 5 electron guns to be 29.5 to 30.5 KV and current are both 3.3~4.3A. After 100~120 minutes of melting, turn off the electron gun. After cooling for 20~40 minutes, push the briquettes in the feed area into the smelting area. At the same time, turn on the electron guns No. 1 to 7 to continue melting. Control 1 ~The voltage of electron gun No. 7 is 29.5~30.5KV, the current of electron gun No. 1~2 is 2.3~3.0A, the current of electron gun No. 3~4 is 5.3~6A, the current of electron gun No. 5 is 3.6~4.6A, the current of electron gun No. 6~7 The current of the electron gun is 1.6~2.6A, while maintaining the ingot pulling speed of 12~18mm/min. Continue to push, melt and pull the ingot until the melting is completed. Then cool to 80~100℃ and take the ingot out of the crystallizer. , cooled to room temperature, and after surface peeling and polishing, a Ti-Al-Nb-Zr-Mo alloy ingot was obtained;

(5) Drill centering holes at both ends of the Ti-Al-Nb-Zr-Mo alloy round ingot in step (4), send it to the heating furnace, heat it to 1100~1200℃, keep it warm for 6~8 hours, and send it to the two-roller cross-rolling machine Perform cross-rolling and piercing on the top, and control: the total reduction rate is 10 to 15%, the reduction rate before the top is 6 to 8%, the ovality coefficient is 1.11 to 1.18, the piercing speed is 0.15 to 0.4m/s, and the temperature is 1080~1120℃, perforated pipe is required;

(6) Send the perforated pipe in step (5) to the three-roll rolling mill for continuous rolling, and control: the total reduction rate is 12 to 18%, the ovality coefficient is 1.05 to 1.15, and the perforation speed is 0.3 to 0.6m /s, the temperature is 950~1000℃, continuous rolling pipes are obtained;

(7) Send the continuously rolled pipe in step (6) into the heating furnace. After heating to 800~900°C, send it to the sizing machine for sizing. At the same time, control the sizing speed to 0.4~0.8m/s to obtain no sizing. seam pipes;

(8) Anneal the seamless pipe in step (7) at 850 to 900°C for 2 to 3 hours, and then cool to room temperature to obtain a Ti-Al-Nb-Zr-Mo alloy seamless pipe.

In step (5), after the Ti-Al-Nb-Zr-Mo alloy ingot is heated, it is necessary to apply glass powder lubricant on the end near the head before entering the cross-rolling machine, and at the same time insert it into the centering hole. Glass powder lubricant wrapped in tin foil to prevent defects in the inner wall of the pipe during the perforation process.

The composition of the Ti-Al-Nb-Zr-Mo alloy seamless pipe in step (8) is: Al: 5.5 wt.%～6.5wt.%, Nb: 2.5 wt.%～3.5wt.%, Zr: 1.5 wt.%～2.5wt.%, Mo: 0.6 wt.%～1.5wt.%, the balance is Ti.

The invention has the following advantages and beneficial effects: the Ti-Al-Nb-Zr-Mo alloy seamless pipe obtained by using the above technical solution has uniform composition and structure, few high and low density inclusions, high purity, and no need for processing during processing. Forging is carried out, and the smelted ingot is directly sent to a two-roller cross-rolling piercing machine to prepare a perforated seamless pipe. The product is then obtained by three-roller continuous rolling, sizing and annealing. This not only shortens the length of the titanium alloy seamless pipe. process, and its mechanical properties are superior to those prepared by existing technologies. The invention has simple process, convenient operation and short process flow, which increases the comprehensive yield of the seamless pipe to about 85%, reduces the production cost by 20 to 30%, and has obvious market application prospects.

Description of the drawings

Figure 1 is a process flow diagram of the present invention.

Figure 2 is a diagram of the metallographic structure of the pipe obtained in Example 1 of the present invention.

Figure 3 is a diagram of the metallographic structure of the pipe obtained in Example 2 of the present invention.

Figure 4 is a diagram of the metallographic structure of the pipe obtained in Example 3 of the present invention.

Figure 5 is a graph showing the mechanical properties of the pipe obtained in Example 1 of the present invention.

Figure 6 is a graph showing the mechanical properties of the pipe obtained in Example 2 of the present invention.

Figure 7 is a graph showing the mechanical properties of the pipe obtained in Example 3 of the present invention.

Detailed ways

The present invention will be further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the content described.

Example 1

A short-process preparation method for Ti-Al-Nb-Zr-Mo alloy seamless pipes, which is characterized by including the following steps:

(1) Prepare materials according to the following mass ratio:

Aluminum niobium alloy 5.7wt.%

Aluminum beans 4.05wt.%

Zirconium sponge 1.5wt.%

Aluminum-molybdenum alloy 1.5wt.%

Titanium sponge 87.25wt.%;

(2) After mixing the materials prepared in step (1), take an appropriate amount of the mixture as bulk material, and press the rest of the mixture into blocks, dry them at 100°C for 6 hours, and cool them with the furnace to obtain briquettes;

(3) Place the bulk material from step (2) in the cooling bed of an EB furnace equipped with seven electron guns, and then place an appropriate amount of briquettes from step (2) into the feeding area of the EB furnace;

(4) When the vacuum degree is 1.8×10 ^-3 torr, turn on the No. 1 to 5 electron guns to melt the bulk materials in the cooling bed. Control the voltage of the No. 1 to 5 electron guns to be 29.5KV and the current to be 3.3A. After 100 minutes of smelting, turn off the electron gun. After cooling for 20 minutes, push the briquettes in the feed area into the smelting area. At the same time, turn on the electron guns No. 1 to 7 to continue melting. Control the voltage of the electron guns No. 1 to 7 to be 29.5KV. The current of electron gun No. 2 is 2.3A, the current of electron gun No. 3 to No. 4 is 5.3A, the current of electron gun No. 5 is 3.6A, the current of electron gun No. 6 to No. 7 is 1.6A, while maintaining the ingot pulling speed of 12mm/min, and so on. Push, melt and pull the ingot until the smelting is completed, then cool to 80°C, take the ingot out of the crystallizer, cool to room temperature, and after surface peeling and polishing, the Ti-Al-Nb-Zr-Mo alloy round is obtained ingot;

(5) After drilling centering holes at both ends of the Ti-Al-Nb-Zr-Mo alloy round ingot in step (4), send it to the heating furnace to be heated to 1100°C and kept for 8 hours. After coming out of the furnace, quickly apply it on the end near the top. Appropriate amount of glass powder lubricant, and at the same time, stuff the glass powder lubricant wrapped with tin foil into the centering hole to prevent defects in the inner wall of the pipe during the perforation process, and then send it to the two-roller cross-rolling machine for cross-rolling and perforation, and control: The perforated pipe is obtained with a reduction rate of 10%, a reduction rate before top of 6%, an ellipticity coefficient of 1.11, a perforation speed of 0.15m/s, and a temperature of 1080°C;

(6) Send the perforated pipe in step (5) to the three-roll rolling mill for continuous rolling, and control: the total reduction rate is 12%, the ovality coefficient is 1.05, the perforation speed is 0.3m/s, and the temperature is 950 ℃, continuous rolling pipes;

(7) Send the continuously rolled pipe in step (6) into the heating furnace. After heating to 800°C, send it to the sizing machine for sizing. At the same time, control the sizing rate to 0.4m/s to obtain seamless pipes;

(8) Anneal the seamless pipe in step (7) at 850°C for 3 hours and cool to room temperature to obtain a Ti-Al-Nb-Zr-Mo alloy seamless pipe;

The composition of the Ti-Al-Nb-Zr-Mo alloy seamless pipe is: Al: 58wt.%, Nb: 2.98wt.%, Zr: 2.00wt.%, Mo: 1.02wt.%, and the balance is Ti;

After mechanical property testing, the mechanical properties of the annealed seamless pipe can meet the requirements. The obtained seamless pipe size is Ф180×12×11452mm (outer diameter×wall thickness×length).

The mechanical properties are shown in Table 1 and Figure 5:

Table 1

Sample No R _m /MPa R _p0.2 /MPa A/% 1 902 793 12.8 2 910 806 12.4 3 896 801 13.2 4 906 794 12.1 5 914 812 12.9 6 903 793 13.2 average value 905 799 12.7

The metallographic structure is shown in Figure 2.

Example 2

A short-process preparation method for Ti-Al-Nb-Zr-Mo alloy seamless pipes, which is characterized by including the following steps:

(1) Prepare materials according to the following mass ratio:

Aluminum niobium alloy 6.3wt.%

Aluminum beans 4.77wt.%

Zirconium sponge 2.5wt.%

Aluminum-molybdenum alloy 1.7wt.%

Titanium sponge 84.73wt.%;

(2) After mixing the materials prepared in step (1), take an appropriate amount of the mixture as bulk material, and press the remaining mixture into blocks, dry them at 120°C for 5 hours, and cool them with the furnace to obtain briquettes;

(3) Place the bulk material from step (2) in the cooling bed of an EB furnace equipped with seven electron guns, and then place an appropriate amount of briquettes from step (2) into the feeding area of the EB furnace;

(4) When the vacuum degree is 3.5×10 ^-3 torr, turn on the No. 1 to 5 electron guns to melt the bulk materials in the cooling bed. Control the voltage of the No. 1 to 5 electron guns to be 30.5KV and the current to be 4.3A. After 120 minutes of smelting, turn off the electron gun. After cooling for 40 minutes, push the briquettes in the feed area into the smelting area. At the same time, turn on the electron guns No. 1 to 7 to continue melting. Control the voltage of the electron guns No. 1 to 7 to be 30.5KV, 1 to 2 The current of electron gun No. 3 is 3.0A, the current of electron gun No. 3 to 4 is 6A, the current of electron gun No. 5 is 4.6A, and the current of electron gun No. 6 to 7 is 2.6A. At the same time, the ingot pulling speed is maintained at 18mm/min, and the material is continuously pushed and melted. and pull the ingot until the smelting is completed, then cool it to 100°C, take the ingot out of the crystallizer, cool it to room temperature, and grind the surface to obtain a Ti-Al-Nb-Zr-Mo alloy round ingot;

(5) After drilling centering holes at both ends of the Ti-Al-Nb-Zr-Mo alloy round ingot in step (4), send it to the heating furnace to be heated to 1200°C and kept for 6 hours. After coming out of the furnace, quickly apply it on the end near the top. Appropriate amount of glass powder lubricant, and at the same time, stuff the glass powder lubricant wrapped with tin foil into the centering hole to prevent defects in the inner wall of the pipe during the perforation process, and then send it to the two-roller cross-rolling machine for cross-rolling and perforation, and control: The reduction rate is 15%, the reduction rate before top is 8%, the ellipticity coefficient is 1.18, the perforation speed is 0.4m/s, and the temperature is 1120°C, the perforated pipe is obtained;

(6) Send the perforated pipe in step (5) to the three-roller for continuous rolling, and control: the total reduction rate is 18%, the ovality coefficient is 1.15, the perforation speed is 0.6m/s, and the temperature is 1000 ℃, continuous rolling pipes;

(7) Send the continuously rolled pipe in step (6) into the heating furnace. After heating to 900°C, send it to the sizing machine for sizing. At the same time, control the sizing rate to 0.8m/s to obtain seamless pipes;

(8) Anneal the seamless pipe in step (7) at 900°C for 2 hours and cool to room temperature to obtain a Ti-Al-Nb-Zr-Mo alloy seamless pipe;

The composition of the Ti-Al-Nb-Zr-Mo alloy seamless pipe is: Al: 6.12wt.%, Nb: 3.02wt.%, Zr: 2.03wt.%, Mo: 1.00wt.%, the balance is Ti ;

The mechanical properties are shown in Table 2 and Figure 6:

Table 2

Sample No R _m /MPa R _p0.2 /MPa A/% 1 921 806 12.9 2 916 814 13.2 3 909 806 12.4 4 913 816 13.0 5 915 807 12.6 6 920 812 12.8 average value 916 810 12.8

After mechanical property testing, the mechanical properties of all parts can meet the requirements. The size of the seamless pipe obtained is Ф180×12×11802mm (outer diameter×wall thickness×length).

The metallographic structure is shown in Figure 3.

Example 3

A short-process preparation method for Ti-Al-Nb-Zr-Mo alloy seamless pipes, which is characterized by including the following steps:

(1) Prepare materials according to the following mass ratio:

Aluminum niobium alloy 6.0wt.%

Aluminum beans 4.62wt.%

Zirconium sponge 2.00wt.%

Aluminum-molybdenum alloy 1.6wt.%

Titanium sponge 58.78wt.%;

(2) After mixing the materials prepared in step (1), take an appropriate amount of the mixture as bulk material, and press the remaining mixture into blocks, dry them at 110°C for 5 hours, and then cool them with the furnace to obtain briquettes;

(3) Place the bulk material from step (2) in the cooling bed of an EB furnace equipped with seven electron guns, and then place an appropriate amount of briquettes from step (2) into the feeding area of the EB furnace;

(4) When the vacuum degree is 2.6×10 ^-3 torr, turn on the No. 1 to 5 electron guns to melt the bulk materials in the cooling bed. Control the voltage of the No. 1 to 5 electron guns to be 30KV and the current to be 3.8A. Melting After 110 minutes, turn off the electron gun. After cooling for 30 minutes, push the briquettes in the feeding area into the melting area. At the same time, turn on the electron guns No. 1 to 7 to continue melting. Control the voltage of the electron guns No. 1 to 7 to be 30KV, and the voltage of the electron guns No. 1 to 2 to be 30KV. The current is 2.8A, the current of electron gun No. 3 to 4 is 5.8A, the current of electron gun No. 5 is 4.1A, and the current of electron gun No. 6 to 7 is 1.9A. At the same time, the ingot pulling speed is maintained at 15mm/min, so as to continuously push, melt and Pull the ingot until the smelting is completed, then cool it to 90°C, take the ingot out of the crystallizer, cool it to room temperature, and grind the surface to obtain a Ti-Al-Nb-Zr-Mo alloy round ingot;

(5) After drilling centering holes at both ends of the Ti-Al-Nb-Zr-Mo alloy round ingot in step (4), send it to the heating furnace to be heated to 1150°C and kept for 7 hours. After coming out of the furnace, quickly apply it on the end near the top. Appropriate amount of glass powder lubricant, and at the same time, stuff the glass powder lubricant wrapped with tin foil into the centering hole to prevent defects in the inner wall of the pipe during the perforation process, and then send it to the two-roller cross-rolling machine for cross-rolling and perforation and control: total pressure The perforated pipe is obtained when the reduction rate is 13%, the reduction rate before top is 7%, the ellipticity coefficient is 1.15, the perforation speed is 0.2m/s, and the temperature is 1100°C;

(6) Send the perforated pipe in step (5) to the three-roller for continuous rolling, and control: the total reduction rate is 15%, the ovality coefficient is 1.09, the perforation speed is 0.5m/s, and the temperature is 980 ℃, continuous rolling pipes;

(7) Send the continuously rolled pipe in step (6) into the heating furnace. After heating to 850°C, send it to the sizing machine for sizing. At the same time, control the sizing rate to 0.6m/s to obtain seamless pipes;

(8) Anneal the seamless pipe in step (7) at 880°C for 2 hours and cool to room temperature to obtain a Ti-Al-Nb-Zr-Mo alloy seamless pipe;

The composition of the Ti-Al-Nb-Zr-Mo alloy seamless pipe is: Al: 6.03wt.%, Nb: 3.0wt.%, Zr: 2.01wt.%, Mo: 0.98wt.%, and the balance is Ti ;

After mechanical property testing, the mechanical properties of all parts can meet the requirements. The size of the seamless pipe obtained is Ф180×12×12542mm (outer diameter×wall thickness×length).

The metallographic structure is shown in Figure 4.

The mechanical properties are shown in Table 3 and Figure 7.

table 3

Sample No R _m /MPa R _p0.2 /MPa A/% 1 914 806 12.8 2 906 801 12.4 3 910 810 12.6 4 908 807 13.4 5 912 809 13.1 6 915 812 12.8 average value 911 807 12.9

It can be seen from the metallographic microstructure of the three embodiments in Figures 2, 3 and 4 that the three embodiments are all lamellar structures, and there are a large number of α phase bundles interlaced with each other.

Figure 5, Figure 6, and Figure 7 are the mechanical performance diagrams of the three embodiments respectively. It can be seen that the uniformity of the mechanical properties is compared with the existing technology, namely: multiple VAR melting ingots, cross-rolled piercing after forging The mechanical properties of the obtained seamless pipe are as shown in Table 4. The mechanical properties of the three embodiments are all better than those of the seamless pipes obtained by the existing technology in Table 4.

The seamless pipe properties of Ti-Al-Nb-Zr-Mo alloy under traditional technology are shown in Table 4

Table 4

alloy R _m /MPa R _p0.2 /MPa A/% TA31 880 785 12

The above are only preferred embodiments of the present invention and do not limit the present invention in any way. Any simple modifications, changes and equivalent structural changes to the above embodiments based on the technical essence of the present invention still belong to the technology of the present invention. .

Claims (2)

1. A short-flow preparation method of a Ti-Al-Nb-Zr-Mo alloy seamless pipe is characterized by comprising the following steps:

(1) The materials are prepared according to the following mass ratio:

5.7 to 6.3 weight percent of aluminum-niobium alloy

4.05 to 4.77 weight percent of aluminum beans

1.5 to 2.5 weight percent of sponge zirconium

1.5 to 1.7 weight percent of aluminum molybdenum alloy

Titanium sponge balance

The sum of the components is 100 wt percent;

(2) Mixing the prepared materials in the step (1), taking a proper amount of the mixture as bulk materials, uniformly pressing the rest of the mixture into blocks, drying at 100-120 ℃ for 5-6 h, and cooling along with a furnace to obtain pressed blocks;

(3) The bulk material in the step (2) is laid in a cooling bed of an EB furnace provided with a seven-rod electron gun, and then a proper amount of pressing blocks in the step (2) are put into a feeding area of the EB furnace;

(4) At a vacuum level of 1.8X10 ^-3 ～3.5×10 ^-3 When in torr, starting an electron gun 1-5 to smelt bulk materials in a cooling bed, controlling the voltage of the electron gun 1-5 to 29.5KV, the current of the electron gun 3.3-4.3A, smelting for 100-120 min, closing the electron gun, cooling for 20-40 min, pushing a briquetting material in a feeding area into a smelting area, simultaneously starting the electron gun 1-7 to continue smelting, controlling the voltage of the electron gun 1-7 to 29.5-30.5 KV, the current of the electron gun 1-2 to 2.3-3.0A, the current of the electron gun 3-4 to 5.3-6A, the current of the electron gun 5 to 3.6-4.6A, and the current of the electron gun 6-7 to 1.6-2.6A, simultaneously keeping the ingot pulling speed of 12-18 mm/min, continuously pushing, smelting and ingot pulling until smelting is completed, cooling to 80-100 ℃, taking out the ingot from a crystallizer, cooling to room temperature, and carrying out skin removing and polishing treatment on the ingot to obtain a round Ti-Al-Mo-Nb alloy;

(5) Punching centering holes at two ends of the Ti-Al-Nb-Zr-Mo alloy round ingot in the step (4), feeding the round ingot into a heating furnace to heat to 1100-1200 ℃, preserving heat for 6-8 h, feeding the round ingot into a two-roll diagonal mill to perform diagonal rolling perforation, and controlling: the total rolling reduction is 10-15%, the rolling reduction before top is 6-8%, the ellipticity coefficient is 1.11-1.18, the perforation speed is 0.15-0.4 m/s, and the temperature is 1080-1120 ℃, so as to obtain perforated pipe;

before the two-roller oblique rolling mill is sent, a glass powder lubricant is required to be smeared at one end close to the plug, and meanwhile, the glass powder lubricant wrapped by tinfoil is plugged into the centering hole, so that defects on the inner wall of the pipe in the perforation process are prevented;

(6) Feeding the perforated pipe in the step (5) into a three-roller continuous rolling mill for continuous rolling, and controlling: the total rolling reduction is 12-18%, the ellipticity coefficient is 1.05-1.15, the perforation speed is 0.3-0.6 m/s, and the temperature is 950-1000 ℃, so as to obtain the tandem rolling pipe;

(7) Feeding the continuous rolling pipe in the step (6) into a reheating furnace, heating to 800-900 ℃, feeding the pipe into a sizing mill for sizing, and controlling the sizing speed to be 0.4-0.8 m/s to obtain a seamless pipe;

(8) And (3) annealing the seamless pipe in the step (7) for 2-3 hours at the temperature of 850-900 ℃, and cooling to room temperature to obtain the Ti-Al-Nb-Zr-Mo alloy seamless pipe.

2. The short-flow preparation method of the Ti-Al-Nb-Zr-Mo alloy seamless pipe according to claim 1, wherein the Ti-Al-Nb-Zr-Mo alloy seamless pipe in the step (8) comprises the following components: al:5.5 wt.% to 6.5wt.%, nb:2.5 wt.% to 3.5wt.%, zr:1.5 0.6 to 1.5wt.% of Mo, and the balance of Ti.