DE1290727B - Process for the production of high strength niobium alloys - Google Patents

Description

It is known that the high-temperature strength of high-alloy steels can be achieved by precipitation hardening can improve. Here, fine metal carbides are embedded in a metallic base material. Similarly, precipitation hardening of niobium alloys can provide an improvement the strength properties lead.

There has also been proposed a non-prior art method for dispersion hardening niobium alloys with at least 0.05% carbon by embedded fine carbide particles, the alloys being subjected to a heat treatment ^{at 980 to 1540 3 C for 1 to 50 hours;} Fine metal carbides are deposited in the matrix. According to this proposal, the final deformation took place after the dispersion hardening, i.e. after the precipitation of the metal carbides (German patent 1,224,944).

The invention now relates to a process for the production of high-strength niobium alloys and is characterized in that one of 0.5 to 12% zirconium, 0.02 to 0.5% oxygen, carbon and / or nitrogen and optionally up to 35% tungsten, up to 10% titanium, up to 25% molybdenum, up to 25% tantalum and / or up to 10% vanadium, the remainder at least 50% niobium, existing alloy ^{solution annealed for 5 minutes to 9 hours at 1600 to 2100 1} C, cooled and either before or after The alloy deformed to the final cross-section after the solution heat treatment is then heat-treated above the recrystallization temperature at 1000 to 1500C for 0.5 to 40 hours. The solution treatment is preferably ^{carried out at 1700 to 2000 C} C, the. subsequent heat treatment, preferably at 1150 to 1300 ° C. A modification of the method according to the invention is that a sheet made of the alloy of almost final thickness is quickly quenched to 1200 C after solution annealing and cold-rolled to the final thickness without intermediate annealing, the sheet thickness being reduced by 15 to 40%, preferably by 15 to 25% and finally subjected to the heat treatment. According to a preferred embodiment of this process, the sheet is ^{solution annealed at 1650 to 1800 3} C for 5 to 15 minutes and the cold-rolled sheet is heat-treated at 1200 to 1425 ° C for 0.5 to 8 hours. Such a sheet is expediently made of an alloy with 0.5 to 3% zirconium, 8 to 12% tungsten, 0.02 to 0.15% carbon, up to 7% tantalum, up to 0.05% other accompanying elements, the remainder niobium and impurities .

The deformation to the final thickness or final cross-section takes place in most cases by cold processing in one or more swipes.

The solution heat treatment of the sheets should not be extended unnecessarily in order to prevent grain growth. In general, a solution heat treatment ranges from 5 to 15 minutes at 1650 to 1800 ⁰ C. The quenching at 1200 ° C is to take place as quickly as possible, for. B. at 300 ° C / min and above.

The cold deformation causes a certain degree of stress hardening. The magnitude of the internal tension is proportional to the reduction in cross-section, i.e. the degree of rolling during rolling. they have one considerable influence on precipitation hardening in the last stage of the process. Used for sheets up to too high a degree of rolling - i.e. a cross-section reduction of more than 40% - rolled, a deterioration in the yield strength of the finished product is observed. If it is insufficient The degree of rolling, i.e. with a cross-section reduction below 15%, is the desired effect not reached.

The duration of the final heat treatment at a temperature above the recrystallization temperature is not critical. It is generally 0.5 hours or more.

The above-mentioned alloys containing zirconium, tungsten and tantalum are particularly high-quality alloys which also have remarkable ductility and high-temperature strength. These properties of tantalum-containing niobium alloys are surprising and are obviously based on an interaction with the other alloy elements, since such an improvement is not achieved by adding tantalum to niobium alone. An amount of tantalum of approximately 5% is most advantageous.
In the niobium alloys to be subjected to the process according to the invention, substances such as zirconium dioxide or various carbides separate out as the second phase. As a result of the solution heat treatment, this second phase largely dissolves in the base mass or matrix. In the case of cold deformation - e.g. B. in the production of sheet metal according to known processes - there is an uncontrollable excretion of oxidic or carbidic, dispersion-hardening substances in the form of a second phase. After the cold forming according to the invention, the substances of the second phase are homogeneous and extremely fineness in the base mass due to the solution heat treatment and subsequent quenching. This brings about the particularly high strength properties, in particular high-temperature strength, hardness and creep resistance. By selecting certain conditions for the treatment of niobium alloys according to the invention, these can be set specifically for the subsequent deformation - such as drop forging, extrusion, rolling or forging - between the solution heat treatment and the heat treatment above the recrystallization temperature. This deformation can take place at any desired temperature above room temperature but below the temperature of the solution heat treatment, e.g. B. to about 1500 ^c C, take place.

The method according to the invention can be carried out with the most varied of variants. The various heat treatments are carried out in a vacuum or in an inert atmosphere in the form of a noble gas. The solution annealing is expediently carried out at 1700 to 2000 ° C. within 1 to 4 hours for workpieces of relatively large cross-section or at 1650 to 1800 ^° C. within 5 to 15 minutes for sheet metal. As is well known, longer times will have to be used at lower annealing temperatures than at higher temperatures. In the case of sheet metal, the final heat treatment is preferably carried out above the recrystallization temperature at 1200 to 1425 ³ C within 0.5 to 8 hours.

The invention is explained in more detail with the aid of the following examples. The test bars had a diameter of 12.5 mm and a length of 125 mm.

example 1

By melting together 396 parts of niobium with a content of 0.025% oxygen and of

4 parts of zirconium with 0.10% oxygen in a water-cooled copper crucible of an electric arc furnace an alloy of niobium and zirconium was made. The cast block was still 6ma! melted and allowed to solidify again to ensure thorough mixing of the metals. The block was then processed into a round rod - diameter 12.5 mm, length 127 mm.

The alloys listed in Table 1 were produced in a similar manner. Each ingot of the alloys was ^{die forged at 1000 3} C with each die producing a reduction in area of 12.5%. A test rod of each alloy was placed in a vacuum furnace at 1950 for 6 hours ^; C - i.e. above the recrystallization temperature - solution annealed, cooled to room temperature and then aged in a vacuum for 30 minutes at 1100 C (C). Another series of test bars of all alloys was held in an inert atmosphere at 1400 ° C for only 16 hours (A). Of all the test rods 0,2-Warmdehngrenze was determined at 1100 ^c C in vacuum. The values are listed in Table 1. This also shows the influence of the heat treatment on the strength propertiesa of the alloys.

Table 1 Table 3

0.2 warm stretch arene Vacuum) composition (1100 C C. (Remainder niobium) A *) kp.mno kp / mm ² 23.9 }% Zr, 0.02% O ₂ 11 "> 27.4 5% Zr. 0.02 ¹ Vo O ₂ 19.7 28.8 JO ¹ Vo Zr. 0.03% O ₂ 25.3

Not treated according to the method according to the invention.

Example 2

Test bars of a niobium alloy were produced from 5% Zr, 10% W. 0.04% O ₂ , remainder Nb, heated in an electric furnace to 1200 to 1300 ^: C and then forged to a cross-section reduction of 50%. This was followed by the heat treatment in a vacuum oven, namely 16 hours at 1400 ^: C (A) or 9 hours at 2000 ^: C, cooling to room temperature and ^{aging for 30 minutes at 1100:} C (3). The strength and ductility were then determined at 1100 ° C. in a vacuum (see Table 2).

55

0.2 warm
yield strength
kp, mm ² Table 2 fracture
strain
O Fracture-
constriction
O,
Vt warmth
treatment 28.1 "
41 Warm
strength
kp / mm ² 20th
3 40
14th A *) ....
B. 35
41.7

warmth
treatment*) load
kp mm ² Time to break (hi A **)
A **)
B. 21.1
17.6
24.6 12.5
30.5
26, ί

*) See example 2.
**) Not according to the method according to the invention.

30th

35

40

Example 4

Made of a niobium alloy of 5% Zr, 15% W. 0.05 °; » O ₂ , remainder Nb, ^{test bars were produced at 1450:} C by extrusion at a compression ratio of 4: 1 and these were forged at 1100 C from a diameter of 50 mm to 9.5 mm. Fig. I shows the creep behavior at ί 100-C, ie the dependency of the service life until break on the magnitude of the tensile load at 1100 "C.

Curve A *): only forged;

Curve B *): forged and 18 hours at

1400 ^; C heat treated;
Curve C: forged, 1 hour at 2000 C.

Solution-hardened and 1 hour at

Aged 1200 ^{: C.}
* t Not treated according to the method according to the invention.

Example 5

Two blocks of a niobium alloy made of 1% Zr, 0.027% O ₂ , 0.008% N ₂ , 0.004% C, remainder Nb, with a diameter of 50 mm were produced. One (C) was extruded at 1260 C and a compression ratio of 4: 1, the other (D) 0.25 seconds at 1620 ^; C solution treated and then extruded at 1620 C and a compression ratio of 4: 1. All test bars were then forged to a diameter of 9.5 mm and heat-treated in a vacuum for 1 hour at 1200 ° C. and the creep rupture strength and high temperature strength were ^{then determined at 1100 ° C. (see Table 4).}

Table 4

Creep behavior at I100 ^c C
load

kpmm-

C *)
D.

Time to break (h)

20th
95

Heat resistance at over 100 ° C

kp..mnr

21.1

35.2

*) Not necessary according to the method according to the invention.

Example 6

*) Not treated according to the process according to the invention.

Example 3

A niobium alloy composed of 5% Zr and 15% W, 0.06% O ₂ , remainder Nb, was tested for its creep strength after various heat treatments at 1100 ° C. in an argon atmosphere (see Table 3).

Wit in example 1 test rods made of niobium

alloys consisting of 1% Zr, 0.03% O ₂ , remainder Nb, of 5% Zr, 0.04% O ₂ , remainder Nb and of 10% Zr, 0.05% O ₂ , remainder Nb Solution heat treated for 8 hours in a vacuum at 2000 ° C., cooled to room temperature and aged for 1 to 16 hours at 1100 ° C. in a vacuum.

It is known that the hardness of metals is a function of their strength. F i g. II shows in one Diagram showing the dependence of the Vickers hardness determined at room temperature on the aging

duration at 1100 C. It follows that the hardness of solution-annealed alloys increases with aging.

Example 7

Test bars were produced according to Example 4, but made of a niobium alloy composed of 5% Zr, 10% W, 0.05% O ₂ , the remainder being Nb. After various heat treatments, the creep rupture strength at 1200 ^° C. and a load of 17.6 kp / mm ² in an inert atmosphere was determined with the following results:

The check rod that deforms at 1450 ⁰ C and an extrusion ratio of 4: 1 was extruded and molded at HOO ³ C (not according to the invention process) showed after a service life up to break of 2.3 hours, a total elongation of 50%. Another test rod, which was solution annealed for 1 hour at 2000 C after shaping and extrusion and then aged for 1 hour at 1100 C, showed a total elongation of 7% after a standing time to break of 16 hours.

Example 8

A niobium alloy composed of 10% Ti, 10% Mo, 0.5% Zr, 0.25% O ₂ , remainder Nb, was produced as described in Example 1. The ingot was forged at 1000 C with a reduction in cross-section of 50%, then solution annealed in vacuo at 2000 C for 8 hours and cooled to room temperature. The test bars were then heat-treated for different periods of time from 1 to 16 hours at 1100.degree. C. in a vacuum in order to determine the effect of different aging times on the Vickers hardness. The hardness values are shown graphically in FIG. III.

Example 9

An alloy of 3.5% Zr, 0.07% C, remainder Nb, was produced as in Example 1, a test rod (E) was extruded at 1870 C at a ratio of 4: 1, at 1100 C up to a rod diameter of 9, Forged 5 mm and heat-treated at 1200 ° C. for 1 hour (method not according to the invention). Another test rod (F) was solution for 1 hour at 2100 "C and then as rod (E) extruded, forged and aged. The hot strength at 1100- ¹ C in vacuo for bar was E 24.6 kgf / mm ² and for bar F 28.8 kgf / mm ² .

Example 10

ίο An alloy of 3.5% Zr, 0.1% C, 0.02% O ₂ , 0.002% N ₂ , remainder niobium, was produced as in Example 1. Two test bars G, H were ^{heated to 1000 3} C and rolled; G test bar was solution then for 1 hour at 2100 ¹ C, H test piece for 1 hour at ^800: C annealed tension-free. Both bars were then cold rolled to a total reduction in cross section of 95% (from the cast ingot) and then aged at 1100 ° C. for 0.5 hours. Test rod G showed a tensile strength in a vacuum of 29.5 kp / mm ² and test rod H (method not according to the invention) ^{showed a tensile strength of 20.4 kp / mm 2} .

Example 11

An alloy according to Example 10 but with 0.005% C was produced. The test rod H (method not according to the invention) showed a tensile strength of 23.2 kp / mm ² and test rod G one of

26 kp / mm ² . _. . -in

^F ex ample 12

An ingot made from an alloy of 10% W, 0.8% Zr, 0.11% C, remainder Nb, with a diameter of 203 mm was extruded and rolled at a temperature not above 1200 "C. Each two metal sheets with a thickness of 1.016 and 0.762 mm were invented once, but with different ones Temperatures and, for comparison, solution heat treated at lower temperatures. After the first heat treatment (= Solution heat treatment) all sheets were rapidly cooled. The processing conditions and physical properties of the sheets are shown in Table 5 below.

Table 5

Sheets

J *)

K *)

Thickness, μΐη

Heat treatment, C,

duration

Cold rolled to μηι

Degree of rolling,%

Aged for 1 hour at ⁰ C.
Yield strength, kp / mm ² ...
Tensile strength, kp / mm ² ...
Elongation at break,%

Hot yield strength

at 1200 C in a vacuum,
kp / mm ²

Hot tensile strength
at 1200 C in a vacuum,
kp / mm ²

Elongation at break *)

762

1200
1 hour

508
33
1200
42.9
58.4
14th

13.4

16.2
29

1016

1200
1 hour

762

25th
1200

48.5

61.2

12th

18.3

20.4
21

762

1650

Minutes

508
33

1200
53.4
69.6
73

21.1

23.9
10

1016

1650

5 minutes

762

25th
1200

52.7

69.6

12th

25.3

28.1
9

762

1750
5 minutes

508
33

1200
56.2
70.3
12th

28.1

30.9
10

1016

1750
5 minutes

762

25th
1200
58.4

77.3

11

29.5

33
9

Do not count among the sheets treated according to the invention.

Example 13

Various alloys were used below 1200C processed into sheets with a thickness of 1.27 mm, these then 10 minutes at 1650 "C in a vacuum Solution annealed, cooled, cold rolled to 1.026 mm and finally aged at 1200 ° C for 1 hour. the chemical composition and tensile strength of the sheets obtained are shown in Table 6.

Tabel

Ta Susami
VV nenst
Zr : tzung
C. % (Rest
O, Nb)
N, Stretch
border
kp / mm ² train
strength
kp / mm ² fracture
strain
% Stretch
border
kp / mm ² At 1200 ⁰ C
train
strength
kp / mm ² fracture
strain
% I.
Stretch
border
kp / mm ² part 1315 "C
train
strength
kp / mm ² fracture
strain
% P. - 10.5 0.9 0.1 0.017 0.008 55.9 70.3 14th 26.6 35.1 14th 24 26th 13th Q 2.8 10.8 0.9 0.13 0.023 65.4 78.7 11 35.6 40.6 17th R. 3 10.5 1.0 0.14 0.022 0.005 59.1 72 17th 39.8 44.8 22nd S. 4.8 10.4 0.7 0.09 0.005 65.3 78.7 11 37.4 42.4 18th 25.5 29.2 24 T 4.8 10.3 0.9 0.10 0.035 0.013 69.55 78 14th 30.8 38.2 18th U 48 103 1 0 011 0.063 0.005 69.4 76.6 18th 34.3 39.8 20th V 46 104 09 0? 0 0.024 0.006 61.4 75 14th 29.4 35.5 18th W. 68 174 1 0 011 0.025 0.015 72 87.2 13th 43.0 47.4 20th X 6 Q 11 5 1 0 01? 0.026 0.005 69.3 81.5 17th 39.0 45.5 21 Y 10 10.3 1.0 0.10 0.025 0.006 64.55 78.7 15th 37.1 41.0 15th

Claims (6)

Patent claims: 1. A method for producing a high strength niobium alloy, characterized in that the 0.5 to 12% zirconium, 0.02 to 0.5% oxygen, carbon and / or nitrogen and optionally up to 35% tungsten, up to 10% titanium , up to 25% molybdenum, up to 25% tantalum and / or up to 10% vanadium, the remainder at least 50% niobium, ^{solution annealed for 5 minutes to 9 hours at 1600 to 2100 c} C, cooled and deformed to final cross-section either before or after solution annealing The alloy is then heat treated for 0.5 to 40 hours above the recrystallization temperature at 1000 to 1500C. 2. The method according to claim 1, characterized in that the alloy is solution annealed ^{at 1700 to 2000 ° C.} 3. The method according to claim 1 or 2, characterized in that the final heat treatment at 1150 to 1300 ⁰ C is carried out. 4. Modification of the process according to a of claims 1 to 3, characterized in that a sheet made of the alloy of almost final thickness is quickly ^{quenched to 1200 0} C after solution annealing and cold rolled to the final thickness without intermediate annealing, the sheet thickness by 15 to 40%, preferably around 15 to 25% and then subjected to the heat treatment. 5. The method according to claim 4, characterized in that a sheet made of the alloy is ^{solution annealed at 1650 to 1800 0} C for 5 to 15 minutes and that the cold-rolled sheet is heat-treated at 1200 to 1425 ° C for 0.5 to 8 hours. 6. The method according to any one of claims 4 or 5, characterized in that a sheet metal from an alloy consisting of 0.5 to 3% zirconium, 8 to 12% tungsten, 0.02 to 0.15% carbon, up to 7% tantalum and up to 0.05% other accompanying elements, the remainder niobium and Impurities, solution heat treatment, cold working and final heat treatment is subjected. 1 sheet of drawings 909511/1555