CH615949A5 - Alloy for manufacturing a forged turbine blade. - Google Patents

Description

The present invention relates to an alloy for the manufacture of a forged turbine blade, the 0.02% yield strength of which is more than 70 kg / mm 2 and the tensile strength of which is more than 90 kg / mm 2, which alloy is thoroughly ferrite-free and has a martensitic structure .

Corrosion-resistant steel alloys with 13% chromium are known. An article by Georg Fischer Aktiengesellschaft, Schaffhausen (Switzerland), published in the Revue de la Metallurgie from July / August 1966, relates to cast steel with 13% chromium, which has high strength and improved weldability. In this article, the modification of the classic steel with 13% chromium is discussed in order to improve its weldability. The alloy composition contains:

The Esco Corp. however, the specific alloy apparently used contains 13% chromium and 4% nickel and is known as alloy 13-4.

Reference is also made to US Pat. Nos. 3,378,367 and 3,385,740,5, which describe steel alloys with 11 to 14% chromium and 4 to 8% nickel. However, US Pat. No. 3,378,367 relates to a steel which is martensitic in structure but contains dispersed austenite. US Pat. No. 3,385,740 describes an austenitic-martensitic steel.

Another known alloy contains 11.25 to 13% chromium, 0.06 to 0.15% carbon and 0.20% molybdenum. However, this known alloy contains a maximum of 0.50% Nikkei. Such alloys are essentially the same as corrosion-resistant AISI 410 steel.

In the prior art it is stated that the chromium content can be reduced somewhat if the carbon content is low (see the article by Georg Fischer). If silicon is present, its amount must be limited to prevent the formation of ferite. If the nickel content is increased, a martensitic microstructure is obtained.

None of these publications contains any indication that the alloy disclosed therein is suitable for forging turbine blades. The present invention is therefore based on the object of providing an alloy which has the higher strength and increased toughness required for producing forged turbine blades, and also has a martensitic structure which is free of ferrite.

According to the invention, this object is achieved with an alloy 30 which essentially consists of the following components in% by weight:

Carbon Mangen 35 silicon phosphorus max. Sulfur max. Nickel chrome 40 molybdenum tin

aluminum

Vanadium

iron

0.05 to 0.07 0.70 to 1.00 0.30 to 0.50 0.020 0.020

3.50 to 4.25 11.20 to 12.25 0.30 to 0.50 0.03 max. 0.03 max. 0.03 max. rest

C Cr Ni Mo

0.04 to 0.06% 12 to 13% 3.5 to 3.9% 0.5%

The author of the above article concludes that a cast steel with the following components undoubtedly has advantages over classic steel with 13% chromium:

C 0.06%

Cr 12.5%

Ni 3.8%

Mo 0.5%

Another article is that of Esco Corp. of Portland, Oregon. This article is titled «Alloy Notebook No. 13 »and contains the following steel composition:

C 0.08% max.

Mn 1.50% max.

Si 1.50% max.

Cr 11 to 14%

Ni 3.0 to 4.5%

Mo 1.00% max.

Fe - rest

A preferred embodiment of the alloy contains 12% chromium, 4% nickel and 0.05% carbon. This alloy is referred to below as B50AH7 and is used as the basis for the tests described below. Compared to the above values, the chromium content can be reduced within the above ranges and the carbon and nickel content can be increased. For example, the chromium content 11.2% and the carbon content 0.07% and the nickel content 4.25%.

55 Forged turbine blades were made from the alloy using a forging process that was carried out with a closed tool. These forgings were subjected to austenitic quenching and tempering, the heat treatment including heating to a temperature of about 955 ± 15 ° C and holding at that temperature for at least 2 hours or 45 minutes per inch. The forgings were then quenched in oil until the surface temperature was less than 100 ° C and then subjected to 65 tempering heat treatments at a temperature of about 550 ± 15 ° C for a minimum of 2 hours. This was followed by air cooling at room temperature. Alignment of the forgings is permitted provided this

3rd

615 949

Alignment is followed by a treatment in which the tensions that arise are removed. The stresses are removed by uniform heating to a temperature of about 510 ± 15 ° C and holding at this temperature for at least 6 hours. Then the forgings are cooled with air to room temperature. Variations in the relationship between time and temperature shown in Table II, Lot A and B can be made. The results of the various tests performed on the forgings made of the B50AH7 alloy are shown below.

The heat treatment to which the material was subjected before being processed into the test specimens is shown in Table I below. Lot A had the following mechanical properties after heat treatment: tensile strength about 102 kg / mm2 (equivalent to 145,000 US pounds / inch2), 0.2% yield strength at approximately 92 kg / mm2 (equivalent to 131,400 US pounds / inch2) , 0.02% yield strength at approximately 80 kg / mm2 (equivalent to 113,300 pounds / inch2), 69.3% RA, where RA is the abbreviation for area reduction. 18.5% stretch (5 cm). The test specimens for stress fracture, tensile strength, erosion and fatigue tests were produced from lot A. The specimens for stress corrosion and the Goodman diagram were subjected to the heat treatment shown for Lot B in Table I below. The hardness of the material treated in this way was Rc = 31, which corresponds to a tensile strength of 101 kg / mm 2 (corresponding to 144,000 US pounds / inch 2).

Table /

Heat treatment from B50AH7

Lot of austenitizing 955 ° C (1 750 ° F) for 2 h

A: Quenching in oil

Tempering ~ 540 ° C (1,000 ° F) for 3 hours

Cooling in air

Tempering 565 ° C (1,050 ° F) for 5 hours

Cooling in air

Table III

Lot austenitizing B: quenching in oil tempering quenching with 5 blowers

955 ° C (1 750 ° F) 2 h 550 ° C (1 025 ° F) 2 h

The properties of B50AH7 with regard to the smooth stress fracture are summarized in Table II below.

)

Table!!

Smooth voltage break from B50AH7

Tension**

Temperature time p *

Deh

R ..

i5 kg / mm2 (ksi)

° C (° F) h x 10 "3

nung

%

%

42 (60)

-455 (850) 915.6

36.62

13

76

2 (i 28 (40)

-510 (950) 90.2

38.00

17th

79

24.5 (35)

-510 (950) 171.3

38.39

21st

84

19 (27)

-525 (975) 208.0

39.19

30th

90

14 (20)

-540 (1000) 579.0

40.52

33

89

* P - Larson - Miller Parameter = (° F + 459.6) (25 + log t) ** Lab Serial No. 970

The results of the tensile strength tests of B50AH7 at elevated temperature are summarized in Table 30 below. It can be seen from these results that the strength initially gradually decreased with increasing temperature up to about 425 ° C (corresponding to 800 ° F), while above this temperature the tensile strength and the yield strength decreased more clearly. The ductility or toughness and the Young's modulus between approximately 20 and 540 ° C (correspondingly 70 and 1000 ° F) are also listed.

Tensile strength of B50AH7 at elevated temperature test temperature ° C (° F) -20 (75) -205 (400)

-315 (600)

-425 (800)

-540

Tensile strength kg / mm2 (ksi)

95.6 (136.0)

88.4 (125.7)

83.7 (119.0)

76.7 (109.0)

59.4 (84.5)

0.2% yield strength kg / mm2 (ksi)

88.4 (125.7)

OO

(118.0)

77 (109.5)

71.4 (101.5)

53.4 (76.0)

0.02% yield strength kg / mm2 (ksi)

77.9 (110.8)

74.9 (106.5)

71.5 (101.7)

57.6 (82.0)

35.7 (51.0)

Strain %

21.0

18.5

17.0

17.0

22.0

R.A. %

73.3

69.7

69.3

71.9

79.3

Young's modulus kg / cm2 (psi) xlO6

2.07 (29.6)

2.05 (29.4)

1.95 (27.9)

1.82 (26.1

1.68 (24.0)

The results of the blowhole erosion studies of Table / V 100 hours in duration are summarized in the following Table IV. 60

Blowhole erosion sample time (h)

B50AH7 2 Rc32 5 11 19 40 64 89 100

Weight loss (g)

0.006 0.024 0.058 0.098 0.154 0.189 0.216 0.229

615 949

The estimated ultimate stress limit with a mean stress of approximately 49.2 kg / mm2 (equivalent to 70,000 pounds / inch2) (approximately half the tensile strength) was a maximum of ± 54.8 kg / mm2 (equivalent to 78,000 pounds) / Inch2). The results of the individual test bars are shown in Table V below. This Goodman chart date shows that the B50AH7 alloy has high fatigue resistance, even with an average tensile load of about half the tensile strength.

The Goodman plot date was determined by applying a static tensile load to cylindrical specimens, rotating each specimen by Hess, with a final load giving a preselected alternating stress on the longitudinal surface of the specimen. Assuming elastic behavior, the maximum stress on the outer surface is the sum of the static tensile stress plus the alternating stress. If this sum is greater than the yield point, as in the present case, the surface is plastically deformed during the initial cycle. This results in a residual compressive stress on the outer surface and the actual maximum stress on the surface is smaller by the amount of the residual stress compared to the calculated stress.

Table V

Goodman diagram data for B50AH7 mean tension = 49.2 kg / mm2 (70 ksi)

AC voltage

Break or

Cycles

sample

± kg / mm2 (ksi)

exhaustion

X10'6

Eq

33 (47)

0

15.2

G2 *

40 (57)

0

17.9

G2 *

53 (77)

0

10.2

G2 *

68.2 (97)

X

0.116

G3

63.3 (90)

X

0.128

G4

56.9 (81)

X

0.145

G5

53 (77)

0

10.4

G6

54.5 (79)

X

0.181

* Sample G2 was loaded gradually

The following table VI summarizes the results of the gradual determination of the fatigue strength of B50AH7 at 425 ° C (corresponding to 800 ° F). The mean limit stress was determined to be ± 44.5 kg / mm2 (corresponding to ± 63 300 US pounds / inch2), which corresponds to only a 20% decrease in the fatigue strength compared to that at room temperature. The ratio of fatigue strength to tensile strength at 425 ° C was determined to be 0.57. In the usual material for blades, the fatigue strength is 32% lower than that shown in Table VI below.

Table VI

Fatigue strength of B50AH7 at 425 C (800 ° F)

AC voltage

Break or

Cycles

Sample kg / mm2 (ksi)

exhaustion

X10 "6

H 10

42.2 (60)

0

10.28

H 10 *

45.7 (65)

X

9.76

H 11

42.2 (60)

0

10.59

H 12

45.7 (65)

0

37.93

H 13

49.2 (70)

X

0.334

H 14

45.7 (65)

X

0.632

H 15

42.2 (60)

X

0.131

* Sample H 10 was loaded gradually

The bucket ZY2654, which e.g. listed in Table VII i5 below was obtained in a properly tempered and stress free condition. It was cut into Charpy test bars and these were subjected to a brittle treatment for about 6 hours at 465 ° C. The bars for the impact test were then machined and then examined 2o to determine the susceptibility of a B50AH7 alloy that had been properly de-stressed to subsequent cracking. Parts of the ZY2654 blade were re-austenitized and tempered. The Charpy test bars were processed, reheated to 25 at about 470 ° C (corresponding to 875 ° F) for 6 hours, oven to approximately 345 ° C (corresponding to 650 ° F) and then cooled in air to make the material brittle . For some of the test bars, the brittleness was reversed by heat treatment at about 540 ° C (corresponding to 1,000 ° F) for 2 hours followed by quenching with a blower and the effect of this treatment was measured by Charpy impact tests at room temperature .

The bucket ZY2715 was e.g. cut into test bars for tensile testing with a diameter of 1.27 cm 35 (corresponding to 0.505 inches) from the middle blade part and from the dovetail part. The investigation took place at room temperature. Four test rods for the Charpy impact test with a V-notch were cut off from the middle part of the blade and from the dovetail part of the blade. 4o The test bars were oriented axially, whereby the notch axis was perpendicular to the forging plane. The impact energy at room temperature and 50% FATT (FATT = transition temperature of the fibrous appearance) was determined.

45 The tensile properties of the middle blade part and the dovetail part are shown in Table VII below. The tensile strength and the 0.2% yield strength are identical for the middle shovel part and the dovetail part, while the 0.02% yield strength for the middle show part is slightly lower than for the dovetail part. The ductility of the dovetail part turned out to be somewhat greater than that of the middle blade part. The tensile properties for both sections were better than the minimum requirements for B50AH7.

5

615 949

Table VII

Mechanical properties of

B50AH7 blades

Delivery description

tensile strenght

0.02% stretch

0.2% stretch

strain

R.A.

Impact energy

kg / mm2 (ksi)

limit kg / mm2

border

(5 cm)%

%

Room temperature

(ksi)

kg / mm2 (ksi)

mkg (ft-lbs)

ZY 2 602 (samples)

.97.3 (138.4)

82.2 (116.8)

20th

70

12.83 (93)

ZY 2 654 (samples)

99.8 (141.9)

83.3 (118.4)

20th

69

12.7 (92)

ZY 2 706 (samples)

99.4 (141.4)

85.2 (121.2)

20th

69

13.11 (95)

average

98.9 (140.6)

83.5 (118.8)

20th

69

12.83 (93)

M&P laboratory

ZY 2 715 dovetail

96.7 (137.5)

81.2 (115.5)

90 (128.0)

20th

67

> 16.15 (> U7)

(Rehearse)

ZY 2 715 shovel

96.7 (137.5)

78.6 (111.8)

90 (128.0)

19th

63

10.63 (77)

(Rehearse)

B50AH7 specification

91.4-105.5

70.3-87.9

15

60

8.28 (60)

(Rehearse)

(130-155)

(100-125)

(min.)

(min.)

(min.)

The results of the FATT determinations of parts from the middle blade and the dovetail are summarized in Table VIII below. The impact energy at room temperature was greater than .5 for the dovetail

for the middle part of the blade and both were above the specification minimum. The FATT of the middle part of the blade was --13 ° C (corresponding to 8 ° F) 19 ° C (corresponding to 34 ° F) above that of the dovetail part.

Table VIII

Charpy impact test with V-notch specimens made from B50AH7

Job

Middle of the shovel

Test temp. absorbed ° C (° F) energy mkg (ft-lbs)

-29 (-20) 3.04 (22)

-18 (0) 5.52 (40)

-4 (25) 4.69 (34)

21 (70) 10.63 (77)

Fibrous - 50% FATT

%

21 53 56 100

'C (° F)

-13 (+ 8)

Swallows- -40 (-40) 4.14 (30) 31

tail -29 (-20) 9.94 (72) 67

-18 (0) 10.63 (77) 77

21 (70)> 16.15 (> 117) 100

-32 (-26)

The longitudinal limit stress for the fatigue strength was ± 51.7 kg / mm2 (corresponding to ± 73 500 US pounds / inch2) for the middle blade part and ± 54.5 kg / mm2 (corresponding to ± 77 500 US pounds / inch2) for the dovetail part ). The individual test results are summarized in Table IX below. The ratio of fatigue strength to tensile strength for both parts of the forging was above the usually assumed value of 0.5, namely 0.53 in the middle blade part and 0.56 in the dovetail part.

615 949

6

Table IX

Fatigue strength of B50AH7 at room temperature

Dovetail AC break or rating kg / mm2 (ksi)

Exhaustion*

Cycles X10 "6

Bucket AC voltage or load kg / mm2 (ksi)

Break or exhaustion *

Cycles XI0 "6

49.2 (70)

O

10.09

49.2 (70)

O

10.08

52.7 (75)

O

10.17

52.7 (75)

X

1.61

56.2 (80)

X

0.30

49.2 (70)

O

10.38

52.7 (75)

X

0.88

52.7 (75)

O

10.01

49.2 (70)

O

10.38

56.2 (80)

X

0.42

52.7 (75)

O

34.21

52.7 (75)

X

0.77

56.2 (80)

X

1.10

49.2 (70)

O

11.27

52.7 (75)

X

1.07

52.7 (75)

X

0.22

49.2 (70)

O

20.63

49.2 (70)

O

20.83

52.7 (75)

O

31.88

52.7 (75)

X

0.66

56.2 (80)

X

1.82

52.7 (75)

O

10.27

56.2 (80)

O

10.02

59.8 (85)

O

10.08

63.3 (90)

X

0.24

59.8 (85)

X

1.09

* Fracture - X Exhaustion - O

The results of the impact resistance tests with holding time O are listed. These test specimens, except for a Charpy test specimen with a V-notch made of brittle ± 3 ° C from the temperature listed for the heat-B50AH7 alloy, are heated in the following table X together to break and then quenched, quantified . Some of the values in this table are marked with a

Table X

Effect of relaxation conditions on the properties of the Charpy test specimens made from B50AH7

Temperature holding- sample- impact energy fibrous- hardness ° C (° F) time h body no. Mkg (ft-lbs)% Rc

315 (600)

6

4U

6.76

49) *

55

29.1

345 (650)

6

4T

7.86

57) *

63

30.0

370 (700)

6

4S

7.04

51) *

59

30.6

400 (750)

6

4R

7.32

53) *

56

31.0

425 (800)

0

9A

11.08

82)

72

29.4

425 (800)

0.2

9B

14.21

103)

98

30.0

425 (800)

0.5

9C

9.36

68)

70

29.1

425 (800)

1.8

9D

7.18

52) *

56

30.5

425 (800)

6

3E1

4.41

32) *

39

29.7

425 (800)

6

3E2

4.41

32) *

44

29.9

425 (800)

17th

9E

4.83

35) *

31

30.1

440 (825)

6

3D1

7.46

54) *

53

30.5

440 (825)

6

3D2

4.14

30) *

40

30.8

455 (850)

6

3C1

4.83

35) *

40

30.2

455 (850)

6

3C2

4.55

33) *

40

29.9

470 (875)

0

4R1

14.07

102)

100

30.0

470 (875)

0

4R2

13.25

96)

100

29.5

470 (875)

0

4A1

14.07

102)

100

30.0

470 (875)

0

4A2

15.04

109)

100

29.3

470 (875)

0

9A

9.94

72)

78

20.7

470 (875)

0.2

9B

9.50

69)

76

30.7

470 (875)

0.5

9C

9.36

68)

77

30.0

7 615 949

Table X

Effect of relaxation conditions on the properties of the Charpy test specimens made from B50AH7

Temperature holding sample impact energy fiber hardness

° C (° F)

time body no.

mkg (ft-lbs)

%

Rc

470 (875)

1.7

9D

5.52

40) *

53

30.4

470 (875)

6

3F3

4.69

34) *

45

30.1

470 (875)

6

3F4

4.69

34) *

35

30.6

470 (875)

17th

9E

4.41

32) *

40

30.4

480 (900)

6

3B1

5.11

37) *

40

29.8

480 (900)

6

3B2

4.55

33) *

35

30.0

488 (910)

6

3W

7.32

53) *

53

30.2

493 (920)

6

3X

4.83

35) *

44

29.3

496 (925)

0

4A

11.22

83)

81

30.1

496 (925)

0.2

4B

7.60

55) *

62

30.1

496 (925)

0.5

4C

7.18

52) *

59

30.1

496 (925)

1.7

4D

5.39

39) *

48

30.4

496 (925)

6

4F

6.21

45) *

56

29.2

496 (925)

17th

4E

12.28

89)

81

29.9

500 (930)

6

3Y

7.32

53) *

61

31.5

504 (940)

6

3Z

10.08

73)

78

30.3

510 (950)

6

3A1

8.29

65)

91

29.5

510 (950)

6

3A2

10.91

79)

81

29.9

524 (975)

1.5

9M

7.60

55) *

72

29.9

524 (975)

6

9N

8.14

59) *

75

29.5

470 (875)

6 (1)

3S1

3.04

22) *

26

30.7

470 (875)

6 (1)

3S2

3.31

24) *

21st

30.4

470 (875)

6 (2)

4SI

5.52

40) *

52

30.8

470 (875)

6 (2)

4S2

7.04

51) *

53

29.8

538 (1000)

2 (3)

4T1

13.94

101)

99

29.5

538 (1000)

2 (3)

4T2

13.66

99)

100

29.1

538 (1000)

3 (3)

4C1

15.04

109)

100

29

538 (1000)

3 (3)

4C2

13.11

95)

100

28

(1) Cooled in the oven to room temperature 540 ° C to remove brittleness

(2) in the oven to 345 ° C and then cooled in air * below the B50AH7 specification minimum of

(3) Treatment (2) followed by heat treatment at ■, '1 8.28 mkg (60 ft-lbs)

C.

Claims (3)

615 949 2. Alloy according to claim 1, characterized in that the chromium content is 12%, the nickel content is 4% and the carbon content is 0.05%. 2nd PATENT CLAIMS 1. Alloy for the production of a forged turbine blade, whose 0.02% yield strength is more than 70 kg / mm2 and whose tensile strength is more than 90 kg / mm2, which alloy is thoroughly ferrite-free, has a martensitic structure and essentially consists of the following components in% by weight: carbon manganese phosphorus sulfur silicon nickel chrome molybdenum aluminum Vanadium tin iron 0.05 to 0.07 0.70 to 1.00 0.020 max. 0.020 max. 0.30 to 0.50 3.50 to 4.25 11.20 to 12.25 0.30 to 0.50 0.03 max. 0.03 max. 0.03 max. rest 3. Alloy according to claim 1, characterized in that the chromium content is 11.20%, the nickel content is 4.25% and the carbon content is 0.07%.