CA1163470A

CA1163470A - Ferritic stainless steel

Info

Publication number: CA1163470A
Application number: CA000348953A
Authority: CA
Inventors: Harry E. Deverell; Thomas H. Mccunn
Original assignee: Allegheny Ludlum Corp
Current assignee: Allegheny Ludlum Corp
Priority date: 1980-01-03
Filing date: 1980-04-01
Publication date: 1984-03-13
Also published as: KR850000980B1; SE436576B; SE436576C; CS216241B2; FR2473068B1; SE8001868L; JPS5698458A; NO800712L; PL124420B1; IT8048292A0; IT8048292A1; NO155351C; KR830002902A; ES492374A0; ES8104832A1; IT1188918B; AT376707B; AU5641980A; ATA268880A; NO155351B

Abstract

FERRITIC STAINLESS STEEL

ABSTRACT OF THE DISCLOSURE

A ferritic stainless steel characterized by superior toughness both prior to and after welding, and by superior crevice and integranular corrosion resistance. The steel consists essentially of, by weight up to 0.08%
carbon, up to 0.06% nitrogen, from 25.00 to 35000% chromium, from 3.60 to 5.60% molybdenum, up to 2.00% manganese, between 2.00 and 5.00% nickel, up to 2.00% silicon, up to 0.5% aluminum, up to 2.00% of elements from the group consisting of titanium, zirconium and columbium, balance essentially iron. The sum of carbon plus nitrogen is in excess of 0.0275%. Titanium, zirconium and columbium are in accordance with the following equation.
%Ti/6 + %Zr/7 + %Cb/8 ? %C + %N

Description

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1 The present invention relates to a ferritic stainless steel.
Canadian Patent Application Serial No. 348,952, filed by the applicant concurrently herewith, describes a ferritic stainless steel which is characterized by superior crevice and intergranular corrosion resistance.
The steel of Application Serial No. 348,952 is distin~uishable from that of Patent Nos. 3,932,174 and 3,929,473 in that it has up to 2% of elements from the group consisting of titanium, zirconium and columbium in accordance with the following e~uation:

~Ti/6 ~ %Zr/7 ~ %Cb/8 ~ ~C ~ ~N

and a carbon plus nitrogen content in excess of 275 par-ts per million. Because of its higher carbon and nitrogen content, it can be melted and refined by less costly procedures than can the steels of U.S. Patent Nos. 3,932,174 and 3,929,473.
Through the present invention, there is provided a steel which is tougher than that of Application Serial No.

348,952. In addition to stabilizers from the group consisting of titanium, zirconium and colun~ium and a carbon plus nitrogen content in excess of 275 parts per million; the steel of the present invention has between 2.00 and 5.00% nickel, and preferably between 3.00 and 4.50%, whereas the steel of Application Serial No. 348,952 has up to 2.00~ and usually less than 1.00~ nickel. Nickel has been found to enhance the toughness of the alloy of Application Serial No. 348,952.

For the reasons noted hereinabove, the alloy o the present invention is clearly distinguishable from that o-E Patent Nos. 3,932,174 and 3,929,473. It is also distinguishable from that of U.S. Patent No. 4,119,765. Ilhe alloy of Patent No.

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1 4,119,765 specifies a maximum molybdenum content below that ~or the present invention.
Another reference of .interest is a paper entitled, "Ferritic Stainless Steel Corrosion Resistance and Economy".

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1 The paper was written by Remus A. Lula and appeared in the July 1976 issue o~ Metal Progress, pages 24-29. It does not disclose the ferritic stainless steel of the present invention.

It is accordingly an object of the present invention to provide a ferritic stainless steel.

The ferritic stainless steel of the present invention is characterized by superior toughness both prior to and after welding, by superior crevice and intergranular corrosion resistance and by good weldabilityO It consists essentially of, by weight, up to 0.08% carbon, up to 0.06%
. nitrogen, from 25.00 to 35.00% chromium, from 3.60 to 5.60%
molybdenum, up ~o 2.00% manganese, between 2.00 and 5.00%
nickel, up to 2.00% silicon, up to 0.5~ aluminum, up to lS 2.00% of elements from the group consisting of titanium, zirconium and columbium, balance essentially iron. The sum of carbon plus nitrogen is in excess of 0.0275~. Titanium, zirconium and columbium are in accordance with the following e~uation:

%Ti~6 + ~Zr~7 ~ ~Cb/8 > ~C ~ ~N

Carbon and nitrogen are usually present in respective amounts of at least 0.005% and 0.010%, with the sum being in excess of 0~0300~O Chromium and molybdenum are preferably present in respective amounts of 28O50 to 30~50~ and 3.75 to

4.75%. Manganese and silicon are each usually present in amounts of less than 1.00~. Aluminum which may be present for its effect as a deoxidizer is usually present in amounts of less than 0.1%.

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1 Titanium, columbium and/or zirconium are added to improve the crevice and intergranular corrosion resistance of the alloy, which in a sense is a high carbon plus nitrogen version of Patent No 3,929,473. It has been determined, that stabilizers can be added to high carbon andjor nitrogen versions of Patent No. 3,929,473, without destroying the touyhness and/or weldability of the alloy. Although it is preferred to add at least 0.15% of titanium, insofar as the sole presence of columbium can adversely affect the weldability of the alloy, it is within the scope of the present invention to add the required amount of stabilizer as either titanium or columbium. Columbium has a ~eneficial effect, in comparison with titanium, on the toughness of the alloy~ A particular embodiment of the invention calls for at least 0.15~ columbium and at least 0.15% titanium. Titanium, columbium and zirconium are preferably present in amounts up to 1~00% in accordance with the following equation:

%Ti/6 ~ %Zr/7 + %Cb/8 = 1.0 to 4.0 (%C ~ %N) Nickel is added to the alloy of the present invention to enhance it~ ~oughness. It is added in amounts be~ween 2.00 and 5.00%, and preferably in amounts between 3.00 and 4.50%.

The ferritic stainless steel of ~he present invention is particularly suitable for use as a welded article.

1 The following examples are illustrative o~ several aspects of the invention.
Ingots from twenty-four heats (Heats A through X) were hea~ed to 2050F, hot rolled to 0.125 inch strip, annealed at temperatures o~ 1950 or 2050F, cold rolled to about 0.062 inch strip and annealed a~ temperatures of 1950 or 2050F. Ho~ rolled and cold rolled specimens were subsequently evaluated for tough-ness. Other specimens were TIG welded and then evaluated ~or toughness.
The chemistry of the heats appears hereinbelow in Table I.
TABLE I.
COMPOSITION (wt. ~) .
Heat C N Cr Mo Mn Ni Si Al Ti Cb Fe A 0.030 0.025 28.96 4.20 0.34 0.45 0.36 0.029 0.50 - Bal.
B 0.030 0.026 29.05 4.18 0.34 0.46 0.37 0.029 0.20 0.32 Bal.
C 0.031 0.025 28.96 4.06 0.36 0.45 0.29 0.027 0.09 0.45 Bal.
~ 0.034 0.027 28.95 4.20 0.43 0.46 0.37 0.040 0.19 0.41 Bal.
E 0.03S 0.026 28.75 4.20 0.40 0.47 0.45 0.025 0.20 0.42 Bal~
F 0.032 0.024 23.52 4.10 0.37 0.51 0.28 0.030 0.31 0.44 Bal.

G 0.013 0.018 29.00 4.00 0.35 4.00 0.37 0.023 0.31 - Bal.
H 0.027 0.018 29.00 4.00 0.35 4.15 0.36 0.026 0.31 - Bal.
I 0.029 0.018 29.00 4.00 0.35 4.16 0.36 0.029 0.60 - Bal.
J 0.025 0.020 28.74 3.90 0.35 4.00 0.36 0.037 - 0.37 Bal.
K 0.034 0.016 29.10 4.00 0.36 4.10 0.38 0.010 - 0.52 Bal.
L 0.032 0.018 29.10 4.00 0.35 4.10 0O39 0.014 0.20 0.38 Bal.
M 0.018 0.025 29.23 4.04 0.32 3.00 0.34 0.050 0.11 0.29 Bal.
N 0.021 0.021 29.08 4.05 0.32 3.01 0.34 0.046 0.20 0.28 Bal.
O 0.019 0.023 28.95 4.10 0.32 3.00 0.35 0.021 0.10 0.42 Bal.
P 0.021 0.024 28.81 4.10 0.31 3.05 0.34 0.043 0.20 0.42 Bal.
Q 0.022 0.020 29.47 4.04 0.33 3.03 0.32 0.017 - 0.43 Bal.
R 0.020 0.023 29.20 4.04 0.33 3.03 0.31 0.040 - 0.64 Bal.
S 0.025 0.023 28.94 3.91 0.34 3.91 0.34 0.051 0.12 0.29 Bal.
T 0.020 0.020 29.23 4.03 0.33 4.18 0.33 0.046 0.20 0.28 Bal.
U 0.017 0.020 29.15 4.04 0.30 4.00 0.28 0.055 0.12 0.43 Bal.
V 0.018 0.022 29.10 4.04 0.30 4.00 0.28 0.021 0.18 0.43 Bal.
W 0.022 0.021 28.94 3.94 0.33 4.08 0.35 0.037 - 0.44 Bal.
X 0.024 0.022 28.96 3.93 0.33 4.10 0.32 0.040 - 0.64 Bal.

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1 Note that Heats A through F are outside the subject invention.
They do not have a nickel content between 2.00 and 5.00~.
The present invention is dependent upon a nickel content in excess of 2.00%.

Additional data pertaining to the chem;stry of the heats appears hereinbelow in Table Il.

TABLE II.
.

Heat ~C + %N%Ti/6 ~ %Zr/7 ~ %Cb/8 A 0.055 0.083 B 0.056 0.073 C 0.~56 0.071 D 0.061 0.083 E 0.061 0.086 F 0.056 0.107 G 0 a 031 0 ~ 052 H 0.045 0.052 I 0.047 0.100 J 0~045 0.046 K 0.050 0.065 L 0.050 0.081 M 0.043 0.054 N 0.042 0.068 O 0.042 0.~9 P O.Q45 0.086 Q 0.042 0.05~
R 0.043 0.080 S 0.0~8 0.~56 T 0c040 0.068 U 0.037 . 0.074 V 0.040 0.084 W 0.043 0.055 X ~.046 0.080 . Toughness was evaluated by determining the transition tempersture using subsize transverse Charpy V-notch specimens for hot rolled and annealed material (0.125 X 0.394 inch specimens), cold rolled and annealed material (0.062 X 0.394 inch specimens), as welded material (0.062 X 0.394 inch - specimens~ and welded and annealed material (0.062 X 0.394 3~7~

1 inch speci~ens). Transition temperature was based upon a 50~ ductile - 50~ bri~tle fracture appearance. The transition temperatures for the hot rolled and cold rolled specimens appears hereinbelow in Table III. Heats A through L were annealed at 1950F. The other heats were annealed at 2050F.

Table III.
TRANSITION TEMPERATURE (F~
-Hot Rvlled Cold Rolled 10and Annealed and Annealed _ Water Air Water Air HeatQuenched Cooled Quenched Cooled L - 40 - -175 ~130 Q - 35 60 -15~ -X -100 -25 ~225 The transition temperatures for the as welded and welded and annealed specimens appears hereinbelow in Table IV. ~eats A through F were annealed at 1950F prior to welding~ The other heats were annealed at 2050F. All heats were water 7~

quenched. Post weld anneals were at 1950F for Heats A
through F and at 2050F for the other heats. All heats were water quenched after the post weld anneal.
TABLE I V .
_ TRANSITION TEMPERATURE (F) Heat As WeldedWelded And Annealed B ~0 35 K ~ 90 -i55 N 0 ~ 40 The benefit of nickel is clearly evident from Tables III and IV. Heats G through X have substantially lower transition temperatures, and are therefore substantially tougher than are Heats A through F. Significantly, Hea~s G
through X are within the present invention whereas Heats A
through F are not. Heats G through X having in excess o~
2.00% nickel.

The lower transition temperatures for Heats G through X is exemplified hereinbelow in Table V which is a composite of Tables III and IV.

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T~BLE V .

TRANSI TION TEMPERATURE ( F ) Heats A - F Heats G - X
Hot Rolled 110 to 210 -120 to 50 and Annealed ~Water Quenched) Hot Rolled 210 to 320 - 25 to 100 and Annealed (Air Cooled) Cold Rolled - 20 to 40 -225 to -120 and Annealed ~Water Quenched) Cold Rolled ` 50 ~o 115 -170 to - 90 and Annealed ~Air Cooled) As Welded 60 to 155 -140 to 0 Welded and 25 to 50 -215 to - 40 Annealed 20 Note that in every instance the maximum transition temperature for Heats G through X is lower than the minimum transi~ion temperature for Heats A through F. The data clearly shows that Heats G through X are tougher than are Heats A through F.

Additional specimens of Heats G through X were evaluated for crevice and intergranular corrosion resistance~
These specimens were prepared as were the specimens referred to hereinabove.

Crevice corrosion resistance was evaluated by immersing 1 inch by 2 inch surace ground specimens in a ;3~

1 10~ ferric chloride solution for 72 hours. Testing was performed at a temperature of 122Fo Crevices were created by employing polytetra~luoroethylene blocks on the front and back, held in position by pairs of rubber bands stretched at 90~F to one another in both longitudinal and transverse directions. The test is described in Designatlon: G 48-76 of ~he American Society for Testing And M~terials.

The results of the evaluation appear hereinbelow in Table VI. Specimens were in the cold rolled and annealed condition, in the as welded condition and in the as welded and annealed condition.

TABLE VI.

10% FERRIC CHLORIDE CREVICE CORROSION TEST

WEIGHT ~

Cold Rolled Welded Heat and Annealed As Welded and Annealed*

G - 0.0001 0.0008 H - 0.1588 0.0005 I - 0.0 0.0004 J - 0.0 0.0001 K - 0~0 0.0015 L - 0.0001 0,0001 M 0.0 0.0004 0.0003 N 0.0009 0.0027 0.0009 ~5 O 0.0 0.0007 0.0001 P 0.0001 0,0004 0.0004 Q 0.0 0.0005 0.0039 R 0.0007 0.0032 0.0068 S 0.0056 0.0007 0.0 T 0.0 0.0001 0.0056 U 0.0002 0.0001 0.0 V 0.0001 0.0078 0,000~
W 0.0001 0.0 0.0063 X 0.0 0.0003 o.n060 *Annealed at 2050F Water Quenched ~ 7~

1 From Table VIr it is noted that the crevice corrosion resistance of Heats G through X is excellent. The alloy of the present invention is indeed characterized by s~perior crevice corrosion resistance.

Intergranular corrosion resistance was evaluated by immersing 1 inch by 2 inch surface ground specimens in a boiling cupric sulfate - 50% sulfuric acid solution for 120 hours~ The usual pass-fail criteria for this test are a corrosion rate of 24.0 mils per year (0.0020 inches per month) and a satisfactory microscopic examination. This test is recommended for stabilized high chromium ferritic stainless steels.

The results of the evaluation appear hereinbelow in Table VII. Specimens were in the as welded condition and in the as welded and annealed condition.

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1TABLE VII.
CUPRIC SULFATE - 50~ SVLFURIC ACID CORROSION TEST
CORROSIO~ RATE ~ICROSCOPIC EXAMINATION
(inches per month) ~at 30X~
5Welded and Welded and Heat As WeldedAnnealed* As Welded~nnealed*
G 0~0004950.000633 NA** NA
H 0.0006460.000582 NA NA
I 0.0005080.000676 NA NA
J 0.0004350.000631 NA NA
K 0.0003680.000735 ~IA NA
L 0.0003780O000595 NA NA
S 0.0005010.000622 NA NA
T 0.0004690.00049~ NA NA
U 0O0004010.000631 NA NA
V 0.0004810.000485 NA NA
W 0.0004810.000505 NA NA
X 0.0005080.000545 ~A NA

*Annealed at 2050F - ~ater Quenched **NA: NO INTE~GRANULAR ATTACK OR G~AIN DROPPING

From Table VII, it is noted that Heats G through L and S
through X exhibit superior intergranular corrosion resistance.
Each specimen passed the test7 It will be apparent to those skilled in the art that the novel principles of the invention disclosed herein in connection with specific examples thereof will suggest various other modifications and applications of the same. It is accordingly desired that in construing the breadth of the appended claims they shall not be 1imited to the specific examples of the invention descrlbed herein.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows.

1. A crevice corrosion-resistant, tough, weldable ferritic stainless steel consisting essentially of, by weight, up to 0.08% carbon, up to 0.06% nitrogen, from 25.00 to 35.00%
chromium, from 3.60 to 5.60% molybdenum, up to 2.00% manganese, between 2.00 and 5.00% nickel, up to 2.00% silicon, up to 0.5%
aluminum for deoxidizing the steel, up to 2.00% of elements from the group consisting of titanium, zirconium and columbium, balance essentially iron; said titanium, zirconium and columbium being in accordance with the following equation:
%Ti/6 + %Zr/7 + %Cb/8 ? %C + %N
the sum of said carbon plus said nitrogen being in excess of 0.0275%; said steel being characterized by its superior as-welded crevice corrosion resistance at 50°C (122°F).

2. A ferritic stainless steel according to claim 1, having between 3.00 and 4.50% nickel.

3. A ferritic stainless steel according to claim 1, having at least 0.005% carbon and at least 0.010% nitrogen, the sum of said carbon plus said nitrogen being in excess of 0.0300%.

4. A ferritic stainless steel according to claim 1, having from 28.50 to 30.50% chromium.

5. A ferritic stainless steel according to claim 1, having from 3.75 to 4.75% molybdenum.
6. A ferritic stainless steel according to claim 1, having up to 1.00% of elements from the group consisting of titanium

Claim 6 continued...

zirconium and columbium in accordance with the following equation:
%Ti/6 + %Zr/7 + %Cb/8 - 1.0 to 4.0 (%C + %N).

7. A ferritic stainless steel according to claim 1, having at least 0.15% titanium.

8. A ferritic stainless steel according to claim 7, having at least 0.15% columbium.

9. A ferritic stainless steel according to claim 1, having at least 0.005% carbon, at least 0.010% nitrogen, from 28.50 to 30.50% chromium, from 3.75 to 4.75% molybdenum, between 3.00 and 4.50% nickel, and up to 1.00% of elements from the group consisting of titanium, zirconium and columbium in accordance with the following equation:
%Ti/6 + %Zr/7 + %Cb/8 = 1.0 to 4.0 (%C + %N) the sum of said carbon plus said nitrogen being in excess of 0.0300%.

10. A crevice corrosion-resistant, tough, weldable welded article whenever made from a ferritic stainless steel consisting essentially of, by weight, up to 0.08% carbon, up to 0.06%
nitrogen, from 25.00 to 35.00% chromium, from 3.60 to 5.60%
molybdenum, up to 2.00% manganese, between 2.00 and 5.00% nickel, up to 2.00% silicon, up to 0.5% aluminum for deoxidizing the steel, up to 2.00% of elements from the group consisting of titanium, zirconium and columbium, balance essentially iron;
said titanium, zirconium and columbium being in accordance with the following equation:

%Ti/6 + %Zr/7 + %Cb/8 ? %C + %N
the sum of said carbon plus said nitrogen being in excess of 0.0275%, said steel being characterized by its superior as-welded crevice corrosion resistance at 50°C (122°F).