NL8001740A - FERRITIC STAINLESS STEEL. - Google Patents

Description

È —M «r • Γ

Ferritic stainless steel.

The invention relates to ferritic stainless steel.

In Dutch patent application no. A ferritic stainless steel is described, which is characterized by a superior resistance to the occurrence of crack corrosion and intergranular corrosion.

That steel is distinguished from the ferritic stainless steel described in U.S. Pat. Nos. 3,932,174 and 3,929,473 in that it contains at most 2% by weight of the elements titanium, zirconium and columbium together, also satisfying the condition% Ti / 6 +% Zr / 7 + ZCb / 8>% C +% N while the carbon content plus nitrogen content is greater than 275 parts by weight per million. Because of the higher carbon and nitrogen content, this steel can be melted and refined using less expensive treatment methods than is the case with the steel alloys of U.S. Pat. Nos. 3,932,174 and 3,929,473.

The invention now provides a steel which is tougher than the steel described in the above-mentioned Dutch patent application. In addition to stabilizers from the group consisting of titanium, zirconium and columbium and in addition to a carbon plus nitrogen content of more than 275 parts by weight per million, the steel of the present invention contains between 2.00 and 5.00% by weight of nickel and preferably between 3.00 and 4.50 wt% nickel, while the steel according to the above Dutch patent application has a nickel content of at most 2.00 wt% and usually contains less than 1.00 wt% nickel. Nickel has been found to improve the toughness of the alloys according to the above 800 1 7 40 2

Dutch patent application enlarged.

For the reasons outlined above, the steel of the present invention is clearly distinct from the steel alloys described in U.S. Pat. Nos. 3,932,174 and 3,929,473. The steel according to the invention is also clearly distinguished from the steel according to U.S. Patent 4,119,765. U.S. Patent 4,119,765 discloses for the alloy composition a maximum molybdenum content lower than the molybdenum content in the alloy of the invention.

Another interesting reference is the article "Ferritic Stainless Steel Corrosion Resistance and Economy" by Remus A. Lula, published in Metal Progress, July 1976, biz. 24-29. Also this literature reference does not describe any steel alloy according to the present invention.

The ferritic stainless steel of the present invention is characterized in that it has superior toughness both before and after welding and in that it has superior crack crack and intergranular corrosion resistance and good welding properties. This steel mainly consists of at most 0.08 wt% carbon dust, at most 0.06 wt% nitrogen, 25.00 to 35.00 wt% chromium, 3.60 to 5.60 wt% molybdenum, at most 2.00 wt.% manganese, between 2.00 and 5.00 wt.% nickel, at most 2.00 wt.% silicon, at most 0.5 wt.% aluminum, at most 2.00 wt. .% of the elements titanium, zirconium and columbium together, residual iron, the sum of the carbon plus nitrogen content being greater than 0.0275% by weight and the titanium, zirconium and columbium being present in such amounts that the condition:% Ti / 6 +% Zr / 7 +% Cb / 8>% C +% N.

Carbon and nitrogen are usually present in amounts of at least 0.005 wt% and 0.010 wt%, respectively, while the sum of both is greater than 0.0300 wt%.

Chromium and molybdenum are preferably present in amounts of 28.50 to 30.50 wt% and 3.75 to 4.75 wt%, respectively.

80 0 1 7 40 * no 3

Manganese and silicon are each usually present in amounts less than 1.00% by weight. Aluminum, which may be present because of its deoxidizing effect, is usually present in amounts less than 0.1% by weight.

Titanium, columbium and / or zirconium are commonly included to improve crack and intergranular corrosion resistance of the alloys which may be considered in some way as a modification of the alloys according to U.S. Pat. script 3.929.473 because they have a high carbon plus nitrogen content. It has been determined that the stabilizers can be added to alloys of the type described in U.S. Patent 3,929,473 provided they are. have a high carbon and / or nitrogen content, without thereby destroying the toughness and / or the welding properties of the leather. Although it is preferred to add at least 0.15 wt% titanium, because if columbium alone is present it may adversely affect the welding properties of the alloys, it is also within the scope of the invention to add the required amount of stabilizer in the form of either titanium or columbium. Columbium, compared to titanium, has a favorable effect on the toughness of the alloys. According to a particular embodiment of the invention, alloys are provided with at least 0.15 wt% columbium and at least 0.15 wt% titanium.

Titanium, columbium and zirconium are preferably present in amounts up to a total of 1.00 wt.%, Satisfying the condition:% Ti / 6 +% Zr / 7 +% Cb / 8 = 1.0 to 4.0 (% C +% N) Nickel is included in the alloys of the invention to increase toughness. It is included in amounts between 2.00 and 5.00% by weight and preferably in amounts between 3.00 and 4.50% by weight.

The ferritic stainless steel according to the invention is particularly suitable for use in the form of welded objects.

800 1 7 40 4

The following examples illustrate various aspects of the present invention.

Cast ingots of 24 alloys (Alloys A to X) were heated at 1121 ° C, hot rolled to a strip with a thickness of 3.1 mm, annealed at temperatures of 1065 or 1121 ° C, cold rolled to a strip with a 1.55 mm thick and tempered at temperatures of 1065 or 1121 ° C. The hot-rolled and cold-rolled samples were then assessed for their toughness. Other samples were welded under an inert gas using a non-fusing electrode (TIG welding) and then assessed for toughness.

The chemical composition of the alloys is shown in Table A.

15 800 1 7 40 5

4_) + J 4-J 4-J -U 4-J UlUIU ^ UU4JU4J4JUUtJ ^ U'UU

(DcoMcocoenw cocflwcncncncocncDwcQwcQwwcocncQ

fn <u <ü cu cu <u cu cucucuaicDajcDiUcDcucDaJcDcucDCDiDcu cm in - cm <1r ^ cMcoCTioocMCMcn'd- <Tioocncn <f <·

, q co -4- -r st -T cninneMCM <fM, <i- \ oeMN <i ’<f <f'O

ü I ft Λ Λ H I »III ftftftftftftftftftftftftftftftft O O O O O .00000000000 0-000

OOOWHO "- - O 0-000 CM O CM CO

«I-i incMO - cMcncocnvo cm - cm - cm - cm - - A A A A A A IS A A A I | IS A A A is | J Λ Λ Λ Is | [oooooo ooo ooooo oooo as axis r ~ omo cnvoös ^ ö '<t'Oso-cii ^ o-vom - i ^ »o r-4 CM CM CM <T CM CH CM M CM n - - in Mf CM <( - - Μ-ΙΠΜΊΠΝηΜ · <1000000 oooooooooooooooooo oooooo oooooooooooooooooo

• -I vo m as m in co n so \ o ά οοβιΜ · Μ · ιθΜ · Μ - m oo oo ia cm CO CO cn CM CO CM COCOCOCOCOCOCOCOCOCOCOCOCOCOCOCMCMCOCO

oooooo oooooooooooooooooo msoiniai ^ - oinvooooo - omcnco - ooooooo • η -τ -a <r <r <rmo - - o - - ooooooas - ooo -! 3 ·· «« - «* · ********* ******** OOOOOO 'ίΜ-'ί'ίΜΜ'ΓΟ ^ Ι ^ ΜηηηΜ'Μ'Μ-Μ-Μ64 fe <f Μ ίο η on minminvoiniNcMcM - coco <moooco (o ai d cq cn <r> -4- <- co cocotofocofocococococococococococococo no g> ·> «·> ·» «*« «******« ***** «.« ·.

^ oooooo ooo o o ooooooooooooo <1 ω ¢ 3 ιΗ · Η CD t — I ftQ l-l td <u o ocosoooo oooooo <rmoosj- <r - cn <r <rsrco

H 4J s CM - O CM CM - OOOOSOOOO - - OOOSOOOOSOS

CO

C · 4 "Mf <· <f -4" <Γ

CD

e cd w vomvDmincM ooo400iocOKi-h04coino4io l-l SS O os os MO Ο Ο Ο M - - CM O OS CO 4 CM OS CM - - OS OS O ·. «» ·> «« co (Ti co co cos asasascoasasasasoocoasooasasasooco

CM CM CM CM CM CM CMCMCMCMCMCMCMCMCMCMCMCMCMCMCMCMCMCM

'm so m mo <coooooosocom - (040cOcomoom - cm

2 CM CM N CM N CM - - - CM - - CMCMCMCMCMCMCMCMCMCMCMCM

OOOOOO oooooooooooooooooo oooooo oooooooooooooooooooo oo - 4 in ci (nNosin4niM-os-cMOinoscocM4 cncncncncncn - cmcmcmcoco - cm - cm cm cm cm cm - - cmcm oooooo oooooooooooooooooo *** ********* oooooooooooooooooooooooo Ö0 ¢ 3

• H

CD

Ü0 <1 Cd U P W h C5P3-HhMiJg | z; OP4apjraHP> | 3M

5 800 1 7 40

·· *. V

6

It should be noted that the alloys A through F are alloys not covered by the invention. They do not have a nickel content between 2.00 and 5.00 wt%. It is essential for the present invention that the alloy has a nickel content of more than 2.00 wt%.

Further data on the chemical composition of the alloys 21jn are shown in Table B.

Table B

Alloy ZC + ZN ZTi / 6 +% Zr / 7 +% Cb / 8 10 A 0.055 0.083 B 0.056 0.073 C 0.056 0.071 D 0.061 0.083 E 0.061 '0.086 15 F 0.056 0.107 G 0.031 0.052 H 0.045 0.052 I 0.047 0.100 20 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 25 0 0.042 0.069 P 0.045 0.086 Q 0.042 0.054 R 0.043 0.080 S 0.048 0.056 30 T 0.040 0.068 U 0.037 0.074 V 0.040 0.084 W 0.043 0.055 X 0.046 0.080 35 The toughness was assessed by the transitional

temperature to be determined from small transverse samples to determine the Charpy-V notched impact strength, from hot-rolled and tempered material (samples of 3.125 x 9.85 mm), cold-rolled and tempered material (samples of 1.55 x 9.85 mm ), welded materials (samples of 1.55 x 9.85 mm) and welded and tempered material (samples of 1.55 x 9.85 mm). The transition temperature was based on the occurrence of a 50% ductile - 50% brittle fracture. The transition temperatures for the hot-rolled and cold-rolled samples are shown in Table C. The alloys A

800 1 7 40 <0 Λ 7 to L were annealed at 1065 ° C. The remaining alloys were annealed at 1121 ° C.

Table C

Transition temperature (° C) 5 Hot rolled Cold rolled and tempered _ and tempered

Alloy air-quenched air-quenched _ water-cooled_ water-cooled_ A 54.4 149 1.7 46.1 10 B 48.9 126 -28.9 18.3 C 43.3 110 -12.2 10 D 57.2 160 4.4 29.4 E 60 160 -12.2 29.4 F 98.9 99 4.4 32.2 15 G -37.2 - -117.8 -73.3 H -43 .3 - -115 -73.3 I -15 - -117.8 -67.8 J -84.4 -. -123.3 '-112.2 20 K -56.7 - -128.9 -76.1 L -40 - -115 -90 M 10 37.8 -90 N 1.7 18.3 - 84.4 0 -15 12.8 - 87.2 25 P - 1.1 21.1 - 92.8 - Q -37.2 15.6 -101.1 R - 9.4 15.6 -109.1 S - 37.2 - 9.4 -120.6 - T -31.7 - 9.4 -117.8 30 U -53.9 -23.3 -115 V -56.7 -31.7 -117.8 - W -67.8 -31.7 -128.9 X -73.3 -31.7 -142.8

The transition temperatures for the welded (non-post-treated) samples and for the welded and annealed samples are shown in Table D. The alloys Δ through F were annealed at 1065 ° C before welding. The other alloys were annealed at 800 1 7 40 8 1121 ° C. All alloys were quenched with water. Annealing after welding took place at 140 ° C for alloys A to F and at 1121 ° C for the other rings. All alloys were quenched with water after the annealing following welding.

5 Table D

Transition temperature (° C)

Alloy As welded Welded and tempered A 43.3 -1.1 B 15.6 1.7 10 C 32.2 4.4 D 40.6 -3.9 E 68.3 4.4 F 54.4 10 15 G -76.1 -76.1 H '-62.2 -70.6 I -42.8 -70.6 J -78.9 -137.2K -67.8 -103.9 20 L -51.1 -84.4 M -51.1 -53.9 N -17.8 -40 0 -28.9 -65 P -23.3 -59.4 25 Q -51.1 -78.9 R -28.9 -59.4 S -40 -92.8 T -51.1 -73.3 ü -78.9 -81.7 30 V -81.7 -84.4 W -73.3 - 106.7 X -95.6 -128.9

The favorable effect of nickel is clearly shown in Tables C and D. The alloys G to X had a considerably lower transition temperature and are therefore considerably tougher than the alloys A to F. It is essential that 800 1 740 9 alloys G through X are alloys of the present invention while alloys A through F are not alloys of the invention. Alloys G through X contain more than 2.00 wt% nickel.

5 The lower transition temperatures for the alloys G through X are again shown in Table E which summarizes Tables C and D.

Table E

Transition temperature (° C)

10 Alloys A-F Alloys G-X

Hot rolled and de-43 to 99 -85 to 10. leave (quenched 'with water)'.

, Hot rolled and let 99 to 160 -32 to 38 15 (cooled in air)

Cold rolled and de-29 to 4.5 -143 to -84 (quenched with water) 20 Cold rolled and de-10 to 46.5. -112.5 to -67.5 (cooled by air)

As welded 15.5 to 68.5 -96 to -17.5

Welded and tempered -3.9 to 10 -137.5 to -40 25 It should be noted that in all cases the maximum transition temperature for the alloys G to X is lower than the minimum transition temperature for the alloys A to F. The numbers clearly show that alloys G to X are tougher than alloys A to F.

Further samples of the alloys G through X were tested for crack resistance and intergranular corrosion resistance. These samples were made in the same manner as the aforementioned samples.

Crack corrosion resistance was assessed by dipping 2.5 x 5 cm samples with a sanded surface in a 10% iron (III) chloride solution for 72 h. The test took place at a temperature of 50 ° G. The cracks were brought about by blocks 800 1 7 40

JO

of polytetrafluoroethylene on the front and back which were held in place by pairs of stretched rubber tires arranged around the samples at an angle of 90 ° to each other in the longitudinal and widthwise directions. The respective tests are described in Designation: G 48-76 of the American Society for Testing And Materials.

The results of this evaluation are set forth in Table F. The samples were in the cold-rolled and annealed condition, in the state resulting from welding, and in the welded and annealed condition.

Table F

Crack corrosion test in 10% iron (III) chloride solution, _

Weight loss (g) 15 Alloy Cold rolled and As welded Welded and tempered ____ tempered_ _ _ G - 0.0001 0.0008 H - 0.1588 0.0005 I - 0.0 0.0004 20 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 25 0 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 30 T 0.0 0.0001 0, 0056 U 0.0002 0.0001 0.0 V 0.0001 0.0078 0.0002 W 0.0001 0.0 0.0063 X 0.0 0.0003 0.0060 35 tempered at 1121 C - quenched with water .

Table F shows that the resistance to 80 0 1 7 40 «= ~ ..

crack corrosion of the alloys G to X is excellent. The alloys of the invention are clearly characterized by superior crack corrosion resistance.

Resistance to intergranular corrosion was assessed by immersing 2.5 x 5 cm samples with a sanded surface in a boiling solution of copper sulfate-50% sulfuric acid for 120 h. The usual criterion for pass or fail in this test is a corrosion rate of 0.6 mm / year (0.05 mm / month) and a satisfactory appearance in microscopic examination. This test. is recommended for stabilized ferritic stainless steel with a high chromium content. The results of this assessment. are listed in Table G. The samples were in the state as it arises during welding and in the welded and annealed state.

Table G

Corrosion test in copper sulfate - 50% sulfuric acid

Corrosion speed Microscopic mm / moon 'search (magnification 30 x) _ 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 800 1 7 40

Alloy Welded Welded and Welded Welded and 2 _ tempered _ tempered 3

G 0.012 0.816 NA ** NA

4

H 0.016 0.0145 NA NA

5

X 0.013 0.017 NA NA

6

J 0.011 0.016 NA NA

7

K 0.009 0.018 NA NA

8

L 0.0095 0.015 NA NA

9

S 0.013 0.0155 NA, NA

10

T 0.012 0.0125 NA NA

11

U 0.010 0.016 NA NA

12

V 0.012 0.012 NA NA

13

W 0.012 0.0126 NA NA

14

X 0.0129 0.0136 NA NA

15

Tempered at 1121 C - quenched with water 16 NA: No intergranular attack.

Table G shows that alloys G through L

12 w- V and S through X had superior intergranular corrosion resistance. Each sample passed the test.

It will be clear that the invention makes all kinds of modifications and variations possible without departing from the scope of the invention.

800 1 7 40

Claims (9)

1. Ferritic stainless steel, consisting essentially of at most 0.08 wt% carbon, at most 0.06 wt% nitrogen, 25.00 to 35.00 wt% chromium, 3.60 to 5.60 5 wt.% molybdenum, at most 2.00 wt.% manganese, between 2.00 and 5.00 wt.% nickel, at most 2., CD wt.% silicon, at most 0.5 wt.% aluminum, at most 2.00% by weight of the elements titanium, zirconium and columbium together, the remainder mainly being iron, the titanium, zirconium and columbium contents being such that the condition:% Ti / 6 +% Zr / 7 + is met % Cb / 8>% C +% N while the sum of the carbon plus nitrogen content is greater than 0.0275 wt%. . Ferritic stainless steel according to claim 15 1, characterized in that it has a nickel content between 3.00 and 4.50% by weight. Ferritic stainless steel according to claim 1 or 2, characterized in that it contains at least 0.005 wt% carbon and at least 0.010 wt%. contains nitrogen where the sum of the carbon plus nitrogen content is greater than 0.0300% by weight. Ferritic stainless steel according to any one of the preceding claims, characterized in that it contains 28.50 to 30.50% by weight of chromium. Ferritic stainless steel according to any one of the preceding claims, characterized in that it contains 3.75 to 4.75% by weight of molybdenum. Ferritic stainless steel according to any one of the preceding claims, characterized in that it contains at most 1.00% by weight of the elements titanium, zirconium and columbium together, the condition being met:% Ti / 6 + % Zr / 7 +% Cb / 8 = 1.0 to 4.0 (% C +% N). Ferritic stainless steel according to any one of the preceding claims, characterized in that it contains at least 0.15% by weight of titanium. Ferritic stainless steel according to claim 7, characterized in that it contains at least 0.15% by weight of columbium. 800 1 7 40 - * ^ V Ferritic stainless steel according to any one of the preceding claims, characterized in that it contains at least 0.005 wt.% Carbon, at least 0.010 wt.% Nitrogen, 28.50 to 30.50 wt.% Chromium, 3.75 to 4.75 wt.% molybdenum, between 3.00 and 4.50 5 wt.% nickel and not more than 1.00 wt.% of the elements together contain titanium, zirconium and columbium meeting the condition% Ti / 6 +% Zr / 7 +% Cb / 8 = 1.0 to 4.0 (% C +% N) where the sum of the carbon plus nitrogen content is greater than 0.0300 wt%. 800 1 7 40