DE2051609B2 - Use of an austenitic stainless steel as a material for the production of welded pressure vessels for cryogenic operation and the production of cold-drawn wire-shaped molded bodies - Google Patents

Description

The invention relates to the use of an austenitic stainless steel consisting of 15.5 to 20% chromium, 11 up to 15% manganese, 1.1 to 3.75% nickel, less than 0.01 to 0.11% carbon, 0.28 to 0.38% nitrogen, the remainder Iron with impurities caused by the smelting exists as a material for the production of welded pressure vessel for cryogenic operation, which has both high strength at room temperature as also have good toughness and stability at cryogenic temperatures, and as a material for the Production of cold-drawn wire-shaped moldings with good toughness at 78 ° K, a good one Resistance to stress corrosion cracking in boiling chloride media and good cold hardening properties.

From the German interpretation 12 61 677 non-magnetizable, austenitic chromium-manganese steel alloys are known, which consist of 10 to 20% chromium, 12 to 25% manganese, up to 5% nickel, up to 0.25% carbon, 0.05 up to 0.5% nitrogen and the remainder iron with impurities. These steel alloys are suitable as a material for the production of drill collars for deep drilling rods, which are brought to a yield point of at least 70 kg / mm ² by cold deformation.

Also from "ASM Picprint 29" Volume 47, 1954, der US Pat. No. 2,778,731 and "ASTM Special Technical Publication 369", 1963, are nickel-containing

^r ) ^r > Chromium-manganese steel alloys known, which have a high strength and a high cold hardening rate. However, these high-strength austenitic alloys with a low nickel content are only of limited suitability for cryogenic operation because

M) they transform into martensite when deformed and therefore have a low resistance to fatigue. It is possible, by increasing their nickel content, to convert them to martensite in the case of cryogenic Temperatures partially prevent the resilience

ti ¹ ; The steel alloys obtained in this way are limited, however, since they only have a relatively low strength at room temperature. In addition, such steel alloys are because of their relative-

moderately high nickel content very expensive. All these known steel alloys also have in common that they have a relatively low resistance to stress corrosion cracking at cryogenic temperatures and in boiling chloride media, even if they contain 5 to 15% nickel.

The object of the invention was therefore to provide a relatively low-alloy, fully austenitic stainless steel To propose steel which, due to its specific critical composition, is a unique combination of properties, namely high strength at room temperature, good resistance to Fatigue, good toughness and stability against transformation to martensite at cryogenic temperatures, good general corrosion resistance, good resistance to stress corrosion cracking, excellent Welding properties, as well as the ability to kahhardened to a very high strength to become so that it can be used as a material for the manufacture of welded pressure vessels for the cryogenic Operation and for the production of cold-drawn wire-shaped shaped bodies with the desired Properties can be used.

It has now been found that this object can be achieved according to the invention through use an austenitic stainless steel, which consists of 15.5 up to 20% chromium, 11 to 15% manganese, 1.1 to 3.75% nickel, less than 0.01 to 0.11% carbon, 0.28 to 0.38% nitrogen, the remainder iron with impurities from the melting process, is used as the material for the Manufacture of welded pressure vessels for cryogenic operation with both high strength Have room temperature as well as good toughness and stability at cryogenic temperatures, and as a material for the production of cold-drawn wire-shaped molded bodies with a good Toughness at 78 ° K, good resistance to stress corrosion cracking in boiling chloride media and good cold hardening properties.

The steel to be used according to the invention has, due to the coordination of its chromium content, Manganese, nickel, carbon and nitrogen on each other a unique combination of beneficial properties, namely, high strength at room temperature, good resistance to fatigue, a good toughness and stability against transformation to martensite at cryogenic temperatures, good General corrosion resistance, good resistance to stress corrosion cracking in boiling chloride media, excellent welding properties as well as the ability to achieve a very high level of strength to be cold hardened.

According to a preferred embodiment, the austenitic stainless steel to be used according to the invention contains Steel preferably 11 to 13.5% manganese, preferably 1.1 to 3.5% nickel, preferably 0.03 to 0.10% carbon, preferably 0.30 to 0.34% nitrogen and preferably 17 to 19% chromium. In addition, the austenitic stainless steel to be used according to the invention can preferably be vanadium / or niobium in an amount of 0.1 to 0.5% and in it can according to a further preferred According to the invention, up to 3.5% chromium in a ratio of 1: 1 can be replaced by molybdenum. Of the Steel to be used according to the invention can also contain up to 0.010% boron.

According to a further preferred embodiment, there is the austenitic to be used according to the invention stainless steel from 15.5 to 20% chrome, 11 to 15% Manganese, 1.1 to 3.75% nickel, less than 0.01 to 0.11% Carbon, 0.28 to 038% nitrogen, up to 0.040% phosphorus, up to 0.030% sulfur, up to 1.0% silicon, The remainder is iron with impurities from the melting process, and according to a further preferred embodiment according to the invention it consists of 17 to 19% chromium, 11 up to 13.5% manganese, 1.1 to 3.5% nickel, 0.03 to 0.10% Carbon, 030 to 0.34% nitrogen, up to 0.040%

ίο phosphorus, up to 0.030% sulfur, up to 1.0% silicon, The remainder is iron with impurities from the melting process.

When it comes to particularly high general corrosion resistance and high temperature resistance, can in the steel to be used according to the invention up to 3.5% chromium in a ratio of 1: 1 through Molybdenum to be replaced. However, the molybdenum reduces the toughness at cryogenic temperatures. To the To increase the strength, niobium and / or vanadium can be added in amounts of 0.1 to 0.5% each will. To increase the heat hardenability, boron can be added in amounts up to 0.010%.

The elements carbon, manganese, chromium, nickel and nitrogen and their chemical equilibrium are critical in any case. If any of these elements are omitted or if their critical contents are not adhered to, one or more of the desired properties are lost. The carbon content of steels is preferably at least about

jo 0.03% to give the steel the required strength and to act as austenite images. In certain areas of application, the carbon content Go below 0.03% and even 0.01%, since you can rely on nitrogen to make you has a corresponding influence on the properties of the steel. A maximum carbon content of 0.10% is preferred. C contents higher than 0.11% are inappropriate, because this contributes to the general corrosion resistance and weldability as well as the toughness cryogenic temperatures are affected.

To ensure a completely austenitic structure and to keep the nitrogen in solution hold, at least 11% manganese is required. Manganese levels higher than 15% and preferably than 13.5% is unsuitable because it increases costs due to manganese losses during melting and there Manganda tends to induce heat fragility. Chromium is used in amounts of at least 15.5% needed to give the alloy the required corrosion resistance and in combination with manganese to keep the nitrogen in solution. More than 20% chromium can be used in the specified carbon, Manganese, nickel and nitrogen contents cannot be tolerated, since chromium is a ferrite former and a larger one than about 2% ferrite content avoided for reasons of good toughness at cryogenic temperatures must become. For these reasons, a maximum chromium content of about 18% is preferred.

The presence of nickel in amounts of

bo at least 1.1% is due both to its function as Austenite former as well as because of its toughness-increasing effect at cryogenic temperatures of essential. Nickel contents higher than 3.75% no longer lead to an increase in toughness

b5 and are therefore inexpedient. In addition, nickel contents in excess of 3.75% make up the Alloy prone to stress corrosion cracking. Besides, it is because of the high price of nickel

expedient to keep the nickel content as low as the interrelation of the other elements with it Nickel without impairing the desired properties.

To achieve high strength at room temperature, at least 0.23% nitrogen is required. In addition, nitrogen is a strong austenite former; Thus, with the specified carbon, manganese and nickel contents, at least 0.2fe ^D / o nitrogen is required Welds occurs

The above shows that a good balance in terms of the amounts of the essential elements must be observed and that the interrelationship of the individual components leads to a new combination of properties within the specified limits it can be seen that certain modifications within the specified limits to an alloy with optimal properties lead to cryogenic use, while other changes lead to an alloy with optimal all-purpose properties, e.g. B. lead to the production of high-strength spring wires.

A preferred alloy for cryogenic areas of application has the following composition:

0.05% carbon, 13% manganese, 18% chromium, 3.0% nickel, 0.32% nitrogen, amounts due to melting of phosphorus, sulfur and silicon and the remainder iron.

Another preferred alloy for cryogenic use with a particularly favorable combination of high strength at room temperature, good stability against transformation into martensite and good toughness at 78 ° K and excellent weldability has the following composition:

0.05% carbon, 13.5% manganese, 18% chromium, 3.5% nickel, 0.35% nitrogen, up to 0.50% vanadium and / or niobium, amounts of phosphorus, sulfur, silicon and the remainder iron due to the melting process.

A preferred alloy for the production of cold-drawn spring wires with a tensile strength of more than 1550 MN / m ² has the following composition:

0.10% carbon, 12% manganese, 18.5% chromium, 1.5% Nick'.l, 0.35% nitrogen, amounts due to the melting process of phosphorus, sulfur and silicon and the remainder iron.

The permissible loads under cryogenic operating conditions are based on the tensile and yield strength values at room temperature, the percentage elongation and necking at room temperature, · the Impact strength at 78 ° K and the degree of conversion to martensite, measured as magnetic conversion.

With the alloys to be used according to the invention, compared to known cryogenic Alloys and alloys with chromium contents above and below the chromium contents of the invention measure to be used alloys and with manganese contents below the manganese contents of the invention alloys to be used, but with the other constituents within the limits for the according to the invention used steels specified limits, such b5 Tests carried out. The compositions of the various alloys examined are in the given in Table I below; the specified properties of the alloys given in Table 1 are compiled in the following table II

In addition to the investigations into the mechanical and metallurgical properties of the Alloys were samples 1 through 14 and 17 through 22 in boiling magnesium chloride (MgCb) for their stress corrosion cracking behavior The test pieces were examined by applying fusion welds on opposite sides of 25.4 mm round rods were produced Fibers of the test pieces caused tensile stresses. While all rehearsals of the first group (1 to 14) showed no signs of cracking within 24 hours was in all samples of the second Grappe (17 to 22) a crack formation can be observed within this time. The main difference in the chemical composition of the two groups is their nickel content. From the results of these experiments It can be seen that with a nickel content of more than 3.75% the resistance to stress corrosion cracking decreases

All batches were melted in an induction furnace, then thermoformed and at 1340 ° K a Left on for half an hour and quenched with water.

The results contained in Table II show that the strength at room temperature of the alloys to be used according to the invention is considerable is higher than that of the comparative alloys. The toughness of those to be used in accordance with the invention Steels at 78 ° K is not as high as the toughness of the comparative steels; in this context, however pointed out that the toughness of the steels to be used according to the invention for cryogenic operating conditions completely sufficient, since a minimum value of 20.3. Joules in the Charpy impact test with a V-notch at a temperature of 78 ° K is considered sufficient.

From Table II it can also be seen that five alloys to be used according to the invention in While deforming at a temperature of 78 ° K will show a slight magnetic conversion the remaining alloys to be used according to the invention have only an extremely low magnetic level Exhibit conversion. In contrast, the comparative alloys show conversion to martensite as a result a strong magnetizability.

In spite of its considerably higher content of alloy components, in particular nickel and manganese, the comparative sample 19 has properties at room temperature and toughness ^{values at 78 °} K, which can be compared with the corresponding values of the alloys to be used according to the invention.

Samples 10 and 11, the manganese in lesser amounts Contain amounts than are required for the alloys to be used according to the invention possessed an unusually low toughness at 78 ° K and converted to martensite at room temperature. By These results show the need for a minimum of 11.0% waste.

High chromium contents (samples 12 and 13) resulted in a two phase structure with a large percentage Ferrite content and an unusually low impact resistance at 78 ° K.

Finally, the one exhibiting a chromium content below the required minimum amount of 15.5% Sample 14 has an unusually low impact strength at 78 ° K.

Table I.

Composition of the different steels examined *)

Sample no. Alloy type C. Mn Cr Ni N 1 required acc. to use 0.046 11.88 17.76 1.97 0.30 alloy 2 the same 0.10 12.07 17.86 1.75 0.38 3 the same 0.054 12.16 17.84 2.74 0.33 4th the same 0.056 12.54 17.46 2.94 0.33 5 the same 0.057 12.79 17.46 3.71 0.33 6th the same 0.041 14.8 18.05 2.05 0.31 9 the same 0.043 14.52 17.41 1.38 0.33 0.21V 0.14Nb 10 Comp. Leg. with 0.045 7.96 17.18 1.98 0.29 low Mn content 11 the same 0.052 5.64 18.07 1.94 0.29 12th Comp. Leg. with 0.06 14.54 25.31 2.29 0.32 high Cr content 13th the same 0.12 14.52 25.30 2.23 0.32 14th Comp. Leg. with 0.10 11.80 12.86 1.71 0.30 low Cr content 15th Comp. Leg. 0.052 1.74 18.29 9.6 0.16 16 the same 0.06 1.66 18.63 10.7 0.12 17th the same 0.060 1.48 18.70 8.36 0.25 18th the same 0.052 1.69 18.94 9.59 0.22 19th the same 0.066 16.08 18.11 5.81 0.30 20th the same 0.054 0.77 18.19 8.81 0.031 21 the same 0.064 1.80 17.58 13.38 0.025 2.66 mo 22nd desel. 0.045 8.95 20.46 6.67 0.29

- ·) In samples 1 to 14 the phosphorus content was 0.007 to 0.027%, the sulfur content 0.010 to 0.029% and de / S !! icmmgeha! T 0.21 to 0.54%.

Tabel II Alloy type Table I. Stretch limit %-Strain %-A- Impact resistance Magne Properties of steels of the tensile strenght at space in 5 cm meas lacing at the Charpy tables sample at space temperature length V-impact Conversion No. temperature (0.2% elongation search in joules *) lung border (MN / m ² ) (Room temp (Room temp (78 ° K) (78 ° K) (MN / m ² ) rature) rature) required to be used Leg. 442 54 70 28 small amount the same 755 510 52 70 23 very 1 828 small amount 2 the same 455 49 71 49 small amount the same 755 435 51 70 58 small amount 3 the same 755 428 49 70 72 small amount 4th the same 755 407 54 70 54 very 5 745 small amount 6th the same 538 42 62 27 very 828 9

ίο

continuation

sample Alloy type tensile strenght Stretch limit %-Strain %-A- Impact resistance Magne No. at space at space in 5 cm meas lacing at the Charpy tables temperature temperature length V-impact Conversion (0.2% elongation search in joules *) lung border (MN / m ² ) (MN / m ² ) (Room temp (Room temp (78 ° K) (78 ° K) rature) rature)

Comp. Leg. with

low

Mn content

the same

795

455

67

870

448

51

12th
13th Comp. Leg. with
high Cr content
the same 765
785 14th
15th Comp. Leg. with
low
Cr content
Comp. Leg. 820
640 16 the same 613 17th the same 725 18th the same 695 19th
20th the same
the same 780
593 21
22nd the same
the same 613
710

510 538 455

318 270 372 338

420 314

310 400

68
63
68

70
71
70
70

69
69

69

70

12th

106

138

87

137

54
149

135
102

*) The impact strength values at room temperature exceeded 135 joules for all samples.

Conversion at room temperature

Conversion at room temperature 35% ferrite

20% ferrite

small amount

Conversion

Conversion

Conversion Conversion

Conversion low

very low

The steel to be used according to the invention was found to be high strength; he can at a target tension of slightly more than 40% strength by cross sectional reduction up to a tensile strength of 1515 to 1725 MN / m ² and a yield strength (0.2% yield strength) of at least 1240 MN / rn are drawn. ² The cold hardening capacity of the alloy arcs to be used according to the invention is considerably greater than that of the known alloys. With regard to the other physical properties, the steels to be used according to the invention can easily be compared with the known steels. The higher cold hardenability of the steels to be used according to the invention makes it possible to pull a steel down to the basic thickness in a single pull, whereas the known steel requires a total cold deformation of the order of 60% in order to achieve a tensile strength of 1515 MN / m ² .

A melt of the composition 18.6% chromium, 11.9% manganese, 1.6% nickel, 0.11% carbon, 038% nitrogen, 0.015% phosphorus, 0.010% sulfur, 0.60% silicon, balance iron investigated for their mechanical cold-drawing properties. The results (obtained at room temperature) are given in Table III below. They were with a non-directional wire, drawn from a 835 mm round bar, which had been started for half an hour at 1340 ⁰ C and then quenched with water is obtained. The tempering hardness was 98 HRB.

Table III

% Cold deformation tensile strength

(MN / m ² )

Yield point at
Room temperature
(0.2% yield strength)
(MN / m ² ) % Elongation in 5 cm
Measuring length % Constriction Rockwell
Hardness C 760 40 63 24 953 25th 58 28 1090 17th 53 32 1240 12th 48 37 1400 10 43 40 1640 10 40 44

1020
1170
1310
1480
1640
1830

The 6.35 mm round rod that was assumed was made from a square bar with a 10.2 χ 10.2 cm cross-sectional area. The bar had a tensile strength of 800 MN / m ² , a yield point (0.2% ^{proof stress) of 448 MN / m 2} , an elongation in 5 cm measuring length of 53%, a necking of 73.5% and a hardness of 96 HRB.

The 6.35 mm round rod had a tensile strength of 825 MN / m ² , a yield point (0.2% ^{proof stress) of 442 MN / m 2} , an elongation in 5 cm measuring length of 63 after a corresponding tempering and quenching with water %, a necking of 69% and a hardness of 98 HRB.

A 6.35 mm round bar hot-rolled from a 10.2 cm bar (square bar) had a tensile strength of 1140 MN / m ² , a yield point (0.2% ^{proof stress) of 895 MN / m 2} , an elongation in 5 cm measuring length of 38%, a necking of 60% and a hardness of 36 HRC.

A steel sleeve was processed into a 2.5 mm rod, annealed at 1310 ⁰ C, and stained with a speed of 30.5 m / min with a cross-sectional reduction of 43% in a single train processed into a 1.9 mm round bar. The tensile strength obtained was 1515 MN / m ² . For comparison, an attempt to draw a wire of the same thickness from a comparative steel required a total deformation of 58% in order to achieve a tensile strength of 1515 MN / m ² . This required two pulls, the first at a speed of 30.5 m / min and the second at a speed of 18.3 m / min to avoid surface defects on the wire.

The steel to be used according to the invention can be melted in an electric furnace, either under Provide access to air or in a vacuum. He can go on

Each · are remunerated, for example by degassing in the Vacuum, and cast into ingots or continuously cast into slabs. Then the Steel is usually made into plates, sheets, strips, rods, rods or wire, e.g. B. spring wire or Welding wire, hot and cold formed. In some cases the steel can be cast or forged State used or processed into molded bodies, which are then welded.

Claims (11)

Patent claims: 1. Use of an austenistic stainless steel consisting of 15.5 to 20% chromium, 11 to 15% manganese, 1.1 to 3.75% nickel, less than 0.01 to 0.11% carbon, 0.28 to 0.38% nitrogen, balance Iron with impurities caused by the melting process, as a material for the production of ι ο welded pressure vessels for cryogenic operation, which both have high strength Room temperature as well as good toughness and stability at cryogenic temperatures. 2. Use of an austenitic stainless steel, consisting of 153 to 20% chromium, 11 to 15% manganese, 1.1 to 3.75% nickel, less than 0.01 to 0.11% carbon, 0.28 to 0, 38% nitrogen, the balance iron with incidental impurities, as material for the production of cold drawn wire-shaped moldings having a good toughness at 78 ⁰ K, a good resistance to stress corrosion cracking in boiling chloride media and a good Kalthärtungsvermögen. 3. Use of an austenitic stainless steel Steel according to claim 1 or 2 with a manganese content of 11 to 13.5% to that in claim 1 or 2 specified purpose. 4. Use of an austenitic stainless steel according to claim 1 or 2 with a Nickel content of 1.1 to 3.5% for the purpose specified in claim 1 or 2. 5. Use of an austenitic stainless steel according to claim 1 or 2 with a J5 Carbon content from 0.03 to 0.10% and a nitrogen content from 0.30 to 0.34% to the in Claim 1 or 2 specified purpose. 6. Use of an austenitic stainless steel according to claim 1 or 2 with a Chromium content of 17 to 19% for the purpose specified in claim 1 or 2. 7. Use of an austenitic stainless steel according to claim 1 or 2 with a content of Vanadium and / or niobium from 0.1 to 03% to the in Claim 1 or 2 specified purpose. 8. Use of an austenitic stainless steel according to claim 1 or 2, in which up to 3.5% Chromium in a ratio of 1: 1 are replaced by molybdenum, to that specified in claim 1 or 2 Purpose. 9. Use of an austenitic stainless steel according to claim 1 or 2, which additionally has Contains up to 0.010% boron for the purpose stated in claim 1 or 2. 10. Use of an austenitic stainless steel according to claim 1 or 2 consisting of 15.5 up to 20% chromium, 11 to 15% manganese, 1.1 to 3.75% nickel, less than 0.01 to 0.11% carbon, 0.28 up to 0.38% nitrogen, up to 0.040% phosphorus, up to 0.030% sulfur, up to 1.0% silicon, the remainder iron with impurities caused by the melting, for the purpose specified in claim 1 or 2. 11. Using an austenitic stainless Steel according to claim 1 or 2, consisting of 17 to 19% chromium, 11 to 13.5% manganese, 1.1 to 3.5% Nickel, 0.03 to 0.10% carbon, 030 to 0.34% Nitrogen, up to 0.040% phosphorus, up to 0.030% sulfur, up to 1.0% silicon, the remainder iron with melt-related impurities,? u the in claim 1 or 2 specified purpose.