DE1231439B - Use of a rustproof nickel-chromium-cobalt steel alloy for objects with a high yield point - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CL:

C22c

German KL: 40 b - 39/22

Number:
File number:
Registration date:
Display day:

1231439
J 27788 VI a / 40 b
March 26, 1965
December 29, 1966

The invention relates to the use of a stainless nickel-chromium-cobalt steel alloy which is cold-worked to a structure with 60 to 99% martensite, the remainder austenite and ^{hardened at 400 to 455 °} C. with a holding time of 1 to 48 hours , as a material for objects such as thin and heavy plates, strips, billets, steel bars, pipes, wire, forged, extruded, stamped and pressed parts, couplings, pressure vessels, barrels, wheel spokes, bolts, rivets, screws, knives , surgical instruments, dental tools, saws and chisels must have a 0.2% yield strength of over 165 kg / mm ^a and a tensile strength ratio in the notched and unnotched state of at least 0.95.

It is known to increase the strength of stainless austenitic chromium-nickel steel alloys by cold working to increase with subsequent curing. Steel alloys of this type essentially exist from 16 to 26% chromium, 6 to 22% nickel, 0.5 to 2% manganese, 0.5 to 1% silicon and, for example, 0.1% Carbon. A nickel-chromium-steel alloy is also already included from US Pat. No. 2,553,330 4 to 70% nickel, 0 to 0.5% carbon, 0 to 40% cobalt, 10 to 60% at least one of the elements Chromium, molybdenum, tungsten, 0 to 20% manganese, 0 to 0.30% nitrogen and 0 to 4% silicon are known. This steel alloy is corrosion resistant, especially against the attack of various acids as well Resistant to scaling and has a high tensile strength and good creep strength at high temperatures. In order to increase the hot deformability of the known steel alloy, you should use rare earths, in particular Cereal and lanthanum can be added.

In the case of stainless austenitic steels, the austenite of which is stable at room temperature, however can be converted into martensite by cold working, the transformability of a number of alloying elements determined, the influence of which results from the so-called nickel equivalent

(% Ni) + 0.68 (% Cr) + 0.55 (% Mn) + 0.45 (% Si) + 27 (% C +% N) + 0.2 (o / _o Co) + (% Mon)

results, which is generally between 17 and 30 for the steel alloys in question.

However, with the cold working of the transformable steel alloys, there is a reduction in their notch toughness tied together. In this respect, the ratio of tensile strength is essential for the usability of such materials of great importance in the notched and unnotched state, which is at least 0.95, preferably

Use of a stainless nickel-chromium-cobalt steel alloy for objects with high yield strength

Applicant:

International Nickel Limited, London

Representative:

Dr.-Ing. G. Eichenberg

and Dipl.-Ing. H. Sauerland, patent attorneys,

Düsseldorf, Cecilienallee 76 /

Named as inventor:

Stephen Floreen, Westfield, N. J. (V. St. A.)

Claimed priority:

V. St. v. America March 31, 1964 (356 037)

however, should be at least 1, but in the case of cold-worked and hardened steel alloys of the aforementioned type, it should generally not be more than 0.9. Another disadvantage is that cold rolling generally has to take place at low temperatures, for example below -4O ⁰ C and the steel alloys have poor mechanical properties as a result of rolling in a direction transverse to the rolling direction.

The object on which the invention is based exists now in, a steel alloy with high yield strength and a high ratio of tensile strength in the to create notched and unnotched condition, the cold deformation of which takes place around room temperature can. According to the invention, therefore, the use of a steel alloy consisting of 3 to 8% nickel, up to 17% chromium, 7 to 13% cobalt, 0.01 to 1%

Manganese, 0.01 to 0.15% carbon, 0.005 to 0.1% nitrogen, 0 to 5% molybdenum, maximum 0.15% Silicon, remainder iron and melting-related

609 749/333

impurities, with a nickel equivalent according to the formula

CV ₀ Ni) + 0.68 (o / _o Cr) + 0.55 (° / ₀ Mn) + 0.45 (% Si)

proposed from 19.5 to 22.

The invention is based on the surprising finding that the silicon content with respect to the Conversion during cold forming as well as for high strength with a high tensile strength ratio at the same time in the notched and unnotched state is essential and the silicon content is therefore below 0.15% must be cherished. As an accompanying element, the steel alloy can contain up to 0.2% aluminum, Contains 0.1% calcium, 0.1% magnesium, 0.1% zirconium, 0.01% boron and 2% copper. The total salary the harmful elements, such as sulfur, phosphorus, bismuth, antimony, tin, lead, and arsenic Beryllium, should not exceed 0.03%, but preferably not exceed 0.02%.

The proposed steel alloys consist of at least 90% austenite and can be used in the temperature range from -15 to 38 ° C with a decrease of at least 20% in view of an optimal Strength after curing, but to avoid mechanical anisotropy and poor toughness not more than 50% cold-formed transversely to the rolling direction and their structure 60 to 99% in Martensite can be converted. In this state, the steel alloys become 1 to Cured for 48 hours. The steel alloys can also be hot or cold worked before the transformation be, it has proven to be useful, cold deformation to transform the structure Pre-glow at 980 to 1150 ° C. The temperature of 980 ° C should be because of the risk of Embrittlement due to carbides or the sigma phase must not be exceeded. Unless the cold deformation takes place in several stages, it may be necessary to change the steel alloy between two deformation stages Allow to cool to ensure the required deformation temperature of -15 to 38 ° C.

The proposed steel alloy preferably consists of 4.5 to 5.5% nickel, 14.5 to 16% chromium, 7.5 to 10% cobalt, 0.01 to 0.5% manganese, 0.04 to 0.09% Carbon, 0.01 to 0.05% nitrogen, up to 0.1% silicon with a nickel equivalent of 20 to 21. Such a molybdenum-free steel has a tensile strength of 180 kg / mm ² and a ratio of the tensile strength in the notched and unnotched state of 1 or more.

The invention is explained in more detail below with reference to five alloy examples.

Table I.

alloy 7oNi 7oCr 7oCo 7oMn 7oSi 7oC 7oN 7oMo 7oFe 7o Ni equivalent 1 6.7 16.1 7.6 0.40 0.01 0.06 0.03 Rest* 21.8 2 5.1 15.7 8.4 0.14 0.02 0.06 0.03 - rest 20.1 3 5.1 14.6 7.7 0.24 0.05 0.05 0.03 2.05 rest 20.6 4th 5.2 12.7 7.8 0.07 0.05 0.07 0.03 3.90 rest 22.0 5 6.1 14.3 11.1 0.23 0.05 0.04 0.03 - rest 20.0

Including low levels of impurities.

In Table II there are four steel alloys that are more or less similar, but not the ones proposed belong listed.

Table II

alloy 7oNi 7oCr 7oCo 7oMn 7oSi 7oC 7oN 7oMo 7oFe 7o Ni equivalent W. 6.0 18.7 3.48 0.21 0.01 0.06 0.03 _ rest 22.0 X 6.5 16.8 3.10 0.45 0.01 0.06 0.03 - rest 21.2 Y 5.2 13.7 7.82 0.19 0.05 0.06 0.03 - rest 18.7 Z 4.2 .13.6 10.7 0.20 0.05 0.05 0.02 - rest 18.5

The alloys W and X contain only 3.5 and 3.1% cobalt, respectively, while in terms of high Strength and hardness should have at least 7% cobalt. The alloys Y and Z have a Nickel equivalents of only 18.7 and 18.5 respectively, but should have a nickel equivalent of 19.5 to 20.

Ingots of alloys 1 to 5 and W to Z were hot-forged and hot-rolled to form blanks of 12.5 mm thickness and then cold-rolled to form sheets of 2.5 mm thickness. The sheets were annealed for 1 hour at 1065 ^° C. and cooled in air to room temperature. In this state, the structure of alloys 1 to 5 consisted of at least 90% austenite, up to 10% martensite and possibly also up to 1% delta ferrite.

The sheets were then plastically deformed by rolling at room temperature, the decrease in thickness being 40%. The rolling took place in several passes with intermediate cooling to room temperature. The rolled sheets, the structure of which was martensitic and which had a thickness of 1.5 mm, were ^{cured at 427 °} C. for 24 hours.

Claims (4)

The mechanical properties of the cured samples are shown in the table below. 0.2% - Tabel III relationship Stretch limit the tensile strength Train-
fpCtlfT- Notch pull in the notched kg / mm ^a XCo LlJJ
I ^ ~ «4- strength and unnotched tion 170.9 KCiL State 188.5 kg / mm ² kg / mm ² 1.00 1 189.8 171.5 171.5 1.00 2 176.3 189.0 189.8 0.99 3 178.1 189.8 187.5 1.10 4th 162.2 176.3 194.7 0.98 5 157.4 178.1 175.8 1.02 W. 154.0 166.0 169.3 1.06 X 156.8 158.1 168.0 1.09 Y 154.0 168.0 0.99 Z 156.8 155.2 The increase in strength caused by the hardening results from the test results of samples of alloy 5, which were examined ^{in the cold-rolled state and after annealing at 482 and 538 ° C. for 24 hours.} The test results are listed in Table IV, in which the test results of the heat treatment at 427 ^° C. from Table III are also listed for the purpose of comparison. Table IV tensile strenght
kg / mm ² temperature
⁰ C 0.2 »/" -
Stretch limit
kg / mm ² 147.0
178.1
155.2
123.8 Rolling temperature
427
482
538 143.3
178.1
151.9
116.8 0.15% carbon, 0.005 to 0.1% nitrogen, 0 to 5% molybdenum, up to 0.15% silicon, remainder Iron and impurities caused by the melting process, with a nickel equivalent according to the formula (% Ni) + 0.68 (% Cr) + 0.55 (% Mn) + 0.45 (% Si) + 27 (% C +% N)
+ 0.2 (% Co) + (% Mo) from 19.5 to 22, which is brought to a structure with 60 to 99% martensite, remainder austenite by cold working and ^{is hardened at 400 to 455 0} C with a holding time of 1 to 48 hours, as a material for objects that, like Thin and heavy plates, strips, billets, steel bars, pipes, wire, forgings, extruded, stamped and pressed pieces, couplings, pressure vessels, barrels, wheel spokes, bolts, rivets, screws, knives, surgical instruments, dental tools, saws and chisels , must have a 0.2% yield strength of over 165 kg / mm ² and a tensile strength ratio in the notched and unnotched state of at least 0.95. 2. Use of a steel according to claim 1, consisting of 4.5 to 5.5% nickel, 14.5 to 16% Chromium, 7.5 to 10% cobalt, 0.01 to 0.5% manganese 0.04 to 0.09% carbon, 0.01 to 0.05% Nitrogen, up to 0.1% silicon, the remainder iron and impurities caused by the melting process, its Nickel equivalent is 20 to 21 for the purpose of claim 1. 3. Use of a steel according to claims 1 and 2, which is in the temperature range of -15 to 38 ° C with a cross-section reduction of 20 to 50% has been cold-worked for Purpose according to claim 1. 4. Use of a steel according to claims 1 to 3, the with a decrease in cross section has been cold worked by at least 30% for the purpose of claim 1. Claims: _{Publications considered} : 1. Using a Stainless Steel Alloy, U.S. Patent No. 2,553,330; consisting of 3 to 8% nickel, 12 to 17% chromium, E. Houdremont, manual of special steel 7 to 13% cobalt, 0.01 to 1% manganese, 0.01 to ₄ o künde, 1956, Volume I, pp. 652 to 653 and 708 ff. 609 749/333 12.56 © Bundesdruckerei Berlin