FR2691982A1 - Stainless steel composition for parts used in high vacuum and low temperature. - Google Patents

Abstract

Stainless steel composition containing from 19 to 22 % by weight of chromium, from 8 to 11 % by weight of nickel, from 2.50 to 4.25 % by weight of manganese, from 2.00 to 3.00 % by weight of molybdenum, from 0.25 to 0.80 % by weight of niobium, from 0.35 to 0.50 % by weight of nitrogen, up to 0.08 % by weight of carbon, up to 0.75 % of silicon, up to 0.025 % by weight of phosphorus, up to 0.01 % by weight of sulphur, the remainder being iron and possible impurities, which has undergone refining in an AOD reactor and optionally remelting under slag. Such a composition makes it possible to produce articles which, after heat treatment and optional work-hardening, exhibit mechanical characteristics, sealing properties and an amagnetism enabling them to be employed in ultravacuum and at very low temperature.

Description

The invention relates to a composition of stainless steel for parts

  ultraviolet and low temperature, having in particular properties

  mechanical, increased water resistance and amagnetism.

  The realization of elementary particle analysis facilities in particular requires the use of stainless steels having the following properties: sealing through the parts because of the pressure difference that exists between the vacuum chamber (more than 10-1 torr, 1.33 10 -Ep> and outside atmospheric pressure, sealing of knife-type joints during seamless joints in the presence of the same pressure difference, mechanical properties both in resistance to traction in toughness up to very low temperatures up to 1.8 K amagnetism up to 1.8 K so as not to disturb

the path of the particles.

  In addition, it is necessary that the stainless steel can withstand, without altering the above properties, the degassing treatment at 950 'C that some users must make him undergo in a few

applications.

  Until now, the most common solution was to use the grade E-Z 2 CND 17 13 + Az having the following nominal composition by weight Carbon 0.03 Chromium 17.00 Nickel 14.00 Molybdenum 2.80 Nitrogen 0.15 Iron Complement

  and having typical properties which will be given below

  after. However, it has now been found that even improved properties are obtained by using a stainless steel composition with a high nitrogen content.

  and containing niobium and manganese.

  According to the invention, a stainless steel having a composition within the following limits is used.% By weight Carbon up to 0.08 Chromium 19 22 Nickel 8 11 Manganese 2.50 4.25 Molybdenum 2.00 3.00 Silicon up to to 0.75 Phosphorus up to 0.025 Sulfur up to 0.01 Niobium 0.25 0.80

Nitrogen 0.35 0.50.

  Iron Complement The nitrogen content gives steel two essential properties: a stable austenitic phase & low temperature, which makes it possible to preserve non magnetism in cryogenic condition. high mechanical characteristics in a wide temperature range including in the field

cryogenic.

  The addition of manganese is necessary to ensure

  the solubility of such a nitrogen content.

  The addition of nobium serves to stabilize the carbon and consequently reinforces the corrosion resistance. This addition improves the heat resistance of the grade and reinforces, indirectly, by refining the grain the limit.

elastic at low temperature.

  The steels according to the present invention are conventionally obtained by elaboration in an arc furnace and then undergo refining by the AOD process (also called "AOD reactor refining") ("argon oxygen decarburization", argon-oxygen decarburization). ) which makes it possible to obtain without difficulty the low content of

sought carbon.

  In order to reduce the content of inclusions, the steel obtained can be subjected to slag remelting, in particular when it is desired to produce with the composition thin walls and knife-type seals. Indeed, the low inclusion content guarantees superior sealing. This treatment is

however not required.

  The parts prepared from a composition according to the present invention undergo a heat treatment at a temperature of 1000 ° C. under cooling in air, oil or water depending on the size of the pieces,

to give a hyper-tempered state.

  It is also possible, after the quenching, to temper at room temperature by rolling.

drawing or drawing.

  Table 1 below groups together a number of strength measurements made by three laboratories on steel bars according to the present invention. The specific composition of the steel used for the production of the test bars is as follows: Bar O 31.75 0 12 O 12 0 45 hyper-hardened hyper-tempered hardened high-tempered carbon 0.033 O 035 0.02? 0.035 Chromium 20.89 20.69 20.10 20.69 Nickel 9.22 9.73 9.09 9.73 Manganese 4.14 3.92 4.00 3.92 Molybdenum 2.10 2.14 2, 10 2.14 Silicon 0.36 0.42 0.37 0.42 Phosphorus 0.022 0.021 0.021 0.021 Sulfur <0.002 <0.002 <0.002 <0.002 Niobium 0.32 0.30 0.30 0.30 Nitrogen 0.42 0.427 0.419 0.427 We note in the compositions traces of impurities

  such as aluminum, copper and cobalt.

TABLE 1

  bar I. Thermal state i super-tempered _

labora-

Temperature area

300 K 1 71 K (*) | 2 & K 1 1.8 K K

  Rm M Pa Rp 0.2% M Pa 41.6 E G Pa l Rm M Pa I Rp 0.2% M Pa

1663 1114

  E G Pa Rm M Pa Rp 0.2% M Pa E G Pa F. Rm M Pa I

Rp 0.2%.

  M Pa 31.75 hyper-tempered 3 942 605 45 210.3 1768 1325 42 187.2 2048 1700 26 204.3 187.2

1828 1345 32 2057 1700 22 217.6

  12 hyper-tempered 2 1007 587 39.6 1954 1374 19.4 2426 2300 1.5

2 1007 595 39.6 1984 1404 18.3 _ _

1 1125 887 21

  12 hardened 2 1060 990 24 1981 1804 18.4

2 1079 1008 '26, 4 1981 1804 16.6

12.5 t hardened I

1088 863

  26 189 | 1942 1597 l 20.5 | 198.7 13.3, 5 I I

(O 3 H

  average hyper-tempered value 650 320 50 1350 700 40 1480 790 28 R typical lm C \ Rm = nresistance Rp = yield strength Ao = elongation E = modulus of elasticity (*) for Labo 2 the test temperature is uncontrolled and presumably close The results obtained clearly show that it is possible to obtain, with the steels in question, from 95/100 K K (OD (.alpha..sub.0) .sub.p). both in the quenched and quenched state, mechanical characteristics Rm and Rp 0.2% high, while maintaining a sufficient ductility In this respect, it will be noted that for applications at temperatures of less than or equal to 20 K, It is not advisable to start from a previously hardened steel, because the results above show that the gain on the elastic limit and the breaking load is low, whereas the ductility is

significantly degraded.

  The rate of hardening that one applies possibly depends on the mechanical characteristics that one wishes to obtain and the single figure shows the evolution of the mechanical characteristics Rm and

  Rp 0.2% depending on the rate of work hardening.

  Table 2 below gives results concerning the magnetic susceptibility of a steel

  stainless according to the present invention.

TABLE 2

  H 0.005 oe 1000 oe Magnetic susceptibility to 1.8 K 5 10-a 5 10-3 The material is therefore classified as non-magnetic at the temperature of 1.8 K. It is thus seen that the stainless steel compositions according to the present invention give parts having mechanical characteristics and non-magnetic properties which make them particularly suitable for the realization of ultrahigh and / or very low temperature installations; they find a particular application in the systems of analysis of the elementary particles and the realization

cryogenic engines.

Claims (3)

  1. Stainless steel composition containing from 19 to 22% by weight of chromium, from 8 to 11% by weight of nickel, from 2.50 to 4.25% by weight of manganese, from 2.00 to 3.00 % by weight of molybdenum, from 0.25 to 0.80% by weight of niobium, from 0.35% to 0.50% by weight of nitrogen, up to 0.08% by weight of carbon, up to 0.75% of silicon, up to 0.025% by weight of phosphorus, up to 0.01% by weight of sulfur, the balance being iron and any impurities, having undergone refining in AOD reactor and   possibly a slag remelting.   2. Parts intended for the production of devices operating in ultra-high vacuum and at low temperature, obtained from the stainless steel composition according to claim 1, with a heat treatment & 1000-1100 ° C.   3. Parts according to claim 2, having undergone   hardening at room temperature.