DE3038193A1 - UNMAGNETIC STEEL FOR DEVICES USED AT EXTREMELY LOW TEMPERATURES AND IN HIGH MAGNETIC FIELDS - Google Patents

Description

Dr. rer. near Horst pupil PATENT ADVOCATE

6000 Frankfurt / Main 1 October 8, 1989 ο Kafoerstrqsse 41 Dr.HS / ki Telephone (0611) 235555 Telex: 04-16759 mapat d

Postal check account ι 282420-602 Frankfurt / M.

Bank account «225/0389

Deutsche Bank AG, Frankfurt / M.

J / 2152

Claimed priority

December 10, 1979, Japan, Patent Application No. 1 59109/1

Applicant: THE JAPAN STEEL WORKS, LTD. No. 1-2, Yurakucho 1-chome, Chiyoda-ku, Tokyo, Japan

Non-magnetic steel for devices used at extremely low temperatures and in high magnetic fields will.

The present invention relates to non-magnetic steel having good austenite stability, excellent strength, toughness and ductility or ductility at extremely low temperature without adding nickel.

The recent technological development in the field of core

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fusion reactors, magnetically suspended or levitated vehicles, superconducting generators or superconducting Motors is quite remarkable. In these devices, the superconducting conductors must close to an extremely low temperature that of the liquid helium (4.2 ° K) are cooled to the superconducting effect to produce, and their peripheral support structures are necessarily at extremely low temperatures used. The materials for these devices must be non-magnetic as they are used in a high magnetic field be, and their non-magnetic property should not be through

athermal martensite transformation or through deformation stress induced martensite transformation caused by plastic deformation during manufacture or during use will be lost.

Although austenitic rust-resistant steels such as SUS 304 and SUS 316 of the Japanese industrial standards, conventionally are used, have excellent toughness and ductility or ductility at low temperatures Austenite is unstable and easily subject to deformation induced Martensite transformation when subjected to plastic deformation at low temperatures and loses its Property of being non-magnetic. In addition, these austenitic rust-resistant steels contain a great deal of expensive Nickel, and its yield strength or yield strength increases only slightly even when it is cooled to an extremely low temperature which indicates their disadvantages in both economic and technical terms.

The object of the present invention is to provide an economical and new non-magnetic steel for devices that are used at extremely low temperatures and in high magnetic fields should, with high performance in terms of strength, low-temperature toughness and austenite stability which mainly contains manganese, chromium and nitrogen as alloying elements.

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The further properties and objects of the present invention are better understood from the detailed description, which is given below with reference to the accompanying drawings.

In the drawings show:

Figure 1 is a graph showing the influence of the carbon content on the tensile strength properties at room temperature and at -196 ° C of 35% Mn-7% Cr-O, 1% N-steel shows which has been subjected to a solution heat treatment after hot rolling;

Figure 2 is a graph showing the influence of the manganese content on the tensile strength properties at room temperature and at -196 ° C of 0.1% O7% Cr-0.16% N-steel shows which has been subjected to a solution heat treatment after hot rolling;

FIG. 3 shows the influence of the chromium content on the tensile strength properties at room temperature and at -196 ° C from 0.1% C-3O% Mn-O, 16% N-steel, which after hot rolling has been subjected to a solution heat treatment;

FIG. 4 shows the influence of the chromium content on the energy absorbed in a 2 mm V-notch of a Charpy sample with a pointed notch at ⁰ ° C. and -196 ° C. of 0.1% C-30% Mn-O, 16% N steel, the has been subjected to a solution heat treatment after hot rolling;

FIG. 5 shows the influence of the nitrogen content on the tensile strength properties at room temperature and at -196 ° C from 0.1% C-35% Mn-7% Cr - steel, made after hot rolling has been subjected to a solution heat treatment, and

FIG. 6 shows the influence of the nitrogen content on the energy absorbed in a 2 mm V-notch of a Charpy sample with a pointed notch at ⁰ ° C. and -196 ° C. of (0.1-0.3)% C-35% Mn-7% -Cr

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Steels that have undergone a solution heat treatment after hot rolling have been subjected.

Through various experiments and studies, the inventors have completed the present invention. The invention will now be explained in more detail below. Nickel, manganese, copper, carbon and nitrogen are known as austenite-forming elements; Of these elements, nickel and copper have the disadvantage that the former is very expensive and the latter has noticeably adverse effects on hot processability. Chrome is a Ferrite-forming element, however, is known for its stabilizing effect on austenite.

Therefore, the chemical composition range in which no delta ferrite is formed in the solidification stage has become the chemical composition range and stable austenite, first sought for steel, supplies manganese, carbon, nitrogen and chromium, but not nickel contains. And then the influences of these elements on the mechanical properties at low temperatures within examined this area. As a result of these studies, the inventors found a non-magnetic steel which possesses good austenite stability, excellent toughness, ductility and ductility, and strength at low temperature.

The chemical composition range for the non-magnetic steel according to the present invention is as follows:

C 0.08 - 0.45% N 0.08 - 0.30%

Si 1.0% or less Ni 0.5% or less

Mn 27-45% Mo 0.5% or less

Cr 4 - 13%

Remainder Fe and unavoidable impurities.

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The percentages given are all% by weight, and this also applies throughout the following description.

The reasons for such a limitation of the range in the steels according to the invention are discussed below.

(1) Carbon: 0.08 to 0.45%

Carbon is a strong austenite-forming element and noticeably strengthens the steel. An excess should be added, however be avoided because of the deterioration in toughness and deformability or ductility at low temperatures.

FIG. 1 is a graph showing the influence of the carbon content on the tensile strength properties at room temperature and at -196 ° C. of 35% Mn-7% Cr-O, 10% N steel which has been subjected to a solution heat treatment after hot rolling. Both at room temperature and at -196 ° C, the 0.2% proof yield point and the tensile strength increase when the carbon content is increased. On the other hand, the elongation at break tends to increase simultaneously with increasing carbon content at room temperature, whereas at -196 C the deformability and toughness are clearly reduced due to grain boundary precipitation of chromium carbide (Cr 1, C _β ) when the carbon content exceeds 0.45%.

For these reasons stated, the upper limit of carbon became content indicated at 0.45%. On the other hand, the lower limit of the carbon content has been set in view of requirements regarding the strength and the equilibrium with the N-content, to which reference will be made later, at 0.08% set.

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(2) Silicon: 1.0% or less

Silicon is necessary as a deoxidation element Refining steel. Since its addition in excess of 1.0% the toughness and ductility or ductility of steel and stability of austenite deteriorated, became the above Limit set to 1.0%. No lower limit is specifically specified.

(3) Manganese: 27-45%

Manganese is a typical austenite-forming element together with nickel. One of the characteristics of the steel according to the invention is that it does not contain the expensive nickel, and austenite is fully stabilized and is stabilized by adding a large amount of manganese that the carbon content and the nitrogen content affect the toughness and deteriorate deformability or ductility at low temperatures, adjusted to the lowest possible values will. Figure 2 is a graph showing the influence of Mn content on tensile properties at room temperature and at -196 ° C from 0.10% C-7% Cr-0.16% N - steel shows which has been subjected to a solution heat treatment after hot rolling. At room temperature, the 0.2% changes The proof elongation limit hardly correlates with the Mn content, whereas the tensile strength is decreased as the Mn content increases. The elongation at break is at most in the vicinity of a 30% Mn content. At -196 ° C, the 0.2% proof yield strength improves simultaneously with the Mn content and reaches a plateau at 25%. the Tensile strength similarly increases up to 25% Mn content, but tends to decrease when the Mn content exceeds 25%. The elongation at break at -196 ° C increases within the range of 25% to 30% Mn content and decreases slightly when the Mn content rises above 30%. With regard to the stability for austenite, the permeability μ of steels with Mn contents increases of 20% and 25% by the magnetic martensite transformation during the tensile deformation at -196 ° C. However, there will be no increase in permeability at the fracture surface of the elongation

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_ 9 samples observed at -196 ° C with an Mn content of over 30%.

Because of these reasons stated, the Mn content range became given as 27 to 45%.

(4) Chromium: 4 to 13%

Chromium is a ferrite-forming element, but it also acts to stabilize and harden austenite when appropriate Amount is added to a steel that contains a large part of manganese. Figure 3 shows the influence of the Cr content on the tensile properties at room temperature and at. -196 ° C from 0.10% C-30% Mn-0.16% N - steel made after hot rolling had been subjected to a solution heat treatment. The 0.2% proof stress increases slightly with the Cr at room temperature and at -196 ° C. The Cr content hardly affects the tensile strength at room temperature but at -196 ° C, the tensile strength increases steeply with the increase of Cr up to 5%, after which the slope of the curve becomes smaller.

Although the elongation at break hardly changes at room temperature by changing the Cr content up to 10%, it starts with a Cr content exceeding 10%. In contrast in addition, the elongation at break rises steeply at -196 ° C with the increase in the Cr content from 0 to 5% and tends to be slightly with a Cr content of 5% or more.

FIG. 4 shows the influence of the Cr content on the energy absorbed in a 2 mm V-notch of a Charpy sample with a pointed notch at ⁰ ° C. and −196 ° C. of 0.10% C-30% Mn-0.16% N - steel which has been subjected to a solution heat treatment after hot rolling. At 0OC, the Charpy absorbed energy decreases as the Cr content increases, while the Charpy absorbed energy peaks at -196 ° C in the range of 5 to 10% chromium.

However, these trends change depending on the Mn content and the low-temperature toughness of the steel with an Mn content im Range from 27 to 45% drops rapidly when the Cr content

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- 10 exceeds 13%.

For the reasons given, the Cr content in the present invention becomes Steel set at 4 to 13%.

(b) nitrogen: 0.08 to 0.30%

Nitrogen is both a strong austenite-forming element and a strong strengthening element. Compared to carbon Undesirable influences on mechanical properties such as precipitation of carbide at grain boundaries occur much less often. As can also be clearly seen from the comparison of FIG. 1 and FIG. 5, the contribution to strength per is more identical Addition amount (wt .-%), in particular for 0.2% proof stress, about the same as carbon at room temperature, but three times larger than carbon at -196 ° C. thats why the addition of nitrogen is quite effective in strengthening the steel without deteriorating toughness. Excessive addition will however, lead to a deterioration in toughness and deformability or ductility, in particular at low temperatures, and should therefore be avoided.

FIG. 5 shows the influence of the nitrogen content on the tensile strength properties at room temperature and at -196 ° C from 0.1% C-35% Mn-7% Cr - steel which, after hot rolling, undergoes a solution heat treatment has been subjected. The changes in tensile properties caused by N increase show the same tendencies at room temperature and at -196 C. In other words, the increase in the N content is accompanied by an increase in the 0.2% proof yield point and the tensile strength, while the elongation at break is lowered. When the influences of nitrogen on strength at room temperature and at -196 ° C are compared, it will be found that nitrogen has a strengthening effect that three to four times at -196 ° C is greater than at room temperature.

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FIG. 6 shows the influence of the N content on the energy absorbed in a 2 mm V-notch of a Charpy sample with a pointed notch at ⁰ ° C. and −196 ° C. of (0.1 to 0.3)% C-35% Mn -7% Cr - steels which have been subjected to a solution heat treatment after hot rolling. At ⁰ ° C., the influence of the N content on the Charpy absorbed energy is not so pronounced, while the Charpy absorbed energy hardly changes at -196 ° C. with the N content up to 0.15%, but the curve does is inclined downward when the N content exceeds 0.15%.

In this way, it was decided that the N content should be in the range of 0.08 to 0.30% for the steel of the present invention Should be adjusted in view of its balance with the carbon content and the strength and toughness.

(6) Nickel: 0.5% or less

Nickel is a highly austenite-forming element, but it is very expensive. Since in the steel according to the invention, the addition of Ni does not show any noticeable effects up to 10%, no Ni addition is made. However, the upper limit was set to 0.5% discontinued taking into account the possibility of nickel entering the steel from scrap or scrap could.

(7) Molybdenum: less than 0.5%

Molybdenum works in such a way that it stabilizes and strengthens the austenitic phase, but it has toughness and ductility or ductility worsened. It's even more expensive than nickel. Although Mo is not usually added to the steel according to the invention is because a sufficiently stable austenitic phase and sufficient strength by the combination of the other Elements can be achieved, the upper limit has been set for reasons similar to those given for nickel, with 0.5% stated.

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The chemical composition of the steel according to the invention was based on the overall assessment of the test results and off determined for the reasons given.

The properties of the steel according to the invention will now be explained in more detail by referring to examples. Table 1 shows the chemical compositions of the materials tested. The materials used for comparison are austenitic stainless steels SUS 304 and 316 and austenitic steel ASTM A-240 Type xM31 Mn-Cr-N.

Table 2 shows the tensile strength properties at room temperature, -196 ° C and -269 ° C (4 ° K) and the magnetic permeability near the broken parts of the tensile or tensile specimens. The tensile strength properties at room temperature of the steel of the invention are about the same as those of the austenitic stainless steel. A-240 type xM31 steel has an extremely high 0.2% proof stress limit, which is about twice is as big as that of other materials. At -196 ° C, the 0.2% proof stress of the steel according to the invention increases to about

2
70 kg / mm and the elongation at break only decreases slightly. Even at -269 ° C, the elongation at break and the reduction in cross-section at break of more than 45% are retained. On the other hand, SUS 304 shows only a very small increase in the 0.2% proof stress limit with decreasing temperature. The 0.2% proof stress of SUS 316 steel is at -196 ° C approximately in the middle between that of the steel according to the invention and that of SUS 304 steel. In the case of A-240-Type xM31 steel, the 0.2% proof stress is extremely high, but its elongation at break and reduction in cross-section are remarkably low. The magnetic permeability of the steels according to the invention near the point of fracture of the fractured strain or tensile test specimens at -269 ° C. is very low, that is to say 1.001, and from this it can be seen that the austenite is very stable. The permeability of SUS 304 steel increases even through deformation at room temperature, while SUS 316

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Steel is comparatively stable at room temperature. The magnetic However, permeability of the latter steel increases when it is deformed at ~ 196 ° C. Owns A-240 type xM31 steel comparatively stable austenite, but it is deficient in that it has ductility or ductility noticeably lower temperatures, as already mentioned.

Table 3 shows test results of 2 mm V-notch in Charpy pointed notch impact tests at 0 to -196 ° C. In this table, numbers in brackets denote near magnetic permeability the fracture surface of Charpy specimens. The low-temperature deformability or ductility of the steel of the invention is about the same as that of austenitic rust-resistant Steels SUS 304 and 316. A-240 type xM31 steel shows stable Austenite structure, but the impact strength decreases noticeably as the temperature drops.

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Table 1: Chemical composition of the tested materials.

stole

Si

Chemical composition (% by weight)

Mn

Ni

Cr

Cu

Mon

according to A 0.10 0.50 39.5 steel B 0.19 0.59 36.6 C 0.11 0.50 31.3

0 , 020 O, 004 0 , 018 O, 010 0 , 019 O, 005

6, 79 0 , 07 0, 155 6, 90 0 / 12 - ο. 103 6, 89 0 , 11 0, 161

SUS 304 0.036 0.54 1.19 0.020 0.009 10.02 18.42

0.08

SUS

0.039 0.53 1.13 0.018

0.009 12.00 16.62 0.10 2.46

A24O type xM31

0.09 0.63 15.6 0.030

17.11 0.09

0.427

O OO CD

Table 2: Results of the tensile strength tests.

stole

Test temperature

Tensile strength properties

0.2% test tensile strength fracture cross-sectional yield strength elongation reduction (kg / mm ² ) (kg / mm ² ) (%) (%)

Magnetic permeability near the break point (at 100 mOe)

inventions, Raumtempedungs- temperature
according to

27.5

57.2

66.5

ßer

• 196 ° C

69.4

113.7

_o Steel room temperature 29.6

61.0

-196 ° C

72.0

117.2

-269 ° C

93.3

155.5

Room temperature 26.6

59.8

-196 ° C

71.6

123.9

A 240 room temperature 48.5 type xM31

120.0

84.1

-196 ° C

155.7

57.2

77.4

65.1

57.6

73.1

53.3

69.4

6.2

1.001

1.001

1, 001

1.001

1.001

1.001

1.001

304 -269 C 95.4 159.1 51.7 49.5 1, 001 SWEET Room temperature 20.7 57.1 65.2 72.4 1.28 316 -196 ° C 31.5 145.5 41.2 51.6 3.60 SUS Room temperature 22.9 57.8 60.1 70.4 1.015 -196 ° C 54.1 135.6 51.1 56.5 3.52

1, 001

1, 016

ui I

Table 3: 2min V Charpy Pointed Notch Test Results

stole SuS 304 2 mm V-Charpy absorbed energy -50 ° C -10O ° C (kg.m) 1) -196 ° C SUS 316 Test temperature 17.8
001) 16.2
(1.001) 12.3
(1.001) invent _&
manic A24O-
Type XM31 O ° C 19.6
001) 20.3
(1.001) -150 ° C 14.4
(1.001) - » more appropriate
Steel ^B 17.4
(1.001) (1, 20.1
001) 17.9
(1.001) 14.7
. (1.001) 14.3
(1.001) 3002 C. 21.6
(1.001) Π, 16.1
.46) 15.4
(1.82) 16.9
(1.001) 14.3
(2.00) ' ο 21.8
(1.001) (1, 16.4
016) 15.3
(1.18) 15.0 '
(1.001) 13.1
(1.44) 16.8
(1.11) (1 10.8
001) 6.9
(1.001) 16.2
(1.94) 1.9
(1.001) 17.3
(1.003) (1, 15.7
(1.30) 14.2
(1.001) (1, 4.0
(1.001)

Note: (1) Average of two samples

(2) Numbers in brackets indicate magnetic permeability near the Fracture surface (at 100 mOe).

OD

CD

As has already been stated, it is very clear that that the steel according to the present invention has excellent properties in terms of (1) strength, (2) low temperature toughness and (3) austenite stability compared to conventional austenitic stainless steels and Mn-Cr-N austenitic steel. In addition, the steel according to the present invention is weldable and it is not necessary to to add expensive elements such as nickel, molybdenum, etc., and its workability is quite excellent in manufacture.

It is possible to use the steel according to the invention not only for To use devices that are intended to be used at extremely low temperatures and in high magnetic fields, but also Use it for many devices that operate at low temperatures from room temperature to extremely low temperatures should be used. Regarding the future prospects for diminishing nickel and molybdenum sources and the consequent rise in prices for these substances must take advantage of the present invention, which is plentiful Dimensionally available, cheap manganese used will be appreciated.

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Claims (2)

Applicant; THE JAPAN STEEL WORKS, LTD. No. 1-2, Yurakucho 1-chome, Chiyoda-ku, Tokyo, Japan claims 1. Non-magnetic steel for devices that operate at extremely deep Temperatures and should be used in high magnetic fields, 'characterized that it, expressed in percent by weight, 0.08 to 0.45% carbon, 1.0% or less silicon, 27 to 45% manganese, 4 to 13% chromium, 0.08 to 0.30% nitrogen, 0.5% or less nickel, 0.5% or less molybdenum and the remainder iron and Fe includes unavoidable impurities and the austenite is extremely stable at extreme temperatures down to 4 K and that it is excellent in strength, toughness and ductility or ductility at low temperature having. 2. Non-magnetic steel for devices that are used at extremely low temperatures and in high magnetic fields 130024/0691 ORIGINAL INSPEClED should be det, according to claim 1, characterized in that it, expressed in Weight percent, 0.08 to 0.25% carbon, 0.2 to 0.8% silicon, 30.0 to 40.0% manganese, 5.0 to 10.0% Chromium, 0.08-0.20% nitrogen and the remainder iron comprises Fe and unavoidable impurities. 130024/0691