JPS6227557A - High-mn nonmagnetic steel for very low temperature use excellent in electron beam weldability - Google Patents

Abstract

PURPOSE:To obtain a high-Mn nonmagnetic steel for very low temp. use for large-sized superconducting magnet excellent in electron beam weldability by incorporating specific percentage of C, Si, Mn, P, S, O, Ni, Cr and N to Fe. CONSTITUTION:The high-Mn nonmagnetic steel consisting of, by weight, 0.01-0.15% C, 0.01-1.50% Si, 10-30% Mn, <=0.03% P, <=0.01% S, <=0.0030% O, 0.5-1.5% Ni, 12-25% Cr, 0.10-0.28% N and the balance Fe with inevitable impurities and satisfying [(%Mn)-0.3(%Ni)+2.0(%Cr)]/(%N)X10<2>>=2.0 is prepared. This steel is excellent in electron beam weldability and has high strength and toughness at a joint at -269 deg.C and has superior magnetic properties as well, so that it is suitably used as large-sized superconducting magnet for nuclear fusion reactor, MHD generator equipment, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention provides a high-Mn alloy for cryogenic use with excellent electron beam weldability.
Regarding non-magnetic steel.

(Prior technology) Superconducting magnets used in nuclear fusion reactors, Ml(D power generation equipment, superconducting generators, etc.) are used at liquid helium temperatures (-269
℃), and is operated under harsh conditions in which high stress is applied repeatedly in a strong magnetic field.

Therefore, structural materials for supporting such superconducting magnets are required to have high strength, high toughness, and excellent magnetic properties at -269°C, and furthermore, since superconducting magnets are very large, Extra-thick steel plates are also used to support this. At the same time, the dimensional accuracy of the equipment is critical, so deformation during welding is required to be as small as possible.

Conventionally, SO3304L austenitic stainless nonmagnetic steel is known as a nonmagnetic steel for cryogenic use. These non-magnetic steels have excellent weldability, but in order to prevent hot cracking during welding, several percent of δ ferrite is generated in the weld metal, so the toughness deteriorates at extremely low temperatures. Alternatively, magnetic permeability increases. Furthermore, the yield strength of the base material and joint portion is 40 to 50 kgf at 1269°C.
/mm”, which is extremely low. On the other hand, 304LN has a value of 0.
It contains about 14% nitrogen and has excellent yield strength, but it has the fatal defect of being prone to blowholes during welding.

In addition, in the past, welding of extra-thick steel plates was done by hand, generally using TIG,
Although MIG welding and the like have been adopted, these methods require a large amount of time for welding work and a large amount of welding material, so they are inferior in workability and economy. Further, the supporting material of the superconducting magnet is largely deformed by the above-mentioned welding, so it requires straightening or a large amount of cutting after welding, resulting in high manufacturing costs. Furthermore, welded joints are also required to have high strength, high toughness, and low magnetic permeability.
As mentioned above, the austenitic stainless steel has problems in that δ ferrite is generated in the weld metal, which deteriorates toughness and increases magnetic permeability.

Therefore, in recent years, electron beam welding has been considered the most suitable welding method for fabricating support structure materials for superconducting magnets.On the other hand, the use of high Mn nonmagnetic steel has attracted attention as a steel material for this cryogenic application. There is. According to electron beam welding, even thick steel plates can be welded in one bus.
This is because welding materials are not required and furthermore, there is little deformation due to welding, so welding workability is dramatically improved and economical efficiency is also improved. Furthermore, since electron beam welding is welding in a vacuum, there is no penetration of oxygen into the weld metal, which has the advantage of high toughness.

(Objective of the Invention) The present invention has excellent electron beam weldability and a temperature of -269°C at the joint so that it can be suitably used, for example, as a structural material for supporting superconducting magnets as described above. The object of the present invention is to provide a high Mn nonmagnetic steel for cryogenic use that has high strength and toughness at high temperatures and has excellent magnetic properties.

(Structure of the Invention) High M for cryogenic use with excellent electron beam weldability according to the present invention
n Non-magnetic steel has, in weight percent, C 0.01 to 0.15%, Si 0.01 to 1.50%, Mn 10 to 30%, P 0.03% or less, S 0.01% or less, 0 0. 0.030% or less, contains 0.5-15% Ni, 12-25% Cr, and 0.10-0.28% N, and [(%
Mn)-0,3(%Ni)+2.0(%Cr)] /(
It is characterized by satisfying 2°0 over %N)×102, with the balance being iron and unavoidable impurities.

First, the reason for limiting the chemical components in the steel of the present invention will be explained.

C is an element effective in stabilizing and increasing the strength of austenite. Addition amount is 0. If it is less than oi%, the above effect will be poor; on the other hand, if it is added in excess of 0.15%, Cr carbide will be generated in the weld metal, impairing the toughness and corrosion resistance of the steel, and the welding Sometimes, it tends to react with 0 in steel and create blowholes, so the upper limit of the amount added is set to 0.
．． It shall be 15%.

St is necessary for deoxidation during steel making, and also increases the fluidity of molten steel during ingot making to reduce internal defects in steel ingots.
It has the effect of increasing the fluidity of weld metal during welding and preventing the occurrence of defects, and in order to effectively express this effect, 0
．． It is necessary to add 0.01% or more. However, 1
．． When added in a large amount exceeding 50%, it not only inhibits high-temperature ductility and reduces toughness, but also causes the fluidity of the weld metal to become excessively large during welding, causing defects such as blowholes. It becomes softer, so the amount added is 1゜50.
% or less.

Like C, Mn also has the effect of stabilizing austenite, improves toughness, and increases the solubility of N in the weld metal, which is effective in preventing the occurrence of defects such as blowholes. To be effective, addition of 16% or more is required.

However, when added in excess of 30%, hot workability deteriorates, and also promotes the formation of δ ferrite in the weld metal, deteriorating toughness and magnetic properties, so the amount of Mn added is The range shall be 30% or less.

Both P and S impair the hot workability and toughness of steel, and also promote hot cracking during welding. Therefore, in the steel of the present invention, it is preferable to suppress the content as much as possible, but in consideration of economic efficiency, the content is set to 0.03% or less for P and 0.01% or less for S.

The content of 0 causes oxide inclusions to be generated not only in the base metal but also in the weld metal, thereby degrading the toughness.

Figure 1 shows the relationship between the amount of O in the weld metal and Charpy absorbed energy (vE-g6.) at -269°C. As shown in the figure, the steel of the present invention has an amount of about 30
ppm or less, preferably about 20 ppm or less,
This is based on the new finding that Charpy absorbed energy increases significantly.

Since electron beam welding is welding in a vacuum, the amount of O in the weld metal does not become higher than that of the base metal, but rather tends to be reduced. Therefore, in the steel of the present invention, the O content in the base metal is 0.0030% or less, preferably 0.0030% or less. OO shall be 20% or less.

Ni is effective in stabilizing austenite and improving toughness, and furthermore, effectively suppresses the formation of δ ferrite in the weld metal. In order to effectively exhibit such effects, it is preferable to add at least 0.5%. However, when adding too much Ni, it not only lowers the solubility of N in the weld metal but also impairs economic efficiency, so the amount of Ni added is 0.5
-15% range.

Cr is an element that is effective in imparting rust resistance to steel and improving yield strength, and is also effective in increasing the solubility of N in the weld metal and preventing the occurrence of defects such as blowholes. In the steel of the invention it is necessary to add at least 12%. On the other hand, addition of a large amount exceeding 25%
Since δ ferrite is likely to be generated in the weld metal and deteriorates toughness and magnetic properties, the amount added should be in the range of 12 to 25%.

Like C, N is effective in stabilizing austenite and improving yield strength. C forms Cr carbides and impairs toughness and induction resistance, while N has no such deleterious effect. In order to effectively express the above effect, the content should be 0.10
% or more. However, when the content exceeds 0.28%, the toughness is significantly reduced.

In addition, defects such as blowholes are likely to occur in the weld metal.

Therefore, the N content is in the range of 0.10-0.28%.

As mentioned above, the steel of the present invention is a high-N steel, so in order to prevent defects such as blowholes during welding, Mn, Ni, Cr, and N must satisfy the following relationship. is necessary.

[(%Mn)-0.3(%Ni)+2.0(%Cr)]
%N) By suppressing the amount of these elements, the occurrence of blowholes during welding is prevented.On the other hand, Ni reduces the solubility of N, so it promotes the occurrence of blowholes.The present inventors therefore determined the amount of these elements added and As a result of extensive research on the influence of the amount of N on the occurrence of welding defects, we have found that when the above formula is satisfied, a joint free of welding defects can be obtained, as shown in FIG.

Furthermore, the steel of the present invention can contain at least one element selected from the group consisting of Nb5V% Ti and Al. All of these elements form carbonitrides and are effective in improving yield strength through precipitation strengthening. In order to effectively express this effect, at least one element must be added in a total amount of 0 to 1. It is necessary to add more than %. However, if the total amount added exceeds 0.50%, the amount of solid solution N in the weld metal will be reduced, resulting in a decrease in proof strength or destabilization of austenite, so the total amount added will be 0.50%. .50% or less.

The steel of the present invention also contains at least one element selected from the group consisting of Cu, MO, and W in a total amount of 0.01 to 2.0% in addition to or independently of the above-mentioned elements.
It can be contained within a range of 0.00%. All of these elements are effective in strengthening the austenite base and increasing its strength. However, when the total amount added is less than 0.01%, the above effect is poor;
If added in excess of 0.01 to 2.00%, the hot workability and toughness of the steel will deteriorate.
The range shall be .

Furthermore, the steel of the present invention contains at least one element selected from the group consisting of Ca, Ce, and Zr in a total amount of 0.001 to 0.050%, either together with the above-mentioned elements or independently. You may. All of these elements improve the toughness of steel by cleaning the steel, making inclusions finer, and spheroidizing them by reducing O content, etc. , = ft
If the total amount is less than 0.001%, the above effect cannot be obtained effectively; on the other hand, if the total amount is less than 0.050%
Addition of an excessive amount exceeding % will actually deteriorate the cleanliness of the steel and the toughness of the steel.

(Effects of the invention) As described above, the steel of the present invention is a high Mn nonmagnetic steel.
In particular, while regulating the amount of zero, Mn and Cr, which are effective in preventing the generation of blowholes during welding, and Ni, which promotes the generation of blowholes, are added in a certain relationship to N.
In this way, it is possible to obtain a high-Mn nonmagnetic steel for cryogenic use that is high in strength and toughness by increasing the N content and has excellent electron beam weldability without blowholes.

(Examples) The present invention will be described below with reference to Examples, but the present invention is not limited to these Examples in any way.

Examples wJl of the present invention having the chemical composition typically shown in Table 1
4 and comparative steels 5 to 8, [(%Mn)-0,3(
%Ni)+2.0(χCr)] and (%N)×1
The relationship between 02 and the presence or absence of contact defects is shown in FIG.

Next, the inventive steels A-D and comparative ME-1 having the chemical components shown in Table 2 are melted by air melting or vacuum melting to form steel ingots or slabs, which are then forged and then hot rolled. A steel plate having the predetermined thickness shown in the table was obtained. The tensile properties, V Charpy absorbed energy (VE-269) at -269°C and magnetic permeability at -269°C of each steel plate are shown in the table. These steel plates were subjected to horizontal electron beam welding, and the o
1 and VB-269 of the weld metal were determined. The results are shown in Table 2.

Next, the inventive steel A-D and the comparative steel E-1 are melted in vacuum to form a steel ingot or slab, forged, and then hot rolled to form a steel plate with a predetermined thickness shown in the table. Obtained.

This W4 plate was subjected to horizontal electron beam welding,
The presence or absence of welding defects was investigated using a ray transmission test. The results are shown in Table 2.

All comparison steels had an O content of 0. More than OO30%,
Furthermore, comparative steel E has a significantly lower amount of N, and comparative steel E
and F is low Mnfi. Therefore, comparative steel E has a significantly low base metal yield strength, and VE-269 also has a low yield strength.

Comparative steel F is a low Mn steel, [(%Mn)-0,3(%
Ni)+2.0(%Cr)] /(%N)×102 (
Hereinafter referred to as A value. ) is 1.8, and on the other hand, comparative steel G has a low N1f4 and an A value of 1.7, so welding defects (blowholes) occur in both cases. Comparative iH and I have a particularly large amount of O, so although the A value exceeds 0.20, vE-zb. is small.

Compared to these comparative steels, it is clear that the steel of the present invention not only has superior base metal properties but also superior electron beam weldability.

[Brief explanation of drawings]

Figure 1 shows the amount of oxygen in the weld metal and the temperature of the weld metal at 269°C.
V Charpy absorbed energy in (SiB-249)
FIG. 2 is a graph showing the relationship between chemical components and the presence or absence of welding defects in electron beam welding. Patent Applicant Kobe Steel Co., Ltd. Agent Patent Attorney Ittsu Makino Department Figure 2 Procedural Amendment (Voluntary) September 4, 1985

Claims (8)

[Claims] (1) C0.01-0.15% by weight, Si0.01-1.50%, Mn10-30%, P0.03% or less, S0.01% or less, O0.0030% or less, Ni0.5 -15%, 12-25% Cr, and 0.10-0.28% N, and [(%Mn)-0.3(%Ni)+2.0(%Cr)]
/ (%N) (2) In weight% (a) C 0.01-0.15%, Si 0.01-1.50%, Mn 10-30%, P 0.03% or less, S 0.01% or less, O 0.0030% or less, Contains 0.5-15% Ni, 12-25% Cr, and 0.10-0.28% N, and (b) N
Contains 0.01 to 0.50% in total of at least one element selected from the group consisting of b, V, Ti and Al,
And [(%Mn)-0.3(%Ni)+2.0(%Cr)]
/ (%N) (3) In weight% (a) C 0.01-0.15%, Si 0.01-1.50%, Mn 10-30%, P 0.03% or less, S 0.01% or less, O 0.0030% or less, Contains 0.5-15% Ni, 12-25% Cr, and 0.10-0.28% N, and (b) Cu
, Mo and W in a total amount of 0.01 to 2.00%, and [(%Mn)-0.3(%Ni)+2.0(% Cr)]
/(%N)×10^2≧2.0, and the balance is iron and unavoidable impurities. A high Mn nonmagnetic steel for cryogenic use with excellent electron beam weldability. (4) In weight% (a) C 0.01-0.15%, Si 0.01-1.50%, Mn 10-30%, P 0.03% or less, S 0.01% or less, O 0.0030% or less, Contains 0.5-15% Ni, 12-25% Cr, and 0.10-0.28% N, and (b) Ca
, Ce and Zr in a total amount of 0.001 to 0.050%, and [(%Mn)-0.3(%Ni)+2.0(% Cr)]
/(%N)×10^2≧2.0, and the balance is iron and unavoidable impurities. A high Mn nonmagnetic steel for cryogenic use with excellent electron beam weldability. (5) In weight% (a) C 0.01-0.15%, Si 0.01-1.50%, Mn 10-30%, P 0.03% or less, S 0.01% or less, O 0.0030% or less, Contains 0.5-15% Ni, 12-25% Cr, and 0.10-0.28% N, and (b) Nb
, at least one element selected from the group consisting of V, Ti, and Al in a total amount of 0.01 to 0.50%, and (c) at least one element selected from the group consisting of Cu, Mo, and W. 0.01 to 2.00% in total amount, and [(%Mn)-0.3(%Ni)+2.0(%Cr)]
/(%N)×10^2≧2.0, and the balance is iron and unavoidable impurities. A high Mn nonmagnetic steel for cryogenic use with excellent electron beam weldability. (6) In weight% (a) C 0.01 to 0.15%, Si 0.01 to 1.50%, Mn 10 to 30%, P 0.03% or less, S 0.01% or less, O 0.0030% or less, Contains 0.5-15% Ni, 12-25% Cr, and 0.10-0.28% N, and (b) Nb
, V, Ti, and Al in a total amount of 0.01 to 0.50%, and (c) at least one element selected from the group consisting of Ca, Ce, and Zr. 0.001-0.050% in total amount
and [(%Mn)-0.3(%Ni)+2.0(%Cr)]
/(%N)×10^2≧2.0, and the balance is iron and unavoidable impurities. A high Mn nonmagnetic steel for cryogenic use with excellent electron beam weldability. (7) In weight% (a) C 0.01-0.15%, Si 0.01-1.50%, Mn 10-30%, P 0.03% or less, S 0.01% or less, O 0.0030% or less, Contains 0.5-15% Ni, 12-25% Cr, and 0.10-0.28% N, and (b) Ca
, at least one element selected from the group consisting of Ce and Zr in a total amount of 0.001 to 0.050%, and (c) a total amount of at least one element selected from the group consisting of Cu, Mo and W. contains 0.01 to 2.00%, and [(%Mn)-0.3(%Ni)+2.0(%Cr)]
/(%N)×10^2≧2.0, and the balance is iron and unavoidable impurities. A high Mn nonmagnetic steel for cryogenic use with excellent electron beam weldability. (8) In weight% (a) C 0.01-0.15%, Si 0.01-1.50%, Mn 10-30%, P 0.03% or less, S 0.01% or less, O 0.0030% or less, Contains 0.5-15% Ni, 12-25% Cr, and 0.10-0.28% N, and (b) Nb
, V, Ti, and Al in a total amount of 0.01 to 0.50%, and (c) at least one element selected from the group consisting of Ca, Ce, and Zr. 0.001-0.050% in total amount
(d) contains 0.01 to 2.00% in total of at least one element selected from the group consisting of Cu, Mo and W, and [(%Mn)-0.3( %Ni)+2.0(%Cr)]
/(%N)×10^2≧2.0, and the balance is iron and unavoidable impurities. A high Mn nonmagnetic steel for cryogenic use with excellent electron beam weldability.