JPH0657379A - Non-magnetic steel with excellent hot workability and corrosion resistance - Google Patents

Abstract

(57) [Summary] [Object] The present invention relates to a low-cost non-magnetic steel having good hot workability and excellent in corrosion resistance and SCC resistance. [Structure] C: 0.01 to 0.80%, Si: 0.01
~ 2.50%, Mn: 9-32%, Cr: 0.1-1
4.5%, Ni: 0.10 to 8.0%, N: 0.001
~ 0.50%, including Al: 0.001 to 0.20%,
If necessary, one or more of Mo, W, Co, Cu, Nb, Ti and V may be Mo + W + Co + Cu = 0.01.
-4.0%, Nb + Ti + V = 0.01-1.5%, and Ca: 0.001-0.02%, with the balance being a high Mn non-magnetic steel composed of unavoidable impurities, with an austenitic stainless steel as the inner layer. A non-magnetic steel material characterized by hot-rolling a cast multi-layer cast slab having as a surface layer. [Effect] A non-magnetic steel material having excellent corrosion resistance can be manufactured at a good yield and at a low cost, and the application range of the non-magnetic structural member is expanded.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-cost non-magnetic steel having good hot workability and excellent corrosion resistance and SCC resistance.

[0002]

2. Description of the Related Art High Mn non-magnetic steel is superior in austenite phase stability to austenitic stainless steel. The austenitic stainless steel has an austenitic ferromagnetic α '
It transforms to the martensitic phase and increases the magnetic permeability. on the other hand,
In the high Mn non-magnetic steel, the austenite phase transforms to the non-magnetic ε-martensite phase even when a work strain is applied, so that the magnetic permeability remains extremely low and does not change. Therefore, high Mn
Since steel exhibits a stable austenite structure,
It is attracting attention in fields requiring extremely low magnetic permeability, such as magnetic levitation high-speed railways and nuclear fusion experimental reactors. In addition, since it is cheaper than austenitic stainless steel, it can be expected to be widely used in the future as a non-magnetic structural member for industrial and consumer use.

However, since the high Mn steel has a completely austenitic structure up to room temperature after the completion of solidification, the hot workability is extremely poor. Therefore, although the raw material cost is lower than that of the austenitic stainless steel, the manufacturing yield is low and the manufacturing cost is increased. Further, the high Mn steel reduces the amount of Cr as much as possible for the purpose of reducing the raw material cost and has almost no corrosion resistance. Moreover, the austenite structure is also inferior in SCC resistance. In view of the above, high Mn steel has not been widely used in the present situation although it has excellent non-magnetism.

[0004]

Therefore, it has been desired to develop a non-magnetic material having good hot workability, excellent corrosion resistance and SCC resistance, and low manufacturing cost. The present invention provides a non-magnetic steel excellent in hot workability and corrosion resistance at low cost in order to meet such a demand.

[0005]

DISCLOSURE OF THE INVENTION The present inventors have noticed that austenitic stainless steel has extremely excellent corrosion resistance as well as good hot workability, and has a problem in corrosion resistance and hot workability. The present invention has been accomplished with the aim of casting an austenitic stainless steel on the surface of a high Mn non-magnetic steel.

That is, according to the present invention, C:
0.01 to 0.80%, Si: 0.01 to 2.50%,
Mn: 9-32%, Cr: 0.1-14.5%, Ni:
0.10 to 8.0%, N: 0.001 to 0.50%, A
1: Hot-workability and corrosion resistance, characterized in that a high Mn non-magnetic steel containing 0.001 to 0.20% and the balance consisting of unavoidable impurities is used as an inner layer and an austenitic stainless steel is used as a surface layer for lamination. Excellent non-magnetic steel material.
Further, the present invention provides the above-mentioned inner layer high Mn non-magnetic steel with Mo, W, C
1 or 2 or more of o, Cu, Nb, Ti and V is Mo
+ W + Co + Cu = 0.01-4.0%, Nb + Ti +
V = 0.01 to 1.5% is added, or C is added to the above-mentioned inner-layer high-Mn non-magnetic steel or further together with the above-mentioned additional element
a: 0.001 to 0.02% can be added.

[0007] Austenitic stainless steel contains a large amount of Cr and Ni and therefore has excellent corrosion resistance. It also has excellent hot workability. However,
As described above, there is a problem in non-magnetism after applying processing strain. However, it has been found that the hot workability is dramatically improved by casting the austenitic stainless steel around the surface layer of the high Mn steel. Hot rolling of solid high-Mn steel slabs gives a depth of several mm to 10 mm on the surface.
A few mm crack occurs. On the other hand, when hot rolling an ingot of austenitic stainless steel on the surface layer, no surface crack occurs.

It has been found that the steel material of the present invention obtained by hot rolling this cast multi-layer cast slab exhibits excellent non-magnetism and is at the same level as pure high-Mn steel even after application of processing strain. FIG. 1 shows the influence of the amount of processing strain on the magnetic permeability of each steel. The magnetic permeability of SUS304 remarkably increases as the processing strain increases. However, the steel of the present invention is pure high M
It was revealed that, like the n-steel, the magnetic permeability did not change even when a work strain was applied, and exhibited extremely good non-magnetism.

Since the surface layer of the steel of the present invention is an austenitic stainless steel, it has excellent corrosion resistance and very low sensitivity to stress corrosion cracking. FIG. 2 shows the number of rupture days when the U-vent SCC test piece was immersed in artificial seawater at 50 ° C. While the pure high-Mn steel fractures after being immersed for 30 days, the steel of the present invention shows no cracking even after being immersed for 60 days.

Also, the high M produced by the cast multi-layer slab
The n-steel-austenitic stainless steel clad steel material is extremely inexpensive in its manufacturing method as compared with the case of being manufactured by the welding assembly method or the explosive deposition method.

From the above findings, hot rolling of a cast multi-layer cast slab of austenitic stainless steel of the surface layer of a high Mn non-magnetic steel has good hot workability, corrosion resistance and corrosion resistance. It has become possible to manufacture non-magnetic steel materials with excellent SCC properties. Next, the limited scope of the present invention will be described.

[Inner Layer Component] C: an austenite stabilizing element, which is an extremely effective element for demagnetization. At the same time, it works to increase strength. For that purpose, it must be contained at least 0.01% or more. However, if the content exceeds 0.80%, the weldability deteriorates significantly, so the upper limit was made 0.80%.

Si: An element effective for increasing the strength, but since it is a ferrite stabilizing element, its inclusion in a large amount is disadvantageous for non-magnetization. Therefore, it is 2.50 when 0.01% or more.
% Or less.

Mn: an austenite stabilizing element, which is an extremely effective element for demagnetization. At the same time, it works to increase strength. For that purpose, at least 9% or more must be contained. However, if the content exceeds 32%, the manufacturing cost due to the alloy cost only unnecessarily increases.

Cr: An austenite stabilizing element, which is an element effective for demagnetization. At the same time, since it is an element effective for increasing strength, at least 0.10%
It is necessary to contain the above. However, the inclusion of more than 7.0% only unnecessarily increases the manufacturing cost due to the alloy cost.

Ni: An austenite stabilizing element, which is extremely effective in demagnetizing and improving toughness. For that purpose, it is necessary to contain at least 0.10% or more. However, a large content increases the manufacturing cost due to the alloy cost, so the content was made 8.0% or less.

N: An austenite stabilizing element, which is an extremely effective element for demagnetization. It also has a remarkable function to increase the strength. For that, at least 0.00
Must contain at least 1%. But 0.5
If it exceeds 0%, the hot workability deteriorates, which causes cracks in the continuous casting process and hot rolling process.
The upper limit was 0%.

Mo, W, Co, Cu: Elements effective for improving the strength of the austenitic material. However, if added in a large amount, the toughness deteriorates, so the total amount is 0.01 to 4.0.
% Is included. Nb, Ti, V: By forming fine carbide, the product structure is made finer and the yield strength is increased. However, a large content causes not only an increase in manufacturing cost due to alloy cost but also a reduction in hot workability, so 0.50%
Below.

As other components, as a deoxidizing element, A
The contents of 1 and Ca of 0.20% or less and 0.02% or less, respectively, are effective in increasing the cleanliness of steel and improving the toughness and hot workability. As an impurity element, S is preferable because it causes deterioration of toughness and is preferably 0.05% or less. Further, P also needs to have a small content in order to reduce toughness, and is preferably 0.040% or less.

[Surface Layer Composition] The steel that surrounds the above-described inner layer high Mn steel was a non-magnetic steel austenitic stainless steel that has good hot workability, corrosion resistance, and SCC resistance.

After the above-mentioned steel for the surface layer and the steel for the inner layer are cast by the cast-girth method and laminated on a multi-layer cast slab, ordinary heat treatment and rolling steps are carried out to produce steel products of various shapes.

[0022]

EXAMPLES Steel No. 1 in Table 1 As shown in Nos. 1 to 11, a multi-layer cast slab having an inner layer of high Mn non-magnetic steel and a surface layer of SUS304 was melted by a casting method. As a comparative material, steel No. 1 in Table 1 was used.
12 to 16 cast pieces were melted by the ingot method. After heating this slab to 1180 ° C., it was hot rolled to a reduction ratio of 50% and evaluated for crack susceptibility.

The results are shown in Table 2. In the section of occurrence of hot work cracks in Table 2, ◯ indicates that no surface cracks were observed after hot rolling, and x indicates that surface cracks occurred.
Furthermore, using a steel plate hot-rolled to a plate thickness of 15 mm, 2
A magnetic field of 200 was applied to the test piece with 0% tensile strain.
Permeability measurements were performed at Oersted according to ASTM-A342-84. Furthermore, a tensile test at room temperature,
A stress corrosion cracking test was conducted. The stress corrosion cracking test is U
The bent test piece was immersed in artificial seawater at 50 ° C., and the cross section was observed with an optical microscope (OM) to determine the presence or absence of SCC.
O indicates that SCC was not observed by OM observation, and X indicates that SCC was observed.

[0024]

[Table 1]

[0025]

[Table 2]

No. 1 according to the present invention. Steel 1 to 11 is 50
% Hot rolling does not cause surface cracking. Further, even when a working strain of 20% was applied to the steel sheet, it exhibited extremely low magnetic permeability and no SCC was observed. On the other hand, steel No. 12-15 pure high Mn non-magnetic steel is
Although it shows extremely low magnetic permeability, cracking occurs during hot rolling and SCC is also observed. In addition, steel No.
16 solid SUS304 has hot workability and SC resistance
Although the C property is not a problem, the magnetic permeability after application of processing strain increases and the non-magnetism decreases.

From the above examples, according to the present invention, the composition of the steel and its multi-layer effect are related to adhesion and work extremely effectively.
It has excellent hot workability as well as excellent corrosion resistance and S resistance.
It is clear that it is possible to inexpensively manufacture the non-magnetic steel material having the CC property.

[0028]

EFFECTS OF THE INVENTION By hot rolling a cast multi-layer slab containing austenitic stainless steel on the surface of a high Mn steel, the manufacturing cost is low and the corrosion resistance and SCC resistance are high.
It has become possible to manufacture a non-magnetic steel material having excellent properties with a good manufacturing yield. The industrial and social significance of this technology is extremely great.

[Brief description of drawings]

FIG. 1 is a diagram showing an influence of a working strain amount (cold working ratio) on a magnetic permeability of steel for each steel type.

[Fig. 2] U-vent SCC test pieces for each steel type at 50 ° C
The figure which shows the crack generation days when immersed in artificial seawater.

Claims (4)

[Claims] 1. As weight%, C: 0.01 to 0.80%, Si: 0.01 to 2.50%, Mn: 9 to 32%, Cr: 0.1 to 14.5%, Ni : 0.10 to 8.0%, N: 0.001 to 0.50%, Al: 0.001 to 0.20%, the balance being a high Mn non-magnetic steel composed of unavoidable impurities, and austenite A non-magnetic steel material with excellent hot workability and corrosion resistance, characterized by laminating a stainless steel as the surface layer. 2. As weight%, C: 0.01 to 0.80%, Si: 0.01 to 2.50%, Mn: 9 to 32%, Cr: 0.1 to 14.5%, Ni : 0.10 to 8.0%, N: 0.001 to 0.50%, Al: 0.001 to 0.20%, and Mo,
One or more of W, Co, Cu, Nb, Ti, and V contains Mo + W + Co + Cu = 0.01 to 4.0%, Nb + Ti + V = 0.01 to 1.5%, and the balance is inevitable impurities. A non-magnetic steel material having excellent hot workability and corrosion resistance, which is obtained by laminating Mn non-magnetic steel as an inner layer and austenitic stainless steel as a surface layer. 3. By weight%, C: 0.01 to 0.80%, Si: 0.01 to 2.50%, Mn: 9 to 32%, Cr: 0.1 to 14.5%, Ni : 0.10 to 8.0%, N: 0.001 to 0.50%, Al: 0.001 to 0.20% Ca: 0.001 to 0.02%, and the balance from unavoidable impurities A non-magnetic steel material excellent in hot workability and corrosion resistance, which is obtained by laminating a high Mn non-magnetic steel as an inner layer and an austenitic stainless steel as a surface layer. 4. Weight%, C: 0.01 to 0.80%, Si: 0.01 to 2.50%, Mn: 9 to 32%, Cr: 0.1 to 14.5%, Ni : 0.10 to 8.0%, N: 0.001 to 0.50%, Al: 0.001 to 0.20% Ca: 0.001 to 0.02%, and Mo:
One or more of W, Co, Cu, Nb, Ti, and V contains Mo + W + Co + Cu = 0.01 to 4.0%, Nb + Ti + V = 0.01 to 1.5%, and the balance is inevitable impurities. A non-magnetic steel material having excellent hot workability and corrosion resistance, which is obtained by laminating Mn non-magnetic steel as an inner layer and austenitic stainless steel as a surface layer.