JPH07243001A - Rust resisting non-magnetic steel - Google Patents

Abstract

PURPOSE:To obtain an inexpensive rust resisting non-magnetic steel excellent in magnetic permeability, machinability, and weldability after cold working and having high strength by specifying respective contents of C, Mn, S, Ni, Cr, and N. CONSTITUTION:This steel is a rust resisting non-magnetic steel which has a composition constaining, by weight, 0.03-0.08% C, 18.0-22.0% Mn, 0.004-0.04% S, 5.5-8.0% Ni, 17.0-20.0% Cr, and 0.15-0.25% N and further containing, if necessary, 0.001-0.01% Ca and/or 0.005-0.03% Se and has superior machinability and weldability. This steel has >=300MPa 0.2% yield strength after solution heat treatment. Moreover, this steel can maintain <=1.010 magnetic permeability even after cold working.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is particularly effective as a structural member of a magnetic propulsion device applying superconductivity such as a linear motor car,
The present invention relates to a non-magnetic steel that maintains stable non-magnetic properties even when cold-worked and is required to have rust resistance because it is used outdoors.

[0002]

2. Description of the Related Art A structural member of a magnetic propulsion apparatus applying superconductivity requires non-magnetic steel which does not exhibit magnetism even when exposed to magnetic lines of force and has high strength. The required characteristics are specifically shown below.

Magnetic permeability: 1.010 or less Strength: 0.2% proof stress: 300 MPa or more Others: Low cost, good machinability, good weldability, and difficult to rust. As the magnetic steel, there is SUS304LN austenitic stainless steel. This has good weldability, rust resistance, and magnetic permeability before cold working, but has problems in strength, price, machinability, and magnetic permeability after cold working. In particular, it is fatal that it contains a large amount of Ni and thus is expensive, and that when cold working, a part of austenite changes to martensite due to work-induced transformation and the magnetic permeability becomes 2.0 or more. is there. In order to solve these problems, Japanese Patent Laid-Open Nos. 54-130428 and 57-155350 have been proposed as non-magnetic steels containing a large amount of Mn and N instead of expensive Ni to stabilize austenite.

Both of these have succeeded in improving the strength, the price and the magnetic permeability after cold working, but on the other hand, regarding weldability, JP-A-54-130428 discloses C of 0.5 to 1.5.
%, JP-A-57-155350 has a problem that the heat-affected zone of the welding is significantly hardened during welding and cracks are likely to occur at the time of welding because it contains 0.4% of C at the maximum, and welding is extremely difficult. Further, since it contains a large amount of Mn and N, there is a problem that work hardening due to cold working is great and machinability such as cold cutting and drilling is poor. In short, the conventionally known non-magnetic steel satisfies some of the above-mentioned required performances but does not satisfy all of them.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an inexpensive rust-resistant non-magnetic steel which simultaneously satisfies the requirements of magnetic permeability, machinability, weldability and high strength after cold working. I am trying. Here, “excellent in weldability” means that welding can be performed without causing cracks in the heat-affected zone of the weld or cracks along non-metallic inclusions immediately below the weld (hereinafter referred to as lamella tear).

[0006]

In order to achieve the above object, the steel components affecting the weldability, machinability, magnetic permeability, and rust resistance may be controlled within an appropriate range. Determining the appropriate component range is not straightforward because of the influence of each other. As a result of repeated studies, the present inventors have found that these required performances can be achieved at the same time by using a steel having the following composition range.

That is, in weight%, C: 0.03% to 0.08%, Mn: 18.0% to 22.0%, S: 0.004% to 0.04%, Ni: 5.
5% or more and 8.0% or less, Cr: 17.0% or more 20.0
% Or less and N: 0.15% or more and 0.25% or less is used, the weldability and machinability are excellent, and the magnetic permeability is 1.010 or less even after cold working. Corrosion-resistant non-magnetic steel can be realized.

Further, by adding at least one of Ca: 0.001% to 0.01% and Se: 0.005% to 0.03% to the lamella.
We have found that the tare is significantly improved.

[0009]

The reason for limiting each component of the rust-resistant non-magnetic steel according to the present invention will be described. (1) C: 0.03% or more and 0.08% or less C is required to be 0.03% or more in order to secure strength and stabilize austenite, but if it exceeds 0.08%, it is affected by heat during welding. It is necessary to suppress the content to 0.08% or less because the portion hardens and cracks easily occur.

(2) Mn: 18.0% or more and 22.0% or less Mn is an austenite stabilizing component that is cheaper than Ni, and produces stable austenite in steel containing 5.5 to 8.0% Ni. To make Mn 15.0 to 2
It is necessary to contain 2.0%. On the other hand, if the Mn content is less than 18%, a good drill life cannot be obtained.
After all, the content is set to 18.0% or more and 22.0% or less from the viewpoint of machinability represented by drill life and nonmagnetic property after cold working.

(3) S: 0.004% or more and 0.04% or less S exists mainly in the form of inclusions in the steel and has the effect of improving the machinability of the steel, but if it is less than 0.004%. Its effect is significantly reduced. On the other hand, even if added over 0.04%, the machinability is not improved so much, and conversely, the disadvantage that lamella and tear are likely to occur during welding becomes remarkable. for that reason,
The content of S is 0.004% or more and 0.04% or less.

(4) Ni: 5.5% or more and 8.0% or less Ni is an important component for stabilizing austenite in a steel containing a large amount of Mn and Cr, such as the steel of the present invention, It is necessary to contain 5.5% or more.
However, if the Mn content is 18.0 to 22.0%, the austenite stabilizing effect is small even if Ni is contained in an amount exceeding 8.0%. Therefore, the Ni content is 5.5% or more and 8.0% or more. % Or less.

(5) Cr: 17.0% to 20.0% Cr is a component necessary for imparting rust resistance to the steel of the present invention.
If the content is less than 7.0%, the rust resistance is insufficient, and if the content exceeds 20.0%, an intermetallic compound mainly containing Cr is formed and austenite is destabilized. The content is 0% or more and 20.0% or less.

(6) N: 0.15% or more and 0.25% or less N not only stabilizes austenite but also exists as a solid solution in the steel matrix, so that N.
It is a component necessary for increasing the 2% proof stress. But 0.
If less than 15%, the effect does not appear, and 0.2
If it exceeds 5%, N penetrates into the weld metal during welding and defects such as blowholes occur, so the content is set to 0.15% or more and 0.25% or less.

(7) Ca: 0.001% or more and 0.01% or less Ca is a component that suppresses deterioration of the drill cutting edge, and the strength of steel can be improved by controlling the morphology of sulfide inclusions in a spherical shape. It has the effect of suppressing lamella and tear during welding without affecting. Therefore, it is an important ingredient for applications that require special attention to lamella thea. However, 0.
If less than 001%, the effect is not exhibited, while 0.01%
If it exceeds, hard oxide inclusions are formed and the drill life is deteriorated and machinability is impaired. Therefore, it is necessary to control the content to be 0.001% or more and 0.01% or less.

(8) Se: 0.005% or more and 0.03% or less Se has the effect of suppressing deterioration of the drill cutting edge as well as Ca, and at the same time suppressing lamella tear during welding. It is an important ingredient for sensitive applications. However, if it is less than 0.005%, the effect is not exhibited, while if it exceeds 0.03%, hard oxide inclusions are formed to deteriorate the drill life and hinder the machinability. Therefore 0.00
It is necessary to control the content to be 5% or more and 0.03% or less.

Here, only one of Se and Ca may be contained, or both of them may be contained, but if the content is within the above range, the above effect is exhibited. The unavoidable impurities include trace elements such as P contained in the raw material during steel production, as well as Si and Al added as deoxidizing agents during steel refining, with Si ranging from 0.10% to 0. Up to 50%, Al is generally added in the range of 0.001% to 0.07%.

Experimental examples based on which the constituents of the steel of the present invention are limited will be described below. FIG. 1 shows the results of measuring the magnetic permeability of 18% Cr-based steel known as inexpensive stainless steel. As shown in Table 1, the test material has Mn and N fixed with Cr fixed at 18%.
i is a component with various changes, and each has a thickness of 2 after hot rolling.
A 0 mm steel plate was subjected to finish solution heat treatment. Then 5
As 0% cold working, the magnetic permeability was measured after reducing the thickness to 10 mm by cold rolling (hereinafter referred to as 50% cold working). The test materials in Table 1 all have a magnetic permeability of 1.010 or less before cold working.

[0019]

[Table 1]

As can be seen from FIG. 1, the Mn content 1
In the range of 5.0 to 22.0%, the austenite of the matrix is stable against cold working, and 1.0% even after 50% cold working.
A magnetic permeability of 10 or less can be maintained. Therefore, the Mn content of the non-magnetic steel targeted by the present invention is 15.0 to 2
It turns out that it should be 2.0%.

Next, the machinability will be described. Figure 2 shows Mn
It is the result of examining the machinability of steel having a content of 15.0 to 22.0%. As shown in Table 2, the test material contained Mn of 15.
Three groups of 0, 18.0 and 22.0% were used, and Ni was changed in the range of 1.5 to 9.5%. The rolling and cold working conditions are the same as those in FIG. The machinability is defined by the drill life as an index, and the drill life is defined as follows. That is, the total length of the holes that can be drilled with one drill was defined as the drill life. Further, when the life of the drill was reached during the drilling and drilling became impossible, it was considered that 50% of the length of the through hole was drilled. For example, if one hole is drilled in a sample material having a thickness of 10 mm, and the drill cannot be cut during the 21st drilling, it becomes 10 mm × (21
-1) +10 mm x 0.5 = 205 mm is the drill life.

[0022]

[Table 2]

As can be seen from FIG. 2, Mn15.0
%, The drill life is at most 400 mm, while Mn is 18.0% and 22.0%, the drill life is Ni.
Has a drill life of 800 mm in the range of 5.5 to 8.0%
This is a dramatic improvement. That is, from the viewpoint of machinability, Mn is 18.0 to 22.0, which is narrower than 15.0 to 22.0%, which is the range limited from the viewpoint of magnetic permeability.
%, And the Ni content is 5.5 to 8.0.
It turns out that it should be limited to the range of%.

Next, the influence of S on the machinability and the susceptibility to lamella tear will be described. In FIG. 3, Mn is 18.0.
To 22.0% and Ni in the range of 5.5 to 8.0%, the S content of the non-magnetic steel, the drill life, and the cross-sectional shrinkage ratio (hereinafter referred to as RAz) in the tensile test in the plate thickness direction were examined. Here, RAz is an index indicating the degree of difficulty of lamella / tea generation, and is 20.
It is known that lamella / tea does not occur if it is at least%. Table 3 shows the components of the test material. The underlined parts in Table 3 are components outside the scope of the present invention.

[0025]

[Table 3]

As can be seen from FIG. 3, when the S content is 0.004% or more, the drill life is improved to 800 mm or more. On the other hand, when the S content exceeds 0.04%, RAz becomes 20% or less and the lamella during welding.
There is a risk of tare. Therefore, it is understood that the S content should be limited to the range of 0.004% to 0.04%.

This rust-resistant non-magnetic steel can be produced by hot rolling the steel adjusted to the composition range of the steel of the present invention in a converter or an electric furnace through a continuous casting method or a mold ingot method. . In principle, this rust-resistant nonmagnetic steel is subjected to solution heat treatment, but depending on the conditions of hot rolling and the cooling rate after hot rolling, solution heat treatment may not be necessary.

[0028]

[Examples] Examples will be described below, and the target performance as a guide was set as follows. Strength: 0.2% proof stress ………… 300 MPa or more Non-magnetic: Permeability ………… 50% After cold working 1.
Machinability: Drill life ………… 800 mm or more Weldability: Crack in heat-affected zone …… None Neither lamella tears nor blowholes ... The steel of the present invention satisfies all target performances, but the present invention It is clear from the following examples and comparative examples that rust-resistant non-magnetic steels that are out of the composition range of steel do not simultaneously satisfy all target performances. (Example 1) Table 4 (a) shows a set of examples of the steel of the present invention. As the test material, steel having the components shown in Table 4 (b) was refined in a converter and Si and Al were added at the same time to deoxidize it, and then a slab produced by continuous casting was hot rolled to a thickness of 20 mm.
After holding at 0 ° C for 30 minutes and performing solution heat treatment of water cooling, 50
% Cold working was used. Hereinafter, the manufacturing method of the test material is all the same, but here, the refining by the converter, the deoxidizing method, the steps of continuous casting are not the essence of the present invention. The effect of the present invention does not change even if it is manufactured by rolling or the like.

As can be seen from Table 4 (a), all of the steels of the present invention D-1 to D-5 satisfy the target performance and only show excellent strength, drill life and weldability. Stable non-magnetic property is exhibited even after cold working.

[0030]

[Table 4]

Comparative examples are shown below to confirm the effectiveness of the present invention. Comparative Example 1: Effects of C and N Table 5 (a) shows experimental results of each performance. The part where the performance is out of the target value is indicated by (*) mark in Table 5 (a). As the test material, the steel having the components shown in Table 5 (b) was subjected to the same treatment as in Example 1. Of the component values in Table 5 (b), those outside the component range of the present invention are indicated by underlining.

D-1 and d- having a C content of less than 0.03%
In d-5 in which 2 and N were less than 0.15%, the 0.2% proof stress was less than 300 MPa. Further, the C content is 0.
With d-3 and d-4 exceeding 08%, the drill life was remarkably inferior, and cracks occurred in the heat affected zone during welding. Furthermore, blow holes were generated during welding in d-6 in which N exceeded 0.25%.

[0033]

[Table 5]

Comparative Example 2: Effects of Mn and Ni Table 6 (a) shows experimental results of each performance. Table 6 shows the test materials.
The steel of the component (b) was subjected to the same treatment as in Example 1. The meanings of (*) mark and underline in the table are the same as those in Table 5 (a) and Table 5 (b), respectively.

With e-1 having a Mn content of 2.6%, the austenite is unstable, so that martensite is easily formed by 50% cold working or working at the time of drilling, the magnetic permeability is increased, and the drill life is increased. Was significantly deteriorated and it could not be used as non-magnetic steel. e-2 is Mn
Content of 15% or more, the austenite is stable and the magnetic permeability after 50% cold working satisfies the target value, but the drill life is inferior. Next, the Mn content is 22
%, The austenite becomes unstable due to the intermetallic work formed when the steel is solidified. As a result, the transmittance after 50% cold working became high.

E-5 and e-6 are cases in which the Ni content is lower than that of the steel of the present invention, and in this case as well, the austenite is unstable, so martensite is formed during drilling and the drill life is deteriorated. .

[0037]

[Table 6]

Comparative Example 3: Effect of S Table 7 (a) shows the experimental results of each performance. Table 7 shows the test materials.
The steel of the component (b) was subjected to the same treatment as in Example 1. The meanings of (*) mark and underline in the table are the same as those in Table 5 (a) and Table 5 (b), respectively.

In f-1 and f-2, since S exceeds 0.04%, lamella tear occurs during welding. Since the S of f-3 was lower than 0.004%, the machinability was poor and the drill life was extremely short.

[0040]

[Table 7] (Example 2) Table 8 (a) shows an example in which the effects of Ca and Se were clarified. As the test material, steel having the components shown in Table 8 (b) was subjected to the same treatment as in Example 1. In addition, Table 7 (a), Table 8
Comparative examples are also shown in (b). The meanings of (*) mark and underline in the table are the same as those in Table 5 (a) and Table 5 (b), respectively.

Ca is out of the range of 0.001 to 0.01%, g-1 and g-2, and Se is 0.005 to 0.03.
The drill life of g-3 and g-4 out of the range of 400 is 400
The length is remarkably short as mm or less and the machinability is not satisfactory. On the other hand, it can be seen that G-1 and G-2 in which Ca and Se are within the range of the present invention have a good drill life and have good machinability.

[0042]

[Table 8]

[0043]

As described above, in the field of non-magnetic steel, the contents of C, Mn, Ni, Cr, S and N are appropriately combined to further affect the machinability of the non-magnetic steel. By containing Ca and Se in appropriate amounts as needed, it is possible to provide a non-magnetic steel that has high strength, excellent weldability, and machinability, and that maintains stable non-magnetism even during cold working.

[Brief description of drawings]

FIG. 1 is a diagram showing the influence of C, Mn, Ni, and N on magnetic permeability.

FIG. 2 is a diagram showing the effect of Mn and Ni on machinability.

FIG. 3 is a diagram showing the influence of the relationship between S content, drill life, and RAz.

Claims (3)

[Claims] 1. Substantially, by weight%, C: 0.03% or more and 0.08% or less, Mn: 18.0% or more and 22.0% or less, S: 0.004% or more and 0.04%. Hereinafter, Ni: 5.
5% or more and 8.0% or less, Cr: 17.0% or more 20.0
%, N: 0.15% or more and 0.25% or less, rust-resistant non-magnetic steel excellent in machinability and weldability. 2. Substantially, by weight%, C: 0.03% or more and 0.08% or less, Mn: 18.0% or more and 22.0% or less, S: 0.004% or more and 0.04%. Hereinafter, Ni: 5.
5% or more and 8.0% or less, Cr: 17.0% or more 20.0
% Or less, N: 0.15% or more and 0.25% or less, and Ca: 0.001% or more and 0.01% or less and Se:
A rust-resistant non-magnetic steel having at least one of 0.005% to 0.03% and having excellent machinability and weldability. 3. The 0.2% proof stress after solution heat treatment is 300.
The rust-resistant non-magnetic steel according to claim 1 or 2, which has a pressure of at least MPa.