JPH08134609A - High strength high manganese non-magnetic steel sheet reduced in softening in weld heat-affected zone - Google Patents

Abstract

PURPOSE: To produce a high strength high Mn non-magnetic steel sheet reduced in softening in a weld heat-affected zone and having high tensile strength by preparing a non-magnetic steel sheet having a specific composition in which respective contents of Nb, Ti, and N are specified. CONSTITUTION: A non-magnetic steel sheet, which has a composition consisting of, by mass, 0.15-0.40% C, 0.05-1.00% Si, 15-30% Mn, <=0.020% P, <=0.005% S, 0.010-0.100% Nb, 0.010-0.100% Ti, <=0.100% N, and the balance Fe with inevitable impurities and satisfying inequalities 60×[C]%+[Mn]%>=36% and [N]%>=1.33×([Nb]%/-6.64+[Ti]%/3.42)+0.007, is prepared. By this method, the high strength high Mn non-magnetic steel sheet, reduced in softening in a weld heat-affected zone and having >=780N/mm<2> tensile strength, can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-magnetic structural steel sheet used for linear motor car orbits, fusion reactors, various generators, and the like. Relates to a high strength and high Mn non-magnetic steel sheet having a value of 780 N / mm ² or more.

[0002]

2. Description of the Related Art In recent years, there is an increasing demand for high Mn non-magnetic steel as a structural material for the above-mentioned superconducting equipment or general heavy electric equipment. Among them, there is a strong demand for higher strength of high Mn non-magnetic steel from the viewpoint of weight reduction of structures.

As means for achieving high strength, Cr, M
o Add a large amount of solid solution strengthening elements such as o and N (for example, Japanese Patent Publication No. 62-8499) or TMCP (controlled rolling / controlled cooling) to reduce the amount of solid solution strengthening elements added. A method for reducing the grain size and increasing the dislocation density (for example, Japanese Patent Publication No. 59-26647) has been studied. In the former method, a large amount of the solid solution strengthening element is added, which causes deterioration of weldability and a large increase in cost. Therefore, in recent years, researches applying the latter method have become popular.

[0004]

[Problems to be Solved by the Invention] However, TMC
When a steel sheet with high strength by applying P is welded, austenite grains are coarsened by welding heat input and a weld heat-affected zone (hereinafter referred to as HAZ) structure is coarsened.
Has a problem that the HAZ fractures from the HAZ at a low stress in a tensile test, and its improvement is desired.
Fracture from the HAZ at low stress is unlikely to occur when the plate thickness is relatively thick due to the plastic deformation restraint effect of the softened part by the high-strength base material and weld metal, and easily when the plate thickness is relatively thin. It seems

The present invention has been made in order to solve the above-mentioned problems of the prior art, and provides a high strength and high Mn non-magnetic steel sheet having a small HAZ softening in welding and a tensile strength of 780 N / mm ² or more. With the goal.

[0006]

The present inventor has, in order to achieve the above object, produced 780 N / mm ² produced by applying TMCP.
HAZ by welding for steels with the above tensile strength
The inventors have earnestly studied the chemical components capable of suppressing softening. Then, the present inventor has found that Nb, Ti, which affects the HAZ softening,
As a result of conducting research on the effect of N content, by adding Nb and Ti in an appropriate range and adjusting the N content, HAZ softening due to welding is small, and tensile strength is 780 N / mm ² or more. The present invention has been accomplished by finding new knowledge that a non-magnetic steel sheet can be obtained.

The gist is (1) C: 0.15 to 0.40%, Si: 0.
05-1.00%, Mn: 15-30%, P: 0.020% or less, S: 0.005
% Or less, Nb: 0.010 to 0.100%, Ti: 0.010 to 0.100%, N:
High strength high Mn non-magnetic steel sheet containing 0.100% or less, the balance consisting of Fe and unavoidable impurities, and having a small tensile strength of 780 N / mm ² or more with small softening in the weld heat affected zone satisfying the following formula Is. 60 × [C]% ＋ [Mn]% ≧ 36% …………………………………………………… [N]% ≧ 1.33 × {[Nb]% / 6.64+ [Ti]% /3.42}+0.007 ………

(2) In addition to the above (1), Cr: 0.10 to 6.00
%, Ni: 0.10 to 2.00%, a high-strength, high-Mn non-magnetic steel sheet containing one or two of which has a small heat-affected zone softening and a tensile strength of 780 N / mm ² or more.

(3) In addition to the above (1), the tensile strength of the weld heat-affected zone containing V: 0.01 to 0.70% and having a small softening is 780 N / mm ²
The high-strength, high-Mn non-magnetic steel sheet described above.

(4) In addition to the above (1), a tensile strength of 780 N / mm ^{2 with} which the softening of the weld heat affected zone containing Ca: 0.010% or less is small.
The high-strength, high-Mn non-magnetic steel sheet described above.

(5) In addition to the above (1), Cr: 0.10 to 6.00
%, Ni: 0.1% to 1% or 2% of 2.00%, V: 0.01
It is a high-strength, high-Mn non-magnetic steel sheet containing ~ 0.70% and having a softening in the weld heat-affected zone and a tensile strength of 780 N / mm ² or more.

(6) In addition to the above (1), Cr: 0.10 to 6.00
%, Ni: 0.1% to 1% or 2% of 2.00% and Ca: 0.0
A high-strength, high-Mn non-magnetic steel sheet containing 10% or less and having a low softening in the weld heat-affected zone and a tensile strength of 780 N / mm ² or more.

(7) In addition to the above (1), V: 0.01 to 0.70%,
A high-strength, high-Mn non-magnetic steel sheet containing Ca: 0.010% or less and having a small softening in the weld heat affected zone and a tensile strength of 780 N / mm ² or more.

(8) In addition to the above (1), Cr: 0.10 to 6.00
%, Ni: 0.1% to 1% or 2% of 2.00%, V: 0.01
It is a high-strength, high-Mn non-magnetic steel sheet containing up to 0.70% and Ca: 0.010% or less and having a low heat-affected zone softening and a tensile strength of 780 N / mm ² or more.

[0015]

The following are the most important elements in the present invention
The reason for limiting the contents of Nb, Ti and N will be described in detail. Conventionally, Nb, Ti, and N have been used to increase the strength of high Mn nonmagnetic steel. NbN which is their precipitate
, TiN is said to have an austenite grain growth inhibitory effect during heating of the billet, so in welding of high Mn non-magnetic steel, suppression of HAZ austenite grain coarsening by welding heat input, that is, HAZ It is also considered to be effective in suppressing softening. However, so far, HAZ
A comprehensive study of Nb, Ti, and N contents for the purpose of suppressing softening has not been made.

First, in order to investigate the effect of the addition of Nb or Ti alone on the HAZ softening by welding and the effect of the combined addition of these elements, for the steel containing a sufficient amount of N,
The following experiment was conducted. 0.25% C-0.30% for the sample steel
Si-25% Mn-0.050% N as base steel, Nb single additive steel
(0.060% Nb), Ti alone addition steel (0.060% Ti), Nb and Ti composite addition steel (0.030% Nb-0.030% Ti) were small-scale melted (90 kg). These steels were hot-rolled to a plate thickness of 16 mm by applying TMCP to produce a steel plate having a tensile strength of 780 N / mm ² or more.

For these steel sheets, a welding rod for high Mn non-magnetic steel (MC-16) was used, a welding joint was prepared with a welding heat input of about 2 kJ / mm, and the Vickers hardness of the welding joint portion was measured. HAZ
The degree of softening was examined. The measurement position was 2 mm below the surface. The result is shown in FIG.

From FIG. 1, the HAZ softening is slightly suppressed by the addition of Nb or Ti alone.
The effect of suppressing softening is greater than that of adding it alone. The reason why the effect of the composite addition is great is that the composite precipitates of Nb and Ti are more stable in the high temperature range to which the HAZ is exposed during welding than the single precipitates of Nb and Ti. It is presumed that the grain boundary pinning effect is increased as a result, and coarsening of the austenite grains is suppressed.

Therefore, further experiments were carried out in order to investigate in detail the relationship between the Nb and Ti contents and the N content, which affects the HAZ softening by welding, in the case of the combined addition of Nb and Ti. Small molten steel with chemical composition shown in Table 1 (90 kg)
Then, with respect to a steel plate having a plate thickness of 16 mm manufactured in the same manner as the above-mentioned experiment, a welded joint was prepared under the same conditions as described above, and the Vickers hardness of the welded joint portion was measured. The degree of HAZ softening was evaluated by the difference between the average hardness of the base material and the minimum hardness of HAZ, ΔHV. The result is shown in FIG.

[0020]

[Table 1]

From FIG. 2, it should be noted that the content (Nb +
This is a new finding that the HAZ softening ΔHV due to welding can be suppressed to 20 or less by defining the N content relative to the Ti) content. That is, the amount of N is [N]% ≧ 1.33 × {[Nb]% / 6.
If 64+ [Ti]% / 3.42} +0.007 is satisfied, a good welded joint with small HAZ softening can be obtained. In addition,
6.64 and 3.42 in the formula are stoichiometric ratios of NbN and TiN (Nb / N = 6.64, Ti / N = 3.42), respectively.

The ranges of the contents of Nb, Ti and N are as follows. Nb and Ti are effective elements for suppressing HAZ softening and strengthening steel, but 0.010%
If it is less than 0.10%, the effect is small, and if it exceeds 0.100%, the cleanliness of the steel is significantly deteriorated and the toughness is lowered. Therefore,
The Nb and Ti contents are in the range of 0.010 to 0.100%.

N is an element effective not only in suppressing the HAZ softening but also in stabilizing the austenite and enhancing the strength.
If the content exceeds 0.100%, the weldability is impaired. Therefore, the upper limit of the N content is 0.100%.

Next, the reasons for limiting the chemical components in the present invention will be explained. C is an element effective in stabilizing and strengthening austenite. But below 0.15%,
These effects are small, and the magnetic characteristics are unstable.
On the other hand, if added in excess of 0.40%, the machinability deteriorates significantly. Therefore, the C content should be in the range of 0.15 to 0.40%.

Si is an element that acts as a deoxidizer during steel melting and is effective for improving strength, so Si is added in an amount of 0.05% or more. However, if added in excess of 1.00%, hot workability is impaired. Therefore, the Si content is in the range of 0.05 to 1.00%.

Mn is an element effective for stabilizing austenite and improving toughness. For that purpose, it is necessary to add at least 15%. However, if it is added in excess of 30%, the hot workability is remarkably reduced. Therefore, the Mn content is 15 to 30.
The range is%. However, in the present invention, basically C and Mn
In order to stabilize the austenite and ensure non-magnetic property in, the relationship between the content of C and Mn, as proposed by the present inventors in JP-A-3-281754, etc. It is necessary to satisfy the condition of 60 x [C]% + [Mn]% ≥ 36%. The reason for defining the relationship between the contents of C and Mn by the formula is that austenite becomes unstable when the contents of C and Mn are both near the lower limit of the limited range.

Both P and S are impurity elements that impair hot workability and weldability. The effect is 0.0 at P.
20%, S becomes larger when it exceeds 0.005%. Therefore, the P content is 0.020% or less, and the S content is 0.005%.
Below.

[0028] Cr is an element effective in stabilizing and strengthening austenite, and is added as necessary.
If it is less than 0.10%, its effect is small, and if it exceeds 6.00%, δ
Ferrite is likely to be generated, which deteriorates toughness and magnetic properties. Therefore, the Cr content is in the range of 0.10 to 6.00%.

Ni is an element effective not only for stabilizing austenite but also for improving toughness, and is added as necessary, but if it is less than 0.10%, its effect is small, and 2.00
If it exceeds%, it is an expensive element and the economy is impaired. Therefore, the Ni content is set to the range of 0.10 to 2.00%.

V is an element effective for increasing the strength of steel,
It is added as needed, but if it is less than 0.01%, its effect is small, and if it exceeds 0.70%, the cleanliness of steel deteriorates significantly,
This causes a decrease in toughness. Therefore, the V content is 0.01-0.
The range is 70%.

Ca is effective in improving the machinability and anisotropy of steel, and is added as necessary. However, if it exceeds 0.010%, the cleanliness of steel is significantly deteriorated and the toughness is lowered. . Therefore, the Ca content should be 0.010% or less.

[0032]

EXAMPLES Examples of the present invention will be described below. Small molten (90 kg) steel with the chemical composition shown in Table 2
By applying MCP, hot rolling to a plate thickness of 16 mm and tensile strength
Steel sheets of 780 N / mm ² or more were manufactured. These steel sheets were welded in the same manner as the above-mentioned experiment, and the degree of HAZ softening was investigated. In addition, in this example, tensile properties and magnetic permeability were also measured.
Table 3 shows the results.

Each of the steels 1 to 11 of the present invention has a small ΔHV, which indicates the degree of HAZ softening, of 20 or less, and has a magnetic permeability of 1.
It is good with less than 01. Of course, the tensile strength is 780 N / mm ² or more.

On the other hand, in Comparative Steels 12 and 14, the amount of N with respect to the combined addition amount of Nb and Ti is [N]% ≧ 1.33 × {[Nb]
% / 6.64 + [Ti]% / 3.42} +0.007 is not satisfied, so ΔHV, which indicates the degree of HAZ softening, is as large as 40 or more.

In Comparative Steel 13, the N content satisfies the formula, but the Nb content is less than the limit range of the present invention.
ΔHV, which indicates the degree of HAZ softening, is as large as 30 or more.

Since Comparative Steel 15 does not contain Ti, H
ΔHV, which indicates the degree of AZ softening, is as large as 30 or more.

In Comparative Steel 16, although the N content satisfies the formula, the value of 60 × [C]% + [Mn]% in the formula is less than 36%, so the magnetic permeability increases and the non-magnetic property Not suitable for steel.

[0038]

[Table 2]

[0039]

[Table 3]

[0040]

As is apparent from the above description,
The high Mn non-magnetic steel sheet according to the present invention has a small HAZ softening due to welding and a tensile strength of 780 N / mm ² or more, and therefore has a high Mn non-magnetic property for welded structures such as linear motor car orbits, fusion reactors and various generators. Suitable as a steel plate.

[Brief description of drawings]

FIG. 1 is a diagram showing a Vickers hardness distribution of a welded joint portion of various high Mn non-magnetic steel sheets.

FIG. 2 is a diagram showing a relationship between Nb and Ti contents and N 2 contents which affect HAZ softening by welding of various high Mn non-magnetic steel sheets.

Claims (8)

[Claims] 1. C: 0.15 to 0.40% by mass%, Si: 0.05 to
1.00%, Mn: 15-30%, P: 0.020% or less, S: 0.005% or less, Nb: 0.010-0.100%, Ti: 0.010-0.100%, N: 0.10
It contains 0% or less, the balance consists of Fe and unavoidable impurities, and satisfies the following formulas and formulas.
High strength and high Mn non-magnetic steel sheet with 0 N / mm ² or more. 60 × [C]% ＋ [Mn]% ≧ 36% …………………………………………………… [N]% ≧ 1.33 × {[Nb]% / 6.64+ [Ti]% /3.42}+0.007 ……… 2. In mass%, Cr: 0.10 to 6.00%, N
i: 0.1% to 2.00%, one or two of which are contained, and the tensile strength at which the heat-affected zone softening in welding is small is 780 N / mm ^2.
The high-strength and high-Mn non-magnetic steel sheet as described above. 3. A high-strength, high-Mn non-magnetic steel sheet having a mass strength of V: 0.01 to 0.70% and having a small softening strength in the weld heat affected zone of 780 N / mm ² or more. 4. The high-strength, high-Mn non-magnetic steel sheet according to claim 1, which further contains Ca: 0.010% or less in mass% and has a low tensile strength of 780 N / mm ² or more with a small heat-affected zone softening. 5. In mass%, Cr: 0.10 to 6.00%, N
i: 1 or 2 out of 0.10 to 2.00% and V: 0.01 to 0.70
%, A high-strength, high-Mn non-magnetic steel sheet having a low weld heat-affected zone softening and a tensile strength of 780 N / mm ² or more. 6. In mass%, Cr: 0.10 to 6.00%, N
i: 0.1 to 2.00%, one or two kinds, and Ca: 0.010% or less, high strength, high Mn having a low tensile strength of 780 N / mm ² or more with low softening of the heat-affected zone of the welding heat affected zone according to claim 1. Non-magnetic steel plate. 7. In mass%, further V: 0.01 to 0.70%, Ca:
The high-strength, high-Mn non-magnetic steel sheet according to claim 1, containing 0.010% or less and having a small softening in the weld heat-affected zone and a tensile strength of 780 N / mm ² or more. 8. In mass%, Cr: 0.10 ~ 6.00%, N
i: 1 or 2 out of 0.10 to 2.00% and V: 0.01 to 0.70
%, Ca: 0.010% or less, the high-strength high-Mn non-magnetic steel sheet according to claim 1, which has a small softening effect in the weld heat-affected zone and a tensile strength of 780 N / mm ² or more.