JPH0215148A - High mn nonmagnetic steel having excellent corrosion resistance - Google Patents

Abstract

PURPOSE:To improve the corrosion resistance and strength of the title steel by specifying C, Si, Mn, Ni, Cr, Mo, N and Al as well as P and Cu. CONSTITUTION:The high Mn nonmagnetic steel is formed with the compsn. constituted of, by weight, 0.1 to 0.5% C, 0.1 to 1% Si, 16 to 30% Mn, <=3% Ni, 0.5 to 8% Cr, 0.05 to 1% Mo, 0.03 to 0.4% N, 0.01 to 0.1% Al, 0.005 to [0.1XMo(%)+0.05XAl(%)] P(%) and 2XP(%) to 1.5Cu. The above nonmagnetic steel is inexpensive and has excellent corrosion resistance and high strength.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a relatively inexpensive high-Mn nonmagnetic steel that has excellent corrosion resistance and high strength.

<Prior art and its challenges> In recent years, the demand for non-magnetic steel has been growing significantly, mainly in fields such as electronic precision equipment, magnetic levitation trains, and medical diagnostic equipment, but recently, corrosion resistance has been required in the marine field, etc. Applications in corrosive environments have also shown a tendency to expand.

By the way, among the above-mentioned non-magnetic steels, "high Mn non-magnetic steel" has non-magnetic properties that are difficult to change due to processing, can achieve high strength, and does not contain any expensive Ni. 5US30, such as not containing or containing only a small amount
It is known that it has many advantages compared to Austenite I stainless steels such as 4 and 5 US316, but on the other hand, conventional high Mn non-magnetic steels are not fully satisfactory in terms of corrosion resistance. As a result, austenitic stainless steel was often used for applications in corrosive environments.

Of course, the means to reduce the corrosion loss value of high Mn non-magnetic steel (
Various studies have been conducted on ways to improve corrosion resistance, including methods for increasing the Cr content to a maximum of about 18% (Japanese Patent Application Laid-open No. 1972.56/1983), and furthermore, methods for increasing the Cr content to a maximum of about 26%. method (Unexamined Japanese Patent Publication No. 59-20
A method of adding a large amount of Cr, which is a corrosion-resistant element, has been proposed, as in No. 54.52), but although adding a large amount of Cr is effective in reducing the corrosion loss value, it does not work in a corrosive environment rich in chlorine ions. In addition, there was a problem in that the tendency for localized corrosion such as pitting corrosion and crevice corrosion to increase at the bottom, and that the economic efficiency, which is one of the characteristics of high Mn nonmagnetic steel, was impaired.

For this reason, austenitic stainless steels such as 5US304 and 5US316 have been the mainstream non-magnetic steels used in corrosive environments, but even these austenitic stainless steels cannot be used in harsh corrosive environments such as the ocean. In many cases, localized corrosion such as pitting corrosion and crevice corrosion occurs, and even if only the corrosion resistance aspect is taken into account, the material cannot be said to be satisfactory. This is because, even if the corrosion is localized, once corrosion occurs, the damage is often fatal to the structure.

Therefore, the main object of the present invention is to provide a non-magnetic steel that does not have the problems of conventional high-Mn non-magnetic steels and austenitic stainless steels, but has only their advantages.

Means for Solving the Problems> In order to achieve the above-mentioned object, the present inventors have developed (8) that the non-magnetic properties of high-Mn non-magnetic steel are not easily changed by processing.

(B) Strength can be easily improved.

(C) Focusing on the characteristics of high-Mn nonmagnetic steel that it is significantly more economical than austenitic stainless steel and that the corrosion form in a corrosive environment is uniform over the entire surface,
We conducted intensive research with the aim of developing an inexpensive means to significantly reduce the corrosion loss value while maintaining the advantages and corrosion morphology of non-magnetic steel. [I], which had never been seen before, exerts a remarkable corrosion weight loss suppressing effect, especially when combined with Cu, Mo, and A2, and under strict control of the contents of P, Cu, Mo, and Aβ. However, it was found that - if the above-mentioned components are adjusted appropriately, it is possible to significantly improve the corrosion loss value of high-Mn nonmagnetic steel without relying on the addition of a large amount of Cr. Moreover, according to this method, there is no concern that the corrosion form tends to cause localized corrosion such as pitting corrosion or crevice corrosion, which is the case when a large amount of Cr, which is a relatively expensive alloying element, is added. This was also confirmed.

The present invention has been made based on the above findings, etc., and is based on the above-mentioned findings.
(wt%) Si: 0.10 to 1.0%, Mn: 16
-30%.

Ni: 3.0% or less, Cr: 0.50-8
．． 0%Mo: 0.05-1.0%, N:
Contains 0.03-0.40% 8i: 0.010-010%, and P and Cu each at 0.005≦
P(χ)≦0.1×Mo(%)→−0,05x Ap
(Ri'2 x P (X)≦Cu l'l:)≦1.5
V: 0.20-1.0% Nb: 0.01-1.
5%Ti: 0.01-1.5%, Zr:
0.01-0.5% Se: 0.03-0.30%,
Te: 0.03-0.080%.

Pb: 0.05 to 0.30% of one or more types -1- is also included, and the balance is composed of Fe, in addition to the magnetic properties of high Mn nonmagnetic steel. It is characterized by the fact that it also has excellent corrosion resistance.

That is, the high-grade nonmagnetic steel according to the present invention contains mostly Cr and N.
Unlike conventional high-Mn nonmagnetic steels, which have been improved in corrosion resistance by increasing the amount of expensive elements such as No.
It is worth mentioning that excellent corrosion resistance can be achieved by reducing the amount of the expensive alloying elements added through appropriate synergistic addition with the above-mentioned alloying elements, and that excellent corrosion resistance can be provided extremely economically.

Next, the reason why the chemical composition of the high Mn nonmagnetic steel is limited as described above in the present invention will be explained in detail together with the effects of each chemical component.

<Function> (a) C C is an element that forms austenite, and has the effect of making steel non-magnetic and increasing its strength at the same time, but if its content is less than 0.10%, the desired effect due to the above effects will not be achieved. On the other hand, if the C content exceeds 0.50%, carbides tend to form, leading to a decrease in the toughness and ductility of the steel and also deteriorating the corrosion resistance. Therefore, the C content should be 0.10%.
It was set at ~0.50%.

(b) 5i SL is a necessary component for deoxidizing during steel melting, and at the same time,
Although it has the effect of improving the corrosion resistance of high Mn non-magnetic steel, it is necessary to have at least 0.1
It is necessary to contain 0% or more. On the other hand, Si is a ferrite-forming element, and addition of a large amount deteriorates non-magnetic properties and makes cracks more likely to occur during hot or cold working, so the upper limit of the Si content is set at 1.0%. Established.

(c) Mn Mn is an essential element for forming a stable austenite phase, that is, obtaining non-magnetic properties, and for this purpose it is necessary to ensure a content of at least 16%. On the other hand, 30
If Mn is contained in an amount exceeding %, hot working becomes difficult.

Therefore, the Mn content was limited to a range of 16 to 30%.

(d) Ni Ni has the effect of ensuring a stable austenite phase together with C, N, and Mn, and is also effective in increasing strength, so it is a component that is preferably added even in a small amount, but it is expensive and has a 3.0 Since Ni content exceeding 3.0% would be disadvantageous in terms of cost, the Ni content was set at 3.0% or less.

(e) Cr The Cr component has a favorable effect of significantly improving the corrosion resistance of steel, but if its content is less than 0.50%, the desired effect due to the above effect cannot be obtained; If Cr is contained in an amount exceeding 0.5%, pitting corrosion and crevice corrosion tend to increase, so the Cr content is set at 0.50 to 8.0%.

(f) M.

The Mo component not only has the effect of improving the toughness and corrosion resistance of steel, but also has the effect of suppressing the strong segregation caused by the addition of P, which will be described later. However, if its content is less than 0.05%, the desired effect due to the above effects may not be achieved. is not obtained.

However, since the addition of MO causes an increase in cost, the Mo content was determined to be 0.05 to 1.0% in consideration of cost.

(gl N N is an element effective in stabilizing the austenite phase and increasing proof stress, and in order to ensure this effect, it must be at least 0.
It is necessary to contain 0.3% or more.

On the other hand, N in an amount exceeding 0.40% increases nitrides in the steel, leading to a decrease in toughness. Therefore, the N content is 0.03~0
．． It was set at 40%.

(h) Af Al needs to be added as a deoxidizing element, and at the same time it also has the effect of improving the corrosion resistance and toughness of steel.

However, if the Af content is less than 0.010%, the desired effect due to the above action cannot be obtained, while if the Af content exceeds 0.10%, the amount of nitride precipitation increases and the toughness of the steel increases. Since this causes deterioration, the Al content should be between 0.010 and 0.01.
It was limited to a range of 10%.

(1) PP significantly improves the corrosion resistance of steel by adding Cu, Cr, Ni, Mo and AN in combination, and at the same time
Although it is a component that can reduce the amount of Cr added,
In order to ensure this effect, it is necessary to contain at least 0.005% or more. On the other hand, since addition of a large amount of P causes an increase in segregation and a decrease in toughness, it is necessary to add it in combination with a segregation-inhibiting element such as Mo or Af. However, Mo and I
Even when combined with V, the P content is (0,]×Mo(
Since the above-mentioned disadvantages cannot be avoided if it exceeds [chi] -1 - 0,05

U) Cu The Cu component not only contributes to stabilizing the austenite phase as an austenite-forming element, but also has the effect of significantly improving corrosion resistance when combined with P. In order to obtain the desired effect of the above action, the Cu content needs to be at least twice the P content.

On the other hand, if the amount of Cu added increases, hot workability deteriorates due to grain boundary embrittlement at high temperatures, so the content must be limited to 1.5% or less. Therefore, the Cu content was limited to a range that satisfied the formula 2 (%).

(kl V, Nb, Ti, and Zr) These elements all have the effect of suppressing the growth of crystal grains and improving the strength and toughness of steel, as well as the effect of improving corrosion resistance. One or more of them may be added if necessary, but if the content is less than 0.20% in the case of (3) and less than 0.01% in the case of Nb, Ti, and Zr, the desired effect will be achieved by the above action. On the other hand, if the content exceeds 1.0%, the Nb and Ti contents exceed 1.5% each, and the Zr content exceeds 0.5%, it becomes disadvantageous in terms of cost. Therefore, ■ is 0.20 to 1°0%, and Nb is 0.
．． The respective contents were determined to be 0.01 to 1.5%, Ti 0.01 to 1.5%, and Zr 0.01 to 0.5%.

(11Se, Te, and pb All of these elements have the effect of improving the machinability of high-Mn nonmagnetic steel, so one or more of these elements may be added as necessary. In both cases, 0.0
If the content is less than 3%, and in the case of pb, less than 0.05%, the desired effect of the above action cannot be obtained; on the other hand, the content of S
0.30% for both e and pb, and Te
If the Se content exceeds 0.080%, the effect will not be improved and the cost of the steel will increase. The amount is 0.03-0.080%, and the pb content is 0.05
0.30%, respectively.

Next, the effects of the present invention will be specifically explained with reference to Examples.

<Example> First, steel having the chemical composition shown in Table 1 was melted by a conventional method.

Next, these materials were soaked and solutionized at around 1050°C, and a tensile test for magnetic permeability measurement, a seawater immersion corrosion test, and a machinability test were conducted, respectively.

The results of these tests are shown in Table 2.

Furthermore, among the test results shown in Table 2, ``corrosion rate''
The "presence or absence of pitting corrosion" is graphed in relation to the "Cr content" and shown in FIG.

As is clear from the results shown in Table 2 and FIG. 1, it can be seen that the corrosion rate of the steel of the present invention is lower than that of the comparative steel even if the Cr content is the same.

Furthermore, it can be confirmed that the pitting corrosion observed in the comparative steels with high Cr content does not occur in the steel of the present invention.

<Summary of Effects> As explained above, according to the present invention, a high Mn nonmagnetic steel with excellent corrosion resistance can be provided at low cost, and can be used outdoors and in marine fields where corrosion resistance and weather resistance are required. This will bring about extremely useful effects in industry, such as making it possible to fully meet the demand for non-magnetic materials.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between Cr content, corrosion rate, and pitting corrosion occurrence tendency in high Mn nonmagnetic steel. Applicant: Sumitomo Metal Industry Co., Ltd.

Claims (1)

[Claims] (1) Weight percentage: C: 0.10-0.50%, Si: 0.10-1.0%
, Mn: 16-30%, Ni: 3.0% or less, Cr: 0
．． 50-8.0%, Mo: 0.05-1.0%, N: 0
．． 03 to 0.40%, Al: 0.010 to 0.10%, and each contains P and Cu at 0.005≦P(%)≦0.1×Mo(%)+0.05
A high Mn nonmagnetic steel with excellent corrosion resistance, containing ×Al (%), 2 × P (%)≦Cu (%)≦1.5, and the remainder being substantially Fe. (2) C: 0.10-0.50%, Si: 0.10-1.0% in weight percentage
, Mn: 16-30%, Ni: 3.0% or less, Cr: 0
．． 50-8.0%, Mo: 0.05-1.0%, N: 0
．． 03 to 0.40%, Al: 0.010 to 0.10%, and each contains P and Cu at 0.005≦P(%)≦0.1×Mo(%)+0.05
×Al (%), 2 × P (%)≦Cu (%)≦1.5, and further includes V: 0.20 to 1.0%, Nb: 0.01 to 1.5%,
Ti: 0.01-1.5%, Zr: 0.01-0.5%
A high-Mn nonmagnetic steel with excellent corrosion resistance, including one or more of the following, and the remainder being substantially Fe. (3) C: 0.10-0.50%, Si: 0.10-1.0% in weight percentage
, Mn: 16-30%, Ni: 3.0% or less, Cr: 0
．． 50-8.0%, Mo: 0.05-1.0%, N: 0
．． 03 to 0.40%, Al: 0.010 to 0.10%, and each contains P and Cu at 0.005≦P(%)≦0.1×Mo(%)+0.05
×Al (%), 2×P (%)≦Cu (%)≦1.5, and further Se: 0.03 to 0.30%, Te: 0.03 to 0.0
80%, Pb: 0.05 to 0.30%, and the remainder substantially consists of Fe. A high Mn nonmagnetic steel with excellent corrosion resistance. (4) C: 0.10-0.50%, Si: 0.10-1.0% in weight percentage
, Mn: 16-30%, Ni: 3.0% or less, Cr: 0
．． 50-8.0%, Mo: 0.05-1.0%, N: 0
．． 03 to 0.40%, Al: 0.010 to 0.10%, and each contains P and Cu at 0.005≦P(%)≦0.1×Mo(%)+0.05
×Al (%), 2 × P (%)≦Cu (%)≦1.5, and further includes V: 0.20 to 1.0%, Nb: 0.01 to 1.5%,
Ti: 0.01-1.5%, Zr: 0.01-0.5%
one or more of the following, and Se: 0.03 to 0.30%, Te: 0.03 to 0.0
80%, Pb: 0.05 to 0.30%, and the remainder substantially consists of Fe. A high Mn nonmagnetic steel with excellent corrosion resistance.