JPS61179834A - Highly corrosion resistant austenitic stainless steel having superior strength at high temperature - Google Patents

Abstract

PURPOSE:To develop high-strength and highly corrosion resistant austenitic stainless steel having superior strength at high temp. as well as excellent corrosion resistance by adding specific elements to high-Cr and high-Ni type austenitic stainless steel. CONSTITUTION:The austenitic stainless steel contains, by weight, <0.15% C, <1.0% Si, <10% Mn, 20-30% Cr, 30-55% Ni, 0.0010-0.500 of Mg and/or Ca, and >=1 kind among 0.3-3.0% Ti, 1-5% Nb, and 0.3-3.0% Al, or further contains 0.001-0.010% B and/or 0.005-0.200% Zr, 0.5-6.0% Mo and/or 1-2% W (when Mo and W are combinedly used, Mo%+W%X0.5 should be adjusted to 0.5-6%), or both of the above two kinds in combination. The high-strength and highly corrosion resistant austenitic stainless stainless steel superior in creep rupture strength 18-8 austenitic stainless steel can be obtained.

Description

[Detailed Description of the Invention] <Industrial Application Field> This invention not only has excellent corrosion resistance but also has extremely good high-temperature strength, and is suitable for use in boilers and chemicals used in high-temperature environments. This relates to austenitic steel that exhibits excellent performance when applied to plant equipment.

<Prior art and its problems> In general, materials for equipment used in high-temperature environments, such as various boiler equipment and chemical plant equipment, have high-temperature strength, corrosion resistance,
Various properties such as weldability are important, and conventionally, 18-8 type austenitic stainless steel has been used, which relatively satisfies these required properties and does not have much of a disadvantage in terms of price. It has been widely used for seed purposes.

However, in recent years, as efforts have been made to improve the efficiency of high-temperature equipment, the conditions under which materials are used have become increasingly severe, and the required material performance has also become progressively more sophisticated. Therefore, the current situation is that the currently used 18-8 austenitic stainless steel cannot sufficiently meet these requirements, including high-temperature strength and corrosion resistance.

Although it is generally known that increasing the Cr content is effective in improving the corrosion resistance of stainless steel, there is no need to point out 5US3103 steel, which is known as a high Cr-containing steel. There was a problem in that even if the .

゛〈Means for solving the problems〉 ゛This invention has corrosion resistance and high temperature strength that surpass that of 1-day-8 austenitic stainless steel, which has been a common material for high-temperature equipment, and it can be used in even better environments. In order to provide steel materials that can adequately withstand the increasingly severe conditions of high-temperature equipment, we focused on the excellent corrosion resistance of high Cr austenitic steels with a Cr content of 201 or more, and sought to dramatically improve their creep rupture strength. This was made through research conducted by the inventors and others, and its characteristics are as follows.

austenitic steel.

C: 0.15% or less (Hereinafter, "C" indicating the component ratio is weight %)
)% Si: 1.0% or less, Mn: 10% or less.

Contains Cr: 20-30%, Ni: 30-55%, one or more of Mg and Ca: 0.0010-0.0500%, and Ti: more than 0.3-3.0%.

Nb: more than 1 to 5 LIb.

A! : 0.3 to 3.0 1a of H [including the above, and if necessary, B: 0
．． 001-0.010%.

Zr: 0.005-0.200 Chi.

Mo: 0.5-6.0’ir.

°W: One or more of the following: 1 to 12 [However, when Mo and W are added in combination, it also includes Mo (@+ + W (= -0, 5 to 6), Fe and unavoidable impurities: By configuring the composition with the remainder, it not only has high corrosion resistance but also has excellent high-temperature strength.

The reason why the content ratio of each chemical component in the austenitic steel of the present invention is numerically limited as described above will be explained below.

(a) C C is an effective component to ensure the tensile strength and creep strength necessary for heat-resistant steel, but its content is 0.1
If it exceeds 5%, the ductility will decrease and the amount of undissolved carbide will increase in the solution state, which will have a negative effect on mechanical properties, so the C content was set at 0.15% or less. .

(b) 5t The Si component is an effective element as a deoxidizing agent for steel.

If the Si content exceeds 1.0, the deterioration of weldability and structural stability becomes noticeable, so the Si content was set at 1.0 or less.

Note that, especially from the viewpoint of structural stability, it is desirable to adjust the Si content to a low value.

(c) Mn The Mn component is an element that has a deoxidizing effect and an effect of improving workability of steel, but if it is contained in a large amount exceeding 10%, it becomes K which causes deterioration of heat resistance properties.

The Mn content was determined to be 10 or less.

(d) Cr The Cr component is an element that exhibits an excellent effect on improving the corrosion resistance of steel, such as oxidation resistance, steam oxidation resistance, and high-temperature corrosion resistance, but if its content is less than 20%, the above effects will not be achieved. On the other hand, the desired effect is not achieved.

If Cr content exceeds 30%, the workability deteriorates and the structure becomes unstable, so the Cr content was set at 20 to 30%.

(e) NiN1 is an essential component for obtaining a stable austenite structure1), and its content is Cr, Mo, W, Ti
, is determined by the amount of added Nb, etc.
In the composition steel of the present invention, when the Ni content is less than 30%, securing of the austenite structure becomes unstable;
The Ni content was set at 30 to 55%, since it would be economically disadvantageous to include more than 30% of N1.

(f) Mg and Ca These elements have deoxidizing effects and improving workability of steel, and are also effective elements for improving creep rupture strength. However, if the total content is less than 0.0010-1, the desired effect cannot be obtained for the above action, and on the other hand, if the content exceeds 0.05001-, the processing Since there is a tendency for the properties to deteriorate, the total content of Mg or Ca was set at 0.0% to 0.0500%.

(g) Ti, Nb, and M These components include NiyuA! , Ni3Ti ,
It has the effect of strengthening steel through the finely dispersed precipitation of intermetallic compounds such as Ni and Nb, so it is essential to add one or more kinds of them, but if the Ti content is 0.3% or less and the Nb content is 1.
Chi or less.

When the M content is less than 0.3%, the desired effect cannot be obtained; on the other hand, when the Ti content is 3.0%, the Nb content is 5%, and the M content is 3%, Since the deterioration of the workability of steel becomes noticeable when exceeding 0.0, the Ti content is more than 0.3 to 3.0, the Nb content is more than 1 to 5, and the M content is were set at 03 to 3.0%, respectively.

(h) B and Zr These components have the effect of strengthening grain boundaries and improving the high-temperature strength of steel, so when it is necessary to further improve high-temperature strength, 1 & or more elements are added. In Although,
B content is less than 0.0011, or Zr content is 0.
If the content of B is less than 0.005%, the desired effect cannot be obtained; on the other hand, if the content of B exceeds 0.010%,
If Zr is contained in excess of 0.00%, weldability deteriorates.

The B content was determined to be 0.001% to 0.010%, the Zr content was determined to be 0%, and the OO5% to 0.200%.

(i) Mo and W These elements also have the effect of effectively improving the high-temperature strength of steel, so if it is desired to further improve the high-temperature strength, 1 m or more of these elements are added as necessary. When added alone, the Mo content is less than 0.5 inches or the W content is 1%.
and in case of compound addition (Mo (@ +
+ When the amount of W (@) is less than 0.5 (%), the desired effect cannot be obtained in the above action, whereas when added alone, M
When the O content is below 6.0 T or the W content is below 12 T, and in case of combined addition K(Mo(@14-W(%
)] If the amount is less than 6 (@), it will lead to deterioration of workability and structure stability, so M.

The content is 0.5-6.0%, the W content is 1-12% [However, in the case of composite addition of one component, Mo(n + -)
w (%) −0.5 to 6 (strong), respectively.

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

<Example> First, steel materials 1 to 2 of the present invention having chemical compositions as shown in Table 1 were prepared by vacuum melting, forging and cold rolling in accordance with conventional methods.
9 and comparative steel materials A-K (however.

Comparative steel material A is conventional SUS 304. Comparative steel material B is SU
S316. Comparative steel material C is SUS 347. The comparative steel material is SUS 321. After obtaining comparative steel material EFiSUS31O8), these were subjected to solid solution treatment (treatment temperature: 120
0°C) and subjected to a creep rupture test.

Creep rupture test was performed on 1 Invention Steels 1 to 29 and Comparative Steel A.
-E were carried out at two temperatures, 700°C and 750°C, and the others were carried out only at 750°C.

1 at each temperature obtained in this way
The creep rupture strength at 000 hr is also shown in Table 1.

The results shown in Table 1, especially the invention steel 1-4 and comparative steel A.
-As is clear from the comparison results with E.

It can be seen that the strength level of the steel of the present invention containing 1 m or more of Ti, At, and Nb is higher than that of the conventional steel.

Note that FIG. 1 shows the steel of the present invention 9. l 5,17,22゜2
4 and 27 and comparison steel F- 750℃X100Ohr
This is a graph comparing the clip rupture strength.

It can also be confirmed from FIG. 1 that the addition of Mg or Ca improves the creep rupture strength of steel regardless of its composition.

Moreover, FIG. 2 shows the steels of the present invention 1, 2. and 10 of 9-12
This is a graph comparing 00hr creep rupture strength.
It can also be seen from FIG. 2 that the creep rupture strength is further improved by adding at least one of B and Zr.

Furthermore, Fig. 3 is a graph showing the effect of the addition amount of %MO or W on the creep rupture strength of steel, and the numbers in the graph indicate the steel rods in Table 1. Also, the addition of Mo or W is effective in improving the creep rupture strength of steel, and the addition effect is (Mo(n + +
It can be seen that comparison 1 can be well organized using the amount of W (%).

Separately, a corrosion resistance test was conducted on two inventive steels 1 to 29, and it was confirmed that they exhibited extremely superior corrosion resistance compared to 18-8% austenitic stainless steel due to their high Cr content. Ta.

Overall Effects> As explained above, the present invention exhibits superior corrosion resistance to 18-8 austenitic stainless steel, which has been widely used as a material for high-temperature equipment, and moreover, 8 Austenitic stainless steel or SUS 31
A high-strength, highly corrosion-resistant austenitic steel with creep rupture strength that far exceeds that of 0S steel has been realized, and is industrially useful as it can greatly contribute to improving the performance and durability of high-temperature equipment such as boilers and chemical plant equipment. This brings about a great effect.

[Brief explanation of drawings]

Figure 1 shows the effect of Mg on the creep rupture strength of steel. A graph showing the influence of Ca addition, Figure 2 shows the effect of B on the creep rupture strength of steel. A graph showing the influence of Zr addition, Figure 3 shows the effect of Mo on the creep rupture strength of steel. It is a graph showing the influence of W addition. Applicant: Sumitomo Metal Industries, Ltd. Agent Tomi 1) Kazuo and 2 other professionals 2 figures

Claims (1)

[Claims] (1) In terms of weight percentage, C: 0.15% or less, Si: 1.0% or less, Mn: 10
% or less, Cr: 20-30%, Ni: 30-55%, one or more of Mg and Ca: 0.0010-0.0500%, and Ti: more than 0.3-3.0 %, Nb: more than 1 to 5%, Al: 0.3 to 3.0%, and Fe and unavoidable impurities: remaining. Corrosion resistant austenitic steel. (2) Weight percentage: C: 0.15% or less, Si: 1.0% or less, Mn: 10
% or less, Cr: 20-30%, Ni: 30-55%, one or more of Mg and Ca: 0.0010-0.0500%, and Ti: more than 0.3-3.0 %, Nb: more than 1 to 5%, Al: 0.3 to 3.0%, and B: 0.001 to 0.010%, Zr: 0.005 to 0.0%. A highly corrosion-resistant austenitic steel with good high-temperature strength, characterized in that it also contains one or more of: 200% of Fe and the remainder of unavoidable impurities. (3) Weight percentage: C: 0.15% or less, Si: 1.0% or less, Mn: 10
% or less, Cr: 20-30%, Ni: 30-55%, one or more of Mg and Ca: 0.0010-0.0500%, and Ti: more than 0.3-3.0 %, Nb: more than 1 to 5%, Al: 0.3 to 3.0%, and Mo: 0.5 to 6.0%, W: 1 to 12%. One or more types of [However, in the case of combined addition, Mo (%)
/2W (%) = 0.5 to 6 (%)], F
A highly corrosion-resistant austenitic steel with good high-temperature strength, characterized by comprising: e and unavoidable impurities: the remainder. (4) Weight percentage: C: 0.15% or less, Si: 1.0% or less, Mn: 10
% or less, Cr: 20-30%, Ni: 30-55%, one or more of Mg and Ca: 0.0010-0.0500%, and Ti: more than 0.3-3.0 %, Nb: more than 1 to 5%, Al: 0.3 to 3.0%, and B: 0.001 to 0.010%, Zr: 0.005 to 0.0%. 200%, and one or more of Mo: 0.5-6.0%, W: 1-12% [However, in the case of composite addition, Mo (%) + 1
/2W (%) = 0.5 to 6 (%)], F
A highly corrosion-resistant austenitic steel with good high-temperature strength and consisting of the remainder: e and unavoidable impurities.