JPS61147838A - Austenitic steel having high corrosion resistance and satisfactory strength at high temperature - Google Patents

Abstract

PURPOSE:To obtain an austenitic steel having high corrosion resistance and satisfactory strength at high temp. by incorporating a specified amount of Ni into a high Cr austenitic steel. CONSTITUTION:The composition of an austenitic steel is composed of, by weight, <0.07% C, <1% Si, <10% Mn, 20-30% Cr, 30-55% Ni, one or more among 0.6-3% Ti, 1-6% Nb and 0.6-3% Al, and the balance Fe with inevitable impurities. The amounts of P and S among the impurities are restricted to <0.02% P and <0.01% S (P+S<0.02%).

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 can be used in high temperature environments. This relates to austenitic steel that exhibits excellent performance when applied to Boi 2 and chemical plant equipment.

<Prior art and its problems> In general, the materials used for equipment used in high-temperature environments, such as wood boiler equipment and chemical plant equipment, have high humidity strength, corrosion resistance,
Various characteristics such as weldability are regarded as the first thing, but in the past, these were important! ! 18-8 type austenitic stainless steel has been widely used for this purpose because it has relatively satisfactory properties and does not cause significant disadvantages in terms of price.

However, in recent years, as the efficiency of high-temperature equipment has been promoted, the requirements for the use of materials have become increasingly severe9, and the required material performance has also increased as follows: Since it has become increasingly sophisticated, the current use of upper ID is 18-
8 austenitic stainless steel is unable to meet these requirements, including high-temperature strength and corrosion resistance, due to its lumpiness.

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 5U83108 steel, which is known as a high Cr-containing steel. Even if it increases, the effect of improving high-temperature strength is not only undesirable, but the problem is that the negative effect is even more noticeable in some cases.

Means for Solving the Problems> This invention has corrosion resistance and high temperature strength that surpass 18-8 austenitic stainless steel, which is common and rare as a material for high-temperature equipment, and has 1! ! In order to provide a steel material that can withstand high-temperature equipment that is becoming increasingly harsh, we focused on the excellent corrosion resistance of high-Cr austenite copper, which has a Cr content of 20 or more. This was accomplished through research conducted by the present inventor and others with the aim of dramatically improving the creep rupture strength, and its characteristics are as follows.

On austenitic steel, C: less than 0.07% (hereinafter, the component ratio is taken as a weight factor), si: x, os or less, Mn: 10% or less, Cr:
20-301, Ni: 30-55%.

and at least one of the following: Ti: over 0.6 to 3.0, Nb: over 1 to 6, At: over 0.6 to 3.0 (however, when added alone, each the lower limit,
Ti: 0.8L, Nb: 1.69&, At: 0.8
If necessary, B: 0.001-0.010%, Zr: 0.005-0.200%, Mo: 0.
．． 5-6.0%.

W: 1 to 12%, including at least one building [however, when adding Mo and Wt in combination, MO (up to) + 1/2 W- to 0.5 to 6 (A)], and the remainder It consists of diFe and inevitable impurities, and the contents of P and S in the impurities are particularly P: 0.0201% or less, S: 0.010% or less, and P (to) + S (a) <0. By forming the steel with a component composition that satisfies 02-, it not only has high corrosion resistance but also has excellent high-temperature strength.

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

(2) C C is an effective component for securing the tensile strength and creep rupture strength necessary for heat-resistant steel, but component yarns aiming at fine dispersion precipitation strengthening of intermetallic compounds as in the steel of this invention In this case, the stiffness-improving effect of C is relatively small, and if the content exceeds 0.071, the decrease in ductility becomes noticeable, so the C content is set at less than 0.07.

(b) 5t St acid component It is an effective element as a deoxidizing agent for steel, but if its content exceeds i, o, #! Since the deterioration of adhesion and structure stability becomes noticeable, the Si content should be set to 1. It is set as O overseas or below.

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

(c) Mn MnFfc is an element that has a deoxidizing effect and a process reforming effect on steel, but if it is contained in a large amount exceeding 10%, it will cause deterioration of heat resistance properties.

The seed content was set at 10 or less.

(iv) Cr The Cr component is an element that exerts the following effects in 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 parts, it does not have the desired effect. The Cr content was determined to be 20 to 30%, because if the Cr content exceeds 1,000,301 tubes, the workability deteriorates and the composite fibers become unstable.

(e) Ni Ni is an essential component for obtaining a stable austenite structure, and its content is CrlMo, W, Ti, N.
b.

It is determined by the amount of At added, etc., but in the steel composition of this invention, if the Ni content is 30%, it will be unstable to secure the austenitic structure, whereas if it exceeds 55%, the Ni content will be unstable. Since this would bring about an economic disadvantage, the Ni content was set at 30 to 55%.

■ Ti, Nb, and μ These components include N 1 @ AL s N
l @ T 1 .

It has the effect of strengthening steel through finely dispersed precipitation of intermetallic compounds such as Ni and Nb, but if the Ti content is 0.6% or less,
Nb content is 1 or less, then: t”At content is 0.6
- In the following cases, the desired effect will not be obtained, and if each of these components is added alone, 'l
'i: 0.8 or more, Nb: 1.64 or more, M
: Unless a gold content of 0.8 or higher is secured, it may be difficult to obtain a stable strength-increasing effect. -10,000, T1
The upper limit of the Nb content is 3.0 yen and the upper limit of the Nb content is 6 yen.
If the upper limit of the M content exceeds 3.0%, the deterioration of the workability of the steel becomes noticeable.

Therefore, the Ti content is 0.6 [~3.0%, Nb
Content is more than 1 - V61A2 content is more than 0.6 ~ 3.0%
(However, in the case of individual addition, the lower limit of each is Ti: 0.8
H, Nb: 1.6%, At: 0.8%).

Ton B, and 7. r Since these components have the effect of strengthening grain boundaries and improving the high temperature strength of steel, these elements are added when there is a need to further improve high temperature strength II-1 or more. , S content is less than 0.001%, or Zr content is 0
．． If the Bt content is less than 0.005qb, the desired effect cannot be obtained; on the other hand, if the Bt content exceeds 0.010%,
．． If Zr is contained in an amount exceeding 200%, weldability will deteriorate, so the S content should be 0.001 to 0.01.
0%. The 2r content was determined to be 0.005 to 0.200%.

(b) M2S and W Since these components also have the effect of effectively improving the high temperature strength of steel, they are elements that are added if necessary to further improve the high temperature strength. When added alone, the Mo content is 0.5, or the W content is 1.
%, and in case of compound addition (Mo(i)+
1/2W■] If the amount is 0.5611, the desired effect cannot be obtained;

In the case of single addition, the Mo content is 6.0% 'i, the W content is 129jt-Ten, and in the case of combined addition, the amount of CMo (4) + 1/2 W ■] is 6 (4) gold. Since building with earthenware will lead to deterioration of workability and structural stability, the Mo content should be 0.5 to 6.0%, and the W content should be 1 to 12%.
LII [However, in the case of combined addition of both components, Mo-+1
72W■=0.5 to 6-].

(i) P and S P and S are impurities that inevitably enter steel (
The P and S levels in general steel are each 0.025
around 0.005 to 0.015), P
The content is 0.020 metal, and the S content is 0.010.
If the P content exceeds t-0, or if the total amount exceeds 0.02 g, the high temperature long-term creep rupture strength at 650 to 750°C will decrease. ,020% or less, S content t-0,0101 or less, and the total amount is 2P61+S% < 0
．． 02 ■ Satisfy each other and each other.

In addition, in steels with high Cr and high alloy component yarns such as the steel of the present invention, it is preferable from the viewpoint of weldability to limit the P and S contents as described above.

Moreover, it is desirable to suppress the total content of P and So to less than 0.015 parts if possible.

In Section 9, 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 manufactured by vacuum bath manufacturing, forging and cold compaction in the usual manner.
3 and comparative steel material A-kLj- were subjected to solid solution treatment (treatment temperature: 1200° C.) and subjected to a creep rupture test.

Creep rupture tests were carried out on inventive steels 1 to 11 and comparative steel A.
-F was carried out at two temperatures, 700°C and 750°C,
For other items, only 750C 'j! Muta.

10"hr at each temperature determined in this way
Table 2 shows the creep rupture strength at 10'hr.

In addition, the jg1 diagram was created by arranging the results of the 1s2 table, CP611+Sf! 14) is a graph showing the influence 411 on the creep rupture strength, and the numbers and alphabets in the graph indicate the steel types in Table 1.

Furthermore, FIG. 2 is a graph comparing the creep rupture strength at 750° C. of the present invention steel and comparative steel, which have similar compositions, and was created by organizing the results in Table 2.

As is clear from these results, inventive steels 1 to 23
Both are made of 18-8 austenitic stainless steel (
5US304H, 5US316H.

5US321H, 5US347H) and 25Cr-2O
It can be seen that among Ni-based stainless steels (SUS310S), the enemy also exhibits a higher strength level than SUS 316H, which has high creep rupture strength.

Refreshingly, the following is clear from Figure 1.

That is, the 10"hr breaking strength at 700°C is not affected by the composition system, and there is no particularly significant difference between the invention steel and the comparative steel. However, the 10"hr breaking strength at 700°C
When looking at the 0'hr rupture strength, lQ''hr rupture strength at 750°C, and 10'hr rupture strength, clear significant differences were observed between the inventive steel and the comparative steel, and I:Pt119
+S%] value of 0.02 or more, the value is 0.
．． It can be seen that the breaking strength is significantly reduced compared to the steel of the present invention with a steel of less than 0.02.

Since this tendency is the same for the other component systems listed in Figure 2, and the steel of the present invention has a high Cr content, 1B-8 austenitic stainless copper (compared to It was also confirmed that the material exhibited extremely excellent corrosion resistance.

As described above, in highly corrosion-resistant austenitic steel with a Cr content of 20 to 30%, P and S, which are impurity elements, have a large influence on the creep rupture strength, and in particular, P and S
By limiting the amounts individually, as well as by limiting the total amount to less than 0.02%, it is possible to obtain a high-strength, highly award-resistant austenitic steel that has extremely excellent creep rupture strength at high temperatures and over long periods of time. That is clear.

Overall Effects> As explained above, the present invention shows superior corrosion resistance to 18-8 austenitic stainless steel, which has been widely used as a material for high-temperature equipment, and
f118-8 austenitic stainless steel or 5US3
10S Steel T - A high-strength, highly corrosion-resistant austenitic steel that also has far superior creep rupture strength has been realized, and can greatly contribute to improving the performance and durability of high-temperature equipment such as boilers and chemical plant equipment. Moreover, useful effects are brought about.

[Brief explanation of drawings]

FIG. 1 is a graph showing the influence of P and S amounts on the creep rupture strength of steel. FIG. 2 is a graph showing the IJ-g rupture strength of various steels obtained in Examples. Applicant Sumitomo Metal Industries Co., Ltd. Agent Tomi 1) Kazuo and others 2 Elderly I class

Claims (3)

[Claims] (1) Weight percentage: C: less than 0.07%, Si: 1.0% or less, Mn: 10
% or less, Cr: 20-30%, Ni: 30-55%, Ti: more than 0.6-3.0%, Nb: more than 1-6%, Al: more than 0.6-3 .0% or more (however, when added alone, the lower limit of each
Ti: 0.8%, Nb: 1.6%, Al: 0.8%), and the balance consists of Fe and unavoidable impurities, and the content of P and S in the impurities is particularly low. P: 0.020% or less, S: 0.010% or less, and is limited to satisfy P (%) + S (%) < 0.02 (%), high temperature Highly corrosion resistant austenitic steel with excellent strength. (2) Weight percentage: C: less than 0.07%, Si: 1.0% or less, Mn: 10
% or less, Cr: 20-30%, Ni: 30-55%, Ti: more than 0.6-3.0%, Nb: more than 1-6%, Al: more than 0.6-3. 0% or more (however, when added alone, the lower limit of each
Ti: 0.8%, Nb: 1.6%, Al: 0.8%), and B: 0.001 to 0.010%, Zr: 0.005 to 0.200%. The remainder consists of Fe and unavoidable impurities, and the content of P and S in the impurities is particularly P: 0.020% or less and S: 0.010% or less. A highly corrosion-resistant austenitic steel with excellent high-temperature strength, characterized in that P (%) + S (%) < 0.02 (%). (3) Weight percentage: C: less than 0.07%, Si: 1.0% or less, Mn: 10
% or less, Cr: 20-30%, Ni: 30-55%, Ti: more than 0.6-3.0%, Nb: more than 1-6%, Al: more than 0.6-3. 0% or more (however, when added alone, the lower limit of each
Ti: 0.8%, Nb: 1.6%, Al: 0.8% I), and Mo: 0.5 to 6.0%, W: 1 to 12%. Species or more [However, in the case of combined addition, Mo (%) + 1
/2W (%) = 0.5 to 6 (%)], the balance consists of Fe and unavoidable impurities, and the content of P and S in the impurities is particularly P: 0.020% Hereinafter, highly corrosion-resistant austenite with excellent high-temperature strength, characterized in that S: 0.010% or less and is limited to satisfy P (%) + S (%) < 0.02 (%) steel. (A) Weight percentage: C: less than 0.07%, Si: 1.0% or less, Mn: 10
% or less, Cr: 20-30%, Ni: 30-55%, Ti: more than 0.6-3.0%, Nb: more than 1-6%, Al: more than 0.6-3. 0% or more (however, when added alone, the lower limit of each
Ti: 0.8%, Nb: 1.6%, Al: 0.8%), and B: 0.001 to 0.010%, Zr: 0.005 to 0.200%. One or more of these, and one or more of Mo: 0.5-6.0%, W: 1-12% [However, in the case of combined addition, Mo (%) + 1
/2W (%) = 0.5 to 6 (%)], the balance consists of Fe and unavoidable impurities, and the content of P and S in the impurities is particularly P: 0.020% Hereinafter, S: 0.010% or less, P (%) + S (%) < 0.02 (%), characterized by having excellent high temperature strength, high Corrosion resistant austenitic steel.