JPS63190144A - High temperature austenitic stainless steel - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is suitable as a structural material for nuclear pressure vessels, pipes, heat exchangers, etc. used in high-temperature environments, as well as for boilers, chemical plant equipment, etc. Regarding stainless steel.

[Conventional technology]

Conventionally, 18-8 series or 17-13-2 series austenitic stainless steels (hereinafter referred to as austenitic steels) have been used for this type of application because high-temperature strength is required. Among these, in terms of high temperature strength, it is 17-13-2.
The austenitic steel of the thread is better, for example, 5US316.5US316L, 5US316N, shown in Japanese Industrial Standard, YRS G4303 (1981).
Steel types such as 5US316LN are known.

In these existing steel types, the content of C and N is determined by taking into account that the strengthening effect of solid solution strengthening of C and N and the precipitation of carbides due to the inclusion of C reduce corrosion resistance. It is not a steel type with improved high temperature strength and ductility.

[Problem that the invention seeks to solve]

In recent years, the operating conditions of equipment used in high-temperature environments as mentioned above have become significantly more severe, and demands for improved reliability have increased, and the performance required of materials for these types of equipment has become more sophisticated. , the result is 18-8 series, 17-13-2
High-temperature strength that exceeds that of other materials is required. In addition, in high-temperature use, not only the high-temperature strength such as the creep rupture strength of the material, but also the ductility at high temperatures,
That is, it is also necessary to pay attention to creep rupture ductility.

The present invention is based on 17-13-2 series austenitic steel with excellent high-temperature strength, c: 0.025% or less, N
: 0.03 to 0.12 inch, Al: 0.04 inch or less, thereby providing an austenitic steel that is superior in both high-temperature strength and ductility than conventional 17-13-2 series austenitic steel. The purpose is to

[Failure to solve the problem]

Generally, improvements in the high temperature strength of austenitic steels are achieved by increasing the amount of C and N. Since both C and N have a solid solution strengthening effect, the high temperature strength can be improved.

The present inventors have conducted various experiments and research on methods for increasing the creep rupture strength and ductility of 17-13-2 materials, and have found that increasing the amount of C increases and coarsens carbides, causing coarse boundary embrittlement. As a result, not only the creep rupture ductility
It was found that this decreases fracture strengthening. Furthermore, it has been found that the effect of improving the creep rupture strength by increasing the amount of N is greater than that of C, and that increasing the amount of N does not lower the creep rupture ductility as much as C. Furthermore, as a result of investigating the effect of M on the high-temperature strength properties of 17-13-2 series materials, we found that increasing the amount of M leads to precipitation of M nitrides, which in turn reduces creep rupture strength and ductility. Obtained.

The present invention is based on the above findings, and provides C: 0.
025% or less, Si: 1% or less, Mn: 2% or less,
P: 0.045% or less, S: 0.03% or less, N1: 1o~5ch, Cr: 16-18%, M
o: 2-3%, N: 0.03-0.12%, Al:
It is a high-temperature austenitic stainless steel characterized by containing less than 0.04 tin, with the remainder consisting of slag and unavoidable impurities.

[Effect]

The reason for limiting the component range in the present invention is as follows.

C: C is a useful component for ensuring the tensile strength necessary for heat-resistant steel, but it causes precipitation of carbides when used at high temperatures, thereby reducing creep rupture strength and ductility.

Therefore, in order to suppress the precipitation of carbides, the thickness was set to 0.025 inches or less.

N: Like C, N is a useful component for ensuring tensile strength, and C is also a useful component for improving creep rupture strength. .0
31 or more is required.

However, an excessive increase in N leads to the formation of nitrides, lowering creep rupture strength and ductility as well as lowering weldability, so the content was set to 0.12% or less. .

u: Al is useful as a deoxidizing component, but it generates nitrides and reduces creep rupture strength and ductility, so it is suppressed to 0.04% or less.

Cr, Ni, Mo, Si, lJu, P and S
: Since there is no particular difference in creep rupture strength and ductility within the composition range of existing steel types of 17-13-2 series materials, the composition ranges were set to be the same as those of existing steel types.

The austenitic stainless steel according to the present invention can be made from existing 17-13-2 series materials, such as SUS, by adjusting the chemical components, especially the contents of C, N, and M, to the above-mentioned ranges.
Has high temperature strength exceeding 316 steel and 5US31
6.5US316L, 5US316N, 5US316
It has ductility at high temperatures exceeding that of LN.

〔Example〕

Examples of the steel of the present invention will be described in comparison with comparative steels.

A steel plate manufactured according to the composition range of the steel of the present invention, and 5US31
An example of a steel plate manufactured using the component range No. 6 will be explained. Table 1 shows the chemical composition of two types of 5US316 conventional steel and two types of steel of the present invention.

These four types of steel all contain 0.04% Al in order to suppress the decrease in creep rupture strength and ductility due to Al.
It is as follows. 55 tests conducted on these four types of steel
The results of the creep rupture test at 0°C are shown in Figures 1 and 2. FIG. 1 shows test results showing the relationship between creep rupture strength and rupture time, and FIG. 2 shows test results showing the relationship between creep rupture elongation and rupture time.

As shown in FIG. 1, the creep rupture strength of the steels of the present invention (3, 4) is significantly superior to that of the conventional steels (1, 2). In terms of creep rupture time, the steel of the present invention has a creep rupture time approximately 10 times that of conventional steel.

Regarding creep rupture elongation, as shown in Figure 2, the steels of the present invention (3, 4) are significantly superior to the conventional steels (1, 2), and the elongation decreases by 9 on the long-term side. This is a small result.

Figures 3 and 4 are the results of a 700°C creep rupture test conducted on the three types of steel shown in Table 2 (excerpted from NRIM CREEP 5H-EET, National Institute for Metal Materials). The three types of steel (5, 6, 7) in Table 2 are all heat exchanger tube materials manufactured with the composition range of SUS 316, and when comparing the chemical composition of these three types of steel, there are no unique differences other than M. I can't. Figure 3 shows these three types of steel (5, 6
Figure 4 shows the test results showing the relationship between creep rupture strength and rupture time for the same steel type. It is decreasing in the order of 5.6. That is, it is clear that the creep rupture strength and elongation at break tend to decrease as the M content increases.

Table-1 Table-2 [Effects of the invention] As is clear from the above examples, the steel of the present invention has both high-temperature strength and ductility far superior to existing 17-13-2 series materials. It is applied to structural materials such as nuclear pressure vessels, pipes, heat exchangers, boilers and chemical plant equipment, and has a great effect on improving reliability and improving economic efficiency by reducing plate thickness. It is something.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between creep rupture strength and rupture time of the steels in Table 1. Figure 2 is a diagram showing the relationship between creep rupture elongation and rupture time of the steels in Table 1. FIG. 4 is a diagram showing the relationship between creep rupture strength and rupture time of the steels in Table 2, and FIG. 4 is a diagram showing the relationship between creep rupture elongation and rupture time of the steels in Table 2.

Claims (1)

[Claims] C: 0.025% (weight%, same below) or less, Si: 1
% or less, Mn: 2% or less, P: 0.045% or less, S:
0.03% or less, Ni: 10-15%, Cr: 16-1
8%, Mo: 2% to 3%, N: 0.03 to 0.12%,
A high-temperature austenitic stainless steel containing Al: 0.04% or less, with the remainder consisting of Fe and inevitable impurities.