JPS5848623B2 - High chromium high nickel alloy with excellent hot workability and corrosion resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high chromium, high nickel alloy that has excellent corrosion resistance, as well as good hot workability and weldability.

Conventionally, metal materials have not been used for equipment that is exposed to a mixed acid consisting of nitric acid and hydrofluoric acid due to the severe corrosion caused by nitric and hydrofluoric acids, and non-metallic materials such as rubber and other acid-resistant resins have been used in these environments. is used.

However, when mechanical strength is required for non-metallic materials,
Another problem is that they cannot be used in high-temperature environments, and furthermore, it is difficult to manufacture large structures using non-metallic materials.

Equipment used at high temperatures, such as when exposed to nitric-fluoric acid;
The structure is a melting tank for spent fuel in a fast breeder reactor, and the equipment material is Inconel 690.
(30 Cr-60Ni, trade name) is known to exhibit good corrosion resistance, but the present invention provides even better weldability and hot workability that enables production of plates and tubes. The present invention provides a high chromium, high nickel alloy that has superior corrosion resistance than Inconel 690, and has a content of (IJ C0.02% or less, SiO-5% or less, Mn
2% or less, 80.005% or less, A70, 5% or less, Y
0.010~0.10%, Cr33~38%, Ni5
(2) C0.04% or less, Nb O. 4% or less, but if C is 0.02% or more, NblOXC% or more, 8
10.5% or less, Mn 2% or less, 80.005% or less,
A7 0. 5% or less, Y0.0 1 0-0.1 0
%, 33 to 38% of Cr, and 0 to 60% of Ni5, with the remainder substantially consisting of Fe.

That is, for corrosion resistance, the amount of Cr was increased to 33% or more,
It was found that reducing the amount of C as much as possible and adding an appropriate amount of Nb improves the properties, and that as the amount of Cr increases, the hot workability deteriorates significantly, and when Nb is added, the fermentation weldability deteriorates. .

The present invention has succeeded in obtaining a high chromium, high nickel alloy which has good workability and weldability and has better corrosion resistance than Inconel 690 by regulating these components in appropriate amounts.

The present inventors melted various alloys whose main components were Cr and Ni, and investigated their corrosion resistance, hot workability, and weldability, and obtained the following results.

■) Corrosion resistance The corrosion resistance in nitric-fluoric acid solution that should be considered is general corrosion resistance and intergranular corrosion resistance.After performing TIG welding on the hot-rolled material of the above ingot alloy, Te 3 fighting thickness XL
A test piece with a width of 0 mm and a length of 40 m was taken and immersed in a boiling solution of a mixed acid consisting of 11 molar nitric acid and 0.1 molar hydrofluoric acid for 6 hours. According to research, the most important component for general corrosion resistance is Cr.
As shown in FIG. 1, the corrosion rate of alloys based on 55% Ni with varying amounts of Cr decreases significantly as the amount of Cr increases.

However, it was found that the effect of increasing Cr is small at 38% Cr or more.

On the other hand, as shown in Figure 2, intergranular corrosion occurs in a 35Cr-55Ni alloy containing approximately 0.2% Si.
If the amount is 0.02% or less or more, N
It has been found that when b/C, qlO, intergranular corrosion at the acid contact area can be prevented.

Note that when the amount of Si exceeded 0.5%, intergranular corrosion occurred even in the range of the amount of C and Nb that did not cause intergranular corrosion.

2) Hot workability A square ingot weighing 30 kg was heated to 1200°C and then hot rolled, and the occurrence of cracking during that process was examined. Hot workability deteriorated as the amount of Cr increased. , especially 3
When the content exceeds 0%, the deterioration is significant, but as shown in Table 1, the hot workability of alloys with varying amounts of Ni based on 35% Cr improves considerably when the content exceeds 50% Ni. However, it is still far from sufficient.

Therefore, as a result of studying the effects of various trace elements on the 35Cr-55Ni alloy, it became clear that hot workability was significantly improved by reducing S and adding an appropriate amount of Y.

As shown in Table 2, when the amount of S is reduced to 0.005% or less and Y is added to the surface by 0.010 to 0.10%,
It was found that the hot workability became good, and that if more than 0.10% was added, the hot workability deteriorated again.

3) Weldability The hot-rolled material described above is subjected to a balestrene test, and the weld crack length is measured to evaluate weldability.

FIG. 3 shows the test results for 35Cr-55Ni.

In the case where the Si content is 0.3%, when 0.4% or more of Nb is added, the crack length increases rapidly and the weldability deteriorates.

In contrast, alloys containing 0.8% Si have 0.2% Si.
I learned that Nb also deteriorates weldability.

Next, based on the above results, the reason for limiting the alloy classification in the present invention will be explained.

Cr: Cr is an essential component that improves general corrosion resistance in nitric-fluoric acid solutions, and requires a content of 33% or more, but the effect is saturated at 38% or more, so the content is set at 33 to 38%.

On the other hand, if it exceeds 33%, hot workability deteriorates.

Ni: 33-38% To improve the hot workability of Cr, 50% or more of N1 is required, and even if it becomes 60% or more, the effect is small, so it is limited to 50-60%.

C and Nb: Intergranular corrosion resistance is improved by reducing the amount of C and adding Nb, but if the amount of Nb is added more than 0.4%, weldability deteriorates, so it is limited to 0.4% or less.

Also, below 0.02%C, Nb is not necessarily necessary, but 0
．． If the amount exceeds 0.02%C, intergranular corrosion is prevented and Nb
/C must be kept at 10 times or more.

To achieve Nb/C depletion of 10 with 0.4%Nb or less, the amount of C must be 0.
．． It is necessary to keep it below 0.04%.

Sj:Si is a necessary component as a deoxidizing agent, but 0.5%
If the content is higher, weldability and intergranular corrosion resistance will be significantly deteriorated, so the content should be 0.5% or less.

Mn: Mn is an element used as a deoxidizing agent and also stabilizes austenite and improves hot workability, and addition of 2% or more is expensive and impractical.

S: If S exceeds 0.005%, hot workability will be significantly deteriorated, so the S content should be 0.005% or less.

Y: Y significantly improves hot workability, and its effect is 0.
It is large in the range of 0.01 to 0.10%.

Al: Effective as a deoxidizing agent, and can be added up to 0.5%.

Next, examples of the present invention will be shown.

The alloys of the present invention and comparative alloys shown in Table 3 were melted and examined for corrosion resistance, hot workability, and weldability.

The same evaluation method as described above was used in both cases, and the results are also shown in Table 3.

As is clear from the above table, the alloy of the present invention has good corrosion resistance (general corrosion resistance and intergranular corrosion resistance), hot workability, and weldability, but the comparative alloy is not sufficient in any of the performances.

Those with a Cr content of less than 33% (A17.18) have poor general corrosion resistance, and those with a C content and Nb content (C0.02 to 0.02%) have poor general corrosion resistance.
04% Nb/C (49.14) and S
When the i content (AI 0.1 6) is outside the range of the present invention alloy, intergranular corrosion occurs in the welded part, and when the Cr content is more than 38% (413) and the Ni content is less than 50% (
A6.12), S content is more than 0.005% (,%
1 1 ) and those having a Y amount outside of 0.010 to 0.10% (/l6.15.16) do not have sufficient hot workability.

In addition, when the Nb amount is more than 0.4% (,%11), and even if the Si amount is less than 0.5%lda (AI0, 16)
) Poor connectivity.

It should be noted that Alloy No. 18 is an alloy equivalent to Inconel 690, and its corrosion rate is higher than that of the alloy of the present invention, and intergranular corrosion occurs.

[Brief explanation of drawings]

Figure 1 shows the relationship between Cr content and corrosion rate in a 55%N1 base alloy, Figure 2 shows the relationship between C% and Nb% on the occurrence of intergranular corrosion in a 0.2Si-35Cr55Ni base alloy, and Figure 3 is a chart showing the relationship between the amount of Nb and weldability in a Si-35Cr55Cr base alloy.

Claims (1)

[Claims] 1% by weight of CO. 0 2% or less, S i 0.
5% or less, Mn 2% or less, 80.005% or less, A7
0. 5% or less, Y0.0 1 0-0.1 0%,
A high chromium, high nickel alloy with excellent hot workability and corrosion resistance, containing 33 to 38% Cr, 50 to 60% Ni, and the remainder substantially consisting of Fe. 2% by weight, C0.04% or less, NbO. 4% or less,
However, if C is 0.02% or more, NblOXC% or more,
S i 0. 5% or less, Mn 2% or less, 80.005
% or less, Al0.5% or less, Y O. 0 1 0-0.
A high chromium, high nickel alloy with excellent hot workability and corrosion resistance, characterized in that it contains 10% Cr, 33-38% Cr, and 50-60% Ni, with the remainder substantially consisting of Fe.