JPS59222560A - Austenitic stainless steel having resistance to hot water containing s - Google Patents

Abstract

PURPOSE:To obtain the titled stainless steel having superior corrosion resistance in environment contg. sulfide and chloride by extremely reducing the amount of S in an austenitic stainless steel having a prescribed composition and by combinedly adding small amounts of Ti, Nb and Mo. CONSTITUTION:This austenitic stainless steel having resistance to hot water contg. S consists of, by weight, 16-20% Cr, 6-15% Ni, <=0.05% C, <=1.0% Si, <=2.0% Mn, <=0.005% S, C%X4+0.1-0.5% Ti, 0.2-1.0% Mo and the balance Fe with inevitable impurities. In the composition, C%X8+0.1-0.7% Nb or Ti+ Nb may be substituted for Ti. By the composition the resitance to pitting corrosion and crevice corrosion in environment contg. sulfide and chloride is improved. The steel is suitable for use as the material of piping for hot spring water, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an austenitic stainless steel having excellent corrosion resistance against S-containing hot water.

In general, hot spring water contains a large amount of various dissolved components and is more corrosive than other domestic water such as tap water or gray water, or industrial river water.

Among them, hot spring water containing sulfides and chlorides is even more corrosive and often causes damage to piping and handling equipment.

Traditionally, suction pipes for wells, asbestos pipes, polyvinyl chloride pipes, and galvanized steel pipes have been used for hot spring water piping systems, but these materials have low mechanical strength. Tashi9. Due to their disadvantages such as poor corrosion resistance and short durability, they are currently being replaced extremely frequently even though they are in practical use.

9. In recent years, in order to overcome this difficulty,
Although it is cheaper than conventional piping materials, it is suitable for industrial piping,
SUS 3 has a proven track record as water supply piping and hot water supply piping.
04 stainless steel pipe material has begun to be used and is gradually becoming more popular.

However, as mentioned above, hot spring water is much more corrosive than tap water or industrial water, and in particular, hot spring water containing sulfides and chlorides tends to cause localized corrosion such as crevice corrosion and pitting corrosion in 5US304. However, its applicability to hot spring water is extremely limited.

In such environments, stainless steel with excellent resistance to localized corrosion such as pitting corrosion and crevice corrosion is made of high Cr steel containing MO (2 or more) or high Cr-Ni steel containing MO (2% or more). , these steel types are considered usable, but 5US
It is significantly more expensive than 304 and is less practical as a piping material for hot springs.

From this point of view, the present inventors have found corrosion resistance against a wide range of S-containing hot water, typified by hot spring water.

What's more, this is the result of various research into stainless steel, which costs about the same as 8US304 as a practical piping material.

We have developed stainless steel for hot springs that has excellent corrosion resistance in hot spring environments containing highly corrosive sulfides and chlorides.

The present inventors made 5US304 austenitic steel extremely low in S and added a small amount of Ti and/or Nb and MO to improve pitting corrosion resistance and crevice resistance in environments where sulfides and chlorides exist. It was found that the corrosivity was significantly improved.

r4iJ2According to the present invention ECr: 16-20%, N
i: 6 to 15%, Si: (1.0% or less,
Mn: (2,0chi, S:<[J, 005%, Ti:C%
X 4 0.1% to 05% or Nb:C%X 8
,+[,1,1%~0.7% or Ti+Nb:C%
A corrosion-resistant S austenitic stainless steel for hot water containing a composite of x s + o, i% to 07%, and the balance consisting of Fe and inevitable impurities is provided.

The reasons for limiting the composition of the steel of the present invention are as follows.

C: +1iiJ From the viewpoint of consistency, the amount contained in 5US304 is sufficient.2 The amount of Ti and Nb added can be determined based on the amount of C, so if the amount of C is large, the amount of Ti and Nb added will also be large. In this case, the amount of C was set to 0.05% or less.

Si: Si remains after being added to the molten metal as a deoxidizing agent, and is usually kept at 1% or less, which is about the same as 5U8304.

Mn: Mn is an element that improves hot workability.

Even if it is added in an amount of 10% or more, there is no improvement effect commensurate with the amount added, but up to 2% is harmless, so it is set at 2% or less.

(If it exceeds 2%, it will impair the corrosion resistance.) Cr: Cr is an essential element to improve copper's local corrosion resistance such as pitting corrosion resistance and crevice corrosion resistance, but if it is in too much, it will increase the price. If it is less than 16%, the corrosion resistance that is the objective of the present invention cannot be achieved, so the appropriate amount range is 160%.
% to 200%.

Ni: is an essential element to make steel into an austenitic structure and improve its corrosion resistance, and its amount is determined by its relationship with the ferrite-forming elements.
．． It becomes 0-15.0%. Adding more than the upper limit will only increase the price.

S: S is an element harmful to local corrosion resistance, so it is desirable that it be as low as possible, but in order to achieve the corrosion resistance that is the objective of the present invention, it should be kept in an extremely trace amount of 0.005'S or less. It is an essential condition to do so.

Mo: Mo is an essential element for improving pitting corrosion resistance and crevice corrosion resistance. Corrosion resistance improves as the amount added increases, but it is an expensive element, leading to an increase in price. 2 Invention 141H
4 characteristics are impaired. It was set as an economical range of 0.02% or more and less than 1.0%, which shows a remarkable extraneous effect. In particular, the present invention aims at a synergistic effect between Mo and Ti or Mo and Nb by adding them in combination to an austenitic structure containing Ni.

The addition of Mo at a low concentration of 0.2% to 1.0% significantly improves the edibility of L oxides and chlorides, considering the balance with other ingredients and cost. 0
The objective is fully achieved within a range of less than %.

'J'i: Til'i is an effective element for improving the corrosion resistance of sulfide and chloride solutions, and also
It is fixed as i-carbide and has the effect of preventing intergranular corrosion.

Point 1: In light, it is necessary to add C%X 4 + 0.1% or more. However, if the amount of Ti is too large, surface defects are likely to occur at the base, so D is preferably 0.5% or less.

Nb: Like Nb I'iTi, it has the effect of improving corrosion resistance and fixing C in the pot to Nb carbide to prevent two-grain boundary corrosion.

In the present invention, it is necessary to add C% x s 100, i% or more, but too much Nb deteriorates workability and weldability, so the upper limit is set to 07 candy as a preferable range. In the case of value addition with Ti, C% x 8 [J, 1
% or more and 0.7% size is preferable.

The invention will now be illustrated with reference to examples.

Table 1 shows the chemical compositions of the steel of the present invention, the conventional steel, and the comparative steel used in the test. Among the test steels, A.

B and C are conventional steel and D-L is comparative steel and M-
R is the invention.

The comparative IdJ and the steel of the present invention were produced by a conventional method.

Desulfurization was carried out by adding CaO-based slag and U.

Ca or Si may be used instead of A10, and desulfurization is also possible by adding REM. In the case of hot metal, Ca C2
It may be processed with

These steels were made into cold-rolled steel plates with a thickness of 2 mm using a conventional method, and test specimens of *omm x 1 am were made from them.

It was subjected to a pitting corrosion resistance test.

200 ppm (J-, 80°C containing 200 ppm5-
Figures 1 to 3 show the results of measuring the pitting corrosion potential in a hot water melt.

1. Figure 1 shows the relationship between S content and pitting corrosion Ik for samples A, K, and L. As seen in curve (a).

When the S content becomes 0.005% or less, the pitting corrosion potential increases rapidly.

FIG. 2 shows the relationship between the contents of Ti and Nb and the pitting potential. The curve (b) in the figure shows the effect of Ti on samples A, B, D, and B, and the second curve (c) is for sample A.

The effect of Nb is shown by C, F, and G.

As seen in this figure, Ti and Nb have a remarkable effect of improving pitting corrosion resistance up to 0.1%, and the effect is saturated at U5~[J, 7%.

FIG. 6 shows the combined addition of Ti and/or Nb and Mo in relation to pitting potential. The curve in the figure) (E) is sample E.
, M', N and Q, R, and represents the test results for Ti+Mo and Ti+Nb+M
o series is shown. (f) shows the test results for samples G, O, and P. Two curves (g) show the test results for the Nb+Mo system.
, H, I, and J, and M
o Shows a single system. As seen in this figure.

Within the range of the alloy of the present invention, the pitting corrosion potential is significantly nobler than that of conventional steels and comparative steels, and the pitting corrosion resistance is significantly superior.

Figure 4 shows the high porosity IH of various 5US304 type steels containing the present invention in solutions containing sulfides and chlorides at different concentrations.
This shows the Ju feeding range. Gap jl'l+corrosion test was performed using 29X 61 with a plate thickness of 2 mm obtained as above.
A gap-forming specimen made by stacking two steel plates of 15×31 mm and 15×31 size was immersed at 80°C for 10 days. The evaluation was based on the weight difference (corrosion loss) before and after the test, and the curve in Figure 2 shows the limit of the presence or absence of corrosion loss as a result of the test. The side with hatching is the non-corrosion area. The uninvented steel has a wider gap J1 corrosion resistance region on the high c side than the comparison steel and conventional steel, and has much better corrosion resistance in solutions containing sulfides and chlorides.

As mentioned above, the two inventors are 18% Cr-9% N.
The soil has an extremely low content of 8 in the austenitic steel of I, below 0005, and a small amount of 1゛I and Mo or Nb and Mo.
Furthermore, due to the synergistic effect of the combined addition of Mo to T i + N b (+ilj), it is possible to provide 'jl' + with a grade comparable to that of SUS 304, which has particularly excellent corrosion resistance in an environment containing oxides and chlorides. In addition, since the carbon in the steel is fixed with specified and appropriate amounts of Ti and Nb, there is the advantage of preventing intergranular corrosion caused by thermal effects during welding.

Thus, the steel of the present invention can be used to treat hot spring water and sludge.

It can be advantageously used as equipment materials and piping materials for equipment used in environments containing sulfides or sulfides and chlorides, such as geothermal power generation and petroleum refining.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between S content and pitting potential in 8US304 type steel. Figure 2 shows the relationship between Ti or Nb content and pitting potential in SUS304 type steel. Fig. 3 is a graph showing T vs. pitting potential of 5US304 type steel.
It is a graph of composite addition of i and/or Nb and Mo. FIG. 4 is a graph showing the influence of the concentration of S and C6 in hot water on crevice corrosion of 5US3'04 type steel, including the steel of the present invention. Patent applicant: Nisshin Steel Co., Ltd. Agent: Patent attorney: Masahiro Matsui (1 other person) 1st m% 2: 2'; 3: Ricobu 4: Illustration procedure corrector: August 25, 1980 Commissioner of the Patent Office: Kazuo Wakasugi 1. Indication of the incident 1982 Patent Application No. 096923 2 Title of the invention 4. Austenitic stainless steel for sulfur-containing hot water 3.
Relationship with the person making the amendment (41 cases) Patent applicant: 4, Agent: 5, Date of amendment order: Voluntary action: 6, No number of inventions increased by the amendment: 8, Contents of the amendment: ■ Invention on page 1, line 6 of the specification The name has been corrected to ``Austenitic stainless steel for sulfur-containing hot water''. ■ The statement of the scope of claims should be corrected as follows. r1. Cr: 16-20%, Ni: 6
~15'16, C:≦005%, Si:<
1.0%, Mn: <2.0, s: kuo, oo
At s%, Ti: CchiX4+0.1~D, 5L
I): An austenitic stainless steel for wire and yellow hot water, characterized in that it contains Mo: 0.2% to less than 10% in a composite manner, and the remainder consists of Fe and inevitable impurities. 2. Cr: 16-2D%, Ni: 6-15%'i-containing. C: <: 0.05%, 8i: < 1.0%, Mn
: <2.0%. S': < O, OO5chi, Nb:C%X 8 +
0.1φ~0.7%, Mo: 0.2%~1.0
1 Contains all complexes. An austenitic stainless steel for use in sulfur-containing hot water, characterized in that the remainder consists of Fe and unavoidable impurities. 6. Cr: 16-20%, Ni: 6-15%. C: <0°05%, Si: <1.0%, Mn: ,
<2.0%. S knee 0.005 yen, Ti+Nb: C ratio xs 100, i chill 0.7%, Mo: 0.2%~1.0
Not $f3: Contains +'D combination. Corrosion-resistant γ-stenite stainless steel for sulfur hot water, characterized in that the remainder consists of Fe and unavoidable impurities. Pages shown in the following table in the Detailed Description of the Invention column. The statement "before amendment" in the line is corrected to "after amendment".

Claims (1)

[Claims] 1 Contains 16 to 20% of Cr and 6 to 15% of Ni. C:<:0.05%, Si:<1.0%, Mn: (
2.0%. s: Kuo, oos%, 1 rin: C%X 4 + [,1,
Contains a composite of 1% to 0.5% and Mo: 0.2% to less than 10%. An austenitic stainless steel for use in S-containing hot water, characterized in that the balance consists of Fe and unavoidable impurities. 2. Contains Cr: 16-20%, Ni: 6-15%. C: <0.05%, 8i: <1.0%, Mn: <
2.0%. S: 0.005%, Nb:C%x s + o, i
Chill 0F%, Mo:D, contains 2% to less than 10% as a composite. S-containing resistant product characterized by consisting of the balance Fe and unavoidable impurities? Austenitic stainless steel for water :):
. 3. Contains Cr: 16-20%, Ni: 6-15%. C: <: 0.05%, Si: < 1.0%,
Mn: <2.0%. S: (0,005%, Ti+Nb:C%X 8 10
．． 1% to 0.7%, and Mo: 0.2% to less than 1.0 in composite form. An austenitic stainless steel for use in S-containing hot water, characterized in that the balance consists of Fe and unavoidable impurities.