JPS62180028A - Mo-containing high cr-ni alloy having excellent corrosion resistance and pitting resistance - Google Patents

Abstract

PURPOSE:To provide an Mo-contg. high Cr-Ni alloy having the corrosion resistance and pitting resistance which are extremely superior to the conventional Ni alloy by incorporating C, Si, Mn, S, Cr, Mo, N, O, Fe, Al, and Mg respectively at prescribed ratios therein and consisting the balance of Ni and inevitable impurities. CONSTITUTION:This Mo-contg. high Cr-Ni alloy contains, by wt%, <=0.03% C, <=0.30% Si, <=0.30% Mn, <=0.005% S, 30-45% Cr, 3-15% Mo, <=0.02% N, <=0.01% O, <=5% Fe, 0.05-0.30% Al, and 0.005-0.020% Mg and consists of the balance Ni and inevitable impurities. The alloy of this invention is the Mo-contg. high Cr-Ni alloy in which the various components are controlled in order to improve the corrosion resistance in the high Cr and high Mo region of an Mo-Cr-Ni alloy. This alloy is the Mo-contg. high Cr-Ni alloy having the excellent corrosion resistance and pitting resistance which are required in environment such as sea water pump of a nuclear power plant and desalting plant to be brought into contact with sea water.

Description

Detailed Description of the Invention [Industrial Application Fields] The present invention is applicable to environments exposed to seawater such as seawater pumps in nuclear power plants and seawater desalination plants, as well as corrosion resistance and resistance required in various chemical plants. Mo with excellent pitting corrosion resistance
It concerns a high Cr-Ni alloy.

[Conventional technology] In recent years, with the development of various industrial fields such as the chemical industry, the atomic crab industry, and oil drilling, the environments in which metal materials are used have become increasingly diverse.
It's getting tougher. Stainless steel has been widely used as a typical corrosion-resistant material in such harsh corrosive environments, but it is still susceptible to various forms of corrosion accidents such as pitting corrosion, crevice corrosion, stress corrosion cracking, intergranular corrosion, and general corrosion. This has caused major economic losses due to suspension of operations due to corrosion damage to parts and maintenance monitoring for corrosion. Conventionally, 5US316 and duplex stainless steel have been used for the normal parts of these plants, and where corrosion resistance is most needed,
Incone1625, which is a Ni-based alloy, and HasLe
l 1oyc-276 etc. are used. However, in some cases, even such a Ni-based alloy may not have sufficient corrosion resistance.

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned problems with corrosion-resistant materials, and aims to develop materials with superior corrosion resistance than these Ni-based alloys, improve the lifespan of plants, The purpose is to lengthen the inspection period and ease the monitoring system.

[Means for Solving the Problems] The Mo-containing high Cr-Ni alloy having excellent corrosion resistance and pitting corrosion resistance according to the first aspect of the present invention has, in weight percent, c: 0.03% or less, Si: 0 .30% or less, Mn; 0.30% or less, S
; O, o O 5% or less, Cr; 30-45%, Mo;
3-15%, N, 0.02% or less, 0.0.01% or less, Fe; 5% or less, Al; 0.05-0.30%, Mg
:0.005 to 0.020%, with the remainder consisting of Ni and inevitable impurities.

The Mo-containing high Cr-Ni alloy excellent in corrosion resistance and pitting corrosion resistance of the second invention of the present invention has, in weight percent, c: 0.03% or less, Si: 0.30% or less, Mn: 0.30. % or less, S
; 0.005% or less, Cr; 30-45%, Mo; 3-
15%, N; o, o 2% or less, O, 0.01% or less, Fe; 5% or less, At; 0.05-0.30%, M
g: 0.005 to 0.020%, W: 2 to 10%, and the remainder consists of Ni and inevitable impurities.

Since the Mo-containing high Cr-Ni alloy having the composition range described in the claims of the present invention has high C and high Mo, it is difficult to forge; It has not been used in the past because it is not suitable for its primary use as a heat-resistant material.

However, with advances in scouring technology and forging technology, it is now possible to manufacture them. In addition, corrosion-resistant materials are made from room temperature to 3.
Since it is used at a relatively low temperature of around 00℃, σ during use
There is no need to consider the formation of phases, and it is only necessary to pay attention to the heat treatment during production. Therefore, alloys in the above composition range can withstand practical use.

Therefore, as a result of intensive research into the influence of various alloy components with a focus on corrosion resistance, the inventors have come up with the invention alloy which has corrosion resistance superior to that of conventional Ni-based alloys. The reasons for limiting the alloy components described in the claims will be described below.

C: o, o 3% or less C acts as a carbide and causes pitting corrosion and intergranular corrosion, so it is desirable to keep it as low as possible, but due to ridgeline constraints, the upper limit was set at 0.03%. .

Si; 0.30% or less Si is mainly added as a deoxidizing element, and is also mixed in from raw materials. However, if added in a large amount, Si compounds are formed, which lowers the melting temperature and impairs hot workability, so the upper limit is set at 0.30%.

Mn: 0.30% or less Mn is also added as a deoxidizing agent, but since adding a large amount impairs hot workability, the upper limit is set to 0.30%.

S: 0.005% or less S is the element that most impairs hot workability, and sulfides also serve as a starting point for pitting corrosion, so the content should be 0.005% or less.

Cr: 30-45% Cr is a basic element that forms a protective film Cr20= and improves corrosion resistance. If the content is 30% or more, corrosion resistance superior to conventional alloys can be obtained, but if it exceeds 45%, the σ phase remains even after solution treatment, reducing workability and toughness and ductility at room temperature. 30-45%.

Mo; 3-15% Mo is a useful element that improves pitting corrosion resistance, and
It dissolves in the matrix to increase strength. If it is less than 3%, the effect will be small, and if it is more than 15%, hot workability will be impaired and the σ phase will be more likely to be generated, so the content should be 3 to 15%.

N, 0.02% or less Forms nitrides and becomes a starting point for pitting corrosion, so the upper limit is set to 0.0.
2%.

0.0.01% or less Since 0 forms oxides, becomes a starting point for pitting corrosion and impairs hot workability, the upper limit is set to 0.01%.

Fe: 5% or less Fe may be mixed in from raw materials, but since it tends to promote the formation of the σ phase, the allowable upper limit is set at 5%.

Al; 0.05 to 0.30% Al is used as a deoxidizing agent, but if it is less than 0.05%, it has little effect, and if it is more than 0.30%, it remains as an oxide and impairs hot workability. 05~0°30%.

Mir: 0.005-0.020% Mg is added because it has a deoxidizing effect and a desulfurizing effect by fixing S, but adding a large amount impairs hot workability, so Mg is added from 0.005 to 0.020%. 020%.

W: 2 to 10% W improves corrosion resistance like Mo. Since it has a large solid solution strengthening effect, it is added to replace Mo when strength is required. Adding a large amount promotes the formation of α-W and σ phases, so 2 to 1
Do it every 09.

[Example] Examples of the present invention will be described to clarify the effects of the present invention.

A 50 kg ingot of an alloy having various components as shown in Table 1 was melted in a vacuum high-frequency induction furnace. In Table 1, alloy N
o, 1 to 3 are the first invention alloys, and alloys N014 to 5 are the second invention alloys containing W. Inconel 625 and 1lastel used for comparison
The chemical composition of loy C-276 is also shown.

The obtained ingot was forged into a bar with a diameter of 20 mm, and
It was subjected to solid solution treatment with water cooling at ℃/1 hr and subjected to a corrosion test.

Corrosion tests were conducted for general corrosion and pitting corrosion, and for general corrosion, the amount of corrosion was measured by immersing the specimen in 10% H2SO boiling liquid for 24 hours. In addition, pitting corrosion is caused by 4% NaCl + 1% F.
e2(S○,), + 0.01. The pitting corrosion generation temperature was measured by immersing it in M HCI. The results of the corrosion test are shown in Table 2.

Table 2 From the corrosion test results shown in Table 2, it is clear that in the general corrosion test, the amount of corrosion of the alloy of the present invention was improved by 20% to 50% compared to the comparative alloy. In addition, in the pitting corrosion test, the alloy of the present invention exhibited a pitting corrosion onset temperature of 8 to 10°C compared to Incone 1625, and a pitting corrosion onset temperature of 8 to 10°C compared to Hastelloy C-276.
It was confirmed that the temperature was improved by more than 2°C.

[Effects of the Invention] As explained above, the present invention is a Mo-containing high Cr-Ni alloy in which various components are regulated in order to improve corrosion resistance in the high Cr and high Mo regions of the Mo-Cr-Ni alloy. , it has the remarkable effect of being extremely superior in corrosion resistance and pitting corrosion resistance compared to conventional alloys.

Claims (2)

[Claims] (1) In weight%, C: 0.03% or less, Si: 0.30
% or less, Mn: 0.30% or less, S: 0.005% or less, Cr: 30-45%, Mo: 3-15%, N: 0.0
2% or less, O: 0.01% or less, Fe: 5% or less, Al
:0.05~0.30%, Mg:0.005~0.02
A high Cr-Ni alloy containing Mo with excellent corrosion resistance and pitting corrosion resistance, with the remainder being Ni and unavoidable impurities. (2) In weight%, C: 0.03% or less, Si: 0.30
% or less, Mn: 0.30% or less, S: 0.005% or less, Cr: 30-45%, Mo: 3-15%, N: 0.0
2% or less, O: 0.01% or less, Fe: 5% or less, Al
:0.05~0.30%, Mg:0.005~0.02
A Mo-containing high Cr-Ni alloy with excellent corrosion resistance and pitting corrosion resistance, which contains W: 0%, W: 2 to 10%, and the remainder is Ni and unavoidable impurities.