JPS62177155A - Fe-base alloy excellent in stress corrosion cracking resistance and its production - Google Patents

Abstract

PURPOSE:To manufacture an Fe-base alloy combining high yield strength with high strength and excellent in stress corrosion cracking resistance, by subjecting an alloy having a specific composition consisting of C, Si, Mn, Ni, Cr, Mo, P, S, and Fe to hot working and heat treatment under proper conditions. CONSTITUTION:The Fe-base alloy consisting of, by weight, <=0.04% C, <=1% Si, <=2% Mn, 25-45% Ni, 25-35% Cr, <=6% Mo, <=0.01% P, <=0.01% S, and the balance Fe is subjected to hot working at 850-1,250 deg.C at >=20% draft. Then the above hot-worked alloy is held at 900-1,150 deg.C for 2min-5hr and cooled at a rapid cooling velocity higher than air cooling. In this way, the solid solution-strengthening-type Fe-base alloy having a 0.2% yield strength under room temp. of >=21kg/mm<2> and a strength of >=52kg/mm<2> tensile strength and excellent in stress corrosion cracking resistance in high-temp. and high- pressure water can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an Fe-based alloy with excellent stress corrosion cracking resistance and a method for producing the same, particularly for use in steam generator heat transfer tube materials and heat exchange materials for light water reactors or fast breeder reactors. The present invention relates to an Fe-based alloy that is applied to dexterous support structural members, piping materials, etc., and a method for producing the same.

[Conventional technology]

Conventionally, Fe-based alloys with excellent stress corrosion cracking resistance include:
Incoloy 800 (trade name) Ni: 5 Q, O ~ 35.0%, Cr: 19
．． IPe-based alloys with 0 to 250% Fe: balance have been used, but Incoloy 800 is highly susceptible to stress corrosion cracking depending on processing conditions, causing stress corrosion cracking in the heat exchanger tubes and structural members, etc. Sometimes.

[Problem that the invention seeks to solve]

Incoloy 800 is said to have relatively excellent stress corrosion cracking resistance in high temperature, high pressure water that does not contain oxygen, but stress corrosion cracking may occur when subjected to cold working. .

The present invention aims to provide an Fθ-based alloy that does not cause stress corrosion cracking as described above, and a method for manufacturing the same.

[Means for solving problems]

The reason why stress corrosion cracking occurred in parts using Incoloy 800, which has been used in the past, was due to the knowledge that the chemical composition of Incoloy 800 and the processing conditions change the metallographic structure of the material, increasing the material's susceptibility to stress corrosion cracking. Based on this, the present inventors have completed the present invention as a result of intensive research into chemical components and processing conditions that reduce the stress corrosion cracking susceptibility of materials.

That is, the present invention provides: (1) C: α04 or less, Si: 1% or less in weight ratio;
Mn: 2% or less, Ni: 25% or more, 45% or less, C
r: 25% or more and 35% or less, Mo: 6% or less, P
, S: [101% or less, the balance F's, an Fθ-based alloy with excellent stress corrosion cracking resistance, and (2) C: by weight ratio
Q, 04chi or less, Sl: 1% or less, Mn: 2% or less,
Ni: 25% or more and 45% or less, Or: 25% or more3
5% or less, Mo: 6% or less, P, S: 0.01% or less,
A Fe base alloy consisting of the balance F's was rolled at a rolling reduction rate of 20% at a rolling stock of 850 to 1250.
After the above hot working, it is held at 900-1150℃ for 2 minutes to 5 hours and then cooled at a faster cooling rate than air cooling.The α2% yield strength at room temperature is 21 kg.
/rtn2 or more, a tensile strength of 53kg/rnrn2 or more, and a solid solution strengthened Fe-based alloy that has excellent stress corrosion cracking resistance in high-temperature, high-pressure water.

[Effect]

Reasons for limiting each alloying element of the present invention Fe-based alloy and heat treatment,
The reasons for limiting the processing conditions are as follows.

Reason for limiting each alloying element C; C is a solid solution strengthening element. To obtain the specified strength,
A certain amount is required. However, if it is included in a large amount, it will become sensitive during the cooling process after solution treatment and reduce stress corrosion cracking resistance, so the content should be 0.04 inches or less.

81, Mn;81. Mn has the effect of removing oxygen as an impurity in the alloy, but on the other hand, when the amount increases, it reduces stress corrosion cracking resistance. Therefore, the lower Si#Mnt is, the better (
Si: 1% or less, Mn: 2% or less.

P, S; P, 8 segregates at grain boundaries and not only reduces grain boundary bonding strength, but is also an electrochemically harmful element, and the lower the content, the better (101% or less).

Ni: Ni maintains the luxation resistance of the alloy and improves stress corrosion cracking resistance in environments containing C2-, so it is better to contain a large amount, but if it is contained in a large amount, Since the stress corrosion cracking resistance in deaerated high temperature and high pressure water decreases, it should be set at 25% or more and 45% or less.

Or; Or is the most important element for maintaining stress corrosion cracking resistance, and is preferably added in an amount of 25% or more. However, if a large amount of slender is added, solidification segregation will occur and it will be difficult to forge, or it will be difficult to form a homogeneous ingot, so it should be set at 35- or less.

MO: MO improves corrosion resistance, but if too much MO deteriorates hot workability significantly, it should be kept at 6% or less.

Reasons for limiting the heat treatment/processing method for the Fe-based alloy of the present invention In order to maintain the hot workability of the Fe-based alloy of the present invention, it is necessary to process it at a relatively high temperature, and the processing conditions are 850-1250.
It is necessary to do it at ℃. Further, K, which maintains stress corrosion cracking resistance, is desirably given a homogeneous and large working rate, and for hot working, the reduction rate is 20% or more.

The heat treatment conditions are 900°C or higher and 1150°C to maintain high strength and high stress corrosion cracking resistance.
Solution treatment is performed below. Solution treatment temperature is 1150℃
If the stress corrosion cracking resistance is exceeded, stress corrosion cracking resistance deteriorates and high strength cannot be maintained.

In order to prove the effects of the Fθ-based alloy of the present invention, the following tests were conducted.

0-stress corrosion cracking test In order to evaluate the stress corrosion cracking resistance when the present four Fθ-based alloy is used for steam generator heat exchanger tubes etc. in a light water reactor environment,
Under the environment shown in Table 1 below, simulating PWR-order system water,
A stress corrosion cracking test was carried out on each diversion member by immersing the UA-and test piece shown in Fig. 1 and applying high stress up to 5oooh.
The presence or absence of cracks was investigated.

Table 1 Test conditions (1) Temperature 360℃ (2) Pressure 2 1 4 kg/cm
2G (3) Water quality pH (at2S℃) approx. 7 H3BO3 concentration (asB) approx. 500 ppmLi0
1 (d degree (asLi) approx. 2 ppmH, approx. 30cc-8TP/9''H20DO2<5p
pb OL-< 0.1 ppm 0 Test material Table 2 shows the chemical composition of the test material (representative example) used in this test.
Heat treatment/processing of sample material /166 in Table 2: Examples of conditions are shown in Table 3.

Table 2 Table 5 7166 (Heat treatment, processing method and stress corrosion cracking resistance of test material D Street.

a) C2Cr Co., heat treatment conditions and stress corrosion cracking resistance As shown in Figure 2, ci is 0.04% or less, Cr content is 25% or more, and solution treatment is performed at 1250°C or less. The treated products have excellent stress corrosion cracking resistance.

b) Si, Mni heat treatment conditions and stress corrosion cracking resistance As shown in Figure 3, the amount of Si is 1% or less, and the amount of Mn is 2%.
Those subjected to solution treatment at 900° C. or higher have excellent stress corrosion cracking resistance.

C) Hot working conditions and stress corrosion cracking resistance As shown in Table 3 above, hot working is carried out at a specified temperature (900 to 1200°C is good for this type of alloy) and at a reduction rate of 20 inches or more. When applied, it has good stress corrosion cracking resistance.

〔Effect of the invention〕

The alloy composition and manufacturing method of the present invention provide an Fe-based alloy with excellent stress corrosion cracking resistance.

[Brief explanation of drawings]

Figure 1 shows a test method for evaluating the stress corrosion cracking resistance of the Fe-based alloy of the present invention, and Figure 2 is a chart showing the influence of the amount of C2Or on the stress corrosion cracking resistance of the Fe-based alloy. Figure 5 shows the effects of Si and M on the stress corrosion cracking resistance of Fe-based alloys.
It is a chart showing the influence of n amount 2. Sub-Agents 1) Meifuku Agent Ryo Hagiwara - Sub-Agent Atsuo Anzai Figure 1

Claims (1)

[Claims] 1) Weight ratio: C: 0.04% or less, Si: 1% or less, M
n: 2% or less, Ni: 25% or more, 45% or less, Cr:
25% or more, 35% or less, Mo: 6% or less, P, S,:
An Fe-based alloy with excellent stress corrosion cracking resistance consisting of 0.01% or less and the balance being Fe. 2) Weight ratio: C: 0.04% or less, Si: 1% or less, M
n: 2% or less, Ni: 25% or more and 45% or less, Cr: 2
5% or more and 35% or less, Mo: 6% or less, P, S: 0.0
Fe-based alloy consisting of 1% or less and the balance Fe, 850-1
Room temperature characterized by hot working at 250°C with a rolling reduction of 20% or more, holding at 900-1150°C for 2 minutes to 5 hours, and then cooling at a faster cooling rate than air cooling. Solid solution strengthened Fe with a lower 0.2% yield strength of 21 kg/mm^2 or more, a tensile strength of 53 kg/mm^2 or more, and excellent stress corrosion cracking resistance in high-temperature, high-pressure water.
Method of manufacturing base alloy.