JPS61210145A - Nickel alloy having superior resistance to stress corrosion cracking - Google Patents

Abstract

PURPOSE:To improve the resistance of an Ni alloy to stress corrosion cracking by specifying the amounts of Cr, Fe and Nb as essential components in the alloy. CONSTITUTION:This Ni alloy contains 14-17wt% Cr, 6-10wt% Fe and 3.5-5wt% Nb as essential components or further contains a proper amount of a deoxidizing agent such as C, Mn, Si or Ti. Since the Ni alloy contains the relatively large amount of Nb, it has higher resistance to intergranular corrosion and stress corrosion cracking than 'Inconel(R)' alloy or the like and also has improved mechanical characteristics such as offset yield stress strength at 0.2% permanent set, tensile strength and elongation. The Ni alloy can be used as a structural material for a light-water reactor.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a Ni-based alloy with excellent stress corrosion cracking resistance.
More specifically, Ni is particularly useful as a structural material for light water reactors.
Regarding base alloys.

[Technical background of the invention and its problems] Nickel-based alloys have excellent corrosion resistance, heat resistance, etc., and are therefore widely used in various industrial fields. Among them, Inconel 800 containing Cr is heavily used as a structural material for light water reactors because of its high corrosion resistance in high-temperature pure water.

However, this Inconel 600 may cause SCC under certain usage conditions.

It is thought that the main cause of SCC in structural materials made of Inconel 800 is a Cr-depleted layer formed at one grain boundary. Therefore, in order to improve SCC resistance, intergranular corrosion resistance (resistance to It is known that it is sufficient to improve the IGC property.

Therefore, the IGC resistance is good, and as a result, the SC resistance is good.
There is a strong demand for the development of stone-based alloys for light water reactor structural materials with excellent carbon properties.

[Object of the Invention] In response to such conventional demands, the present invention aims to provide a nickel-based alloy that has excellent IGC resistance and, as a result, good SCC resistance, and is particularly useful as a light water reactor structural material.

[Summary of the Invention] In order to achieve the above object, the present inventor conducted various studies based on the composition of Inconel 800, and found that an alloy having a composition containing a predetermined amount of Wb as an additive element, as described later, The present invention was completed based on the discovery that the IGG resistance and, in turn, the ##SCC properties are dramatically improved by 2 times compared to Inconel 600.

Namely, the Ni-based alloy of the present invention includes chromium and iron.

An alloy containing niobium and nickel as essential components,
It is characterized by containing 14 to 17% by weight of chromium, 6 to 10% by weight of iron, and 3.5 to 5% by weight of niobium.

In the Ni-based alloy of the present invention, Cr is an element that contributes to corrosion resistance and oxidation resistance, and if it is too small, the corrosion resistance and oxidation resistance will be impaired, and if it is too large, the workability will be reduced. % range. Preferably it is 15 to 16% by weight.

In addition, Fe is an element that contributes to the strength and malleability of the alloy, and if it is too little, the desired strength cannot be obtained, and if it is too large, the malleability deteriorates, so the blending amount is 6 to 10.
Weight%. Preferably it is 7 to 8% by weight.

In the alloy of the present invention, in addition to the above components, C+M
n + S r + T i may be blended as a deoxidizing agent.

These are elements effective in improving the hot workability of the obtained alloy. If the amount of these elements is too small, the above effects will not be fully exhibited, and if it is too large,
Since inclusions increase in the alloy and cause structural defects, the respective blending amounts should be 0.15% by weight or less, 1.00% by weight or less, 0.50% by weight or less, and 0.50% by weight or less. be. Preferably, C: 0.035 to 0.055% by weight, Mn: 0.50 to 1.00% by weight.

Si: 0.20-0.40% by weight, Ti: 0.2
0 NO, 30% by weight.

Furthermore, in addition to the elements listed above, as deoxidizers,
All may be blended. If too much of this element is blended, it will reduce hot workability, so the blending amount is as follows:
It is 0.35% by weight or less, preferably 0.10% by weight or less.

The Ni-based alloy of the present invention contains 3.5 to 3.5 Wb as an additive element.
The biggest feature is that it contains 5.0% by weight.
Nb improves the IGC resistance of the obtained alloy and also improves the S resistance.
This greatly contributes to improving CC properties. When the blending amount of Nb is 3.5% by weight without swirling, the above-mentioned dramatic IGC resistance is achieved.
It is not possible to expect an improvement in the properties and, by extension, the SCC resistance.
On the other hand, even if Wb is added in an amount exceeding 5.0% by weight, the effect reaches saturation, and furthermore, the workability of the resulting alloy is reduced. Preferably 3.5-3.9% by weight
It is.

The Ni-based alloy of the present invention can be easily prepared by blending the above-mentioned elements in a predetermined ratio and melting the mixture by a conventional method.

In addition, various parts can be manufactured by processing the Ni-based alloy of the present invention.

For example, when manufacturing the above-mentioned light water reactor structural materials.

After the molten material is forged by a conventional method, it is preferable to perform a prescribed hot working process (hot rolling or hot extrusion). Since the deteriorated workability of the alloy of the present invention is sufficiently compensated for, it becomes possible to easily manufacture various members with excellent SCC resistance.

[Examples of the Invention] Examples 1 to 4 Each element was blended in the indicated ratio and then melted, and the melt was cooled to cast ingots of various alloys.

After cutting and removing the epidermis of each ingot, each ingot was
Forged at 0 to 1250℃, then cut to 20℃
A test piece with a diameter of 0 mmφXfL was prepared.

For each test piece obtained, 0.2% proof stress, tensile strength,
In addition to measuring elongation, corrosion resistance (IGC resistance) was evaluated by a striker test.

For comparison, one type of alloy corresponding to Inconel B00 (
Comparative Example 1) and the three alloys (Comparative Examples 2 to 4) that differ from the present invention only in the amount of Nb added were also applied to Examples 1 to 4 above.
A test piece was prepared in the same manner as above, and a similar evaluation test was conducted, and the results of 8 or more are collectively shown in the table.

[Effects of the Invention] As is clear from the above description, the Ni-based alloy of the present invention contains a relatively large amount of Nb, and therefore has higher durability than Inconel B00 and Ni-based alloys with a relatively low Nb content. The IGG properties and, by extension, the SCC resistance have been dramatically improved, and at the same time, the mechanical strength such as 0.2% proof stress, tensile strength, and elongation has also been further improved. In place of Inconel 600, it is extremely useful as a Ni-based alloy with excellent stress corrosion cracking resistance.

Claims (1)

[Claims] An alloy containing chromium, iron, niobium and nickel as essential components, with chromium being 14-17% by weight and iron being 6-10% by weight.
A nickel-based alloy with excellent stress corrosion cracking resistance, characterized by containing niobium in an amount of 3.5 to 5% by weight.