JPH0483841A - Fe-ni series alloy excellent in high temperature corrosion resistance and weldability - Google Patents

Abstract

PURPOSE:To obtain an Fe-Ni series alloy showing excellent corrosion resistance in a high temp. corrosive environment including chlorides and furthermore excellent in weldability at low cost by specifying the compsn. constituted of C, Si, Mn, Ni, Cr, Mo, Al and Fe. CONSTITUTION:This is an Fe-Ni series alloy contg. 0.015 to 0.100% C, 1.5 to 6.0% Si, <=2.0% Mn, 30.0 to 80.0% Ni, 10.0 to 26.0% Cr, 1.0 to 9.0% Mo, <=0.2% Al and the balance Fe with impurities and excellent in high temp. corrosion resistance and weladability, in which Ni effective for high temp. corrosion resistance is incorporated by >=30% as well as Si is incorporated by >=1.5% and by their synergistic effect, high temp. corrosion resistance is increased.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to FeNi alloys that have excellent high-temperature corrosion resistance and weldability. Fe-N exhibits excellent corrosion resistance and oxidation resistance even in corrosive environments, and has excellent weldability.
We propose i-based alloys.

In recent years, cooking appliances have become popular, but these
For example, in the case of the outer cladding tube of a cooking heater for an electric stove, there are problems with high-temperature corrosion due to chlorides and weldability, and various research and development efforts are currently underway. Materials that are particularly suitable for this type of field are NaC, since they are used in the presence of chlorides at high temperatures.
When 1 comes into contact with the steel surface, the Fe in the steel reacts with NaC1, generating highly volatile NaFeC1, which accelerates corrosion. Therefore, it should be considered from a different perspective than the usual high temperature oxidation resistance. It is something that must be done.

Furthermore, the present invention proposes an Fe-Ni alloy that is suitably used as a material for incinerators used under similar conditions and as a material for chemical plants where corrosion by high-temperature concentrated nitric acid is a problem.

[Conventional technology]

For example, if a material like the above-mentioned cooking heater outer cladding tube is susceptible to adhesion of soy sauce or salt, if it is exposed to high-temperature air with these substances still adhering to it, it will suffer from high-temperature corrosion (dry weight). The higher the temperature, the more severe the damage.

Conventionally, NCF300 (JIS G4901) material and N
CF600 material is used. On the other hand, N.C.
Conventionally, ropes with low Ni content have been proposed as VA materials for F800. For example, in Japanese Patent Publication No. 64-8695 (steel for high-temperature corrosive environments in the presence of chlorides), Ni is in the range of 16 to 30-t% (hereinafter simply expressed as "%"), and in particular MO and proposed the effect of reducing Ni by adding W and ■, and in JP-A-64-73056,
It is disclosed that Ni promotes internal corrosion and is harmful, and that Si is effective for oxidation resistance. Furthermore, Japanese Patent Application Laid-open No. 63-65058 proposes a steel with excellent high-temperature corrosion resistance characterized by an increased amount of Si.

Other examples of alloys with excellent high-temperature corrosion resistance include Mo-containing, high-Si-containing, Ni-based alloys as disclosed in Japanese Patent Publication No. 62-6623 (Japanese Unexamined Patent Publication No. 58-117847). .

As explained above, regarding the influence of alloying elements on high-temperature corrosion in environments containing chlorides, etc., there have been conflicting reports on both effectiveness and toxicity, and there are still The reality is that it is not confirmed.

Regarding the weldability of Fe-Ni alloys containing C and Si, Si: 0.04 to 1.42%, according to "Summary of the National Conference of the Welding Society of Japan" (Vol. 39, 1986 Nα219. p128-129). gate in the range of. improves weldability, but C has no effect, rather 0.10%
It has been reported that it is harmful if the amount exceeds

[Problem to be solved by the invention]

Now, in recent years, 200 V wiring to general households has been promoted1, and demand for electric heaters is expected to increase accordingly. In particular, the power of the sheathed heater for cooking mentioned above is increasing, and the outer covering material of the sheathed heater is also JIS NCF6.
It is expected that high-temperature materials such as 00 materials will be increasingly used. However, this NCF600 material has major problems that still need to be resolved regarding cost and high-temperature corrosiveness (corrosion resistance in high-temperature corrosive environments containing chlorides), and recently there has been a strong desire for an alternative material to appear. be.

However, the alloys proposed in the above-mentioned Japanese Patent Publication Nos. 64-8695, etc. are all similar to the NCR600.
The reality is that it has poorer corrosion resistance than other materials, making it impossible to achieve the desired properties. Moreover, these alloys have a high susceptibility to solidification cracking because Si and Ni, which are added to improve high temperature corrosion resistance, nitric acid resistance, and stress corrosion cracking resistance, form a low melting point eutectic of Ni silicide. It has been pointed out that hot workability and weldability are significantly deteriorated, and the reality is that no solution has yet been found to date.

Furthermore, the alloy disclosed in Japanese Patent Publication No. 62-6623 is C
Since the content is extremely high (0.55 to 2.0%), it contains many carbide precipitates. However, carbide precipitation in the alloy is rather harmful to high-temperature corrosion caused by common salt, and furthermore, this carbide precipitate significantly deteriorates not only weldability but also hot workability and cold workability. .

On the other hand, the conventional technology described in the collection of lecture summaries of the Welding Society has a low Si content and poor high-temperature corrosion resistance, so it cannot be said to be an alloy fundamentally aimed at solving the problem of the present invention.

The object of the present invention is to provide a material that exhibits sufficient corrosion resistance even when exposed to an atmosphere where accelerated oxidation occurs due to the adhesion of chlorides in a high-temperature atmospheric atmosphere, and which also exhibits remarkable properties in terms of weldability. The object of the present invention is to overcome the problems of each of the above-mentioned prior art techniques.

[Means to solve the problem]

For the above purpose, the present inventors investigated the effects of alloying elements on corrosion resistance and weldability in high-temperature corrosive environments.
I gained new knowledge. This is different from the case of single addition,
This means that synergistic effects between certain alloying elements may produce unexpectedly superior effects. That is, in the present invention, 10 to 25% C
Regarding the FeCr-Ni alloy containing r, the following was clarified from the mutual influence of each of these additive elements.

(1) Basically, in this ternary alloy, surprisingly, Ni
: At a high Ni content of ≧30%, localized erosion such as grain boundary erosion can be prevented without causing any other significant damage.

(2) Regarding the action of St, if the amount of Ni is small, it has the effect of inducing bit-like local corrosion, but if the amount of Ni is increased to a certain extent, the high temperature corrosion resistance is significantly improved.

In alloys with Si increased by 1.5% or more, if a certain amount of C is contained, the precipitation of Mo silicide is promoted, and therefore N reduces the susceptibility to solidification cracking.
Precipitation of i-silicide is suppressed, resulting in improved weldability.

(3) As mentioned above, addition of Si is effective for high temperature corrosion properties. However, in this Ni-based alloy, the amount of solid solution of Si is originally small and tends to form various forms of compound silicide, which causes a significant deterioration in weldability.

It has been found that this can be prevented by controlling the form of the precipitate in advance to precipitate a compound in a useful form.

That is, the present invention is first characterized in that it focuses on the synergistic effect of Ni and St. In other words, even if the Ni amount is lower than the conventional NCF600 material, the Ni and 5i are controlled (increased to 1.5% or more), respectively.
According to the method of simultaneously adding , it is possible to obtain an alloy with excellent high-temperature corrosion resistance and weldability.

Second, we focused on molybdenum silicide as the compound silicide precipitated.
It suppresses the formation of Ni silicide, which is harmful to weldability, and precipitates Ni silicide, so it is effective in improving weldability.

Thirdly, in a high Ni-based alloy system with a large amount of Si, -
In boat fishing, weldability deteriorates due to the eutectic formation of Si and Ni. However, in terms of improving weldability, it has been found that when a certain amount of C is included in alloy systems that precipitate Mo silicide, high-St alloys are more effective in improving weldability, especially in maintaining weldability. It was found that there is a suitable quantitative relationship between Ni, Si, and Mo for the purpose.

Based on this knowledge, the present invention has developed the following Fe-Ni
developed a new alloy.

That is, C: 0.015-0.100%, Si: 1
．． 5-6.0%, Mn≦2.0%, Ni
: 30.0-80.0%.

Cr: 10.0-26.0%, Mo:
It is an Fe-Ni alloy containing 1.0 to 9.0% AI≦0.2%, the balance being Fe and impurities, and having excellent high-temperature corrosion resistance and weldability.

[Function] According to the research conducted by the present inventors, Ni is effective in high-temperature corrosion resistance.
In Fe-Cr-Ni alloys containing 30% or more of Si, when Si is added to 1.5% or more, the effect of ordinary Si addition is significantly improved beyond the expected range due to the synergistic effect with Ni. can be used, which is a traditional low-N
It was found that the alloy had high high temperature corrosion resistance, which was not possible with i-Cr-Fe alloys.

The details of the composition of the alloy of the present invention will be explained below along with the explanation of the reasons for the limitations.

C: In this type of alloy, it is a necessary element to suppress the precipitation of raw Ni silicide and promote the precipitation of molybdenum silicide during solidification, and to suppress solidification cracking to obtain weldability and high-temperature strength. . However, if the amount of C is too large, the amount of carbide precipitated increases, leading to deterioration of corrosion resistance and workability. In addition, at high temperatures, this C combines with the Cr element to precipitate Crz:+C6 at the grain boundaries, and Cr near the grain boundaries.
The lower the content is, the more desirable it is because it forms a deficient phase and promotes the progression of high-temperature corrosion. Therefore, the upper limit of C was set at 0.10%.

Figure 1 shows weld cracking rate = (total crack length/bead length)
It is a diagram showing the relationship between xloo and 0%, and 3%5t-6
0%Ni-3%Mo-Remaining Fe total Fe is 0%:
It is clear that when the content is 0.015 to 0.10%, almost no cracking occurs.

Si: This is the element that plays the most important role in the alloy of the present invention, and when Ni≧30%, the synergistic effect with Ni shows remarkable effects on oxidation resistance, high temperature corrosion resistance, and nitric acid resistance. This effect far exceeds the general effect of St, which is said to have an effect of improving corrosion resistance in high-temperature environments where chlorides are present. Therefore, under the condition that Ni≧30%, the effect of its addition occurs with a lower limit of 1.5%.

On the other hand, when the amount added exceeds 6.0%, it impairs the weldability of high-Ni fully austenitic steel, and also promotes the precipitation of intermetallic compounds such as σ, which deteriorates the ductility and toughness after long-term use at high temperatures. Therefore, the Si content was determined to be 1.5 to 6.0%.

Mn: An element necessary to maintain the hot workability of steel, but if it is contained in an amount exceeding 2.0%, corrosion resistance and oxidation resistance will deteriorate in high-temperature environments where chlorides are present. Therefore, the Mn content was determined to be 2.0% or less. In addition,
It is preferable to adjust the Mn content to 0.1 to 0.5% if possible.

Ni: Extremely effective in improving high-temperature corrosion resistance and oxidation resistance in high-temperature corrosive environments containing chlorides, especially when the Ni content is 30% or more, it has the effect of dramatically improving the high-temperature corrosion resistance of Si. If the Ni content is less than that, the disadvantages of high Ni content, such as precipitation of σ phase, will be exacerbated, which is not preferable.

Therefore, Ni should be 30% or more.

Additionally, the addition of Ni is effective in improving the structural stability and weldability against the precipitation of intermetallic compounds consisting of Cr, Si, Mo, etc. In this sense, the more the better, and adding up to 80% is effective. It is. Preferably 50~
It is preferably within the range of 75%.

Cr: High temperature corrosion resistance in environments where chlorides exist and 90
It is effective for improving general oxidation resistance at around 0°C, but if the amount is less than 10%, the scale peels off even in a high-temperature corrosive environment due to chlorides, and the desired effect cannot be obtained. The above shall apply.

However, since too much content promotes internal erosion, the upper limit is set at 28%. It is preferably within the range of 16.0 to 20.0%.

Mo = One of the elements that acts extremely effectively to improve corrosion resistance and weldability in high-temperature environments where chlorides exist, and is effective for weldability in
It has the effect of significantly increasing the effect on weldability, and it is necessary to add at least 0.5%. However, this M
If the amount of O added is too large, the toughness and corrosion resistance will deteriorate and the scale exfoliation will increase, so the amount is set to 9.0% or less. Preferably it is 4% or less.

^1: In coexistence with Cr, it can be expected to have the effect of improving high-temperature corrosion resistance and oxidation resistance, but it is harmful to weldability and needs to be suppressed to 0.2% or less.

W, (1)+Zr+Cu: Has the same effect as MO on high temperature corrosion resistance in the presence of chlorides. However, when any of the elements is contained in an amount exceeding 3.0%, precipitation of intermetallic compounds is promoted, which impairs workability and increases scale exfoliation.

In addition, Fig. 2 is a diagram showing the influence of Si% and Si% on weld cracking.
r - In alloys with balance Fe, Si≧1.5%,
It can be seen that no cracks are generated under the condition of Mo≧1.0%.

〔Example〕

This example confirms the high temperature corrosion resistance and weldability of the alloy of the present invention. In the test, alloys (Nos. 1 to 9) having the composition shown in Table 1 were heated in an atmospheric induction furnace for 10 minutes.
kg ingot, hot forged and cold rolled to yield 2.0
and Q, 5 mm t plates were used for the test. First, the high-temperature corrosion test piece was cut into pieces with a thickness of 0.5+w+wt, a width of 20 m, and a length of 30 m, and then oxidized in the atmosphere at 1050° C. for 30 minutes, and then subjected to the following high-temperature corrosion test.

The high-temperature corrosion test consists of immersion in saturated saline (5 minutes) → drying (10 minutes).
minutes) → Repeated oxidation (800″C x 30 minutes → Air cooling 5 minutes 50
The results of a 4-cycle test are shown, with 1 cycle being 1 cycle.

On the other hand, the welding test was conducted at a current of 50A and a speed of 900mm/ll.
This is a restrained weld cracking test when performing 1 inch restrained butt TIG welding. The results are shown in Table 1.

As is clear from these test results, the alloy of the present invention (Sou 1
-Nα4) had a smaller maximum erosion depth than the comparative alloys (N05 to Nα9), and no weld cracking occurred, confirming the effectiveness of the alloys of the present invention.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to provide at a low cost an Fe-Ni alloy that exhibits excellent corrosion resistance in a high-temperature corrosive environment containing chlorides and also has excellent weldability. Therefore, the alloy of the present invention is required to have corrosion resistance against (1) external cladding tubes of sheath heaters such as electric stoves, (2) boilers and heat exchangers such as garbage incinerators containing halogens and halides, and (3) corrosion resistance such as nitric acid. Materials for chemical plants; (4) It is advantageously used to produce high-Si, high-Ni content steel plates and strips.

[Brief explanation of drawings]

Figure 1 is a graph showing the influence of the amount of C on the weld crackability of an alloy containing 3%5i-60%Ni-3%Mo. Figure 2 is a graph showing the influence of Si and Mo on the weld crackability. This is a graph showing. 0.05 0.15 C (%) 2nd

Claims (1)

[Claims] 1, C: 0.015-0.100wt%, Si: 1.5
~6.0wt%, Mn≦2.0wt%, Ni:30.0
~80.0wt%, Cr:10.0~26.0wt%,
A Fe-Ni alloy having excellent high-temperature corrosion resistance and weldability, containing Mo: 1.0 to 9.0 wt%, Al≦0.2 wt%, and the balance being Fe and impurities.