JPH0369977B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an Fe-Ni alloy with excellent high-temperature corrosion resistance and a method for producing the same, particularly in severe corrosive environments such as contact with high-concentration chloride-containing substances at high temperatures. , and also exhibits excellent corrosion resistance.
We propose Fe-Ni alloy and its manufacturing method. In recent years, cooking appliances have become popular, but for example, in the case of the outer cladding tube of the cooking heater for electric stoves, there are problems with high-temperature corrosion (oxidation and sulfidation) due to chlorides and weldability, and there are currently various problems. Research and development is underway. Materials that are particularly suitable for this type of field are used in the presence of high-temperature chlorides.
When NaCl comes into contact with the steel surface, Fe and NaCl in the steel
This reaction with NaFeCl ₄ generates highly volatile NaFeCl 4 and accelerates corrosion, so this must be considered from a different perspective than normal high-temperature oxidation resistance. [Prior Art] Materials such as the above-mentioned cooking heater outer cladding tube, to which soy sauce, salt, etc. tend to adhere, are susceptible to high-temperature corrosion (dry corrosion) if they are exposed to high-temperature atmosphere with these substances still attached. Therefore, the higher the temperature, the more significant the damage. Conventionally, NCF800 (JIS G4901) material or
NCF600 materials are used. In contrast,
Steel with low Ni content has also been proposed as a VA material for NCF800. For example, in Japanese Patent Publication No. 64-8695 (steel for high-temperature dry corrosion environments where chlorides are present), Ni is in the range of 16 to 30 wt% (hereinafter expressed simply as "%"), and especially Mo and W , proposed the effect of reducing Ni by adding V, and also published in JP-A-64
No.-73056 discloses that Ni promotes internal corrosion and is harmful, and that Si is effective for oxidation resistance. Furthermore, in JP-A No. 63-65058, Si
We are proposing a steel with excellent high-temperature corrosion resistance, which is characterized by a large amount of steel. In addition to the above, there are many reports on the effects of alloying elements on high-temperature corrosion.For example, Shinada et al. (30th Corrosion Prevention Discussion (1983) p50-53), and regarding the corrosion resistance of Ni, RDKMisra et al (Oxdation of
In Metals Val.25 (1986) p83-83), NiO
reported protection against NaCl. moreover,
Fujikawa et al. (Materials and Processes Vol. 1 (1988)
p1799) reports that even if it contains 3.5% Si, 550
It has been reported that significant erosion occurs at temperatures above ℃. As explained above, the effects of alloying elements on high-temperature corrosion in chloride-containing environments have been reported in conflicting ways, both in terms of effectiveness and toxicity, and are still unclear. The reality is that they have not. Regarding the weldability of Fe-Cr-Ni alloys containing Si,
40 (1987) No.4.p128), it is reported that the addition of Mo is effective. [Problem to be solved by the invention] In recent years, 200V wiring to general households has been promoted, and along with this, demand for electric heaters is expected to increase. In particular, the sheath heaters for cooking described above are becoming more and more powerful, and it is expected that high-temperature materials such as JIS NCF600 material will increasingly be used for their outer covering materials. However, this
NCF600 material has major problems that still need to be resolved regarding cost and high-temperature corrosion (corrosion resistance in high-temperature corrosive environments containing chlorides), and recently there has been a strong desire for an alternative material to appear. However, all of the steels proposed in the above-mentioned Japanese Patent Publication No. 64-8695, etc.
The reality is that the corrosion resistance is inferior to NCF600 material, and the target properties cannot be achieved. Moreover, it has been pointed out that hot workability and weldability of these alloys deteriorate significantly due to the low melting point eutectic of Si and Ni added to improve high temperature corrosion resistance, and even now The reality is that no solutions have been found for these issues. An object of the present invention is to overcome the problems of the prior art described above by providing a material that not only has excellent corrosion resistance in a high-temperature corrosive environment in the presence of chlorides but also has excellent weldability. [Means for Solving the Problems] As a result of intensive research to solve the above-mentioned problems, the present inventors have discovered new knowledge regarding the influence of alloying elements on corrosion resistance in high-temperature corrosive environments containing chlorides. Obtained. This means that, unlike when added alone, certain alloying elements may work synergistically to produce unexpectedly superior effects. That is, in the present invention, the following has become clear from the mutual influence of each of these additive elements regarding the Fe-Cr-Ni alloy containing 16 to 25% Cr. (1) Surprisingly, in this ternary alloy, Ni:
At a high Ni content of 35%, localized erosion such as grain boundary erosion can be prevented without causing any other significant damage. (2) Regarding the effect of Si, when the amount of Ni is small, it has the effect of inducing pit-like local corrosion, but when the amount of Ni is increased, the high-temperature corrosion resistance is significantly improved. In other words, the present invention is characterized by focusing on the synergistic effect of Ni and Si, and even if the amount of Ni is smaller than the conventional NCF600 material, Ni and
This work was completed by focusing on the fact that by simultaneously adding Si, it was possible to obtain an alloy with excellent high-temperature corrosion resistance. In addition, similar to hot workability, weldability deteriorates due to the eutectic formation of Si and Ni. However, in terms of improving weldability, at the same time as the effect of Mo, which was known in conventional low Ni alloys, in the high Ni side of 35% Ni, Ni
It was newly discovered that increasing the weldability improves weldability, and it was found that there is a suitable quantitative relationship among Ni, Si, and Mo in order to maintain weldability. Based on this knowledge, the present invention has developed an Fe--Ni alloy having the following main features. The first one is C0.05%, Si: 1.5-4.5
%, Mn1.0%, Ni:35.0~75.0% and Cr:
Contains 12.0 to 25.0%, and Ni and Si are represented by the following formula;
It is an Fe-Ni alloy with excellent high-temperature corrosion resistance, containing a satisfactory amount of 3Ni105+20Si, and containing 0.03% or less of S and 0.03% or less of P as impurities, with the balance being Fe and other impurities. The second one is C0.05%, Si: 1.5-4.5
%, Mn1.0%, Ni: 35.0~75.0%, Cr: 12.0~
25.0%, and at least one selected from Mo6.0%, W3.0%, and V3.0%, and Ni, Mo, and Si meet the following formula;
Contains 3Ni + 10Mo105 + 20Si satisfactorily,
And as impurities, S is 0.03% or less and P is 0.03%.
It is an Fe-Ni alloy with excellent high-temperature corrosion resistance, with the balance being Fe and impurities.In addition, in each of the above alloys, REM
An Fe-Ni alloy with excellent high-temperature corrosion resistance characterized by adding at least one of 0.05wt%, Ca0.02wt%, and Mg0.02wt% is also an alloy of the present invention. These alloys are prepared by heating the alloy materials having the above-mentioned component compositions in the temperature range of 1150°C to 1280°C at t・exp(−1443/T−1814)1 (where t is the soaking time (minutes), T is heating temperature (℃)
It is. ) can be homogenized and then hot worked to produce an Fe-Ni alloy with excellent high-temperature corrosion resistance. [Function] According to the research conducted by the present inventors, in a Fe-Cr-Ni alloy containing 35% or more of Ni, which is effective for high-temperature corrosion resistance, when containing 1.5% or more of Si, the Ni
Due to the synergistic effect with Si, the effect of ordinary Si addition can be significantly improved beyond the expected range.
It was found that this alloy has a high resistance to high-temperature corrosion that cannot be obtained with conventional low-Ni-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: An element necessary to obtain high-temperature strength, but C combines with the Cr element at high temperatures and forms at grain boundaries.
It precipitates as Cr ₂₃ C ₆ and forms a Cr-deficient phase near the grain boundaries, which promotes the progression of high-temperature salt corrosion, and also causes intergranular corrosion due to condensed water during rest, so a lower value is preferable, and the upper limit should be 0.05% or less. And so. Si: This is the element that plays the most important role in the alloy of the present invention, and at 35% Ni, its synergistic effect with Ni has a remarkable effect on corrosion resistance. This effect far exceeds the general effect of Si, which is said to improve corrosion resistance in high-temperature environments where chlorides are present. Therefore, Ni≧35
%, its addition effect occurs with a lower limit of 1.5%. On the other hand, if the amount added exceeds 4.5%, it will impair the weldability of high-Ni fully austenitic steel, and will also promote the precipitation of intermetallic compounds such as σ, which will deteriorate the ductility and toughness after long-term use at high temperatures. , the Si content was determined to be 1.5-4.5%. Mn: An element necessary to maintain the hot workability of steel, but if it is contained in an amount exceeding 1.0%, corrosion resistance will deteriorate in high-temperature environments where chlorides are present, so Mn is included. The amount was set at 1.0% or less. In addition, the Mn content should preferably be 0.1~
It is preferable to adjust it to 0.5%. Ni: Extremely effective in improving high-temperature corrosion resistance in high-temperature corrosive environments containing chlorides, especially in this
When the Ni content is 35% or more, it has the effect of dramatically improving the high temperature corrosion resistance of Si, and when it is less than that,
In fact, the disadvantages of having a high Ni content are exacerbated, which is not desirable. Therefore, Ni is 35%
The above shall apply. Further, the addition of Ni is effective in improving the structural stability against precipitation of intermetallic compounds consisting of Cr, Si, Mo, etc., and in improving weldability, and in this sense, the more the Ni, the better, and more preferably 50% or more. Cr: Effective in improving high-temperature corrosion resistance in environments where chlorides exist and general oxidation resistance at around 900°C, but if the amount is less than 12%, scale exfoliation is significant even in high-temperature corrosion environments caused by chlorides. ,
Since the desired effect cannot be obtained, it is set to 12% or more. However, since too much content promotes internal erosion, the upper limit is set at 25%. Preferably 16.0-20.0
It is better within the range of %. Mo: Mo is one of the elements that is extremely effective in improving corrosion resistance in high-temperature environments where chlorides are present, and is particularly effective in suppressing internal corrosion and weldability. However, if the amount of Mo added is too large, the scale removability will increase, so
6.0% or less. Preferably it is 4% or less. W, V: High temperature corrosion resistance in the presence of chlorides
It has the same effect as Mo. However, if any element is contained in an amount exceeding 3.0%, it will promote the precipitation of intermetallic compounds, harming workability and increasing scale exfoliation.
was set as the upper limit. REM, Ca, Mg: These elements act effectively as deoxidizing agents and desulfurizing agents, and have the effect of improving hot workability. However, if the amount is too high, it will work to accelerate high-temperature chloride corrosion, so the upper limits for each addition should be set to REM: 0.05% and Ca: 0.02%.
%, Mg: 0.02%. S: The less S there is as an impurity, the better, especially
If it exceeds 0.03%, hot workability and weldability deteriorate, so this amount needs to be 0.03% or less. P: P is an impurity component that adversely affects weldability, and if it exceeds 0.03%, the Ni, Mo,
Even if Si satisfies the above-mentioned relationship, welding cracks occur, so it is necessary to keep it at 0.03% or less. In addition, in the alloy of the present invention, Al, Cu,
Ti and Nb may each be added in an amount of 0.5% or less without causing any particular change in the effect of the addition of the above-mentioned main components. Next, when considering the above-mentioned composition from the viewpoint of weldability, the relationship of Ni-Si-Mo needs to be defined as follows. In other words, Figure 1 shows the effects of Mo and Ni on weldability.
It is a figure showing quantity dependence. The weldability test is the first
Butt restraint TIG welding was performed using the alloy of the present invention shown in the table and 2.0 mm thick plates of an alloy based on 17% Cr-3% Si-Fe with various changes in Mo and Ni.
The evaluation is based on the bead length cracking rate. In the case of base alloy (17%Cr-3%Si-Fe), 10Mo+
It can be seen that no cracking occurs under the 3Ni165 conditions. When changing the Si content from the base alloy (17% Cr-3% Si-Fe) to 1.5%, the boundary line in Figure 1 moves to the dotted line (10Mo+3Ni=135). If the Si content is increased by 1.5%, the Ni content must be increased by approximately 10%, and when taking into account the dependence on the Si content, the result is that
10Mo+3Ni105+20Si. Therefore, if Mo is not included, it is necessary to satisfy 3Ni105+20Si. Next, the method for manufacturing the alloy of the present invention will be explained, particularly focusing on the heat treatment conditions. An alloy material (ingot) having the above-mentioned composition requires homogenization heat treatment. This is due to the following reasons. In other words, it contains a lot of Si.
Fe-Cr-Ni alloys may have significantly poor hot workability if they are left as cast. this is,
This is thought to be due to the formation of a low melting point eutectic of Si and Ni due to solidification segregation, and this hot embrittlement can be prevented by homogenization through high temperature heat treatment. Its treatment is essential. The heat treatment conditions for this reason are t・exp(-1443/T-1814)1 (where t is the soaking time (minutes) and T is the temperature range of 1150℃ to 1280℃. heating temperature (°C)). Figure 2 is a diagram showing the results of a study on hot workability. Using an air-melted ingot of the invention alloy (No. 1) in Table 1, a soaking treatment was carried out in the range of 1150 to 1280°C. This study investigated the aperture value due to ultra-high temperature tension. The high-temperature tensile test was conducted at 1000 to 1200°C, and evaluation was made based on the minimum aperture value. From this figure, it was found that in the case of the alloy of the present invention, the workability was improved when heat treatment was performed in the range of t·exp(-1443/T-1814)1. [Example] In this example, an alloy (No.
1 to No. 10) were made into 10Kg ingots in an atmospheric induction furnace, hot forged and then cold rolled into 2.0 and 0.5mmt ingots.
It was made into a plate and used for testing. High temperature corrosion test specimen thickness
After cutting into 0.5mm thick, width 20mm, length 30mm, 1100℃×
After being oxidized in the atmosphere for 10 minutes, it was subjected to the following high-temperature corrosion test. The high-temperature corrosion test consisted of immersion in saturated saline (5 minutes) → drying (10 minutes) → repeated oxidation (800°C x 30 minutes → air cooling for 10 minutes).
The test was carried out for 4 cycles, with 50 times per minute as one cycle, and the results are shown in Table 1. As is clear from the high temperature corrosion test results, the alloys of the present invention (No. 1 to No. 7)
The maximum erosion depth is smaller than that of comparative alloys (No. 8 to No. 10);
Alloy, No. 10 alloy, high Ni% but low Si%
This is noticeable when compared to No. 9 alloy.

【table】

〔Effect of the invention〕

As explained above, the present invention can provide an Fe--Ni alloy that has excellent corrosion resistance in a high-temperature corrosive environment containing chlorides and has excellent weldability at a low cost. Therefore, the alloy of the present invention can be used in (1) outer cladding tubes of sheath heaters such as electric stoves, (2) boilers and heat exchangers such as garbage incinerators containing halogens and halides, and (3) high Si and high Ni containing steels. It is advantageously used in the production of plates and strips.

[Brief explanation of drawings]

Figure 1 is a graph showing the dependence of the amount of Ni and Mo on the weld cracking properties of alloys containing 3% Si and 17 to 23% Cr. However, ○ indicates no cracking, and ● indicates cracking. show. FIG. 2 is a graph showing the influence of soaking conditions on hot workability of the Az cast material of Invention Alloy 1. The drawing ratios determined by the ultra-high temperature tensile test are indicated by ○, drawing >80%, △.
The mark indicates 50-80%, and the x mark indicates aperture <50%.

Claims (1)

[Claims] 1 C0.05wt%, Si: 1.5 to 4.5wt%, Mn
1.0wt%, Ni: 35.0~75.0wt% and Cr: 12.0~
25.0wt%, Ni and Si satisfy the following formula: 3Ni105+20Si, and S is contained as an impurity.
Contains 0.03wt% or less, P is 0.03wt% or less, and the balance is
A Fe-Ni alloy consisting of Fe and other impurities that has excellent high-temperature corrosion resistance. 2 C0.05wt%, Si: 0.5-4.5wt%, Mn
1.0wt%, Ni: 35.0~75.0wt%, Cr: 12.0~
Contains 25.0wt%, and Mo6.0wt%, W
Contains at least one selected from 3.0wt% and V3.0wt%, and contains Ni, Mo and
Si satisfies the following formula: 3Ni+10Mo105+20Si, and S is added as an impurity.
Contains 0.03wt% or less, P is 0.03wt% or less, and the balance is
Fe with excellent high-temperature corrosion resistance consisting of Fe and impurities
-Ni alloy. 3. In the product according to claim 1 or 2, further REM0.05wt%, Ca0.02wt% and
An Fe-Ni alloy with excellent high-temperature corrosion resistance characterized by adding at least one of Mg0.02wt%. 4. The alloy material according to any one of claims 1, 2, and 3 is heated in a temperature range of 1150°C to 1280°C t・exp(−1443/T−1814)1 (where t is the soaking time (minutes) ), T is heating temperature (℃)
It is. ) with excellent high-temperature corrosion resistance, characterized by homogenization heat treatment and subsequent hot working.
Method for manufacturing Fe-Ni alloy.