JPH03120310A - Method for refining heat resisting alloy excellent in room temperature elongation characteristics - Google Patents

Abstract

PURPOSE:To improve the yield of Ti addition, to reduce the contamination of molten metal with TiO2, and to produce a heat resisting alloy excellent in room temp. elongation characteristics by carrying out refining in a vacuum atmosphere at the time of refining an Ni-Cr-Co heat resisting alloy. CONSTITUTION:At the time of refining a heat resisting alloy having a composition consisting of, by weight, 0.3-0.6% C, <2.0% Si, <2.0% Mn, 22-32% Cr, 26-42% Ni, 9-26% Co, 3-16% W, 0.05-2.0% Ti, and the balance Fe, the atmosphere in the refining is controlled so that it is a vacuum atmosphere of <=5.0mmHg during the period between the initiation of refining and 30min at the longest after the initiation of refining, and further, the additive quantity of Ti is regulated to <=2.5%. Since the oxidation of Ti does not occur and deterioration in the cleanliness of the molten steel due to TiO2 is prevented because the refining is performed in vacuum, the heat resisting alloy excellent in room temp. elongation characteristics can be stably produced.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an improvement in the melting process for heat-resistant alloys used for internal parts of various industrial furnaces.
The present invention relates to a method for producing a heat-resistant alloy that has high creep rupture strength even when exposed to high temperatures, has excellent oxidation resistance, and has excellent elongation characteristics at room temperature.

[Prior art] Furnace parts of industrial furnaces used at high temperatures of 1000°C or higher are subject to long-term oxidation and long-term stress, so the materials used for them must be resistant to acid at high temperatures. It is required to have excellent chemical properties and high creep rupture strength. Furthermore, since it is subjected to thermal cycles of heating and cooling, high thermal fatigue strength is required. A nickel-chromium-cobalt heat-resistant alloy containing a small amount of Ti has been proposed as a material compatible with this (for example, JP-A-55-119
155).

[Problems to be Solved by the Invention] The above-mentioned nickel-chromium-cobalt-based heat-resistant alloy is intended to improve its thermal fatigue strength by adding a small amount of TI.

However, the above-mentioned alloys have poor weldability and room temperature elongation properties, so they often break during material processing.

The known alloys mentioned above are melted in the atmosphere. However, in the case of atmospheric dissolution, when Ti is added, part of T1 becomes slag (
(Ti oxide, nitride, etc.), therefore, an excessive amount of Ti is usually added in anticipation of the reduction. The slag that floats is removed from the alloy, but the slag that does not float gets caught up during casting and not only causes casting defects but also causes a decrease in room temperature elongation properties.

It is also known that there is a correlation between room temperature elongation properties and weldability, and that if room temperature elongation properties are improved, weldability will be correspondingly improved.

[Object of the invention] The present invention is directed to the addition of a small amount of Ti to a nickel-chromium-cobalt system.
The purpose is to increase the cleanliness of heat-resistant alloys containing added chlorine and improve the room temperature elongation properties.

[Means for Solving the Problems] In order to prevent excessive addition of Tf in the melting stage, the present inventors focused on degassing melting. According to degassing melting, as shown in the following equation, a deoxidizing reaction occurs, [0] (oxygen in molten steel) is removed, the amount of reaction between Ti and oxygen decreases, and the amount of Tf added is This is because it is thought that this can be reduced compared to the case of atmospheric dissolution.

[C] + [0] -Go (g) Specifically, in weight%, c: 0.3 to 0.6%, Si: 2.0%
Below, Mn: 2.0% or less, Cr: 22-32%, Nt
:26~42%, co=9~26%, W:3~16%,
In the melting stage of a heat-resistant alloy containing T i 0.05 to 2% and the balance consisting of Fe and unavoidable impurities, the melting process is carried out in a vacuum state of 5 On + mHg or less for at most 30 minutes from the start of the melting. The amount of Ti that is sometimes added is 2.5% or less.

[Effect of the invention] Although it is not necessary to add excessive Ti in the melting stage, Ti
Almost no oxide slag is generated, the cleanliness of the melted alloy is good, and the room temperature properties of the alloy are improved. Also, 10
Demonstrates high creep rupture strength and excellent oxidation resistance when used at high temperatures of 00°C or higher.

Therefore, when the heat-resistant alloy produced by the method of the present invention is applied to the inner parts of industrial furnaces such as hearth rolls, radiant tubes, and trays, it has excellent workability and its properties are fully exhibited even when used at high temperatures. be done.

[Reasons for Limiting Ingredients] The melting method of the present invention is directed to a heat-resistant alloy having the above-mentioned composition, and the reasons for limiting the composition of the heat-resistant alloy are as follows.

C: 0.3 to 066% If the C content is less than 0.3%, the creep rupture strength will decrease significantly. On the other hand, if the content exceeds 0.6% (:
Since only r and W double carbides increase, solid solution of these elements not only makes it difficult to secure high temperature strength, but also significantly reduces oxidation resistance. Therefore, C is 0.3-0.6%
shall be. In addition, it is more preferable to contain within the range of 0.45 to 0.55%.

Si: 2.0% or less Si is an element that impairs high temperature strength, and its tendency is
This is particularly noticeable at high temperatures of 00°C or higher. However, since it also has the effect of improving castability, it is contained within a range of 2.0% or less.

Mn: 2.0% or less Mn lowers oxidation resistance and high temperature strength, so it is not preferable to include it in a large amount. However, it improves the castability of castings and is also effective as a deoxidizing agent and desulfurizing agent. Therefore,
It is contained within a range that does not significantly reduce oxidation resistance and high temperature strength, that is, within a range of 2.0% or less.

Cr: 2Z to 32% If the Cr content is less than 22%, the material cannot have sufficient oxidation resistance as a high temperature material of 1000° C. or higher. On the other hand, if the content exceeds 32%, the occurrence of casting cracks will significantly increase and high temperature strength will also decrease. Therefore, the content is specified at 22 to 32%.

In addition, it is more preferable to contain within the range of 24 to 28%.

Ni: 26-42% Ni coexists with Cr oxide in the presence of W, forms a dense oxidation-resistant film with excellent high-temperature stability, and has the effect of stabilizing the base austenite. Also,
It has the effect of ensuring high temperature strength through interaction with WSCrSC. Therefore, the content is specified to be 26 to 42%. In addition, it is more preferable to contain within the range of 33 to 37%.

CO: 9-26% CO has the effect of increasing the solubility of C and improving creep rupture strength. However, if the content is less than 9%, no effect will be observed. Moreover, if the content exceeds 26%, the creep rupture strength will improve, but the oxidation resistance will decrease. Therefore, the content is defined as 9 to 26%.

In addition, it is more preferable to contain within the range of 14 to 16%.

W: 3-16% W is solid solution reinforcement of austenite base and Cr.

It is an effective element for strengthening grain boundaries through grain boundary precipitation of W double carbides. 1000 if the content is less than 3%
No significant effect was observed in improving creep rupture strength at high temperatures of ℃ or higher. On the other hand, even if the content exceeds 16%, not only will no corresponding strength improvement effect be observed, but the content will also relatively reduce the amount of C and Nf, leading to a decrease in oxidation resistance. is defined as 3 to 16%.In addition, 4
．． The content is more preferably within the range of 0 to 6.0%.

Ti: 0.05 to 2% Ti improves high temperature strength such as creep rupture strength and thermal shock resistance by forming carbonitrides and the like. Its content is 0.0
If it is less than 5%, its effect cannot be fully exhibited. The effect increases as the content increases, but if the content exceeds 2%, the precipitates become coarser and the amount of oxide-based inclusions increases, resulting in a decrease in strength. Therefore, the content is 0,0
It is specified at 5-2%.

The remainder of the above alloy is Fe and unavoidably mixed P and S.
Consists of other impurity elements. Note that impurities may be contained within the range normally allowed for this type of alloy.

[Example] Next, the effects of the degassing and dissolving method of the present invention will be specifically explained using examples.

Table 1 shows the chemical composition of test materials of a heat-resistant alloy produced by degassing melting (inventive example) and a heat-resistant alloy produced by atmospheric melting (comparative example). Table 2 shows the cleanliness and mechanical properties of these test materials at room temperature. The cleanliness was determined based on JIS G 0555. For mechanical properties, yield strength, tensile strength, and elongation were examined based on JIS test methods.

In the table, Xα1 and Nα2 represent comparative examples, and Nα3 and Nα4 represent inventive examples, respectively. In addition, in Table 1, especially Ti
In order to clarify the effect of degassing and dissolution, the amount added is also shown.

(The following is a blank space) As is clear from Table 2 and Table 1, when focusing on the amount of Ti added, it can be seen that the amount of Ti added in the examples of the present invention is significantly smaller than that in the comparative examples. That is, in the case of the present invention example, it is sufficient to add about 1.2 times the amount that should be contained in the alloy at the melting stage, whereas in the comparative example, it is necessary to add about twice the amount. Since the Ti content of the alloy targeted by the present invention is at most 2%, as defined in the claims, the Ti content is at most 2.5%.
The purpose can be achieved by adding %.

As is clear from Table 2, it is proved that the cleanliness and elongation properties of the alloy are significantly improved as a result of reducing the amount of Ti added. That is, the cleanliness of the present invention example is 0.05~
The cleanliness of the comparative example was 0.15, while it was 0.06%.
~0.17%. Moreover, the elongation of the present invention example is 1O08
~11.1%, while the elongation of the comparative example was ~4.4%.
It is 5.1%.

When melting is performed in a vacuum state of 5.0 mmHg or less for at least about 15 minutes and at most about 30 minutes after the start of melting, regardless of whether the atmosphere during casting is vacuum, Ar gas, or air, It was also found that there was no difference in the quality of the cast products. This indicates that the molten metal, once degassed, is not affected by the amount of gas absorbed during the period from tapping to casting.

Claims (1)

[Claims] (1) In weight%, C: 0.3 to 0.6%, Si: 2.
0% or less, Mn: 2.0% or less, Cr: 22 to 32%,
Ni: 26-42%, Co: 9-26%, W: 3-16
%, Ti: 0.05 to 2%, and the balance is Fe and unavoidable impurities. A method for producing a heat-resistant alloy with excellent room temperature elongation properties, characterized by adding at least 2.5% of Ti.