JPH07103436B2 - Heat-resistant alloy with excellent carburization resistance - Google Patents

Description

TECHNICAL FIELD The present invention has excellent carburization resistance, which is useful as a material for a cracking tube for ethylene production, a reformer tube or a hearth roll for heat treatment of steel in the petrochemical industry. Regarding heat-resistant alloys.

(Prior Art) As a material for a cracking tube for ethylene production,
HP material with high Si content (0.4C-1.75Si-25Cr
-35Ni-Fe) and HP improvement material (0.45C-25Cr-35Ni-Nb, W, Mo
-Fe) is used.

(Technical problem to be solved) These conventional materials have a problem that their carburization resistance is insufficient when they are used in a temperature range exceeding 1100 ° C, and the materials deteriorate due to carburization. With the recent increase in operating temperature, it has been required to replace the tube in the outlet pipe section of the ethylene production plant due to the occurrence of carburization, and to improve the carburization resistance at high temperature.

By the way, it is said that an oxide layer is formed on the surface of the material in the actual use process, and the oxide layer suppresses the internal diffusion of carbon attached to the surface of the material. Therefore, the carburization resistance can be improved by optimizing the alloy components so that the oxide layer has adhesiveness and stability with respect to the heat cycle. However, in reality, due to the difference in coefficient of thermal expansion,
The oxide layer is easy to peel off.

The present inventor has focused on the alloy composition that can suppress the internal diffusion of carbon, rather than fixing the oxide layer. That is, the content of Cr, which easily bonds with C, is reduced and, instead, a large amount of Mo is contained. That is, Mo utilizes the property that it has a large atomic radius and is less likely to bond with C than Cr. If a large amount of Mo is contained, diffusion of C into the interior is suppressed as much as possible. I found it. It was also found that dispersion formation of an oxide due to internal oxidation of Al also suppresses diffusion of C.

(Technical Means and Actions) The heat-resistant alloy according to the present invention, in% by weight, is C: 0.3% or less, Si: 3% or less, Mn: 2% or less, Mo: 10 to 35%, Al: 3% or less. And Fe 10% or less, and the balance consists essentially of Ni.

Further, the alloy of the present invention, in order to improve the creep rupture strength, Ti: 0.5% or less, Zr: 0.5% or less and B: 0.05% or less components selected from the group consisting of It can contain at least one kind.

Further, the alloy of the present invention, in order to improve the carburization resistance,
As required, Ca: 0.001 to 0.5%, Y: 0.5% or less and Hf:
It can contain at least one component selected from the group consisting of 0.5% or less.

Further, the alloy of the present invention may contain Cr: 3.50% or less, if necessary, in order to enhance the oxidation resistance.

The heat-resistant alloy of the present invention has excellent carburization resistance when used in a temperature range exceeding 1100 ° C.

The reasons for limiting the components of the heat resistant alloy of the present invention are as follows.

C: 0.3% or less C has the effect of improving the castability of the alloy and contributes to the improvement of high temperature strength. However, since the alloy of the present invention contains a large amount of Mo, if the content of C is too large, the material hardens due to the relationship with the Mo content and causes embrittlement. Therefore, the upper limit is
0.3%

Si: 3% or less Si has the effect of improving the fluidity of molten steel as well as the deoxidizing action during melting. Since the alloy of the present invention contains a large amount of Ni and the viscosity of the molten steel becomes low, it has a remarkable effect also in improving the castability. Further, the carburization resistance is improved with the increase of Si. However, if it exceeds 3%, creep rupture strength and weldability are deteriorated, so the upper limit is made 3%.

Mn: 2% or less Mn acts as a deoxidizer like Si, and also fixes S (sulfur) during melting to improve weldability. But 2
Even if the content is more than%, the corresponding effect cannot be obtained, so the upper limit is made 2%.

Mo: 10-35% Mo is a solid solution in Ni and has a remarkable effect in improving high temperature strength and preventing C intrusion. The effect is recognized when the content is 10% or more, and when it exceeds 35%, the ductility is remarkably reduced. Therefore, the content is specified to be 10 to 35%.

Al: 3% or less Al is an element effective in improving carburization resistance. However, if the content exceeds 3%, ductility is lowered and fluidity of molten steel is lowered. Therefore, the upper limit is 3%.

Fe: 10% or less Fe reduces the oxidation resistance. Therefore, the upper limit is 10% or less.

The heat-resistant alloy of the present invention contains the above-mentioned component elements, and the balance consists of Ni and unavoidably mixed impurity elements. Ni is an austenitizing element and is an element necessary for imparting oxidation resistance and improving carburization resistance. Therefore, it is necessary to contain a large amount.

The heat-resistant alloy of the present invention can contain at least one of the following elements, if necessary, in addition to the above elements.

Ti: 0.5% or less Ti contributes to the improvement of creep rupture strength, but even if it exceeds 0.5%, the corresponding effect cannot be obtained, so the upper limit is made 0.5%.

Zr: 0.5% or less Like Zr, Zr also contributes to the improvement of creep rupture strength.
However, even if the content exceeds 0.5%, the corresponding effect cannot be obtained, so the upper limit is made 0.5%.

Ca: 0.001 to 0.5% Ca forms an oxide on the surface of the material when the material is heated to a high temperature, has the effect of suppressing C from diffusing inside the material, and contributes to the improvement of carburization resistance. Therefore, 0.001% or more is contained, but if contained too much, the weldability and other material properties are impaired, so the upper limit is made 0.5%.

B: 0.05% or less B strengthens the grain boundaries and contributes to the improvement of creep rupture strength. However, if contained too much, the weldability and other material properties are impaired, so the upper limit is made 0.05%.

Y: 0.5% or less Y contributes to the improvement of carburization resistance. In order to exert its effect, it can be contained up to 0.5%.

Hf: 0.5% or less Hf, like Y, contributes to the improvement of carburization resistance and can contain up to 0.5% in order to exert its effect.

Cr: 3.50% or less Cr is useful as an element that enhances oxidation resistance. But,
When it is used as a material for a cracking tube or the like, it preferentially bonds with C that has penetrated into the material, thus making the material brittle. In the case of a cracking tube, since the inside of the tube is a reducing-weakly oxidizing atmosphere, there is no particular problem even if the Cr content is suppressed to a low level. Therefore, Cr, which causes carburization, is set to 3.50% or less even when it is added to improve the oxidation resistance.

Next, the effect of improving the carburization resistance of the alloy of the present invention will be specifically described with reference to examples.

(Example) An alloy of various components was melted in a high frequency induction melting furnace, and an ingot was manufactured by centrifugal casting. Table 1 shows the chemical composition of each test material.

A test piece (thickness 15 mm, width 25 mm, length 70 mm) was prepared from each test material, and a carburization test was performed on the test piece. The test is based on the solid carburizing test, and the carburizing conditions are shown in FIG. The carburizing test was performed 17 times under the conditions shown in Fig. 2 (48
hrs. × 17 times = 816 hrs.) Carburizing treatment was repeated, chips were collected from the surface of the test piece at a pitch of 0.5 mm, and the chips were chemically analyzed to examine the amount of increase in carbon. The results are shown in FIG.

In Table 1, sample materials No. 1 and No. 2 are conventional alloys, and sample materials No. 3 to No. 13 are alloys according to the present invention. Among them, No.7 to No.9 are alloys containing one or two kinds of Ti and Zr, No.1
Nos. 0 to 13 are alloys containing any one of Ca, B, Y and Hf. No.1 ~ No.2 conventional alloy, No.3 ~ No.6, No.7, No.1
The carburizing test results for the alloys of the present invention of No. 0 and No. 12 are shown in FIG. In addition, No.8, No.9, No.11 and N
Carburization test was also conducted for o.13, but No.8 and No.9
The same results as No. 7 are shown, No. 11 and No. 13 are No. 10 and N.
Since the result is the same as that of o.12, its display is omitted in FIG.

As is clear from the results shown in FIG. 1, the alloy of the present invention is superior to the conventional alloy in carburization resistance.

(Effect of the Invention) The heat-resistant alloy of the present invention has excellent carburization resistance when used in a temperature range exceeding 1100 ° C. Therefore, the alloy of the present invention is suitable as a material for cracking tubes and reforming tubes in the petrochemical industry,
Further, it is also suitable for structural materials such as in-furnace parts requiring carburizing resistance such as radiant tubes for heat treatment of steel and hearth rollers.

[Brief description of drawings]

FIG. 1 is a graph showing the amount of carbon increase in a carburizing test, and FIG. 2 is an explanatory diagram of carburizing conditions.

Claims (4)

[Claims] 1. In% by weight, C: 0.3% or less, Si: 3% or less, M
A heat-resistant alloy containing n: 2% or less, Mo: 10 to 35%, Al: 3% or less and Fe: 10% or less, and the balance being substantially Ni, which has excellent carburization resistance. 2. Ti: 0.5% or less, Zr: 0.5% or less and B: 0.05%
At least one component selected from the group consisting of
The heat-resistant alloy according to claim 1, which contains a seed. 3. Ca: 0.001 to 0.5%, Y: 0.5% or less, and Hf: 0.5
%. The heat-resistant alloy according to claim 1 or 2, containing at least one component selected from the group consisting of% or less. 4. The heat-resistant alloy according to claim 1, which contains Cr: 3.50% or less.