JPS59153878A - Manufacture of steel product subjected to alloy cementation - Google Patents

Abstract

PURPOSE:To manufacture the titled product having an alloy layer of a uniform thickness and showing superior corrosion resistance at high temp. by burying a steel product to be treated in a powdered mixture of Ni-Mn alloy powder with Al2O3 powder to form a cementation layer of the alloy and by carrying out chromizing. CONSTITUTION:A steel product to be treated is buried in a powdered mixture of Ni-Mn alloy powder with Al2O3 powder, and it is heated to 1,050-1,300 deg.C which is higher than the m.p. of the alloy in a nonoxidizing atmosphere to form a cementation layer of the Ni-Mn alloy of a uniform thickness on the surface of the steel product. Chromizing is then carried out by a conventional powder packing method to enrich the cementation layer with Cr having a significant effect of improving the resistance to corrosion at high temp. and oxidation due to steam. At this time, the amount of Mn is reduced by the substitution reaction with Cr, thus, sigma-embrittlement is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an alloy diffusion infiltration treated steel product, and more particularly to a method for producing an alloy diffusion infiltration treated steel product by combining hot-dip plating of a nickel-manganese alloy and chromizing treatment.

Conventionally, a method of performing Cr diffusion and penetration treatment on the surface of m products using a powder bag method (chromization treatment) is known.

However, in cases where combustion stops are frequently repeated, such as in incinerators, coatings obtained by diffusion infiltration treatment not only exhibit excellent resistance to high-temperature corrosion, such as corrosion caused by combustion gas or corrosion caused by molten salt. There is a strong demand for materials with extremely good adhesion.

By the way, in the usual chromizing treatment, a σ layer is precipitated in the chromized layer during use, resulting in so-called σ embrittlement. In order to prevent such σ embrittlement, even in the conventional technology, Cr
It has been proposed to coat the steel surface with an alloy of Ni and Ni. For example, Ni-Cr alloy, Ni-Cr-
Spraying Fe alloy or Ni, Cr, Fe mixed powder,
After dipping or applying a mixture with adhesive, annealing is performed.
A treatment method characterized by diffusing Ni, Cr and Fe on the steel surface (Japanese Patent Application Laid-open No. 55-85665), and a method in which Ni powder is mixed with a binder and applied to the surface of the heat-resistant alloy in advance, then baked, and then A treatment method characterized by coating chromium by chemical vapor deposition (Japanese Unexamined Patent Publication No. 5
No. 5-82772).

However, in both of these methods, Ni powder is coated with a binder or by a method such as spraying, baked, and then chromized. The coating obtained by such a method is insufficiently alloyed with the steel surface, has poor adhesion, and may peel off during use. Also, simply coating or spraying the powder with a binder followed by annealing and diffusion results in a coating that is quite porous and does not serve as a sufficient protective coating against gas corrosion and molten salt corrosion.

Thus, the present inventors first immersed the steel product to be treated in a nickel-manganese molten bath to form a nickel-manganese molten bath prior to chromizing treatment in order to form a diffusion permeation layer with excellent high-temperature corrosion resistance and good adhesion. A method for forming a manganese melt-plated layer was disclosed (Japanese Patent Application No. 57-59632).

However, in the method described above in which a steel product is immersed in a nickel-manganese molten alloy bath, in the case of large steel products, it takes a long time for the temperature of each part of the steel product to become uniform. By the way, on the other hand, the reaction between the molten alloy and the steel on the surface of the steel product occurs extremely quickly, and if the reaction time exceeds 5 minutes, the thinning of the steel will become excessively large, which is not preferable. However, in such a short time, if the steel product has a complicated shape as described above, it is difficult to make the temperature uniform in each part. The temperature of the steel surface determines the rate of formation of the nickel-manganese alloy layer, so if the temperature differs in each part of the steel product,
The thickness of the nickel-manganese layer changes at each location where the temperature is different, which is undesirable.

Furthermore, as mentioned above, the reaction rate between the molten alloy and steel is extremely fast, so if a metal container such as steel or nickel alloy is used as the hot container, it will suffer severe melting damage and will not be practical. Therefore, ceramic containers such as Zr02 and MgO are used. By the way, long containers are required to process long pipes such as boiler tubes, but long containers such as the ceramic containers described above are not only extremely difficult to manufacture, but also There are practical problems such as easy damage due to thermal stress when the temperature rises or falls.

Therefore, the purpose of the present invention is to provide a method for manufacturing alloy diffusion and penetration treated products that eliminates these drawbacks.In order to achieve this purpose, we have continued our intensive research and have found that alumina powder is The present invention was completed by discovering that Ni and Mn alloy diffusion and penetration treatment was also possible by the so-called powder bag method used.

Here, the gist of the present invention is to embed a steel product to be treated in a mixed powder of nickel-manganese alloy powder and alumina powder, and to heat the product to a temperature of 1050 to 1300 in a non-oxidizing atmosphere.
This is a method for producing an alloy diffusion-infiltration treated steel product, which is characterized by heating the nickel-manganese alloy diffusion-infiltration treatment layer to (M) and then subjecting it to chromization treatment.

According to the present invention, when applying a nickel-manganese alloy diffusion layer to the surface of a steel product as described above, there is no need to prepare an alloy molten bath, and the layer is simply coated in a mixed powder of nickel-manganese alloy powder and alumina powder. All you need to do is bury the treated steel products. Next, the alloy is heated in a non-oxidizing atmosphere (that is, an inert gas atmosphere or a hydrogen gas atmosphere) to a temperature of 1050 to 1300° C., which is a temperature higher than the melting point of the alloy. The nickel-manganese alloy powder is heated above its melting point. However, the above-mentioned mixed powder does not form a molten phase, and the mixed powder does not form a lump even after being cooled after processing.

The proportion of alumina (A1203) powder in the mixed powder is preferably 30 to 70% (by weight).

However, it is not limited to this. In addition, the processing time is 5 μm thick at a temperature of 1050 to 1300°C.
Although the time is not limited as long as it is sufficient to form the above alloy layer, for example, one hour is generally sufficient.

When heating nickel-manganese alloy powder in alumina powder, it is necessary to heat the alloy to a temperature higher than the melting temperature of the alloy (1050°C or higher), but on the other hand, processing at a temperature exceeding 1300°C is not suitable for treating steel products. This is undesirable because it causes deformation and coarsening of the grain size, and increases wear and tear on the processing furnace.

The reason why nickel-manganese alloys were selected as alloys in the present invention is that they can form a nickel-manganese alloy layer on the steel surface at relatively low temperatures, i.e., 1050 to 1300°C. It is from.

In addition, in the process of enriching the amount of Cr, which has a large effect on improving high-temperature corrosion resistance and steam oxidation resistance, by cloise treatment, Mn is reduced by the substitution reaction with Cr as shown below, and σ embrittlement is practically a problem. Because it will disappear.

Cr + 2NH4C1-2NH3 + CrCl2 +
H2CrCI2+Mn-4MnC12+
CrThe composition of this nickel-manganese alloy is not particularly limited, but in terms of weight% Mn is 40 to 60%, Ni is 60 to 40%.
% is preferable. By setting the nickel content to 40% or more, σ embrittlement of the alloy layer can be prevented even if the Cr content is increased to 35% (weight) or more in the subsequent chromizing treatment. In order to process in the range of 1050 to 1300°C and to ensure a sufficient nickel-manganese alloy layer, N
It is preferable to limit the content to 440 to 60% and Mn to 60 to 40%. For the subsequent chromization treatment, it is sufficient to employ the conventional powder pack treatment, since sufficient performance can be ensured by performing the conventional powder pack treatment at 1100 to 1250°C. There are no particular limitations in the present invention.

As described above, in the present invention, the conventional powder pack treatment is sufficient, but if necessary, the chromization treatment may be performed by other appropriate means such as a vapor phase deposition method.

Further, after the prior-Mn alloy diffusion and infiltration treatment, it may be carried out immediately, or it may be carried out after cooling to room temperature. In short,
The present invention will be explained in more detail with reference to Examples.

5TB42 steel (carbon steel) and S 11 S 347 I+ steel (austenitic stainless steel) having the chemical compositions shown in Table 1 were used as test materials as treated steel products. The thickness distribution of the Ni--Mn alloy layer was measured while varying the alloy composition of Ni and Mn and the treatment temperature. However, the blending ratio of Al2O3 during the penetration treatment of the nickel-manganese alloy is (Ni-Mn alloy) /A l 203 = 70
/30 (weight ratio).

Thickness 5-80℃ at processing temperature 1050-1300℃
A nickel-manganese alloy diffusion permeation layer with a uniform thickness of μm was obtained. There was a tendency for the alloy layer thickness to increase under the same conditions as the manganese content increased. The preferred Mn content was 40 to 60%. The treatment time was 1 hour in all cases.

Next, the nickel-manganese alloy plated steel product obtained as described above was further subjected to chromization treatment by a conventional powder bag method. These processing conditions are summarized in Table 2. In addition, we investigated the composition distribution of the coating after solution treatment, and also investigated the aging treatment (
A bending test and a high-temperature corrosion test were conducted after 650° C. for 1000 hours.

Some of these test results are summarized in Table 2, and according to those results, Ni-Mn diffusion infiltration treatment
When carried out at a temperature below 50°C, the Ni-Mn alloy layer is
It becomes less than μm. Therefore, Fe during chromizing treatment
It has been found that it is difficult to sufficiently suppress the diffusion of , for example, σ phase is generated during aging treatment, and cracking occurs during bending tests. In addition, with Ni-Mn alloy composition, Mn60
In the high region of ~70%, the amount of remaining Mn exceeds 20% at most even by removing Mn in the chromizing process. As a result, it was found that cracks occurred in the diffusion layer in the post-aging bending test. The results of the high-temperature corrosion tests were all good.

Claims (1)

[Claims] The steel product to be treated is buried in a mixed powder of nickel-manganese alloy powder and alumina powder, and heated for 10 minutes in a non-oxidizing atmosphere.
A method for producing an alloy diffusion-infiltration treated steel product, which comprises heating to 50 to 1300°C to obtain a nickel-manganese alloy diffusion-infiltration treatment layer, followed by chromizing treatment.