JPS60149762A - Coating method by spraying for providing corrosion resistance - Google Patents

Abstract

PURPOSE:To obtain a corrosion resistant sprayed coating layer having high adhesive strength and causing no cracking by spraying a spraying material consisting of specified percentages of Ni and an Ni-P alloy contg. a specified amount of P on an iron-base alloy material to coat the material and by heat treating the coated material at a specified temp. CONSTITUTION:A spraying material consisting of 20-80wt% Ni-P alloy contg. 5-25wt% P and of 80-20wt% Ni or Ni-Cr alloy contg. 5-60wt% Cr is sprayed on an iron-base alloy material to coat the material B, Si, or C may be contained in the Ni-P alloy besides Cr, and Al, an Al-Si alloy or an Al-Y alloy may be added. The coated blank is heat treated at 600-1,000 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION (Object of the Invention) The present invention relates to a method of treating a corrosion-resistant thermal spray coating.

(Prior Art) Since iron-based alloy materials have weaknesses in corrosion resistance at room temperature and oxidation resistance at high temperatures, their use is often restricted. Stainless steel is no exception to this.

To improve high-temperature corrosion resistance, coating of At or needles by thermal spraying with Ni or Cr or by a pack method has conventionally been carried out.

Although the NiCr alloy thermal spraying method can improve high-temperature corrosion resistance to some extent, there are pores in the thermal-sprayed coating layer, so high-temperature oxidation corrosion progresses during long-term use, and it is also difficult to use in a wet corrosive environment. However, there is a drawback in that the adhesiveness at the interface between the material and the coating layer is weakened, resulting in peeling of the coating layer.

Coating with At or Cr using the polymerization method is performed by burying the material in a packing agent containing a hydrogenation activator such as NH4C4, NaCt, or NH4F and At or Cr powder, and heating and diffusing it in an inert gas to form AA. Another method is to create an alloy phase with a high Cr content, but it has the drawbacks of difficulty in coating multiple elements at the same time, the complexity and cost of the processing method, and poor shape and dimension maintenance of the treated material. .

Recently, a method has been devised in which N1-P alloy powder and flux are placed on the surface of a component as a low-melting brazing filler metal and heated in a vacuum or an inert atmosphere to melt and diffuse the N1-P alloy. used for processing.

By applying this method, we have found a method to thermally spray coat the N1-P alloy onto the surface of a component, then heat treat the component to melt and diffuse the thermally sprayed coating layer to obtain a dense coating with high adhesion strength. The produced thermal spray coating layer has the disadvantage that many cracks occur in the coating layer due to the poor toughness of the N1-P alloy coating layer, and corrosion easily occurs from the cracks during use.

(Objective of the Invention) An object of the present invention is to overcome the drawbacks of the above-mentioned conventional methods and to provide a processing method for obtaining a thermally sprayed coating with excellent corrosion resistance.

(Structure of the Invention) The present invention uses a thermal spray material containing N1-P alloy and Ni or Ni-Cr alloy in an amount of 20 to 80% by weight and 80 to 20% by weight, and coats an iron-based alloy material by thermal spraying. This is a corrosion-resistant thermal spray coating treatment method in which the coating material is then heat-treated at 600 to 1000°C.

The P composition in the N1-P alloy is 5 to 25% by weight, and the Ni
The Cr composition in the -Cr alloy is 5 to 60% by weight.

The present invention takes advantage of the properties of the N1-P alloy that has good corrosion resistance and low melting point at normal to high temperatures and forms a coating layer at a relatively low temperature, and at the same time prevents cracks in the N1-P alloy coating layer. In order to prevent corrosion, Ni or Ni, which is easy to alloy with N1-P alloy and has high corrosion resistance and toughness, is used.
We have proposed a method to prevent cracks in the coating layer and form a corrosion-resistant thermal sprayed coating with high adhesion to the base material by simultaneously spraying -Cr alloy with N1-P alloy and then heat treatment. It is something. That is, N1-P alloy and Ni
Alternatively, if a mixed or composite powder of Ni-Cr alloy is thermally sprayed and heat treated at an appropriate temperature, adhesion can be improved due to interdiffusion between the iron-based material and the N1-P alloy.
The coexistence of Cr alloy further increases the effect, and Ni or N
The i-Cr alloy plays the role of a binder and a cushioning material, and therefore the adhesion and denseness of the coating are significantly improved and cracking can be prevented.

The reason why the composition of P in the N1-P alloy is set to 5 to 25% by weight in the present invention is that if it is less than 25%, the melting point of the alloy is high and the coating adhesion due to diffusion in the heat treatment temperature range of the present invention is insufficient. In addition, when it exceeds 25q6, it is not only difficult to produce N1-P alloy powder, but also the N1-P alloy
Alternatively, even if coated and heat treated at the same time as a Ni-Cr alloy, the coating tends to crack due to poor toughness of the coating.

The reason for setting the Cr composition in the Ni-Cr alloy to 5 to 60% by weight is that if the Cr content is less than 5%, the effect of adding Cr to improve corrosion resistance is not recognized, and if the Cr content exceeds 60%, the N1-P alloy is When sprayed at the same time, the toughness of the coating layer is impaired and diffusion occurs with the N1-P alloy.

This is because reactions are less likely to occur.

The content of Ni or Ni-Cr alloy is 20 to 80% by weight.
The reason for this is that if it is less than 20%, the toughness of the coating layer after heat treatment will be poor and cracks will easily occur, and if it exceeds 80%, the diffusion adhesion of the N1-P alloy to the iron-based material will decrease due to heat treatment. This is because, at the same time, the density of the coating is significantly reduced.

The reason why the heat treatment temperature after thermal spraying is set at 600 to 1000°C is that at temperatures below 600°C, a coating with excellent corrosion resistance cannot be formed due to insufficient diffusion of the N1 alloy into the Fe-based alloy, low adhesion, and peelability. Moreover, if the temperature exceeds 1000°C, not only will oxidation of the material due to diffusion adhesion be promoted during heat treatment of the material, but also it will be difficult to maintain constant shape and dimensions such as deformation of the material.

The heat treatment can be carried out in the air, but it can also be carried out in a non-oxidizing atmosphere or in a vacuum, and corrosion resistance is significantly improved compared to heat treatment in the air.

As a thermal spray coating method, plasma spraying or explosive thermal spraying, which cause less oxidation, is preferable, but other generally known thermal spraying methods can be applied.

In the present invention, in addition to Cr, B+Sl+C is added to the N1-P alloy.
Not only is there no particular problem with the inclusion of , but in fact it exhibits an effect similar to that of self-fusing alloys and improves the wear resistance of the coating.

In addition, in addition to Ni + Ni-Cr alloy, the addition of At, At-8i alloy, At-Y alloy, etc., which have high temperature corrosion resistance and toughness, as additive materials does not pose any particular problem and is actually effective in improving high temperature corrosion resistance. Furthermore, Ni-Cr
Using an MO-containing alloy with excellent corrosion resistance, such as Hastelloy, as an alloy can be said to be an effective method for obtaining a corrosion-resistant spray coating as one aspect of using the Ni--Cr alloy of the present invention.

Next, the present invention will be explained by examples.

Mixed alloy thermal spray samples of the present invention shown in the Examples table 1.2, 3°4.
5 and 6 were adjusted to have a grain size of 10 to 63 μm, and these were made into a 5S41 steel plate (dimensions: 50 x 50 x 4 tr).
An) was subjected to plasma spraying using Ar-He gas to obtain a sprayed coating with a thickness of 0.2 mm. 600-100 each sample
0℃.

After the heat treatment for 1 hour, the cross-sectional structure of the coating was observed, the HC1 aqueous solution immersion test, and the high temperature oxidation resistance test were conducted.

Moreover, in order to compare with the above-mentioned present invention sample, comparative sample 6.7.
Samples No. 8 and No. 9 were also subjected to the same thermal spraying and heat treatment as above, and the same tests as above were conducted to compare with the samples of the present invention. The results are summarized in the table below.

However, the heat treatment time was 1 hour, and other test methods and criteria were as follows.

(1) Coating cross-sectional structure observation O9 No cracks observed △: 1 to fine cracks ×: 6 or more cracks/0. 5 wn2 is observed (2) HC1 aqueous solution immersion corrosion resistance test Aqueous solution: HC4l 0% Liquid temperature. 20℃ ○. Corrosion rate (5g/m2・day △. Same as above)
-5~100g/m2・dayO x 2 (same as above)
100 g/m" Day O (3) High temperature oxidation test Test conditions. Hold at 900°C for 20 hours ○: Oxidation weight increase (5 m'i/cm2 △゛ Same as above -5 to 50 m9/1yn2 Thing ×: Same as above
) 50m9/1yn2 According to the above test results, no cracks were observed in the coating cross-sectional structure in any of the corrosion-resistant thermal spray coating methods of the present invention, and the coating had sufficient corrosion resistance and high-temperature oxidation resistance against HC4 liquid corrosion and high-temperature oxidation. It is clear that

Further, photographs of the coated cross-sectional structures of Samples A 8 , A 1 0 and Flat 2 are shown in FIGS. 1, 2 and 3, respectively.

According to this, large cracks are observed in the structure of Fig. 1 (sample plate 8), and slight cracks are observed in the structure of Fig. 2 (sample A.lO), which indicates that the base material is iron. An oxide layer is widely seen at the interface with the base alloy, indicating poor adhesion.

However, in FIG. 3 (sample A2, one embodiment of the present invention), there is no clear boundary between the base material and the coating layer, that is, sufficient mutual diffusion occurs between the base material and the coating layer. In addition to an improvement in adhesion, no cracks or pores were found within the coating layer. Based on this, it is clear that the method of the present invention is superior.

[Brief explanation of the drawing]

Figures 1, 2, and 3 show sample plate size 8 and plate size 1, respectively.
0 (above comparative example) and sample plate 2 (one embodiment of the present invention) are shown. Patent Applicant Showa Denko K.K. Patent Attorney Sei Kikuchi Kidney', 1 Shi, (9,., (X2oQ) Calyx, 21 Vision (X200) Sen 3

Claims (1)

[Claims] A thermal spray material containing 20 to 80% by weight of a nickel-phosphorus alloy containing 5 to 25% by weight of phosphorus and 80 to 20% by weight of a nickel-phosphorus alloy containing nickel or 5 to 60% by weight of chromium. 1. A corrosion-resistant thermal spray coating treatment method, which comprises coating an iron-based alloy material by thermal spraying, and then heat-treating the coating material at 600 to 1000°C.