JPS61253357A - Method for restoring hardness of thermally sprayed film - Google Patents

Abstract

PURPOSE:To restore and increase again the hardness of a thermally sprayed metallic layer which is decreased by the irradiation of a laser by subjecting the surface of a steel, etc. to a heat treatment under specific conditions after the irradiation of the laser in the stage of spraying thermally and forming the corrosion- and wear- resistant metallic film on said surface then irradiating the laser thereto to improve the adhesiveness of the thermally sprayed metallic layer. CONSTITUTION:The film is formed on the iron or steel material by spraying thermally a metal such as Cu, Ni, Co, Cr, Ti or Mo or the alloy thereof in order to improve the corrosion and wear resistance of said material. The laser is irradiated to the thermally sprayed film by which the thermally sprayed film is once melted and is secured to the iron or steel base to improve the adhesiveness of the thermally sprayed film and the iron or steel base material. The hardness of the sprayed film is decreased by the irradiation of the laser and therefore the iron or steel base is heated to >=350 deg.C to weld the film to the iron or steel base in the stage of irradiating the laser and thereafter the iron or steel material is heated to 200-700 deg.C and is air-cooled by which the intermetallic compd. and carbide are precipitated in the film and the hardness of the film is again improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for treating a steel product having a thermally sprayed coating on the surface of a substrate.

[Prior art]

Recently, in order to impart corrosion resistance or wear resistance to steel products, corrosion-resistant or wear-resistant Cu+Ni, instead of plating, has been used.
A thermal spray coating of metals such as Co, Cr, Ti, Mo, or alloys thereof is formed.

When an alloy is thermally sprayed, the adhesion between the thermally sprayed coating and the substrate is poor, and the thermally sprayed coating itself has pores, making it easy for defects such as cracks to occur in the coating, and deformation of the metal substrate due to thermal strain. One of the methods to eliminate these drawbacks is to treat them with laser irradiation.

Furthermore, the cooling rate of the coating melted by laser irradiation is extremely fast, about 1,000°C/sec, which causes problems such as hardening due to martensitic transformation after heating the material and deterioration of the surface condition. In order to reduce thermal effects, preheating is usually performed at a temperature of 350° C. or higher before laser irradiation.

[Problem that the invention seeks to solve]

However, due to this preheating, the interdiffusion phenomenon between the thermal spray coating layer and the base material becomes remarkable, and the Pa in the base material increases.

Atoms such as C penetrate into the coating layer and cause a decrease in the hardness of the coating. In addition, when irradiating a substance with a high melting point, it is recognized that the irradiation of a material with a high melting point is irradiated.

This decrease in hardness not only causes the base material itself to lose its hardness and other properties, but also deteriorates the properties of the sprayed coating itself, reducing the coating's inherent wear resistance. .

An object of the present invention is to recover the hardness of a thermally sprayed coating after laser irradiation.

[Means for solving problems]

The above object of the present invention can be achieved by heating the coating after laser fusing to an appropriate temperature.

The structure of the coating melted by laser irradiation after solidification is in an unstable crystalline state in which alloying elements are dissolved in supersaturated solid solution. Therefore, by heating the laser-fused coating, the intermetallic compound is removed.

This method increases the hardness of the coating by precipitating carbides into the coating structure.

Although the heating temperature after laser irradiation strictly depends on the material or base material of the sprayed coating, it is possible to sufficiently recover the hardness of the sprayed coating by heating to a temperature range of 400 to 700°C.

In addition, the heating time for this purpose is sufficient as long as the sprayed coating is heated uniformly; if it is too long, the intermetallic compounds and carbides precipitated at the grain boundaries will dissolve into the sprayed material and cause a decrease in hardness again. .

Furthermore, the heating also restores the toughness of the heat-affected zone of the base body caused by laser irradiation.

〔Example〕

After cleaning the surface of a steel plate with dimensions of 1000 m in length, 500 fi in width, and Iotm in thickness by shot blasting, it was coated with a self-fluxing alloy having the composition shown in Table 1 to a thickness of 500 μm by gas flame spraying. .

This thermally sprayed steel plate was heated to 400°C, and while maintaining this temperature, a CO2 laser with a power of 1 in 5 was heated to 0.5°C in the atmosphere.
Irradiation was performed at a speed of 1 m/win. After irradiation, 200°40
The temperature was maintained at 0, 600 and 800°C for 30 minutes and 60 minutes, respectively. FIG. 1 shows the cross-sectional hardness of the sprayed coating after heating, and FIG. 2 shows the change in the heat-affected zone of the substrate due to the heating. As shown in Figure 1, the hardness of the cross section of the coating is 30 minutes and 60 minutes.
It can be seen that in both cases of holding for 30 minutes, the hardness recovered at 200°C, reached a peak at 600°C, and decreased again at 800°C. Moreover, as shown in FIG. 2, it can be seen that the hardness of the heat-affected zone of the base body decreased, and the toughness recovered.

〔Effect of the invention〕

By the thermal spray coating treatment method of the present invention, it is possible to restore the properties of the substrate and thermal spray coating that have been degraded by laser irradiation,
Laser irradiation of the sprayed coating can fully bring out the effects of improving the adhesion between the substrate and the coating and the properties of the sprayed coating itself.

[Brief explanation of drawings]

The attached figure shows the state of recovery of the properties of the thermally sprayed coating and the heat-affected zone of the substrate by heating after laser irradiation. FIG. 1 shows the state of recovery of the hardness of the sprayed coating, and FIG. 2 shows the state of recovery of the properties of the heat-affected zone of the substrate.

Claims (1)

[Claims] 1. Form a thermal spray coating on the surface of the steel substrate and heat the same substrate to 350°C.
While maintaining the temperature above, laser irradiation is performed on the coating material to heat the coating material to a temperature above the melting point, and the steel substrate and the coating are fused at the interface thereof, and then
A method for recovering the hardness of a thermally sprayed coating, characterized by heating it to a temperature of 700°C and cooling it in air.