JPS602384B2 - Method for manufacturing a steel member having a double coating layer of a Nb or V carbide layer and a Cr carbide layer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a steel member having a double coating layer of a Nb or V carbide layer and a Cr carbide layer.

Carbides of Group Va elements, namely V, Nb, and Ta, in steel,
Coating with Ti carbide or Cr carbide improves the wear resistance, corrosion resistance, etc. of steel depending on the characteristics of the carbide.
Because of their improved oxidation resistance, these carbide coatings have already been effectively put to practical use industrially. However, when we examine the properties of these carbides in detail, we find that group Va element carbides are extremely wear-resistant, and when coated on parts that require particularly high wear resistance, they have a high resistance to wear. Durability improves dramatically, but because it has poor oxidation resistance, when used continuously at temperatures above 400-500°C, the carbide layer becomes oxide and easily falls off or wears out. Therefore, it is not possible to exhibit the excellent wear resistance.

On the other hand, when Cr carbide is coated on the surface of a hot forging die used at high temperatures, for example, it has extremely high oxidation resistance at high temperatures, but is considerably inferior in terms of wear resistance. In order to provide a new and useful steel member by skillfully combining the properties of the various carbides described above, the present inventors have conducted various studies and found that Nb or V, which has excellent wear resistance, is added to the surface of the steel matrix. By applying an intermediate coating layer made of carbide and an outermost coating layer made of Cr carbide, which has excellent oxidation resistance, it is first exposed to a high-temperature oxidizing atmosphere, and then has durability such as wear resistance during use. It was confirmed that a steel member suitable for use as a material for molds requiring properties such as hot forging molds, extrusion molds, die-casting molds, and glass molding molds was confirmed.

An object of the present invention is to provide a method for manufacturing a steel member having such a double coating layer. That is, the present invention provides an intermediate coating consisting of a carbide layer of Nb or V on the surface of the steel matrix by holding the steel material immersed in a molten acid bath containing Nb or V, using carbon present in the steel base as a carbon source. The first step is to form a layer, and then the steel material is immersed and held in a molten acid bath containing Cr to further form an outermost coating layer made of a Cr carbide layer on the intermediate coating layer. A steel having a double coating layer of a carbide layer of Nb or V, characterized by a second step, in which the steel material and the intermediate coating layer, and the intermediate coating layer and the outermost coating layer are firmly bonded. This is Bumura's manufacturing method.

Since the mold made of the steel member manufactured according to the present invention has a coating layer made of Cr carbide on the outermost surface, there is no risk of oxidation during preheating, and therefore the wear resistance of the intermediate layer is improved. The excellent Nb or V carbide coating layer is completely protected from high temperature oxidizing atmospheres, so that even if the Cr carbide layer is worn out in actual use, the Nb
It is protected by the Nb or V carbide layer and is in contact with the workpiece for a long time during use, so there is almost no risk of oxidation, and the Nb or V carbide layer sufficiently exhibits its wear resistance and extends the life of the mold. can be extended.

In addition, when a double coating layer is applied to a deep drawing die according to the present invention, oxides that affect the surface texture of the deep drawn product, such as in the case of a die with a Nb or V carbide coating layer, may be used. There are advantages that layer formation can be avoided and durability can be increased.

In particular, the steel member manufactured according to the present invention has the following advantages.

{1' There is a metallic bond between the coating layers and the steel material, and the bond is very strong.

Furthermore, the formed carbide layer is also a dense layer without pinholes or cracks. '2' No oxide is present at the interface between the intermediate coating layer and the outermost coating layer.

That is, after the first step, the Nb formed on the steel surface
Alternatively, the carbide layer of V cannot avoid oxidation when taken out from the molten metal into an oxidizing atmosphere such as the atmosphere. However, if the steel material is immersed in a molten shelf acid as the second step, the oxides formed on the surface of the steel material due to the action of the shelf sand will fall off and be removed from the surface of the steel material. Since a Cr carbide layer is formed on the Nb or V carbide layer cleaned in this way, the Cr carbide layer has good adhesion and strong bonding with the Nb or V carbide layer on all surfaces. are doing. The steel member manufactured according to the present invention also has the following advantages.

In other words, in order to prevent scratches, the surface of decorative items is often coated with a highly hard carbide layer, but since such a carbide layer has poor oxidation resistance, oxides are formed on the surface. It may lose its luster and reduce its value as a decorative item. In such a case, by forming a thin Cr carbide layer on the long surface, it is possible to provide a metallic luster and to provide an ornament that is resistant to deep scratches. A method for manufacturing a steel part having a double coating layer according to the present invention will be described in detail.

In the first step, a base steel material such as ordinary steel, low alloy steel, high alloy steel, iron alloy, etc. is immersed and held in a molten side acid bath containing Nb or V.

At this time, Nb or V in the molten metal adheres to the surface of the steel base, and then reacts with carbon existing near the surface of the steel base to form a carbide layer of Nb or V on the steel surface, and then subsequently on the surface of the steel base. Carbon is present on the steel matrix surface and in the carbide layer. diffuses into the bath and reacts with Nb or V in the bath on the carbide surface to form a Nb or V carbide layer on the steel surface. Next, as a second step, it is kept concentrated in a molten column acid bath containing Cr.
At this time, the Cr element in the molten metal adheres to the surface of the Nb or V carbide layer described above, and then reacts with the carbon that has diffused and permeated through the steel base and the carbide layer to form a Cr carbide layer on the surface of the carbide layer. After that, a Cr carbide layer is formed on the surface of the Nb or V carbide layer by reacting with carbon that has diffused and permeated from the steel matrix. The first step and the second step may be carried out consecutively, that is, the steel material may be taken out from the first step and immediately transferred to the second step, or the steel material may be taken out from the first step, cooled, and then heated with hot water. After removing the adhering substances from the first step by washing rice bran or the like, it may be transferred to the bath for the second step. Thus, N on the surface of the base steel material.
A double coating layer can be formed having an intermediate layer made of a carbide of Cr or V and an outermost layer made of a Cr carbide.

The carbide layer of the steel member of the present invention produced in this way is formed by diffusion of carbon using the carbide of the steel base as a carbon source, so the intermediate coating layer formed on the surface of the steel base is the same as the surface of the steel base, Further, the intermediate coating layer is metallically bonded to the long surface coating layer, and is very strongly bonded to each other.

Furthermore, the formed carbide layer is also a dense layer without pinholes or cracks. Therefore, the Cr carbide layer of the outermost surface coating layer can completely shield the Nb or V carbide layer of the intermediate coating layer from the oxidizing atmosphere. Another advantage is that the Cr carbide layer on the surface and the Nb or V carbide layer in the middle are difficult to peel off even when thermal shock or mechanical shock is applied when used as a mold. The present invention will be explained based on examples.

Example 1 The present invention was applied to a nesting pin (manufactured by SKD61, diameter 1 port, length 160 willow) attached to an aluminum alloy die-casting mold.

Coating the nesting pin with a Nb carbide layer reduces the adhesion of aluminum alloy base metal and significantly improves the life of the pin, but heating the die casting mold to 650-700 °C before use will cause the nesting to deteriorate. Since the Nb carbide layer on the surface of the pin was worn out by oxidation, the lifespan of the pin made of the same material without the Nb carbide layer was not significantly different from 6,000 to 8,000 shots.

Therefore, according to the present invention, an intermediate layer made of Nb carbide and a Cr
A nesting pin with a double coating layer was fabricated, with the outermost layer consisting of carbide.

The coating method is as follows.

After immersing the core pin in a molten shelf sand bath at 980°C to which 2% by weight of Fe-Nq powder was added for 6 hours, it was taken out and immediately exposed to Cd.
1 in 980 qo of molten shelf sand containing 15% by weight of
It was soaked for an hour, then taken out, cooled in oil, and returned to temperature at 600°C.

When this pin was attached to a die-casting mold and used, it showed a life of 12,000 shots.

Example 2 A steel material of SK4 was immersed for 1 hour in a 950° C. molten shelf sand bath to which 2% by weight of Fe-V powder was added.

After taking it out, it was immersed for 1 hour in a molten shelf sand bath at 950° C. to which 15% by weight of Cr powder was added, and then taken out. FIG. 1 shows a cross-sectional micrograph (400 magnification) of the coating layer formed on the surface of the steel material. It was found that a double coating layer was formed on the surface of the steel material. And X-ray microanalyzer analysis of the coating layer (
The results are shown in FIG. 2), and from the results of X-ray diffraction, it was confirmed that the surface layer of the coating layer was a Cr carbide layer, and the intermediate coating layer was a V carbide layer.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional micrograph of the coating layer on the surface of the steel material obtained in Example 2, and FIG. 2 is a diagram showing the results of X-ray microanalyzer analysis of the same coating layer. Figure 1 Figure 2

Claims (1)

[Claims] 1 A first step in which a steel material is immersed and held in a molten boric acid bath containing Nb or V to form an intermediate coating layer consisting of a carbide layer of Nb or V on the surface of the steel material matrix using carbon present in the steel material matrix as a carbon source. step, and then a second step of forming an outermost coating layer made of a Cr carbide layer on the intermediate coating layer by immersing and holding the steel material in a molten boric acid bath containing Cr. A method for manufacturing a steel member having a double coating layer of Nb or V carbide layers, wherein the steel material and the intermediate coating layer, and the intermediate coating layer and the outermost coating layer are firmly bonded.