JPS62127460A - Surface treatment - Google Patents

Abstract

PURPOSE:To stably form carbide layer superior in surface roughness on steel stock surface, by embedding steel stock into mixture of powder of metals and alloy of these in groups IVa-VIa of the periodic table, refractory powder and halogenide and heating, holding at a specified temp. in vacuum then cooling them. CONSTITUTION:10-60wt% total of one or 2 kinds among powders of metals such as Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W in groups IVa, Va, VIa of the periodic table, or alloy of these, 30-85wt% refractory powder such as oxide and nitride of Al, Si, Ca, Mg having 0.1-10mum particle diameter and 0.2-30wt% NH4Cl, NaCl and the other halogenides are mixed. Steel stock of >0.1% C finished to mirror surface is embedded into the mixture, these are heated and held at 700-1,200 deg.C in vacuum. Generated halogenide vapor of the metal is reacted with C in steel and high hardness metal carbide such as TiC, Cr3C2, WC is formed on steel stock surface in superior surface roughness state.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a surface treatment method for forming hard carbides on the surface of steel.

[Conventional technology]

Conventionally, there is a method of embedding steel in powder to form a diffusion layer of metal such as Cr on the surface of the steel (for example, Japan Institute of Metals, Volume 1, Surface Treatment, pages 54-35), and a method of forming a carbide layer ( For example, Japanese Patent Application Laid-Open No. 52-62140) is known. In this case, in order to prevent oxidation of the powder and the material to be treated, it is necessary to heat it in a hydrogen stream or to perform the heat treatment in the atmosphere with the container firmly sealed with a sealant or the like.

[Problem that the invention seeks to solve]

However, when heating in a conventional hydrogen stream, the equipment becomes expensive due to safety considerations, and there is a problem in that the formation of a carbide layer is not sufficient. Furthermore, even when the container is sealed and heated in the atmosphere, the remaining oxygen in the container oxidizes the powder and the material to be treated, resulting in a short service life for the expensive powder and insufficient formation of a carbide layer. was there.

In view of the above problems, the present invention aims to provide a surface treatment method that can prevent oxidation of powder and treated materials and stably obtain good surface roughness.

[Means for solving problems]

The present invention provides a total of one or more metals or alloy powders of group IVa + group Va and group VIa elements of the periodic table.
0 to 60 wt%, 30 to 85 wt% of refractory powder with a powder particle size of 0.1 to 10 μm, and 0.2 to 30 wt% of a halide salt.
Steel is immersed in a powder containing a mixture of wt%, heated and maintained in a vacuum, and cooled to coat the surface of the steel with groups IVa of the periodic table,
The above object is achieved by a surface treatment method characterized by forming a carbide layer of one or more types of Va group and VIa group elements.

[For production]

The reasons for the limitations of the present invention will be described below.

According to the present invention, since the object to be treated and the mixed powder are heated in a vacuum, they are not oxidized by oxygen in the air, and the service life of the powder is greatly improved, while the carbide layer is also stabilized. It can be formed by Especially at room temperature or 70℃
After sufficient vacuum degassing to a temperature below 0°C at which the evaporation of the halide salt is relatively small, reducing the exhaust volume by adjusting a valve, etc., or completely sealing and heating, the reaction vapor (e.g. VCLx, etc.) It is effective because it has the effect of suppressing the emission of.

Compared to the present invention, the formation of a carbide layer is not sufficient in the heating method in a hydrogen stream, and the life of the powder is short. This is due to the fact that VCl2 and other reaction vapors cannot be completely removed, and that the reaction vapors such as VCl2 are exhausted together with the hydrogen stream and do not work effectively. Similarly, the method of heating a sealed container in the atmosphere also fails to remove residual air and water vapor inside the container.

In contrast, in the present invention, vacuum degassing can sufficiently remove air and water vapor adsorbed between powder particles and on the powder surface, so the above phenomenon does not occur. Powders of metals or alloys of Group VIa elements react at elevated temperatures with vapors of halide salts that are mixed in at the same time to generate vapors of halogen compounds such as VCl2. This vapor is reduced on the surface of the steel and has the effect of forming carbides of group IVa, group Va, and group VIa elements together with carbon in the steel.

However, the total amount of one or more metals or alloy powders of group Fv'a, Va group + Wa group elements is 10 wt%.
If it is less than 60wt, the carbide layer will not be stably formed, and conversely
If it exceeds 96, the powder will sinter together or the powder and the object to be processed will sinter, significantly impairing workability and further deteriorating the surface shape. This causes disadvantages such as the inability to reuse the powder.

Sources of Group IVa, Group Va, and Group VIa elements include Ti +Zr +Hf +V+Nb +Ta pc
It may be a metal powder such as Mo or W, or it may be an alloy powder of these metals. Furthermore, the above metal and Fe,
Ni.

An alloy powder with Cor Mn or the like can also exhibit sufficient effects. Although the particle size of the powder is not particularly limited, a particle size of about -20 mesh is excellent in terms of the surface quality of the material to be treated and the sintering resistance of the powder.

The refractory powder is added in an amount of 50 to 85 wt% for the purpose of preventing sintering of the gold l1r4 or alloy powder of the above Group IVa, Group Va, and Group VIa elements and the object to be treated or the powder. The sintering prevention effect is small, and on the contrary, 85
%, the formation of the carbide layer becomes unstable. The refractory powder is not particularly limited as long as it is stable at high temperatures and has a property of being less likely to react with metals, such as ht+StrCa+Mg oxides and nitrides.

The particle size of the refractory powder greatly influences the surface roughness of the carbide layer formed. If the surface roughness is poor, the wear resistance will be poor, and it may not be applicable to the field of precision processed products that require severe surface properties.

If the refractory powder grains are sufficiently larger than the crystal grain size of the carbide layer, the refractory powder that is in contact with the object to be treated will be embedded in the carbide layer and adhere to it, resulting in worsening of the surface roughness. This is the cause of

Therefore, in the present invention, the particle size of the refractory powder is made equal to or smaller than the carbide crystal grain size formed in the carbide layer to prevent the refractory powder from being embedded in the carbide layer and from adhering. The carbide crystal grain size varies depending on the formation temperature, but under the general conditions of this method, it is usually 0.1 μm.
˜10 μm, so this can be applied as the refractory powder particle size range.

On the other hand, if the particle size of the refractory powder is too fine, it will be difficult to eliminate an adverse effect on the vacuum system when vacuum degassing the powder, which is also undesirable from the viewpoint of hygiene in trench work. Furthermore, since there is a risk that a powder that is too fine may have another negative effect on the carbide layer, the lower limit of the powder particle size is set to 0.1 μm.

As mentioned above, the halogenated salts are Group IVa and Group Va.

It has the effect of generating halogen compound vapor of group VIa elements and promoting the reaction of forming a carbide layer on the steel surface.

If the amount of the halosaponide salt added is less than 2 wt%, the above effects will be small, whereas if it exceeds 30 wt%, fusion and solidification will occur, which will significantly impede workability and reusability of the powder. Halogenated salts include NH4C1, Na CL +KC
1+ NH4F + NaF * 10 such as NH4I
Active evaporation occurs at temperatures below 00°C, and group R'a,
Group Va.

It is not particularly limited as long as it has the property of forming a vapor of a halogen compound of a Group VIa element.

Steel in the present invention includes steel materials such as conventional steel and #special purpose steel containing 0.1% or more carbon, as well as cast iron, forged steel, and sintered materials, and includes 0.1% or more carbon. If it contains carbon, it has the effect of reducing the halogen compound vapor and forming a carbide layer on its surface.

The temperature at which the object to be processed is immersed in the mixed powder and heated is 70°C.
Select between 0°C and 1200°C. The treatment time can be arbitrarily changed depending on the treatment temperature and the desired thickness of the carbide layer, and it is necessary to determine the appropriate time in advance through preliminary experiments.

After heat treatment at a heating temperature and time within the above range, it is preferable to cool it in vacuum to a predetermined temperature below the treatment temperature (usually 500°C or below) at which the carbide layer formed on the steel surface is not oxidized. In particular, when it is desired to increase the cooling rate, the present invention can be carried out by introducing an inert gas such as N2 or Ar for cooling. [Example] Next, an example of the present invention will be described.

Example 1 60wt of 20 mesh Fe-V powder (86%V)
% and industrial NHsC4 powder 2 wt%, the balance is At20
A mixed powder to be used as S powder was placed in a stainless steel bot with a diameter of about 150 mm, and a round bar material (30 mm in diameter) of 5KD61 with a bezel finish was thoroughly washed and buried in the mixed powder.

The ALzOs powder particle size is less than 350 μm (average diameter approximately 200 μm)
3s), 70 μm or less (average diameter approximately 30 μm), and 10 μm or less (average diameter approximately 3 μm) were used. The pot was placed in a vacuum heating furnace, degassed under vacuum, and then heated to 930°C. When the heating was completed, the pulp connected to the vacuum system was closed, and the pot was maintained for 8 hours before being cooled. Table 1 shows the surface roughness of the carbide layer for each At*Os particle size. Although the pulp was similarly treated in a closed atmosphere by adjusting the pulp, no carbide layer was formed.

Table 1 From Table 1, when the Al2O5 powder particle size is IOam (% average particle size about 3 μm) (test A I ), the surface roughness of the 70 layer is 350 μm or less (average particle size 2
00 μm) and 70 μm or less (average particle size 0 μm).

FIG. 1 shows the results of an abrasion test using test pieces related to Tests A I and A3. The test was conducted using the Okoshi type abrasion test, with a friction distance of 40 C1t, #P, a load of 6.8 mm, and a mating material SCM of 21. In addition, the results of the abrasion test for JISSKDll and 5KD61 without surface treatment are also shown. The figure shows that the present invention significantly improves wear resistance.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to significantly improve the surface roughness of the carbide layer obtained by the powder method, which has been insufficient in the past, and also to prevent oxidation of the carbide layer and impart good membrane rupture properties. The practicality of the surface treatment method is greatly improved.

[Brief explanation of drawings]

FIG. 1 shows the present invention, a comparative example, and JIS 5KD11 without surface treatment according to the Okoshi type abrasion test. 61 is a diagram showing the results of the wear test of No. 61. Figure 1 Friction speed 1m/11

Claims (1)

[Claims] 1. A total of 10 to 60w of one or more metals or alloy powders of group IVa, Va, and VIa elements of the periodic table.
refractory powder with t% and powder particle size of 0.1 to 10 μm.
Steel is immersed in powder made of a mixture of 85 wt% and 0.2 to 30 wt% of halide salts, heated and held in vacuum, and cooled to coat the surface of the steel with Group IVa, Va, and VIa elements. A surface treatment method comprising forming one or more carbide layers.