JPS6147905B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for coating titanium carbide on the surfaces of tools and machine parts such as cemented carbide, ceramic steel products, etc. Titanium carbide (TiC) has high hardness and wear resistance, and can improve performance by coating the surface of tools and machine parts made of steel, cemented carbide, cermet, etc. to a thickness of several micrometers or more. It is common knowledge that it is useful. However, all of them are processed at high temperatures of over 900℃. For this reason, in the case of steel, decarburization at the coating boundary due to movement of carbon in the base metal through the coating cannot be avoided, and although treatments such as carburization are taken before and after treatment, they are not always sufficient. Furthermore, in the case of carbide cermets, the binder metal such as cobalt or nickel moves and diffuses into the coating, reducing the performance of the base material and causing a decrease in the hardness of the coating. For this reason, the lower the coating temperature, the better.
Various physical vapor deposition methods such as ion brating have been proposed and put into practical use, but they lack mass productivity and uniform coverage. For these reasons, we have studied and arrived at the following objectives. (A) Prevention of η phase generation and high-temperature deterioration of the base material in cemented carbide and cermet, and (B) Prevention of coarsening of the quenched and tempered structure after treatment and decarburization at the boundary between the TiC film and the base material in steel. In order to prevent this, the annealing temperature for steel and 800°C or lower for carbide cermets is desirable, and we have arrived at this by researching a processing method to obtain a practical coating at this temperature or lower. That is, in normal high-temperature TiC coating, hydrocarbons such as methane (CH ₄ ) and propane (C ₃ H ₈ ) are used as carbon sources, but the reaction is TiCl ₄ + CH ₄ = TiC + 4HCl... (1) TiCl ₄ +1/3C ₃ H ₈ +1.33H ₂ =TiC+4HCl... (2) Therefore, a practical coating requires a treatment temperature of 900°C or higher. However, with the coating using CH ₃ Cl (methyl chloride) as the carbon source by this method, the temperature is higher than 650℃.
TiC precipitates. The reaction formula is TiCl ₄ (g) + CH ₃ Cl (g) + 1/2H ₂ = TiC (s) + 5HCl ... (3) △GT゜ = 570℃, and as a stoichiometric consideration, the free energy of the formation reaction is If you calculate and compare the changes (see Figure 1)
△GT゜=0 at around 840〓 (567℃), and there is a possibility that TiC will be generated above this temperature. In reality, TiC precipitation was clearly seen at around 650°C, but a productive and practical coating was obtained at temperatures above 700°C. Furthermore, at temperatures above 900°C, CH ₃ Cl rapidly decomposes near the gas inlet in the coating furnace, causing uneven coating depending on the position of the product in the furnace, so 700 to 900°C was the appropriate treatment temperature. We were able to lower the lower limit of the practical treatment temperature for CH ₄ and C ₃ H ₈ by more than 200°C. In addition, C ₂ H ₂ (acetylene) used as a reference generates a lot of soot in the furnace, sooting occurs on the product surface, and even though △GT゜=0 is similar to CH ₃ Cl, the reaction drive at high temperatures is The force (amount of change in △GT°) was small and inappropriate. The concentration of CH ₃ Cl used in this method was adjusted as shown below depending on the treatment temperature, but it was found to be effective. For example TiCl ₄ 1
650-700℃ for volume (gas) CH ₃ Cl 2-3 volumes 750-900℃ 〃 1-2〃 It is desirable to reduce the amount as the processing temperature increases. Cemented carbide, cermet 700-800℃ Iron Steel 750 Processing temperatures of ~850°C are optimal. In addition, H ₂ (hydrogen) or a mixture of H ₂ and argon (Ar) or helium (He) is suitable as the atmospheric gas, and the proportion of these mixed gases is preferably 70% or less (Ar or He). Effective for coating low carbon steel (C0.6 or less). However, these gases have high temperatures and a H ₂ atmosphere is usually economical. Example (i) Conditions

[Table] (ii) Treatment results For the Γ carbide throw-away chip (P30 type), the coating thickness was 6 to 8μ, the coating hardness was Hv2800 to 3400 (load 50gr), Co was diffused into the film, and the η phase was generated. None (Photo 1) For Γ steel and SUJ2SKH55, the coating thickness was 7 to 10μ and the coating hardness was Hv3000 to 3400. (iii) Test results (see Figure 2) Γ Carbide: Cutting conditions are shown in the figure. By coating with this method, the carbide TiC coating has a cutting speed 8 times that of the non-coating, and approximately 2.0 times that of the 1000℃ coating. An improvement in cutting performance was observed. ΓSUJ2: The grinding wheel adapter (wear-resistant part) that was subjected to standard heat treatment after coating showed a 5 times improvement in performance compared to the uncoated one. ΓSKH55; Piercing punch with under hard heat treatment (base material hardness HRC63±1)
゜) was able to improve performance by 3 to 5 times. In addition, TiCN using TiC according to this method as a basic coating,
It is possible and effective to construct multilayer coatings such as TiNαAl ₂ O ₃ .

[Brief explanation of the drawing]

FIG. 1 is a graph showing changes in temperature and free energy of the formation reaction, and FIG. 2 is a graph showing a comparison of cutting performance between a tool tip coated by the method of the present invention and a conventional product.

Claims (1)

[Claims] 1 Using hydrogen or a mixed gas of hydrogen and argon or helium as the atmospheric gas, methyl chloride (CH ₃ Cl) gas as the carbon source for titanium carbide, and titanium halide gas as the titanium source, at a temperature of approximately 700°C. A titanium carbide coating method characterized by coating titanium carbide by heating at a temperature of 900°C to 900°C.