JP2600359B2 - Manufacturing method of surface coated tungsten carbide based cemented carbide cutting tool - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a tungsten carbide (hereinafter referred to as WC) having a hard coating layer.
The adhesion strength to the surface of the base cemented carbide substrate is remarkably high, and a hard surface layer mainly composed of β-solid solution can be stably formed on the surface of the substrate, and excellent wear resistance during cutting can be obtained over a long period of time. The present invention relates to a method for producing a surface-coated WC-based cemented carbide cutting tool that can be effectively used.

[Conventional technology]

Conventionally, in general, a raw material powder is formed of one or more of iron group metals as a binder phase-forming component: 5 to 25%, and a group 4a, 5a, and 6a metal of the periodic table as a disperse phase-forming component. One or more of carbides and nitrides of the above, and two or more of these solid solutions: 5 to 60%, WC as a disperse phase-forming component: the remainder, a composition comprising Indicates weight%), wet- or dry-mixed under normal conditions, press-molded into green compacts, and then 1380-1450 ° C in vacuum.
Sintered at a predetermined temperature within the range of WC base cemented carbide substrate,
Then, on the surface of the substrate, carbides, nitrides, oxides, and borides of the metals of Groups 4a, 5a, or 6a of the periodic table, and the two kinds thereof, using ordinary chemical vapor deposition and physical vapor deposition. The above solid solution and aluminum oxide (hereinafter Al)
₂ O ₃ ) and zirconium oxide (hereinafter referred to as ZrO ₂ ) to form a hard coating layer comprising a single layer or two or more layers with an average layer thickness of 1 to 20 μm. A method for producing a coated WC-based cemented carbide cutting tool is known.

Further, in the production of the above-mentioned surface-coated WC-based cemented carbide cutting tool, a hard surface mainly composed of a β-solid solution composed of the above-mentioned dispersed phase forming component is provided on the surface portion for the purpose of improving wear resistance. WC formed with an average layer thickness of 2 to 10 μm
It is also known to use a base cemented carbide substrate. Further, as a method for forming a hard surface layer on the surface of the substrate, (a) for example, as described in JP-A-55-104475, A hard alloy substrate is heated and maintained at a temperature equal to or higher than the liquid phase appearance temperature of the substrate in a mixed gas atmosphere of N ₂ gas and CO gas, for example, N ₂ partial pressure: 150 torr, CO partial pressure: 50 torr 200
a method of performing heat treatment for 2 hours at a temperature of 1400 ° C. in a reduced pressure atmosphere of torr. (b) Similarly, heating to 1400 ° C. in a vacuum as described in Examples of JP-A-63-103069 in the WC-based cemented carbide substrate under the conditions of retention sintering, cooling from sintering temperature, N ₂ partial pressure: in an N ₂ gas atmosphere at 5 torr, a method of gradually cooling at a cooling rate of 0.5 ° C. / min , And other methods have been proposed.

[Problems to be solved by the invention]

However, in the above method (a), since the N ₂ partial pressure in the atmosphere is high and the heating temperature is higher than the liquid phase appearance temperature,
The surface of the substrate becomes rough, and in the above method (b), the cooling rate from the sintering temperature is extremely low at 0.5 ° C./min. Similarly, surface roughness tends to occur easily, so the N ₂ partial pressure in the atmosphere is set to 5 torr, but if the N ₂ partial pressure in the atmosphere is low, the formation of a hard surface layer is remarkable. The hard coating layer formed on a substrate having a rough surface has a low adhesion strength, and is easily peeled off during cutting. At present, the effect of improving the wear resistance by forming the coating layer cannot be sufficiently exerted.

[Means for solving the problem]

In view of the above, the present inventors have developed a surface-coated WC-based cemented carbide cutting tool in which the hard coating layer has high adhesion strength to the substrate surface and exhibits excellent wear resistance during cutting. As a result of research focusing on a WC-based cemented carbide substrate having a hard surface layer, (1) when forming a hard surface layer on the surface of a WC-based cemented carbide, The composition of the green compact before sintering of the alloy substrate is as follows: Co powder: 3 to 15% as a binder phase-forming component; Ti, Ta, Nb, and W carbide, Ti, Ta as a hard dispersed phase-forming component , And Nb nitrides, and two or more of these solid solutions (hereinafter collectively referred to as (Ti, Ta, Nb, W) C
One or more of the following): 5-60
%, Also as a hard dispersed phase forming component, the composition is composed of the above-mentioned dispersed phase forming component, when the composition is specified to consist of: WC powder: remaining, and the atmosphere pressure is limited to a relatively high pressure of 300 to 760 torr. A hard surface layer mainly composed of β-solid solution,
It can be formed stably without variation.

(2) In the high-pressure atmosphere described in the above item (1), if the surface of the substrate, that is, the surface of the hard surface layer is thick and easily roughened, and the treatment temperature is higher than the liquid phase appearance temperature of the substrate, Even if the treatment time is shortened, the component forming the β-solid solution, particularly the metal component, rapidly diffuses from the inside of the substrate through the liquid phase to the surface portion, so that the growth of the hard surface layer takes place in the early stage of the formation of the hard surface layer. In this case, the hard surface portion is similarly roughened because it progresses at almost the same high speed until the later stage when the rough surface tends to occur, but the binder phase on the substrate surface portion is solidified from the liquid phase together with the growth of the hard surface layer. When the phase is changed and the processing temperature is decreased with growth, the growth rate of the hard surface layer at the later stage of the formation of the hard surface layer is reduced because the growth rate of the hard surface layer constitutes the β-solid solution, particularly the diffusion rate of the metal component is reduced. Late, table The surface roughness is suppressed,
Such a hard coating layer formed on a substrate having a smooth surface without surface roughness has a strong adhesive strength.

(3) In order to change the binding phase from the liquid phase to the solid phase earlier than the inside from the inside, rapid cooling may be performed. In addition, the rapid cooling can control the thickness of the hard surface layer and can form a relatively thin layer having an average thickness of 0.02 to 2 μm.

The findings described in the above items (1) to (3) were obtained.

The present invention has been made based on the above findings, and sinters a green compact formed from a mixed powder under a normal condition to form a WC-based cemented carbide substrate, and applies the same condition to the surface of the substrate. When manufacturing a cutting tool made of a surface-coated WC-based cemented carbide by forming a surface coating layer with, the composition of the green compact is 3 to 15% Co powder, (Ti, Ta, Nb, W) One or more of C and N powders: 5 to 60%, WC powder: Remaining, with the following composition: WC after sintering at the sintering temperature or after sintering The base cemented carbide substrate has a predetermined pressure in the range of 300 to 760 torr, carburizing,
In a nitriding or oxidizing atmosphere, or a mixed atmosphere of two or more of them, a temperature ranging from a predetermined temperature in the range of 1500 to 1270 ° C. to a predetermined temperature of
Quenching heat treatment at a predetermined cooling rate in the range of ~ 50 ° C / min to form a hard surface layer mainly composed of β-solid solution and having a smooth surface on the surface of the WC-based cemented carbide substrate. Thus, the present invention is characterized by a method of manufacturing a surface-coated WC-based cemented carbide cutting tool having a high adhesion strength of a hard coating layer.

Next, the reason why the manufacturing conditions are limited as described above in the method of the present invention will be described.

A. Blending composition (a) Co powder Co powder has a function of forming a binder phase of the substrate and imparting toughness to it, but if the blending amount is less than 3%, the predetermined toughness cannot be secured. On the other hand, if the compounding amount exceeds 15%, plastic deformation or the like is likely to occur, causing a decrease in wear resistance. Therefore, the compounding amount is set to 3 to 15%.

(B) (Ti, Ta, Nb, W) C / N powders. These powders not only increase the hardness of the substrate, improve the abrasion resistance, but also function to smoothly form the hard surface layer. However, if the compounding amount is less than 5%, the desired effect cannot be obtained in the above-mentioned action, while if the compounding amount exceeds 60%, the toughness rapidly decreases. It was set at 60%.

B. Heat treatment conditions (a) Atmospheric pressure Limiting the atmospheric pressure is indispensable for the stable formation of the hard surface layer. Therefore, if the pressure is less than 300 torr, the formation of the hard surface layer becomes unstable, while Is 760t
If it exceeds orr, it will be in a pressurized state with respect to the atmosphere.
The surface pressure of the hard surface layer is determined to be 300 to 760 torr because the surface is likely to be roughened. Note that an atmospheric pressure of 500 to 760 torr is desirable.

(B) Rapid quenching start temperature When this temperature is higher than 1500 ° C., the surface of the hard surface layer is liable to be roughened. On the other hand, when this temperature is lower than 1270 ° C., it becomes difficult to form the hard surface layer. The quenching start temperature was set at 1500 to 1270 ° C. In addition, desirably, 1380 to 1270 ° C. around the temperature region where the solid phase and the liquid phase coexist
Is good.

(C) End of quenching The formation of the hard surface layer proceeds up to the maximum temperature of 1250 ° C, and when the temperature becomes 1250 ° C or lower, the binding phase becomes a solid phase and the formation stops. Therefore, quenching to 1250 ° C is sufficient. is there. Therefore, it is a matter of course that the sintering step may be shortened by rapidly cooling to a predetermined temperature of 1250 ° C. or less, for example, about 100 ° C.

(D) Cooling rate If the cooling rate is lower than 10 ° C / min, the binder phase is left in the liquid state for a long time, so that the surface roughness of the hard surface layer becomes remarkable, while 50 ° C / min. If the cooling rate exceeds, the formation of the hard surface layer will be suppressed, so this is 10 ~ 50 ℃ / min, preferably 20 ~ 40 ℃
/ min.

〔Example〕

Next, the method of the present invention will be specifically described with reference to examples.

As raw material powders, various (Ti, Ta, Nb, W) CN powders and Co powders each having an average particle size of 1 μm,
Prepare 3.5μm WC powder, blend each of these raw material powders into the composition shown in Table 1 and ball mill.
72 h wet mixed, dried at a pressure of 10 kg / mm ^2, IS
Press-molded into green compacts A to F conforming to O-standard SNMG120408, and then these green compacts A to F
In a vacuum of ~ 0.09 torr, the sintering temperature shown in Table 2
Sintered under the condition of holding for 1.5 hours, at the time of cooling from this sintering temperature, or after cooling to room temperature in the same vacuum as the sintering atmosphere, and then reheating to the quenching start temperature, each is shown in Table 2. A WC-based cemented carbide substrate having a hard surface layer on the surface is formed by heat treatment under the conditions, and the surface portion in a longitudinal section of the substrate is observed, and the average of the hard surface layer mainly composed of β-solid solution is observed. The thickness of the layer was measured, and the surface roughness of the substrate was also measured (these measurement results are shown in Table 3). Subsequently, the results are shown in Table 2 under the same conditions using a conventional chemical vapor deposition apparatus. By performing a method 1 to 12 of the present invention by forming a hard coating layer having a composition and an average layer thickness on the surface of the substrate, a cutting tool made of a surface-coated WC-based cemented carbide (hereinafter referred to as the coated cemented carbide of the present invention) (Chip 1-12)
Was manufactured respectively.

For the purpose of comparison, the green compact A was held at 1420 ° C. for 1 hour in a vacuum of 0.08 torr, and then sintered under furnace cooling conditions to form a WC-based cemented carbide substrate. while polishing the upper and lower surfaces, N ₂ partial pressure: 150 torr, CO partial pressure consisting 50torr pressure: reduced-pressure atmosphere of 200 torr, temperature: 1400 ° C. and subjected to a heat treatment under conditions of 2 hours holding in its surface portion A conventional method 1 was performed by forming a hard surface layer on the substrate, performing observation and measurement under the same conditions in this state, and then forming a hard coating layer of TiC: 6 μm on the substrate surface under the same conditions. A surface coating layer WC-based cemented carbide cutting tool (hereinafter referred to as conventional coated cemented carbide chip 1) was manufactured.

Furthermore, for purposes of comparison, a green compact A, in a vacuum of 0.09Torr, it held 1 hour at a sintering temperature of 1420 ° C., during cooling from the sintering temperature, by introducing N ₂ gas, N ₂ Partial pressure: 5 torr atmosphere and in this atmosphere Slowly cool to 1200 ° C at a cooling rate of 0.5 ° C / min, and then perform furnace-cooling heat treatment to room temperature in a vacuum to form a WC-based cemented carbide substrate having a hard surface layer on the surface. Was observed and measured under the same conditions, and under the same conditions, a conventional method 2 was performed by forming a hard coating layer made of TiC: 6 μm on the substrate surface, and cutting the surface coated WC-based cemented carbide. A tool (hereinafter, conventionally referred to as coated cemented carbide chip 2) was manufactured.

Then, for each of the coated cemented carbide tips obtained as described above, the hard coating layer was scratched off with a diamond indenter using a scratch tester, the adhesion strength at this time was measured, and the work material: SNCM432 (hardness) : round bar of H _B 240), cutting speed: 180 m / min, cut: 3 mm, feed Ri: 0.3 mm / rev, cutting time:. performs dry continuous cutting test of steel in 10min, conditions, the cutting edge The flank wear width was measured. Table 3 shows the results of these measurements.

〔The invention's effect〕

From the results shown in Tables 2 and 3, the coated cemented carbide chips 1 to 12 of the present invention manufactured by the methods 1 to 12 of the present invention were formed on the surface of the WC-based cemented carbide substrate constituting the chips. The surface of the hard surface layer is smoother than that of the conventional coated cemented carbide chips 1 and 2 manufactured by the conventional methods 1 and 2, and this result indicates that the adhesion strength of the hard coating layer formed thereon is low. The present coated cemented carbide tips 1 to 12 having a high adhesion strength of the hard coating layer have a relatively low adhesion strength of the hard coating layer even in the cutting test, and the hard coating is relatively early. It is evident that the layer shows excellence in wear resistance as compared with the conventional coated cemented carbide tips 1 and 2 in which peeling occurs and abnormal wear is inevitable.

As described above, according to the method of the present invention, a hard surface layer having a stable, smooth surface can be formed on the surface of the WC-based cemented carbide substrate without any variation. A surface-coated WC-based cemented carbide cutting tool with extremely high adhesion strength to the surface of the WC-based cemented carbide substrate can be manufactured.Therefore, if this is used for cutting, the hard coating layer will not peel off, etc. In addition, it exhibits excellent wear resistance due to the coexistence of the hard surface layer, and exhibits industrially useful effects such as exhibiting excellent cutting performance over an extremely long period.

Claims (2)

(57) [Claims] 1. A green compact formed from a mixed powder is sintered under ordinary conditions to form a tungsten carbide-based cemented carbide substrate, and a hard coating layer is formed on the surface of the substrate under the same ordinary conditions. When manufacturing a cutting tool made of a tungsten carbide-based cemented carbide, the composition of the green compact is, in weight%, as a binder phase forming component, Co powder: 3 to 15%, and a hard dispersed phase forming component, Ti, Containing carbides of Ta, Nb, and W, nitrides of Ti, Ta, and Nb, and one or more powders of two or more of these solid solutions: 5 to 60%; Similarly, with a composition comprising tungsten carbide powder as a hard dispersed phase forming component, and at the time of cooling from the sintering temperature during sintering, having a predetermined pressure in the range of 300 to 760 torr, carburizing,
In a nitriding or oxidizing atmosphere, or a mixed atmosphere of two or more of them, a temperature ranging from a predetermined temperature in the range of 1500 to 1270 ° C. to a predetermined temperature of
By performing a heat treatment of quenching at a predetermined cooling rate within the range of ~ 50 ° C / min, a surface part of the tungsten carbide-based cemented carbide substrate is mainly composed of β-solid solution, and a hard surface layer having a smooth surface is formed. A method for producing a surface-coated tungsten carbide-based cemented carbide cutting tool having a high adhesion strength of a hard coating layer, characterized by being formed. 2. A green compact formed from the mixed powder is sintered under ordinary conditions to form a tungsten carbide-based cemented carbide substrate, and a hard coating layer is formed on the surface of the substrate under the same ordinary conditions. When manufacturing a cutting tool made of a tungsten carbide-based cemented carbide, the composition of the green compact is, in weight%, as a binder phase forming component, Co powder: 3 to 15%, and a hard dispersed phase forming component, Ti, Containing carbides of Ta, Nb, and W, nitrides of Ti, Ta, and Nb, and one or more powders of two or more of these solid solutions: 5 to 60%; Similarly, the tungsten carbide-based cemented carbide substrate after sintering has a predetermined pressure within the range of 300 to 760 torr, while having a composition comprising tungsten carbide powder as a hard dispersed phase forming component.
In a nitriding or oxidizing atmosphere, or a mixed atmosphere of two or more of them, a temperature ranging from a predetermined temperature in the range of 1500 to 1270 ° C. to a predetermined temperature of
By performing a heat treatment of quenching at a predetermined cooling rate within the range of ~ 50 ° C / min, a surface part of the tungsten carbide-based cemented carbide substrate is mainly composed of β-solid solution, and a hard surface layer having a smooth surface is formed. A method for producing a surface-coated tungsten carbide-based cemented carbide cutting tool having a high adhesion strength of a hard coating layer, characterized by being formed.