JPH02190403A - Production of cutting tool made of surface-coated tungsten carbide-based sintered hard alloy - Google Patents

Abstract

PURPOSE:To obtain a cutting tool having high bonding strength of the coating layer and superior wear resistance by specifying components forming a binding phase and a hard dispersed phase in a green compact for a WC-based sintered hard alloy substrate and by limiting the pressure of an atmosphere and conditions at the time of cooling from a sintering temp. CONSTITUTION:Powdery starting material having a compsn. consisting of 3-15wt.% Co powder ad a component forming a binding phase, 5-60wt.% powder of one or more kinds of compds. selected among the carbides of Ti, Ta, Nb and W, the nitrides of Ti, Ta and Nb and solid solns. of them as a component forming a hard dispersed phase and the balance WC powder as a component forming the hard dispersed phase is compacted and sintered. At the time of cooling from the sintering temp., rapid cooling is carried out from 1,500-1,270 deg.C to <=1,250 deg.C at 10-50 deg.C/min cooling rate in an atmosphere such as a carburizing, nitriding or oxidizing atmosphere under 300-760Torr pressure. By this heat treatment, a cutting tool made of a WC-based sintered hard alloy substrate having a beta-solid soln.-based smooth hard surface layer is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is directed to a hard coating layer of tungsten carbide (hereinafter referred to as WC).
It has extremely high adhesion strength to the cemented carbide substrate surface (shown by ), and it is possible to stably form a hard surface layer mainly composed of β-solid solution on the substrate surface, providing excellent wear resistance during cutting over a long period of time. The present invention relates to a method for manufacturing a cutting tool made of a MWC-based cemented carbide that exhibits surface waves.

[Conventional technology]

Conventionally, raw material powder is generally mixed with one or two iron group metals as binder phase forming components.
More than species: 5 to 25%, 4a and 5a of the periodic table as dispersed phase forming components.

and carbides and nitrides of Group 6a metals, and one or more solid solutions of two or more of these = 5-
60%, WC as a dispersed phase forming component, and the remainder (the above weight %, below % shows weight %), wet or dry mixing under normal conditions, and compacted powder. After press forming, it is sintered in vacuum at a predetermined temperature within the range of 1380 to 1450°C to form a WCC cemented carbide base, and then the surface of this base is coated using ordinary chemical vapor deposition and physical vapor deposition. carbides, nitrides, oxides, and borides of group 4a, 5a, or 6a metals of the periodic table, solid solutions of two or more thereof, and aluminum oxide (
(hereinafter referred to as A 120 a) and zirconium oxide (
A single layer or two of the following Z r O2)
A method of manufacturing a surface wave@WC-based cemented carbide cutting tool by forming a hard coating layer consisting of multiple layers with an average layer thickness of 1 to 20 layers is known.

In addition, when manufacturing the above-mentioned surface-coated WCC cemented carbide cutting tool, a hard surface layer mainly composed of β-solid solution composed of the above-mentioned dispersed phase forming components is added to the surface for the purpose of improving wear resistance. W formed with an average layer thickness of 2 to 10m
It is also known to use a CC cemented carbide substrate, and 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, Hard metal base, N2 gas and C
In a mixed gas atmosphere of O gas, heat and maintain at a temperature higher than the liquid phase appearance temperature of the substrate, for example, N2 partial pressure: 150 torr
, C0 partial pressure: 200 torr consisting of 50 torr
(b) Heat treatment at 1400°C for 2 hours in a reduced pressure atmosphere; (b) Heat treatment at 1400°C in vacuum as also described in Examples of JP-A-83-103069; When sintering a WCC cemented carbide substrate under the following conditions, cooling from the sintering temperature is performed slowly at a cooling rate of 0.5°C/main in a N2 gas atmosphere with a N2 partial pressure of 5 torr, etc. method has been proposed.

[Problems to be Solved by the Invention] However, in method (a) above, the N2 partial pressure in the atmosphere is high and the heating temperature is also high, exceeding the liquid phase appearance temperature, so the substrate surface becomes rough and In method (b) above, the cooling rate from the sintering temperature is 0.5°C/m I
n, the temperature is kept at a temperature higher than the liquid phase appearance temperature for a long time, and surface roughness also tends to occur.
However, if the N2 partial pressure in the atmosphere is low, the formation of the hard surface layer becomes extremely unstable, and the layer thickness tends to vary. The hard coating layer formed on the substrate has low adhesion strength and tends to peel off during cutting, so that the effect of improving wear resistance by forming the hard coating layer cannot be fully exhibited.

[Means to solve the problem]

Therefore, from the above-mentioned viewpoints, the present inventors have developed a surface-coated WC-based cemented carbide cutting material whose hard coating layer has high wear resistance against the substrate surface and which exhibits excellent wear resistance during cutting. In order to manufacture tools, we conducted research focusing on WCC cemented carbide substrates having a hard surface layer. (1) When forming a hard surface layer on the surface of WCC cemented carbide, WCC cemented carbide The blending composition of the green compact before sintering the base material is as follows: CO powder: 3 to 15% as a binder phase forming component; Ti+Ta, Nb as a hard dispersed phase forming component.

and W carbide, T1. Nitride of Ta and Nb,
and powder of one or more of these two or more solid solutions (hereinafter collectively referred to as (Ti, Ta, Nb, W)CN): 5 to GO%, also hard By specifying a composition consisting of WC powder as a dispersed phase forming component and limiting the atmospheric pressure to a relatively high pressure of 300 to 760 torr, a β-solid solution composed of the above dispersed phase forming component can be formed. The main hard surface layer can be stably formed without variation.

(2) In the high pressure atmosphere shown in item (1) above, the surface of the substrate, that is, the surface of the hard surface layer is thick and easily roughened, and the processing temperature is higher than the liquid phase appearance temperature of the substrate. Even if the treatment time is shortened, the components that form the β-solid solution, especially the metal components, rapidly diffuse from the inside of the substrate through the liquid phase to the surface. The process progresses at almost the same high speed from the beginning to the later stage when roughness is likely to occur, so that the hard surface becomes rough in the same way, but the bonding phase on the substrate surface grows as the hard surface layer grows. If the phase is changed from a solid phase to a solid phase and the treatment temperature is lowered as the hard surface layer grows, the diffusion rate of the metal components that constitute the β-solid solution will slow down as the hard surface layer grows. The growth rate is slowed down, surface roughness is suppressed, and a hard coating layer formed on a substrate with a smooth surface and no surface roughness has strong adhesion strength.

(3) In order to change the bonding phase on the surface of the substrate from a liquid phase to a solid phase more quickly than inside, it is sufficient to perform rapid cooling. Moreover, the layer thickness of the hard surface layer can be controlled by this rapid cooling, and it is possible to form a relatively thin average layer thickness of 0.02 to 2 mm.

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

This invention was made based on the above knowledge, and a green compact formed from a mixed powder is sintered under normal conditions to form a WCC cemented carbide base, and the surface of the WCC cemented carbide is sintered under normal conditions. When manufacturing a cutting tool made of surface-coated WCC cemented carbide by forming a hard coating layer, the composition of the green compact is as follows: Co powder = 3 to 15%, (Ti, Ta, Nb, W)C- One or more types of powder of N: 5 to 60%, WC powder: the remainder, and the composition is as follows: When cooling from the sintering temperature during sintering, or after sintering, the WCC is a hard metal substrate, a predetermined pressure within the range of 300 to 780 torr;
150 in a carburizing, nitriding, and oxidizing atmosphere, or a mixed atmosphere of two or more of these.
The WCC cemented carbide substrate is subjected to rapid cooling heat treatment from a predetermined temperature in the range of 0 to +270'C to a predetermined temperature of 1250C or less at a predetermined cooling rate in the range of lO to 50C/win. This method is characterized by forming a hard surface layer mainly composed of β-solid solution and having a smooth surface on the surface portion, thereby producing a surface-coated WCC cemented carbide cutting tool with high adhesion strength of the hard coating layer. be.

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

A. Blend composition (a) Co powder Co powder forms a binder phase for the base material and has the effect of imparting toughness to it, but if its blending amount is less than 3%, it is not possible to secure the desired toughness. On the other hand, if the amount exceeds 15%, plastic deformation is likely to occur and cause a decrease in wear resistance, so the amount added is set at 3 to 15%.

(b) (Ti, Ta, Nb, W)C-N powder. These powders have the effect of increasing the hardness of the substrate and improving wear resistance, as well as smoothing the formation of a hard surface layer. However, if the amount is less than 5%, the desired effect cannot be obtained, and if the amount exceeds 60%, the toughness will decrease rapidly. It was set at 60%.

B. Heat treatment conditions (a) Atmospheric pressure Limiting the atmospheric pressure is essential for the stable formation of a hard surface layer. Therefore, if the pressure is less than 300 torr, the formation of the hard surface layer will become unstable; If the pressure exceeds 780 torr, the pressure is increased relative to the atmosphere, which not only makes it impossible to use in the current vacuum sintering furnace, but also makes the hard surface layer more likely to become rough. ~760 torr. Note that an atmospheric pressure of 500 to 760 torr is desirable.

(b) Rapid cooling start temperature When this temperature increases beyond 1500°C, surface roughness tends to occur on the hard surface layer;
If the temperature is lower than this, it becomes difficult to form a hard surface layer, so the quenching start temperature was set at 1500 to 1270°C. Note that it is preferably 1380 to 1270°C, which is the temperature at which the solid phase and liquid phase coexist.

(c) The formation of a hard surface layer progresses until the maximum temperature at which the rapid cooling ends is 1250°C.
Below this, the bonded phase becomes a solid phase and its formation stops, so it is sufficient to rapidly cool it to 1250°C. Therefore, it goes without saying that the sintering process may be shortened by rapidly cooling to a predetermined temperature of 1250° C. or lower, for example, about 100° C.

(d) If the cooling rate is slower than 10°C/min, the binder phase will remain in the liquid phase for a long time, so the surface roughness of the hard surface layer will appear significantly. aki
If the cooling rate exceeds n, the formation of a hard surface layer will be suppressed, so this was set as 10~b.

〔Example〕

Next, the method of the present invention will be specifically explained using examples.

As raw material powders, various (TI, Ta, Nb, W)C-N powders and C
o powder and WC powder of 3.51a were prepared, and these raw material powders were each blended into the composition shown in Table 1, mixed for 72 hours in a ball mill, dried, and then lQkg/mJ. ISO standard S N M G
120408, and then these green compacts A to F were each 0.0
7-Q, in a vacuum of 0.9 torr, sintered at the sintering temperature shown in Table 2 for 1 to 1.5 hours, and when cooled from this sintering temperature, or in the same vacuum as the sintering atmosphere. After cooling in the furnace to room temperature and then reheating to the quenching start temperature, heat treatment is performed under the conditions shown in Table 2 to form a WCC cemented carbide base having a hard surface layer on the surface. While observing the surface part in the longitudinal section of
The average layer thickness of the hard surface layer mainly composed of β-solid solution was measured, and the surface roughness of the substrate was also measured (these n1 constant results are shown in Table 3), and then a conventional chemical vapor deposition apparatus was used. , Methods 1 to 12 of the present invention were carried out by forming a hard coating layer having the composition and average layer thickness shown in Table 2 on the surface of the substrate under the same normal conditions, and the surface coating W
CC cemented carbide cutting tools (hereinafter referred to as coated cemented carbide chips 1 to 12 of the present invention) were manufactured, respectively.

In addition, for the purpose of comparison, compacted powder 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 WCC cemented carbide base, and on this base, With the upper and lower surfaces polished, N2 partial pressure = 150 torr,
C0 partial pressure: pressure crab consisting of 50tOrr 20Otor
In a reduced pressure atmosphere of
Next, under the same conditions, conventional method 1 was carried out by forming a hard coating layer consisting of Tic:6 on the substrate surface, and a surface wave IWCU cemented carbide cutting tool (hereinafter referred to as conventional coated cemented carbide tip 1) was carried out. ) was manufactured.

Furthermore, for the purpose of comparison, powder compact A was set at 0.09 torr.
The temperature was maintained at a sintering temperature of 1420°C for 1 hour in a vacuum of
A WCC cemented carbide alloy substrate having a hard surface layer on the surface was formed by slowly cooling it to 1200°C at a cooling rate of /min and then performing a heat treatment of furnace cooling in a vacuum to room temperature. Observation and /IpJ determination were carried out under the same conditions, and conventional method 2 was carried out by forming a hard coating layer of 6 m of T i C on the surface of the substrate under the same conditions. A cutting tool (hereinafter referred to as conventional coated cemented carbide tip 2) was manufactured.

Next, with respect to the various coated cemented carbide chips obtained as a result, the hard coating layer was scratched and peeled off with a diamond indenter using a scratch tester, and the adhesion strength at this time was measured. Hardness: HB Cutting speed:
180 m / 1 line s depth of cut: 3 mm.

Feed: OJ mm/rev, Cutting time:
10m1n.

A dry continuous cutting test was conducted on steel under the following conditions, and the flank wear width of the cutting edge was determined to be i'l11. These measurement results are 24
0) round bar, shown in Table 3.

〔Effect of the invention〕

From the results shown in Tables 2 and 3, it can be seen that in the coated cemented carbide chips 1 to 12 of the present invention manufactured by the methods 1 to 12 of the present invention, there was no 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 method 1.2, and this result is reflected in the adhesion strength of the hard coating layer formed thereon. In this way, the coated cemented carbide chips 1 to 2 of the present invention, which have a high adhesion strength of the hard coating layer, have a relatively low adhesion strength of the hard coating layer in the cutting test, and the hard coating layer is removed at a relatively early stage. It is clear that the wear resistance is significantly superior to that of the conventional coated cemented carbide tips 1 and 2, in which peeling occurs in the layers and abnormal wear is unavoidable.

As described above, according to the method of the present invention, a hard surface layer with a stable, smooth surface can be formed on the surface of a WCC cemented carbide substrate, so that a hard surface layer with a smooth surface can be formed on the surface of a WCC cemented carbide substrate. It is now possible to manufacture a surface-coated WCC cemented carbide cutting tool that has extremely high adhesion strength to the surface of a WC-based cemented carbide metal-containing substrate, and therefore, when used for cutting,
It has industrially useful effects such as no peeling in the hard coating layer, excellent wear resistance due to the coexistence of the hard surface layer, and excellent cutting performance over a long period of time. It is.

Claims (2)

[Claims] (1) A green compact formed from mixed powder is sintered under normal conditions to form a tungsten carbide-based cemented carbide base, and a hard coating layer is formed on the surface of this under normal conditions to form a surface-coated tungsten carbide base. When manufacturing a cutting tool made of base cemented carbide, the blending composition of the green compact is as follows: Co powder: 3 to 15% as a binder phase forming component, Ti, Ta, Contains 5 to 60% powder of carbides of Nb and W, nitrides of Ti, Ta, and Nb, and solid solutions of two or more of these, and the rest is similarly hard. A composition consisting of tungsten carbide powder as a dispersed phase forming component, and a carburizing, nitriding, and oxidizing property having a predetermined pressure within the range of 300 to 760 torr upon cooling from the sintering temperature during sintering. 15 in any of the following atmospheres or a mixed atmosphere of two or more of these.
The above-mentioned tungsten carbide-based cemented carbide can be produced by performing a heat treatment of rapidly cooling from a predetermined temperature in the range of 00 to 1270 °C to a predetermined temperature of 1250 °C or less at a predetermined cooling rate in the range of 10 to 50 °C/min. A method for manufacturing a surface-coated tungsten carbide-based cemented carbide cutting tool with high adhesion strength of a hard coating layer, which is characterized by forming a smooth hard surface layer mainly composed of β-solid solution on the surface of a base body. . (2) A green compact formed from a mixed powder is sintered under normal conditions to form a tungsten carbide-based cemented carbide base, and a hard coating layer is formed on the surface of this under normal conditions to form a surface-coated tungsten carbide base. When manufacturing a cutting tool made of base cemented carbide, the blending composition of the green compact is as follows: Co powder: 3 to 15% as a binder phase forming component, Ti, Ta, Contains 5 to 60% powder of carbides of Nb and W, nitrides of Ti, Ta, and Nb, and solid solutions of two or more of these, and the rest is similarly hard. The composition is composed of tungsten carbide powder as a dispersed phase forming component, and the tungsten carbide-based cemented carbide base after sintering has a carburizing property, a nitriding property, and a predetermined pressure within the range of 300 to 760 torr. 15 in an oxidizing atmosphere or a mixed atmosphere of two or more of these.
The above-mentioned tungsten carbide-based cemented carbide can be produced by performing a heat treatment of rapidly cooling from a predetermined temperature in the range of 00 to 1270 °C to a predetermined temperature of 1250 °C or less at a predetermined cooling rate in the range of 10 to 50 °C/min. A method for manufacturing a surface-coated tungsten carbide-based cemented carbide cutting tool with high adhesion strength of a hard coating layer, which is characterized by forming a smooth hard surface layer mainly composed of β-solid solution on the surface of a base body. .