JPS596304A - Preparation of coated surface cutting tool made of sintered hard alloy - Google Patents

Abstract

PURPOSE:To prepare the titled tool excellent in anti-wear property and toughness and having no decarburization layer at all, by a method wherein a pressed powder body based on a WC powder and containing carbide of a metal belonged to groups IVa, Va or VIa and a ferrous metal is sintered after nitrification treatment and the sintered one is subsequently coated by a hard layer. CONSTITUTION:A pressed powder body is molded from a mxed powder based on a WC powder and containing carbide of a metal belonged to groups IVa, Va or VIa or one kind or more solid solution powder comprising two kinds or more thereof and a ferrous metal powder. This pressed powder body is subjected to nitrification treatment at 1,000-1,300 deg.C in a nitrogen-containing atmosphere and the carbide powder of the above mentioned metal other than the WC powder is converted to a fine carbonitride powder to precipitate fine free carbon. Succeedingly, the pressed body is sintered at 1,350-1,500 deg.C under vacuum of 0.5Torr or less to prepare a hard alloy substrate having a surface layer with a thickness of 5-100mum comprising WC, free carbon and the ferrous metal and an interior comprising WC, free carbon and metal carbonitride. This surface layer is 5-40% lower than the interior in hardness Hv. In the next step, the surface of the substrate is coated with an anti-wear hard layer.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a surface-coated cemented carbide cutting tool in which no decarburized layer, which causes toughness deterioration, is formed on the surface of the substrate during the formation of the hard layer.

Generally, the main component is tungsten carbide (hereinafter referred to as WC), and one or more carbides and nitrides of metals from groups 4a, 5a, and 6a of the periodic table, and iron group metals. on the surface of a cemented carbide substrate containing one or more of the same (carbides, nitrides, and oxides of group 4a, 5a, and 6a metals, and one or more of aluminum oxide). A hard layer with excellent wear resistance consisting of a single layer or multiple layers with a thickness of 2 to 20μ
It is well known that surface-coated cemented carbide formed by coating with a layer thickness of m is used as a cutting tool.

However, in the conventional surface-coated cemented carbide cutting tool, a decarburized layer is likely to be formed on the surface of the cemented carbide substrate, especially when the hard layer is formed by chemical vapor deposition.
When a decarburized layer is formed in this way, the hard layer becomes extremely brittle compared to the cemented carbide base, and
The toughness of the surface of the base material deteriorates, and as a result, the cutting edge is more likely to be damaged during practical use, often resulting in a shortened tool life.

For this reason, various studies have been conducted to prevent the formation of a decarburized layer on the surface of the substrate of surface-coated cemented carbide cutting tools during the formation of the hard layer.
Powder is the main ingredient, less.

A mixture containing one or more nitride and carbonitride powders of metals from groups 4a, 5a, and 6a of the periodic table of the elements and one or more iron group metal powders. The powder is molded into a green compact, and the green compact is pressed into a pressure crab 1.
By sintering in a vacuum below tOrr at a temperature within the temperature range of 1300-1500°C, the layer thickness: 5-200
The surface layer of μm is made of WC and iron group metal, while the inside is
Producing a substrate made of a cemented carbide containing WC as a main component and containing at least carbonitrides of the above metals and iron group metals,
A method of manufacturing a surface-coated cemented carbide cutting tool has been proposed, which involves forming a hard layer with extremely high wear resistance on the surface of this substrate by a conventional method.

However, in the above method, nitride powder or carbonitride powder is used as the raw material powder as described above, but these raw material powders have large mutual variations in nitrogen content and are difficult to use during sintering. Since the amount of denitrification in the cemented carbide is extremely unstable, the amount of carbon in the cemented carbide substrate during sintering tends to fluctuate, which also causes a decarburized layer to form on the surface of the substrate during hard layer formation. It is something.

Therefore, from the above-mentioned viewpoint, the present inventors have developed a hard layer with excellent abrasion resistance on the surface of a cemented carbide substrate, which does not have the formation of a decarburized layer on the surface of the substrate. As a result of conducting research to manufacture surface-coated cemented carbide cutting tools with excellent plastic deformation resistance and toughness, WC
When producing a cemented carbide substrate mainly composed of carbide powders of metals from Groups 4a, 5a, and 6a of the Periodic Table of the Elements, and one or two of these two or more solid solution powders. In an atmosphere containing nitrogen, a green compact formed from this blended powder is
When nitriding is performed at a temperature within the temperature range of 1000 to 1300°C, the carbide powder becomes an extremely fine carbonitride powder, and fine free carbon is precipitated.
Next, this nitrided powder compact was passed through a pressure crab at 0.5 torr.
When sintered at a temperature within the temperature range of 1350 to 1500°C in a vacuum of r or more, the internal Vickers hardness is 5 to 40.
It has low hardness and has a surface layer with a layer thickness: 5 to 100 μm composed of WC, free carbon, and iron group metals, while the inside is composed of WC, fine carbonitrides of the above metals, and iron group metals. In the resulting cemented carbide base, it is extremely difficult to form a decarburized layer during the formation of the hard layer due to the presence of free carbon in the surface layer, and They also found that toughness is ensured by the fine carbonitrides.

This invention was made based on the above knowledge, and contains WC powder as a main component, and contains elements 4a and 5a of the periodic table.
, and carbide powders of group 6a metals.

A powder compact is formed from a mixed powder containing one or more of these two or more solid solution powders and an iron group metal powder, and the compact is placed in an atmosphere containing nitrogen. The carbide powder of the metal other than the main component WC powder is converted into fine carbonitride powder by nitriding at a temperature within the temperature range of 1000 to 1300C, and fine free carbon is precipitated. The nitrided green compact is heated at 1350 to 1500°C in a vacuum of 0.5 torr or less.
Sintered at a temperature within the temperature range of A cemented carbide substrate having a surface layer, one direction of which is composed of WC, free carbon, fine carbonitrides of the metals, and iron group metals is manufactured, and subsequently, on the surface of this cemented carbide substrate, By coating a well-known hard layer with excellent wear resistance with a normal layer thickness of 2 to 20 μm, it has excellent wear resistance, plastic deformation resistance, and toughness, and there is no formation of a decarburized layer on the surface of the base. The present invention is characterized by a method for manufacturing a surface-coated cemented carbide cutting tool.

Next, the reason why the degree of nitriding and the sintering conditions are limited as described above in the method of the present invention will be explained.

(a) Nitriding temperature If the temperature is less than 1000°C, nitriding will be insufficient, resulting in insufficient refinement of carbonitride powder and precipitation of free carbon, and as a result, the toughness of the cemented carbide substrate will not improve. In addition, when forming a hard layer on the surface of a cemented carbide substrate by, for example, chemical vapor deposition, a decarburized layer is likely to be formed on the surface of the cemented carbide substrate;
If the temperature exceeds 1,000 yen, molten liquid will be generated inside the green compact, and the surface will become rough.This surface roughness will cause the dimensional accuracy of the cutting tool to deteriorate.
The temperature was set at 000 to 1300°C.

(b) Sintering conditions Among the sintering conditions, if the sintering temperature is less than 1350°C, it is difficult to perform sufficient sintering, and as a result, the desired toughness cannot be secured; If the sintering temperature is set to 1,350 to 1,350 to 1,350, the toughness decreases due to grain growth of WC and carbonitride.
The temperature was set at 500°C. In addition, the sintering atmosphere pressure affects the layer thickness and hardness of the substrate surface layer, and the pressure
Above orr the desired layer thickness and hardness, i.e. 5μ
It has a layer thickness of m or more, and a hardness of 5 to 5 Vickers hardness.
Due to the inability to form a 40% lower surface layer,
The pressure was set at 0.5 torr or less.

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

Examples of raw material powders include WC powder and TiC powder, both of which have an average particle size within the range of 05 to 3.0 μm.

Z r C powder, VC powder, NbC powder, TaC
Powder, Cr3C2 powder, (), N1)) C powder,
(Ti, Mo)C powder, (Ti, W)C powder +
('I'i, Ta, W) C powder, Fe powder, Ni powder, C.

These raw material powders were mixed into the composition shown in Table 1, wet-pulverized and mixed in the usual way, dried, and then subjected to ISO standard S at a pressure of 10 kg/ma.
After molding into green compacts having the shapes of NMG4 and 32, and then nitriding these green compacts under the conditions shown in Table 2, the N2 gas was removed and the powder compacts were also processed under the conditions shown in Table 2. A cemented carbide substrate is produced by vacuum sintering under the conditions shown.
．． The hardness and layer thickness of the surface layer in the resulting cemented carbide substrate, the hardness and carbonitride particle size inside the substrate, and the distribution state of free carbon distributed throughout the substrate (J
These results are shown in Table 2 along with those of the comparative cemented carbide substrate described later).
Then, cutting tools 1 to 20 of the present invention were manufactured by forming a hard layer having the structure shown in Table 3 on the surface of the cemented carbide substrate using a conventional chemical vapor deposition method, and further comparison was made. Except for not performing the above nitriding treatment for the purpose of
Comparative cutting tools 1 to 20 were each manufactured by manufacturing a comparative cemented carbide base under the same conditions and forming a hard layer under the same conditions.

Next, the following conditions A to 1 were applied to the resulting cutting tools 1 to 20 of the present invention and comparative cutting tools 1 to 20.
D, that is, (1) Condition A Rigid material: SNCM-8 (Hardness: HB230., Cutting speed: 15om7'm=, Feed: 0.36 H/rev,
, depth of cut:], 5mm, cutting time: 1om=(referred to as continuous cutting condition A).

(2) Condition B Work material: FC30' (hardness: HB140), cutting speed:
2oom/m=, Feed: 0.25 mm/rev, Depth of cut: ],, 5 mm, Cutting time: 15 m1q (referred to as continuous cutting condition B).

(3) Condition C Work material: SNCM-8 (Hardness: HB280), Cutting speed: 100 m/an, Feed rate: 0.3 mm/
rev, , depth of cut: 3 dragons 1 cutting time: 2 = (referred to as interrupted cutting condition C).

(4) Conditioned work material: SNCM-8 (hardness: HB280), cutting speed: 140m/min, feed: 0.275 Hz/re
v,, Depth of cut: 2 mm + Cutting time: 3 mm (referred to as intermittent cutting conditions) were conducted on 10 test pieces, and in the continuous cutting test under condition A above, the flank wear depth and rake face wear depth of the cutting edge were measured. , In the continuous cutting test under condition B above, the flank wear depth of each cutting edge was measured and the average value was calculated, and in the intermittent cutting test under condition C0 The number of missing cutting edges was measured. These results are shown in Table 3.

In addition, FIGS. 1 and 2 also show the cutting tool 1 of the present invention (first
The hardness distribution curves from the surface of Fig. 9) and 9 (Fig. 2) are shown.

As is clear from the above results, cutting tools 1 to 1 of the present invention
No. 20 has fine free carbon distributed throughout the substrate, and the surface layer of the substrate consists of a phase of WC-free carbon-iron group metal without carbonitride, while the inside of the substrate has fine carbonitride. It has excellent wear resistance because it has a structure consisting of WC - free carbon monocarbonitride monoiron group metal phase.

In contrast, comparative cutting tools 1 to 20 have no free carbon because they are not subjected to nitriding treatment, and the carbonitrides are relatively coarse. Furthermore, since a decarburized layer is formed during the formation of the hard layer, the toughness is particularly poor.

As described above, according to the method of the present invention, it is possible to produce a cemented carbide substrate having a structure in which free carbon exists throughout the substrate and extremely fine carbonitrides exist inside the substrate. Therefore, when forming a hard layer on the surface of the cemented carbide substrate, no decarburized layer is formed on the surface of the substrate due to the presence of the free carbon, and excellent toughness is achieved due to the fine carbonitrides inside the substrate. Therefore, when the resulting surface-coated cemented carbide is used as a cutting tool, it exhibits excellent performance over a long period of time.

[Brief explanation of the drawing]

1 and 2 are curve diagrams showing the hardness distribution from the surface of the cutting tools 1 and 9 of the present invention. Applicant Mitsubishi Metals Co., Ltd. Agent Tomi 1) Kazuo No. 1 Figure 0 10 20 30 40 50$I
#・5. ? i huge 1 (1, Im) 12 figure 0 20 40 60 80 +00 rice force゛4;1? Distance N (pm)

Claims (1)

[Claims] The main component is tungsten carbide powder, which is 4th in the periodic table of elements.
A green compact is formed from a mixed powder containing carbide powders of group a, 5a, and 6a metals, one or more of these two or more solid solution powders, and iron group metal powder. After that, this green compact is placed in an atmosphere containing nitrogen.
Nitriding treatment is carried out at a temperature within the temperature range of 1000 to 1300°C to convert the metal carbide powder other than the main component tungsten carbide powder into fine carbonitride powder, and to precipitate fine free carbon, followed by The nitrided green compact is
Pressure crab In a vacuum of 0.5 torr or less, 1350 to 1
It is sintered at a temperature within the temperature range of 500°C, has a hardness 5 to 40 points lower on the Vickers hardness than the inside, and has a layer thickness of 5:5, consisting of tungsten carbide, free carbon, and iron group metals.
A cemented carbide substrate having a surface layer of ~100 μm, while the interior is composed of tungsten carbide, free carbon, carbonitrides of the metals, and iron group metals, is then coated on the surface of the cemented carbide substrate. A method for manufacturing a surface-coated cemented carbide cutting tool characterized by coating it with a hard layer with excellent abrasion properties.