JPH02209448A - Sintered hard alloy containing composite area - Google Patents

Abstract

PURPOSE:To combinedly provide the sintered hard alloy with excellent toughness and wear resistance, in a sintered hard alloy constituted of a hard dispersed phase contg. WC and a bonding phase of iron-group metal, by forming the area of the alloy surface having changed quantity of the bonding phase as compared to that of the inside. CONSTITUTION:The sintered hard alloy is constituted of a hard dispersed phase contg. WC and a bonding phase of iron-group metal; the alloy surface contains the area having reduced quantity of the bonding phase as compared to that of the inside; and compressive stress is produced on the surface part of the alloy. Since the sintered hard alloy contains the area having reduced quantity of the bonding phase of Co, etc., on the surface, wear resistance on the alloy surface can be maintained or improved. At the same time, the quantity of the bonding phase of Co, etc., can relatively be increased inside of the alloy which does not contribute to the wear resistance, so that high toughness can be imparted as a whole. Furthermore, for obtaining the sintered hard alloy, powder having prescribed quantity of the bonding phase is packed into a forming mold and powder having reduced quantity of the bonding phase is packed into the part to form the surface which is subjected to press forming sintering. Or, the method of subjecting powder having prescribed quantity of the bonding phase to press forming and repeating carburization and decarburization in the sintering stage can be used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a cemented carbide having both excellent toughness and wear resistance.

[Conventional technology]

Conventionally, cemented carbide comprising a hard dispersed phase containing WC, Tie, etc., and a binder phase of an iron group metal such as E'es Nis Co has been used as an alloy for tools. In particular, WC-C is used for forged tools such as punches and headers that require wear resistance and impact resistance.

Cemented carbides are mainly used.

In order to improve the performance of these cemented carbides as tools, efforts have been made to improve wear resistance and toughness by adjusting the amount of Co and making the WC finer.

However, since wear resistance and toughness are contradictory properties,
It was difficult to improve both at the same time. For example, in Wc-C10 cemented carbide, increasing the amount of Co to impart high toughness will inevitably reduce the wear resistance, and conversely, decreasing the amount of Co will improve the wear resistance but reduce the toughness. descend.

Due to these circumstances, the use of cemented carbide as wear-resistant and impact-resistant tools has been limited compared to high speed steel.

[Problem to be solved by the invention]

In view of such conventional circumstances, an object of the present invention is to provide a cemented carbide that has both excellent toughness and wear resistance and is suitable as a wear-resistant and impact-resistant tool.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a cemented carbide comprising a hard dispersed phase containing WC and a binder phase of iron group metal.
It is characterized by having a region on the alloy surface in which the amount of binder phase is reduced compared to the inside of the alloy, producing compressive stress on the alloy surface.

As a means of forming a region on the surface of a cemented carbide with a reduced amount of binder phase than the inside of the alloy, a press forming mold is filled with powder of a predetermined amount of binder phase (average amount of binder phase), and the surface and the There is a method in which a powder with a reduced amount of binder phase is filled into a part, which is then press-formed and then sintered.Alternatively, after press-forming using only powder with a predetermined amount of binder phase, the sintering process G
There is also a method of repeating carburization and decarburization to segregate the binder phase on the surface into the interior of the alloy, resulting in the formation of a region on the surface in which the amount of binder phase is reduced.

[Effect]

Since the cemented carbide of the present invention has a region in which the amount of binder phase such as cobalt is reduced on the alloy surface, wear resistance on the alloy surface is maintained or improved. At the same time, it is possible to relatively increase the amount of a binder phase such as Co within the alloy that does not contribute to wear resistance, so it is possible to provide high toughness as a whole.

The ratio ts/ld of the thickness td of the region with the lowest binder phase decrease to the thickness ts of the average binder phase amount region other than this region is 1, Q ~
A range of 100 is preferred.

Since two regions with different compositions are formed on the surface and inside of the cemented carbide, residual stress of tensile force or compressive force is generated on the surface of the alloy during the cooling process after sintering. That is, the residual stress σ of the alloy surface portion is determined by the thickness td of the region with the lowest binder phase reduction, the thermal expansion coefficient αd, the Young's modulus Kd, and the thickness ts of the other average binder phase content region.

The coefficient of thermal expansion αS and Young's modulus Es are expressed by the following formula: σ=K(αS-αd)Ed・△T (K is the value determined by ts/ld and Es/Ed, and △T is the value determined by ts/ld and Es/Ed. It represents the temperature difference between freezing temperature and room temperature.) Therefore,
By selecting the composition, thickness, etc. of the region of minimum binder phase reduction and the region of average bonding amount, it is possible to generate compressive stress on the alloy surface.

For example, WC-CO cemented carbide has the above ratio ts/ld
In the range of approximately 1.0 to 100, the residual stress σ becomes compressive stress. Specifically, the alloy surface was coated with WC-10wt%
WC inside CO and alloy! The drawing shows the relationship between the residual stress σ on the alloy surface and the ratio ts/ld of the thickness of both head regions for the cemented carbide of the present invention composed of -15 wt% CO.

In this manner, by applying compressive stress to the alloy surface portion, the tensile strength and fracture toughness values can be further improved compared to the alloy surface portion of the same composition without compressive stress.

〔Example〕

Example 1 W was further added to the outer periphery of WE-15wt% CO powder which was press-molded into a cylindrical shape with an outer diameter of 20mm and an inner diameter of 10mm using a mold.
e-7 wt% CO powder with a thickness of 0.1 mm, 0.5
It was press-molded to have a multilayer structure with fntn, l srn, and sintered at 1400C. Ratio ts/l of the thickness td of the region with the lowest binder phase reduction on the alloy surface (outer periphery) of the obtained alloy and the thickness ts of the average binder phase amount region other than this region
d was 50.10 and 1 for samples ASB and C, respectively.

Further, when the residual stress on the alloy surface was measured by X-ray analysis, samples A, B, and C had weights of -10 to -24 kg, and -0.5 kg, Anyn, respectively.

Using each Aigasa sample as a punch for forward extrusion, 5OR21
A life test was conducted at a cross-sectional reduction rate of 58% and an extrusion length IQsm. For comparison, normal WC-7wt%CO alloy (sample D) and WC! -15wt% CO alloy (sample E)
A punch made of was also tested in the same way. As a result, 120,000 shots, 300,000 shots, and 80,000 shots were possible for Samples A, B, and C, which are alloys of the present invention, respectively. However, after 60,000 pieces, sample E developed cracks and reached the end of its life, and sample E was so worn that it became unusable after 40,000 pieces.

Example 2 Using the same samples A, B, and C as in Example 1, a 3150 with an initial shape of 32 mm in diameter and a length/diameter of 1.5 was forged (forward extruded) to fabricate a cab blank.

The lifespan of the punches at this time was 80,000, 300,000, and 60,000 for Samples A, B, and C, respectively.

However, the normal WC-7wt%C carried out for comparison
O alloy (sample D) and WC! In a similar test using a -15wt% CO alloy (sample E), the sample plate developed cracks and reached the end of its life after 20,000 pieces, and sample E was so worn that it became unusable after 3000 pieces.

〔Effect of the invention〕

According to the present invention, it is possible to provide a cemented carbide having both excellent toughness and wear resistance by forming regions with different amounts of binder phase on the surface and inside the alloy.

Therefore, this cemented carbide is suitable as a wear-resistant and impact-resistant tool used in forging and the like.

[Brief explanation of the drawing]

The drawing shows a specific example of the cemented carbide of the present invention, the residual stress σ on the alloy surface, the thickness td of the region with the lowest binder phase reduction on the alloy surface, and the thickness ts of the average binder phase amount region other than this region. It is a graph showing the relationship between the ratio ts/ld and the ratio ts/ld.

Claims (1)

[Claims] (1) In a cemented carbide consisting of a hard dispersed phase containing WC and a binder phase of iron group metal, the alloy surface has a region where the amount of binder phase is reduced compared to the inside of the alloy, producing compressive stress on the alloy surface. A cemented carbide that is characterized by its hardness.