JPS61194147A - Sintered hard alloy - Google Patents

Abstract

PURPOSE:To improve resistance to heat, impact, heat checks, and oxidation of a sintered hard alloy by composing a binding phase out of W, Ni, Co, Fe, and Cr, by specifying weight ratios among the above elements, and by forming WC into spheroidized grain shape. CONSTITUTION:The binding phase of the WC-base sintered hard alloy is composed of W, Ni, Co, Fe, and Cr. The additive quantities of each element are controlled so that they satisfy, by weight, Fe/(Ni+Co+Cr+Fe+ W)=0.3/100-2/100, Cr/(Ni+Co+Cr+Fe+W)=1/20-1/5, W/(Ni+Co+Cr+Fe+ W)=1/10-2.5/10, Co/Ni=1/9-1, and Ni+Co+Cr+Fe+W=10-30wt%. Further, WC grains are spheroidized so as to inhibit the cracks between the WC and the binding phase from propagating. This sintered hard alloy has excellent properties as material for use in rolls for hot rolling and in hot working tools.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a cemented carbide for hot working, such as a hot rolling roll or a hot forging die, which is exposed to relatively high temperatures.

Tungsten carbide-Co cemented carbide is widely used in cutting tools, wear-resistant tools, etc. In particular, as a wear-resistant layer, the binder phase ranges from Co alone to Co-Ni.

Ni-Cr, Go-Ni-Cr, etc. have been used to improve corrosion resistance, thermal shock resistance, thermal fatigue resistance, etc.

[Problem that the invention seeks to solve]

However, under conditions that require severe high-temperature characteristics, conventional W
Defects may occur in C-(Co or Ni) alloys,
In addition, the life is short and sufficient characteristics are not exhibited, and Cr
In systems where Cr is added, Cr is dissolved in Go or Ni to improve oxidation resistance, thermal shock resistance, thermal fatigue resistance, etc. However, Cr also suppresses the solid solution of WC, so it does not form a binder phase. It is also an element that inhibits solid solution strengthening by W.

An object of the present invention is to provide a heat-resistant cemented carbide having high heat resistance, impact resistance, heat cracking resistance, and oxidation resistance.

[Means for solving problems]

The present invention provides a WC-MiIi hard bond in which the binder phase is composed of W+NitCo*Fe, Cr,
IL amount ratio: Fe/(Ni+Co+Cr+Fe+W)~
0.3/100-2/100, Cr/(Ni+C.

+Cr+Fe+W) = 1/20 to 1/5,
W/(N i + Co + Cr + W) ~ 1/
10~2.5/10, Co/Ni =1/9~1, N
i+Co+Cr+Fe+W=10 to 30% by weight,
Moreover, WC is characterized by having a spherical particle shape.

[For production]

The cemented carbide of the present invention has a solid solution strengthening effect of W on Co and Ni, and provides excellent heat resistance and thermal fatigue resistance due to Cr.
I) The solid solution of W is suppressed by the addition of r.

Therefore, if the bonding metal is the same, the higher the amount of solid solution of W in the bonding phase, the better the high temperature properties will be. In order to increase the amount of solid solution of W, there is a method of using powder in which W metal is dissolved in solid solution in advance or using an additive.

Therefore, as a result of examining various metals, carbides, nitrides, etc., it was found that adding a small amount of Fe is effective in improving high-temperature properties without reducing the strength at room temperature.

A small amount of Fe dissolves in solid solution in the binder phase, greatly improving the plastic deformability of the binder phase, lowering the amount of C in the alloy and increasing the amount of solid solution such as W, which deteriorates the physical properties at room temperature. It improves properties at high temperatures, especially IT oxidation resistance and heat cracking resistance.

However, as the amount of solid solution in the binder phase increases, the strength of the binder phase deteriorates, and plastic deformation increases especially at high temperatures.
00 or less. Moreover, if the ratio is less than 0.3/100, there is no addition effect because it is essentially the same as the bonding phase of (Ni + Co + Cr + W).
It was set as 100.

Or improves thermal properties, but Cr/(Ni+Co+C
If the ratio (r+W) is less than 1/20, there is almost no effect, and if it exceeds 115, the strength will drop by 1.

When CO and Ni coexist, QCo and N
Solid solution strengthening with i and W solid solution strengthening with Co and Ni suppresses strength loss at high temperatures and has significant effects on thermal fatigue and thermal shock.

The amount of W solid solution in the bonded phase is W/(Ni+Co x Cr+Fe
+W) ratio of 1/10 to 2.5/10 is 1/1
If it is less than 0, the solid solution strengthening will not be sufficient. If it exceeds 2.5/10, solid solution precipitation will begin in the WC, causing a decrease in the strength of the alloy, making it unusable for practical use.

If the Co/Ni ratio in the alloy is less than 1/9, there is almost no effect, and if it exceeds 1, the Go content becomes large, resulting in triangular or square particle shapes and deteriorating impact resistance.

The total of the bonded phase (Ni + Co + Cr + Fe + W) is 10%
If it is less than 30%, the toughness will be insufficient, and if it exceeds 30%, the thermal properties will deteriorate severely.

The reason why the WC particles were spheroidized was to increase the propagation of cracks through the bond between the WC and the binder phase into L.

〔Example〕

WC powder (average particle size 5μ (up)), Co powder (average particle size 1.2)
/Jw+), Ni-Cr powder (2 μm), F6 powder (1 μm), and W powder (0.6 μm) were blended into the composition shown in Table 1, mixed with attritor for 5 hours, and then % of paraffin was added, and after drying, press molding was performed.
Vacuum sintering was performed at 400°C. Next, transverse rupture strength and hardness at room temperature, and properties at high temperatures such as oxidation resistance and thermal shock resistance were measured, and the results are shown in Table 2.

Oxidation resistance is expressed as oxidation weight gain (ms/cm") after an in-air oxidation test at 900°C for 5 hours.

Thermal shock resistance was evaluated by rapidly cooling in a furnace (N2 atmosphere) (temperature difference 800°C) and the number of repetitions until cracking occurred.

From the results in Table 2, Fe
Adding 0.1 to 2.0% of oxidation resistance can improve the oxidation resistance without deteriorating the plastic deformability.

Next, the present invention alloy No. 2, 3, 5 and the comparative alloy No.
8 was used in a hot forging die for an engine valve made of austenitic heat-resistant steel, and the total number of strokes until the forging die became unusable due to wear and local scratches was investigated. Steel for hot molds 5Kl
) 61 and W C-Co based cemented carbide alloys were compared with those made using the same conditions, as shown in Table 3.

The conditions for using the above forging die are as follows:
°C, number of strokes 20 strokes/min, load during forging 2
At 00 tons, a mixed mold release agent of oil and graphite was sprayed onto the forging mold to also serve as a cooling agent.

〔Effect of the invention〕

As mentioned above, in the present invention, the solid solution strengthening of the binder phase applies severe thermal stress due to repeated rapid heating and rapid cooling, and severe mechanical shock at high temperatures, and wear resistance at high temperatures is required. As a material for hot rolling rolls and hot tools for hot forging, etc., it has achieved performance that conventional WCC cemented carbide could not achieve.

Claims (1)

[Claims] In WC-based cemented carbide, the binder phase is W, Ni, Co
, Fe, and Cr, with a weight ratio of Fe/(Ni+Co+
Cr+Fe+W)=0.3/100~2/100, Cr
/(Ni+Co+Cr+Fe+W)=1/20~1/5
, W/(Ni+Co+Cr+Fe+W)=1/10~2
．． 5/10, Co/Ni=1/9~1, Ni+Co+C
A cemented carbide characterized in that r+Fe+W=10 to 30% by weight, and WC has a spherical particle shape.