JPS5847942B2 - Cobalt-based casting alloy casting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for casting a cobalt-based casting alloy, and more particularly to a method for casting a cobalt-based casting alloy that can prevent breakage when subjected to compressive stress, particularly at high temperatures.

Generally speaking, cobalt-based casting alloys have traditionally been
The base contains C, W, Cr, etc., and has excellent hardness at room temperature and high temperature.

In particular, because of its high wear resistance, deformation resistance, and compressive strength at high temperatures, it is used for high-temperature type steel, tool steel, and the like.

However, although this cobalt-based casting alloy has excellent properties, it has extremely low ductility at high temperatures of 700 to 800°C.

This is because the structure of the cobalt-based cast alloy contains approximately 50% C-Cr and C-W-Co carbides, and these carbides have an angular or rod-like shape. Carbides easily cause brittle fracture, and cracks progress from this fractured carbide as a starting point with other carbides acting as a bridge.

In this case, if the shape of the carbide is angular or rod-like, the bridging role described above is further promoted.

Furthermore, since the outer surface of cobalt-based casting alloys is in contact with the casting mold, directional solidification is likely to occur, and long carbides with acicular microstructures are formed, which is extremely detrimental to crack resistance. be.

The above-mentioned problems occur in cobalt-based casting alloys because acicular carbides are formed on the outer surface of cobalt-based casting alloys when they are cast, for example, by sand casting. In addition, needle-like or rod-like carbides grow near the center of the wall thickness, which is extremely disadvantageous for cracking resistance.

The present invention solves the various problems of cobalt-based casting alloys described above. Specifically, when casting a cobalt-based casting alloy, directional solidification from the outer surface of a cast product of the alloy is prevented. They discovered a method for casting uniform cobalt-based casting alloys with no directionality, and by heating the casting mold to a high temperature and casting at an appropriate pouring temperature, cobalt-based casting alloys can be cast. This is a cobalt-based alloy casting method that does not produce acicular or rod-shaped carbides on the outer surface or thick center of the alloy casting, and can obtain a structure consisting mainly of granular carbides.

The characteristics of the cobalt-based casting alloy casting method according to the present invention are as follows: CI. 5-30%, Si 1.0% or less, Mn
1.0% or less, Cr25-35%, W8-17%, Fe
3% or less, P0.03% or less, 8003% or less, Ni
A cobalt-based casting alloy containing 3% or less and the remainder substantially Co is cast at a mold temperature of 650-900°C and a casting temperature of 1330-140°C.
The purpose is to cast at 50°C.

The cobalt-based casting alloy casting method according to the present invention will be explained in detail.

First, a portion and a portion of the composition of the cobalt-based casting alloy used in the cobalt-based casting alloy casting method according to the present invention will be explained.

C is a carbide-forming element, and if its content is less than 1.5%, few carbides will be formed, resulting in insufficient hardness and deterioration of wear resistance and deformation resistance. A large amount of crystallizes and precipitates, resulting in significant embrittlement.

Therefore, the C content is set to 1.5 to 3.0%.

Si is an effective element as a deoxidizing agent and oxidation resistance, and improves castability, but if contained in a large amount, it reduces high temperature strength.

Therefore, the Si content is set to 10% or less.

Mn improves castability and is an effective element as a deoxidizing agent, but if it is contained in a large amount, it reduces high temperature strength.

Therefore, the Mn content is set to 1.0% or less.

Cr is an element that imparts oxidation resistance and hardness. If the content is less than 25%, high-temperature oxidation resistance is insufficient, the amount of Cr carbide is small, and the resistance is insufficient. If it exceeds this value, embrittlement due to Cr carbide becomes noticeable.

Therefore, the Cr content is set to 25 to 35%.

W is a carbide-forming element, and if the content is less than 8%, there will be few W-based carbides and the hardness will be insufficient, and if the content exceeds 17%, the crystallization of W-based carbides will increase, resulting in significant embrittlement and ,
Casting becomes difficult.

Therefore, the W content is set to 8 to 17%.

Fe1P1S and Ni are normal impurities that are inevitably included in the production of cobalt-based casting alloys, and the smaller the content, the better. Fe3
% or less, P0.03% or less, 8003% or less, Ni3%
The following shall apply.

Next, the mold temperature and pouring temperature in the method of casting a cobalt-based casting alloy according to the present invention will be explained.

In other words, as the temperature of the mold before casting increases, needle-like and rod-like carbonized substances decrease on the outer surface and the center of the wall thickness, and when the temperature of the mold before pouring exceeds 650°C, the quality of the cast product decreases. No needle-like or rod-like carbide was observed on either the outer surface or the center of the wall thickness, and when the mold temperature exceeded 900°C, the survival of the carbide was not much different from when the mold temperature was below 900°C. Moreover, there are problems with the durability of cobalt-based casting alloys.

Therefore, the mold temperature is in the range of 650 to 900'C.

Further, good results are obtained when the casting temperature is in the range of 1330 to 1450°C, and if it exceeds 1450°C, the durability of the cobalt-based casting alloy deteriorates.

If the casting temperature is lower than 13,300, the fluidity of the molten metal deteriorates, wrinkles occur in the casting, and defects such as blowholes and pinholes occur.

If the casting temperature is 1450° C. or higher, the cast structure becomes coarse, the carbides in the microscopic structure become coarse, and the coarse carbides tend to crack, resulting in poor durability.

In addition, when the mold temperature is 650 to 900℃, the casting temperature is 13℃.
When casting at a temperature of 30 to 1450'C, the durability is slightly higher when the mold temperature is constant, when the casting temperature is around 1330°C than when it is cast at around 1450°C.

The reason for this is that the casting structure when cast at around 1330°C is slightly finer than that when cast at 1450°C.

Therefore, it is desirable to perform casting at a low temperature of 1330 to 1450°C.

Examples of the method for casting a cobalt-based casting alloy according to the present invention will be described below.

EXAMPLE A cobalt-based casting alloy was manufactured to have the components and composition shown in Table 1, and was cast at the mold temperature and pouring temperature shown in Table 1.

The results are also shown in Table 1.

As is clear from Table 1, when casting similar cobalt-based casting alloys, if the mold temperature and pouring temperature are other than the temperatures used in the casting method according to the present invention, the durability of the cast cobalt-based casting alloy is poor. extremely inferior (for example, 應1~//65, /I67 and waste 14 in Table 1)
).

On the other hand, in the casting method according to the present invention, Column No. 8 in Table 1 shows that the cobalt-based casting alloy has extremely excellent durability.

As can be seen from Table 1, extremely good results are obtained when the mold temperature is in the range of 650 to 900°C and the casting temperature is in the range of 1330 to 1450°C.

Incidentally, Figures 1a and b are micrographs of conventional sand casting. Figure 1a shows a large amount of acicular carbide formed near the outer surface, and Figure 1b shows that a large amount of acicular carbide is formed near the outer surface. This shows that acicular and rod-like angular carbides are formed in the center of the wall thickness.

Figures 2a and b are micrographs of a case where the alloy is cast in a mold with a mold temperature of 600°C by the cobalt-based casting alloy casting method according to the present invention. There was no formation of needle-like or rod-like carbides in this part, indicating that the carbides were mainly granular carbides.

As explained above, since the cobalt-based casting alloy casting method according to the present invention has the above structure, by suppressing directional solidification from the mold surface, that is, the outer surface of the cast product, the outer surface At the same time, it is possible to prevent the formation of needle-like carbides in the wall thickness center, and at the same time, it is possible to prevent the formation of needle-like and rod-like carbides in the central part of the wall thickness. At the same time, it prevents the propagation of cracks.

[Brief explanation of the drawing]

Figure 1 is a micrograph of the outer surface and center of the wall thickness of a cobalt-based cast alloy cast by the conventional sand casting method;
The figure is a micrograph of the outer surface and the central part of the wall thickness of a cobalt-based casting alloy cast by the cobalt-based casting alloy casting method according to the present invention.

Claims (1)

[Claims] I C1.5 to 3.0%, Si 1. O% or less, Mn 1.0% or less, Cr25-35%, W8
~17%, Fe3% or less, P0.03% or less, 80.0
1. A method for casting a cobalt-based casting alloy, which comprises casting a cobalt-based casting alloy consisting of 3% or less Ni, 3% or less Ni, and the remainder substantially Co at a mold temperature of 650 to 900°C and a casting temperature of 1330 to 1450°C.