JPS63183151A - Low-expansion cast iron having excellent machinability - Google Patents

Abstract

PURPOSE:To produce a low-expansion cast iron having excellent machinability by preparing the cast iron contg. specific ratios of C, Si, Mn, Ni, Co with P and having a eutectic type graphite structure. CONSTITUTION:The eutectic type graphite is crystalized by using a method, etc., by which the austenite cast iron having comps. of 1.0-2.4% C, 1.0-2.4% Si, 0.1-1.0% Mn, 30.0-34.0% Ni, 2.0-6.0% Co, <=0.2% P and the balance Fe is cast into a metallic mold. In this way, the cast iron having improved machinability is obtd. without lowering tensile strength and low-heat expansivity.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to eutectic graphite cast iron suitable for machine parts that require low thermal expansion and high machinability. be.

(Prior art) Flake graphite or spheroidal graphite cast iron containing 34.0 to 36.0% nickel and having an austenite base is heat resistant.
Because it has excellent corrosion and abrasion resistance and low thermal expansion, it is used in the chemical industry, scientific equipment, and molds for glass components.

However, since this cast iron has an austenite base, it has poor machinability, making it difficult to obtain a smooth flat surface that meets the required dimensional accuracy, and shortening the tool life of cutting tools, making it difficult to apply to precision machine parts. There was a problem that it was difficult.

(Problems to be Solved by the Invention) The present invention was made to solve the above problems, and has low thermal expansion, mechanical properties, especially tensile strength, which are comparable to conventional products, and machinability. The purpose of this invention is to provide graphite cast iron with austenitic properties that have significantly improved properties.

[Constitution of the Invention (Means and Actions for Solving Problems) That is, the present invention consists of 1.0 to 2.4% carbon and 1.0 to 2.4% silicon.
, manganese 0.1-1.0%, nickel 30.0-34
．． 0% cobalt, 2.0 to 6.0% cobalt, 0.2% or less phosphorus, and the balance is iron. Compared to conventional austenitic cast iron, it is possible to obtain a low expansion cast iron that has dramatically improved tool life and finished surface roughness, and has significantly improved machinability.

The reason why the composition range of the free-cutting, low-expansion cast iron of the present invention is limited as described above will be explained below.

First, if the carbon content exceeds 2.4%, the coefficient of thermal expansion increases, and if it is less than 1.0%, shrinkage cavities, chills, etc. are likely to occur, and as a result, castability deteriorates, which is not preferable.

Therefore, carbon is limited to a range of 1.0 to 2.4%. Moreover, when silicon exceeds 2.4%, the coefficient of thermal expansion increases,
If it is less than 1.0%, the graphitization effect is insufficient and lithyl is likely to be generated, resulting in poor castability. Therefore, silicon is 1.0
~2.4%.

When the manganese content exceeds 1.0%, manganese segregation occurs and the coefficient of thermal expansion increases. Also, 0.1
%, the coefficient of thermal expansion becomes large. Therefore, manganese is limited to a range of 0.1 to 1.0%. Furthermore, the nickel content exceeds 34.0% or 30.0%
The nickel content is limited to 30.0% to 34.0% because the thermal expansion coefficient increases with less than 30%.

Next, if the cobalt content exceeds 6.0% or is less than 2.0%, the coefficient of thermal expansion also increases, so the cobalt content is limited to 2.0 to 6.0%.

Furthermore, if the phosphorus content exceeds 0.2%, highly hard steadite precipitates at grain boundaries, impairing machinability. Therefore, the phosphorus content is limited to 0.2% or less. When fine eutectic graphite is crystallized in the austenitic cast iron having the above composition, it acts as a lubricant and a source of microcracks during cutting, causing the austenite base to become superficial in appearance. As a result, it is possible to solve the conventional problems of austenite cutting, such as welding to tools and deterioration of finished surface roughness due to high ductility, and significantly improve tool life and machinability in terms of finished surface roughness. .

Methods for crystallizing this eutectic graphite include casting in a mold, casting by embedding chilled metal in a sand mold, and adding special elements such as sulfur and titanium.

(Example) Cast rods A-G (φ100×N 40
Table 1 shows the results of casting 0) and measuring the coefficient of thermal expansion at 0 to 50°C and 0 to 100°C.

Table 1 From Table 1, less than 1.0% carbon, less than 1.0% silicon,
and if carbon exceeds 2.4%, silicon 2.4%
%, it can be seen that the coefficient of thermal expansion increases in all cases.

Next, cast iron rods (φ100×
Table 2 shows the results of preparing β400)HR and measuring the thermal expansion coefficient at room temperature to 100°C.

Table 2 From Table 2, nickel is less than 30.0% or 34.0%
If it exceeds, cobalt is less than 2.0% or 6.0%
It can be seen that the coefficient of thermal expansion increases when the temperature exceeds .

Based on the previous results, composition E (2.2% carbon, 2.1% silicon, 1 manganese) has a smaller thermal expansion coefficient.
．． 0%, nickel 32.0%, cobalt 4.2%, phosphorus 0.07%).
), a total of four cast iron rods (φ100) made of eutectic graphite (c, d)
×N 400) and each at room temperature to 10
Table 3 shows the results of measuring the thermal expansion coefficient and tensile strength at 0°C.

Table 3 (b) shows the spheroidization treatment performed with the addition of 2.7% of the Fe-SFe-5if%Mg) alloy, and (C) and (d) use a chilled metal.

A eutectic graphite structure was obtained.

Table 3 shows that the cast irons of the present invention (C, d) have almost no difference in coefficient of thermal expansion and tensile strength compared to the conventional products (a, b).

As a result of conducting cutting tests on each of these cast iron bars under the following conditions, Figure 1 shows the relationship between cutting time and tool friction, Figure 2 shows the amount of tool wear for a constant cutting area of each cast iron bar, and the surface roughness curve. are shown in Figure 3.

Cutting conditions Tool K 20 (WC-Co based carbide material) Cutting speed 200 m/min Feed rate 0.4 mm/rev
Depth of cut: 2.0 mm In this Fig. 3, ■ is the cast iron rod (C) according to the present invention.
, ■ respectively show the case of the conventional cast iron bar (b).

From these figures, it is clear that the cast iron of the present invention has significantly improved machinability compared to conventional products.

[Effect of the invention] As is clear from the examples, by crystallizing eutectic graphite in austenitic low expansion cast iron, machinability can be significantly improved without reducing tensile strength and low thermal expansion. .

4. Brief explanation of the figures Figure 1 is a characteristic diagram showing the relationship between cutting time and tool wear amount for the present invention and the conventional example, and Figure 2 is for a constant cutting area (650cm).
J) A diagram showing the amount of tool wear on each cast iron bar when shaved. FIG. 3 is a diagram showing the surface roughness curves of the present invention and the conventional example.

Claims (1)

[Claims] Carbon 1.0-2.4%, Silicon 1.0-2.4%,
Manganese 0.1-1.0%, nickel 30.0-34.
0% cobalt, 2.0 to 6.0% cobalt, 0.2% or less phosphorus, the balance iron, and is characterized by having a eutectic graphite structure and having excellent machinability.