JPS63162841A - Free cutting alloy having low thermal expandability - Google Patents

Abstract

PURPOSE:To improve the machinability and castability of an iron alloy and to reduce the thermal expandability, by specifying the amts. of C, Si, Mn, Ni, Co, Mg, S and P in the alloy and uniformly dispersing a proper amt. of graphite in the matrix. CONSTITUTION:The compsn. of an alloy is composed of, by weight, 0.2-0.8% C, <1.0% Si, <=1.0% Mn, 30.0-34.0% Ni, 4.0-6.0% Co, <=0.5% Mg, <=0.5% S, <=0.5% P and the balance Fe with inevitable impurities. The matrix structure of the alloy is that of low carbon Super invar and contains about 1vol% uniformly and finely distributed graphite. Since the alloy has high machinability and low thermal expandability, it can be used to manufacture various precision instruments.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a low thermal expansion alloy that has excellent free machinability and is low cost, suitable for use in precision mechanical parts that require low thermal expansion. It is something.

[Prior Art] Among the practical metal materials currently used for the purpose of low thermal expansion, Super Invar and Invar are
The coefficient of thermal expansion α in the temperature range is 2.0×10/° C. or less, and it has the property of having very little thermal expansion.

These are mainly formed by plastic working and are supplied as materials such as wires, plates, and rods.

Therefore, a lot of machining is required to make a finished part, but the machinability is low and the cost is high, so the scope of use is limited.

The reason why Super Invar and Invar have low machinability is 1.
) This is thought to be due to heat generation due to high cutting resistance, 11) short tool life, 111) poor chip disposal, and iv) easy work hardening.

As a means to solve this problem, S, Ca, Pb.

Although materials have been provided that have free machinability by adding Zr, Se, etc., they have the disadvantages of lowering mechanical properties, increasing coefficient of thermal expansion, and complicating the manufacturing method. .

On the other hand, in the 1980s, special public interest was given to Super Invar, which gave it castability.
The material described in Publication No. 51547 and ASTM, A-438, Type 5, A-439, Type D-5, etc., which are also invar with castability, produce graphite in the structure during the solidification process, so super invar and Cutting performance is improved compared to Invar bow, but 3.0X10/
It is accompanied by an increase in the coefficient of thermal expansion around C, and is insufficient for applications requiring even higher precision.

[Problems to be Solved by the Invention] The present invention solves the aforementioned problems of Super Invar, Invar, and low thermal expansion cast iron, etc., namely: 1) In Super Invar and Invar, I) Low machinability it) Limitations on the shape of the material be.

2) High thermal expansion coefficient in low thermal expansion cast iron.

It is an object of the present invention to provide a low thermal expansion alloy that is excellent in all aspects of free machinability, thermal expansion property, and castability.

[Means for solving the problems] The present invention provides, on a weight basis, C: 0.2% or more and less than 0.8%, Si: less than 1.0%, Mn: 1°0% or less, Ni
:30.0~34.0%, Co:4.0~6.0%, M
g: 0.5% or less, S: 0.5% or less, P: Q, 5
It is a free-machining, low-thermal-expansion alloy characterized by being made of iron, with the remainder containing unavoidable impurities.

[Function] The present invention has discovered the optimum composition range and heat treatment conditions in order to achieve both free machinability and low thermal expansion.

That is, by using low carbon Super Invar as the base structure and achieving a state in which an appropriate amount of graphite is uniformly distributed, free machinability and low thermal expansion properties can be obtained at the same time.

Usually, cast iron contains 2 to 4% carbon by weight, and carbon that exceeds the solid solubility of carbon in the matrix is precipitated as graphite.

For example, ASTM, A-439, T, which is a low thermal expansion cast iron.
In ypeD-5, the volume fraction of graphite is approximately 4 to 7%.

This material has improved machinability compared to Super Invar and Invar, but this is due to the graphite present in the structure, which reduces the contact resistance with the tool and allows chips to be broken into thin pieces without joining. It's for a reason.

As a result of investigating the relationship between machinability and graphite volume fraction, the present inventor found that the graphite volume fraction required to improve machinability is about 1%, and that it is sufficient to distribute it uniformly and finely. Ta.

The findings obtained are as follows. That is, 1) In conventional low thermal expansion cast iron, graphite is present in an amount more than necessary for free machinability, which causes deterioration of finished surface accuracy and appearance.

2) Also, in terms of thermal expansion characteristics, the presence of excessive graphite slightly increases the thermal expansion coefficient α.

3) Furthermore, excessive carbon content promotes supersaturated solid solution of carbon into the matrix, causing an increase in the coefficient of thermal expansion α. In other words, when the solute carbon increases by 0.1%, the thermal expansion coefficient α increases by 0.6.
When the amount of graphite increases by 1%, the thermal expansion coefficient α increases by about 0.05X 10/'C.

4) Furthermore, at the carbon concentration of the present invention, silicon = 6 silicon has a thermal expansion coefficient α of 1.3 XIO/ 1%.
C increases.

5) Also, as a means to reduce the thermal expansion coefficient α, 600
What is necessary is just to carry out the rapid cooling treatment from a temperature of ~1000°C.

In other words, when heated and rapidly cooled to the above temperature, the supersaturated carbon in the base precipitates as fine graphite, reducing the carbon content in the base, and the micro-segregation of nickel is relaxed, increasing the coefficient of thermal expansion α. Quantification using a scanning electron microscope revealed that this was due to the decrease in size.

Next, the reasons for limiting the components of the low thermal expansion alloy of the present invention will be described.

C: Since carbon is dissolved as a solid solution in the matrix of this type of alloy up to about 0.2%, it is necessary to contain 0.2% or more, which is the solid solubility limit, in order to obtain graphite, which is a free-cutting material. Carbon also lowers the melting temperature,
Improves castability. If it exceeds 0.8%, the improvement in free machinability will reach a plateau, and the amount of solid solution of supersaturated carbon will increase, increasing the coefficient of thermal expansion α, so it is set to be 0.2% or more and less than 0.8%.

Si: Silicon is an element added to improve castability and deoxidize, but if it exceeds 1.0%, the increase in the coefficient of thermal expansion α cannot be ignored, so it is set to less than 1.0%.

Mn: Manganese tends to cause segregation and promotes the formation of carbides, leading to an increase in the coefficient of thermal expansion α.If it exceeds 1.0%, the effect is significant, so this value was set as the upper limit.

Ni: Nickel is the element that has the greatest effect on the coefficient of thermal expansion α, and even if the amount of cobalt is adjusted, it will still be less than 30%, and if it exceeds 34%, the coefficient of thermal expansion α will increase significantly, so it will be 30.0 to 3.
The range was set at 4.0%.

co=cobalt has a nickel content of 30.0 to 34.0%
When the combination is less than 4% and more than 6x, the thermal expansion coefficient α increases, so the range is set to 480 to 8.0%.

Mg: In the composition of the present invention, even without adding a spheroidizing agent, the graphite forms a dot-like independent distribution, but is added when spheroidizing is desired to improve mechanical properties.

For that purpose, if it exceeds 0.5X, the cleanliness deteriorates, so the amount was set to 0.5% or less.

P, S: Phosphorus and sulfur are elements that are unavoidably mixed, and if they exceed 0.5%, embrittlement is significant, so the amount of each is set to 0.5% or less. ``The remainder consists of iron containing unavoidable impurities.

Next, examples of the present invention will be described.

[Example] A sample material having the chemical composition shown in Table 1 below was melted in a 30 KVA high-frequency electric furnace, and was melted in a COL silica sand mold according to JIS
G-51228 test piece and furan silica sand mold, φ1
Processed specimens of 00 x (200 to 400) + mm were cast.

φ7.5 +mm
was measured using a push rod type thermal dilatometer, and the results of the thermal expansion coefficient shown in Table 2 were obtained.

Inventive alloys 1 to 4 were tested in the annealed state -&4. OXIO/”C, 1.5 XIO/ in quenched state
It showed a coefficient of thermal expansion smaller than 'C.

Furthermore, if an appropriate composition is selected within the alloy composition range of the present invention, the coefficient of thermal expansion α<1 can be achieved, which is comparable to super invar cast steel thread.
．． It was found that OXIO/'C was obtained.

il, it Chemical composition of the sample material (wt%) Table 2 Coefficient of thermal expansion a (20-100°C average We investigated each of these.

Figures 1 and 2 are metallurgical micrographs showing the microstructures (X100) of a conventional material and an alloy of the present invention as comparative materials, respectively. It is clear that the distribution is uniform.

Figure 3 is a metallurgical micrograph of the microstructure of a cross section of a chip, showing that the workpiece structure flows due to the force of the tool, and as a result, the graphite stretches, forming a sharp notch and improving chip disposal. I understand.

Figure 4 shows the cutting speed (m) of the present invention alloy and the conventional comparative material.
Figure 5 is a graph showing the relationship between the cutting force (kg/m♂) and specific cutting force (kg/m♂).
This is a graph showing the relationship between tool life (m/min) and tool life, and it is clear that the properties of the alloy of the present invention are excellent.

[Effects of the invention] By applying the free-machining, low thermal expansion alloy of the present invention to various precision machines, such as machine tools, measuring instruments, semiconductor manufacturing equipment, optical machines, etc., Super Invar and Invar, which were conventionally used, can be improved. In this field, the same precision can be obtained at a much lower cost, and the effects of the present alloy on the related fields are immeasurable.

[Brief explanation of the drawing]

Figures 1 and 2 are metallurgical micrographs showing the microstructures of a conventional material and the alloy of the present invention as comparison materials, Figure 3 is a metallurgical micrograph of a cross section of a chip, and Figure 4 is a comparison of the alloy of the present invention and the conventional alloy. Cutting speed with material (m7 min) and specific cutting force (kg/
t+♂) FIG. 5 is a graph showing the relationship between cutting speed (m7 minutes) and tool life between the alloy of the present invention and a conventional comparative material.

Claims (1)

[Claims] Based on weight, C: 0.2% or more and less than 0.8%, Si:
Less than 1.0%, Mn: 1.0% or less, Ni: 30.0~
34.0%, Co: 4.0-6.0%, Mg: 0.5%
Hereinafter, a free-machining, low thermal expansion alloy characterized by comprising iron containing 0.5% or less of S, 0.5% or less of P, and the remainder containing unavoidable impurities.