JPH036216B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is based on high nickel cast iron, and contains carbon,
This invention relates to an austenitic cast iron with a low thermal expansion coefficient that is lower than that of conventional high nickel low thermal expansion cast irons by limiting the silicon content to a certain range. [Conventional technology] Conventionally, ASTM-A436 was used as a low thermal expansion cast iron.
Type 5 and ASTM-A439 type D5 are known. The average coefficient of thermal expansion α of these low thermal expansion cast irons is 20
At a temperature of ~100℃, it is about 1/2 to 1/2 that of ordinary cast iron or ordinary steel.
3 (α=5 to 6×10 ^-6 /°C), and has been used for the purpose of suppressing thermal displacement. However, this method is insufficient to meet the demand for high precision in the field of application of low thermal expansion cast iron, and there has been a desire for a material with an even lower coefficient of thermal expansion. In contrast, the low thermal expansion cast iron disclosed in Japanese Patent Publication No. 60-51547 contains 0.8 to 3.0% carbon and 1.0 to 3.0% silicon.
%, Nickel 30.0-34.0%, Cobalt 4.0-6.0%,
Manganese 2.0% or less, sulfur 1.0% or less, phosphorus 1.5%
The following discloses an austenitic low thermal expansion cast iron consisting of 1.0% or less of magnesium and the remainder of iron containing impurities. However, this low thermal expansion cast iron is extremely expensive and contains cobalt, whose supply is highly unstable, and while a low thermal expansion coefficient can be achieved, there is a problem in that it is accompanied by high costs. [Problems to be Solved by the Invention] The purpose of the present invention is to provide an austenitic cast iron having a coefficient of thermal expansion even lower than that of the conventional low thermal expansion cast iron described above, which does not contain any cobalt and at the same price as the conventional low thermal expansion cast iron. That is. [Means for solving the problems] The present invention provides C: 0.6 to 1.4% on a weight basis;
Si: 0.5-1.0%, Mn: 1.0% or less, Ni: 34.0-36.0
%, S: 0.5% or less, P: 0.5% or less, Mg or Ca
A low-heat product characterized by being made of iron containing 0.05 to 0.5% of one or two of the above, and the remainder containing inevitable impurities, with a C and Si content within the range of the following formula (C + 0.4 x Si) ≦ 1.6%. It is expanded cast iron. [Effect] The mechanism of the low coefficient of thermal expansion in alloys such as low thermal expansion cast iron is explained by the fact that the spontaneous magnetization strain that occurs at temperatures below the magnetic transformation point in ferromagnetic alloys cancels out the thermal vibrations of the lattice. Among steel materials, Invar (Amber) and Super Invar (Super Invar) have been put into practical use, and their coefficient of thermal expansion α is 0 to 1.5×10 ^-6 /
very small in °C. On the other hand, the coefficient of thermal expansion α of 35% nickel cast iron is 5 to 6×10 ⁻⁶ /°C, which is quite different from that of steel-based materials with low coefficient of thermal expansion. Since the structure of graphite cast iron is a mixed structure of a low carbon austenite base and graphite, the present inventors focused on the influence of the base composition on the coefficient of thermal expansion α, and achieved the present invention. That is, the solid solubility of carbon in austenite containing around 35% nickel is originally supposed to be 0.2% or less. (Metals Handbook 8th edition vol.8, P413)
On the other hand, the inventor has developed a method using 0.2% carbon and nickel.
As a result of measuring the thermal expansion coefficient α of cast steel containing 36%, α
= 2.4×10 ^-6 /°C was obtained. Using this value, calculate the coefficient of thermal expansion α of cast iron with 2% total carbon, (1.8% graphite), and 36% nickel using the following formula:
α = [α of base] × [volume ratio of base] + [α of graphite] ×
The following formula for [volume ratio of graphite] is [α of base] α _M =2.4×10 ^-6 /℃ [volume ratio of base] V _M =0.94 [α of graphite] α _G =8.0×10 ^-6 /℃ [Volume ratio of graphite] V _G = 0.06, and α is calculated by substituting them respectively: α = 2.7×10 ^-6 /℃
The value was approximately 1/2 of the actual α. From this result, it was considered that the base of conventional low thermal expansion cast iron contained 0.2% or more of carbon.
This invention was made based on the knowledge that in the above-mentioned 36% nickel cast steel, when the solute carbon increases by 0.1%, α increases by about 0.6×10 ^-6 /°C. When the amount of carbon in the base was measured using a scanning electron microscope (EPMA), it was confirmed that approximately 0.4% of carbon was dissolved in solid solution. When calculated using this value, α=3.9×10 ⁻⁶ /°C, which is close to the actual value, but the calculated value is still smaller than 1.0×10 ⁻⁶ /°C. As the cause of this, we focused on silicon, which is added in large amounts in cast iron, and investigated the relationship between the amount of silicon and α.As shown in the example below, when silicon increases by 1%, α becomes approximately 1.3×10 ^-6 / It was found that ℃ increases. From the above experiments and considerations, we found that the first
As shown in the figure, it was found that a lower coefficient of thermal expansion than conventional low thermal expansion cast iron could be obtained by lowering the total carbon content, reducing the amount of carbon in the matrix, and limiting the amount of silicon added. That is, the low thermal expansion cast iron of the present invention described above has a
An average coefficient of thermal expansion α3.0 to 4.0×10 ⁻⁶ /°C at 50°C is obtained. Next, the reasons for limiting the components of the low thermal expansion cast iron of the present invention will be described. C: When carbon is dissolved in the austenite base, the coefficient of thermal expansion α will significantly increase, but by precipitating it as graphite, machinability and castability can be improved compared to cast steel. If it is less than 0.6%, the amount of graphite is small;
Machinability approaches that of cast steel Invar, and manufacturing becomes difficult due to increased melting temperature. If it exceeds 1.4%, the desired low coefficient of thermal expansion cannot be obtained, so the range is set at 0.6 to 1.4%. Si: If silicon is less than 0.5%, the solubility of carbon in the base increases, and the effect of reducing the low coefficient of thermal expansion α is lost.
If it exceeds 1.0%, the desired low coefficient of thermal expansion cannot be obtained, so the range is set at 0.5 to 1.0%. Furthermore, even if the quantitative ratio of carbon to silicon is within the above range, as shown in the scope of the invention in FIG.
If the content of C and Si exceeds (C+0.4×Si)=1.6%, a low coefficient of thermal expansion cannot be obtained.
×Si) = 1.6%. 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 cannot be ignored, so it was set to 1.0% or less. Ni: Nickel is the element that most affects the thermal expansion coefficient α, and if it is less than 34.0% and exceeds 36.0%, the thermal expansion coefficient α will significantly increase, so it was set to 34.0 to 36.0%. Mg, Ca: Magnesium or calcium is added to make graphite spheroidal, thereby improving mechanical properties. For this purpose
It is necessary to add 0.05 to 0.5% of one or both of Mg and Ca. P, S: Phosphorus and sulfur are elements that are inevitably mixed in, and if they exceed 0.5%, embrittlement will be significant.
It was set to 0.5% or less. The remainder consists of iron containing unavoidable impurities. Next, examples of the present invention will be described. [Example] Example 1 Materials with the composition shown in Table 1 were melted in a 30KVA high-frequency electric furnace, and a JISG-5122B test piece was cast in a CO ₂ silica sand mold to form a test piece for thermal expansion coefficient measurement of φ9 x L50mm. was processed, and the coefficient of thermal expansion α from 20 to 200°C was measured using a differential thermal expansion meter. For mechanical properties, 0.2% proof stress, tensile strength, and elongation were measured using a high-temperature tensile test piece (parallel part φ10) according to JISG-0567. Table 1 shows the composition and test results, and FIG. 1 shows a graph of the relationship between the carbon and silicon compositions and the coefficient of thermal expansion α.

【table】

[Table] * Shows the amount added.
** Quartz (+0.5×10 ⁻⁶ /℃) corrected calculated value The material of the present invention has a thermal expansion coefficient α of 3.0 to 3.7×10 ⁻⁶ /
℃, approximately 3/4 to 3/4 of conventional high nickel low thermal expansion cast iron
1/2, and a very low coefficient of thermal expansion was obtained. No. 1 exhibits a coefficient of thermal expansion α similar to that of No. 9 containing cobalt, and has the advantage of being low cost and having a coefficient of thermal expansion α comparable to that of cobalt-containing materials. In addition, the mechanical properties are almost at the same level as conventional low thermal expansion cast iron, and no special considerations regarding material strength are required. No. 3 is 1.9×10 ^-6 / lower than conventional low thermal expansion cast iron.
℃ small thermal expansion coefficient α and 0.2% yield strength 5Kgf/
mm ² or higher, which is advantageous in actual use. Example 2 A solid casting as shown in FIG. 2 was manufactured with the composition shown in Table 2 according to Example 1, test pieces were cut out from each position as shown in FIG. 2, and subjected to thermal expansion according to Example 1. The rate α was measured and the results shown in Table 3 were obtained. Figure 2 is an explanatory diagram of the actual casting shape and test piece collection locations, where the values in parentheses ( ) indicate dimensions and the others indicate collection locations. The casting temperature is 1515℃ for No.10 and 1550℃ for No.11.
Castability was good and no problematic defects were observed.

【table】

〔Effect of the invention〕

By applying the low thermal expansion cast iron of the present invention to important parts of various precision machines, such as machine tools, measuring instruments, semiconductor manufacturing equipment, optical machinery, etc., it can be used at the same cost as conventional high nickel cast iron with a low thermal expansion coefficient, and at a higher cost. Excellent high precision can be obtained, and the effects on related fields will be immeasurable.

[Brief explanation of the drawing]

FIG. 1 is a graph of the relationship between the carbon and silicon compositions and the coefficient of thermal expansion α in Examples, and FIG. 2 is an explanatory diagram of the solid casting shape and the sampling position of the test piece.

Claims (1)

[Claims] 1. On a weight basis, C: 0.6 to 1.4%, Si: 0.5 to 1.0
%, Mn: 1.0% or less, Ni: 34.0 to 36.0%, S: 0.5
% or less, P: 0.5% or less, 0.05 to 0.5% of one or both of Mg or Ca, and the remainder consists of iron containing inevitable impurities, and the content of C and Si is as follows: (C + 0.4 × Si) ≦ Low thermal expansion cast iron characterized by a range of 1.6%.