KR20010061818A - Low thermal expansion cast iron and manufacturing method thereof - Google Patents

Abstract

PURPOSE: Low thermal expansion compacted vermicular(CV) graphite cast iron free from chunky graphite in the structure and excellent in castability, mechanical properties and processability is provided, which improves a degree of precision and performance caused by acceleration when applied to a precision machine tool. CONSTITUTION: This low thermal expansion cast iron having a shape factor of graphite of 0.2 to 0.5 and compacted vermicular graphitization rate of 80% or more comprises 2.0 to 3.0% by weight of C, 1.52 to 2.5% by weight of Si, below 1.0% by weight of Mn, below 0.045% by weight of P, below 0.020 by weight of S, 34 to 35% by weight of Ni and 0.012 to 0.023% by weight of Mg.

Description

Low thermal expansion cast iron and manufacturing method

The present invention relates to a low thermal expansion cast iron material and a method for manufacturing the same, in particular, a cast vermicicular graphite cast iron-based low thermal expansion cast material and improved castability, mechanical stiffness, and workability that gray cast iron and nodular graphite iron can have at the same time It relates to a manufacturing method.

In general, where ultra-precision processing is required in the fields of precision measuring equipment, electronics, electrical, and semiconductor-related equipment, low thermal expansion materials with little deformation of materials due to thermal expansion are limited. Such low thermal expansion materials are mainly rolled as steel. Products and forgings have been mainly used, but in recent years, the use of casting materials has been increasing with the improvement of casting technology.

These low thermal expansion castings are largely divided into cast steel and cast iron. Cast steel has a smaller coefficient of thermal expansion and a higher tensile strength and elongation than cast iron, whereas cast iron contains a large amount of graphite, resulting in low thermal expansion and mechanical properties. While relatively inferior to cast steel, it has excellent castability, machinability, and dust absorption.

Gray cast iron and spheroidal graphite cast iron have been mainly used as cast iron-based low-expansion casting materials. Gray cast iron and cast iron have excellent castability and absorption, but the thickness reduction of the product is large. There was a problem that it is difficult to use where the rigidity of the material is required.

Table 1 shows the components and mechanical properties of the low-expansion casting of the gray cast iron and the nodular cast iron.

Chemical Composition and Properties of Materials division Chemical composition (wt%) Coefficient of linear expansion Mechanical property C Si Mn Ni Cr Cu T.S (N / mm2) Hardness (HB) Gray cast iron <2.50 1.0-2.0 0.5-1.5 34-36 <0.2 <0.5 4-6 > 120 120-140 Nodular Graphite Iron ≤2.40 1.5-3.5 - 34-36 <0.2 <0.5 4-6 > 370 130-180

As shown in Table 1, the gray cast iron system has a basic coefficient of linear expansion, which is the same as that of spheroidal graphite iron, but the tensile strength is greatly decreased.

Therefore, spherical graphite cast iron-based low thermal expansion casting materials have been developed and used in recent years. In this case, however, the graphite contained in spheroidal graphite iron is spheroidized, so that the strength is more than twice that of gray cast iron, but the thermal conductivity is relatively higher. Falling, there is a problem that casting defects such as shrinkage holes in the casting during casting.

In order to solve the above problems, the present invention relates to a low thermal expansion cast material and a method of manufacturing the same, which have improved castability, mechanical rigidity, and workability that gray cast iron and nodular cast iron cannot have at the same time.

Low thermal expansion cast iron material of the present invention for achieving the above object, C: 2.0-3.0wt%, Si: 1.5-2.5wt%, Mn: 0.1-1.0wt%, P: 0.045 or less, S: 0.020 or less, Ni: 34-36wt%, graphite's shape factor is 0.2-0.5, Mg content is 0.012-0.023wt%, and CV graphite is over 80%, Mo: 1.0-4.0 wt%, V: 1.0-5.0 wt%.

Here, CV graphitization rate means the ratio which CV graphite occupies among the area which all graphite occupies in a micrograph.

Ni in the alloying element has a large influence on the coefficient of thermal expansion, depending on the content of the alloy element, and is a basic or minimum requirements for low expansion castings.

In addition, the method for producing a low thermal expansion cast iron material for achieving another object of the present invention, the step of making the molten metal by charging pig iron, scrap iron and heating to 1500 ℃ or more,

Adjusting molten metal so that C: 2.0-3.0wt%, Si: 1.5-2.5wt%, Mn: 0.1-0.3wt%, P: 0.045wt% or less, S: 0.020wt% or less in the final composition,

After heating up to 1500-1600 ℃, the alloy was added so that the content of alloy element in the final composition was Ni: 34-36wt%, Mg: 0.012-0.023wt%, Mo: 1.0-4.0wt%, V: 1.0-5.0wt% Adding step,

Heating the predetermined alloy so that the added alloy element is in a molten state and then tapping it;

It characterized in that it comprises a CV and the inoculation step in the ladle at the time of tapping.

1 is a diagram showing a linear expansion coefficient curve of Ni-Fe alloy;

2 is a tissue photograph of an embodiment specimen of the present invention.

Hereinafter, with reference to the accompanying drawings, an embodiment of the present invention will be described in detail.

The low thermal expansion cast material of the present invention is a weight wt%, C: 2.0-3.0wt%, Si: 1.5-2.5wt%, Mn: 0.1-1.0wt%, P: 0.045 or less, S: 0.020 or less, Ni: 34- 36wt%, the graphite has a shape coefficient of 0.2-0.5, the content of Mg to make the CV graphitization ratio of 80% or more is 0.012-0.023wt%, Mo: 1.0-4.0wt%, V: 1.0-5.0 wt%.

Ni in the alloying element has a large influence on the coefficient of thermal expansion, depending on the content of the alloy element, and is a basic or minimum requirements for low expansion castings.

Figure 1 shows the coefficient of linear expansion of the Fe-Ni alloy, the adjustment of the Ni component is important, even if the Ni component is adjusted to the minimum sufficient condition, the adjustment of the C and Si values, which are the basic elements of cast iron, also affects the coefficient of linear expansion. C: 2.0-3.0wt%, Si: 1.5-2.5wt% because it is crazy, the reason is as follows.

C increases the coefficient of linear expansion as its amount is increased than when no addition is made. This is because the effective distribution coefficient of Ni becomes larger than 1 by the addition of C, and Ni is easily dissolved in primary austenite, causing segregation of Ni.

Therefore, in the present invention, the amount of C is limited to 2.0wt% or more in terms of securing fluidity and vibration damping performance of the molten metal, and the amount of C is lowered to 3.0wt% or less since the dissolved carbon decreases in 3.0wt% or more. .

Si acts as an element for promoting graphitization and even serves as a slight deoxidation.

However, the increase in Si is also accompanied by an increase in the coefficient of thermal expansion, limiting the 1.5wt% -2.5wt% range that gives a minimum loss of the coefficient of thermal expansion within the good castability.

When Mn is added 1wt% or more, the coefficient of thermal expansion is increased, so it is limited to less than 1wt%. In this composition, only the amount required for the reaction with S is added.

Mo inhibits graphitization and promotes carbide generation, but does not affect the coefficient of thermal expansion so much. Mo is added in parallel with V in terms of increasing the hardness.

Like Mo, V is an element that promotes carbide generation, and at the same time, segregates into a liquid phase during solidification, thereby inhibiting growth of the process cell, thereby increasing the number of process cells and increasing hardness.

The component values which obtain maximum hardness by adding V and Mo simultaneously are V: 1-5wt% and Mo: 2-4wt%.

The component range proposed in the present invention is set to have a required hardness value without significantly lowering the coefficient of thermal expansion, and a method for producing a low thermal expansion cast material having a range of the above components will be described below.

That is, charging the pig iron, scrap iron and heating to 1500 ℃ or more to make a molten metal,

Adjusting molten metal so that C: 2.0-3.0wt%, Si: 1.5-2.5wt%, Mn: 0.1-0.3wt%, P: 0.045wt% or less, S: 0.020wt% or less in the final composition,

After heating up to 1500-1600 ℃, the alloy was added so that the content of alloy element in the final composition was Ni: 34-36wt%, Mg: 0.012-0.023wt%, Mo: 1.0-4.0wt%, V: 1.0-5.0wt% Adding step,

Heating the predetermined alloy so that the added alloy element is in a molten state and then tapping it;

When the above-mentioned tapping ladle is subjected to CV treatment, at this time, a Ca-Si-based CVing agent of less than 2.5 wt% of rare earth metal (REM) is ladle-treated at a temperature of 1370-1400 ° C, and then Fw-Si-based inoculant is added. The low thermal expansion cast iron is manufactured through a casting step including an inoculation step.

EXAMPLE

Charge the pig iron and scrap metal and heat it to 1500 ℃ or above to make the molten metal, adjust the components of the molten metal as in the final composition as shown in Table 2, heat it to 1500-1600 ℃, and then Ni: 34.5wt%, Mg: 0.02wt %, Mo: 2.18wt%, V: 2.34wt% The alloy was added and heated again so that the added alloy element is molten state.

In addition, CV lamination and inoculation were performed in the ladle at the time of tapping.

Chemical composition division C Si Mn P S Mg Ni Mo Cu V Content (wt%) 2.01 2.29 0.34 0.030 0.019 0.02 34.5 2.18 0.03 2.34

Specimen measured mechanical properties according to the examples of the chemical composition as shown in Table 2 was used 1-inch-Y block, the shape coefficient of graphite was used for the image analyzer (Image-Analizer).

Mechanical properties Tensile Strength (N / ㎡) Elongation (wt%) Hardness (HB) Coefficient of linear expansion Test piece 340 8.4 157 4-6 1 inch Y block

As a result of analyzing the structure in the product cast from the component element of this example, a good CV low thermal expansion casting material having a CV graphitization rate of 80% or more and a shape coefficient of graphite of 0.40-0.50 was obtained.

As such, the present invention is an excellent material having castability, mechanical rigidity, and processability that existing gray cast iron and spheroidal graphite cast iron-based low-expansion castings cannot have. You can expect a performance improvement.

Claims (3)

C: 2.0-3.0wt%, Si: 1.52-2.5wt%, Mn: 1.0wt% or less, P: 0.045 or less, S: 0.020 or less, Ni: 34-35wt% and Mg content is 0.012-0.023wt% A low thermal expansion cast iron, characterized in that the graphite has a shape coefficient of 0.2-0.5 and a CV graphitization rate of 80% or more. The low thermal expansion cast iron according to claim 1, further comprising Mo: 1.0-4.0wt% and V: 1.0-5.0wt% to improve hardness. Charging pig iron and scrap metal and heating it to 1500 ℃ or more to make a molten metal, Adjusting molten metal so that C: 2.0-3.0wt%, Si: 1.5-2.5wt%, Mn: 0.1-0.3wt%, P: 0.045wt% or less, S: 0.020wt% or less in the final composition, After heating up to 1500-1600 ℃, the alloy was added so that the content of alloy element in the final composition was Ni: 34-36wt%, Mg: 0.012-0.023wt%, Mo: 1.0-4.0wt%, V: 1.0-5.0wt% Adding step, Heating the predetermined alloy so that the added alloy element is in a molten state and then tapping it; The method of manufacturing a low thermal expansion cast iron material, characterized in that comprising the step of performing the CV treatment and inoculation treatment in the ladle at the time of tapping.