JPS61133360A - Spheroidal graphite cast iron for metallic mold - Google Patents

Abstract

PURPOSE:To provide spheroidal graphite cast iron giving a metallic mold having a fine appearance and satisfactory mechanical characteristics by specifying the contents of C, Si, Ni, Cu, Mo and Mg and regulating the carbon equiv. CONSTITUTION:This spheroidal graphite cast iron for a metallic mold consists of, by weight, 2.8-3.8% C, 1.5-3.0% Si, (C+1/3Si=3.8-4.3%), 4.5-6.0% Ni, 0.3-2.5% Cu, 0.2-1.0% Mo, 0.02-0.07% Mg and the balance Fe with inevitable impurities. The spheroidal graphite cast iron does not contain spheroidal graphite of >100mum maximum grain size by the graphite grain refining effect of Ni and Cu, and the average grain size of graphite is <=60mum. The average grain size of graphite in a casting surface is reduced to <=30mum by a rapid cooling effect produced by contact with the surface of a casting mold. When a metallic mold made of the cast iron is used, a thick-walled casting having a smooth surface and high dimensional accuracy is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to spheroidal graphite cast iron suitable for forming molds.

(Prior Art) Molds whose main body is made of cast iron are used for press molds, rubber molds, and the like because of their good castability. Among cast products, spheroidal graphite cast iron has excellent mechanical properties, so its use as molds has expanded, but as the thickness of the cast product increases, crystallized graphite grows and becomes coarse. This has the disadvantage that good surface properties cannot be obtained because of the oxidation.

(Problems to be Solved by the Invention) Here, as a means of refining graphite, methods such as examining inoculation conditions and quenching by using a mold with good thermal conductivity are used, but these methods In addition to requiring advanced production techniques, in thick-walled castings, graphite can only be refined in the surface layer, and graphite grains become coarser inside the casting where cooling is slow, resulting in poor appearance and mechanical properties of the machined surface. It had the disadvantage of having a negative impact.

Further, casting molds mainly made of cast steel have the disadvantage that it is difficult to cast molds with good dimensional accuracy because steel has a large shrinkage rate when solidified.

The purpose of the present invention is to eliminate the above-mentioned drawbacks, and also to easily obtain fine spherical graphite even in thick-walled cast products, so that the surface is smooth, the dimensional accuracy is good, and the mechanical properties are excellent. The present invention aims to provide spheroidal graphite cast iron for molds.

(8!Means to solve I point) The present invention is C2.8 to 3.8% by weight.

5i 1.5-3.0%, Ni 4.5-6.0%,
Cue, 3-265%, Mo0.2-1.0%, MO
0.02 to 0.07%, the balance consisting of Fe and unavoidable impurities, and the carbon equivalent (C++Si) is 3.8 to 4.3%
It is characterized by consisting of, preferably,
The particle size of the spherical graphite particles distributed on the casting surface is 30 μm.
or less, and in areas other than the casting surface, the average graphite particle size is 60 μm or less, and the maximum graphite particle size is 100 μm.
m or less.

(Function) The effect of refining the graphite grains of the spheroidal graphite cast iron in the present invention is largely due to its composition, and a detailed explanation thereof will be given below.

C and 3i are included in general cast iron, but if the CI is less than 2.8%, the amount of volumetric shrinkage during solidification will be large, making it impossible to obtain good dimensional accuracy as a mold. 2.8% or more, and if it exceeds 3.8%,
Since primary crystal graphite is generated during solidification and easily becomes coarse, the C content was set at 8 to 3.8%.

Next, regarding 3i, if it exceeds 3.0%, it will promote the generation of primary crystal graphite, so it should be 3.0% or less, and if it is less than 1.5%, the processability will deteriorate due to the generation of chill, so 1 .5
% or more. Roughly speaking, if the value of carbon equivalent (C%++Si%) in the relationship between C and the amount of 3i is less than 3368, good dimensional accuracy of the mold cannot be obtained due to an increase in the freezing point and an increase in the solidification temperature range. If it exceeds 4.3, good surface properties cannot be obtained due to generation of primary graphite and coarsening (C% + s + %) -3.8 to 4.3.

Next, Ni and CIJ are elements whose contents play a very important role in the refinement of graphite grains and mechanical properties. Figure 1 is a graph showing the effect of the addition of Ni and Cu on graphite particle size.
This figure shows the results of measurements taken from Miku 0111 in the center of the casting after casting and as-casting. As shown in Figure 1, when Ni is contained at the same time as Cu, especially in thick-walled cast products with a slow solidification rate, Ni exhibits a remarkable graphite refining effect when the Ni content is 4.5% or more, and it is most excellent when the Ni content is 10% or more. becomes.

However, if Ni exceeds 6%, martensite increases in the structure in the as-cast state, impairing workability as a mold, so the Ni content was set at 4.5 to 6%. C
Regarding u, as shown in Figure 1, it is an element that promotes the graphite refining effect of N1, but if Cu is less than 0.3%, the effect is small (and if it exceeds 2.5%, it will precipitate at grain boundaries). Cu0.
It was set at 3 to 2.5%.

Although MO itself does not affect the particle size of graphite, the above-mentioned C and S+.

By adding 0.2 to 1% MO to the composition of Ni and Qu, it has the effect of converting the base structure into a bainite structure under slow cooling conditions after casting, and this bainite formation makes it difficult to use as a mold. It has good mechanical properties. Here, if MO is less than 0.2%, the effect of bainiticization cannot be obtained, and if it exceeds 1%, carbides are likely to be formed and workability is deteriorated.
It was set to 0%.

Ma is a graphite spheroidizing element, and was set at 0.02 to 0.07% as in usual spheroidal graphite cast iron.

In the spheroidal graphite cast iron material with the above composition, there is no spheroidal graphite with a maximum graphite particle size exceeding 100 μm due to the aforementioned graphite grain refining effect of Ni and Cu, regardless of casting conditions, casting size, and shape. The average graphite particle size is 60 μm or less, and the average graphite particle size is 30 μm or less on the casting surface due to the quenching effect caused by contact with the mold surface. It goes without saying that the above graphite particle size can be further reduced by improving the inoculation method, downsizing the casting, and using a mold with good thermal conductivity. Here, for example, if the Ni or Cu content is lower than the predetermined value mentioned above, the growth and coarsening of spheroidal graphite will occur, and if the graphite particle size on the casting surface exceeds 30 μm, the surface smoothness will deteriorate. However, it becomes difficult to obtain a good molding surface. Furthermore, if the maximum graphite particle size inside the casting exceeds 100 μm or the average graphite particle size exceeds 60 μm, not only the appearance of the machined surface will deteriorate, but also the mechanical properties will deteriorate.

In the mold obtained by casting the spheroidal graphite cast iron shown above, the spheroidal graphite particle size does not change at all even after heat treatment such as quenching, tempering, annealing, etc., and the spheroidal graphite grain size is distributed on the casting surface. Since the particle size is 30 μm or less, 1. It has a better casting surface than conventional cast iron molds, and the internal graphite grain size is less than 100 μm at maximum, and less than 60 μm on average, and the structure is bainitic, resulting in good machined surface appearance and mechanical properties. It is something that you have. Also, unlike steel, spheroidal graphite cast iron
Since the shrinkage rate during solidification is small, it can be cast with high dimensional accuracy.

A specified amount of high-purity pig iron, extremely mild steel, electrolytic Ni, electrolytic copper, Fe
- After melting Mo and Fe-8i using a high frequency furnace, N
r-Ma and)-e-8i, the composition shown in Table 1 No. 1 to 6 (No. 1.2 in the present invention)
The non-alloyed spheroidal graphite cast iron shown in No. 7 and the cast steel shown in No. 8 were cast using a ceramic mold to obtain a mold each having a cavity of 300 mm x 600 m5 x lo G-1. Ta. Here, for Nos. 1 to 7, the casting temperature was 1300°C.

For N008, the casting temperature was 1530°C, the casting weight was approximately 600 kg, and the average wall thickness was 150 mm, and the dimensions of the mold were determined in consideration of the dimensional shrinkage rate of each casting so that a casting having a cavity with the above dimensions could be obtained. be.

The average graphite grain size and the internal maximum graphite grain size in the surface layer and inside of these molds, the surface roughness when the as-cast surface of the mold molding surface is polished to No. 3000, and the dimensional accuracy in the longitudinal direction of the capacity. and tensile strength, elongation.

As is clear from Table 2, mold No. 1 according to the present invention
．． 2 is a general spheroidal graphite cast iron mold (No.

Since the graphite grains are finer compared to 7), the surface smoothness is much improved and it has a good appearance.Furthermore, the mechanical properties of the as-cast layer are also improved because the base structure is a bainite structure. Together they are good. It also exhibits extremely high dimensional accuracy compared to general cast steel.

However, in the case where Ni and Qu are out of the composition range of the present invention (No. 3, 4), the graphite grain refinement effect decreases, so the graphite grains become coarse and the surface smoothness is not only inferior. The stability of dimensional shrinkage rate and mechanical properties are also slightly degraded. In addition, when the amount of C and Si deviates to the upper limit side of the composition range of the present invention (No, 5), it shows the same tendency as N'o, 3.4 due to the presence of coarse primary graphite, and it deviates to the lower limit side. In the case (No. 6), good dimensional accuracy cannot be obtained due to deterioration of castability due to the increase in melting point.

Although the casting mold according to the present invention has good mechanical properties even in the as-cast state, the mechanical properties can be further improved by heat treatment such as surface hardening such as fire hardening, quenching, or tempering. Needless to say.

(Effects of the Invention) As is clear from the above explanation, the spheroidal graphite cast iron of the present invention is a suitable material for molds produced by casting, and even in thick-walled cast products, the spheroidal graphite particle size in the surface layer portion By easily reducing the diameter to 30 μm or less, a molded surface with extremely high smoothness can be obtained.

Furthermore, since molds with good mechanical properties and dimensional accuracy can be obtained by casting, they have properties comparable to molds machined from alloy steel, and the cost and lead time can be significantly reduced, especially for large molds. Molds can be easily obtained, and this contributes greatly to the development of the industry.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the effect of adding Ni and Cu on graphite particle size.

Claims (1)

[Claims] 1. C2.8-3.8% in weight percent, Si1.
5-3.0%, Ni4.5-6.0%, Cu0.3-2
．． 5%, Mo0.2-1.0%, Mg0.02-0.0
7%, the balance consisting of Fe and unavoidable impurities, (C+
Spheroidal graphite cast iron for molds, characterized in that 1/3Si) is 3.8 to 4.3%. 2. The spheroidal graphite cast iron for molds according to claim 1, wherein the average particle size of the spheroidal graphite is 60 μm or less, and the maximum particle size of the spheroidal graphite is 100 μm or less. 3. Claims 1 or 2, characterized in that the mold main body is made of spheroidal graphite cast iron, and the average particle size of the spheroidal graphite distributed on the casting surface is 30 μm or less. Spheroidal graphite cast iron for molds.