JPS5871353A - High-strength ni-resist cast iron - Google Patents

Abstract

PURPOSE:To obtain high-strength Ni-resist cast iron with superior corrosion resistance by adding a specified amount of an Ni-Mg alloy as a spheroidizing agent to Ni-resist cast iron contg. specified percentages of Ni and Cr and by specifying the residual Mg content. CONSTITUTION:To Ni-resist cast iron contg. 18-22wt% Ni and 1.5-2.5wt% Cr is added 0.01-0.03wt% Ni-Mg alloy as a spheroidizing agent, the residual Mg content of the cast iron is specified to 0.010-0.025wt%, and a structure contg. roundish graphite flakes is provided. The Ni-Mg alloy used as the spheroidizing agent contains about 85-95wt% Ni and about 5-15wt% Mg. Thus, high-strength Ni-resist cast iron with 25-35kg f/mm.<2> tensile strength, superior castability and high machinability is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention has excellent corrosion resistance and
This relates to high-strength NiRegis) M iron having a strength of f-.

Alloyed cast iron containing nickel and chromium in a predetermined range in its composition is generally called Niresist cast iron, and is widely used as a material for seawater pump parts and other applications because of its excellent corrosion resistance.

Table 1 shows an example of the composition of Ni-resist cast iron, with Ni:1
By containing 8 to 22 wtq6, Cr: 1.5 to 2.5 wt%, corrosion resistance against acids, salts, alkalis, seawater, etc. is excellent.

Table 1 (wt, chi) However, in conventional Niresist cast iron, the graphite in its structure is flaky, and the flaky graphite has sharp tips.
Since it acts as an internal notch in the Fe matrix, stress is concentrated at the tip of the graphite and a notch crack is likely to occur. For this reason, Niresist cast iron has a tensile strength of 20 to 25 kg.
f/, the hardness is about 130 HB, and the strength is low. Therefore, when used as a material for a pressure-resistant member, for example, the thickness must be increased to improve strength and safety.

On the other hand, ductile Niresist cast iron, in which the graphite in the structure of Nirenost Lj iron is spheroidized, has almost the same composition as the Nirenost cast iron mentioned above, and has excellent corrosion resistance. , so there is less stress concentration, and therefore its tensile strength is 40-50 A1
1f/, hardness is approximately 140HB, and has excellent strength.

However, conventional ductile resist cast iron has drawbacks when casting ductile cast iron. Nirenost cast iron suffers from problems with castability, such as shrinkage during solidification, which tends to cause casting defects such as cavities, and requires a large amount of feeder, reducing product yield. It has the problem of high cost, such as being inferior to

This invention, from the above-mentioned viewpoint,
It provides high-strength Ni-resist cast iron that has a tensile strength of 25 to 35 #f/-, which is greater than M iron, and has excellent castability and machinability. Ni: 18 to 22
Weight factor, Cr: Contains 1.5-2.5% by weight, and nickel-magnesium alloy as a spheroidizing agent contains 0.01-2.5% by weight.
Residual Mg in cast iron added at a rate of 0.03 wt.
The amount is 0.010 to 0.025% by weight, the structure has rounded flake graphite, and the tensile strength is 25 to 35 kg.
f/.

In this invention, a nickel-magnesium alloy is used as a spheroidizing agent, and its composition is Ni:
Appropriate amounts are 85 to 95% by weight and Mg: about 5 to 15% by weight. In addition, the amount of nickel-magnesium alloy added is 0.01 to 0.0 based on the total amount of molten Nilenost cast iron.
The reason for this ratio is 3% by weight.
The amount of residual Mg in cast iron, which will be described later, is 0.010 to 0.02.
This is to make it 5% by weight.

The amount of residual Mg in cast iron is 0.010~o, o 25% by weight
The reason for this is that if the amount of residual Mg is less than 0.010% by weight, the flaky graphite in the structure cannot be rounded, so the desired strength cannot be obtained.
This is because if it exceeds 25% by weight, the graphite in the structure becomes completely spheroidized, resulting in poor castability and cutting workability.

Further, the amounts of Ni and Cr are necessary for imparting corrosion resistance to cast iron and exhibiting the performance as Nirenost cast iron.

Next, the present invention will be explained with reference to examples.

Bearings, which are seawater pump parts, are made to support 65.
A 5-ton low-frequency melting furnace is used to melt residual molten metal of the raw material ductile resist cast iron, steel scrap, and pig iron, and melt Ni, Cr, and C.
The composition was adjusted by adding an appropriate amount of Nirenost cast iron molten metal 1.600 AV having the chemical composition shown in Table 2.

As a spheroidizing agent when tapping the Nirenost cast iron molten metal,
2.62 AV of a nickel-magnesium alloy containing 85% by weight of Ni and 15% by weight of Mg was placed in a ladle. Table 3 shows the chemical composition of the molten metal after charging the nickel-magnesium alloy.

Note that the tapping temperature is 1510'O.

Figure 1 (A) is a photograph showing the cross section of the riser part when the above molten metal is cast, Figure 1 (B) is a photograph showing the cross section of the feeder part when the molten metal of conventional ductile resist cast iron is cast, and Figure 1 (C) is a photograph showing the cross section of the feeder part when the above molten metal is cast. These are photographs showing cross-sections of the riser parts when molten Nirenost cast iron was cast. From the drawings, it can be seen that the cast iron of the present invention has excellent castability, with significantly fewer cavities than ductile Niresist cast iron and almost the same level as conventional Nirenost cast iron. I understand.

The reference photograph is an example of a cast product made of the cast iron of the present invention, which was made by casting the above-mentioned molten metal. Figure 2 (a) is a microscopic microstructure photograph (100x magnification) of a test piece taken from the cast iron casting of the present invention shown in the reference photograph, and the same figure (b) is a conventional ductile Nirenos) & 4 iron specimen. A microscopic microstructure photograph (100x magnification) of a test piece taken from a cast product, and a microscopic iλ microstructure photograph (100x magnification) of a test piece taken from a cast product made of U iron. From the drawings, it can be seen that in the case of the cast iron of the present invention, its graphite structure has been improved, resulting in flake graphite with a rounded shape intermediate between flake graphite and spheroidal graphite.

Table 4 shows a comparison of mechanical properties between the above-mentioned cast iron of the present invention and conventional Niresist cast iron.

Table 4 From Table 4 above, the cast iron of the present invention has a tensile strength of 25#.
f/- or more, it can be seen that it has superior mechanical properties compared to conventional Niresist cast iron.

In addition, face milling and Teno seven-shank drilling were performed on specimens of cast iron of the present invention and conventional ductile resist cast iron, and a comparative test of machinability was conducted. The ductile resist cast iron has a lot of chips adhering to the cutting tool, and the cutting edge of the cutting tool is severely worn, whereas the cast iron of the present invention has less chips adhering to the tooling tool, and the life of the cutting tool is longer than that of the conventional ductile resist cast iron. Compared to Niresist cast iron, it has grown approximately 1 to 5 times.

As mentioned above, the cast iron of the present invention is 25 to 35A? f/
- It has high strength, has excellent castability, good cutting workability, can be manufactured economically with high yield, etc., and provides excellent industrial effects.

[Brief explanation of drawings]

Figure 1 is a photograph showing the cross-section of the feeder section of the cast iron of the present invention in comparison with the cross-section of the conventional cast iron. Figure (c) shows conventional Niresist cast iron. Figure 9g2 is a micrograph (100x magnification) showing the graphite shapes of the cast iron of the present invention and the conventional FI3 iron, and the same figure (A) is the H6g of the present invention,
The same figure (b) shows the conventional ductile resist cast iron;
C) is conventional Niresist cast iron. Applicant Ebara Corporation Agent Keitabe Tsutsumi (1 other person) Figure 1

Claims (1)

[Claims] Contains Ni: 18-22% by weight, Cr: 1.5-2.5% by weight, and a nickel-magnesium alloy is added as a spheroidizing agent at a rate of 0.01-0.03% by weight.
A high-strength Niresist with a tensile strength of 25 to 35 Hf7-, characterized by having a residual Mg amount in cast iron of 0.010 to 0.025% by weight and having rounded flaky graphite in its structure. cast iron.