JPH06128684A - Heat resistant spheroidal graphite cast iron - Google Patents

Abstract

PURPOSE:To improve the heat resistance of a spheroidal graphite cast iron to a greater extent and also to improve its high temp. fatigue strength by adding one or more elements among Nb, Mo, V, Ti, and Ta to a spheroidal graphite cast iron containing specific amounts of Ni and Si by the amount of specific precentage based on the weight of Si. CONSTITUTION:One or >=2 elements among Nb, Mo, V, Ti, and Ta are added to a spheroidal graphite cast iron containing, by weight, 13.0-40.0% Ni and 4.0-10.0% Si by the amount of 5-30% based on the weight of Si. By this method, the heat resistance of a casting made of this cast iron can be improved, and also its high temp. fatigue strength can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-resistant spheroidal graphite cast iron containing a large amount of Ni.

[0002]

2. Description of the Related Art Heat-resistant spheroidal graphite cast iron containing a large amount of Ni is widely used because it has good heat resistance. Some have been added.

[0003]

By the way, when the amount of Si added to this type of heat-resistant spheroidal graphite cast iron is increased, the mechanical properties such as strength of the casting decrease with the increase of the amount of Si, which causes It may impair the practicality as an industrial material.

The present invention has been made in view of such circumstances, and further improves the heat resistance of a casting, and
In particular, the purpose is to improve the high temperature fatigue strength.

[0005]

In order to achieve this object, the invention according to claim 1 provides 13.0 to 40.0% Ni and 4.0
Spheroidal graphite cast iron containing ~ 10.0% Si, Nb, Mo, V,
1 or 2 or more elements in Ti and Ta are added to the above Si weight of 5
Characterized by the addition of ~ 30%.

[0006]

[Operation] When elements such as Nb are added to spheroidal graphite cast iron containing 13.0 to 40.0% Ni and 4.0 to 10.0% Si, the heat resistance of the casting is improved.

In this case, if one or more elements of Nb, Mo, V, Ti, and Ta are added at a rate of 5% to 30% of the Si content, the high temperature fatigue strength of the casting is also improved. Can be made.

Therefore, the heat-resistant spheroidal graphite cast iron according to claim 1 can further improve the heat resistance of the casting and the high temperature fatigue strength thereof.

[0009]

EXAMPLES The present invention will be described below with reference to examples.
First, the table. 1, a description will be given of the case where only Nb is used as the additional element according to the present invention. Table. 1 shows the component composition of each sample in% by weight.

[0010]

【table. 1] The above table. 1, the sample 1 is a comparative example, and is a conventionally known so-called Ni-resist ductile cast iron type D2 (AST
M A439 D-2, JIS FCDA-NiCr20 2 equivalent).

Samples 2 to 7 are all examples of the present invention and are additive elements of these samples 2 to 7.
The weight ratio of Nb to Si amount is 9.2% for sample 2 and sample 3
24.2%, Sample 4 28.9%, Sample 5 14.6%, Sample 6
22.7% and sample 7 are 24.7%.

In order to evaluate the heat resistance of a casting having these component compositions, each of the samples 1 to 7 was melted under the same conditions and poured into a predetermined mold to form a casting having a constant shape. A sample for heat resistance test was prepared by cutting out a predetermined rectangular parallelepiped shape from the inside excluding the black skin part of this casting.

First, a heat resistance evaluation test using these samples will be described.

As the heat resistance evaluation test, sample 1 as a comparative example and samples 2 to 7 as examples of the present invention were used.
For and, the following heating holding test and repeated heating test were performed.

In the heating and holding test, each sample formed in a predetermined rectangular parallelepiped shape is uniformly heated in a heating furnace and held at a certain temperature for a certain period of time, and then the mass of each sample is measured to reduce the oxidation loss. In this heating and holding test, the heating temperature was set to 900 ° C, the heating and holding time was 4 hours, and
Oxidation weight loss at each time point was obtained as 20 hours.

The results are shown in FIG. In addition, in the figure, A shows the oxidation weight loss at the time of heating and holding time of 4 hours, and B shows the oxidation weight loss at the time of 20 hours.

As can be understood from FIG. 1, the weight loss due to oxidation in the heating and holding test is largest in Sample 1 as a comparative example, and is a value smaller than Sample 1 in Samples 2 to 7, which are Examples of the present application. Has become. It can be seen that the difference in the weight loss due to oxidation tends to increase as the heating time increases.

Therefore, from the results of this heating and holding test, it can be confirmed that each of the examples of the present invention has better heat resistance than existing heat-resistant cast iron.

On the other hand, the repeated heating test is a test in which heating is repeatedly performed in a constant heat cycle by moving between a low temperature part and a high temperature part in the heating furnace, and an oxidative loss is measured.

In this repeated heating test, the temperature of the low temperature part was set to 200 ° C., the temperature of the high temperature part was set to 870 ° C., each sample was heated 200 times, 500 times and 1000 times respectively, and the mass was measured at each time point. Oxidation weight loss was obtained by measurement.

The results of this repeated heating test are as shown in FIG. In the figure, C indicates the weight loss at 200 times, D indicates the weight loss at 500 times, and E the weight loss at 1000 times.

As is clear from FIG. 2, no matter which the number of times of repeated heating was, Sample 1 as a comparative example was used.
Is the largest, and all of the samples 2 to 7 which are the examples of the present invention are smaller than that.

Therefore, it can be seen from the results of this repeated heating test that each example of the present invention has better heat resistance than the existing heat resistant cast iron.

In particular, Sample 6 shows a value significantly smaller than the oxidation loss of the existing heat-resistant cast iron in the results of both the heating and holding test and the repeated heating test, which indicates extremely excellent heat resistance. It is clear that

Then, in order to evaluate the high temperature fatigue strength of the casting having such a composition, the following test was conducted.

That is, the high temperature fatigue strength is a relationship when a cast article having a certain shape is subjected to a combined action of deterioration of mechanical properties of a material under high temperature and thermal stress.

Therefore, in this test, the casing part for the turbocharger, which has a predetermined container-like shape, is used as it is as a test piece, and this test piece is repeatedly heated under the same conditions as the above-mentioned repeated heating test, so that the thermal stress in that shape is reduced. The high temperature fatigue strength was defined as the number of times of heating until damage occurred in the concentrated area.

The result is shown by the solid line in FIG. In addition, in FIG. 3, the number with a circle indicates the sample number corresponding to the component composition.

As can be seen from FIG. 3, the high temperature fatigue strength of the turbocharger casing having the same composition as each of the samples according to the present invention is determined by the ratio of the Nb addition amount to the Si amount (hereinafter, simply the Si amount. 5% to 30% of the ratio), and the high-temperature fatigue strength in this range is higher than when the Si content ratio on both sides of this range is less than 5% or more than 30%. It is understood that the high temperature fatigue strength is improved by the addition of Nb.

As is clear from the above test results, the heat-resistant spheroidal graphite cast iron according to the present invention has heat resistance and high-temperature fatigue strength superior to those of the prior art, and therefore has high practicality as an industrial material. It is equipped with.

Next, Mo is added as an additional element according to the present invention.
The case of using only Nb will be described, but it is almost the same as the case of Nb described above, and its component composition is shown in Table. 2 in% by weight.

[0032]

【table. 2] The above table. 2, the sample 1 is shown in Table. This is the same comparative example as described in 1, and sample 8 is a new comparative example.

Samples 9 to 15 are all examples of the present invention, and the weight ratio of Mo as an additive element of each of Samples 9 to 15 to the amount of Si is 23.0% in Sample 9,
Sample 10 is 11.5%, Sample 11 is 16.9%, Sample 12 is 22.2%
%, Sample 13 is 29.2%, Sample 14 is 25.9%, Sample 15 is
It is 24.7%.

With respect to castings having these component compositions, heat resistance test samples were prepared in the same manner as in the case of Nb.
Oxidation weight loss was measured for each of these samples 8 to 15 by the same heat retention test and repeated heating test as the above Nb in the same manner as described above, and all of them were existing heat-resistant cast iron, showing a value smaller than that of sample 1. It showed good heat resistance.

The weight loss on oxidation of sample 9 which is one example of the present invention was 0.015 mg / cm ² , and sample 8 as a comparative example.
The weight loss due to oxidation was 0.026 mg / cm ² . From this, Mo
It can be seen that the addition of Al improves the heat resistance of the casting.

The above table. 1 corresponds to Sample 6 described in 1 in terms of component composition, and Sample 14 is Samples 9 to 1 as examples.
The best heat resistance was shown in No. 5.

Even when Mo was added, the same number of times of repetition was obtained by the same repeated heating test using a predetermined casing part for turbocharger as a test piece as in the case of Nb.

The result is shown by the broken line in FIG.

Also in this result, when the Si content ratio is in the range of 5% to 30%, a tendency of medium to high is shown as in the case of Nb, and the addition of Mo improves the high temperature fatigue strength.

Therefore, the heat-resistant spheroidal graphite cast iron according to the present invention to which Mo is added also has heat resistance and high-temperature fatigue strength superior to those of the prior art, and therefore has high practicality as an industrial material. Is.

In each of the embodiments described above, Nb or Mo was added as an additional element according to the present invention independently within the range of 5% to 30% of the amount of Si in the composition component of each embodiment. It is a thing.

However, considering the properties of the elements of Nb and Mo, it is possible to use V, Ti, and Ta in addition to these elements, and two or more elements of these Nb, Mo, V, Ti, and Ta can be used. It is considered that the same effect can be obtained by using the above together and adjusting the total amount of addition within the range of 5 to 30% of the Si weight.

[0043]

As described above, according to the invention of claim 1, an element such as Nb is added to the spheroidal graphite cast iron containing 13.0 to 40.0% Ni and 4.0 to 10.0% Si. Then,
The heat resistance of the casting is improved.

In this case, if one or more elements of Nb, Mo, V, Ti, and Ta are added at a rate of 5% to 30% of the Si content, the high temperature fatigue strength of the casting is also improved. Can be made.

Therefore, the heat-resistant spheroidal graphite cast iron according to claim 1 can further improve the heat resistance of the casting and the high temperature fatigue strength thereof.

[Brief description of drawings]

FIG. 1 is a graph showing a result of a heat retention test when Nb is used as an additional element.

FIG. 2 is a graph showing the results of a repeated heating test when Nb is used as an additional element.

FIG. 3 is a graph showing high temperature fatigue strength.

Claims (1)

[Claims] 1. 13.0 to 40.0% Ni and 4.0 to 10.0% Si
A heat-resistant spheroidal graphite cast iron containing 5 to 30% of the Si weight, containing 1 or 2 or more elements of Nb, Mo, V, Ti, and Ta. .