JPS5834543B2 - High strength spheroidal graphite cast iron - Google Patents

Description

[Detailed description of the invention] The present invention relates to high strength spheroidal graphite cast iron.

Conventionally, cast iron castings used under high temperature conditions are 500℃.
There is a pearlite-based spheroidal graphite cast iron that has high strength at high temperatures up to.

However, the room temperature strength of this pearlitic spheroidal graphite cast iron is J
60 kgf/mri with material equivalent to IS standard FCD60
Above, FCD obtained by heat treatment etc.
Even with 70, the normal temperature strength is 70kgf/- or more 1ookyf/
- less than or equal to

The strength of these materials decreases as the operating temperature increases.

As shown in Figure 1, the state of the change in strength due to the rise in service temperature is as follows.
f/ma, and 60kgf/'i at 400°C
n (edited by the Japan Institute of Metals: "Theory and Practice of Spheroidal Graphite Cast Iron", Marukubi, (1966) P2S5).

On the other hand, nodular/acicular iron containing Ni of 2.3 ωt% or less and MO of 1 ωt% or less can be heat-treated for a long time at 250°C for 15 hours to achieve room temperature strength of 100.
kg f/ma (Tohei Otoya, Hiroshi Tokunaga: "Castings Jvol, 33./468. (19
61) P570).

The problems when using the above-mentioned pearlitic spheroidal graphite cast iron and nodular acicular cast iron as materials for high-temperature equipment are: (1) The strength decreases as the temperature rises.

■ Heat treatment is required to obtain high strength.

■ The material properties of low-Ni, low-Mo materials such as nodular/acicular cast iron in high-temperature zero atmosphere have not been clarified.

etc.

The present invention was made in view of the conventional problems, and exhibits high strength of 100 kgf7- or more at 300°C when as-cast (without heat treatment), and furthermore, the strength increases as the temperature rises up to 300°C. The present invention provides high-strength spheroidal graphite cast iron with significantly increased strength.

The high-strength spheroidal graphite cast iron according to the present invention has a C of 1.7 to 3.
8ωt%+Si 0.8~3ωt%yMn 1~2ωt
%, contains 6 to 12 ωt% of Ni, and is characterized by high high-temperature strength in an untempered state.In addition to these chemical components, it is allowed to contain trace amounts of unavoidable impurities. .

Next, the reason for limiting the content range of each chemical component will be described.

Si: The amount of Si can be added within the range of ingredients used to manufacture normal spheroidal graphite cast iron, and should be determined based on the need not to reduce the fluidity characteristic of cast iron, and the amount of Si introduced during the spheroidization process. The lower limit was set to 0.8 ωt%.

In addition, addition of 3ωt% or more causes a decrease in elongation, so
The upper limit was set to 3ωt%.

C: Since C can be added within the range of components that produce normal spheroidal graphite cast iron together with Si, the amount added is set to 1.7 to 3.8 ωt%.

Ni: Ni does not inhibit the spheroidization of cast iron.

However, addition of less than 6 ωt % cannot guarantee the strength at 300° C., and addition of 12 ωt % or more saturates the addition effect.

Mn: 3Mn does not inhibit the spheroidization of cast iron.
The amount added may be within the range of components used to manufacture normal spheroidal graphite cast iron; addition of more than 2ωt% will result in a decrease in fluidity;
Addition of less than t% does not stabilize the base structure.

Therefore, the appropriate amount of Mn to be added is set to 1 to 2 ωt%.

An experimental example is shown below.

Experimental Example 1 A molten cast iron containing the chemical components shown in Table 1 in the amounts shown in the same table was produced, and electrolytic Ni was added to the molten cast iron in a high-frequency heating furnace to produce Fe45%Si-3. ,5
After spheroidization treatment with %Mg and inoculation treatment with Fe-75%Si, a test material weighing 40 kg of molten metal was cast and sampled.

This test material is as shown in FIGS. 4 and 5 (hereinafter referred to as Y block test material).

) In Table 1, P and S are unavoidable impurities.

The Y block used as the test material was an as-cast material, and when the strength change at high temperature was measured for this as-cast material according to JIS GO567, the results shown in FIG. 2 were obtained.

The results of measuring changes in elongation at high temperatures for this as-cast material are also shown in FIG. 2.

As can be seen from Figure 2, the room temperature strength of this as-cast material is comparable to that of conventional FCD60 equivalent materials, and the tensile strength at 300°C is 110 to 115 kgf/ma, and the tensile strength at 400°C is nearly 110 kgf/m4. Moreover, this as-cast material showed a significant increase in tensile strength with increasing temperature up to 300°C.

On the other hand, the elongation was 2% at 300°C and 3% or more at 400°C.

Experimental Example 2 Using the same method as Experimental Example 1, the amount of Ni added was adjusted to 6 to 12Ω.
Test materials were produced by varying the amount of Ni in the range of t%, and the relationship between the amount of Ni added and the tensile strength was investigated at 300°C.

The results are shown in Figure 3. As can be seen from Figure 3, Ni
The addition of an appropriate amount of Cr significantly improves the bowing strength of the as-cast material (Y block test material) at 300°C.

As described above, the high-strength spheroidal graphite cast iron according to the present invention,
No heat treatment is required to obtain high strength, and the as-cast condition is 30%
It has a high strength of 100 kgf/- or more at 0°C, and the strength increases significantly as the temperature rises to 300°C.

Therefore, materials for equipment equipment used in high temperature atmospheres,
It is particularly suitable as a material for pallets of sintering equipment.

In other words, the use of the high-strength spheroidal graphite cast iron according to the present invention as a material for sintering equipment pallets has great significance in preventing deformation due to lack of high-temperature strength caused by long-term exposure to high-temperature freezing air. be.

[Brief explanation of the drawing]

Figure 1 is a graph showing the high-temperature tensile strength of conventional pearlitic spheroidal graphite cast iron, Figure 2 is a graph showing the high-temperature tensile strength of high-strength spheroidal graphite cast iron according to the present invention, and Figure 3 is N
A graph showing the relationship between the amount of i added and tensile strength, FIG. 4 is a plan view of the test material, and FIG. 5 is a side view of the same.

Claims (1)

[Claims] 1 C is 1.7 to 3.8 ωt% + S+ is 0.8 to 3 ωt
%. A high-strength spheroidal graphite cast iron containing 1 to 2 ωt% of Mn and 6 to 12 ωt% of Ni, and having high high-temperature strength in an unrefined state.