JPS5919985B2 - Heat resistant casting alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat-resistant casting alloy, and more particularly to a heat-resistant casting alloy that has excellent creep rupture strength without deteriorating its thermal oxidation resistance.

Traditionally, as this type of heat-resistant casting alloy, 1-(N40, f(P40) has been used as a material for reaction tubes in the petrochemical industry.
i-Remaining Fe) has been used for a long time as a material for glue former tubes at temperatures below 1000℃, but
When used in an atmosphere of 1000°C or higher, the creep rupture strength decreases due to coarsening of carbide growth, and at the same time, oxidation resistance also decreases at temperatures higher than 1100°C.

On the other hand, HP40 material (O, 4C-25Cr-35Ni with residual Fe) has better creep rupture strength and oxidation resistance than HK40 material at an operating temperature of around 1100°C, but it is not sufficient at this operating temperature. do not have. In other words, the creep rupture strength is 1 at a high temperature of approximately 1100°C.
This is because the spheroidization of secondary carbides and the growth and coarsening of secondary precipitates cause a decrease in creep rupture strength. As explained above, the present invention has higher creep rupture strength than the HK40 material and HP40 material conventionally used as heat-resistant casting alloys, and also has improved oxidation resistance. It is a heat-resistant cast alloy.

The characteristics of the heat-resistant casting alloy according to the present invention are that C0
．． 35-0.6%, 5i0.5-2.0%, Mn0.3
~0.9%, Cr24~30%, Ni30~40%, W
3 to 6 articles, Nb0.1 to 095% Po, 04% or less,
80.04φ or less, and the remainder consists essentially of Fe.

The heat-resistant casting alloy according to the present invention will be explained in detail below.

First, the components and component ratios of the heat-resistant casting alloy according to the present invention will be explained.

C is an effective element for increasing the creep rupture strength of heat-resistant cast alloys, and the creep rupture life increases as the C content increases.

For a high creep rupture life at a service temperature of 1000°C or higher, the C content must be at least 0.235%, and the C content must be at least 0.135%.
This effect cannot be obtained if the amount is less than that.

In addition, as the C content increases, the creep rupture life increases, but when the C content exceeds 0.96%, the creep rupture life tends to decrease, and furthermore, the amount of secondary carbon precipitates increases, resulting in embrittlement. Cause. Therefore, the C content is 003
5 to 096%. Si is an element that is effective in deoxidizing during steel manufacturing and increasing carburization resistance during use, and is usually mixed in at a concentration of about 0.2 to 0.3 from melted raw materials. In order to provide sufficient deoxidizing effect and carburization resistance, it cannot be expected if the Si content is less than 0.5%, and if the content exceeds 2%, weldability will decrease. .

Therefore, the Si content is set to be in the range of 0.5 to 2.0. Mn is contained as a deoxidizing agent and an element that fixes S, but if the content is less than 0.3%, this effect cannot be expected;
Furthermore, if the content exceeds a factor of 0.9, the oxidation resistance will deteriorate under severe usage conditions at high temperatures of about 1100°C.

Therefore, the Mn content is set to be in the range of 0.3 to 0.9. Cr
Cr is an effective element for obtaining oxidation resistance and high-temperature strength. Considering that it is used at a high temperature of approximately 1100°C, oxidation resistance is poor if the Cr content is less than 24%. If the content exceeds 30%, the Cr content will increase and the oxidation resistance will improve, but if the content exceeds 30%, the toughness will decrease.

Therefore, the Cr content is set at 24 to 30. Ni stabilizes austenite and improves oxidation resistance, carburization resistance, and
It is an element that improves high-temperature strength, and when used at high temperatures of approximately 1100°C, if the Ni content is less than 301%, oxidation resistance and carburization resistance are poor, and if the content exceeds 40%, the Ni content will be poor. has no effect.

Therefore, the Ni content is set at 30 to 40. W is an element that increases high-temperature strength, but when the content is less than 3%, the increase in creep rupture strength is small, and when the content exceeds 3%, the creep rupture strength increases significantly, and further, Although the creep rupture strength increases even if the content exceeds 6, the material itself hardens, resulting in a decrease in ductility at low temperatures.

Therefore, the W content is set to 3 to 6. Nb is an element that increases creep rupture strength, and if the content is less than 0.1%, it has no effect, and if the content exceeds 0.1%, the higher the content, the more effective it is.

However, due to the combination with W, Nb has a
At high temperatures exceeding °C, oxidation resistance is significantly impaired, and this becomes clear when Nb is contained in excess of 0.5%. Therefore, the Nb content is set to 0.1 to 0.5%. P. When S exceeds 0.04%, it adversely affects weldability.

Therefore, P. The S content shall be 0.04% or less. Examples of heat-resistant casting alloys according to the present invention will be described together with comparative examples.

35 kg was melted in a high-frequency induction melting furnace so as to have the components and component ratios shown in Table 1, and was cast by centrifugal casting to a size of outer diameter 135 φ, wall thickness 25 t, and length 5201 mm.

Table 1 shows the results of the creep rupture test and the oxidation resistance test.

This creep rupture test was conducted using a parallel part diameter of 6.4 mm CrL2
Tests were conducted with dimensions of 5 mTIL.

The oxidation resistance test is the average value obtained by performing a 11507C-300Hr test in the atmosphere on three 12φ-507ftN specimens.

As shown in Table 1 of Atsuko, comparative material (1) (HK
4O material), comparative material (2) (HP4O material), and comparative materials (3) and (4), which are low W-containing materials, have a short creep rupture life.

When the W content increases as in comparative materials (5) and (6), the creep rupture life is considerably improved. In addition, comparative material (7
), the creep rupture life is significantly improved by containing Nb in a ratio of about 0.8 to W. On the other hand, the oxidation resistance deteriorates when the W content exceeds the range (comparative material (6)) and when the Nb content increases in combination with the W content. In contrast to these comparative materials, the present invention materials (1), (2), and (3) have improved oxidation resistance by combining W and a small amount of Nb, as shown in Table 1. It can be seen that the creep rupture strength is good without significantly inhibiting the properties of the steel, and that it is extremely suitable as a high temperature member of 1100 to 1150 C.

The heat-resistant casting alloy according to the present invention includes cranking tubes,
It is suitable as a material for the petrochemical industry such as reformer tubes and tube samarts, as a material for steel such as hearth rolls and radiant tubes, and as other high-temperature parts used at temperatures of 1000°C or higher. be.

Claims (1)

[Claims] 1 C0.35-0.6%, Si0.5-2.0%, M
n0.3~0.9%, Cr24~30%, Ni30~4
0%, W3-6%, Nb0.1-0.5%, P0.04
% or less, S0.04% or less, and the remainder is substantially F.
A heat-resistant casting alloy characterized by comprising e.