JPS597346B2 - Heat-resistant cast steel with excellent thermal shock resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a chromium-nickel-iron material that has particularly excellent thermal shock resistance and is used in, for example, heat treatment trays, heat treatment jigs, and radiant tubes that are exposed to high temperatures of about 650 to 10,000C. This relates to heat-resistant cast steel.

Heat-resistant cast steel generally suffers from thermal shock cracks due to thermal shock during its use, for example, in the case of heat treatment trays, due to repeated heating and cooling during loading and unloading of furnace charges, oil cooling, water cooling, or air cooling. When the heat-resistant cast steel product reaches the end of its service life and becomes thick (and grows), it is discarded.

Therefore, heat-resistant cast steel used in the above-mentioned applications is required to have superior thermal shock resistance, which has the greatest effect on its life. In the following specification, % is weight %
shows. Conventionally, as this type of heat-resistant cast steel material, C0.
2-006%, Si2, O% or less, Mn2, O% or less,
Cr-Ni-Fe alloy (American AC
I (Alloy Casting Institute) Standard H
H material, HK material, and their equivalent materials) are known.

The present inventors have discovered that it is possible to obtain a heat-resistant cast steel with superior thermal shock resistance based on the above-mentioned Cr-Ni-Fe alloy. This invention was made based on this knowledge, and its characteristics are that C0.2-086%
, Si28O% or less, Mn2, O% or less, Cr20-3
0%, Ni10-25%, B0.002-0.0so%
and the remainder essentially consists of Fe.

Next, in this invention, the reason for limiting the numerical values as described above will be explained. C: 0.2-066% C dissolves in solid solution in austenite, increases the hardness of the base material, and forms carbides with Cr and the like.

If the content is less than 0.2%, sufficient creep strength cannot be obtained, and a sufficient improvement effect on thermal shock resistance cannot be obtained. On the other hand, if it exceeds 0.6%, high-temperature oxidation resistance deteriorates, high-temperature strength also decreases, and thermal shock resistance deteriorates, which is not preferable.Si: 2.0% or lessSi acts as a deoxidizing agent. , increases the fluidity of molten metal, improves oxidation resistance and carburization resistance, but by 280%
If it exceeds this, it becomes brittle and the creep strength and thermal shock resistance decrease.

Mn■ 2.0% or less Mn is effective in deoxidizing and improving the creep strength of fabrics, but if it exceeds 260%, oxidation resistance deteriorates.

Cr: 20-30% Cr is a component that determines oxidation resistance at high temperatures; if it is less than 20%, sufficient oxidation resistance cannot be obtained, while if it is contained in more than 30%, it will not be sufficient in the service temperature range (
The effect of improving oxidation resistance at temperatures of about 700 to 1000°C is small (and therefore uneconomical).

Ni: 10-25%Ni makes the dough have an austenitic structure and increases toughness and high-temperature strength, but at least 10% is necessary to stabilize austenite.
On the other hand, if the content exceeds 25%, the above-mentioned stabilizing effect is small, and the high-temperature hardness only decreases, which is rather uneconomical.

B: 0.002 to 0.080% B is an extremely effective component for strengthening grain boundaries and improving thermal shock resistance, but if it is less than 0.002%, the effect is not sufficient. Even if the content exceeds 0s0%, no significant improvement effect on thermal shock resistance is observed.

The remainder of each of the above components is substantially Fe, and the alloy of the present invention can be produced by the same conventional melting process as the conventional melting process of the above-mentioned Cr-Ni-Fe alloy. be.

Next, examples of the present invention will be described.

Example 1 Table 1 below shows the chemical compositions of Examples of the present invention, conventional materials, and other comparative examples.

Table 2 shows the results of investigating the high temperature thermal shock properties of alloys selected from those in Table 1. The high-temperature thermal shock property test was conducted using an outer diameter of 25 mm, an inner diameter of 14 mm, an eccentricity of 3.5 mm, and a thickness of 7 mm.
mm eccentric ring test piece was cooled with water at room temperature, heated to 850°C in 4 minutes, held at 850°C for 20 minutes, and then immediately immersed in water for 30 seconds. After 250 cycles of treatment, this test piece was subjected to a die check test to measure the number of thermal shock cracks that occurred.

From the above table, the alloys of the present invention (A4-14) are the same as the conventional materials (YA1,
It is clear that the thermal shock resistance value (the number of cracks generated) is 1/3 or less compared to 2), indicating extremely excellent thermal shock resistance.

Furthermore, the comparative materials (X19, 20) are alloys in which the content of B is lower than the specified range of the present invention, and therefore the thermal shock resistance is not as high as that of the present alloy. 〉Tables 3 and 4 below are the results of investigating the tensile strength and creep rupture strength of alloys selected from Table 1.
From these tables, it is clear that the alloys of the present invention (A.6, 15 to 18) exhibit high-temperature strength that is comparable to, but considerably superior to, the conventional material (AI, 3). Example 2 Furthermore, as a practical test, conventional materials (ACI standard HH material, CO
．． 2-0.5%, Si2. 0% or less, Mn2. 0% or less, Cr24-28%, Nill-14%, Fe balance) and the alloy material of the present invention (0.0% B in the composition of ACI standard HH material)
(added in the range of 1 to 0.02%) as shown in Figures 1 and 2.
m, applied to 11 sheets each as a heat treatment tray with a rib width of 10 mm, furnace temperature: 900°C, furnace atmosphere: carburizing gas,
Holding time: 5 hours. As a result of repeated use under oil quenching treatment conditions after removal from the furnace, the number of cycles until the end of life due to thermal shock cracking was 300 to 300 times compared to conventional materials.
Compared to 400 cycles, the inventive alloy lasted 450-550 cycles, demonstrating a significant improvement in life.

The present invention is as described above, and by specifying the component composition as described above, it not only provides extremely superior thermal shock resistance compared to conventional materials, but also has excellent high-temperature strength. It increases the lifespan and safety of the product when used in other applications, and its industrial value is significant.

[Brief explanation of the drawing]

Figure 1 is a front view of the heat treatment tray used in the high temperature thermal shock practical test used in Example 2, and Figure 2 is a front view of the tray shown in Figure 1.
It is a sectional view taken along the A line.

Claims (1)

[Claims] 1% by weight C0.2-0.6, Si2.0 or less, Mn
2.0 or less, Cr20-30, Ni10-25, B0.
002 to 0.080 and the remainder substantially consisting of Fe. A heat-resistant cast steel having excellent thermal shock resistance.