JPH0124219B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to Fe-Ni-Cr heat-resistant cast steel that has excellent strength and corrosion resistance at high temperatures.
More specifically, austenitic heat-resistant cast steel based on iron and containing Ni-Cr, Nb, N and Ce, La
The present invention also relates to a heat-resistant and corrosion-resistant cast steel that has high-temperature strength and high-temperature corrosion resistance that can withstand harsh operating environments at high temperatures, especially over 800°C, by adding a certain amount of rare earth elements such as Y in combination. When manufacturing cement, the red-hot cement clinker fired in a kiln is rapidly cooled by heat exchange on a plate-shaped grate plate with ventilation holes.
JIS/SCH-13 (ACI-HH) (heat-resistant cast steel) is used, but in recent years, as operating conditions have become more severe, problems have arisen in high-temperature strength, high-temperature corrosion, and metal structure stability. There is a strong demand for the development of materials with excellent strength and corrosion resistance at high temperatures. In order to meet the above requirements, the present invention has a basic composition of austenitic heat-resistant cast steel containing Ni-Cr,
As a result of extensive research into the effects of various additive elements on high-temperature properties, we have found that strength and corrosion resistance at high temperatures can be improved by adding certain amounts of rare earth elements such as Nb, N, Ce, La, and Y. Fe-Ni-Cr with excellent castability
We have now provided austenitic heat-resistant and corrosion-resistant cast steel. That is, the heat-resistant and corrosion-resistant cast steel of the present invention contains C 0.2 to 0.7%, Si 0.3 to 2.0%, Mn 0.3 to 2.0%,
Ni 5-14%, Cr 15-30%, Nb 0.3-2.0%, N
It is a heat-resistant and corrosion-resistant cast steel characterized by containing 0.21 to 0.7% and 0.05 to 2.0% of rare earth elements such as Ce, La, and Y, with the balance being Fe. The reason for the composition of the heat-resistant and corrosion-resistant cast steel of the present invention will be explained in detail below. In addition to improving castability, C is necessary to form secondary carbides in coexistence with Nb and to increase strength at high temperatures. If it is less than 0.2%, the strength will drop significantly at high temperatures and the structure will become unstable, so at least 0.2% or more is required. Moreover, if it exceeds 0.7%, carbides with Cr will precipitate excessively and the toughness will decrease, so the upper limit is set at 0.7%. In addition to serving as a deoxidizing agent during melting, Si
Effective in improving oxidation and corrosion resistance at high temperatures. It is also an element that improves the castability of castings,
These effects are weak when less than 0.3% is added. In addition, if it exceeds 2.0%, the strength at high temperatures will decrease;
2.0% when taking into account oxidation and corrosion resistance at high temperatures
is the upper limit. Like Si, Mn functions as a deoxidizer and is an effective element that fixes S (sulfur) in molten steel and renders it harmless. The content is limited to 0.3 to 2.0% since it deteriorates the chemical properties. When Cr coexists with Ni, it austenitizes the cast steel structure and has a remarkable effect of increasing strength at high temperatures, acid resistance, and corrosion resistance. And the effect is Cr
In particular, it is necessary to add at least 15% in order to fully exhibit strength, acid resistance, and corrosion resistance at temperatures above 800°C. However, if too much is added, the metal structure will become unstable, so the upper limit is set at 30%. As mentioned above, Ni coexists with Cr to form an austenitized structure in cast steel, and is an effective element for stabilizing the structure and increasing strength, corrosion resistance, and oxidation properties at high temperatures. If less than 5% is added, the structure will become unstable. Even when added in excess of 14%, the increase in strength at high temperatures is not so pronounced;
Although Ni itself does not have corrosion or oxidation resistance, it indirectly contributes to the stability of the film and increases its corrosion and oxidation resistance. Therefore, the Ni content is set to 5 to 14%. In addition to the above elements, the cast steel of the present invention contains Nb,
The biggest feature is that a certain amount of N and rare earth elements such as Ce, La, and Y are added in a composite manner.
Although the combined addition of these elements dramatically improves the strength at high temperatures and the corrosion resistance against sulfide corrosion, even if any one element is missing,
You won't get that effect. Nb is a strong carbide-forming element and is effective in increasing strength at high temperatures. However, to obtain this effect, it is necessary to add at least 0.3% or more. On the other hand, if added in excess, the strength at high temperatures, corrosion resistance, and oxidation resistance will deteriorate, so 2.0
The upper limit is %. Note that Nb usually includes unavoidable Ta. Ta is Nb
Since it is an element with the same effect as Nb, if Ta is included, it is the same as Nb.
It is sufficient if the total Ta is 0.3 to 2.0%. N is a strong austenite stabilizing element, but its effect is small at less than 0.21%, and at 0.7%
If it is added in excess of 0.21 to 0.7%, carbonitrides will become coarser and even deteriorate. Rare earth elements such as Ce, La, and Y are effective in improving corrosion resistance and oxidation resistance at high temperatures as well as increasing strength, but if the amount added is less than 0.05%, the effect is weak, and if the amount exceeds 2.0%, the effect is weak. Since there is no noticeable effect even if it is added, the upper limit is set at 2.0%. Also,
Since rare earth elements such as Ce, La, and Y are equivalent elements, the total content of these elements may be 0.05 to 2.0%. Other impurities such as S and P may be present within the range normally allowed for this type of cast steel. Next, embodiments of the present invention will be specifically described. 1st
The table shows the chemical composition of various alloys used in the present invention.

【table】

[Table] In Table 1, No. 1 is the conventional alloy of SCH-13, Nos. 2 to 7 are comparative alloys for the present invention,
Nos. 8 and 9 are examples of alloys of the present invention. The creep rupture test was conducted in accordance with JIS Z2272 at a temperature of 800°C and a load of 8.5Kg/mm ² and 7.0Kg/mm ² . In addition, high-temperature tensile tests were conducted at temperatures of 800°C and 1000°C in accordance with the regulations of JIS G0567. On the other hand, for corrosion tests at high temperatures, reagent-grade anhydrous
The sample was embedded in a corrosive medium made by adding about 20% Na ₂ SO ₄ to ordinary cement clinker crushed into 100-150 meshes, held at a temperature of 900°C for 100 hours, and the change in weight was measured. Table 2 shows the samples shown in Table 1 with a load of 7.0 at 800℃.
These are the results of creep rupture tests under the conditions of Kg/mm ² and 8.5 Kg/mm ² .

[Table] The material numbers in this table correspond to the sample numbers in Table 1 above. As can be seen from Table 2, the creep rupture strength of the alloys of the present invention is significantly improved. Table 3 shows the samples shown in Table 1 at 800℃ and 1000℃.
The results of a high-temperature tensile test are shown.

[Table] The sample numbers in this table correspond to the sample numbers in Table 1.
As can be seen from Table 3, the alloys of the present invention have significantly improved tensile strength at high temperatures. Figure 1 shows that the samples shown in Table 1 are ground into 100 to 150 meshes of ordinary cement clinker.
The results of a sulfide corrosion test conducted at a temperature of 900°C for 100 hours in the presence of 20% Na ₂ SO ₄ are shown. As can be seen from the figure, the alloy of the present invention has significantly improved corrosion resistance against sulfidation corrosion at high temperatures compared to the comparative material. As described above, the alloy of the present invention is an alloy that has high strength and high corrosion resistance at temperatures of 800°C or higher, and is particularly excellent in sulfide corrosion resistance. This type of alloy is useful for parts that require high corrosion resistance.

[Brief explanation of drawings]

The figure is a bar graph showing the corrosion test results of the sample materials.

Claims (1)

[Claims] 1% by weight, C 0.2-0.7%, Si 0.3-2.0%,
Mn 0.3-2.0%, Ni 5-14%, Cr 15-30%,
Nb 0.3-2.0%, N 0.21-0.7%, and Ce,
A heat-resistant and corrosion-resistant cast steel that contains 0.05 to 2.0% of rare earth elements such as La and Y, with the remainder consisting of Fe, and is characterized by excellent sulfide corrosion resistance.