JPS6357490B2 - - Google Patents

Description

[Detailed description of the invention]

Conventionally, Fe-Ni-Cr heat-resistant cast steel was used for heat-resistant cast alloys for heating furnaces such as skid rails, but
In recent years, from the perspective of emphasizing high-temperature strength, Fe
- Heat-resistant cast alloys with increased high-temperature strength by adding Co, such as Ni-Co-Cr and Co-Ni-Cr, have also come into use. However, these Co-containing alloys have drawbacks such as insufficient oxidation resistance compared to their high-temperature strength and high price. The present invention has high-temperature strength equivalent to Co-containing alloy,
The present invention provides a heat-resistant casting alloy for skid rails that is cheaper than Co-containing alloys and has excellent oxidation resistance. The present invention has a weight percentage of C0.20~0.60%, Si0.2~
1.3%Mn1.3% or less, Cr25~35%, Fe5~15%,
An austenitic heat-resistant cast alloy for skid rails with excellent high-temperature oxidation resistance, containing 0.02 to 0.30% Ti, 50% or more Ni, and the remainder consisting of impurities, or an austenitic heat-resistant cast alloy for skid rails containing 5% or less of W in addition to the above alloy. Made of austenitic heat-resistant cast alloy for skid rails. C has the effect of forming M ₇ C ₃ type eutectic carbide in the alloy of the present invention and precipitating M ₂₃ C ₆ type carbide within the austenite grains to impart high-temperature strength. If the C content is less than 0.20%, the amount of eutectic carbide is small, and the eutectic carbide changes to unstable M ₂₃ C ₆ type, deteriorating the high temperature strength, so the C content is required to be 0.20% or more. On the other hand, if C exceeds 0.60%, the amount of eutectic carbides increases excessively, the high-temperature strength becomes saturated, and the toughness decreases, so it is preferable to keep C at 0.60% or less. For the above reasons, the amount of C in the alloy of the present invention is from 0.20 to
Limited to 0.60%. Si and Mn significantly affect the oxidation resistance of the alloy of the present invention. Table 1 shows the oxidation loss after repeating the cycle of heating and cooling at 1250°C for 16 hours 10 times.The oxidation resistance of Si is good in the range of 0.2 to 1.3%, and even if it is lower than this, it is still high. The oxidation resistance also deteriorates. On the other hand, as shown in Table 1, Mn
shows good oxidation resistance in the range of 1.3% or less,
Exceeding this will deteriorate the oxidation resistance. On the other hand, Mn
A small amount is necessary as a deoxidizing agent. For the above reasons, the Si content in the alloy of the present invention is set to 0.2 to 1.3%, and
Mn is limited to 1.3% or less.

[Table] In the alloy of the present invention, Or combines with C to form primary carbides and secondary carbides and has the effect of imparting high-temperature strength. It also forms a dense oxide of Or on the surface of the alloy, protecting the interior and increasing the oxidation resistance of the alloy. Table 2 shows the effect of Cr content on the oxidation loss after repeating the cycle of heating at 1250°C for 16 hours and then cooling to room temperature five times, and the creep rupture time at 850°C - 8Kg/ ^mm2 .
If it is lower than 25%, the creep rupture time is low;
When Cr exceeds 35%, oxidation resistance deteriorates. For the above reasons, the amount of Cr in the alloy of the present invention is 25 to 35%.
limited to.

[Table] Fe and Ni are the basic elements constituting the austenite matrix in the alloy of the present invention.
One of the important discoveries of the present invention is that the balance between Fe and Ni is important for oxidation resistance. Table 3 shows the influence of the balance of Fe and Ni on the oxidation loss after repeating the cycle of heating at 1250°C for 16 hours and cooling to room temperature 10 times.When Fe is 5 to 15% and Ni is 50% or more, The better the oxidation resistance, the better. For this reason, in the alloy of the present invention, Fe is limited to 5 to 15% and Ni is limited to 50% or more.

[Table] Ti is an essential element for improving high temperature strength in the alloy of the present invention. Ti precipitates from the austenite matrix as TiC, and becomes a nucleus for the subsequent precipitation of M ₂₃ C ₆ carbide, resulting in M ₂₃ C ₆
It has the effect of finely dispersing the precipitation of and improves high temperature strength. Table 4 shows 0.4%C-0.6%Si-1.0%
This shows the effect of Ti addition on the creep rupture time in the Mn-30%Cr-10%Fe-58%Ni system.
Addition of Ti improves creep rupture time by about twice. In order for such an effect of Ti addition to clearly appear, a minimum amount of Ti of 0.02% is required.
On the other hand, if the Ti content becomes too high, the oxidation resistance will deteriorate, so the Ti content in the alloy of the present invention is limited to 0.02 to 0.30%.

[Table] W has the effect of strengthening the austenite matrix as a solid solution and increasing high-temperature strength in the alloy of the present invention, but when it exceeds 5%, it causes primary carbides to change from M ₇ C ₃ to
When W is added to the alloy of the present invention, it is limited to 5% or less since it changes to M ₂₃ C ₆ and deteriorates high temperature strength and oxidation resistance. Table 5 shows the influence of W on creep rupture strength and oxidation resistance.

[Table] Among other elements, Nb and Co in particular deteriorate the oxidation resistance, so they should not be added to the alloy of the present invention unless unavoidably mixed as impurities. Furthermore, Al can be added up to about 0.2% as a deoxidizing agent. Next, examples of the alloy of the present invention will be described.
Table 6 shows the chemical composition of samples prepared to compare the properties of the alloy of the present invention with those of conventional alloys. All samples were melted in the air and cast into the shape of a JIS No. 4 tensile test piece. Cut out a sample from this and heat it to 850℃.
A creep rupture test at 1050℃ and an oxidation resistance test were conducted by repeating the cycle of heating at 1250℃ for 16 hours and then cooling to room temperature 10 times. Table 7 shows a comparison of creep rupture time and oxidation loss.The alloy of the present invention has a creep rupture strength higher than that of the conventional alloy that does not contain Co, and equivalent to that of the conventional alloy that contains Co, and the oxidation resistance is higher than that of the conventional alloy that does not contain Co. It can be seen that it is superior to both.

【table】

[Table] As stated above, the alloy of the present invention has the same high-temperature strength as conventional alloys containing Co, and has the advantage of being cheaper and having better oxidation resistance than these, so it can be used as a heat-resistant material for furnaces such as Schittrail material. It can be widely used as

Claims (1)

[Claims] 1. C0.20 to 0.60%, Si 0.2 to 1.3% in weight percentage,
Mn1.3% or less Cr25~35%, Fe5~15%, Ti0.02~
Austenitic heat-resistant casting alloy for skid rails with excellent high-temperature oxidation resistance, containing 0.30% Ni, 50% or more Ni, and the remainder being impurities. 2 C0.20~0.60%, Si0.2~1.3% in weight percentage,
Mn1.3% or less, Cr25~35%, Fe5~15%, Ti0.02
An austenitic heat-resistant casting alloy for skid rails with excellent high-temperature oxidation resistance, containing ~0.30%, W5% or less, and Ni50% or more, with the remainder being impurities.