JPS634898B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a heat-resistant alloy useful as a cracking tube material for ethylene production in the petrochemical industry. [Prior art and its problems] ASTM HP40 material (0.4C-25Cr-35Ni-
Fe) and its improved materials (0.4C−25Cr−35Ni−Nb, W
−Fe) is used. This HP40 material is generally used in a temperature range of 900 to 1050°C, and has sufficient oxidation resistance, carburization resistance, and mechanical strength in this temperature range. However, in the temperature range exceeding 1050℃,
There are problems with carburization resistance and mechanical strength, especially creep rupture strength. In addition, HP improved materials (0.4C−25Cr−35Ni−Nb,
W-Fe) exhibits better carburization resistance than HP40 material at temperatures up to 1100℃, but above 1100℃, the oxidation resistance, creep rupture strength, and carburization resistance decrease significantly, especially acid resistance. The deterioration in chemical resistance is significant. Therefore, there is a need to develop a new material for the tube that has various properties that can sufficiently withstand high-temperature operations exceeding 1100°C, particularly excellent creep rupture strength, oxidation resistance, and carburization resistance. In addition, TIG welding, MIG welding, or shielded arc welding are used to assemble the coil by joining tubes together or joining tubes and bends, so it has excellent weldability. This is required. The present invention aims to provide a new heat-resistant alloy that satisfies such requirements. [Technical means and effects] The heat-resistant alloy according to the present invention contains C: 0.3 to 0.5%,
Si: 2.0% or less, Mn: 2.0% or less, P: 0.03% or less, S: 0.03% or less, Cr: 30.0-40.0%, Ni:
30.0~40.0%, Co: 5.0~20.0%, Al: 0.02~0.6
%, N: 0.08% or less, and Nb: 0.3 to 1.8%,
It has a component composition consisting of one or two of W: 0.5 to 6.0%, one or two of Ti: 0.02 to 0.5%, Zr: 0.02 to 0.5%, and the remainder substantially Fe ( Ingredient content (%) is by weight). The alloy of the present invention can be used in a temperature range exceeding 1100℃, especially
It has high creep rupture strength at high temperatures around 1150°C, as well as excellent oxidation and carburization resistance. Moreover, weldability is also good. The reasons for limiting the components of the alloy of the present invention are as follows. C: 0.3 to 0.5% C dissolved in the matrix during casting and solidification precipitates as chromium carbide when the tube is heated during actual use, thereby contributing to improving the creep rupture strength. To obtain high creep rupture strength in the temperature range above 950℃, at least 0.3
% is required. The effect increases as the content increases, but if it exceeds 0.5%, embrittlement due to excessive precipitation of Cr carbides will increase, so the upper limit should not be exceeded.
0.5%. Si: 2.0% or less Si is added as a deoxidizing agent during alloy melting. It also has the effect of increasing the fluidity of molten steel and improving castability. However, if it exceeds 2.0%, it will have a negative effect on creep rupture strength and weldability.
The upper limit is %. Mn: 2.0% or less Mn has the effect of preventing hot cracking during welding by deoxidizing molten steel and fixing S, an impurity element, as MnS. but,
Even if the content exceeds 2.0%, the effect will be small considering the increase in content, so 2.0% is set as the upper limit. P: 0.03% or less, S: 0.03% or less The impurity elements P and S both increase susceptibility to hot cracking during welding, so each should be 0.03% or less.
The upper limit is %. Cr: 30.0-40.0% Cr has the effect of increasing oxidation resistance and high temperature strength. To ensure oxidation resistance and high-temperature strength for long-term use in high-temperature ranges of 1100℃ or higher
It is necessary to contain 30.0% or more. Oxidation resistance and high temperature strength improve as the content increases, but a content of up to 40.0% is sufficient for service temperatures up to 1200°C. Sideways
30.0-40.0%. Ni: 30.0-40.0% Ni is an element that stabilizes the austenite phase and has the effect of increasing oxidation resistance and high-temperature strength. In order to stabilize the austenite phase in relation to the Cr content and to ensure stable oxidation resistance and carburization resistance at 1100 to 1200°C, the Ni content is specified to be 30.0 to 40.0%. Al: 0.02-0.6% Al forms a protective film on the alloy surface in a high temperature range and prevents C from entering from the carburizing atmosphere. In order to obtain this effect of improving carburization resistance, the content needs to be 0.02% or more. Note that Al has little effect on improving creep rupture strength, and if it is contained in a large amount, the ductility at room temperature will decrease. Therefore, 0.6
The upper limit is %. Co: 5.0-20.0% Co, like Ni, stabilizes the austenite phase,
It is also effective in improving oxidation resistance and high-temperature strength. At least 5.0% is required to achieve this effect. The effect increases as the content increases, but
For operating temperatures up to 1200°C, a maximum content of 20.0% is sufficient in consideration of the amount of Ni. Therefore, it is set at 5.0 to 20.0%. N: 0.08% or less N is an impurity element, and if it is contained in a large amount, hardening progresses and embrittlement occurs, so the upper limit is set at 0.08%. In addition to the above elements, the alloy of the present invention further contains Nb,
It contains one or two elements selected from the group W, and one or two elements selected from the group Ti and Zr. Nb: 0.3 to 1.8% Nb crystallizes eutectic NbC at grain boundaries, increasing creep fracture resistance at grain boundaries. This effect is
It is recognized from 0.3% and increases as the content increases, but when it exceeds 1.8%, the effect is small despite the increase. Therefore, the upper limit is 1.8%, preferably 1.0%.
% or less. W: 0.5 to 6.0% W is effective in improving creep rupture strength by solid solution in the austenite phase and formation of grain boundary carbides. This effect is recognized from the content of 0.5%,
The effect increases as the dose increases. However, if the content is too large, it will harden, resulting in poor ductility and poor workability and weldability, so the upper limit is set at 6.0%. More preferably, it is 1.0 to 5.0%. Ti: 0.02 to 0.5% Ti contributes to improving creep rupture strength by retarding the growth and coarsening of chromium carbides generated in the austenite phase due to reheating during actual use as tubes and the like. To achieve this effect, a content of at least 0.02% is required. However, if it is contained in a large amount, it causes a decrease in strength due to coarsening of precipitates, increased amount of oxide inclusions, etc., so the upper limit is set at 0.5%. The more preferable content is
It is 0.1-0.4%. Zr: 0.02 to 0.5% Zr dissolves in solid solution in the austenite phase, and its solid solution strengthening increases creep rupture strength. At least 0.02% is required to obtain this effect as well. The effect increases as the content increases, but if it exceeds 0.5%, the cleanliness of the molten steel decreases. Moreover, the effect is small considering the addition of expensive materials. By then, 0.5
The upper limit is %. More preferably, it is 0.1 to 0.3%. [Example] Molten alloy produced in a high-frequency induction melting furnace was subjected to centrifugal casting to form hollow castings (outer diameter 138 mm x wall thickness 23.5 mm).
× length 520 mm) was obtained. The chemical composition of each test casting is shown in Table 1. A test piece was taken from each casting,
An oxidation test, a carburization test, and a creep rupture test were conducted for each using the following test methods.
The results shown in the table were obtained. [A] Oxidation test A test piece (12 mmφ x 50 mm) was exposed to 1200
Heat and hold at ℃ for 100 hours. After the test, remove scale from the surface of the test piece, measure the amount of weight loss due to oxidation, and determine the amount of corrosion (mm/year). [B] Carburizing test A test piece (12 mmφ x 60 mm) was kept in a solid carburizing agent (Degussa KG30) at a temperature of 1150°C for 300 hours. After the test, chips are collected at a pitch of 0.25 mm from the surface of the test piece, and the amount of carbon increase at a depth of 1 mm from the surface is determined by chemical analysis. [C] Creep rupture test According to the provisions of JIS Z 2272. Test temperature: 1150
℃, load: 1Kgf/mm ² .

【table】

【table】

〔Effect of the invention〕

The heat-resistant alloy of the present invention has material properties superior to conventional materials, HK40 material and HK improved material, in the high temperature range exceeding 1100°C, and has excellent oxidation resistance, carburization resistance, and creep rupture resistance even at around 1150°C. Indicates strength. Therefore, it is suitable as a cracking tube material and guarantees greater durability and stability than conventional materials. Of course, its uses are not limited to those mentioned above, and it is also suitable as a material for re-formed tubes, and is further useful as a structural material for various high-temperature applications such as radiant tubes and hearth rollers.

Claims (1)

[Claims] 1 C: 0.3-0.5%, Si: 2.0% or less, Mn: 2.0%
Below, P: 0.03% or less, S: 0.03% or less, Cr:
30.0~40.0%, Ni: 30.0~40.0%, Co: 5.0~20.0
%, Al: 0.02 to 0.6%, N: 0.08% or less, and
Any one or two of Nb: 0.3-1.8%, W: 0.5-6.0%, Ti: 0.02-0.5%, Zr: 0.02
A heat-resistant alloy with excellent creep rupture strength, oxidation resistance, and carburization resistance, consisting of ~0.5% of one or two types, and the remainder substantially Fe.