Gas-phase aluminizing of HP40Nb steel used in reformer tubes: Synthesis, characterization, and its implications for the microstructure and high-temperature creep resistance of the base alloy
This study investigates the microstructure and creep behavior of gas-phase aluminized High-Performance (HP40Nb) steel. Microstructures of coated and base alloy were examined by electron and optical microscopes. Gas-phase aluminizing of HP steel resulted in the formation of a top AlNi layer over an i...
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| Published in: | The International journal of pressure vessels and piping Vol. 200; p. 104833 |
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| Main Authors: | , , , |
| Format: | Journal Article |
| Language: | English |
| Published: |
Elsevier Ltd
01-12-2022
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| Subjects: | |
| Online Access: | Get full text |
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| Summary: | This study investigates the microstructure and creep behavior of gas-phase aluminized High-Performance (HP40Nb) steel. Microstructures of coated and base alloy were examined by electron and optical microscopes. Gas-phase aluminizing of HP steel resulted in the formation of a top AlNi layer over an interdiffusion zone (IDZ) on the base alloy. Results also showed that there were hardly any cavities or discontinuities formed in top layer and IDZ during the aluminizing process. The creep test results showed that the gas-phase aluminized steel had significantly a higher minimum creep rate and consequently a shorter time-to-rupture, as compared to uncoated HP40Nb steel. Microscopic examinations revealed that the main reason for the fracture of the steel after the creep test was formation of micro-cavities in the vicinity of carbides and growth of micro-cracks along the grain boundaries and alongside inter-dendritic areas. Also, fractography analysis showed that a quasi-cleavage fracture had occurred for both coated and uncoated steel. The implication of gas-phase aluminizing on creep resistance of coated HP40Nb steel, and its interrelation between the microstructure and observed mechanical properties are discussed and explained through the paper.
•High-temperature creep behavior of gas-phase aluminized HP40Nb steel was investigated.•The main structure of the coating is composed of single-phase AlNi.•Creep life of the coated sample was shorter than the bare HP40Nb steel due to the heat treatment applied during aluminizing.•The main mechanism of creep fracture for both coated and bare HP40Nb was the cavity nucleation along grain boundaries. |
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| ISSN: | 0308-0161 1879-3541 |
| DOI: | 10.1016/j.ijpvp.2022.104833 |