Effect of Long-term Thermal Exposure on Microstructure and Performance of GH2070P Ferronickel-based Hi-temperature Alloy
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Abstract
The thermal exposure tests at 675℃ and for 1 000,3 000 h and 5 000 h respectively are conducted to the GH2070P ferronickel-based hi-temperature alloy tube as key candidate material for the boiler with 675℃ parameter,and the post thermal exposure mechanical properties and microstructure evolutions of the alloy are investigated. The facts as follows are revealed with the alloy tube as thermal exposed at 675℃ and for 1 000 hours. The γ' phase is precipitated in grain and the M23C6 carbide phase is precipitated at grain boundary;the ambient temperature tensile strength,the yield strength and the hardness of the alloy are obviously increased,whereas it’s impact toughness goes down;along with the increase of thermal exposure time going up to 5 000 h,the size of the γ' phase is coarsened,which is in alignment with the LSW coarsening theory;and the size of the M23C6 carbides are increased slightly,but are still presenting an intermittent distribution state at the grain boundary,and no network structure is formed;In general the ambient temperature tensile strength,the yield strength and the hardness of the alloy consistently keep at a rather high level,while its impact toughness reduction speed is getting slow.
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