Post weld heat treatment for chemically stabilized austenitic stainless steel
AssigneeFluor Technologies Corporation
InventorsBarry Messer, Terrell T. Phillips, Vasile Oprea
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Abstract
Thermo-mechanical properties of welds in stainless steel is substantially improved by the implementation of a post weld heat treatment that iliminates sigma phase in the heat treated zone and favors niobium carbonitride precipitate formation in a desirable size range. In most cases, post weld heat treated material can be employed in pressurized devices at temperatures exceeding 550° C., which is currently regarded the upper safe temperature limit, and material according to the inventive subject matter was tested at temperature of up to 850° C. without reheat cracking.
Claims20
A method of treating austenitic stainless steel having a weld, comprising:
- subjecting the weld to a stress relief temperature that is below a temperature in which a metal carbonitride is formed;
- subjecting the weld to a solution anneal temperature that is effective to dissolve delta ferrite and that is below a temperature in which grain growth occurs;
- and
- subjecting the weld to a stabilization anneal temperature that is effective to avoid sigmatization and to promote formation of niobium carbonitride precipitates having a size between 300 Å to 600 Å.
A method of treating austenitic stainless steel having a weld, comprising:
- heating the weld to a stress relief temperature of between 510° C. and 648° C. using a ramp-up rate of at least 14° C. per minute;
- heating the weld to a solution anneal temperature of between 1010° C. and 1177° C. using a ramp-up rate of at least 18° C. per minute;
- and
- cooling the weld to a stabilization anneal temperature of at least 930° C. using a ramp-down rate of less than 3° C. per minute.
A post weld heat treated austenitic stainless steel material comprising a weld that is substantially free of a sigma phase and further has niobium carbonitride precipitates with a size between 300 Å to 600 Å, and wherein the weld has an increased toughness compared to a toughness before the heat treatment as determined by an impact notch test.
Dependencies are inferred from the claim text.