INFLUENCE OF THE MICROSTRUCTURE AND THE GRAIN BOUNDARY PRECIPITATES ON THE BEHAVIOUR OF PH-AUSTENITIC STAINLESS STEEL IN COMPARISON WITH Ni-BASE SUPERALLOY DURING HIGH TEMPERATURE CREEP
Amer Eid Ali Amer;
Abstract
In this investigation; precipitation hardenable austenitic stainless steel (A-286) was used to study the influence of microstructure and grain boundary precipitations on the high temperature creep behavior at different stresses compared with that for
Nickel base super alloy.
Different creep cycles were applied for both PH-stainless steel non welded and laser beam welded alloy (6KW C02), namely at 625 and 650 °C at applied controlled creep stresses of 400 and 450 MPa.The base material sheets were solution treated ( 30
P. min, 960 °C, WQ) and aged in two steps (760 °C, 24h, FC and 705 °C, 16 h, AC)
befor being tested. On the other hand, the Ni-base alloy sheet was solution treated (1150°C, 10 min, WQ) and precipitation hardened (800°C, 8 h, AC) before being subjected to the creep tests.
To examine the changes in microstructure, Philips EM 400 TEM with an acceleration voltage of 120KV, and SEM with EDX analysis, as well as light microscopes were used.
It was found that, laser beam welded samples (LBS) of the precipitation hardenable steel investigated after creep deformation at temperature up to 625°C and at controlled stress of 400 and 450 MPa have a higher creep resistance and rupture life
2-3 times longer than that for base material at the same conditions. This increase in
creep strength and rupture life time of laser beam welded saples (LBS) over that for base material is attributed to the grain growth of austenite at HAZ and the formation of cellular and lamellar substructure in melted zones which allow dissolution of much TiC and hence increase the stability of austenite phase in which retardation of coarse MC, M23C6 and TJ phase ocurred. The absence of continuous carbide film of
uncoalescent M23C6 at grain boundaries together with the uneven grain boundaries
pinned with very fine l phase and carbides resulted in higher dislocation
interactions.
On the other hand, It was found also that the creep test performed at 650 °C at the same stress values offsets any gain in creep resistance of welded joints as compared with that for the base material at the same conditions. The elimination of
Nickel base super alloy.
Different creep cycles were applied for both PH-stainless steel non welded and laser beam welded alloy (6KW C02), namely at 625 and 650 °C at applied controlled creep stresses of 400 and 450 MPa.The base material sheets were solution treated ( 30
P. min, 960 °C, WQ) and aged in two steps (760 °C, 24h, FC and 705 °C, 16 h, AC)
befor being tested. On the other hand, the Ni-base alloy sheet was solution treated (1150°C, 10 min, WQ) and precipitation hardened (800°C, 8 h, AC) before being subjected to the creep tests.
To examine the changes in microstructure, Philips EM 400 TEM with an acceleration voltage of 120KV, and SEM with EDX analysis, as well as light microscopes were used.
It was found that, laser beam welded samples (LBS) of the precipitation hardenable steel investigated after creep deformation at temperature up to 625°C and at controlled stress of 400 and 450 MPa have a higher creep resistance and rupture life
2-3 times longer than that for base material at the same conditions. This increase in
creep strength and rupture life time of laser beam welded saples (LBS) over that for base material is attributed to the grain growth of austenite at HAZ and the formation of cellular and lamellar substructure in melted zones which allow dissolution of much TiC and hence increase the stability of austenite phase in which retardation of coarse MC, M23C6 and TJ phase ocurred. The absence of continuous carbide film of
uncoalescent M23C6 at grain boundaries together with the uneven grain boundaries
pinned with very fine l phase and carbides resulted in higher dislocation
interactions.
On the other hand, It was found also that the creep test performed at 650 °C at the same stress values offsets any gain in creep resistance of welded joints as compared with that for the base material at the same conditions. The elimination of
Other data
| Title | INFLUENCE OF THE MICROSTRUCTURE AND THE GRAIN BOUNDARY PRECIPITATES ON THE BEHAVIOUR OF PH-AUSTENITIC STAINLESS STEEL IN COMPARISON WITH Ni-BASE SUPERALLOY DURING HIGH TEMPERATURE CREEP | Other Titles | تأثير البنية المجهرية والترسبات على حدود الحبيبات فى سلوك الصلب الاوستينيتى الذى لايصدأ من النوع المصلد بالترسب مقارنة بسبيكة النيكل الفائقة وذلك اثناء التعرض لاجهاد الزحف فى درجات الحرارة العالية | Authors | Amer Eid Ali Amer | Issue Date | 2004 |
Attached Files
| File | Size | Format | |
|---|---|---|---|
| B14179.pdf | 949.22 kB | Adobe PDF | View/Open |
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