A mechanistic study of retained δ-ferrite in additively-manufactured Grade 91 steel
A combined experimental, characterization, and simulation study has been conducted to develop a quantitative description for microstructural evolution during Laser-Directed Energy Deposition (L-DED) of Grade 91 steel. Initial L-DED deposits of Grade 91 made without preheat exhibiting much greater vo...
Saved in:
| Main Authors: | , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Elsevier
2025-05-01
|
| Series: | Journal of Materials Research and Technology |
| Subjects: | |
| Online Access: | http://www.sciencedirect.com/science/article/pii/S2238785425009937 |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| _version_ | 1850201064168488960 |
|---|---|
| author | Zhe Lyu William Hoffmann Waris Khan Thomas Lienert Leijun Li |
| author_facet | Zhe Lyu William Hoffmann Waris Khan Thomas Lienert Leijun Li |
| author_sort | Zhe Lyu |
| collection | DOAJ |
| description | A combined experimental, characterization, and simulation study has been conducted to develop a quantitative description for microstructural evolution during Laser-Directed Energy Deposition (L-DED) of Grade 91 steel. Initial L-DED deposits of Grade 91 made without preheat exhibiting much greater volume fractions of δ-ferrite and much less martensite than anticipated, with non-uniform hardness values and lower average hardness levels. Based on our hypothesis for this result, preheating was applied to subsequent deposits, but not for the conventional reasons related to control of austenite decomposition. Rather, the results were consistent with the concept that greater times in the higher temperature range for the δ to γ transformation permitted the transformation to progress further toward completion during L-DED of Grade 91 owing to slower cooling rates resulting from increased preheating. Increasing preheat temperatures up to 350 °C resulted in deposits with progressively lower volume fractions of retained δ-ferrite with greater fractions of martensite and higher average hardness values. The final phase fractions and resulting hardness levels are dependent on the δ to γ transformation kinetics that are dictated by the cooling rates for transformation, which in turn are governed by the preheat temperatures. The results of our work have broader implications toward rationalizing the microstructures and properties for AM with rapid cooling rates of many hardenable alloy steels that solidify as δ-ferrite. Finally, the model results were used to develop a novel revision to the continuous cooling transformation diagram for Grade 91 that captures the kinetics of the δ to γ phase transformation. |
| format | Article |
| id | doaj-art-db442f115dce4de58a4cefe8da8c5e11 |
| institution | OA Journals |
| issn | 2238-7854 |
| language | English |
| publishDate | 2025-05-01 |
| publisher | Elsevier |
| record_format | Article |
| series | Journal of Materials Research and Technology |
| spelling | doaj-art-db442f115dce4de58a4cefe8da8c5e112025-08-20T02:12:07ZengElsevierJournal of Materials Research and Technology2238-78542025-05-01365128514310.1016/j.jmrt.2025.04.173A mechanistic study of retained δ-ferrite in additively-manufactured Grade 91 steelZhe Lyu0William Hoffmann1Waris Khan2Thomas Lienert3Leijun Li4University of Alberta, Edmonton, AB, CanadaGKN Aerospace, Lake Worth, TX, USAUniversity of Alberta, Edmonton, AB, CanadaUniversity of Alberta, Edmonton, AB, Canada; T. J. Lienert Consulting, LLC, Los Alamos, NM, USAUniversity of Alberta, Edmonton, AB, Canada; Corresponding author.A combined experimental, characterization, and simulation study has been conducted to develop a quantitative description for microstructural evolution during Laser-Directed Energy Deposition (L-DED) of Grade 91 steel. Initial L-DED deposits of Grade 91 made without preheat exhibiting much greater volume fractions of δ-ferrite and much less martensite than anticipated, with non-uniform hardness values and lower average hardness levels. Based on our hypothesis for this result, preheating was applied to subsequent deposits, but not for the conventional reasons related to control of austenite decomposition. Rather, the results were consistent with the concept that greater times in the higher temperature range for the δ to γ transformation permitted the transformation to progress further toward completion during L-DED of Grade 91 owing to slower cooling rates resulting from increased preheating. Increasing preheat temperatures up to 350 °C resulted in deposits with progressively lower volume fractions of retained δ-ferrite with greater fractions of martensite and higher average hardness values. The final phase fractions and resulting hardness levels are dependent on the δ to γ transformation kinetics that are dictated by the cooling rates for transformation, which in turn are governed by the preheat temperatures. The results of our work have broader implications toward rationalizing the microstructures and properties for AM with rapid cooling rates of many hardenable alloy steels that solidify as δ-ferrite. Finally, the model results were used to develop a novel revision to the continuous cooling transformation diagram for Grade 91 that captures the kinetics of the δ to γ phase transformation.http://www.sciencedirect.com/science/article/pii/S2238785425009937Additive manufacturingDirect-energy deposition (DED)Cooling rateFerrite to austenite transformationδ-ferriteExtended CCT Diagram |
| spellingShingle | Zhe Lyu William Hoffmann Waris Khan Thomas Lienert Leijun Li A mechanistic study of retained δ-ferrite in additively-manufactured Grade 91 steel Journal of Materials Research and Technology Additive manufacturing Direct-energy deposition (DED) Cooling rate Ferrite to austenite transformation δ-ferrite Extended CCT Diagram |
| title | A mechanistic study of retained δ-ferrite in additively-manufactured Grade 91 steel |
| title_full | A mechanistic study of retained δ-ferrite in additively-manufactured Grade 91 steel |
| title_fullStr | A mechanistic study of retained δ-ferrite in additively-manufactured Grade 91 steel |
| title_full_unstemmed | A mechanistic study of retained δ-ferrite in additively-manufactured Grade 91 steel |
| title_short | A mechanistic study of retained δ-ferrite in additively-manufactured Grade 91 steel |
| title_sort | mechanistic study of retained δ ferrite in additively manufactured grade 91 steel |
| topic | Additive manufacturing Direct-energy deposition (DED) Cooling rate Ferrite to austenite transformation δ-ferrite Extended CCT Diagram |
| url | http://www.sciencedirect.com/science/article/pii/S2238785425009937 |
| work_keys_str_mv | AT zhelyu amechanisticstudyofretaineddferriteinadditivelymanufacturedgrade91steel AT williamhoffmann amechanisticstudyofretaineddferriteinadditivelymanufacturedgrade91steel AT wariskhan amechanisticstudyofretaineddferriteinadditivelymanufacturedgrade91steel AT thomaslienert amechanisticstudyofretaineddferriteinadditivelymanufacturedgrade91steel AT leijunli amechanisticstudyofretaineddferriteinadditivelymanufacturedgrade91steel AT zhelyu mechanisticstudyofretaineddferriteinadditivelymanufacturedgrade91steel AT williamhoffmann mechanisticstudyofretaineddferriteinadditivelymanufacturedgrade91steel AT wariskhan mechanisticstudyofretaineddferriteinadditivelymanufacturedgrade91steel AT thomaslienert mechanisticstudyofretaineddferriteinadditivelymanufacturedgrade91steel AT leijunli mechanisticstudyofretaineddferriteinadditivelymanufacturedgrade91steel |