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Quenching and partitioning (Q&P) processing of third-generation advanced high strength steels generates multiphase microstructures containing metastable retained austenite. Deformation-induced martensitic transformation of retained austenite improves strength and ductility by increasing instantaneous strain hardening rates. This paper explores the influence of martensitic transformation and strain hardening on tensile performance. Tensile tests were performed on steels with nominally similar compositions and microstructures (11.3 to 12.6 vol. pct retained austenite and 16.7 to 23.4 vol. pct ferrite) at 980 and 1180 MPa ultimate tensile strength levels. For each steel, tensile performance was generally consistent along different orientations in the sheet relative to the rolling direction, but a greater amount of austenite transformation occurred during uniform elongation along the rolling direction. Neither the amount of retained austenite prior to straining nor the total amount of retained austenite transformed during straining could be directly correlated to tensile performance. It is proposed that stability of retained austenite, rather than austenite volume fraction, greatly influences strain hardening rate, and thus controls strength and ductility. If true, this suggests that tailoring austenite stability is critical for optimizing the forming response and crash performance of quenched and partitioned grades.
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This content will become publicly available on January 1, 2027
Compressive-tensile yield asymmetry and aging-induced embrittlement in a selective laser melted 17-4 PH stainless steel
We studied the compressive-tensile yield asymmetry (CTYA) and its sensitivity to standard post-processing treatments for a 17-4 PH stainless steel processed with selective laser melting (SLM). Quasistatic tensile and compression tests at ambient temperatures reveal a consistent CTYA for all tested conditions, with compressive yield strengths exceeding tensile values. In the as-printed state, yield asymmetry (Δσ) is ∼113 MPa. Stress-relieving at 300 °C results in only a marginal decrease in asymmetry (Δσ ∼109 MPa), suggesting that the residual stresses generated during SLM have a negligible effect on the observed CTYA. Our analyses indicate that “dynamic softening” due to a stress-assisted austenite-to-martensite transformation governs the yield behavior similar to that observed in transformation-induced plasticity (TRIP)-assisted steels containing mechanically unstable retained austenite. This interpretation is further supported by the increased asymmetry, Δσ ∼127 MPa, observed in a solution-treated and aged specimen, which has a slightly higher retained austenite volume fraction (24 % vs. 21 %). Direct aging at 482 °C of the as-printed steel with a ferritic microstructure causes severe embrittlement. Brittle fracture occurs under tensile stresses well below the yield strength. This pronounced loss of ductility most likely arises from a strong <001> fiber texture along the build direction developed during SLM, which is known to promote cleavage-type fracture on {001} planes. A solution treatment at 1000 °C for 1 h, austenitizes the microstructure completely, and subsequent quenching produces a predominantly martensitic structure with a much weaker crystallographic texture, which restores a favorable strength-ductility balance after aging.
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- Award ID(s):
- 2105362
- PAR ID:
- 10659664
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Materials Science and Engineering: A
- Volume:
- 950
- Issue:
- C
- ISSN:
- 0921-5093
- Page Range / eLocation ID:
- 149537
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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