Nanocrystalline Advanced High-Strength Steel Produced by Cold Rolling and Annealing

28 Pages·2016·2.74 MB·English

by  Jennifer Greenfelder

Nanocrystalline Advanced High-Strength Steel
Produced by Cold Rolling and Annealing
D. C. Van Aken and D. M. Field
Materials Science and Engineering
Missouri S&T
Center launched July 1,
2013
•12 industrial members
•$750,000 current research
•7 funded research projects
−Refractory technology (2)
−Deformation processing (1)
−Casting technology (1)
−Steel alloy development (1)
−Foundry technology
3
3rd Generation Advanced High-Strength Steel
• NSF / DOE funded work on Nano Acicular
Duplex Steels
− Meghan McGrath Ph.D. (2012)
− Krista Limmer Ph.D. (2014)
• PSMRC funded work on Two-stage TRIP AHSS
− Scott Pisarik M.S. (2014)
− Dan Field Ph.D. (2018)
• Industrial partners: Nucor, AK Steel, USS and
ArcelorMittal
3rd Generation Property Space
• Survey work to
determine chemistry
& properties
• Batch Annealed
material promising
route to 3rd Gen
AHSS
• All alloys produced
and tested are shown
What is Two-Stage TRIP?
= γ-austenite = ε-martensite = α-martensite
Two-Stage Grain Refinement
Y
Y
X
X
Athermal transformation
• ε-martensite segments the austenite
• 6 variants of a-martensite segments the ε-martensite
Carbon’s Effect Upon ε- M
S
Increased C content
•
decreases the
martensite start
temperature for ε-
martensite
Carbon content should
•
be kept below 0.2 wt%
to ensure TRIP effect
at room temperature
Prefer Mse >Msa
•
Koyama et al., Mater. Sci. Eng. A
vol. 528, (2011) 7310-7316.
Thermodynamic Modeling
• Gibbs free energy for the γ→ε phase transformation can
be expressed using a regular solution model

• Stacking fault energy SFE describes ε-martensite
stability relative to γ-austenite

• n=4 for e-martensite
• Reported SFE are RT calculated
Thermodynamic Model for M ε Temperature
S
S&T
Composition limits in wt.% of the 90 alloys from literature
M ε Map for FeMnSiAl Alloys
S
• Carbon and nitrogen fixed at 0.07 wt.% and 0.017 wt.%
• n=4 in SFE calculation