[PPT] - High Mn, High Al Steels for Thick Plate Applications M ATERIALS & PowerPoint Presentation

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Materials & Advanced Manufacturing (M&AM)

High Mn, High Al Steels for Thick Plate Applications

MATERIALS & ADVANCE MANUFACTURING (M&AM) TECHNICAL SESSION AUGUST 7-9, 2018 - NOVI, MICHIGAN

Katherine Sebeck, PhD Ian Toppler Matt Rogers U.S. Army TARDEC Warren, MI Krista Limmer, PhD Bryan Cheeseman, PhD Daniel Field, PhD US Army Research Lab Aberdeen, MD LTC Ryan Howell, PhD US Army PEO GCS Warren, MI William Herman, PhD General Dynamics Land Systems Sterling Heights, MI DISTRIBUTION A. Approved for public release: distribution unlimited. OPSEC #1061

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Materials & Advanced Manufacturing (M&AM)

Outline

Background and Motivation
Industrial Pour Outcomes
Rolling and Forging of Plates
Heat Treatment
Plate Characterization
Welding
Machining
Conclusions and Continuing Work

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Materials & Advanced Manufacturing (M&AM)

FeMnAl - Collaborators

Funding Acknowledgements: Advanced Vehicle Power Technology Alliance (AVPTA) "Extended Enterprise" Joint DoE/DoD Effort FY17 Army ManTech “Manufacturing Processes for Lightweighting Heavy Combat Vehicles” Individual Acknowledgements: Craig Niese, Chris Karas (GDLS) Zhili Feng, Dean Pierce (ORNL) Matt Sinfield (ONR) Ryan Nicol, Jeff Krzeszak, Jared Wysocki, Ed Barshaw(PdM Abrams) Fred Fletcher (Arcelor Mittal) Jim Kane, Joe DeGennova (EQS) Carl Johnson (TARDEC)

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Materials & Advanced Manufacturing (M&AM)

What is FeMnAl?

Alloys contain between 10-30 wt.% Mn, 3-12 wt.% Al, 0-1 wt.% C, 0-1 wt.%

Si

– Al, Si, and C reduce the density 2 ways – direct substitution into the matrix and matrix dilation

Also may contain Cr, Ni, Mo, Nb, V
Current target: 28Mn-9.5Al-0.9C-1.0Si-0.5Mo
FeMnAl evolved from Hadfield steels (Mangalloy) of Fe-13Mn-1.2C & FeAl

alloys

– Intermittently investigated going back to 1943 – Adding Mn to Fe-Al alloys to improve ductility

Navy investigated as alternative to Cr and Ni austenitic stainless steels

– Emphasis on corrosion resistance, rather than mechanical properties

Age hardenability discovered in late 1960s

– High hardnesses opened possibilities for additional applications

Recent works emphasizing thin sheet for automotive body frames

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Materials & Advanced Manufacturing (M&AM)

Programmatic Drivers

Weight and Performance

– 7.8 g/cc vs 2.7 g/cc (steel vs Al) – Space considerations – Strength/Density vs Threat Performance/Density

Going thinner is not necessarily better, or possible

– Rigid structures and underbody required in military vehicles

Automotive lightweighting is driven by meeting fuel

economy standards

Army lightweighting is driven by meeting performance

requirements for changing threats, new equipment, and maintaining logistic supports

– Army bridges, NATO rail car, and highway equipment transport trailer (HETT) designed for 70T capacity – Weight reduction needs driven by “hard points” instead of $/lb motivation

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Materials & Advanced Manufacturing (M&AM)

Steel Processing Steps

Raw Materials

Ferromanganese vs

electrolytic Mn

Target chemistry

Melt Practices

Sequence of

additions

Ar stirring
Cover gases
Ca treatment
Ladle refractories
Melt time
Target

temperatures

Ingot Pour

Ladle superheat
Mold flux
Mold geometry
Gate sizes
Mold preheat
Quenching
Volume per pour
Lancing
Removal timing
Cooling rate

Pre-rolling processes

Painting
Forging
Grinding

Rolling

Pre-heat

temperature

Heating

time/method

Single vs double

conversion

Descale passes
Edging Passes
Cooling
Pickling
Piece width

Heat Treatment

Solutionizing
Temperature
Time
Ageing
Temperature
Time
Multi-stage cycles

Cut to Plate

Cutting Type
Feed Rate

Machining and Assembly

Surface grinding
Drilling
Welding

Items in black are known values Items in green are preliminary Items in white are to be determined

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Materials & Advanced Manufacturing (M&AM)

Industrial Pours – Teeming Flux

Typical steel fluxes have high SiO2 content to ensure good flow, coverage
SiO2 reacts with Al to form Si and Al2O3

– [Al] + SiO2 -> [Si] + Al2O3

– Resulted in significant Al losses in first heat attempt

Compared 4 different fluxes

Ingot # Flux

1 Typical SiO2 2 High C 3 1:1 Lime alumina 4 Soda lime alumina +CaF A (higher CaF) 5 Soda lime alumina +CaF B

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Materials & Advanced Manufacturing (M&AM)

Industrial Pours – Quality Control

Due to the high alloy content and shrinkage behavior, large ingot sizes may not be possible

– 34”x47” ingot fractured during cooling

Chemistry analysis in production typical is performed with Optical Emission Spectroscopy

– Tends to overestimate Mn, Al compared to Inductively Couple Plasma Spectroscopy (ICP), underestimates C content

Pour Date Mn Al C Mo Si Fe (bal) July 17 (ICP) 28.8 9.1 1.01 0.5 0.6 59.9 July 17 (OES) 29.19 9.9 0.92 0.5 0.96 58.53 Feb 2018 (OES) 29.7 9.6 0.84 0.54 0.8 58.2

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Materials & Advanced Manufacturing (M&AM)

Rolling Temperature

Compressive testing via Gleeble
Flow stress drops off rapidly between 1175°C to

1200°C during tensile deformation

1950°F (1065°C)

22 Aug 2017

2128°F (1121°C)

12 Oct 2017

2200°F (1202°C)

12 April 2018 UNCLASSIFIED//DIST. A

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Materials & Advanced Manufacturing (M&AM)

Forging Effects

A1132-4B: Forged between 2150 – 2200° F
Improved surface finish compared to as-cast ingot A1132-5

– Similar edge cracking magnitude

A1131-1: Rolled to 1.5” plate – soak at 1950° F A1131-5: Forged then rolled to 1.5” plate – soak at 2150° F

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Materials & Advanced Manufacturing (M&AM)

Forging Effects - Microstructure

Right: Forged, as rolled (1”)
Left: As rolled (1”)
Forged microstructure shows more

homogenous grain shape, fewer elongated stringers

Similar grain size distribution through

thickness

As rolled hardness:

– Forged – 201 BHN – As-cast – 251 BHN

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Materials & Advanced Manufacturing (M&AM)

Heat Treatment - Ageing

Homogenize/Austenitize and rolling preheat between 1000°C to 1150°C (~1850°F - 2100°F)
Water quench preferred (no martensitic transformation)
Age <550°C (~1000°F)

κ-carbide cubic perovskite crystal structure (E21)

Al Al Al Al Al Al Al Al C

[Fe, Mn] [Fe, Mn] [Fe, Mn] [Fe, Mn] [Fe, Mn] [Fe, Mn]

Micrograph of wrought FeMnAl base metal, showing two small islands of ferrite in a predominately austenitic microstructure

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Materials & Advanced Manufacturing (M&AM)

Heat Treatment – Single Stage Aging

As-Rolled (HB)
Hot rolling to gauge followed

by air cooling

Initial hardness within target

hardness range

Hardness increases with time
Solution Treated &

Quenched (STQ)

1922oF (1050oC)
2 hours
Water quench to room

temperature

Peak/Target occurs at ~20 hrs
Aging
1000oF (538oC)
Variable times

STQ: 195 ± 4 BHN STQ+30hr: 320 ± 5 BHN STQ+30hr: 320 ± 5 BHN

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Materials & Advanced Manufacturing (M&AM)

Heat Treatment – Two Phase Aging

A two-stage heat treatment has begun to

improve the carbide precipitation reaction

Low initial nucleation step followed by a high

temperature growth step

Purpose:
Accelerate heat treatment times
Prevent formation of carbides at grain

boundaries

Two-stage aging increased energy

adsorption

Higher toughness at reduced aging times

without sacrificing hardness

HT A and HT E have lower toughness for

equivalent hardness to the two-stage aging

Impact energy still below target value for

application

A. 30 hours at 985oF B. 2 hours at 840oF + 2 hours at 1110oF C. 4 hours at 840oF + 4 hours at 1110oF D. 4 hours at 840oCoF + 1 hour at 1110oF E. 4 hours at 1110oF

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Materials & Advanced Manufacturing (M&AM)

Heat Treatment - Decarburization

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 5 10 15 20

Carbon (wt %)

Furnace Time (hrs)

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Materials & Advanced Manufacturing (M&AM)

Base Material Charpy Impact

Charpy impact toughness performing below

expectations

Decreasing sulfur improved performance in

solution treated & quenched condition

– No impact on performance in the aged condition – Testing alternative aging sequence to adjust precipitation path

Charpy Impact Cross Section 340 BHN, tested at 20°C Grain boundary failure

STQ: BHN 200±5, CVN 200J Aged: BHN 340±10, CVN 14J

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Materials & Advanced Manufacturing (M&AM)

Base Material Tensile Test

Modulus ≈ 150 GPa

1. Quasi-Static Compression (0.001/s) – YS ≈ 1080 MPa 2. High-Rate Compression (~925/s) – YS ≈ 1435 MPa 3. Quasi-Static Tension (0.001/s) – YS ≈ 950 MPa; UTS ≈ 1600 MPa 4. Intermediate-Rate Tension (~1/s) – YS ≈ 1055 MPa; UTS ≈ 1660 MPa

Initial mechanical testing results for aged

laboratory scale plate (~350 BHN), industrial material to follow

High rate and high temperature testing is

underway

Ductile failure observed at high-rates, counter to

Charpy implications

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Materials & Advanced Manufacturing (M&AM)

Welding – ER316LSi

Gas Metal Arc Welding - Pulse (GMAW-P) T-joint (left)
Groove weld (middle)
Plate machined for mechanical testing (right)

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Materials & Advanced Manufacturing (M&AM)

Welding – Tensile Strengths

Tensile samples failed consistently in the weld material

– Some cracking seen at boundary on 2 of 12 samples – Base plate shows excellent elongation to failure

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Materials & Advanced Manufacturing (M&AM)

Welding – Charpy Impact Toughness

Charpy Impact samples

taken from VIM lab plate

Samples cut subsized

(7mm x 10mm) and can’t be directly compared to

ther results
Base metal shows brittle

failure, low breaking energy

– Some inclusions visible, transgranular fracture

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Materials & Advanced Manufacturing (M&AM)

Welded Microstructure

No voids observed in the fusion zone
Some grain enlargement in the HAZ, as expected
Boundary between weld and base metal shows void formation: these voids are believed to be due to

interdentritic shrinkage, and may be eliminated with the use of a higher Si weld wire

Baeslacket al. Unmixed zone formations in austenitic stainless steel weldments. Weld J. 1979

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Materials & Advanced Manufacturing (M&AM)

Weld Compositional Analysis

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Materials & Advanced Manufacturing (M&AM)

Welding - Hardness

Vicker’s hardness map of double vee groove weld bead and heated affected zone of ER 316L filler on cast FeMnAl base plate

with weld bead to the right of the image.

Image scale is from 150HV to 600HV.

FeMnAl and 316L RHA and 316L

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Materials & Advanced Manufacturing (M&AM)

Machining – Tool Wear

Chip is very short, rather than continuous curls
Bits show accelerated wear compared to expectations from RHA
Significant dross observed in typical plasma cutting

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Materials & Advanced Manufacturing (M&AM)

Machining/Cutting – General Best Practices

Challenges due to residual stresses, requires careful fixturing
Water jet cutting is most consistent

– Powder assisted plasma cutting more effective – High dross seen with standard plasma cutting practices

No significant hard spots found
Higher feed rate, lower angle
Typically gummy, abrasive, produces heat if machined with standard RHA practices

– Gummy character leads to material built up on the tooling

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Materials & Advanced Manufacturing (M&AM)

Conclusions

A commercially viable path to production of wrought FeMnAl plate has been

identified

– Traditional steel pouring methods are effective in achieving the target chemistry – Large scale rolling is temperature sensitive – Necessity of forging is still being evaluated

Work has begun to identify paths to effective integration

– Welding trials with 300 series stainless underway – Additional machining trials continuing on production scale wrought material

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Materials & Advanced Manufacturing (M&AM)

Future Work

Manufacturing
Heat Treatment
Welding

– Gleeble simulation of HAZ – Hydrogen embrittlement testing

Machining trials on production wrought plate
Additional validation of armor performance
Toughness improvements

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Materials & Advanced Manufacturing (M&AM)

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