Materials & Advanced Manufacturing (M&AM)

Materials & Advanced Manufacturing (M&AM)

18/10/2018

Investigation of Hot Cracking Phenomena in Light-Weight Armor Steel

William Evans, Antonio Ramirez – The Ohio State UniversityKatherine SeBeck – U.S. Army TARDEC


DISTRIBUTION STATEMENT A. Approved for public release; distribution unlimited. 8/10/2018 2

Author Bios

William Evans• B.S. Welding Engineering (2017)• M.S. Welding Engineering (in

progress)• Currently employed as GRA at

The Ohio State University• Previous work experience with

EWI, Q2Power, Emerson Climate Tech

Dr. Katherine Sebeck• Ph.D University of Michigan

(2015)• Research Engineer for Materials

Application and Integration at US Army TARDEC

• Specializes in fundamental materials research focused on amorphous materials and alloy maturation



Project Motivation

• Current Research is focused on optimizing manufacturing procedures

• Hot Rolling• Casting• Machining

Project Goal: • Investigate hot-

cracking response• Try to predict Casting

Defects



FeMnAl Background

• FeMnAl is a family of age-hardenablesteels with high additions of Al to reduce overall density

• Derived from Hadfield Steels• Initially researched by U.S. Navy as a

cheaper stainless steel• Recent work has examined FeMnAl as a

candidate for an AHSS • Research is currently being conducted by

U.S. Army for thick plate armor applications

Applications of High Mn Steels



Microstructure and Physical Metallurgy

Howell & Gerth (2017)

• Reported to solidify as FCC (γ)

• Transforms into BCC (α)• Additional

transformations also reported

• 𝜅𝜅 - carbides• 𝛽𝛽 – Mn phase

• Classic age-hardening reaction

Cast

Wrought



A New Class of Armor Steel (Howell & Gerth 2017)

• Research conducted which sought to examine the ability of FeMnAl to pass military standards for armor steel

• Showed FeMnAl can be manufactured by current steel manufacturing techniques

• Ballistics testing showed FeMnAl similar to RHA steels

• Howell and Gerth concluded that in similar volumes FeMnAl plates could pass for RHA

• Meaning a direct reduction in overall density could be possible via substituting FeMnAl for RHA steels

• Additional research is needed to prove FeMnAl is a feasible replacement for RHA

Change in liquidus temperature with Si

Density and Specific Strength

Hardness and V50 Specifications



Hot Cracking in Metals

Lippold (2015)

• Requirements:• Microstructure• Segregation• Tensile restraint• Liquid Films

• Welding: Solidification Cracking, Liquation Cracking

• Castings: Hot Tearing • Hot rolling may induce

liquation

Liquation Cracking in 304L SS

Centerline Solidification Crack in Carbon Steel



Cast Pin Tear Testing (CPTT)

Stress Riser

• Invented by Hull (1960’s)• Redesigned by OSU • Test Procedure:

• Insert charge of material• Inert melting chamber • Levitation melt charge • Drop material into pin• Allow to solidify then

remove for evaluation• Reasons to use CPTT

• Uses a little material• Excellent for comparing

different compositions• Self restraining



Experimental Methodology

Initial Testing• Three samples for metallography

• As received (cast)• Melt Button (equilibrium

Solidification)• Autogenous GTA spot (Rapid

Solidification) CPTT

• CPTT adequate to reduce material usage• Procedure taken from previous work at

OSU• Each pin analyzed for defects

• Pins with defects related to poor casting process were rejected

• Determined cracking response for comparison

Example Cracking Response, Lenzo (2016)

Nominal Composition of Material



Experiment Results – Initial Results

Cast Button

Casting – Howell & Gerth (2017)

OSU cast button• Similar to Howell

& Gerth’s images• SEM highlighted

phase difference• Small particles

also identified scatteredGTA spot weld

• Heavy segregation• Cracking in HAZ• Second phase

along cracks

GTA Spot Weld

FZ

HAZ



Experiment Results - CPTT

UCT

LCT

Cracking Observed in 1” pins

Cracking Observed in 1.375” and 1.5” pins

Cast FeMnAl CPTT Results

• Results from first round of CPTT

• One heat of material tested

• Minimum 3 pins for each pin length used for this analysis



Experiment Results - CPTT

• Fractography shows evidence of solidification at failure

• Classic “egg crate” fracture surface• Confirms Solidification cracking failure

• Images taken from 1.5” cast pin• This particular pin was separated

and the fracture surface preserved for imaging



Comparison to Literature

• FeMnAl response compared to two studies from OSU

• J. Lenzo (2016) – CPTT of Mn Steels• M. Orr (2016) – CPTT of Ni-base FM

• High Mn FM similar to FeMnAl• FeMnAl falls between two heats of

FM-82

• J. Lenzo claims that the threshold for a “good” cracking response is a LCT above 1”

• Using this definition this heat of FeMnAl has a “bad” response

Avg. Cracking in CPTT Literature



Summary of Work

• Solidification cracking was observed in several cast pins, this was confirmed through fractographic analysis on failed pins

• Comparing this study to M. Orr’s study on Ni-base FM this heat of FeMnAl can be ranked between the “bad” and “good” heat of filler metal

• Compared to other High Mn steel FM FeMnAl was comparable • J. Lenzo stated these Mn FM exhibited a “poor” response

• The main takeaway from this CPTT study on cast FeMnAl is that this particular heat of material has shown a susceptibility to solidification cracking

• This needs to be confirmed through other testing methods• This composition contains a high level of Si, could explain the high levels of liquid

• Results of the initial autogenous GTA weld shows a high susceptibility to HAZ liquation cracking, as well as a high level of segregation in the FZ of this material

• Has bad implications for fabrication issues, Unable to solve issue with FM



Future Work

• Solidification Cracking: Trans-Varestraint at OSU• Liquation Cracking : Spot-Varestraint, hot ductility signature at OSU• Examine segregation and liquation mechanisms to help understand

cracking phenomena • Hope to develop FeMnAl specific filler metals• Future FSW trails at OSU to alleviate cracking, and control weld

toughness• Similar study underway on RHA steel



Acknowledments

Thanks to TARDEC, and Katherine Sebeck for material, and Guidance

Additional thanks to my graduate advisor Antonio Ramirez, OSU


DISTRIBUTION STATEMENT A. Approved for public release; distribution unlimited.

References

1. Hadfield, R., Burnham, T. H., “Special Steels”, 2nd ed., p.100, The Pitman Press, New York (1933).2. Ham, J. L., Cairns, R. E., “Manganese Joins Aluminum to Give Strong Stainless, ”Product Engineering, Dec, pp. 51-52 (1958).3. Howell, Ryan A., "Microstructural influence on dynamic properties of age hardenable FeMnAl alloys" (2009). Doctoral Dissertations. Paper 1940. 4. Yinghua Jiang and Chunqian Xie 2017 IOP Conf. Ser.: Mater. Sci. Eng. 207012053 5. Fuqiang Yang, Renbo Song, Yaping Li, Ting Sun, KaikunWang,Tensile deformation of low density duplex Fe–Mn–Al–C steel, Materials & Design, Volume 76, 2015, Pages 32-39, ISSN 0261-3069. 6. Zhang, X., Yang, H., Leng, D., Zhang, L., Huang, Z., & Chen, G. (2016). Tensile Deformation Behavior of Fe-Mn-Al-C Low Density Steels. Journal of Iron and Steel Research, International,2016(23(9)), 963-972. Retrieved May 18, 2018. 7. Fatma Hadef, Solid-state reactions during mechanical alloying of ternary Fe–Al–X (X=Ni, Mn, Cu, Ti, Cr, B, Si) systems: A review, Journal of Magnetism and Magnetic Materials, Volume 419, 2016, Pages 105-118, ISSN 0304-8853. 8. Liu, J., Chen, W., Jiang, Z., Liu, L., & Fu, Z. (2017). Microstructure and mechanical properties of an Fe-20Mn-11Al-1.8C-5Cr alloy prepared by powder metallurgy.

• Chen, S., Rana, R., Haldar, A., & Ray, R. K. (2017). Current state of Fe-Mn-Al-C low density steels. Progress in Materials Science,89, 345-391. doi:10.1016/j.pmatsci.2017.05.002

• 10. Howell, R. and Gerth, R., "Fe-Mn-Al-C Alloy Steels – A New Armor Class," SAE Technical Paper 2017-01-1703, 2017, doi:10.4271/2017-01-1703.

• 11. Lippold, J. C. (2015). Welding metallurgy and weldability. Hoboken: John Wiley & Sons.

• 12. F. C. Hull, "Cast-Pin Tear Test for Susceptibility to Hot Cracking," Welding Journal, vol. 38, pp. 176-179, 1959.

• 13. T. Luskin, Master's Thesis: Investigation of Weldability in High-Cr Ni-base Filler Metals, Columbus, OH, 2013.

• 14. Orr, M. R., & Lippold, J. C. (2016). Solidification cracking performance and metallurgical analysis of filler metal 82(Unpublished master's thesis). The Ohio State University.

• 15. Lenzo, J. C., & Lippold, J. C. (2016). Evaluation of the effect of tungsten and boron additions on the microstructure and solidification cracking susceptibility of Fe-Mn-C filler metals. The Ohio State University

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Questions?

William Evans – Dept. of Welding Engineering, [email protected]

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Materials & Advanced Manufacturing (M&AM)