Steel Properties & Advanced

High Strength Steels

Product oriented research

Success Story: Lightweight Steel P900 Armor • Need to reduce the

logistics cost. Cost of fuel in Afghanistan including delivery, distribution, protection etc. is $600/gal.

• ARL sponsored the program

• New lightweight steel developed to reduce P900 weight by ~15%

• Ballistic properties approaching steel industry standard rolled homogeneous armor

• Ballistic testing successful

FIELD ISTALLED Armor & Hanger Brackets

Atomic models of the steel structure

helped design a successful alloy and produce P900 armor

plate

Cast Lightweight Steels with Aluminum • Austenitic steels

• Fe-30Mn-1Si-0.5Mo with Al ranging from 2.7 wt.% to 9 wt.%

• Al lowers the USFE

• Al increases SFE

• Fe-Al-C Short range order – Increases

ductility

– Reduces dynamic strain aging

– Lowers wear resistance

 

Effect of Si upon k-carbide precipitation

• Austenitic, precipitation hardening

• Fe-30Mn-9Al-1Si-0.9C-0.5Mo

• Competes with quench and tempered 4130

• ~15% lighter weight

• Atom probe studies to determine role of Si

3rd Generation Advanced High Strength Steel

Alloy formulation Casting Hot rolled product

Modeling

• Thermodynamic

• Density functional theory

• Hypothesis testing by direct experiment

3rd Generation AHSS: TRIP • Reduce C and

increase Mn

– Reduced stacking fault energy

• No d-ferrite stringers

• 27% retained austenite; 13% α-martensite; 60% ε-martensite

• Stage I: g to e

• Stage II: e to a

• Stage III: segregated regions TRIP

3rd Generation AHSS: Acicular Ferrite

• Fe-13.92Mn -4.53Al-1.28Si-0.11C

• Duplex (d+g) hot rolled

• Acicular ferrite upon cooling

• Low misfit galaxite and MnO2

• Stability of oxide is temperature dependent

0

50

100

150

200

250

300

350

400

450

Method B Method B Aged for 47 hours

Annealed 1100°C after Aging

Incl

usi

on

De

nsi

ty, m

m-2

MnS AlN AlN-MnS

Al2O3 AlN-Al2O3 MnO2

Si-Al-O Al2O3MnO MnO2-MnS

0.98

1

1.02

1.04

1.06

1.08

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

600 700 800 900 1000 1100 1200 1300

Weigh

t Percentage o

f Inclu

sion

s (d

ashed

lines)

Wei

ght P

erce

nta

ge o

f In

clu

sio

ns

(so

lid li

nes

)

Temperature, °C

Al2O3MnO

MnS

SiO2

AlN

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

0 20 40 60 80 100 120

Fe

rrite

Pla

te D

en

sity,

mm

-2Viable Inclusion Density, mm

-2

Method A + 850°C Annealed

Method B + 850°C Annealed

1100°C Annealed

ρα (mm-2)= 440ρinclusions + 2,800 R2 = 0.97

Modeling

δ

γ

<?>γx

Mo

ld W

all

Vδ|| thermal gradient

<010>δL

δ + γ δ + γ + L δ + L

δ

δ

γ

Crystallography of the Peritectic Reaction

δ

γγ

δ

δγ

Solid

ific

ati

on

dir

ecti

on

δ

δ

γSF

SF

• Effected by primary d-ferrite

• Better castability with < 40% d-ferrite

• Kurdjumov-Sachs orientation relationship – With > 60% d-ferrite

content

– Slows the solid state peritectic transformation

0

2

4

6

8

10

<010> <110> <111> <other>

fre

qu

en

cy

ColumnarEquiaxedChill

0

3

6

9

12

15

<010> <110> <111> <other>

fre

qu

en

cy

ColumnarEquiaxedChill

γ

δ

γ

γ

δ

d g

Effect of Co on Cu precipitation in 17-4PH

Co additions

• Co produces neither solid solution strengthening or softening

• Increase number density of Cu precipitates

• Narrows size distribution of Cu precipitates

• Co is rejected from Cu – islands or shell on

Cu particle and/or distribute into the Fe matrix

– Increases cleavage stress if at interface

Potential Topics/Areas of

Physical Metallurgy Research

Your product

Thermodynamic Modeling

Density Functional

Theory

Physical Metallurgy

Microstructural Characterization

Performance Testing