Utilization of Cu in Ferrous Utilization of Cu in Ferrous MaterialsMaterials

Syarif JunaidiSyarif JunaidiDept. Mechanical & Materials Eng. Dept. Mechanical & Materials Eng.

National University of MalaysiaNational University of Malaysia

Presentation content

1. Introduction2. Objectives3. Strengthening Mechanism4. Effect of Cu in solid-solution5. Advantage of Cu nanoparticles6. Combination of nano steel (ultra fine grained

steel) and Cu nanoparticles7. Summary

• In Japan, the amount of steel scraps reached 1billion ton (2000), on the other hand, Japan’s steel production : 100million ton/year. (Japan has “natural resource” of steel for 10 years)

• The recycling of steel scraps is retarded because the scraps are contaminated by Cu which is difficult to be eliminated.

• Accumulation of the scraps becomes national problem in Japan.

Does Cu have advantage?Does Cu have advantage? (Fe-Cu binary alloy)(Fe-Cu binary alloy)

Fe-Cu phase diagram is similar to Fe-C phase diagram

0

wide single phase

wide single phase

•No intermetallic phase•Pearlitic structure or fine second phase•Exhibit martensitic transformation•Effect of heat treatment and cooling rate?

4 Cu (mass%)

850C

1.8

910C

Cu

Objectives:Objectives:

In terms of the promotion of recycling steel scraps, Cu has been tried to be utilized as an effective alloying element.

Some of utilization of Cu such as solid solution strengthening and precipitation strengthening will be introduced in the presentation.

Strengthening Mechanism

How to increase the strength of metals?

Illustration of Strengthening Mechanism in steel

Dislocations (cars on highway) move easily within a steel

Solid solution strengthening

bumpy road

Precipitation strengthening

Dislocation strengthening

Grain refinement strengthening

traffic jam

riverbed road

dead-end road

To disturb motion of car = To increase strength = strengthening

Solute Cu

Cu nanoparticles

Ultrafine grained steel with Cu nanoparticles

Cold-rolled steel

Effect of Cu in solid-solution

Why do we utilize Cu in solid-solution?

Heat treatment of Cu bearing steel

Cu

Solution treatment

W.Q

Aging

or ’ (single phase)+ solute Cu

(super saturated)

Cu

Effect of solute Cu on microstructure (ferritic steel)

Pure iron 1%Cu steel

2%Cu steel

Ferrite single phase (Cu in solid solution)Ferritic grains are refined owing to Cu addition

Steel: Fe-0~2%Cu alloy

Effect solute Cu on microstructure and mechanical properties

Microstructure of martensite

Structures are refined as Cu content increases

Prior grain sizes tend to decrease

200m

8%Ni-1%Cu 8%Ni-3%Cu 8%Ni

Effect solute Cu on yield strength0.

2% p

roo

f st

ress

, σ

0.2 / M

Pa

(Cu content; [Cu])1/2 / (at.%)1/2

600

750

700

650

Cu content, [Cu] / mass%

1.50 1.0 2.00.5

2.00 1.0 3.00.5

150

100

50

200

17×[at.%Cu]1/2

57×[at.%Cu]1/2

Ferritic steels

Martensitic steels

Solid solution strengthening

The addition rule is not suited to the case of the martensitic Cu steel

The influence of the solid solution strengthening by Cu clearly decreases

J. Syarif, K. Nakashima, T. Tsuchiyama and S. Takaki, ISIJ International, 2007, 2

Difference of strengthening mechanism between the ferritic steel and the martensitic steel

Ferritic steel

b

Martensitic steel

b

Solute Cu dislocation Solute Cu dislocation

dislocation

Solid solution strengthening Dislocation strengthening

Advantage of Cu nanoparticlesHow strong is it? Useful?

Precipitation strengthening of Cu

E. Hornbogen and R.C. Glenn : Trans. Met. Soc. AIME, 218(1969), 1064

873K-162ks

K.NAKASHIMA et. al, ISIJ International, Vol. 42 (2002), No. 12, pp. 1541–1545

Precipitation behavior of Cu

bcc Cu 9R 3R fcc() Cu

During aging, Cu in solid solution will transform to

P.J. Othen, M.L. Jenkins, and G.D.W. Smith: Phil. Mag., 1994, vol. 70, pp. 1–24.

Precipitation strengthening of Cu nanoparticles

What is strengthening mechanism of Cu nanoparticles??

Mechanism of precipitation strengthening

When a moving dislocation is pinned by dispersed precipitates as shown in Figure, shear stress ( ) required for bowing the dislocation with angle is expressed by the Eq. (1).

= (Gb/ )sin .................. (1)

Tensile stress () is given by multiplying Taylor factor to the shear stress and expressed using another constant (b) as follows:

Carbon steels with carbide: =2.8, because = /2.

=(Gb )sin ............................(2)

Mean particle spacing; was calculated with the Eq. (3).

=1.25(dp3/6fdp)1/2 - ( dp

2/4dp)...........................(3)

Where dp is diameter of the precipitates. The f is volume fraction of the precipitates

Mechanism of precipitation strengthening

Bowing degree of Cu nanoparticles is smaller than/2

Not the Orowan mechanism, so?

Mechanism of precipitation strengthening1. Strong obstacles

= /2

< /2

2. Weak obstacles (Cu nanoparticles)

Conversely, dislocation cuts off the particles for passing trough. Thus, </2.

Moreover, Kelly proposed

Strengthening due to differing Elastic modulus between matrix and particle

Utilization of Cu nanoparticlesin structural steels

Are the properties changed??

1. HSLA steels

Acceleratedcooling

Tf : 910, 850, 723C

1150C

910C-1hr

DQ RQ

W.Q.

Chemical compositions of the steel

Cu

350-690C-1hr

TMCP

Microstructure of Cu bearing HSLA steels

RQ DQ, 910C

DQ, 850C DQ, 753C

HSLA steelsaged at 630C

Cu nanoparticles

HSLA steels

Recent development, Sumitomo corp has patented YP480 MPa plate steel for offshore use (fulfilled API standard) by Cu addition.

One of the largest steel companies in Japan has been developing YP550MPa.

Why?1. Cu can substitute C, thus weldability will be improved2. C u increases the strength without deteriorating ductility

2. Utilization of Cu in a cryogenic steel

Steel: Fe-9%Ni-0.1%C-0~3Cu alloy

CuW.Q

Cu

1223K-3.6ks873K-3.6ks

Cu nanoparticles

Utilization of Cu in a cryogenic steel

The improvement of strength–ductility balance in Cu bearing 9%Ni steels are derived from 1. Strengthening of martensitic matrix by precipitation strengthening by Cu particles 2. an increase in uniform elongation due to the rise of work-hardening rate caused by TRIP assisted effect of reversed .

3. Utilization of Cu in Heat-Resistant SteelSteel: Fe-9%Cr-(0~4)%Cu alloy

W.Q

1223K~1423K-3.6ks

Full martensitic structure

Utilization of Cu in Heat-Resistant Steel

CuW.Q

1223K-3.6ks873K-140MPa

Creep-properties is improved owing Creep-properties is improved owing to Cu nanoparticlesto Cu nanoparticles

Combination of Cu nanoparticles and ultrafine grain

The ultimate method??

Ultra-fine grained steel

Yttria powder Iron powder

Cu powder

mixing

M.M

Tubing

Hot rolling

Steel: Fe- 1.5%Cu-3vol%Y2O3

Cu

773K

Aging

Addition Cu in Ultra-fine grained steel

Cu nanoparticles within UFF grain Effect of Cu is not significant

Why? It is thought that1. Hardness of UFG steel is too high, 2. Addition rule of the strengthening mechanism cannot be applied

SummarySummaryIt is shown that addition of Cu can improve the mechanical properties of ferrous materials for structural use.

Both of solid solution and precipitation states, Cu can increase the hardness of the steels. Moreover, the strength-ductility balance is also improved in the low alloy and cryogenic steel.

On the other hand, the effect of Cu nanoparticles is inferior in the ultra-fine grained steel.

Recommendation Recommendation

Few works have been done to clarify the effect of Cu nanoparticles on wear behavior and fatigue properties of steels.

Effect solute Cu on low temperature toughness

solute Cu

Fractography of sample Charpy-tested at -50oC

Pure iron: cleavage fracture (brittle)1%Cu steel: dimple (ductile)

Pure iron1%Cu steel

Microstructure of near fracture surface

Pure iron

Pure iron

1%Cu steel

1%Cu steel

In -50C:Pure iron: twin deformation 1%Cu steel: slip deformation due to dislocation

DBT behavior of 8Ni-Cu steels