On the Comparison of Microstructure Characteristics and Mechanical Properties of High Chromium White Iron with the Hadfield Austenitic Manganese Steel

doi:10.4236/jmmce.2013.11005

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Journal of Minerals and Materials Characterization and Engineering, 2013, 1, 24-28

http://dx.doi.org/10.4236/jmmce.2013.11005 Published Online January 2013 (http://www.scirp.org/journal/jmmce)

On the Comparison of Microstructure Characteristics and

Mechanical Properties of High Chromium White Iron with

the Hadfield Austenitic Manganese Steel

Johnson O. Agunsoye1*, Talabi S. Isaac2, Agbeleye A. Abiona1

1Department of Me t a l l urgical and Materials Engineering, University of Lagos, Lagos, Nigeria

2Department of Materials and Metallurgical Engineering, University of Ilorin, Ilorin, Nigeria

Email: *[email protected]

Received October 7, 2012; revised November 15, 2012; accepted November 27, 2012

ABSTRACT

In this study, high chromium white iron (HC-Wi) alloy and the Hadfield steel were studied. The microstructure of this

high-chromium iron was studied using Metallurgical optical microscopy (OM) and compared to the Hadfield steel. The

hardness and unnotched charpy impact strength of the HC-Wi alloy and Hadfield steel were examined at ambient tem-

perature in the as-cast and heat-treated conditions. A pin-on-disc test at linear speed of 1.18 m/s and a 10 N normal load

was employed to evaluate the wear behavior of both steel samples. Microstructural results showed that varying the car-

bon level in HC-Wi alloys can affect the chromium carbide morphology and its distribution in the austenite matrix

which leads to considerable changes of the mechanical properties. Abrasion test sh owed that HC-Wi alloys have supe-

rior wear resistance, about three times of the Hadfield steel.

Keywords: High Chromium White Iron; Hadfield Steel; Microstructure; Wear

1. Introduction

When there was a challenge to develop steel which pos-

sesses two extreme properties at the same time, Sir Ro-

bert Hadfield invented Hadfield steel in 1882. The idea

was to have steel which is tough and at the same time

hard. This type of steel with its austenitic matrix has high

toughness, high ductility, and high work-hardability.

Majority of the cast Hadfield steel are excellent candi-

dates in variety of applications such as: earthmoving,

mining, railways, quarrying, dredging and drilling in the

oil/gas [1,2].

The global economic recession has continue to place

heavy burden on foundries world-wide and Nigeria in

particular to look for means of improving their produc-

tivity and higher products quality, as well as to strive to

achieve the optimum economy in wear industries; in the

past decade, the use of carbon steel ball in dry mill

grinding has been replaced with in situ ceramic-steel

composite synthesis technique to increase the life of the

wear parts. In this technique, hard ceramic forming ele-

ments are introduced to the molten steel as an alloying

element and a more thermodynamically stable reinforc-

ing phase will be fo rmed during solidification b y the nu-

cleation and growth mechanism in the parent matrix [3].

One of the most common ceramic reinforcing materials

being used in iron base alloys is carbides and among

them chromium carbide due to its high hardness of about

1020 - 1835 Hv [4], h ave prov ed to b e a un ique choice to

wear resistance of cast high chromium white iron with

martensitic microstructure [5,6]. However, less attention

has been paid to the research on Hardfield Austenitic

Mangane s e s teel.

In general terms, the high chro mium iron suitable for

wear r esi stin g a ppl icat ions fal l w ith in th e co mpo sit iona l

limits bounded by the austen itic ph ase field of the tern ary

liquidus surface of the iron, chromium, carbon diagr am.

Solidification takes place by a eutectic process The pro-

ducts of the eutectic reactio n are austenite and chromium

rich carbides of the (FeCr7)C3. For high chromium white

iron with a Cr concentration of some 18 - 20 wt%

(hypoeutectic composition), solidification starts with the

nucleation of dendritic primary austenite (γ), follo wed by

the formation of γ + M7C3 carbide and its morphology

have been well documented by several researchers [7].

The HC-Wi alloy has an austenitic matrix structure at

ambient temperature with chromium carbide dispersed

within the matrix. The wear resistance of this material is

achieved at the surface when the abrasive particle or im-

pact load transforms the unstable Austenite to martensite

by strain induced mechanism. This phenomenon of Aus-

*Corresponding author.

J. O. AGUNSOYE ET AL. 25

tenite transformation to martensite causes increased sur-

face hardness and less wear rate loss. Carbon content

plays a significant role in chromium carbide formation

and its morphology as well as hardness, impact tough-

ness and wear resistance. In this study, the effect of car-

bon content on the microstructure, mechanical proper-

ties and wear characteristics of HC-Wi has been studied

and compared to the Hadfield steel.

2. Materials

HC-Wi and Hadfield Steel grade of materials were pro-

duced in Nigerian Foundries Limited (NFL), Otta, Nige-

ria using the charge makeup in Tables 1 and 2 respec-

tively. An Electric Induction Furnace of 500 kg neutral

lined was used for the melting operation and the sample

representative taken from the molten bath at 1550˚C d

and poured into a CO2 sand improvised moulds (11 × 11

× 200) mm. The charge makeup used in obtaining the

specification is tabulated below.

After the first heat from Ta ble 1, a sample representa-

tive was taken and casted. For subsequent batches, fine

granules of graphite were added in their various compo-

sitions of 1.6% C, 2.2% C, 2.7% C and 3.3% C respec-

tively to the molten bath and the temperature maintained

at 1520˚C - 1543˚C for 10 minutes to enable the graphite

granules dissolve adequately. This process was repeated

Table 1. Charge makeup for HC-Wi.

Elemental Contribution (%)

Raw Materials Mass (Kg) C Si Mn P S Cr

Returns 156.25 0.94 0.21 0.01 0.01 0.017.19

Steel Scraps 223.21 0.09 0.09 0.04 0.02 0.020.00

Fe-Cr 98.21 0.10 - - - - 17.68

Fe-Si 2.23 - 0.33 - - - -

Fe-Mn 4.46 0.07 - 0.58 - - -

Graphite 3.80 0.51 - - - - -

Total 500 1.55 0.63 0.63 0.03 0.03 24.87

Table 2. Charge makeup for Hadfield Steel.

Elemental Contribution (%)

Charge makeup

for Hadfield

SteelRaw Material

Mass

(Kg) C Si Mn P S Cr

Returns 187.83 0.410 0.190 4.760 0.005 - 0.570

Steel Scraps 234.80 0.095 0.120 0.120 - - -

Fe-Cr 7.04 0.001 - - - - 1.280

Fe-Si 2.00 - 0.300 - - - -

Fe-Mn 63.40 0.140 - 9.640 - - -

Graphite 4.93 0.66 - - - - -

Total 500 1.30 0.610 14.52 0.005 0.0001.850

for all incremental granules addition. To reduce the ten-

dency for oxidation, 1 Kg of Aluminum Briquette was

added to the melt. Besides, Hadfield steel melt was pre-

pared according to ASTM 128 C standard as presented in

Table 2.

The overall chemical composition obtained for the 2

heats and 5 batches is presented in Table 3.

A calibrated Hilger Analytical Direct Optical Emission

Polyvac Spectrometer E980 C with 20 analytical channe ls

was used for the analysis of the chemical composition of

the HC-Wi and Hadfield steel. Hadfield steel is difficult

to machine due to its work-hardening propensity. Hence,

a sample representative was taken from the Hadfield

steel molten bath and poured in to a (10.20 × 10.2 × 200)

mm preheated medium carbon steel mould so as to obtain

the required (10 × 10 × 50) mm bar for the impact test.

This technique was aimed at avoiding the need to ma-

chine the samples. To investigate the effect of the heat

treatment of Hadfield steel on the properties of HC-Wi,

halves of all the specimens with the size (10 × 10 × 50)

mm were solution annealed at 1050˚C for 30 minutes and

then water quenched.

2.1. Microstructure

For microstructural analysis, all the as-cast and heat-treat-

ed samples were cut from the bottom end, ground with

tehrapol-31, then polished using a colloidal suspension of

0.04 µm silicon dioxide and then etched in 100 ml alco-

hol and 3 ml HNO3 acid after polishing using Allegrol

with diamond suspension at the Metallographic Labora-

tory, Department of Mechanical Engineering of the Uni-

versity of Ot t a wa , Ca nada. A metallurgical optical m icro-

scopy was used to study the microstruc tures.

2.2. Mechanical Properties

Vickers micro hardness of tested samples was measured

using Duramin-1 microhardness tester struers. The re-

ported hardness values were the average of five meas-

urements. Charpy unnotched impact test was also carried

out on (10 × 10 × 50) mm standard Hadfield and HC-Wi

specimens at room temperature. In order to compare the

wear resistance of the developed HC-Wi alloys with

Hadfield steel, abrasive wear tests were conducted on all

Table 3. Chemical composition of the HC-Wi.

MaterialCMnSiCrP S Mo Ni AlFe

HC-Wi-11.550.630.6324.870.03 0.03 0.02 0.01 0.01Balance

HC-Wi-22.220.630.6224.600.03 0.03 0.01 0.01 0.01Balance

HC-Wi-32.730.590.6024.200.03 0.03 0.01 0.015 0.02Balance

HC-Wi-43.260.560.6023.600.03 0.03 0.01 0.01 0.02Balance

Hadfield

Steel 1.3014.520.611.850.01 0.00 - - 0.15Balance

J. O. AGUNSOYE ET AL.

cast sample in the as-cast and heat-treated conditions us-

ing a pin-on-disc wear machine as per ASTM G99-95

Standard. The disc used is En-32 steel hardened to 62

HRC, 200 mm track diameter and 12 mm thick with sur-

face roughness of 20 µm Ra. The sample with cross sec-

tion 10 mm × 10 mm was taken from the fracture impact

test and used for the wear test. Applied normal load on

all the samples was 10 N over a sliding distance of 70.8

m on a fresh 120 grit SiC abrasive paper. Before and

after each test, the sample was carefully cleaned with

acetone and weighed using an analytical balance with an

accuracy of 0.001 g. The relative wear resistance was

given by the weight loss of HC-Wi alloy samples related

to the weight loss of the heat-treated Hadfield steel sam-

ple. The reported values are the average of four test runs

on each composition material.

3. Results and Discussion

3.1. Microstructural Analysis

Figures 1(a)-(d) show the effect of carbon content on

the morphology and distribution of primary chromium

carbides in HC-Wi alloys in the as-cast condition. When

the high chromium molten alloy starts to solidify; chro-

mium carbide nucleation takes place and grows in the

mel t a n d crystalliz es as coarse primary chromium carbides

between the liquidus and solidus temperatures. It has

been observed from the data available from Table 3 and

Equation (1),









%Carbide12.33 %C0.55 %Cr15.2

(1) [8]

that as the carbon content of the HC-Wi increases, the

amount of chromium carbide increases (Table 4) and

primary chromium carbides change from the fairly round,

strip into spherical shape and they are distributed more

uniformly up to carbon content of 2.73 but further in-

crease in the carbon content decreases the homogeneity

of the chromium carbide distribution within the austenitic

matrix (Figures 1(b) and 1(c)).

In HC-Wi alloy, due to the presence of >20% Chro-

mium in the composition as one of the strongest carbide

forming elements in steel compared to iron or manganese

(very high affinity of chromium to absorb carbon), chro-

mium reacts with the dissolved carbon of the molten steel

resulting to the formation of chro mium carbide instead of

iron manganese carbide.

In as-cast Hadfield steels, austenite grain boundary

steel are surrounded by a continuous network of segre-

gated and brittle (FeMn)3C shown in Figure 3(a). Solu-

tion annealing between the temperature range of 1000˚C -

1050˚C dissolves these carbides in austenite and subse-

quently quenching in water prevents the formation M3C

in grain boundary as shown in Figure 3(b) [9].

In high chromium austenite steel, due to the presence

(a) (b)

Figure 1. Optical micrograph of HC-Wi in the as-cast con-

dition. (a) HC-Wi-1 (b) HC-Wi-2 (c) HC-Wi-3 (d) HC-Wi-4.

Table 4. The amount of chromium carbide (Cr3C7, %) in

the as-cast conditions.

Sample HC-Wi-1HC-Wi-2 HC-Wi-3 HC-Wi-4

Volume of Cr7C317.59 25.70 31.77 37.98

(a) (b)

Figure 2. Optical micrograph of HC-Wi in heat-treated condi-

tion. (a) HC-Wi-1 (b) HC-Wi-2 (c) HC-Wi-3 (d) HC-Wi-4.

(a) (b)

Figure 3. Optical micrograph of the hadfield steel (a) a s-cast

condition (b) heat-treated condition.

J. O. AGUNSOYE ET AL. 27

of more than 20% chromium, chromium is one of the

strongest carbides forming element in steel compared to

iron or manganese (chromium has high affinity for car-

bon), chromium reacts with the dissolved carbon in the

molten steel leading to the formation of a more stable

chromium carbides instead of iron manganese carbides.

When compar ed to Figure 3, iron manganese carbides in

HC-Wi samples virtually non-existence and form a con-

tinuous network of brittle phase around the austenite

grains.

3.2. Mechanical Properties

Initially measured values of Vickers hardness of all sam-

ples in as-cast and heat-treated conditions before the ab-

rasion test are presented in Figure 4. It shows that the

hardness of HC-Wi alloys is almost 69% higher than

Hadfield austenitic manganese steel due to the presence

of high percentage of extremely hard chromium carbide

Cr3C7 in the microstructure. Solution annealing has less

influence on the hardness changes of HC-Wi alloy com-

pared to Hadfield austenitic steel. Hadfield steels contain

some segregated hard grain boundary carbide of the form

Cr3C7 within the softer austenite matrix. This is clearly

responsible for the increase in overall hardness in the

as-cast conditions. Figure 4 also showed that austenite

matrix in HC-Wi alloys is more than twice the hardness

of the Hadfield steel (in both as-cast and heat-treated

conditions).

This considerable increase in austenite hardness is re-

lated to the solution of carbon and ch romium elements in

iron lattice coupled with the precipitation of secondary

chromium carbide (Figures 1 and 2) in austenite which

strengthens the soft matrix.

Figure 5 shows Charpy unnotched impact toughness

of the materials. The main difference in impact energy

values before and after the heat treatment was observed

in the Hadfield steel and it is due to the disso lution of the

100

200

300

400

500

600

Har dn ess(Hv)

As‐cast

Figure 4. Vickers micro-hardness of as-cast and heat-treated

materials.

HC‐Wi‐1HC‐Wi‐2HC‐Wi‐3HC‐Wi‐4Hadfield

St ee l

ImpactToug hness(J)

AsCast

He attreated

Figure 5. Impact toughness of HC-Wi alloys and Hadfield

steel.

brittle carbide, segregated along the austenite grain

boundaries in the as-cast condition (Figure 3(a)). These

brittle phases with lamellar/acicular morphology along

the boundaries cause stress to be built-up in the matrix,

leading to dislocation pile up, crack initiation, propaga-

tion and crack growth and subsequently low impact

toughness of the Hadfield steel in as-cast condition. For

HC-Wi alloys, chromium carbide morphology and its

distribution both influence significantly the impact en-

ergy. HC-Wi-1 composition with uniform distribution of

chromium carbide has the highest impact toughness,

while the HC-Wi-4 has the lowest impact toughness. As

the carbon content increases, the morphologies of the

chromium carbides in the matrix also change. The dis-

tribution of the chromium carbide influences the me-

chanical properties of the material.

3.3. Wear Resistance

The wear loss of HC-Wi alloys compared to the heat-

treated Hadfield steel in the as-cast and heat-treated con-

ditions are presented in Figure 6. The predominant wear

mechanism in the pin-on-disc abrasion test is micro cutt-

ing and surface hardness of the materials plays a signifi-

cant in determining the wear resistance. Hence, HC-Wi

alloys shows remarkab le higher wear resistance (3 times)

than Hadfield steel due to higher surface hardness caused

by the existence of hard carbide phase dispersed within

the austenite matrix. Despite the low surface hardness of

HC-Wi-3 compared to HC-Wi-4, the wear resistance of

HC-Wi-3 is superior and higher than HC-Wi-4 (Figure

6). This is because the carbide distribution in HC-Wi-4 is

heterogeneous (Figure 2(d)). Hence, that the distribu-

tions of the hard second phase carbide also affect the

wear resistance.

4. Conclusions

1) High chromium white iron alloy have superior wear

resistance compared to hadfield austenitic manganese steel

due to the presence of hard chromium carbide distributed

within the matrix of the microstructure.

J. O. AGUNSOYE ET AL.

110

130

150

170

190

Hadfield

Steel

HC‐Wi‐1HC‐Wi‐2HC‐Wi‐3HC‐Wi‐4

weightloss(mg)

As‐Cast

He at treated

Figure 6. Weight loss of HC-Wi alloys and Hadfield steel.

2) The presence of chromium carbide lowers the im-

pact toughness of HC-Wi alloys compared to Hadfield

austenitic manganese steel.

3) The mechanical properties of HC-Wi alloys are af-

fected by the distribution of the hard second phase parti-

cles in the austenite.

4) For practical application where replacements of

worn-out mechanical components result to frequent plant

shutdown with associated high maintenance cost, the more

expensive HC-Wi alloys are recommended over the chea-

per Hadfield manganese steel.

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