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Journal of Minera ls & Materials Ch ar ac teri zatio n & Engineeri ng, Vol. 9, No.12, pp.1087-1100, 2010
jmmce.org Printed in the USA. All rights reserved
An Experimental Study on Mechanical and Fracture Behavior
of Phosphoric Iron
A. K. Vishnoia*, B.K. Mishraa, S. Prakashb
a Department of Mechanical and Industrial Engineering, IIT Roorkee, India
b Department of Metallurgical and Materials Engineering, IIT Roorkee, India
*Corresponding Author: email@example.com
Phosphoric iron of two different phosphorus content, namely P1 (Fe-0.30P-0.226C), P2 (Fe-
0.11P-.028C) were first prepared by ingot casting route. The ingot were soaked and forged at
1150oC. The microstructures of the phosphoric iron and its relevant mechanica l properties such
as hardness and tensile properties have been cha racterized. J-R curves o f th e m ateri al have b een
determined at room temperature. Fracture behaviour under tearing load has been studied
through fracture toughness tests on phosphoric iron using Compact Tension (CT) specimens of
Width (W) =50 mm and thickness (B) =12.5mm. J-R curves were obtained from specimens pre-
cracked to a/W = 0.5 .The single specimen unloading compliance method have been used for
generating J-R curves.
Simple fracture is the separation of body into two pieces in response to the applied stresses. The
applied stresses may be tensile, compressive, shear or torsional or a combination of them.
Fracture of engineering structures is one of the most dreadful failures of the structural materials
as it involves human lives and the structures itself. The problem of fracture has been greatly
increased due to the amplified use of complex structures. As a result, extensive investigation
were initiated in many countries and the work revealed that pre-existing flaws or high stress
concentration region present in structure could initiate the crack and the propagation of such
crack lead to the final fracture of the component or structure.
The corrosion behaviour of iron containing high phosphorous or phosphoric irons is an
unexplored area of corrosion science and engineering. Recent research work on Delhi Iron Pillar
[1-4], a good example of high phosphorus containing iron, has revealed some of its corrosion
resistance properties. Research on Delhi Iron Pillar (DIP) provided the current impetus to
1088 A. K. Vishnoi, B.K. Mishra, S. Prakash Vol.9, No.12
understand the corrosion behaviour of Fe-P alloy. The average composition of phosphorous in
the DIP is about 0.25 wt%, while that of carbon is 0.15 % . Irons, containing phosphorous
contents of this order have been subjected to research by Balasubrahmaniyam et al . His group
has studied the corrosion properties of phosphoric iron manufactured by the ingot route .
Phosphorus increases the yield and ultimate tensile strengths with a corresponding reduction in
ductility as measured by elongation and reduction in area, to a point where brittle failure occurs.
This loss of ductility occurs during prolonged exposure of steel in the temperature range of 250-
6000C [6-9]. This condition is frequently encountered in tempering of steel. Hence it is called
temper embrittlement. Phosphorous increases the ductile to brittle transition temperature of steel.
It causes brittleness in steel during cold working [10-12].
In present work, an attempt has been made to determine the mechanical properties and fracture
behaviour of phosphoric iron for two different phosphorus content, namely P1 (Fe-0.30P-
0.226C), P2 (Fe-0.11P-.028C).
2. EXPERIMENTAL PROCEDURE
The materials used for the present investigation are the two compositions of phosphoric iron. The
phosphoric irons were produced by ingot casting. For obtaining 1 kg of phosphoric iron
containing 0.1 % P, we require 0.001 kg P. For obtaining 50 kg phosphoric iron with 0.1 % P, we
require 0.050 kg P = 50 gm P. As 0.176 kg P is present in 1 kg Fe-P alloy, 0.050 kg P is present
in 0.050/0.176 = 284 gm Fe-P = 0.284 kg of Ferro-phosphorous alloy. Similarly, for obtaining
0.3 % P, we require 0.003 kg P. For obtaining 50 kg phosphoric iron with 0.3 % P, we require
0.150 kg P = 150 gm P. As 0.176 kg P is present in 1 kg Fe-P alloy, 0.150 kg P is present in
0.150/0.176 = 852 gm Fe-P = 0.852 kg of ferro-phosphorous alloy.
2.1.1 Melting and casting
Utilizing a high frequency induction-melting furnace of 300 Kg capacity, 100 Kg of soft iron
was first melted. To the molten iron, initially 25 Kg of steel scrap was added. During melting,
slag covered the melt. Some of this slag was removed from the top of the melt. After proper
melting of soft iron and steel scrap, approximately one third of the meet was transferred to a
ladle, which was in the form of bucket of about 1.5 feet height. As per the calculations, the
required amount of Fe-P mother alloy was added during taping of the melt into the ladle.
Finally, the melt from the ladle was poured from the top side into a square mould, 50 cm height
and 100cm square cross-section.
2.1.2 Reheating and soaking
A high temperature furnace was used for reheating the ingots and soaking at desired temperature
(11500C). The ingots were placed in the furnace and the furnace was then heated. It took about 5
Vol.9, No.12 An Experimental Study on Mechanical and Fracture Behavior 1089
hours to reach the temperature (11500C). Ingots of different compositions were soaked at
11500C, successively for two hours of soaking. The logic for selecting 1150oC is as follows.
Heat- treating at this temperature is expected to produces a duplex microstructure consisting of
austenite in the grain boundaries of ferrite.
Each ingot was forged at 11500C in to 25 mm thick plates. In successive stages of forging, each
reduced plate was reheated again to 11500C for a short time for the further reduction of
dimension. For example, when the thickness was reduced down to around 40 mm, the reduced
plate is again reheated at 11500C for 15 minutes in the furnace for reheating purpose because
longer time of reheating may lead grain growth. The 40 mm thick plate was again forged to
obtain 25 mm thickness.
Table 1: Average composition of phosphoric iron after soaking and forging
C P Si Mn S Ni Cr Mo V Cu
P1 0.226 0.30 0.159 0.223 0.009 0.026 0.145 0.005 0.001 0.031
P2 0.028 0.11 0.029 0.046 0.017 0.026 0.044 0.004 0.003 0.033
2.2 Hardness Evaluation
Hardness was evaluated with the help of a Vickers Hardness Tester using a load of 10 kgf. The
specimen surfaces used for hardness studies were polished prior to hardness examination. At
least five indentations were taken to estimate the average value of hardness of the phosphoric
iron under investigation.
2.3 Tensile Testing
Round specimens of diameter 4mm and gauge length 16mm were fabricated for tensile tests
following the ASTM standard E8  from the as received block . The nominal dimensions of
the tensile specimens are shown in Fig. 1. Specimens were fabricated for evaluating tensile
properties. All tests were carried out at a cross-head velocity of 0.003 mm/sec. The tests were
conducted at room temperature. The tensile data were analyzed to estimate the yield strength
(YS), ultimate tensile strength (UTS), uniform elongation (eu), total elongation (et) and
reduction in area.
Standard cylindrical tensile specimen according to ASTM E-8 used for tensile testing. Length of
reduced section (A) is 20 mm, distance between shoulders (B) is 28 mm, diameter of reduced
section (D1) is 4 mm, grip diameter (D2) is 8 mm, and radius of curvature (R) is 4mm.
1090 A. K. Vishnoi, B.K. Mishra, S. Prakash Vol.9, No.12
Figure 1: Nominal dimensions of the tensile specimens
2.4 J-Integral Test
2.4.1 Specimen preparation
The fracture toughness tests in this investigation were planned on compact tension specimens in
L-T orientation. Considering the available form of the material, standard CT specimens were
machined following the guidelines of ASTM E 399-90 , in orientation, LT of the crack
plane. Typical configuration of a specimen is shown in Fig. 2 the designed dimensions of the
specimens were; thickness (B) = 12.5mm, width (W) = 50mm and machine notch length (aN ) =
Figure 2: Dimensions of CT specimen
Vol.9, No.12 An Experimental Study on Mechanical and Fracture Behavior 1091
2.4.2 Fatigue pre-cracking
Testing was done at room temperature at cyclic stress frequency of 10 Hz. In the test fatigue
crack was initiated and propagated under tension sinusoidal loading for a stress ratio R = 0.1,
pre-cracking load calculated by the following formula
Where B = thickness of CT specimen, is yield strength, a initial crack length, b uncrack
ligament, W = width of CT specimen.
For pre-cracking load condition is 0.4 PL, Pmax, Pmin are calculated for pre-cracking of specimen
P max = 0.4 PL
Pmin = 0.1 Pmax (stress ratio 0.1)
2.4.3 Fracture toughness testing
In the single specimen J-integral tests unloading should not exceed more than 50% of the current
load value and hence design and control of the test procedure is important. Some initial trial
experiments indicated that a specific actuator displacement control for the selected iron could
lead to the desired test procedure. This control consisted of loading a specimen to a level of
0.3mm, unloading through 0.15mm, reloading through 0.15mm and then repeating the sequence
till an appreciable load drop was noticed on the load displacement plot. The displacement cycles
were carried out using an actuator rate of 0.003 mm s-1. The tests were controlled through a
computer attached to the machine. The actuator displacement, load and the load line
displacement (LLD), were recorded continuously throughout the test at a frequency of 2 Hz. The
magnitude of LLD was monitored by a crack opening displacement (COD) gauge of 10 mm
gauge length attached to the specimen. A minimum of approximately 35 data points of load-LLD
was collected from the unloading part of the loading sequence for crack length calculations.
2.4.4 Generation of J-R curve:
Calculation of J: The magnitude of J is the sum of its elastic and plastic component denoted by
Jel and Jpl. The elastic component of J was calculated using the equation
J = Jel + Jpl
Jel = Ki2 (1-ν2) / E + Jpl
where Ki the elastic stress intensity parameter is evaluated using the expression given below 
1092 A. K. Vishnoi, B.K. Mishra, S. Prakash Vol.9, No.12
The magnitude Jpl of was calculated by considering only load vs. plastic load line displacement.
In order to obtain the latter, the elastic part of displacement at different loads was first calculated
from the slope of the initial load-LLD diagram. A simple subtraction of the elastic component
from the total displacement yielded the plastic part of LLD. The area under the load vs. plastic
LLD data from the start of the test to the load of interest was calculated to obtain the magnitude
of .This was done by using the expression 
The quantity is the increment of plastic area under the force versus plastic load-
line displacement record between lines of constant displacement at points i-1 and i. The quantity
represents the total crack growth corrected plastic J at point i and is obtained in two steps by
first incrementing the existing and then by modifying the total accumulated result to
account for the crack growth increment .Accurate evaluation of from the above relationship
requires small and uniform crack growth increments consistent with the suggested elastic
compliance spacing .The quantity can be calculated from the following equation.
Vpl(i) = plastic part of the load-line displacement, V(i) – (P(i) CLL(i), and
CLL(i) = experimental compliance, (∆V/∆P), corresponding to current crack size
2.4.5 Calculation of crack size:
The inverse of the slope yielded the compliance (Ci) of the specimen corresponding to the load
from which the unloading has been carried out. The obtained Ci –values were corrected for the
Vol.9, No.12 An Experimental Study on Mechanical and Fracture Behavior 1093
specimen rotation using the following expression to get the corrected compliance (Cci) of the
specimen at that particular load .
H = initial half-span of the load points (centre of pin holes)
R = radius of rotation of the crack centre line, (W + a)/2 where a is the updated crack length.
D = one half of the initial distance between the displacement measurement points
θ = angle of rotation of a rigid body element about the unbroken midsection line, or
dm = Total measured load-line displacement
The crack length (ai) at this point of interest was next estimated using the expression suggested
by Hudak et. al. 
W =width of the specimen
B = total thickness of the specimen
The obtained values of J and the corresponding crack extension Δa were plotted to get the J- Δa
curves of the material in various test conditions.
The end of the ductile crack extension during loading of the specimens, subjected to J-integral
test, was marked by post fatigue cracking, and then the specimens were loaded to fracture. The
fractured surfaces were ultrasonically cleaned and examined using a scanning electron
microscope. This was done to record the interesting features of stable crack extension.
3. Results and Discussions
Hardness was evaluated with the help of a Vickers Hardness Tester using a load of 10 kgf as
shown in Table: 2. The five indentations were taken to estimate the average value of hardness of
the steel under investigation.
1094 A. K. Vishnoi, B.K. Mishra, S. Prakash Vol.9, No.12
Table 2: Hardness value of specimens
SAMPLE Hardness HV
3.1 Tensile Test
The tensile tests were conducted at room temperature. The stress strain plot for P11 and P12 is
shown in Fig. 3 while for P21 and P22 is shown in Fig. 4 along with the tensile properties in Table
Table 3: Tensile Properties of Phosphoric Iron P1
Specimen Yield stress, (MPa) Ultimate tensile stress (Mpa
P11 434.7 664
P12 344.2 573
P13 480 610
Figure 3: Stress strain diagram for specimen P11 and P12
0.0 0.1 0.2 0.3 0.4
strees strain curve of phosphoric iron(P11)
0.0 0.1 0.2 0.3 0.4 0.5
strees strain curve of phosphoric iron(P12)
Vol.9, No.12 An Experimental Study on Mechanical and Fracture Behavior 1095
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
strees strain curve of phosphoric iron(P21)
Figure 4: stress strain diagram for specimen P21 and P22
3.2 J-integral Fracture Toughness
Pre-crack load was calculated as below:
= 16.9 KN
Then an exclusion line is drawn parallel to the construction line intersecting the abscissa at 0.15
mm. A second exclusion line is drawn parallel to the construction line intersecting the abscissa at
1.5 mm. A J - ∆a data points that fall inside the area enclosed by these two parallel lines are
In order to fit the power law equation for J-R curve, the experimental points of J vs. Δa lying
between two exclusion lines were considered. The exclusion lines were constructed parallel to
the experimental blunting line at Δa-offset values of 0.15 and 1.5mm following the ASTM
standard E-1820 .
A line parallel to the experimental blunting line at Δa = 0.2mm was next constructed. The
intersection of this offset line with the fitted J-R curve was considered as the critical value of J,
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
strees strain curve of phosphoric iron(P22)
1096 A. K. Vishnoi, B.K. Mishra, S. Prakash Vol.9, No.12
A 0.2mm offset blunting line was drawn. The intersection of the blunting line with the power law
curve at an offset of 0.2 mm was considered as JQ. Ji was determined at intersection of blunting
line with power law curve as shown in Figure 5-8.
0.0 0.2 0.4 0.6 0.8 1.0 1.21.4 1.6 1.8 2.0 2.2 2.4
Crack Extension (Δa), mm
Material: phosphoric iron (P1)
Specimen type: CT
Figure 5 : J-R for curve specimen
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.02.2 2.4
Crack Extension (Δa), mm
Material: POSPHORIC IRON
Specimen type: CT
Figure 6: J-R for curve specimen P12
Vol.9, No.12 An Experimental Study on Mechanical and Fracture Behavior 1097
0.0 0.2 0.4 0.60.8 1.0 1.2 1.4 1.61.8 2.0 2.22.4
Crack Extension (Δa), mm
Material: phosphoric iron (P2)
Specimen type: CT
Figure 7: J-R for curve specimen P21
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4
Crack Extension (Δa), mm
Material: POSPHORIC IRON (P22)
Specimen typ e : CT
Figure 8: J-R for curve specimen P22
Table 4 : Thickness validity criteria of the specimens for fracture toughness test:
Specimen σo MPa JQ KJ/m2B 10(JQ/ σo)
P11 549 170 12.5 3.0
P12 458 210 12.5 4.5
P21 376.4 500 12.5 13.3
P22 371.1 590 12.5 15.8
σo = flow stress, JQ = critical value of J
B = specimen thickness, and 10(JQ/ σo) = thickness criterion.
1098 A. K. Vishnoi, B.K. Mishra, S. Prakash Vol.9, No.12
3.3 J Integral Fracture Toughness of Phosphoric Iron
The estimated average J-integral fracture toughness values of the phosphoric iron at room
temperature are 170 KJ/m2 (Table 4) for specimens P11. And for specimen P12 is 210 KJ/m2. J
integral fracture toughness for P21 is 500 KJ/m2. P21and P22 specimen is fail in thickness criteria.
The fractured surfaces were ultrasonically cleaned and examined using a scanning electron
microscope. For P1 specimen:
Figure 9 : SEM micrograph of fracture surface of specimen P1 obtained at different
Figure 10: SEM micrograph of fracture surface of specimen P2 obtained at different
The fracture surface of specimen decohesive P1(Figure 9) rupture (which is also called as inter-
granular fracture) and brittle trans-granular cleavage fracture. Fracture surface of specimen as
Vol.9, No.12 An Experimental Study on Mechanical and Fracture Behavior 1099
received P2 revealed equiaxed and elliptical dimple (Figure 10) under SEM which show the
The phosphoric iron P1 (Fe-0.30P-0.226C), P2 (Fe-0.11P-.028C) were prepared by ingot casting
route. The ingots were soaked and forged at 1150 0
C. The microstructures were subjected to
metallographic examination. Mechanical properties and JIC were evaluated and compare with
Hardness of as received phosphoric iron increased with increasing phosphorus content, indicative
of solid solution strengthening effect of phosphorus in phosphoric irons. Effect of phosphorus in
phosphoric iron was confirmed from the observed increasing trend of yield stress and ultimate
tensile stress with increasing phosphorus content. A decreasing trend of ductility (both
percentage elongation and percentage reduction in area at failure) with increasing phosphorus
content was also noted. The JQ fracture toughness value of CT of P1 specimen prepared from the
phosphoric iron satisfy the criteria suggested in ASTM E- 1820 standard. Fracture toughness for
specimen P1 (Fe-0.30P-0.226C) is 170 KJ/m2 and 210 KJ/m2. It is comparable to mild steel
(179KJ/m2). Fracture surface of specimen as received P2 revealed equiaxed and elliptical dimple
under SEM, while that of P1 (Fe-0.30P-0.226C) revealed both decohesive rupture and
transgranular cleavage fracture. Phosphoric iron is a new class of engineering materials with
good fracture toughness and corrosion resistance properties.
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