Development of dual phase steel and determination its of mechanical properties

INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 7, July (2014), pp. 151-159 © IAEME
AND TECHNOLOGY (IJMET)
ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)
Volume 5, Issue 7, July (2014), pp. 151-159
© IAEME: www.iaeme.com/IJMET.asp
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151

IJMET
© I A E M E
DEVELOPMENT OF DUAL PHASE STEEL AND DETERMINATION OF
IT'S MECHANICAL PROPERTIES AND COMPARISON WITH LOW
CARBON STEEL
1Vishnu Pratap Singh*, 2Abhishek Gaikwad, 3Mohammad Zahid Rayaz Khan,
4Kamlesh Tiwari
1M.Tech Student, Department of Mechanical Engineering, Shepherd School of Engineering
Technology, SHIATS University, Allahabad, U.P., INDIA
2Assistant Professor , Department of Mechanical Engineering, Shepherd School of Engineering
Technology, SHIATS University , Allahabad, U.P., INDIA
3, 4Assistant Professor, Department of Mechanical Engineering, Institute of Technology
Management, GIDA, Gorakhpur, U.P., INDIA
ABSTRACT
In this paper, the development of dual phase steel from low carbon steel and mechanical
properties have been studies. Dual phase steel is developed by intercritical annealing in order to
improve the hardness and impact toughness. Low carbon steel of 0.21% carbon content is first
intercritically heated in furnace and then rapid cooling in water is done to obtain the martensitic
steels. Different samples of DP steels are prepared by the intercritical annealing process temperature
ranging from740°C to 840°C. The heating temperature and different time of heating of the steel is
used to make different percentage of Maternsite steel. Dual phase steel so obtained is now tested and
properties of the DP steel are evaluated. Hardness, charpy, microstructure test for each specimen is
conducted to compare its hardness and toughness with low carbon steel. The mechanical properties
of heat treated and non heat treated specimens are obtained and compared. The result indicates that
the specimen hardness and toughness are proportional to amount of martensite and amount of
martensite depends on intercritical annealing temperature.
Keyword: Dual Phase Steel, Intercritical Annealing, Ferrite, Martensite, Hardness, Microstructure,
Toughness, Mechanical Properties.

152
1. INTRODUCTION

Steels whose structures consist of mixtures of ferrite and martensite are often referred to as
dual phase (DP) steel. DP steels are low carbon steel that posses a microstructure consisting of a
ferrite and martensite. In DP microstructure although small amounts of retained austenite, bainite and
/or pearlite may also be present. These phases are arranged such that the hard martensite is present in
island located at the grain boundaries within a soft ferrite matrix [1]. The island can be separated,
such as shown in fig 1. The soft ferrite phase provides the required ductility where as the hard phase
martensite imparts the required strength [6], [7].
Fig 1: Diagram of dual phase steel microstructure [2]
These steels possess some special properties viz., absence of yield point phenomena, large
ratio of tensile strength to yield strength, high rates of work hardening, high total and uniform
elongation, excellent forming characteristics and high fracture toughness. The mechanical properties
of the dual phase steels can be enhanced by changing the amount of martensite in the structure, by
carrying out intercritical annealing heat treatment for different holding times followed by water
quenching[8].The amount of martensite present in ferrite-martensite steel depends on the intercritical
annealing temperature in the ferrite plus austenite region. Due to superior properties and relatively
simple processing, the dual phase steels show a great promise for a wide range of applications. These
steels have been employed in several automotive components [3]. The use of these steels in
automobiles has led to a weight reduction of up to 30% with a notable increase in the life of the
components [4]. Evergrowing demand for newer materials with improved mechanical properties has
led to the development of wide variety of dual phase steels. Intercritical heat treatment is an effective
way to transform low carbon steels to dual phase steels with superior strength. For dual phase steel,
heat treatment can be applied to low-carbon steels with carbon content higher than 0.1% and to
specimens which have sections larger than 1.0 mm [5].Heat treatment involves heating the steel to
intercritical temperature range to obtain ferrite and austenite followed by quenching to get ferrite-martensite
dual phase structure. The hardness and toughness of dual phase steel is considerably
improved due to the presence of harder martensite phase compared to the normal steel with ferrite
pearlite microstructure[9], [10], [11]. Several attempts have been made to establish the overall
mechanical properties of dual phase steels from the properties of individual constituents DP steel
[12]-[16].The present investigation is to develop DP steel by varying intercritical temperature and
period of annealing using hardness and toughness properties as criteria. In summary, the present
study has been carried out in order to correlate the microstructure evolved after the intercritical
annealing with the observed mechanical properties. The knowledge base generated through this
study is expected to provide a better understanding of this unique class of steels and help utilize its
potential as a future material

2. MATERIALS AND INVESTIGATION METHODS
153

The test samples used for the present work 10 mm thick low carbon square steel rod. The
chemical composition of material is shown in table-
Table 1: Chemical Compositions of the Steel Used
Element C Mn Si S P Cr Cu
Wt% 0.21 0.50 0.25 0.018 0.019 0.06 0.09
Different processing operation required to be done on raw material for the specimen
preparation before doing any test on it. The samples are subjected to various tests before and after the
heat treatment in order to determine their mechanical properties and compared with parent steel.
2.1 Development of Dual Phase Steels-Dual phase steels are developed by heating low carbon steel
of 0.21% carbon content into two phase ferrite-austenite (a+g) region of Fe-C phase diagram,
followed by rapid cooling to transform austenite (g) into martensite, resulting in a structure of ferrite
and martensite that is known as dual phase steel. Method mainly used for developing dual phase
microstructure in steels, namely intercritical annealing
Figure 2: Iron-carbon phase diagram showing area of interest for typical dual phase steels
2.1.1 Intercritical Annealing
Dual phase microstructure in steels may be developed by heat treatment of either continuous
intercritical annealing or box-annealing [8]. The continuous annealing technique is mostly used
because of higher production rates and better uniformity in properties. The possibility of use of either
low carbon steel strips or low alloy steel is also an added advantage of this technique. However, box-annealing
has also been used where continuous annealing facilities are not available. In the
continuous annealing technique, the steel strip is heated for a short time in intercritical temperature,
to form ferrite-austenite mixtures. This is followed by rapid cooling so as to allow the transformation

of austenite into martensite. The actual cooling rate depends on the sheet thickness and quenching
conditions on a given production line. In the box-annealing technique, similar heat treatment is
carried out but the duration of annealing is relatively much longer (~ 3 hours) and the cooling rates are
slower (200C/ hr). Due to this slow cooling rate, there is a need to have much higher level of alloying
in steels to achieve the desired hardneability. First of all the intercritical annealing of the charpy test
specimen is done on the muffle electric furnace. Procedure for intercritical annealing the work
specimens:-
154

1. Switch ON the furnace and set 740°C temperature in the controller which controls the
voltage, current and the temperature inside the furnace.
2. Gradually the temperature of the furnace reaches 740°C in 40min to 50 min.
3. Temperature will fluctuate between 739°c to 741°C due to error in the thermocouple used so
wait for the stable value.
4. Now put the work piece on ceramic plate.
5. Set timer in the mobile for required time.
6. In the end of set time, open the lid of the furnace Remove the material and drop the work
piece in the water pool
7. Use asbestos plate to cover the furnace to avoid heat loss.
8. Remove the material and repeat steps for other material.
The production route for intercritical annealed DP steels is schematically shown in Figure 3,
where, Ac1 and Ac3 are the start and finish temperatures of austenite formation during
heating.
Figure 3: Heat treatment path for intercritical annealing
Different heating temperature and holding time selected as shown in table:-
Table 2: Increasing intercitical temp. constant holding temperature
Specimen 1 2 3 4
Temperature (0C) 0 760 800 840
Holding time(min) 0 2 2 2
Table 3: Constant intercritical temp, increasing holding time
Specimen 1 2 3 4
Temperature (0C) 760 760 760 760
Holding time(min) 2 3 5 10

155
2.2 Charpy Impact Testing

Charpy impact is practical for the assessment of brittle fracture of metals. An impact test
signifies toughness of material that is ability of material to absorb energy during the plastic
deformation. The Charpy test sample has (10x10x55) mm3 dimensions, a 45o V notch of 2 mm depth
and a 0.25 mm root radius will be hit by a pendulum attach opposite end of the notch as shown in
Figure 4:
Figure: (5)
As the pendulum is raised to a specific position, the potential energy (mgh) equal to
approximately 300J is stored. The potential energy is converted into the kinetic energy after releasing
the pendulum. Charpy test procedure:-
1. Raise the pendulum to position of135° with the vertical and hold it there with the help of stop
device and safety lever should be in the charpy position
2. Mark the loose dial pointer in contact with the pointer fixed with the pendulum.
3. Release the pendulum with the help of trigger when there is no specimen in the vice
4. Note down the reading of pendulum by the position of loose dial pointer, This reading is E1.
5. Bring the pendulum to static position and raise it again to position of135°and holt it there by
stop device
6. Place test piece in the vice in simply supported position
7. Release the pendulum with the help of trigger. It will strike at specimen with the speed of 3-
4m/s.
8. Note down the reading of pendulum again by the position of loose dial pointer
9. The difference of energy between E1and E2is the energy absorbed by the specimen.
2.3 Hardness Test
The hardness of heat treated and untreated samples are determined using Rockwell Hardness
testing machine using C scale (HRC).The purpose of this test is to make comparison of the hardness
properties between the specimen (intercritical annealing temperature between the760°C to 840°C)
with the low carbon steel. Rockwell Hardness is probably the most used hardness testing method
because it is simple and self contained. For hardness testing, oxide layers formed during heat
treatment are removed by disc grinding machine and then polished using different grades emery
papers. The hardness are measure at 3 or 4 different location of the each test sample and then average
value are taken. An initial load of 10 Kg is applied on specimen through the indenter to set the
specimen and to eliminate the surface imperfection. For “C”scale (diamond) indentor is used and
major load are 150 Kg.
2.4 Microstructure Examination
Microstructure examination of steels is an important analysis to be carried out. It is very
useful since it can provide important information about grain size, material properties. It can show
the surface cracks or other machining defects.Microstructure examination of the treated and

untreated samples are carried out.The microstructure examinations are performed on the flat surface
as the follows:-
156

1. Oxide layers formed during heat treatment are removed by using different grades of emery
papers (220,400,600, 800, 1000) using disc grinder.
2. After this rotating disc polishing machine is used for generating fine surface
3. The polished surfaces are etched by NITAL etching solution, nitric acid of percentage 2cm³
with 100cm³ of alcohol
4. Finally photographs of the microstructure are taken using microscope.
2.5 Determination of Mechanical Properties
Mechanical properties of the heat treated and untreated samples are determined using
standard method. Hardness of each samples are determined by using Rockwell Hardness testing
machine and toughness of each samples are determined by using charpy test.
3. RESULTS AND DISCUSSION
The experimental results show that dual phase steels have excellent mechanical properties in
terms of hardness and toughness.
Table 4: Mechanical properties of heat treated and untreated steel
Specimen Temp. Holding Time(min.) Toughness(J) Hardness(HRC)
0°C 0 196 6
760°C 2 208 9
800°C 2 260 12
840°C 2 272 13
Table 5: Mechanical properties of heat treated and untreated steel
SpecimenTemp. Holding Time(min.) Toughness(J) Hardness(HRC)
0°C 0 196 6
760°C 2 208 9
760°C 3 224 10
760°C 5 252 12
760°C 10 282 14
Table 4 and 5 show that the hardness and toughness value of dual phase steel and low carbon
steel. It is clear that hardness and toughness of dual phase steels are higher than the low carbon steel.
The hardness and toughness value of dual phase steels increase with growing intercritical annealing
temperature and heating time. The increase is due to increasing martensite volume. When the
intercitical annealing temperature increases, more pearlite changes to austenite. Austenite then
transform to martensite by rapid cooling. Hence the percentage of martensite in DP steel is increased.
Tougher martensite formed at higher temperature. The dual phase steels have better hardness and
toughness properties as it consists of ferrite and martensite structures. The experimental results show
that dual phase steels have excellent mechanical properties in term of hardness, toughness.
Microstructure:-The DP steel obtained after after the heat treatment consists of ferrite and
martensite microstructure but may consists small amount retained austenite, bainite or pearlite.
Martensite is dispersed in soft ductile ferrite matrix. The soft provides the required ductility and hard

phase martensite provides the strength for DP steel. The micrographs of DP steel with different
intercritical temperature shown.
157

Figure: (6)
Figure: (7) Figure: (8)
Graph: (1) Graph: (2)

158

Graph: (3) Graph: (4)
The above Fig.5 to 7 represent the the microstructure of DP steel intercritical temperature
760°C, 800°C, 840°C respectably. The structure shows that there are three phase, ferrite (white
region) pearlite (dark region) martensite (light brown area). The percentage volume fraction of
martensite in DP steel is influenced by variation in the intercritical annealing temperature. The
percentage volume fraction of martensite in DP steel increases as intercritical temperature increases.
This is because when the intercritical annealing temperature increases, more pearlite changes to
austenite. Austenite then transform to martensite. Table 4 and 5 and graph 1 to 4 show that the
hardness and toughness value of dual phase steel and low carbon steel. It is clear that hardness and
toughness of dual phase steels are higher than the low carbon steel. The hardness and toughness
value of dual phase steels increase with growing intercritical annealing temperature and heating time.
The increase is due to due increasing martensite volume. When the intercitical annealing temperature
increases, more pearlite changes to austenite. Austenite then transform to martensite by rapid
cooling. Hence the percentage of martensite in DP steel is increased. Tougher martensite formed at
higher temperature. The dual phase steels have better hardness and toughness properties as it consists
of ferrite and martensite structures. The experimental results show that dual phase steels have
excellent mechanical properties in term of hardness, toughness.
4. CONCLUSION
Dual phase steel can be developed from low carbon steel by intercritical annealing process.
The investigations are carried out on various samples to study the effect of temperature and time in
the martensite phase of of dual phase steel. As the content of martensite in the DP steel increases by
increasing the heating temperature and time. The hardness and toughness of DP steel increases. It is
clear that hardness and toughness of dual phase steels are higher than the low carbon steel. The result
obtained confirmed that improvement in the mechanical properties that can be obtained by subjecting
low carbon steel to intercitical annealing heat treatment and testing charpy, microstructure and
hardness test in this study. DP steels have better mechanical properties as it consists of ferrite and
martensite structure. By simply heat treatment of steel, the mechanical properties are improved and
cost adding costly material is saved.

159
ACKNOWLEDGMENT

This works are carried out at ITM Gorakhpur and SHIATS university Allahabad. The efforts
of the technical staff at mechanical engineering labs and workshops are highly appreciated.
REFERENCES
1. Williams, E.W., and L.k. Davies, “Recent Developments in annealing”, ISI Special Report
79,1963
2. K Hulka, “Dual phase and Trip steels”, ASM Metals Park Ohio, Pp.14, 2000.
3. J.W. Marrow, G. Ther and R.M.Busk, intercritical annealed Dual phase steel for automotive
applications formable HSLA Dual phase steels A.T.Deevenport, TME-AMIE, the
metallurgical society. NewYork, Warrenendale PA.1979.
4. Abdalla, A. J., Hein, L. R. O., Pereira, M. S. and Hashimoto, T. M., (1999), “Mechanical
Behaviour of Strain Aged Dual Phase Steels,” Mater. Sc. and Tech., Vol. 15, pp. 1167-70
5. OguzhanKelesternur, M HalidunKelestemur, ServetYildiz, “Improvement of Mechanical
Properties of Reinforcing Steel Used in the Reinforced Concrete Structures”, Journal of Iron
and Steel Research, International, Vol. 16, No. 3, Pp. 55-63, 2009.
6. Hills D J, Llewellyn D T, Evans P J, “Rapid Annealing of Dual-Phase Steels”, Iron making
and Steel making, Vol. 25, No.1, Pp. 47-54, 1998.
7. Davies R G, Magee C L, “Structure and Properties of Dual-Phase Steels”, The Metallurgical
Society of AIME, Warrendale, PA, Pp. 1-19, 1979.
8. Maleque, Ma., Poon, Ym., Masjuki, Hh., The effect of intercritical heat treatment on the
mechanical properties of AISI 3115 steel, Journal of Materials Processing Technology,
153-154, pp.482-487, 2004.
9. A.Oyetungi, I.Y.Suliman, Effect of Ferrite-Martensite Microstructure Evolution on Hardness
and Impact toughness Behaviour of High Martensite Dual phase steel. Australian Journal of
Basic and Applied Science, 2000.
10. R G Davies, “Influence of martensite composition and content on the properties of dual phase
steels”, Metall. Transactions: A, Vol. 9, Pp. 671-679, 1978.
11. Nath, S. K., (1989) “Influence of Intercritical Annealing on the Mechanical Properties of
Plain-Carbon Dual Phase Steels,” Ph.D.Thesis, University of Roorkee, Roorkee, p. 91.
12. Ahmad Zare, A Ekrami, “Influence of martensite volume fraction on tensile properties of
triple phase ferrite-bainite-martensite steels”, Materials Science and Engineering: A, Vol.
530, Pp. 440-445, 2011.
13. G Thomas and J Y Koo, “Structure and properties of dual phase steels”, AIME, NewYork,
Pp. 183-201, 1979.
14. Ebrahim NajafiBirgani, MajidPouramani, “Effect of martensite volume fraction on the work
hardening behaviour of dual phase steels”, HradecnadMoravicí, Czech Republic, Pp.19-21,
2009.
15. Matsuoka, T. and Yamoori, K., (1975), “Metallurgical Aspects of Cold-Rolled High Strength
Steel Sheets,” Metall. Mater. Trans., Vol. 6A, pp. 1613-22.
16. Mould, P. R. and Skena, C.C., (1979), “Structure and Properties of Cold-Rolled Ferrite-
Martensite (Dual Phase) Steel Sheets,” Proc. on Formable HSLA and Dual-Phase Steels,
Kot, R.A. and Morris, J.W., ed., AIME, New York, pp. 183-205.
17. Fadi A. Ghaith and Fahad A. Khan, “Three Dimensional Nonlinear Finite Element Modeling
of Charpy Impact Test”, International Journal of Mechanical Engineering Technology
(IJMET), Volume 4, Issue 4, 2013, pp. 377 - 386, ISSN Print: 0976 – 6340, ISSN Online:
0976 – 6359.

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