Study and Analysis on Heat Treatment Process and Microstructure of Low Carbon Steel

International Journal of Advanced Research in Technology, Engineering and Science (A Bimonthly Open Access Online
Journal) Volume2, Issue3, May-June, 2015.ISSN:2349-7173(Online)
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Study and Analysis on Heat Treatment Process and
Microstructure of Low Carbon Steel
Sindhusuta Rout1
,Mr. R.R.Panda2
, Dr R.C.Mohanty3
_______________________________________________
Abstract: Low carbon steel is easily available and cheap
having all material properties that are acceptable for many
applications. Heat treatment on low carbon steel is to improve
ductility, to improve toughness, strength, hardness and tensile
strength and to relive internal stress developed in the material.
Here basically the experiment of harness and ultimate tensile
strength is done to get idea about heat treated low carbon steel,
which has extensive uses in all industrial and scientific fields.
___________________________________________________
Keywords: Mechanical properties, Heat treatment,
Microstructure study etc
___________________________________________________
Introduction
Low carbon steel has carbon content of 0.10% to 0.35%. Low
carbon steel is the most common form of steel as it's provides
material properties that are acceptable for many applications. It
is neither externally brittle nor ductile due to its lower carbon
content. It has lower tensile strength and malleable
The process heat treatment is carried out first by heating the
metal and then cooling it in water, oil and brine water. The
purpose of heat treatment is to soften the metal, to change the
grain size, to modify the structure of the material and relive the
stress set up in the material. The various heat treatment process
are annealing, normalizing, hardening, austempering, mar
tempering, tempering and surface hardening
The various heat treatment processes commonly employed in
engineering practice as follows:-
1.1 Annealing:-
Makes a metal as soft as possible
Hypoeutectoid steels (less than 0.83% carbon) are
heated above upper critical temp., soaked and cooled
slowly.
Hypereutecoid (above 0.83%) are heated above lower
critical temp., soaked and allowed to cool slowly
_________________________________________________
First Author Name: Sindhusuta Rout, Mechanical Engg Dept., CUTM, BBSR.
Email: sindhusutarout @gmail. Com
Second Author Name: RashmiRanjan Panda, Mechanical Engg Dept., CUTM,
BBSR. Email: rashmi.panda @cutm.ac.in
________________________________________________________________
1.2 Normalising:-
Internal stresses caused by rolling and rolling or forging are
removed. Steels are heated above upper critical temp., soaked
and cooled in air. The cooling rate is faster than annealing
giving a smaller grain structure.
1.3 Hardening:-
The Process hardening consist of heating the material to a
temperature of 35 to 55 c above the upper critical point for
hypo-eutectoid steels.
1.4 Austempering:-
In this process the steel is heated above the upper critical
temperature at above 870c where the structure consist entirely of
austenite
1.5 Tempering:-
This process consists of reheating the hardened steel to some
temperature below the lower critical temperature.
1. Experimental Details:
The experimental details for the project work can be listed as:
Specimen preparation
Heat treatment
Harden testing
Mechanical property study
Microstructure study
Material selection- Mild steels of the required dimensions were
purchased from the local market and the test specimens were
prepared from it. The chemical composition of mild steel in wt.
% is given as follows C-0.10, Si-0.03, Mn-0.30, S-0.06, P-0.3,
Ni- 0.02, Cu-0.02, Cr-0.02 and Fe. The specimens are prepared
as per ASTM standard.
Specimen for abrasive wear and hardness test: - Dimensions
(4cm x 2.5cm x 0.5cm)
Specimen for toughness test: - As per ASTM standard Length-
5.5 cm Width-1cm Thickness-1cm Notch depth-0.5cm
2.1 Specimen Preparation
The sample that I got was Mild steel. AISI8620:It is one of the
American standard specifications of the mildSteel having the
pearlitic matrix (up to70%) with relatively less amount of ferrite
(30-40%). And so it has high hardness with moderate ductility
and high strength asspecified below. So we can also say that it is
basically a pearlitic/ferritic matrix
2.2Heat Treatment
Normalizing:
At the very beginning the specimen was heated to the

temperature of 900 deg Celsius.
There the specimen was kept for 2 hour.
Then the furnace was switched off and the specimen
was taken out.
Now the specimen is allowed to cool in the ordinary
environment. i.e. the specimen is air cooled to room
temperature.
The process of air cooling of specimen heated above
Ac1 is called normalizing
Quenching:
This experiment was performed to harden the cast iron. The
process involved putting the red hot cast iron directly in to a
liquid medium.
The specimen was heated to the temp of around
900˚Celsius and was allowed to homogenize at that
temp for 2 hour.
An oil bath was maintained at a constant temperature
in which the specimen had to be put.
After 2 hour the specimen was taken out of the furnace
and directly quenched in the oil bath.
After around half an hour the specimen was taken out
of the bath and cleaned properly.
Now the specimen attains the liquid bath temp within
few minutes. But the rate of cooling is very fast
because the liquid doesn't release heat induce some
amount of softness in the material by heating to a
moderate temperature range.
Tempering
First the '4' specimen were heated to 900 deg Celsius
for 2 hour and then quenched in the oil bath maintained
at room temp
Among the 4 specimen 2 were heated to 250
degCelsius. But for different time period of 1 hour,
1and half hour and 2 hour respectively.
Now 3 more specimens were heated to 450 deg
Celsius and for the time period of 1 hour, 1and a half
hour and 2 hour respectively.
The remaining specimens were heated to 650˚Celsius for
same time interval of 1 hour. 1 and half and 2 hour
respectively.
After the specimens got heated to a particular temperature
for a particular time period, they were air cooled. The heat
treatment of tempering at different temp for different time
periods develops variety of properties within them.
. Austempering
This is the most important experiment carried out for the
project work. The objective was to develop all round
property in the material.
The specimen was heated to the temperature of 900 degree
Celsius and sufficient time was allowed at that temperature,
so that the specimen got properly homogenized.
A salt bath was prepared by taking 50% NaN03 and 50 %
KnO3 salt mixture. The objective behind using NaNO3 and
KNO3 is though the individual melting points are high the
mixture of them in the bath with 1: 1 properties from an
eutectic mixture this eutectic reaction brings down the
melting point of the mixture to 290 deg Celsius. The salt
remains in the liquid state in the temp range of 290-550 deg
Celsius whereas the salt bath needed for the experiment
should be at molten state at 350 deg Celsius
After the specimen getting properly homogenized it was
taken out of the furnace and put in another furnace where
the container with the salt mixture was kept at 350d deg
Celsius.
At that temp of 350 degree the specimen was held for 2
hrsIn this time the austenite gets converted to bainite. The
objective behind
choosing the temperature of 350 deg Celsius is that at this
temperature will give upper bainite which has fine grains so
that the properties developed in the materials are excellent.
An oil bath also maintained so that the specimen can be
quenched.
So after sufficient time of 2 hr the salt bath was taken out of
the furnace and the specimen were quenched in the oil bath.
An oil bath is also maintained so that specimen can be
quenched. Now the specimens of each heat treatment are
ready at room temperature. But during quenching in a salt
bath, or oil bath or cooling due to slight oxidation of the
surface of cast iron, there are every possibility of scale
formation on this surface if the specimens are sent for testing
with the scales in the surface then the hardness value will
vary and the specimen will also not be gripped properly in
the UTS To avoid this difficulties the specimens were
ground with the help of belt grinder to remove the scales
from the surface. After the scale removal the Specimens are
ready for the further experiments.
2.3 Hardness testing:
The heat treated specimens hardness were measured by means
of Rockwell hardness tester. The procedure adopted can be
listed as follows:
First the brale indenter was inserted in the machine; the load
is adjusted to100 kg.
The minor load of a 10 kg was first applied to seat of the
specimen.
Now the major load applied and the depth of indentation is
automatically recorded on a dial gage in terms of arbitrary
hardness numbers. The dial contains 100 divisions. Each
division corresponds to a penetration of .002 mm. The dial
is reversed so that a high hardness, which results in small

penetration, results in a high hardness number. The
hardness value thus obtained was converted into C scale by
using the standard converter chart.
3. Result & Discussion
3.1 Microstructure study
The initial structures of the specimens subjected to the heat
treatment were: ferrite with some fraction of pearlite, low-
carbon martensite and primary austenite with a grain size of
about 12Pm (Fig.1) .It was found that the martensite
morphology exhibits substantial differences dependent on the
initial structure of the steel. The specimens heat-treated I
have a ferritic matrix and the martensite is located on boundaries
of the Dphase as an irregular envelope (Fig. 2).The location of
martensite is strongly dependent on a distribution of the
austenite formed due to a carbon enrichment of the boundary-
zones of ferrite connected with a decomposition ofpearlite
grains. During annealing of the investigated steel at a
temperature of 750°C the privileged diffusion of carbon on the
boundaries of the D-phase is occurred. The underhardening
from an increasing annealing temperature leads to the
increase of martensite volume fraction, keeping a network
distribution of this phase on grain boundaries of the D-
phase (Fig. 3).
The martensite fraction in the steel quenched from a
temperature of 750°C equals about 22% and increases to
40% after quenching from a temperature of 810°C. A result
of the increase of martensite fraction together with
increasing the underhardening temperature is unfavorable
decreasing the carbon concentration in austenite and
increasing the Mstemperature of this phase. For 22% volume
fraction of martensite, the carbon concentration in the J-phase
equals about 0.47% and the Ms temperature of this phase about
290°C.
3.2 Hardness Test
More is the tempering temperature, less is the hardness or
more is the softness (ductility) induced in the quenched
specimen. (ductility) induced in the quenched specimen. This is
due to grain growth due to heat treatment.
Table 1 Hardness vs. tempering temperature for constant
tempering time of 1 hour
Specimen Specification Time(in
hours)
Hardness
Quenched from 900˚C
and
tempered at 250˚C
1 hour 43
and
tempered at 450˚C
1 hour 36
and
tempered at 650˚C
1 hour 33

3.3 Tensile Test
Table 2 Tensile properties for different tempering temperature for 1 hour tempering time
Specimen Specification Time(in hours) UTS(MPa) Yield Strength
(in MPa)
Elongation%
Quenched from 900˚C and
tempered at 250˚C
1 548 334 9.65
tempered at 450˚C
1 497 297 14.369
tempered at 650˚C
1 318 234 20.476
Fig. 1 Boundaries of primary austenite grains
of the steel quenched from a temperature of
900°C
Fig. 2 Boundaries of primary austenite grains of
the steel quenched from a temperature of 900°C
Fig 3. Ferritic – martensitic structure of the
steel quenched from a temperature of
810°C
Fig. 4Ferritic – martensitic structure of the steel
twice quenched from the temperatures of 900°C
and 750°C

Journal).Volume2, Issue3, May-June, 2014. ISSN: 2349-7173(ONLINE)
200 400 600
20
25
30
35
40
45
Hardness(HV)
Temperature (Degree)
1 hr
2 hr
Fig 5. Hardness vs. tempering temperature for constant tempering time of 1 hour& 2 hr
200 400 600
250
300
350
YieldStrength(MPa)
Temperature (Degree)
1hr
2hr
Fig. 6 Tensile properties for different tempering temperature for 2 hour tempering time
More is the tempering time (keeping the tempering
temperature constant), more is the ductility induced in the
specimen. This clearly implies that the UTS and also to some
extent the yield strength decreases with increase in
tempering time where as the ductility (% elongation)
increases. For a given tempering time, an increase in the
tempering temperature decreases the UTS value and the
yield strength of the specimen whereas on the other hand
increasing the % elongation and hence the ductility.

Journal).Volume2, Issue3, May-June, 2014. ISSN: 2349-7173(ONLINE)
4.CONCLUSION
From the various results obtained during the project work it
can be concluded that:
Twice quenching of the steel from the temperatures 900°C
and 750°C and quenching after the
partial γ-α transformation results in a various shape of
martensite.
The mechanical properties vary depending upon the various
heat treatment processes.
Hence depending upon the properties and applications
required we should go for a suitable heat treatment processes.
Ductility is the only criteria tempering at high temperature
for 2 hours gives the best result among all tempering
experiments however it is simply the hardness of the low
carbon steel that is desired than we should go for low
temperature tempering for 1 hour or so.
It is seen that annealing causes a Tremendous increase in %
elongation (ductility). It can be clearly seen comparing all the
heat treatment processes, optimum Combination of UTS,
Yield Strength, % Elongation as well as hardness can be
Obtained through austempering only.
5. REFERENCES
[1] John V.B (1980), Introduction to material science, 2nd edition.
Pp 321-324.
[2] Alawode, A.J 2002, Changing in the mechanical properties and
stresses due to cold work on the steel. University of iorin, Nigeria.
[3] T. Senthilkumar and T. K. ajiboye.Heat treating on the
mechanical properties of medium carbon steel and materials
characterization. Vol. 11, no-2 pp.143-152, 2012 jmmce.org printed
in USA.
[4] ASTM international, ASTM hand book, volume 4, heat treating,
American society for metals park, Ohio, 1991
[5] S. K. Akay, M. Yazici, A. Avinc. The heat treating
onthemild steel to get desired properties. Proceedings of
Romanian academy Series A, Volume 10, Number 1/2009, pp. 000–
000.
[6] Bayram, A.uguz, A.ulam, Changing due to heat treating on
microstructure and notches on the mechanical properties of dual-phase
steels, Material Characterization, 43, pp. 259-269, 1999.
[7] B.S. Motagi, Ramesh Bhosle, Changing due to heat treating on
microstructure and mechanical properties of mild carbon steel, journal
of engineering research and development ISSN: 2278-067, VOL.
issue(July 2012), pp.07-13.
[8] Eiichiwakai, shingomatsukawal, mechanical properties of F82H steel
doped with boron and nitrogen, material transactions, vol.45, no-8(2004)
pp.2641-2643.
[9] EiichiWakail, Shingo Matsukawal, ShiroJitsukawa 45 (2004) 407-
401.
[10] Kai LIU, Yiyin SHAN, Zhiyong YAN, Jianxiong LIANG, LunLU
and Ke YANG, Changing due to Heat Treating on Grain Size and
Mechanical Property of a F82H Stainless Steel, J. Material testing.Vol.22
No.6, 2006.
[11] Y. He, K. Yang.Material science technology, 2003, 19,117.
[12] D.L. Corn and A.R. Wazan, iron steel institute, 1968, 6,600.
[13] B. Gajda, A.K. Lis, Intercritical annealing with isothermal
holding of TRIP CMnAlSi steel, Journal of Achievements in Materials
and Manufacturing Engineering 20 (2007) 439-442.
[14] S. Vercammen, B. Blanpain, B.C. De Cooman, P. Wollants, Cold
rolling behaviour of an austenitic Fe-30Mn-3Al-3Si TWIP-steel,
ActaMaterialia 52 (2004) 2005-2012.
[15] S. Allain, J.P. Chateau, O. Bouaziz, Constitutive model of the TWIP
effect in a polycrystalline high manganese content austenitic steel,
Steel Research 73 (2002) 299-302.

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