investigation of hardenability of en8 steel using …...micro-structure test and to compare the...

DOI:10.23883/IJRTER.2018.4207.A5QQH 67

INVESTIGATION OF HARDENABILITY OF EN8 STEEL USING

PHASE CHANGE MATERIAL DISPERSED IN WATER

S. Saravana Kumar1, R. Thivakar2, A.K. Rakesh Kumar3, S. Suriya4, S. Kishore5

1234 UG Student, Department of Mechanical Engineering, 5Assistant Professor, Department of Mechanical Engineering,

K. Ramakrishnan College of Engineering, Samayapuram, Trichy

Abstract: Medium Carbon steel is widely used for applications which require better properties than mild steel but does not justify the costs of an alloy steel. This project is to analyse the hardenability of

medium carbon steel quenched in the PCM material along with water, through micro-hardness and

micro-structure test and to compare the hardenability of the medium c-steel quenched in water. Here

the specimen is heated in the furnace at the critical temperature and quenched in different conditions.

Thereby microstructure is analysed using an optical microscope and micro-hardness is measured using

Vickers micro-hardness test apparatus. In this process, microstructural changes and micro-hardness is

observed from the centre towards the edge of the specimen.

Keywords: PCM, Hardenability, Quenched, Micro-Structure, Micro-Hardness.

Ι. INTRODUCTION

A. Medium carbon steel

Steel is an alloy of iron with the definite percentage of carbon ranging from 0.15-1.5%. These plain

carbon steels are classified on the basis of their carbon content, as their major alloying element is

carbon. Steels with carbon content varying from 0.30% to 0.60% are classified as medium carbon steel,

while those with carbon content less than 0.30% are termed as low carbon steel. The carbon content of high carbon steels usually ranges within 0.60-1.5%. Steel is mainly an alloy of iron and carbon,

where other elements are present in quantities too small to affect its properties. The other alloying

elements alloyed in plain-carbon steel are manganese, silicon and phosphorus. Steel with low carbon

content has the same properties as iron i.e. soft but easily formed. As carbon content rises, the metal

becomes harder and stronger but less ductile. Medium carbon steels are used for fabrication. In

addition, machined parts such as bolts, turbine casing and concrete reinforcing bars are made of this

class of carbon steel. Gears, wire rods, seamless tubing, hot-rolled/cold-finished bars and forging

products are also some objects constructed from medium carbon steel. Although the number of steel

specifications runs into thousand, plain carbon steel accounts for more than 90% of the total steel

output. The reason for its importance is that it is a tough, ductile and cheap material with reasonable

casting, working and machining properties, and also amenable to simple heat treatments to produce a

wide range of properties.

Heat treatment is a combination of controlled heating and cooling applied to a particular metal or alloy

in the solid state in such ways so as to produce certain microstructure and desired mechanical properties

(hardness, ultimate tensile strength, yield strength and elongation). Annealing, normalizing,

hardening/quenching and tempering are the most important heat treatments often used to modify the

microstructure and desired mechanical properties in steel. Heat treatment process leads to change in

phase microstructural and crystallographic changes in the material. The purpose of heat treating carbon

steel is to obtain mechanical properties of steel usually ductility. The heat treatment develops hardness,

International Journal of Recent Trends in Engineering & Research (IJRTER) Volume 04, Issue 04; April- 2018 [ISSN: 2455-1457]

@IJRTER-2018, All Rights Reserved 68

softness and improves the mechanical properties such as ductility. This process also helps to improve

machining effect and make them versatile. Heat treatment is also used to increase the strength of

materials and to relieve stresses induced in the material after manufacturing, forging and welding.

Hardened/quenched specimen has the highest tensile strength and hardness with lowest ductility and

impact strength when compared to other heat treated specimen. Hardening/quenching is strongly

recommended when the strength and hardness are the prime desired properties in design. Quenching

in water resulted in higher tensile strength and hardness possibly due to the formation of martensite

structure which is one of the strengthening phases of steel.

EN8 steel which is used in fabrication industries for massive production. Hence there is need to carry

out this work for the further enhancement of desired mechanical properties in the material which in

turn increases the durability and performance of components made by this material. Present work deals

with the influence of PCM on hardening property of EN8 steel with the objective of improving its

hardenability.

B. Heat treatment

Heat treatment is a process that involves a combination of time-controlled heating and cooling

operations of metal without changing the product shape that will produce desired mechanical

properties and to observe the microstructure after heat treatment. Heat treatment is used to improve

the mechanical properties of the metal alloys. Basically, the product performance will improve when

the strength of material increased. It can be divided into three main processes namely annealing,

quenching and tempering. In general, the procedure of heat treatment process consists of three stages.

First stage is heating the material. Second, hold the temperature for a period of time and third, cool

down the metal to room temperature. The treatment of medium carbon steel with heat can significantly

change the mechanical properties, such as ductility, hardness and strength. Heat treatment of steel

slightly affects other properties such as its ability to conduct heat and electricity as well. A variety of

methods exist for treating steel with heat. The carbon and manganese content in medium carbon steel

make quenching and tempering the most common method of heat treatment for this type of steel. This

process generally involves repeatedly heating the steel to less than 1,333°F (about 723°C) and cooling

it rapidly by quenching it in a liquid such as oil or water. The temperature and time of this process

allow the manufacturer to precisely control the final properties of the steel.

C. Phase Change Material (PCM)

Phase change material is a substance with a high heat of fusion which, melting and solidifying at a

certain temperature, is capable of storing and releasing large amounts of energy. Heat is absorbed or

released when the material changes from solid to liquid and vice versa; thus, PCMs are classified as

latent heat storage (LHS) units. Initially, solid-liquid PCMs behave like sensible heat storage (SHS)

materials; their temperature rises as they absorb heat. Unlike conventional SHS materials, however,

when PCMs reach the temperature at which they change phase (their melting temperature) they absorb

large amounts of heat at an almost constant temperature. The PCM continues to absorb heat without a

significant rise in temperature until all the material is transformed to the liquid phase. When the

ambient temperature around a liquid material falls, the PCM solidifies, releasing its stored latent heat.

A large number of PCMs are available in any required temperature range from −5 up to 190°C. Within

the human comfort range between 20–30°C, some PCMs are very effective. They store 5 to 14 times

more heat per unit volume than conventional storage materials such as water, masonry or rock.



ΙΙ. SELECTION OF MATERIALS

A. EN 8

EN8 carbon steel is a common medium carbon and medium tensile steel, with improved strength over

mild steel, through-hardening medium carbon steel. EN8 carbon steel is also readily machinable in any

condition.EN8 steels are generally used in the as supplied untreated condition. But EN8 steels can be

further surface-hardened by induction processes, producing components with enhanced wear

resistance. Steel EN8 materials in its heat treated forms possess good homogenous metallurgical

structures, giving consistent machining properties. It is chosen because of its wide general engineering

applications. Typical applications include shafts, studs, bolts, connecting rods, screws, rollers.

Carbon C 0.35-0.44%

Phosphorous P 0.05%

Manganese Mn 0.60-1.00%

Sulphur S 0.005%

Silicon Si 0.10-0.40%

Table 1. EN8 Composition

B. Phase Change Material

For this analysis, we selected Zinc Nitrate Hexahydrate as PCM due to its melting property. It is an

inorganic chemical compound with the formula Zn(NO3)2•6H2O. This white, crystalline solid is highly

deliquescent and it is soluble in both water and alcohol. It has a sharp melting point of 36.4°c.

C. Copper tube

Copper tubing is most often used for the supply of hot and cold tap water, and as a refrigerant line in

HVAC systems. Copper offers a high level of corrosion resistance but is becoming very costly.

Because of its high heat transfer capacity copper tube is used to encapsulate the PCM.

ΙΙΙ. EXPERIMENTAL WORK

A. Components used

Copper tube, Stirrer, Aluminium vessel, Glass wool, Thermometer, Muffle furnace are used as the

components for the experimental setup. The Muffle furnace used for the experiment is equipped with

6 thermocouples on 4 sides for temperature measurement. It is based on American Petroleum

Instruction and capacity is 600*600*600mm. Maximum temperature it can reach is 1200ºc.

Figure 1. Muffle furnace



B. Experimental setup

Now the aluminium tank is filled with 6 litres of water then the stirrer and a copper tube filled with

PCM are dipped in water at the time of requirement. Then glass wool is tied around the aluminium

vessel in order prevent the loss of heat through heat transfer to the surrounding. Stirrer is operated

around 500rpm. Thermometer and stopwatch are used to note the temperature of water at regular

intervals at the time of quenching of hot specimen in water.

Figure 2. Experimental setup

C. Experimentation

First, the EN 8 rod is cut into pieces at a dimension of 50*50mm and placed in a furnace for heat

treatment. The rate of heating is set as 266.6ºc/hr for 3hours in order to reach the temperature of 800ºc

above the critical temperature. Then the specimen is soaked for 30minutes in the furnace itself in order

to obtain uniform temperature around the material. Then the specimen is quenched in 3 different

conditions in order to improve the hardness. The three different conditions are

Normal quenching in water

Normal water quench with a stirrer

Normal water quench with stirrer and PCM enclosed in a copper tube

Figure 3. Specimen Before Heat treatment

Thermometer

Stirrer

PCM encapsulated

Copper tube

Water

Aluminium vessel

Glass wool

Glass wool

50mm



Figure 4. Specimen After Heat treatment and Quenching

The noted temperature at a specific time for various quenching conditions are tabulated below

S.NO CONDITIONS TIME(mins) TEMPERATURE(ºc)

1

Normal Water Quench

1 48

5 45

10 43

2

Normal Water Quench with Stirrer

1 44

5 42

10 40

3

Normal Water Quench with Stirrer and PCM

enclosed in Copper tube

1 40

5 39

10 37

Table 2. Temperature readings

Ⅳ. TEST AND RESULTS

The following tests were conducted on the specimens:

1. Vickers Micro-hardness test.

2. Optical Microscope test.

Figure 5. Machined specimens for test



A. Vickers Microhardness test

The Vickers hardness test method also referred to as a microhardness test method is mostly used for

small parts, thin sections, or case depth work. The Vickers method is based on an optical measurement

system. The Microhardness test procedure, ASTM E-384, specifies a range of light loads using

a diamond indenter to make an indentation which is measured and converted to a hardness value. It is

very useful for testing on a wide type of materials, but test samples must be highly polished to enable

measuring the size of the impressions. A square base pyramid shaped diamond is used for testing in

the Vickers scale. Typically loads are very light, ranging from 10gm to 1kgf, although "Macro" Vickers

loads can range up to 30 kg or more. Here we applied a load of 300gm for indentation of all the 3

specimens. To know the hardness of heat treated specimen’s hardness is taken in 3 points on the

specimen they are named as Point A, B and C.

Figure 6. Indentation points

LOAD – 300gm

S.NO

INDENT

POINTS

STILL WATER

QUENCH

STIRRER

QUENCH

PCM & STIRRER

QUENCH

(HV) (HV) (HV)

1

Core

200

201.3

203

2

Middle

182

187

193.2

3

Periphery

216

214

227.3

Table 3. Hardness value of Specimens



Figure 5.1. Hardness comparison graph

The above Vickers hardness test result shows that the hardness of specimen at middle region is low

compared to core and periphery hardness is higher than other two points, this variation is uniformly

seen in all 3 quench conditions. So, the hardness value reduces from core at middle and again increases

at periphery. Hence there is a uniform hardness improvement in all the specimen. From the table, the

hardness value of normal water quench specimen is low with stirrer utilised quench specimen and

hardness value of PCM quenched specimen is higher than stirrer utilised specimen. By comparing the

individual specimen hardness, PCM enclosed copper tube quench specimen’s hardness is high

compared to other two: stirrer quench and normal water quench specimen.

B. Optical microscope test

The optical microscope, often referred to as the light microscope, is a type of microscope that

uses visible light and a system of lenses to magnify images of small subjects. Optical microscopes are

the oldest design of microscope and were possibly invented in their present compound form in the 17th

century. Basic optical microscopes can be very simple, although many complex designs aim to

improve resolution and sample contrast. Here the microstructure of specimens are captured at 500X at

3 points like Vickers test and image scale is 50µm.

Figure 7.1. Specimen 1- Core Figure 7.2. Specimen 1- Middle Figure 7.3. Specimen 1- Periphery

170

180

190

200

210

220

230

core middle periphery

Ha

rdn

ess

va

lue

(HV

)

Test Points

water quench stirrer pcm quench

https://en.wikipedia.org/wiki/Microscope

https://en.wikipedia.org/wiki/Visible_spectrum

https://en.wikipedia.org/wiki/Lens_(optics)

https://en.wikipedia.org/wiki/Compound_microscope

https://en.wikipedia.org/wiki/17th_century

https://en.wikipedia.org/wiki/17th_century

https://en.wikipedia.org/wiki/Simple_microscope

https://en.wikipedia.org/wiki/Optical_resolution

https://en.wikipedia.org/wiki/Contrast_(vision)





The above images obtained from optical microscope shows the white martensite structure increases

from core to middle and middle to periphery. And like this the black pearlite structures goes on

decreasing from core to middle and middle to periphery. This variation is seen in all specimen. From

these images, it can be inferred that the structural variation is uniformly distributed.

Ⅴ. CONCLUSION

By conducting microhardness and microstructure test in still water, stirrer in water, PCM and stirrer in

water quenched samples we obtained following outcomes:

Microstructure study clearly reveals that the hardness varies over the region due to the presence

of pearlite and martensite, the martensite structure is seen as bright and pearlite is observed as the dark

region.

Microstructure study also reveals that the presence of martensite over the region can be seen to

increase in case of the PCM quenched specimen compared to the other two samples.

Microhardness reading of all three quenched samples showed the variation of structure from

core to periphery which is proved by the variation of hardness value over the samples.

Microhardness is improving in all three quench conditions but PCM quenched specimen

hardness showed more uniform distribution over its region compared to other specimens, its hardness

value is also comparatively high.

So PCM quenched EN8 sample shows high hardenability distribution over its region compared to other

EN8 test samples.



REFERENCES I. Ashish Verma and Pravin Kumar Singh, “Influence of Heat Treatment on Mechanical Properties of Aisi1040

Steel”, (IOSR-JMCE), e-ISSN: 2278-1684, p-ISSN: 2320-334X, Volume 10, Issue 2 (Nov. - Dec. 2013), PP 32-

38.

II. Noor Mazni Ismail, Nurul Aida Amir Khatif, Mohamad Aliff Kamil, “The effect of heat treatment on the hardness

and impact properties of medium carbon steel”, IOP Conf. Series: Materials Science and Engineering 114 (2016)

012108 doi:10.1088/1757-899X/114/1/012108.

III. P. Sarathkumar, A.R. Sivaram, R. Rajavel, “Experimental Investigations on The Performance of a Solar Pond by

using Encapsulated Pcm with Nanoparticles”, Elsevier, Materials Today: Proceedings 4 (2017) 2314–2322.

IV. Dogan Ciloglu and Abdurrahim Bolukbasi, “The quenching behaviour of aqueous nanofluids around rods with

high temperature”, Elsevier, Nuclear Engineering and Design 241 (2011) 2519–2527.

V. Farah Souayfane, Farouk Fardoun and Pascal-Henry Biwole, “Phase Change Materials (PCM) for cooling

applications in buildings: A review”, PII: S0378-7788(16)30241-9, DOI:

http://dx.doi.org/doi:10.1016/j.enbuild.2016.04.006, Reference: ENB 6557.

VI. S.M. Adedayo, A.S. Adekunle and T. Oladimeji, “Effect of Quench Immersion Speed in Water on the

Mechanical Properties of C30 Carbon Steel”, Proceedings of the World Congress on Engineering 2014 Vol II,

WCE 2014, July 2 – 4,2014, London, U.K.

VII. Ersoy ERİŞİR, Serap GÜMÜŞ and Oğuz Gürkan BİLİR, “Microstructural characterization of medium carbon

dual phase steels after intermediate quenching”, Researchgate,

https://www.researchgate.net/publication/261697094.

VIII. Peter Fernandes, K. Narayan Prabhu, “Effect of section size and agitation on heat transfer during quenching of

AISI 1040 steel”. Elsevier, Journal of Materials Processing Technology 183 (2007) 1–5.

IX. B. Radha Krishnan, R. Aravindh, M. Barathkumar, “Prediction of Surface Roughness (AISI 4140 Steel) in

Cylindrical Grinding Operation by RSM”, ResearchGate, Volume-9, Issue-3(Mar-18) ISSN (O): - 2349-3585.

http://dx.doi.org/doi:10.1016/j.enbuild.2016.04.006

investigation of hardenability of en8 steel using …...micro-structure test and to compare the...

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