DRY TURNING OF AUSTENITIC STAINLESS STEEL (316L) USING CVD COATED TOOL

International Journal of Innovative Research in Advanced Engineering (IJIRAE) ISSN: 2349-2163
Issue 05, Volume 5 (May 2018) www.ijirae.com
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DRY TURNING OF AUSTENITIC STAINLESS STEEL
(316L) USING CVD COATED TOOL
Aby M Philip*
M.Tech. (Mech.) Student, Department of Mechanical Engineering,
National Institute of Technology, Silchar, Assam
abyphilip1992@gmail.com
Dr.Kalyan Chakraborty
Associate Professor, Department of Mechanical Engineering,
National Institute of Technology, Silchar, Assam
kalyan.ch2013@gmail.com
Manuscript History
Number: IJIRAE/RS/Vol.05/Issue05/MYAE10089
Received: 08, May 2018
Received: 14, May 2018
Final Correction: 19, May 2018
Final Accepted: 21, May 2018
Published: May 2018
Citation: Philip & Chakraborty (2018). DRY TURNING OF AUSTENITIC STAINLESS STEEL (316L) USING CVD
COATED TOOL. IJIRAE::International Journal of Innovative Research in Advanced Engineering, Volume V, 197-205.
doi://10.26562/IJIRAE.2018.MYAE10089
Editor: Dr.A.Arul L.S, Chief Editor, IJIRAE, AM Publications, India
Copyright: ©2018 This is an open access article distributed under the terms of the Creative Commons Attribution
License, Which Permits unrestricted use, distribution, and reproduction in any medium, provided the original author
and source are credited
Abstract— Austenitic Stainless steel (316L) is a low carbon high chromium containing high alloy steel, it has a good
number of application because of its high strength, high ductility and corrosion resistance. It is used in jet engine
parts, heat exchanger application and pharmaceutical application. It is compatible in cryogenic temperature to red
hot temperature. The paper presents an experimental investigation on different parameters which affect the cutting
process and also cause significant effect on the chip formation in machining of Austenitic Stainless steel (316L). In
this study, experiments were conducted on Austenitic Stainless steel (316L) at different cutting speed, feed and
depth of cut and the effect of different influential parameters on the process of chip formation has been studied
subsequently. Quality characteristic of machined item is depending much on material behaviour during machining.
Present experimental analysis on machining has been performed by implementing Von Mises stress evaluation
employing true stress-true strain behaviour of the materials under consideration. Experimental true stress-true
strain plot was required to find out the strength coefficient and strain hardening exponent of the material and using
the same, Von Mises stress was estimated by using material property consideration. Experimental study on
machining was performed on austenitic stainless steel (316L) to know the trend of variation of chip thickness, shear
angle, Von Mises stress and total work done with respect to cutting velocity. From the study it showed that
austenitic stainless steel gets work hardened at higher cutting speed. Therefore this type of material can be
machined at lower cutting speed only.
Keywords— Metal cutting; machining; chip thickness; work hardening; machinability ;
I. INTRODUCTION
Stainless steel has a great importance in manufacturing industries. It has a wide application in many fields as it has a
great combination of mechanical properties and higher corrosion resistance. During fabrication the properties of
the material can change due to machining condition.

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Stainless steel can be classified on the basis of their crystalline structure as austenitic, ferritic and martensitic.
Austenitic stainless steel has a great application. It is compatible from cryogenic temperature to red hot
temperature. Austenitic structure gives excellent toughness in cryogenic temperature and has high formability and
strength. These are generally used in fabrication of food processing and chemical equipment and in machineries
which require high corrosion resistance e.g. in marine engines and in heat exchangers. Austenitic stainless steel
work hardens when it is deformed, this property of austenitic stainless steel is known as transformation induced
plasticity property.
Austenitic stainless steel is having high tendency to work harden and to form built up edge, its machinability is
affected adversely due to this. The machinability of this material is also affected because of higher strength and
lower thermal conductivity. The tendency of austenitic stainless steel to work harden causes superior tool wear
causing poorer surface finish. Austenite is also known as gamma phase of iron. As temperature of alpha iron changes
from 912°C – 1394°C, it causes a phase transformation from body centered to face centered cubic structure known
as gamma iron. Higher amount of nickel in this material act as a austenite stabilizer. Because of its stable austenitic
microstructure, it possesses certain characteristic such as ductility, good weldability, formability and maintains
toughness at cryogenic temperature. Austenitic stainless steel contains chromium to enhance the corrosion
resistance.
The present work is aimed at experimental investigation of chip formation process, through machining of austenitic
stainless steel (316L), giving more emphasis on to the effect of material properties during chip formation. Quality
characteristic of machined item relies on properties of material during machining. The formation of plasticity
transition of the material creates a complex situation during machining. The quality characteristic of the machined
item depends much on formation of different phenomena particularly in the transitional and secondary flow regions.
Assessment on the development of Von Mises stress during machining is an essential task. The experimental
investigation has been carried out to asses Von Mises stress through tensile testing analysis of the material. Material
properties “n” and “K” are required for estimation of Von Mises stress. Therefore, a correlation can be formed
between the plasticity transition and subsequent loading. The Von Mises stress was estimated by considering
material property. In addition, total work done during machining was also estimated through material property
consideration in terms of "n" and "K". The formation of machining chip is rigorously depending on plastic
deformation. These chips are developed under both high strain and high strain rate conditions. Thickness of chip
shows the extent of plastic distortions that occurred as a result of machining. Therefore full integrated investigation
needs to be performed from plasticity transition point of view. The thickness of chip plays a crucial role in
experimental studies. However the measurement of chip thickness is usually problematic due to the occurrence of
chip curls. Conventional measuring instruments like micrometre, Vernier-calliper etc.is not suitable. Therefore
measurement of the chip length and weight were used to estimate the thickness of the chip. Experimental study on
machining was carried out on austenitic stainless steel (316L) to understand the effect of chip thickness, shear angle,
total work done and Von Mises stress with respect to cutting speed. Macroscopic examination of chip sample was
done under various experimental conditions. The analysis was further carried out by performing SEM examination
of various chips at different magnifications.
II. EXPERIMENTAL ANALYSIS
The assessment of machinability of Austenitic stainless steel (316L) was done on the basis of generation of Von
Mises stress and chip formation mechanism. The workpiece is of dimension as 300mm length and 60mm diameter.
The cutting tool used is Tungaloy made (chemical vapour deposition (CVD) coated carbide grades consist of a
cemented carbide substrate TiCN). Coatings are deposited to 3 to 16 μm thick by means of a chemical vapour
deposition method. The coating layer is hard and improves heat and oxidation resistance to make it chemically
stable. With these advantages the coated grades prolong tool life and increase machining efficiency.
TABLE I Chemical composition of austenitic stainless steel (316L)
C% Mn% Si% P% Cr% Ni% Mo% S% Fe
0.010 1.623 0.321 0.010 16.122 10.147 2.123 0.005 Balanced
Central lathe is used for turning operation, with all gear drive having speed range from 45 rpm to 1000 rpm and
feed range 0.06 mm/rev to 1.72 mm/rev
A. Tool Used
Holder Specification: ASBNR 25*25 M12-A
Carbide inserts Specification: SNMG 120404 TM T9125

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B. Selection of Process parameters
The parameters for machining were selected on the basis of values available on the lathe. The values available on
the lathe are shown in Table II.
TABLE II Machining parameters
Coding -√2 -1 0 1 √2
Speed (m/min) 10.23 14.24 31.65 70.34 97.9
Feed (mm/rev) 0.01 0.11 0.14 0.18 0.20
DOC(mm) 0.56 0.67 1 1.5 1.77
Central composite design of the input parameters was followed for the analysis of the machining operation of the
workpiece. 24 different combinations of these machining parameters were used to perform this experiment. After
mounting, machining operation is carried out with these parameters using Tungaloy made cutting tool. For each
cutting parameters chips formed are collected. These are given in Table III.
TABLE III Different combination of cutting parameters used in machining
Sr No. Assigned Code
v f d
Speed(v)
(m/min)
Feed(f)
(mm/rev)
Depth of cut(d)
(mm)
1 1 1 1 70.34 0.18 1.5
2 1 1 -1 70.34 0.18 0.67
3 1 -1 1 70.34 0.11 1.5
4 1 -1 -1 70.34 0.11 0.67
5 -1 1 1 14.24 0.18 1.5
6 -1 1 -1 14.24 0.18 0.67
7 -1 -1 1 14.24 0.11 1.5
8 -1 -1 -1 14.24 0.11 0.67
9 √2 0 0 97.90 0.14 1
10 -√2 0 0 10.23 0.14 1
11 0 √2 0 31.65 0.20 1
12 0 -√2 0 31.65 0.01 1
13 0 0 √2 31.65 0.14 1.77
14 0 0 -√2 31.65 0.14 0.56
15 0 0 0 31.65 0.14 1
16 0 0 0 31.65 0.14 1
17 0 0 0 31.65 0.14 1
18 0 0 0 31.65 0.14 1
19 √2 0 0 97.90 0.14 1
20 -√2 0 0 10.23 0.14 1
21 0 √2 0 31.65 0.20 1
22 0 -√2 0 31.65 0.01 1
23 0 0 √2 31.65 0.14 1.77
24 0 0 -√2 31.65 0.14 0.563
Fig. 1 Austenitic stainless steel (316L) mounted on lathe

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III.THEORY AND RESULT
After performing the machining operation, chip thickness was measured for different experiments and subsequently
chip reduction coefficient, shear angle, Von Mises stress and Total Work done were also calculated. Chip thickness,
Width of the chip, Uncut chip thickness, Chip reduction coefficient, Shear angle, Von Mises stress are calculated from
the theoretical relations which are shown in equations given below.
Chip thickness t2 =
Where, t2 =Chip thickness
W = Weight of chip in grams
= Density of chip in g/cm3
w = Width of chip in cm
= Average length of the chip in cm
Width of chip w
Where, d=Depth of cut in mm
=Principle approach angle (in degree)
=Density of austenitic stainless steel, 8g/cm3
Uncut chip thickness t1,
t1 = f *sin
Where, f = Feed in mm
=Principal Cutting edge angle (in degree)
Chip reduction coefficient ζ ,
ζ =
Shear angle 0,
Where, = Rake Angle (in degree)
Von-Mises Stress v,
v =1.74K(ln )n
Where, K = Strength Coefficient (N/mm2)
n = Strain hardening Exponent
These two parameters are calculated by using the plot of true stress vs true strain on the log- log graph paper. The
values of true strain and true stress are calculated by using the results of tensile test performed on the specimen.
Fig.2 stress vs strain graph

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Fig. 3 Broken specimen after tensile test
From the results of tensile test, true stress and true strain are evaluated at different points between the ultimate
stress point and yield point, these results are then plotted on log-log graph and from that log-log plot, values of n
and K were evaluated. Strain hardening exponent “n” is the slope of straight line and “K” is the true stress value
when the extrapolated graph coincide with true strain at numerical value 1. True stress and true strain are
determined by equations.
True stress, t = (1+ϵ)
True strain, ϵt = ln(l+ϵ)
Where, = Stress at different points on stress vs. strain plot. ϵ = Strain at different points on stress vs. strain plot.
From the log-log graph paper values of “n” and “K” comes out to be 0.55 and 850N/mm2
Fig. 4 True stress vs true strain graph
So the power law equation is established from the true stress vs true strain graph and final power law
equation becomes as
For total work done, firstly elemental work done is calculated as shown in equation
Elemental work done WE,
Total Work done TW.
Tw = WE*v*f*d*t
Where, v = Cutting speed (m/min)
f = Feed (mm/rev)
d = Depth of cut (mm)
t = Time in minute
Fig. 5 Variation of cutting velocity vs chip thickness

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The deviation of chip thickness, chip reduction coefficient, shear angle, von mises stress and total work done with
respect to cutting velocity keeping feed and depth of cut constant (0.14mm/rev and 1mm respectively) are shown in
following fig.
Fig. 6 Variation of cutting velocity vs Chip reduction coefficient
Fig. 7 Variation of cutting velocity vs shear angle
Fig. 8 Variation of cutting velocity vs Von Mises stress
Fig. 9 Variation of cutting velocity vs total work done
It is found from the above graphs decrease in chip thickness and chip reduction coefficient at higher cutting speed is
mainly due to work hardening effect. Value of chip thickness seems to decrease at higher value of shear angle. Von
Mises stress is also found to be higher at very low cutting speed keeping feed and depth of cut constant at
0.14mm/rev and 1mm respectively. This is attributed to the austenitic retention effect. Total work done is found to
be increasing with increase in cutting speed.
A. SEM Testing Results
SEM testing was performed on the chips obtained by machining austenitic stainless steel (316L) with Carbide insert
tool. The chip formation mechanism is established from the SEM images.

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SEM images were taken at the highest and the lowest values of the cutting parameters (speed, feed, and depth of cut)
for comparison. The parameters are denoted by:
(v, f, d) = (√2, √2, √2) and (-√2, -√2, -√2)
SEM images taken at different magnifications for cutting velocity of 97.9 m/min, feed of 0.199 mm/rev and depth of
cut of 1.774 mm:
(a) (b)
(c) (d)
Fig. 10 SEM images of chips at 50X magnification (a) Top surface (b) Bottom surface (c) Side surface
(d) Side surface
From the observation of SEM images, it is concluded that at higher cutting parameter conditions, the chip formation
occurs by saw tooth mechanism. This is mainly due to thermal instability during machining at higher cutting speed.
Lower thermal conductivity of austenitic stainless steel causes adiabatic shear instability which leads to saw tooth
chip formation. The process of chip formation is adverse during machining at higher cutting speed. SEM images
taken at different magnifications for cutting velocity of 10.23 m/min, feed of 0.098 mm/rev and depth of cut of
0.5636 mm:
(a) (b)
(c) (d)
Fig.11 SEM images of chips at 50X magnification (a) Top surface (b) Bottom surface (c) Side surface
(d) Side surface
From the observation of SEM images, it is concluded that at minimized cutting parameter conditions, the chips are
produced by shear sliding mechanism. Chip formation mode is found to be favourable at this condition.

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B. Effect of Von Mises Stress on Machining (Theoretical analysis)
The second order equation for Von Mises stress was found by using analysis of variance (ANOVA) using
experimentally calculated values of Von Mises stress corresponding to cutting speed, feed and depth of cut.
Y(Von Mises stress)=1263.4+0.1X1-22.0X2-44.0X3+20.8X1
2+49.8X2
2-93.7X3
2+78.3X1X2-98.2X1X3+102.5X2X3
Where, X1= Cutting speed
X2= Feed
X3= Depth of cut
Effect of Von Mises stress on machining is observed at different machining parameters. The values of Von Mises
stress at different cutting speed, feed and depth of cut is used and graphs are plotted at speed code 0 and speed code
1 in Fig. 12.
Fig.12 Variation of von mises stress with feed code and doc at different speed code
Speed code 0 (left) and speed code 1 (right)
From fig. 12, it is seen that increase of feed has negligible effect on Von Mises stress at lower speed code 0, but with
increase of depth of cut, Von Mises stress reduces. This is attributed to easy chip breaking at higher depth of cut
condition. From fig. 12, it can be seen that extent of Von Mises stress is comparatively higher at higher speed code 1,
specifically at higher feed and moderate depth of cut which is attributed to the much work hardening effect leading
to phase transformation at this condition. However, at higher speed code 1, specifically at lower feed and higher
depth of cut condition the Von Mises stress is seen to be reduced because of easy chip breaking condition under
work hardening stage leading to brittle transition at this specific cutting condition.
IV. CONCLUSIONS
i. Chip thickness reduces with increase in cutting velocity under specific cutting condition and increased value of
chip thickness causes decrease in shear angle.
ii. Von Mises stress reduces with increase of cutting speed at specific cutting condition. Theoretical studies shows
with increase in cutting speed Von Mises stress increases because of work hardening of austenitic stainless
steel leading to phase transformation, this adversely affects the machinability of material.
iii. Adverse chip formation mode occurs due to adiabatic shear instability at higher cutting speed causing saw
tooth chip. This is because of the lower thermal conductivity of the material. Chip formation mode is found to
be favourable at lower cutting speed.
iv. Low speed machining can be recommended for this type of material.
v. Machining on austenitic stainless steel (316L) is found to be influenced by austenitic retention effect and
transformational effect during the machining work.
ACKNOWLEDGMENT
The authors gratefully acknowledge the financial assistance provided for this work by our institution NIT Silchar,
and express deep gratitude towards the production engineering lab of NIT Silchar and SEM lab of IIT Kanpur to
conduct different experiments related to this project and to all other people who helped in success of this work.

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