Improving Cutting Tool Properties through Forging and Heat Treatment

Proceedings of the 2nd
International Conference on Current Trends in Engineering and Management ICCTEM -2014
17 – 19, July 2014, Mysore, Karnataka, India
115
STUDY OF EFFECT OF FORGING ON CUTTING TOOL PROPERTIES
Bharath H S1
, T S Siddalingaprasad2
, H S Shivashankar3
1, 3
Department of Mechanical Engineering, SIT, Tumkur, India
2
Department of Mechanical Engineering, KIT, Tiptur, India
ABSTRACT
In this paper an attempt has been made to improve the properties of cutting tool like hardness,
toughness & wear resistance by forging & heat treatment process. Hence we selected D-series tool
steel (D1, D2, D3, D4) for our test. Common applications of these tool steels are forging dies, die-
casting die blocks, drawing dies etc., the experiment evaluates Rockwell hardness test, Micro
hardness test, Force analysis, Turning operation & wear test. The results revels that in force analysis
during turning operation the heat treated D-series tool steels perform better than forged & heat
treated tools. The forged & Heat treated D2 tool steel has low wear rate.
Keywords: Micro Hardness, Forging Process, Heat Treatment, Wear Test.
1. INTRODUCTION
Metal cutting is one of the oldest and most important material shaping process, which is
widely, used in automotive, railway, ship-building, aircraft industry etc., Cutting tool is very
important field in the manufacturing industry. A lot of discussions & studies have been made to
improve the quality & usage of the cutting tool. Cutting tool has to have certain aspects such as
hardness, toughness & wear resistance. Commonly used cutting tool materials are High speed steel
(HSS), diamond tools, abrasive tools, carbide tools etc., for several application. Further, some cutting
tools such as drill bits for construction saw blades, grinding wheels etc., for several applications.
Further, some cutting tools such as drill bits for construction saw blades, grinding wheels etc., has
materials such as aluminum oxide ceramics or tungsten carbide as the abrasive component. However,
super abrasives such as cubic- or polycrystalline boron nitride and diamonds offer distinct
advantages, such as greater wear resistance and cleaner finish. These characteristics result in
increased tool life. D-type tool steels contain between 10% and 18% chromium. These steels retain
their hardness up to a temperature of 425 °C (797 °F). Common applications for these tool steels
include forging dies, die-casting die blocks, and drawing dies. Due to their high chromium content,
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certain D-grade tool steels are often considered stainless or semi-stainless; however their corrosion
resistance is very limited due to the precipitation of the majority of their chromium and carbon
constituents as carbides.
2. PROBLEM IDENTIFICATION
The main disadvantage of abrasive, HSS and super abrasives are cost which can be as much
as ten times greater than ceramic or carbide. Even machining/cutting some composite materials
carbide or diamond tools fails unpredictably. Also, at high temperatures oxide formation takes place
on high/low carbon steel and even carbide tools which leads to friction in machining.[6,7] When
speaking of cutting tool we cannot avoid the world tool wear. Tool wear is an area that many
researchers always wanted to eliminate or minimize. Reduction of tool wear will results in many
beneficial outcomes like cost reduction & improvement in machining quality. In order to improve the
tool life, study of tool wear characteristics is very essential. To overcome this problem a tool must be
develop such that it must be cost effective, good mechanical machine ability and properties should
match the conventional tool’s properties. Here we are making an attempt to make cutting tools which
of high carbon steel which can be forged and heat treatable. Further the tool must also able to
withstand the heat generated in the metal-cutting process. This cutting tool must have good
characteristics like hardness, strength, toughness, wear resistance and also with stand cutting edge at
high temperature. Heat treatment for the forged tool will helps to attain a good property value,
preheating, normalizing, annealing, nitriding these are some of the heat treatment process done for
forged tool. These heat treatment process will helps to improve grain structure, improves toughness
hardness wear resistance and as well as tool life. In this work we are focusing on characterization and
property evaluation of forged cutting tools. These tools will have standard geometry and
specifications. This forging includes cold forged/hot forged and subjected to some specific heat
treatment. This will improve grain structure, improves toughness hardness wear resistance and as
well as tool life and reduce cost and also help to cut specific materials in different industrial
application.
3. EXPERIMENTAL PROCEDURE
3.1Raw material
The raw material selected are D-series tool steels (D1, D2, D3 & D4) because according to
AISI these steels are of high carbon & high chromium tool steels alloyed with molybdenum and
vanadium. Also these steels are not widely recommended for cutting operation.
TABLE 3.1: Composition of D1 tool steel
Content C Mn Si Co Cr Mo V P Ni Cu S
% 1.4-
1.6
0.6 0.6 1 14.12 0.9 1.1 0.03 0.3 0.25 0.03
Content C Si Mn Cr Mo V
% 0.9-
1.10
0.35 0.3 11.5 0.72 0.68

117
3.2 Forging Process
D type tool steels are subjected to press forging individually by using belt drop hammers of
weight 500N. The materials are hot forged by heating it to above recrystallization temperature. In
this forging process the material is heated to 10000
C.The dimension of D-type tool steel before
forging is 15*15*100 (b*h*l). The dimension after forging is 12*12*120 (b*h*l).
Fig 3.1: Forging of D series tool steels.
3.3 Heat Treatment Process
Heat treatment is a process of controlled heating and cooling of metals to alter their physical
& mechanical properties without changing the product shape. Heat treatment technique includes
annealing, case hardening, precipitation strengthening, tempering & quenching. In this work D-series
tools are heated and oil-quenched. Heat treatment improves machine ability, formability, restore
ductility etc., steels are heat treated for one of the reason softening, hardening, material modification.
Pre-heating temperature = 550
Raise in temperature = 9800
C for D1 & D2,
9400
C for D3 & D4
Oil quenching is done using servo quench oil.
Hardening time = 30min
Furnace used is salt bath.
Content C Si Mn Cr Ni V W P S Cu
% 2-
2.35
0.6 0.6 12.36 0.3 1 1 0.03 0.03 0.25
Content C Mn Si Cr Ni Mo V P S Cu
% 2.05-
2.4
0.6 0.6 13.78 0.3 0.93 1 0.03 0.03 0.25

118
3.4 Rockwell Hardness test
The Rockwell scale is a hardness scale based on indentation hardness of a material. The
Rockwell test determines the hardness by measuring the depth of penetration of an indenter under a
large load compared to the penetration made by a preload. There are different scales, denoted by a
single letter, that use different loads or indenters.
Type of scale = C scale.
Load = 150kg.
Indenter = Diamond cone indenter.
Time = 20sec.
3.5 Micro hardness test
The term micro hardness test usually refers to static indentations made with load not to
exceed 1 kgf. The indenter used is Vickers diamond pyramid. The procedure for testing is similar to
that of standard Vickers hardness test, except that it is done on a microscopic scale with higher
precision instruments.
Load applied = 1kg-f
Time = 30sec.
Objective lens = 40x
Resolution = 0.0001.
Accuracy = ± 0.5 micrometers.
3.6 Force analysis
The Force analysis of D-type tool steel is to measure force that tool steel can sustain. The
cutting forces were measured using strain gauge type three component lathe tool dynamometer
mounted on specially designed fixture. It consists of three force components measurement circuit’s
i.e. cutting force (thrust), feed force and radial force components with balancing for initial zero
setting of the bridge settings. The strain gauge with D- type tool was attached to the tool post of the
lathe machine. The readings for cutting forces were recorded after output stabilization and have been
used for analysis.
Fig. 3.2: Finding forces using lathe tool dynamometer

119
3.7 Wear test
Wear is related to interactions between surfaces and more specifically the removal and
deformation of material on a surface as a result of mechanical action of the opposite surface. Some
commonly referred to wear mechanisms (or processes) include:
Adhesive wear
Abrasive wear
Surface fatigue
Fretting wear
Erosion wear
In this experiment we conducted adhesive wear (pin on disc wear) by varying the temperature.
Fig. 3.3: wear testing machine
4. RESULTS AND DISCUSSION
The heat treated as well as forged & heat treated D-series tools are subjected to Rockwell
hardness, micro hardness, force calculation, wear test, impact test & density test for different trials,
the results and discussion of the obtained results are shown below.
4.1 Rockwell hardness test
Indenter = 120o
Diamond Cone Indenter
Scale = C scale
Time = 20sec
Load = 150kg
The test is conducted for 3 trials and by taking average the hardness value is tabulated below

120
Fig. 4.1: Rockwell hardness of D-series tool steel.
From graph above it can be seen that the hardness of D-series raw material is around 40 but
once it is forged, heat treated & forged and heat treated the hardness doesn’t vary much but among
the four tools D2 has high hardness after forging and heat treatment. This is because of high carbon
& chromium content. Carbon & chromium increases the strength and hardness of the material.
4.2 Micro hardness test
Fig. 4.2: Micro harness of D series tool steels
Micro hardness test is done to know the hardness in micro meter scale; it helps to know the
resistance of the material, also in this test the hardness is found by applying smaller load on to the
surface of the material. From the above graph Micro hardness of D4 raw material is high compare to
other D series raw material; once the material is forged, heat treated & forged and heat treated the D2
tools has high hardness compare to all other tools this is because of high carbon & chromium content
and also after forging & heat treatment the grain growth occurs and the internal stresses are relieved
hence the hardness increases.
0
10
20
30
40
50
60
70
D1 D2 D3 D4
Hardness
Materials
ROCKWELL HARDNESS TEST
RAWMATERIAL
FORGING
HEAT TREATMENT
FORGING & HEAT
TREATMENT
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
D1 D2 D3 D4
MicroHardness
Material
Raw Material
Forging
Heat Treatment
Forging & Heat
Treatment

121
4.3 Force analysis
In force analysis we analyse force in two cases
Case 1: Cutting speed is varied and depth of cut & feed rate is kept is constant.
Feed rate = 0.2mm/rev
Depth of cut = 0.5mm
Graph 4.3: Resultant forces for forged & heat treated tools.
From graph it can be observe that resultant force decreases as cutting speed increases. This
because when the speed increases the contact between the tool tip and the workpiece material
decreases. During turning operation D2 & D4 of forged & heat treated tools get blunted at 250rpm,
this is because of some property loss dusing fabrication of tools, but D1 and D4 tools perform
effectivelt at all the three kinds of cutting speeds.
Graph 4.4: Resultant forces for heat treated tools.
Above graph shows that resultant force decreases as the cutting speed increases. This because
when the speed increases the contact between the tool tip and the workpiece material decreases.in
0
20
40
60
80
100
D1 D2 D3 D4
ResultantforcesinN
Tools
FORCES FOR FORGED & HEAT TREATED TOOLS
52 rpm
150 rpm
250 rpm
0
10
20
30
40
50
60
70
D1 D2 D3 D4
ResultantforcesinN
Tools
FORCES FOR HEAT TREATED TOOLS
52 rpm
150 rpm
250 rpm

International Conference on Current Trends in Engineering and Management ICCTEM
heat treated case on tool get blunt during the turning operation. Hear D2 & D4 tool perform better
cutting at different cutting speeds than other tool.this is because D2 & D4 tools contain 0.03 5 of
phosphrous that will increase the machineability, also these tools two tools prepared more number of
alloying elements that improves the properties & there by machining is improved. All the tools are
operated at a feed rate of 0.2mm/rev and depth of cut of 0.5mm
7.4.2: Feed rate is varied by keeping cutting speed and depth of cut as constant
Cutting speed = 150rpm
Depth of cut = 0.5mm
Graph 4.5: Resultant forces for forged & heat treated tools.
In this case as the feed rate increases resultant forces
between the tool tip and the work piece material is increased. In this case also during the turning
operation D2 & D4 tools get blunt at 250rpm but at D3 tool perform better, at all the three different
feed rates amnog these four tools. This is because presence of more alloying elements and especially
phosphrous & sulphur that improves machine ability.
Graph 4.6: Resultant forces for heat treated tools.
Graph shows that resultant force increases as the feed rate ra
contact between the tool tip and the work piece material is increased. Hear D2 tool perform better in
0
20
40
60
80
100
D1
ResultantforcesinN
0
10
20
30
40
50
60
70
80
90
D1
ResultantforcesinN
International Conference on Current Trends in Engineering and Management ICCTEM
122
rous that will increase the machineability, also these tools two tools prepared more number of
operated at a feed rate of 0.2mm/rev and depth of cut of 0.5mm.
7.4.2: Feed rate is varied by keeping cutting speed and depth of cut as constant
: Resultant forces for forged & heat treated tools.
In this case as the feed rate increases resultant forces increases. This is because the contact
og these four tools. This is because presence of more alloying elements and especially
phosphrous & sulphur that improves machine ability.
: Resultant forces for heat treated tools.
Graph shows that resultant force increases as the feed rate rate increases. This is because the
D2 D3 D4
Tools
0.2 mm/rev
0.3 mm/rev
0.4 mm/rev
D2 D3 D4
Tools
0.2 mm/rev
0.3 mm/rev
0.4 mm/rev
19, July 2014, Mysore, Karnataka, India
rous that will increase the machineability, also these tools two tools prepared more number of
increases. This is because the contact
og these four tools. This is because presence of more alloying elements and especially
te increases. This is because the
0.2 mm/rev
0.3 mm/rev
0.4 mm/rev
0.2 mm/rev
0.3 mm/rev
0.4 mm/rev

123
all the three different feed rates when compare to other tools & in this case also the tools did not get
blunt so we can say that heat treated tools perform better cutting operation by varying both cutting
speed & feed rate the forged & heat treated tool. And among D1, D2, D3 & D4 tools D2 tool has
good machinablity (Max.50 %) compare to other tools. but only disadvantage is in forged & geat
treated condition D2 tool blunt at 250rpm, by varying the composition and heat treatment method we
can over come this problem.
4.4 Wear Test
The graph below shows the wear rate of the forged & heat treated tools, from graph it can be
seen that at 2000
C the wear rate of all D-series tools are almost same there is no much difference in
wear rate. But at 4000
C the wear rate of D1, D3, D4 is very high but wear rate of D2 tool steel is less
hence the forged and heat treated D2 tool steel has high wear resistance than other tools.
Fig. 4.7: Wear rate of forged and heat treated tools
Fig. 4.8: Wear rate of heat treated tool steels
The above graph shows the wear rate of the heat treated tools, from graph it can be seen that
at 2000
C the wear rate of tools are almost same there is no much difference in wear rate. But at
0.00E+00
5.00E-06
1.00E-05
1.50E-05
2.00E-05
2.50E-05
D1 D2 D3 D4
WearRate
Materials
wear rate at 200
degreee
wear rate at
400 degree
0
0.5
1
1.5
2
2.5
D1 D2 D3 D4
Wearrate
Tools
WEAR TEST
Forged & Heat
treated

124
4000
C the wear rate of D2, D3, D4 is very high but wear rate of D1 tool steel is less hence the heat
treated D1 tool steel has high wear resistance than other tools.
5. CONCLUSION
From the experimental results of harness test, force analysis, wear test & impact test we
conclude the work in the fallowing ways
From the result of hardness test it can be observed that Heat treated material is having good
hardness numbers, next comes forged plus heat treated material and then forged material.
From force analysis we conclude that heat treated D-series tool steels perform better turning
operation than forged tool steels, that to D2 tool has good machine ability then other D-series
tools.
From wear test we came to know that in both forged & heat treated as well as only heat treated
material D2 tool steel pocess high wear rate than other materials. This is because the presence
of more chromium content, chromium improves the resistance to wear, improves the harden
ability and strength of the material it also offers the higher critical temperature.
Also from impact test we came to know that the forged and heat treated D2 tool steel has good
impact strength than heat treated D2 steel and other steels. This is because of high nickel &
cobalt content. Nickel improves the toughness, corrosion resistance, improves resistance to
oxidation also gives the refined grain structure. Whereas cobalt is a highly radioactive material
and it resist material softening at elevated temperature.
Hence among D1,D2,D3&D4 heat treated D2 tool steel performance is good and it can be used
as a cutting tool with properties like toughness, hardness & tool life.
Future work is by Statistical analysis method we can improve the casting properties of tool
steels. There are also other series of tool steels like water hardening type, air hardening type, oil
hardening and cold working type; by similar method or process we can check their
performance.
Also for similar tools by varying the composition we can cast the new tool and evaluate the
properties in the similar process.
6. REFERENCES
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properties of a micro alloyed cast steel by hot forging and post-forging heat treatment
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microstructure and room temperature tensile properties in Ti-25 Al-10Nb-3v-1Mo (super
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