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International Journal of Mechanical Engineering Research. ISSN 2249-0019 Volume 7, Number 2 (2017), pp. 83-97 © Research India Publications http://www.ripublication.com Optimization of Process Parameters in Induction Hardening of 41Cr4 Steel by Response Surface Methodology S. P. Metage 1 and J. S. Sidhu 2 1 P.G. Scholar, MGM’s College of Engineering, Nanded 2 Associate Professor & Head, Department of Mechanical Engg., MGM’s College of Engineering, Nanded Abstract The analysis of an induction hardening process is a complex process because induction hardening is a combination of heat transfer, electromagnetic and metallurgical phenomenon. Now a days, steel parts are induction hardened for better mechanical properties in case of automobile and aerospace applications. This paper deals with the optimization of process parameters in induction hardening process for 41Cr4 steel material. The selected process parameters are Power (Kw), Feed rate (mm/sec), Dwell time (sec), Quench flow rate (litre/min). The responses selected are Case Hardness (HRC) and Effective Case depth (mm). Response surface methodology was used to determine optimum values of process parameters and that were - Case Hardness 59.83HRc and Effective Case Depth (ECD) 2.7mm. Analysis of variance is conducted to investigate the influence of each parameter on responses. Also microstructure analysis is done for justification of hardening. Keywords: induction hardening, process parameters, optimization, RSM, Analysis of Variance, microstructure analysis. INTRODUCTION Induction heating is a method of heating electrically conductive materials by the application of a varying magnetic field whose lines of force enter the work-piece. In this process, the varying magnetic field induces an electric potential (voltage), which can then create an electric current depending on the shape and the electrical

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International Journal of Mechanical Engineering Research.

ISSN 2249-0019 Volume 7, Number 2 (2017), pp. 83-97

© Research India Publications

http://www.ripublication.com

Optimization of Process Parameters in Induction

Hardening of 41Cr4 Steel by Response Surface

Methodology

S. P. Metage1 and J. S. Sidhu2 1P.G. Scholar, MGM’s College of Engineering, Nanded

2 Associate Professor & Head, Department of Mechanical Engg., MGM’s College of Engineering, Nanded

Abstract

The analysis of an induction hardening process is a complex process because

induction hardening is a combination of heat transfer, electromagnetic and

metallurgical phenomenon. Now a days, steel parts are induction hardened for

better mechanical properties in case of automobile and aerospace applications.

This paper deals with the optimization of process parameters in induction

hardening process for 41Cr4 steel material. The selected process parameters

are Power (Kw), Feed rate (mm/sec), Dwell time (sec), Quench flow rate

(litre/min). The responses selected are Case Hardness (HRC) and Effective

Case depth (mm). Response surface methodology was used to determine

optimum values of process parameters and that were - Case Hardness

59.83HRc and Effective Case Depth (ECD) 2.7mm. Analysis of variance is

conducted to investigate the influence of each parameter on responses. Also

microstructure analysis is done for justification of hardening.

Keywords: induction hardening, process parameters, optimization, RSM,

Analysis of Variance, microstructure analysis.

INTRODUCTION

Induction heating is a method of heating electrically conductive materials by the

application of a varying magnetic field whose lines of force enter the work-piece. In

this process, the varying magnetic field induces an electric potential (voltage),

which can then create an electric current depending on the shape and the electrical

84 S.P. Metage and J.S. Sidhu

characteristics of the work-piece. These so-called eddy currents dissipate energy

and produce heat by owing against the resistance of an imperfect conductor.

Because all metals are fair electrical conductors, induction heating is applicable to

several types of metal processing operations such as melting, welding, brazing, heat

treating, and heating prior to hot working. Generally, Induction heating process is

used to surface harden crankshaft, camshaft, gears, crank pins and axles.

Amit Kohli et. al. (2010) studied the effect of process parameters on mean effective

case depth of induction hardened AISI 1040 steel and studied optimization of

process parameters of AISI 1040 steel using RSM. Experimental investigation

shown that for making shafts, axles or automobile components from medium carbon

steel, raw material should be first normalized and then induction hardened so that

uniform hardness of material can be obtained [1, 2]. Mert Onan et. al. (2012)

discussed experimental investigation on AISI 1040 steel and analyzed the

optimization of process conditions for induction hardened steel. The selection of

higher power ratio and lower scan rate affected micro structural transformation

during hardening process. As a result of applying higher power ratio or lower scan

rate induction hardening allowed high surface hardness [3]. Kochure et al. (2012)

studied hardening of EN8D steel by Taguchi method wherein effects of process

parameters such as power, heating time on hardness and case depth were expressed

[4]. Sandeep et al. performed parametric optimization of sintered iron alloy by using

intelligent techniques and concluded that the mechanical and metallurgical

properties fully depend on heat treatment process. The properties like tensile

strength, ductility and toughness would be improved by adding alloying elements

like Cr, Mo, P and Ni etc. [5]. Mishra et al. (2014) has performed investigation to

find out optimization of input process parameters such as medium frequency power,

feed rate, quench pressure and temperature for induction hardening of AISI 1045

steel component based on desirability function to enhance quality responses like

effective case depth and hardness. Selection of both heating and quenching

parameters proved significant for quality characteristics evaluation proved as a

useful strategy [6]. Mugendiran et. al. (2014) investigated optimization of surface

roughness and wall thickness on AA5052 Aluminium alloy by incremental forming

using response surface methodology. A second order quadratic model has been

obtained to predict the surface roughness and wall thickness as function of spindle

speed, tool feed and step size variables [7]. Gajanana et. al. (2015) investigated

effect of input parameters such as scan speed, voltage and rotation speed of

induction hardening process and microstructure analysis of micro-alloyed steel

roller shaft of an undercarriage and concluded that smaller inductor coil produces

higher case depth in hardening of shafts [8].

In this paper, Case Hardness and ECD of induction hardened parts have been

optimized using RSM, as it is mostly preferred method to solve the optimization

Optimization of Process Parameters in Induction Hardening of 41Cr4 Steel… 85

problem in manufacturing industry. Since time and money are involved while

performing experimentation, it is pertinent to reduce the number of runs while not

compromising the desired goals.

MATERIALS AND METHODS

Material

Cylindrical samples of 41Cr4 steel were selected as material for investigation. This

material is used for the manufacture of front vehicle axle, crankshafts and steering

components. The chemical composition of 41Cr4 Steel was 0.40% Carbon, 0.27%

Silicon, 0.82% Manganese, 1.11% Chromium, 0.026% Sulphur and 0.017%

Phosphorus.

Experimental Setup

All experiments were performed on Inductotherm make induction hardening

machine (30 KHz, 50 Kw) with major components (i) Imported ball screw, (ii) A.C.

servo drive and motor for scanning, (iii) Siemens CNC system, (iv) Top and bottom

tooling, (v) Job rotation. A source of high frequency electricity is used to drive a

large alternating current through a copper coil. The passage of current through this

coil generates a very intense and rapidly changing magnetic field in the space within

the work coil. The work piece to be heated was placed within this intense

alternating magnetic field. Induction temperature was maintained between 850oC

and 900oC. The core of the component remained unaffected. It was controlled by

setting various process parameters.

Experimental Plan

Based on preliminary investigation and review of literature, range of input

parameters were selected after performing pilot runs. These were power supplied,

feed rate, dwell time and quench flow rate. Rotatable central composite design

(CCD) has been used to carry out the experiments. The design plan is shown in

Table 1.

Table 1. Levels of process parameters

Sr.

No. Input Parameters Units

Levels

-1 0 1

1 Power (P) kw 10 12.5 15

2 Feed rate ( F) mm/sec 200 300 400

3 Dwell Time (D) sec 0.1 0.2 0.3

4 Quench Flow rate (Q) litre/min 10 12 14

86 S.P. Metage and J.S. Sidhu

Experimental Technique

Based on the foregoing inputs, the complete experimental run layout (Table 2) was

produced using MINITAB software. Those performance tests involved 30 runs of

the material. After induction hardening process, surface hardness was measured by

Rockwell hardness tester for C scale at 150 Kg load, having diamond indenter at

120 degree. Additionally cylindrical samples were cut from the middle of material

for investigation of case depth.

Table 2. Experimental Data for Case hardness and Effective case depth

Sr.

No.

Power

[Kw]

Feed rate

[mm/sec]

Dwell

Time [sec]

Quench Flow

rate [litre/min]

Case Hardness

[HRC]

Case Depth

[mm]

1 12.5 300 0.1 12 55 1.8

2 12.5 400 0.2 12 53 1.7

3 12.5 300 0.3 12 56 2.1

4 12.5 200 0.2 12 54 1.9

5 12.5 300 0.2 12 53 1.6

6 12.5 300 0.2 10 54 2.2

7 15 300 0.2 12 58 2.5

8 12.5 300 0.2 14 55 2.0

9 10 300 0.2 12 50 1.4

10 12.5 300 0.2 12 55 1.6

11 10 400 0.3 14 51 1.3

12 12.5 300 0.2 12 54 1.7

13 15 400 0.3 14 58 2.3

14 10 200 0.3 10 49 2.0

15 12.5 300 0.2 12 53 1.6

16 10 200 0.1 10 48 1.3

17 15 200 0.1 14 59 2.2

18 15 200 0.1 10 58 2.4

19 12.5 300 0.2 12 55 1.8

20 10 400 0.1 14 50 1.1

21 15 200 0.3 14 60 2.9

22 15 400 0.1 14 59 2.3

23 10 200 0.1 14 51 1.3

24 12.5 300 0.2 12 55 2.1

25 10 400 0.3 10 51 1.7

26 10 200 0.3 14 53 1.9

27 15 200 0.3 10 59 2.7

28 10 400 0.1 10 50 1.0

29 15 400 0.1 10 56 2.3

30 15 400 0.3 10 58 2.5

Optimization of Process Parameters in Induction Hardening of 41Cr4 Steel… 87

RESULTS AND DISSCUSSION

Case hardness was measured thrice for each trial and its average was considered,

whereas Effective case depth was measured on Vickers micro hardness tester and

both the responses are plotted in Table 2. Further analysis was done using

MINITAB.

Analysis of Variance (ANOVA)

ANOVA table has been used to summarize the test for significance of regression

model, test for significance for individual model coefficient. It indicates which

parameters are significantly affecting the output parameters. In the analysis the sum

of squares and variance are calculated. F-test values at 95% confidence level are

used to decide the significant factors affecting the process and percentage

contribution. Degrees of freedom (df) mean the number of values that can vary

independently of one another. In Case hardness the p values for power, dwell time

and quench flow rate are less than 0.05 (shown in bold) and larger F values

(88.62) indicates that these factors have statistically significant effects on the

performance. In Effective Case Depth the p values for power, feed rate, and dwell

time are less than 0.05 and larger F value (42.43) indicates that these factors have

statistically significant effects on the performance.

R2 is the percentage of total variation in the response which depends on the factors

in the model. In this case R2 value for case hardness is 93.40% and for ECD is

87.20%. The higher the value of R2, the better the model fits the data. The sequential

sum of squares in the analysis of variance table indicates the relative importance of

each factor. The factor with the biggest sum of squares has the greatest impact; here

power is the most important factor in both responses. The ANOVA results for case

hardness and case depth are shown in table 3 and 4. It revealed that quadratic model

is statistically significant for both case hardness and effective case depth.

Table 3. ANOVA results for Case Hardness

Predicator Coefficient SE Coefficient T P

Constant 29.833 1.883 15.84 0.000

Power [p] 1.6 0.08721 18.35 0.000

Feed rate [F] -0.002778 0.002180 -1.27 0.214

Dwell Time [D] 5.0 2.180 2.29 0.031

Quench Flow rate [Q] 0.3611 0.1090 3.31 0.003

S = 0.924962 R-Sq = 93.4% R-Sq (adj) = 92.4%

Source DF SS MS F P

Regression 4 303.278 75.819 88.62 0.000

Residual error 25 21.389 0.856

Total 29 324.667

88 S.P. Metage and J.S. Sidhu

Source DF Seq. SS

Power 1 288

Feed rate 1 1.389

Dwell Time 1 4.5

Quench Flow

rate

1 9.389

Table 4. ANOVA results for Case Depth

Predicator Coefficient SE Coefficient T P

Constant -0.3656 0.3736 -0.98 0.337

Power [P] 0.2022 0.0173 11.69 0.000

Feed rate [F] -0.00133 0.0004326 -3.08 0.005

Dwell Time

[D]

2.0556 0.4326 4.75 0.000

Quench Flow

rate [Q]

-0.02222 0.02163 -1.03 0.314

S = 0.183521 R-Sq = 87.2% R-Sq (adj) = 85.1%

Analysis of Variance

Source DF SS MS F P

Regression 4 5.7167 1.4292 42.43 0.000

Residual error 25 0.8420 0.0337

Total 29 6.5587

Source DF Seq. SS

Power 1 4.6

Feed rate 1 0.32

Dwell Time 1 0.76

Quench Flow

rate

1 0.0356

Regression Model Equations for Case hardness and ECD

The regression coefficients of the second order equations have been obtained by

using the experimental data (Table 3 & 4). The regression equations for the

responses as a function of four input parameters are given below:

Case Hardness = 29.8 + 1.6 × Power (P) - 0.00278 × Feed rate (F) + 5 × Dwell time

(D) + 0.361 × Quench flow rate (Q)

Effective Case Depth = - 0.366 + 0.202 × Power (P) - 0.00133 × Feed rate (F) +

2.06× Dwell time (D) - 0.0222× Quench flow rate (Q)

Optimization of Process Parameters in Induction Hardening of 41Cr4 Steel… 89

Main Effects Plots

Figure 1 shows the main effects of process parameters on Case Hardness and

Effective Case Depth. It is observed that as power increases, case hardness also

increases conceding direct relation between power and case hardness. Similarly, as

feed rate increases case hardness decreases. Case hardness increases with increase

in dwell time and quench flow rate.

Figure 1. Main effects plot for case hardness and case depth

In ECD graph, as power increases, ECD also increases showing direct relation of

power with ECD. As feed rate increases ECD decreases, hence there is inverse

relation between ECD and feed rate. ECD increases with increase in dwell time.

ECD decreases initially with increase in quench flow rate and then increases.

90 S.P. Metage and J.S. Sidhu

Surface and Contour Plots of Case Hardness

Figure 2a shows the effect of power and feed rate on case hardness. Case hardness

increases with increase in power and it decrease with increase in feed rate, keeping

other parameters constant i.e. dwell time 0.2 sec, quench flow rate 12 lit/min.

In contour plot, Power is plotted on x axis and feed rate on y axis and dark blue

colour shows max case hardness.

3

400

50.0

00

52.5

55.0

10

57.5

12 20014

ase Hardness [HRC]

Feed rate [mm/sec]

Power [Kw]

Dwell Time [sec] 0.2

Quench Flow rate [litre/min] 12

Hold Values

Surface Plot of Case Hardness [HRC] vs Feed rate [mm/sec], Power [Kw]

Power [Kw]

Fe

ed

rate

[m

m/s

ec]

151413121110

400

350

300

250

200

Hold Values

Dwell Time [sec] 0.2

Quench Flow rate [litre/min] 12

Case

54

54 - 56

56 - 58

Hardness

> 58

[HRC]

< 52

52 -

Contour Plot of Case Hardness [HRC] vs Feed rate [mm/sec], Power [Kw]

Figure 2. a) Surface and Contour Plots of Case Hardness vs Feed rate, Power

As power increases, case hardness also increases, maximum case hardness falls in

the range of 14-15 Kw. Case hardness decreases with increase in feed rate,

maximum case hardness falls in the range of 200-250 (mm/sec) keeping other

parameters constant.

0

0.3

53 .2

54

55

200

56

300 0.1400

Case Hardness [HRC]

Dwell Time [sec]

Feed rate [mm/sec]

Power [Kw] 12.5

Quench Flow rate [litre/min] 12

Hold Values

Surface Plot of Case Hardness [H vs Dwell Time [sec], Feed rate [mm/se

Feed rate [mm/sec]

Dw

ell

Tim

e [

se

c]

400350300250200

0.30

0.25

0.20

0.15

0.10Hold Values

Power [Kw] 12.5

Quench Flow rate [litre/min] 12

Case

54.0

54.0 - 54.3

54.3 - 54.6

Hardness

54.6 - 54.9

> 54.9

[HRC]

< 53.7

53.7 -

Contour Plot of Case Hardness vs Dwell Time [sec], Feed rate [mm/sec]

Figure 2. b) Surface & Contour Plots of Case Hardness and Dwell time vs Feed rate

Figure 2b shows the effect of dwell time and feed rate on case hardness. As dwell

time increases case hardness increases, feed rate increases case hardness decreases

keeping other parameters constant power 12.5 Kw, quench flow rate 12 lit/min.

In contour plot graph feed rate (mm/sec) plotted on x axis and dwell time (sec)

plotted on y axis and dark blue colour shows max case hardness. As feed rate

Optimization of Process Parameters in Induction Hardening of 41Cr4 Steel… 91

increases case hardness decreases, maximum case hardness gets in the range of 200-

250 mm/sec whereas dwell time increases case hardness increases, maximum case

hardness gets in the range of 0.25-0.30 sec keeping other parameters constant.

14

1

54

2

55

56

0.1

57

0.2 100.3

Case Hardness [HRC]

Quench Flow rate [litre/mi

Dwell T ime [sec]

Power [Kw] 12.5

Feed rate [mm/sec] 300

Hold Values

Surface Plot of Case Hardness [H vs Quench Flow rate, Dwell Time [sec]

Dwell Time [sec]

Qu

en

ch

Flo

w r

ate

[li

tre

/min

]

0.300.250.200.150.10

14

13

12

11

10

Hold Values

Power [Kw] 12.5

Feed rate [mm/sec] 300

Case

54.0

54.0 - 54.5

54.5 - 55.0

Hardness

55.0 - 55.5

> 55.5

[HRC]

< 53.5

53.5 -

Contour Plot of Case Hardness vs Quench Flow rate and Dwell Time

Figure 2. c) Surface & Contour Plots of Case Hardness and Quench flow rate vs

Dwell time

Figure 2c shows the effect of quench flow rate and dwell time on case hardness. As

dwell time increases case hardness increases, quench flow rate increases case

hardness increases keeping other parameters constant power 12.5 Kw, feed rate 300

mm/sec.

The contour plot represents dwell time (sec) on x axis and quench flow rate (lit/min)

on y axis and dark blue colour shows max case hardness. As dwell time increases

case hardness increases, maximum case hardness falls in the range of 0.25-0.3 sec.

Whereas, as quench flow rate increases, case hardness increases and maximum case

hardness falls in the range of 13-14 lit/min keeping other parameters constant.

Surface and Contour Plots of Effective Case Depth (mm)

Figure 3a shows the effect of power and feed rate on case depth. As power increases

case depth increases it shows direct relation between power and case depth, feed

rate increases case depth decreases keeping other parameters constant dwell time

0.2 sec, quench flow rate 12 lit/min.

92 S.P. Metage and J.S. Sidhu

Power [Kw]

Fe

ed

rate

[m

m/s

ec]

151413121110

400

350

300

250

200

Hold Values

Dwell Time [sec] 0.2

Quench Flow rate [litre/min] 12

Effective

1.75

1.75 - 2.00

2.00 - 2.25

Case Depth

2.25 - 2.50

> 2.50

[mm]

< 1.50

1.50 -

Contour Plot of Effective Case Depth vs Feed rate and Power

Figure 3. a) Surface and Contour Plot for Case Depth vs feed rate, power

In contour plot graph, power (Kw) is plotted on x axis and feed rate (mm/sec) on y

axis and dark blue colour shows max case depth. As power increases case depth

also increases, maximum case depth gets in the range of 14-15 Kw whereas feed

rate increases case depth decreases, maximum case depth gets in the range of 200-

250 (mm/sec) keeping other parameters constant.

Figure 3b shows the effect of dwell time and feed rate on case depth. As dwell time

increases, case depth increases, also as feed rate increases case depth decreases,

keeping other parameters constant i.e. power 12.5Kw, quench flow rate 12 lit/min.

In contour plot graph, feed rate (mm/sec) is plotted on x axis and dwell time (sec)

plotted on y axis. As feed rate increases case depth decreases, maximum case depth

gets in the range of 200 mm/sec whereas dwell time increases case depth increases,

maximum case depth gets in the range of 0.30 sec keeping other parameters

constant.

Feed rate [mm/sec]

Dw

ell

Tim

e [

se

c]

400350300250200

0.30

0.25

0.20

0.15

0.10

Hold Values

Power [Kw] 12.5

Quench Flow rate [litre/min] 12

Effective

- 1.7

1.7 - 1.8

1.8 - 1.9

Case

1.9 - 2.0

2.0 - 2.1

2.1

Depth

- 2.2

> 2.2

[mm]

< 1.6

1.6

Contour Plot of Effective Case Depth vs Dwell Time and Feed rate

Figure 3. b) Surface and contour plot for case depth vs dwell time, feed rate

Figure 3c shows the effect of quench flow rate and dwell time on case depth. As

dwell time increases case depth increases, quench flow rate increases case depth

decreases keeping other parameters constant power 12.5Kw, feed rate 300 mm/sec.

1.0

1.5

2.0

101212

14

2.0

2.5

300

400

20014

Effective Case Depth [mm]

Feed rate [mm/sec]

Power [Kw]

Dwell Time [sec] 0.2

Quench Flow rate [litre/min] 12

Hold Values

Surface Plot of Effective Case D vs Feed rate [mm/se, Power [Kw]

1.50

1.75

2.00

200200300

2.00

2.25

400400

0.2

0.1

0.3

Effective Case Depth [mm]

Dwell Time [sec]

Feed rate [mm/sec]

Power [Kw] 12.5

Quench Flow rate [litre/min] 12

Hold Values

Surface Plot of Effective Case D vs Dwell Time [sec], Feed rate [mm/se

Optimization of Process Parameters in Induction Hardening of 41Cr4 Steel… 93

Dwell Time [sec]

Qu

en

ch

Flo

w r

ate

[li

tre

/min

]

0.300.250.200.150.10

14

13

12

11

10

Hold Values

Power [Kw] 12.5

Feed rate [mm/sec] 300

Effective

- 1.8

1.8 - 1.9

1.9 - 2.0

Case

2.0 - 2.1

> 2.1

Depth

[mm]

< 1.7

1.7

Contour Plot of Effective Case Depth vs Quench Flow rate and Dwell Time

Figure 3. c) Surface & contour plot for case depth vs dwell time, and quench flow

rate

In contour plot graph, dwell time (sec) is plotted on x axis and quench flow rate

(lit/min) plotted on y axis and dark blue colour shows max case depth. As dwell

time increases case depth increases, maximum case depth gets in the range of 0.25-

0.3 sec whereas quench flow rate increases case depth decreases maximum case

depth gets in the range of 10-11 lit/min keeping other parameters constant.

Multiple Response Optimizations

MINITAB software was used for maximizing (achieving target values) hardness

and ECD. The optimum values of process parameters obtained were power 15 Kw,

feed rate 200 mm/sec, dwell time 0.30 sec and quench flow rate 14 lit/min, the

maximum case hardness and ECD obtained 59.83 HRC and 2.70 MM. All the

values were within 95% prediction interval.

Table 5. Multiple response optimizations

Response Goal Lower Target

Case hardness [HRC] Maximum 48 60

E Case depth [MM] Maximum 1.4 2.8

Table 6. Experimental validation

Trial

No.

Optimum

conditions

Case hardness % error Effective Case depth %

error

Experimental Predicted Case

Hardness

Experimental Predicted Case

depth

01 P= 15kw;

F = 200

mm/sec; D=

0.3 sec;

Q=14

litre/min

58.0 59.83 3.05 2.58 2.7 4.44

02 59.0 59.83 1.38 2.6 2.7 3.7

94 S.P. Metage and J.S. Sidhu

MICROSTRUCTURE ANALYSIS

The goal of heat treatment of steel is very often to attain a satisfactory hardness. The

important micro-structural phase is then normally martensite, which is the hardest

constituent in low-alloy steels. The hardness of martensite is primarily dependent on

its carbon content. If the micro-structure is not fully martensitic, its hardness is

lower. In practical heat treatment, it is important to achieve full hardness to a certain

minimum depth after cooling, that is, to obtain a fully martensitic microstructure to

a certain minimum depth, which also represents a critical cooling rate.

A finely distributed structure like tempered martensite is more rapidly transformed

to austenite than, for instance, a ferritic-pearlitic structure. This is particularly true

for alloyed steels with carbide-forming alloying elements such as chromium and

molybdenum

In case of induction hardening process uniform distribution of carbon cannot be

assumed, the time spent at the austenitizing temperature can be so brief that carbon

cannot diffuse to a uniform concentration throughout the microstructure.

Determination of 100% martensite is subjective and difficult to determine optically

(Tartaglia Eldis 1984). The figure shows microstructure image light microscope

photograph at 20X of the surface of sample piece of low hardness at 48 HRc and of

optimum hardness at 60 HRc of induction hardened 41Cr4 steel, polished and

etched at 3% Nital solution. No micro cracks observed in the induction hardened

zone.

Figure 4. Microstructure of sample piece low hardness at 48 HRc a) Micrograph at

interface hardened and unhardened zone b) Micrograph at unhardened zone c)

Micrograph at hardened zone

Optimization of Process Parameters in Induction Hardening of 41Cr4 Steel… 95

Figure 5. Microstructure of sample piece optimum hardness at 60 HRc a)

Micrograph at interface hardened and unhardened zone b) Micrograph at

unhardened zone c) Micrograph at hardened zone

CONCLUSIONS

From this experimentation study it has been concluded that

1. The most influencing parameters for the case hardness (CH) are the power;

quench flow rate and Dwell time, in descending order.

2. The most influencing parameters for the Effective case depth (ECD) are the

power; Dwell time and feed rate, in descending order.

3. The common optimum values of the process parameters for both responses case

hardness (CH) and Effective case depth (ECD) are: Power = 15kw; Feed rate =

200 mm/sec; Dwell time = 0.3 sec; Quench flow rate = 14 litre/min. As the error

between the experimental and predicted values is less than 5%, validates the

experiment.

4. In the hardened region, complete martensitic phase was observed which confirms

the hardening of the material

ACKNOWLEDGEMENTS

Authors express their sincere gratitude towards Mr. P. Hurdale, Pune Heat, Bhosari,

Pune for their resource courtesy.

REFERENCES

[1] Amit Kohli and Hari Singh, Optimizing mean effective case depth of induction

hardened parts (rolled condition) using response surface methodology,

International Journal of Emerging Technologies 1 (1):87-91 (2010)

96 S.P. Metage and J.S. Sidhu

[2] Amit Kohli and Hari Singh, Optimization of processing parameters in induction

hardening using response surface methodology, Sadhana, Vol. 36, Part 2, April

2011, pp. 141–152.© Indian Academy of Sciences

[3] Mert Onan, H. Ibrahim Unal, Kasim Baynal, Furkan Katre, Optimization Of

Induction Hardened Aisi 1040 Steel By Experimental Design Method And

Material Characterization Analysis, Proceedings of the ASME 2012 International Mechanical Engineering Congress & Exposition IMECE2012, November 9-15, 2012, Houston, Texas, USA

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