Canale L.C.F., Mesquita R.A., Totten G.E. Failure Analysis of Heat Treated Steel Components

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When a machine component that has been

surface induction hardened in this way is sub-

jected to an external load (Fig. 96c), additional

tensile residual stresses can be noted in the ﬁrst

and second layers (Ref 15).

Since fatigue of a machine component is a

very delicate problem connected with the total

sum of tensile stresses in the second zone, there

is a danger that the effects of fatigue are trans-

ferred to the surface, due to the size, shape, and

Fig. 96

Stress proﬁle in a round bar in the loaded state, where residual stresses after induction surface hardening and loading stresses

add up. Source: Ref 15

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location of the hardened trace. When a loaded

layer is exposed to tensile external stress up to

the surface, the surface becomes very sensitive

to the occurrence of cracks (Fig. 96d) (Ref 15).

This propensity to cracking is further increased

if defects are present in the surface of the

workpiece material.

A critical state in the second zone of the hard-

ened surface layer occurs on locally hardened

workpieces, where the surface was overheated

or nonuniformly heated. The conditions are

quite the opposite in surface heating of work-

pieces, such as in nitriding and cementation

or intensive but shallow quenching of steel

(Fig. 97) (Ref 15). In these surface heat treat-

ment procedures, heating is carried out through-

out the whole machine component, followed by

slow cooling, for example, nitriding or quench-

ing such as in cementation. Residual stresses

in nitrided and cemented surface layers are

compressive, while tensile residual stresses

occur in the central part with the reﬁned pearlite

microstructure.

The distribution of residual stresses in heat

treatment procedures where only the surface of

the workpiece is heated (induction hardening,

ﬂame hardening) differs greatly from the pro-

cedures where heating is performed throughout

the entire volume (nitriding, cementation). In

nitriding and cementation, the aforementioned

second layer in the subsurface does not appear at

all, because the direction of the heat ﬂow is

opposite to the direction of the heat ﬂow in

induction and ﬂame hardening. The resultant

operating tensile stresses on the surface or in the

surface layer can thus be considerably smaller.

Due to the hardness of the surface, induction and

ﬂame hardening lowers the fatigue strength of

machine components. Therefore, care should be

taken to diminish all detrimental effects in the

surface layer.

A typical example of induction surface hard-

ening is surface hardening of gears that are

heated with a low heating rate and relatively low

current frequency. The outer hardened zone

includes almost the entire height of the gear

teeth, whereas the second zone is in the tooth

root area. A gear heat treated in this way will

meet the wear resistance requirements expected

of the gear tooth, while the strength of the other

part of the tooth is of minor importance. The

fatigue strength will be relatively low due to

high tensile residual stresses in the tooth root,

that is, in the second zone where the operating

or load tensions and the tensile residual stresses

are summed up. The energy input in heating a

gear tooth or the whole gear was such that

the second zone has not appeared. A similar

heat treatment can be applied to the spline inside

the gear. A gear heat treated in this way is

more resistant to wear and corrosion and should

have high resistance to fatigue in bending

because of a smaller thickness of the layer in the

second zone.

Residual Stresses in Carburized Machine

Parts. Carburizing is a process in which an

austenitized ferrous alloy is brought into contact

with an environment of sufﬁcient carbon

potential to cause absorption of carbon at the

surface and, by diffusion, to create a carbon-

concentration gradient in the thin surface layer.

As this deﬁnition clearly indicates, two factors

may control carburizing. Either the carbon-

absorption reaction at the surface or the diffu-

sion of carbon in the steel will determine the

rate of carburizing. Carburizing is done at ele-

vated temperature, generally in the range of

850 to 950



C, although occasionally at tem-

peratures as low as 790



C and as high as

1095



Fig. 97

Stress proﬁle in a round bar in the loaded state, where

residual stresses after carburizing or nitriding and

loading stresses add up. Source: Ref 15

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With the hardened steel, that is, hardened

machine part, the following was studied:

 Effective case depth

 Depth at which martensitic microstructure is

present

 Hardness variation in the transition zone

between martensite and matrix

 Microstructural composition in the transi-

tion zone with bainite-pearlite-ferrite

The characteristics obtained are essentially

affected by:

 The grade, chemical composition, and

microstructure of steel in the soft state

 The size, that is, mass, of the machine part

Considering that certain properties described

by the previously mentioned characteristics are

speciﬁed for the machine part, adequate condi-

tions for quenching from the austenitizing tem-

perature should be speciﬁed too. The quenching

conditions are described with reference to the

mass of the machine part.

Thus, in steel quenching, the following are

studied:

 Volume, that is, dimensional changes due to

the differences in microstructure between

the initial material condition and the hard-

ened condition of the same material

 Distortion of the machine part due to incor-

rect shaping of the machine part and/or an

improper quenching procedure

 Residual stresses due to volume changes

occurring between the hardened zone and

unhardened zone of the machine part

Residual stresses may result from a defor-

mation of the machine part during the quenching

process. Internal forces due to temperature

stresses during quenching may exceed the yield

stress of the material, which results in plastic

deformation during the quenching process and

residual stresses after cooling. The magnitude of

residual stresses is related to the yield stress of

the material at the temperature at which the

deformation occurred.

Thus, in the case of through hardening in

which a complete and homogeneous austenitic

microstructure turns into a martensitic one, a 4%

volume change of the machine part or a 1.3%

linear increase in the machine-part size is

obtained:

 100=4%

In incomplete hardening, the volume changes at

the surface are greater than in the core, which

produces transformation strains. The residual-

stress variation thus depends on:

 Quenching/cooling conditions

 Temperature difference between the surface

and the core during the quenching process

 Temperature interval between the beginning

and end of martensitic transformation and

the cooling rate in this zone

An image of the magnitude of internal stresses

during the quenching process can be provided by

a test of quenching cylindrical specimens from a

temperature lower than the transformation tem-

perature. During the quenching process, tem-

peratures are measured at the specimens, that is,

at their surface and in their core. Maximum

thermal stresses can thus be calculated (Ref 1,

20, 71, 72). The maximum thermal stresses

found in the cylindrical specimens with the

smallest diameter, 25 mm, and further specimen

diameters in a geometrical ratio with a factor of 2

are given in Table 5.

As an approximate orientation to the cooling

rates obtained, a calculation was made for a

temperature of 500



C. Comparative data on

maximum thermal stresses refer to air cooling

and oil quenching. With air cooling, the stresses

obtained in the specimen with the smallest dia-

meter, 25 mm, equal only 7 MPa, whereas for

the specimen with the largest diameter, 800 mm,

the stresses are as much as 200 MPa. The maxi-

mum thermal stresses, however, are con-

siderably higher with oil quenching; they range

between 230 MPa with the 25 mm diameter

specimen and 620 MPa with the 800 mm dia-

meter specimen. The latter represents an extre-

mely high internal thermal stress that may result

in material plastiﬁcation. The data exclude

stresses due to phase changes and stresses due to

inhomogeneity, which additionally increase

their value.

Results of the measured residual stresses with

surface-hardened steels are given in Table 6.

The stresses were measured by the x-ray dif-

fraction technique just below the surface, that is,

0.05 mm. The results refer to steel grades

832M13, 805A20, 805A17, 897M39, 905M39,

and cold rolled steel after induction hardening,

with the longitudinal residual stresses being

measured. The values of longitudinal stresses

after carburizing to 1.0 to 1.5 mm case with

0.8% surface carbon and direct quenching

without tempering range between 190 and

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400 MPa, which depends on the steel grade

selected. With steel 832M13, testing of speci-

mens after quenching and by undercooling to

80 and 90



C with tempering and without

tempering was performed. Tempering con-

tributes to obtaining tempered martensite and

possible transformation of retained austenite,

which produces a reduction, that is, a compen-

sation, of the existing residual-stress proﬁle.

Thus, the lowest residual stress is obtained in

steel quenching by undercooling and subsequent

tempering. In nitriding of steel 897M39 to a

depth of 0.5 mm, however, a residual stress

ranging between 400 and 600 MPa is obtained.

In steel 905M39, however, a considerably

higher residual stress, ranging between 800 and

1000 MPa, is obtained in nitriding to the same

depth. The highest residual stresses were mea-

sured in cold-rolled steel subjected to additional

induction surface hardening without tempering.

A maximum value obtained was 1000 MPa.

With additional tempering at 200



C, martensite

will become tempered and the residual stresses

reduced to 650 MPa. By additional tempering at

an even higher temperature, at which martensite

disintegrates, the maximum measured stresses

decrease. For example, at a tempering tem-

perature of 400



C, they decrease to 170 MPa or

a factor of 6 lower than those obtained imme-

diately after steel quenching.

Figure 98 shows the results of carbonitriding

SAE 1118 steel with reference to the contents of

carbon and nitrogen at the surface and the gra-

dient of the two in the subsurface (Ref 71). The

austenite content, that is, the austenite gradient

of the two in the subsurface, and the way a

complementary residual-stress variation pro-

ceeds in the subsurface are very important.

With a gradual reduction of austenite content

to a depth of 0.5 mm, the residual stresses

decrease as well, and the maximum pressure

achieved is 200 MPa. To a depth of 45 mm,

the stresses gradually increase to tensile values,

and at a depth of 1.5 mm, they are as much as

+100 MPa.

Input and Output Control of Steel for

Induction Surface Hardening of Gears

Production automation necessitates an ever-

increasing demand for greater uniformity of the

Table 6 Residual stresses measured in surface

heat treated steels

Steel Heat treatment

Residual stress

(longitudinal),

MPa

832M13 Carburized at 970



C to 1.0 mm

case with 0.8% surface carbon

280

Direct quenched, 80



C subzero

treatment, no temper

340

Direct quenched, 90



C subzero

treatment, tempered

200

805A20 Carburized and quenched 240–340(a)

805A20

Carburized to 1.1–1.5 mm case

at 920



C, direct oil quench,

no temper

190–230

805A17 400

805A17 Carburized to 1.1–1.5 mm case

at 920



C, direct oil quench,

tempered at 150



150–200

897M39

Nitrided to case depth of

approximately 0.5 mm

400–600

905M39 800–1000

Cold

rolled

steel

Induction hardened, untempered 1000

Induction hardened, tempered

at 200



650

Induction hardened, tempered at

300



350

Induction hardened, tempered at

400



170

(a) Immediately subsurface, that is, 0.05 mm. Source: Ref 71

Table 5 Cooling rate thermal stresses in simple

rounds with no transformation

Diameter

of round

(D), mm

Air cooled Oil quenched

Cooling rate

at 500 °C

500

), °C/s

Maximum

thermal stress

max



, MPa

Cooling

rate at 500 °C

500

), °C/s

Maximum

thermal stress

max



, MPa

25 0.662 7 20.0 230

50 0.312 15 6.12 290

100 0.146 28 1.88 370

200 0.070 54 0.59 450

300 0.0445 73 0.29 510

400 0.0326 100 ... (540)

800 0.0158 200 ... (620)

Source: Ref 1, 71

Fig. 98

Residual stress, carbon, nitrogen, and retained aus-

tenite through a carbonitrided case on SAE 1118

steel. Source: Ref 71

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properties of heat treated steel parts (Ref 73).

Therefore, a general market demand is for a

certain prescribed quality that is usually the

result of various properties (Ref 41, 74–82). One

of the most important properties is hard-

enability, which should be a uniform and con-

stant property of steel regardless of the treatment

conditions in the ironworks. In the experimental

part of the study, the starting point was the

analysis of steel hardenability according to the

Jominy test (Ref 40, 74–76). On this basis, the

conditions for induction hardening were pre-

scribed for a worm gear tooth. The success of the

induction hardening was veriﬁed by the micro-

hardness measurement along the tooth proﬁle

centerline (Ref 83, 84).

Figure 99 shows Jominy curves for the hard-

ness proﬁles of the specimen front of AISI 1050,

4150, and 4340 steels (Ref 40, 41). It generally

applies that Jominy curves for common test-

specimen heating differ strongly from those for

the specimens induction heated and quenched in

the same way. Hardness differences in the

Jominy test specimen are minimal at the surface

and increase through the depth. It is important

that the hardness proﬁles of the furnace-heated

test specimens or short-term induction-heated

specimens differ less if carbon steels have a

smaller carbon content (AISI 1050) and differ

more strongly with alloyed steel, as was the case.

Figure 100 shows Jominy curves for furnace

heating and induction heating. Both ﬁgures

indicate that the through-height hardness proﬁle

of a Jominy specimen depends on the maximum

temperature obtained at the surface (Fig. 100b)

and on heating time (Fig. 100a), the power

density being given (Ref 40, 41). Induction

heating was performed under the conditions

given and with different heating times. Furnace

heating of Jominy specimens at 870



C provides

the highest hardness values for the hardened

front.

In induction heating at the same temperature,

870



C, a quite different hardness proﬁle of the

Jominy specimen hardened front is obtained

(Fig. 100a). With an increasing surface auste-

nitizing temperature, the through-height hard-

ness proﬁle of the specimen increases so that at a

temperature of 1040



C, there is negligible dif-

ference in the hardness proﬁle of the Jominy

specimen, regardless whether it was furnace

heated or induction heated.

The prescription for the veriﬁcation of the

effects of induction hardening was carried out

for the upper- and lower-limit microhardness

from the tooth top and to a depth of

of the

tooth height. The experiments on heat treatable

carbon steel C35 with a different history have

Fig. 99

Jominy curves for end-quenched bars of (a) AISI

1050, (b) 4150, and (c) 4340 steels, austenitized

conventionally and by short-time induction heating. Source: Ref

40, 41

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shown that with the existing heat treatment con-

ditions, it is not possible to achieve the micro-

hardness proﬁle required by the user (Ref 79).

First, it was necessary to ﬁnd a Slovenian

substitute for the French steel CC35. This was

done with the help of a cooperative industry.

Steel CC35 is a heat treatable steel that has been

mechanically machined and induction hardened

to ensure a uniform quality.

Steel C35, chosen as a substitute, is classiﬁed

among the high-grade, unalloyed, heat treatable

carbon steels with a maximum phosphorus and

sulfur content lower than 0.035%. It is intended

for parts smaller than 100 mm, subjected to

lower loads, and with high requirements on

homogeneity of material after heat treatment

and mechanical machining.

For the selected heat treatable carbon steel

C35, a suitable acceptance control procedure

had to be prescribed, with special emphasis on

hardenability.

Based on the corresponding criteria, the

acceptance conditions should enable the classi-

ﬁcation of steels into quality classes in accor-

dance with the different heat treatment

prescriptions. The chemical composition of the

steel is presented according to International

Organization for Standardization (ISO) stan-

dards and that of the French according to the

Association Francaise de Normalisation

(AFNOR). The chemical composition is given

by quoting the upper and lower content limit for

each particular part. The limits of the Slovenian

steel are much more constrained than that of the

French. In the French steel, there is a higher

content of carbon, manganese, and traces of

chromium, which leads to somewhat better

hardenability compared to the Slovenian steel

C35.

Figure 101 presents the hardness curves of the

Jominy specimen versus the distance from the

face (Ref 83). The starting point for the analysis

was the upper and lower conﬁdence limit for

Slovenian steel C35 as prescribed by the pro-

ducer, Ravne Ironworks.

The given conﬁdence limits are presented by

the hatched area on the extreme right of the

ﬁgure. Since testing enables a successful selec-

tion of steel as well as optimal heat treatment

conditions, it was decided to test the upper and

lower conﬁdence limits of a small-sized, hard-

ened worm gear (Fig. 102a) (Ref 83). This gear

must have hard, wear-resistant surfaces and an

increased strength due to loading conditions or

expected load-carrying capacity of the teeth.

Both of these properties are achieved by induc-

tion hardening. The success of the heat treatment

was veriﬁed by Vickers microhardness mea-

surements at a loading of 0.3 daN acting along

the centerline of the tooth proﬁle. The veriﬁca-

tion of the effects of surface hardening and

simultaneous heat treatment of the teeth was

carried out in ten measurements: the ﬁrst on the

tooth top and then each subsequent measure-

ment at a distance of

h or 0.367 mm. Thus,

in ten measurements the microhardness was

measured down to the depth of

of the tooth

height, as shown in Fig. 102(b) (Ref 83). When

ordering the gear, the customer speciﬁed

the prescribed allowable hardness for forming

the upper and lower conﬁdence limits along the

height of the gear tooth.

Fig. 100

Effect of (a) time at an 870



C austenitizing tem-

perature and (b) maximum surface temperature

on the Jominy curves for induction-hardened AISI 4150 steel.

The curve for conventional furnace-heated 4150 is also shown

in (b). Source: Ref 40, 41

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The microhardness limit values were:

 On the tooth top at h = 0, the microhardness

is 680 to 800 HV

0.3

 In the depth of

h or 1.45 mm, the micro-

hardness is 520 HV

0.3

maximum.

 In the depth of

h or 2.90 mm, the micro-

hardness is 520 HV

0.3

maximum.

 In the depth of

h or 3.30 mm, the micro-

hardness is 220 to 275 HV

0.3

On the basis of hardenability testing, the fol-

lowing conclusions can be drawn:

 Due to a higher content of carbon, manga-

nese, and some traces of chromium, the

French steel CC35 displays a very favorable

hardenability according to the Jominy tests.

Even to a depth of 7 mm, the hardenability

curve shows 40 HRC, then hardness begins to

decrease rapidly and, at a depth of 10 mm, is

only 22 HRC.

 The Slovenian steel C35 produced by the

Ravne Ironworks has a slightly lower con-

tent of carbon and a considerably lower

content of manganese. For example, for steel

of charge “B”, the carbon content is lower by

0.06% and the manganese content by 0.35%,

according to the French steel. On the basis of

the data in the literature, it was determined

that this considerably lower manganese

Fig. 101 Hardenability of the analyzed steels and determination of the upper and lower conﬁdence limit. Source: Ref 83

Fig. 102 Worm characteristics after induction surface hardening. Source: Ref 83

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content reduces the effect of hardenability

by a factor of 1.5. The relative effect of

silicon on hardenability is practically negli-

gible, although the content may vary within

0.1 to 0.4%.

The results of the hardenability testing of the

discussed steels are presented in Fig. 101 (Ref

83). Based on the mean values and their devia-

tions, it was determined that the curve of hard-

enability or hardness shows solid progress into

the depth in the French steel CC35 and steel C35

of charge “C” and “D”. On the other side, the

hardenability of Slovenian steel C35 of charge

“C” and “D” is much lower, so that at a depth of

4 to 5 mm, the lower conﬁdence limit is excee-

ded. The input control of steel should be focused

mainly on the lower conﬁdence limit of hard-

enability, because the progress of hardness has a

decisive inﬂuence on the strength properties of

the gear teeth. It was determined that the upper

conﬁdence limit corresponds to the maximum

hardness achieved, and that it cannot be ex-

ceeded in any way. It was therefore decided that

the place of the corrected lower conﬁdence limit

would be deﬁned using Jominy hardenability

tests, determining the actual progress of hard-

ness. As a criterion for the correction of the

lower conﬁdence limit, the microhardness along

the tooth height (

h), limited by the maximum

and minimum microhardness, was used. This

helped to establish the primary criteria con-

ditioning the microhardness distribution on the

product, which was also limited by the upper and

lower conﬁdence limit. The answer to which

charges of the steel are more suitable for use can

be obtained by associating the corresponding

microhardness conﬁdence limits on the product

and also on the Jominy specimen. The desired

product characteristics were deﬁned on the basis

of the following conditions of induction hard-

ening:

 Generator power—22.5, 24.0 and 25.5 kW

 Heating time—3.9, 4.4, and 4.9 s

 Time/pause between the end of heating and

the beginning of quenching—0.1 s

 Quenching time—4.0 s

The results of induction hardening on the gear

are presented in Fig. 103 for the French steel

CC35 (Ref 83), and in Fig. 104 for the Slovenian

steel C35 at the given power values of a high-

frequency generator and heating times (Ref 83).

The diagrams show the upper and the lower

conﬁdence limits for microhardness along the

tooth height. The results of microhardness dis-

tribution along the tooth height must fall within

the mentioned limits. However, it can be seen

that it is possible to reach only a lower micro-

hardness on the tooth that results from a lower

hardenability of the steel or from unsuitable heat

treatment conditions. The lower conﬁdence

limit is deﬁned only by the microhardness of the

basic material at a depth of

h and

represents only a theoretical limit. The data on

Fig. 103 Hardness distribution along the tooth symmetry line after heat treatment of the French steel CC35. Source: Ref 83

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the steel properties and heat treatment condi-

tions provide various actual measured micro-

hardness distributions, where the microhardness

of the basic material is reached in the depth from

h to

h in the French steel CC35 and from

h to h in the Slovenian steel C35. From all these

data, it can be stated that it is possible, with

adequate heating and quenching conditions and

adequate hardenability, to reach the desired

microhardness distribution in the tooth. From

Fig. 103, it can be noted that in the case of the

French steel CC35 only three out of nine heat

treatment conditions fall out of the conﬁdence

limit at the minimum power P = 22.5 kW (Ref

83). Quite the contrary can be found from

Fig. 104 presenting Slovenian steel C35. Here,

a desirable distribution of microhardness

along the tooth height was achieved only in

the conditions of maximum power (Ref 83). This

means that for an equal efﬁciency of induction-

hardened gears from the French steel CC35, a

signiﬁcantly shorter heating time is necessary

than with steel C35. This time is estimated to be

for even a second shorter and represents a 25%

shorter heat treatment cycle, contributing to

lower costs of manufacturing.

Induction surface hardening of machine

components and especially gears is a very

complex process involving a whole range of

possible heat treatment methods, which are all

reﬂected in either good or bad serviceability of

machine components. The heat treatment engi-

neer must be aware of the different effects of

particular design shapes of induction coils, be

familiar with electromagnetic phenomena and

eddy currents, and have some experience in the

right choice of energy inputs necessary for

heating. The energy needed for heating can be

provided by changing the generator power as

well as the frequency of the current. In pro-

gressive hardening, to achieve a suitable energy

input, the workpiece feed rate or the rate at

which the coil is moved must be adjusted,

whereas in single-shot hardening, suitable

energy input is achieved by adjusting the heating

time with a high-frequency current. An essential

advantage of induction surface hardening is that

it is possible to achieve a sufﬁcient repeatability

of the hardened layer thickness on the workpiece

as well as a desirable or even prescribed hard-

ened-layer proﬁle, ensuring sufﬁcient hardness

and favorable distribution of residual stresses in

the hardened layer. A variety of steels and a

whole range of induction-hardening methods

provide the possibilities for very accurate plan-

ning of the size and distribution of residual

stresses. This is of growing importance, since

manufacturers are frequently required to pro-

duce machine components that, among other

surface properties, must possess quite speciﬁc

residual-stress distribution along the depth of the

hardened layer. It has become a proven fact that

high compressive stresses ensure high fatigue

strength of machine components and reduce the

danger of the occurrence and growth of cracks

on the surface of components. As far as induc-

tion surface hardening is concerned, it is also

quite important to choose the right quenching

Fig. 104 Hardness distribution alon g the tooth symmetry line after heat treatment of the Slovenian steel C35. Source: Ref 83

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medium and method of quenching. For this

reason, engineers must direct their attention not

only to the method of heating and possible

overheating of the surface layer but also to the

methods of quenching and the right choice of the

medium for quenching.

With increasing surface heating power in

the ﬁnal phase, an increase in microhardness

along the tooth symmetry line is also reached,

especially in the depth from 0.5 to 2.5 mm,

whereas by making the heating time longer, a

more pronounced effect directed into the depth

can be achieved. In this way, an adequate heat

treatment can ensure the required surface hard-

ness (52 HRC) as well as an increased strength of

the gear in the tooth-root part, which is of

extreme importance for certain operating con-

ditions.

Tests have shown that it is necessary to move

the lower hardenability limit at least on the level

indicated by the scattered microhardness values

of the French steel CC35. The new lower con-

ﬁdence limit is named the corrected limit,

ensuring the prescribed microhardness dis-

tribution in the subsurface at a power P =

24.0 kW and P = 25.5 kW.

On the basis of the tests, it can be concluded

that the criterion of hardenability can be very

successfully applied in the input control of

steels. Hardness decreases with the distance

from the face of the Jominy specimen and must

fall within the conﬁdence limits. In some cases,

that is, with Slovenian steel C35 of charge “A”

and “B”, when the hardenability exceeds the

lower conﬁdence limit, an adequate selection of

induction-hardening conditions (power in kilo-

watts and heating time in seconds) can ensure

the desired microhardness along the tooth sym-

metry line. The results conﬁrm that heat treat-

ment conditions can be successfully determined

by relatively simple experiments that also make

the procedure more economical.

REFERENCES

1. H.C. Child, Surface Hardening of Steel,

Engineering Design Guides 37, Published

for the Design Council, The British Stan-

dards Institution and the Council of Engi-

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Press, Oxford, U.K., 1980

2. P.A. Hassell and N.V. Ross, Induction Heat

Treating of Steel, Heat Treating, Vol 4,

ASM Handbook, ASM International, 1991,

p 164–202

3. R.E. Haimbaugh, Practical Induction Heat

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4. S. Lampman, Introduction to Surface

Hardening of Steels, Heat Treating, Vol 4,

ASM Handbook, ASM International, 1991,

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5. T. Ruglic, Flame Hardening of Steels, Heat

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6. K. Sridhar and A.S. Khanna, Laser Surface

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turm, Characteristics of

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on Quenching and the Control of Distortion

(Cleveland, OH), 1996, p 193–200

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Handbook, Butterworth, London and

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14. K.E. Thelning, Chapter 6.6.2: Steel Grades

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London and Boston, 1975, p 434–435

15. J. Grum, Induction Hardening, Materials

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Ljubljana, 2001

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