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

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Initiation of fatigue fractures occurs at the

border between the layer and the substrate, in a

zone characterized by hardness higher than that

of the core by 50 HV. The features initiating

fatigue fractures are nonmetallic inclusions of

calcium sulﬁdes (Fig. 3), originating from the

metallurgical process.

Results of investigations of yield strength in

bending indicate that variation of both the tem-

pering temperature as well as the nitriding time

affects its value insigniﬁcantly, not exceeding

7%. The values of R

are all within the range of

1850 to 1980 MPa.

Results of metallurgical evaluations of nitri-

ded layers (Table 1) show that extension of the

nitriding time from 4 to 16 h causes an almost

doubled growth of the effective minimum ten-

dency to increase the case depth with a lowering

of the tempering temperature. A similar but clear

trend is observed in the surface hardness of

layers, where lowering of the tempering tem-

perature from 620 to 550



C with a 4 h nitriding

time cycle causes a rise in HV1 surface hardness

by approximately 100 units and in HV10 hard-

ness by 50 units.

Figure 4 shows the changes taking place in the

character of the microhardness proﬁle as a

function of process time, with tempering tem-

perature at 590



C. As can be seen, extension of

the nitriding time causes a drop in the angle of

inclination of the microhardness proﬁle. Similar

changes in the microhardness proﬁle versus

process time occur for the remaining tempering

temperatures.

Fatigue Evaluation of Nitrided Steels

An evaluation of fatigue properties requires

an understanding of the mechanism. This

mechanism also depends on the condition and

mutual relationship between the substrate and

the surface layer. This requires determination of

the strength condition of the system: substrate-

surface layer, as a function of external loading.

Among the most important parameters

describing the condition of the surface layer are

microstructure, degree of strengthening, state of

stresses, and roughness. Other important para-

meters include texture, surface energy, and

chemical composition (Ref 2, 3).

In engineering practice, usable properties

such as tensile strength, R

and fatigue limit,

may be determined as functions of mechanical

parameters, that is, hardness, H, or tensile

strength, R

, or surface roughness (Ref 4). Such

correlations maintain their validity for a material

homogeneous throughout its cross section. For

heterogeneous materials (e.g., ones that have

been surface treated), such correlations cannot

be applied directly. The character of distribution

Fig. 4

Microhardness traverses for different nitriding process

times

Fig. 3

Precipitation on the fracture surface of a specimen

which served as the source of the fatigue fracture.

Original magniﬁcation: 500 ·

Fig. 5

Fatigue characteristics for 1, a homogeneous material,

and 2, a heterogeneous material

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of basic mechanical properties (hardness,

residual stresses, as well as their signiﬁcant

effect on fatigue properties) vary in different

ways for homogeneous or heterogeneous mate-

rials (Fig. 5). Homogeneous materials (curve 1,

Fig. 5) have constant properties through the

cross section. Heterogeneous materials (curve 2)

have variable properties.

The fatigue characteristic, which is shown

by the distribution of the fatigue limit, s,isa

function of hardness, H, and residual stresses, s

s=f H,s

ðÞ (Eq 1)

The method of designing a usable characteristic

for the fatigue limit distribution has been

described in publications (Ref 3–5).

The distribution of stresses from extraneous

loading constitutes a signiﬁcant characteristic,

because it enables the determination of the

strength condition for the surface layer. Loading

characteristics are typical distributions of

stresses across the section of a component or

specimen for the investigated types of loading:

tensile-compressive, bending, or torque. For

smooth specimens, their determination does not

present any problems. Some difﬁculties may

arise when determining the distribution of

stresses in a notched specimen.

Distribution of stresses from extraneous

loading for notched specimens in conditions of

bending is (Ref 3):

max

xðÞ=s

 a 17

2 x



3a2

(Eq 2)

where s

max

(x) is the value of local stress at a

distance of (x) from the surface, s

is the

nominal stress, a is the coefﬁcient of stress

concentration, and d is the cross-sectional

dimension.

Knowledge of the fatigue characteristic, as

well as the loading characteristic, allows the

determination of the fatigue strength condition

for any location on the component cross section:

1

(Eq 3)

where s

l

is the fatigue limit at any location on

the specimen cross section, and s

is the value

of stresses from extraneous loading at the given

location i.

The investigations were conducted on struc-

tural steels 40HM (4140) and 38HMJ (Nitralloy

135M). The steels were hardened and tempered

prior to nitriding at two temperatures: 550 and

620



C (Ref 1). Nitriding was carried out using

two types of atmosphere, that is, NH

-NH

3(diss)

and NH

-N

. In the nitriding processes, the

atmosphere gas composition was varied, as were

the time of nitriding (4 and 16 h) and the

nitriding potential, K

(from 1.65 to 4.8).

Fatigue resistance tests were carried out on

the PUNZ machine (manufactured by Schenck),

applying rotational bending stresses with a

notch (a = 1.02). The specimen diameter was

W = 5.88+0.02 mm. The results of the fatigue

resistance tests, metallurgical evaluation and

process parameters are shown in Table 3.

Figure 6 shows microhardness traverses in the

nitrided case for 40HM-grade steel, while Fig. 7

shows the same for the 38HMJ grade.

Test results show that the tempering tem-

perature has an effect on the properties of the

nitrided case. The effect of the tempering tem-

perature on the basic properties of the nitrided

case depends on the steel grade. A higher

increase in hardness (by approximately 50%) as

well as in case depth is observed for the low-

alloy chromium steel 40HM.

As can be seen in Fig. 7 for the 38HMJ steel,

the effects of tempering temperature on the

Table 3 Technological parameters and test results

Steel grade

Tempering

temperature,

°C

Nitriding

time, h

Core

hardness

0.5

hardness

Fatigue limit

1

), MPa

Residual stresses

Max

on cross

section

surface

surface,

MPa

Depth at which

stress changes

sign, mm

40HM (4140) 550 4 402 677 757 820 600 0.32

550 16 396 642 757 840 650 0.52

620 4 343 715 826 735 600 0.37

690 16 343 343 642 745 900 0.55

38HMJ

(Nitralloy 135M)

550 4 356 1030 1373 805 900 0.25

550 16 343 1030 1227 785 600 0.48

620 4 318 1030 1273 766 450 0.30

620 16 296 1030 1304 810 800 0.45

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changes in hardness and case depth are smaller

than for the 4140 steel. It was found that low-

ering the tempering temperature raises the fati-

gue resistance of the core-case system. Shorter

nitriding time, following a low tempering tem-

perature, does not affect the volume fatigue

resistance (Ref 6).

The effect of heat treatment of the core on

fatigue resistance is shown in Fig. 8. From the

illustration, it is seen that raising the core hard-

ness moves the fatigue resistance characteristic,

that is, the distribution of the speed limit value,

across the section in the direction of higher stress

values.

Data to determine the characteristics in Fig. 8

are shown in Table 4. To calculate the fatigue

limit, the following formula was used:

1

=1:98H70:0011 HV

ðÞ

(Eq 4)

where HV is Vickers surface hardness, and HV

is Vickers hardness at i location on the cross

section. The relationship is valid for a hardness

range of 340jHVj900.

A signiﬁcant increase in the fatigue limit

value (to 820 MPa) with a tempering tempera-

ture of 550



C and up to 735 MPa with a tem-

pering temperature of 620



C, relative to prior

values of 618 and 550 MPa, determined at the

location of fatigue crack initiation (Fig. 9) (on an

average 0.5 mm from the surface) should be

interpreted as the favorable effect of compres-

sive stresses in the nitrided case (Ref 7).

It follows from Fig. 8 that fatigue crack

initiation of nitrided cases (compare with Fig. 7)

takes place under the surface because stresses

from extraneous loading locally exceed the

value of the fatigue limit, and, in accordance

with curve 3 in Fig. 8, material decohesion must

occur.

Fatigue Property Characteristics after

Carbonitriding

In most modern methods of manufacturing, it

is recommended that the design stage consider

the different manufacturing technologies. In

connection with that, there is an urgent need to

determine material characteristics, especially of

materials after the application of modern tech-

nological property-enhancing treatments. There

also exists the need to develop calculation

methods of fatigue resistance after thermal and

thermochemical treatment. This, however, is the

next stage of activity and is possible to carry out

only when the basic fatigue properties of the

steel following heat treatment are known.

The carbonitriding treatment is used for

components exposed to lighter loads and sub-

jected to wear as well as bending (Ref 8–10). For

those components, which are subjected to con-

tact fatigue during service, the case depths are

designed deeper. For the present series of tests, a

Fig. 6

Microhardness traverses across a nitrided case on

40HM (4140)-grade steel. 1, tempering temperature

550



C, time 4 h; 2, tempering temperature 550



C, time 16 h; 3,

tempering temperature 620



C, time 4 h; 4, tempering tem-

perature 620



C, time 16 h

Fig. 7

Microhardness traverses across a nitrided case on

38HMJ (Nitralloy 135M)-grade steel. 1, tempering

temperature 550



C, time 4 h; 2, temperi ng temperature 550



time, 16 h; 3, tempering temperature 620



C, time 4 h; 4, tem-

pering temperature 620



C, time 16 h

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case depth of 0.7 mm was selected. The optimal

microstructure of carbonitrided components is

ﬁne acicular martensite with a small amount of

retained austenite and containing no coarse

carbide precipitations (Ref 8–10).

Specimens prepared to meet the aforemen-

tioned conditions were subjected to rotational-

bending and one-point bending fatigue tests.

Such types of loading were selected based on the

premise that bending is the most common

method of loading during service, as well as the

fact that it is during bending that one can observe

the most favorable and strongest effect of sur-

face strengthening.

Simpliﬁed Smith curves were plotted to

determine the fatigue resistance for at least three

Table 4 Fatigue limit values across the specimen

section

Fatigue limit (s

1

MPa

Experimental

results

Theoretical

results

Tempering temperature

550 °C 620 °C 550 °C 620 °C

Core 613 550 618 550

At surface ... ... 852 819

At location of initiation

of fracture

820 735 618 550

Fig. 9.

Location of fatigue crack initiation on nitrided 40HM

(4140)-grade steel. Original magniﬁcation: 100·

Fig. 8

Distributions of fatigue limit, curves 1 and 2; residual stresses, curve 3 (550



C) and curve 4 (620



C); extraneous loading,

curves 5 and 6, 40HM (4140)-grade steel

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methods of bending (the Wo

hler curve), as well

as static strength and yield strength for a given

type of loading and materials. The fatigue tests

were carried out with the following coefﬁcients

of cycle asymmetry: R = 1, R = 0.1, and R =

0.3. The coefﬁcients of 0.1 and 0.3 were selected

to ensure the possibility of running the tests only

within the range of one-sided bending stresses.

The fatigue characteristic was developed for a

material in the quenched and tempered condition

as a reference and, for materials with a diffusion

case, heat treated to the same condition as the

heat-treated-only version. Once these values

were known, the surface coefﬁcient of strength-

ening was determined from the equation:

1

(Eq 5)

where s

1

is the fatigue limit of the enhanced

specimen, and s

1

is the fatigue limit of the

reference specimen.

Rotational-bending fatigue tests were carried

out on the Schenck fatigue machine with a

constant distribution of the bending movement

along the length of the specimen. The frequency

was 100 Hz.

One-point bending tests were carried out on

the Amsler machine. In order to obtain the

bending effect on this machine, a prototype

addition was designed that, through a lever,

allows loading of the tested section of the speci-

men under a constant bending moment (Fig. 10).

The frequency was 150 Hz. Tests were carried

out to N

= 10

cycles.

The material used in these tests was the

18HGT grade, normalized, with a ﬁne-grained

ferritic-pearlitic microstructure. The chemical

composition is given in Table 5. Tests were also

carried out on carbonitrided specimens. Carbo-

nitriding of specimens from 18HGT-grade steel

was carried out at a temperature of 860



Cin

an endothermic atmosphere enriched with am-

monia and natural gas.

Metallurgical evaluations were carried out on

18HGT steel in the quenched and tempered only

and carbonitrided condition. In the normalized-

only condition, the specimens showed a ferritic-

pearlitic microstructure with very ﬁne-grained

pearlite (Fig. 11). The microstructure of speci-

mens with diffusion cases was determined based

on micrographs and microhardness measure-

ments.

Specimens made from 18HGT steel, after

carbonitriding and quenching and tempering,

exhibit a microstructure of tempered martensite

in the subsurface zone (Fig. 12) and a bainitic-

martensitic microstructure in the core (Fig. 13).

The microstructure of the core was 550 HV

0.1

To determine the fatigue resistance, a static

bending test was carried out. For the heat treated

Fig. 10

Schematic of equipment for fatigue testing in the

rotational-bending mode

Table 5 Chemical composition of specimens

prepared from steel grade 18HGT

Specimen

No./diameter,

Chemical composition, %

C S Mn Cr Si Ni Cu Ti

1ø 12 0.187 0.014 0.89 1.07 0.26 0.06 0.13 0.05

2 ø 12 0.185 0.015 0.87 1.12 0.28 0.06 0.12 0.05

3 ø 12 0.189 0.014 0.89 1.12 0.32 0.06 0.12 0.05

1 ø 14 0.216 0.009 1.00 1.00 0.35 0.13 0.13 0.07

2 ø 14 0.225 0.009 1.02 1.02 0.34 0.13 0.12 0.08

3 ø 14 0.215 0.009 0.98 1.02 0.33 0.12 0.14 0.08

Fig. 11

Microstructure of heat-treated-only 18HGT-grade

steel. Etched with nital. Original magniﬁcation: 500·

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(normalized)-only steel, it was not possible to

obtain a fatigue resistance value because of the

ductility of the material. Only the yield strength

was determined, and it amounted to 822.8 MPa

on specimens.

The static bending test carried out on carbo-

nitrided specimens is shown in Fig. 14. In this

case, it was not possible to determine the yield

strength, and only the relative bending strength

was established as 2289.8 MPa.

In order to obtain a full characteristic of the

properties of surface-enhanced materials and of

the reference version, a static tensile test was

performed. The average value of tensile strength

for specimens without a diffusion case was

599.8 MPa, and yield strength was determined

as R

= 430 MPa. Similarly, as in the case of the

technological bending test, it was not possible to

determine the yield strength for the carboni-

trided material (Fig. 15).

An analysis of static test results delivers new

data. The tensile plot for the carbonitrided

material is characteristic of brittle materials.

There is no necking and no elongation of the

specimen. Similar behavior was noted when the

bending strength test was performed. In neither

case was it possible to determine the yield

strength.

Based on fatigue tests for rotational bending,

which were performed on specimens made from

carbonitrided and heat treated (normalized)-

only material, it was possible to determine the

coefﬁcient of surface strengthening, that is, the

ratio of m = s

1

(with diffusion case) to s

1

(with no case). For 18HGT steel after carbo-

nitriding, this coefﬁcient was 2.48.

With the aid of results obtained in static and

fatigue tests for the case of two- and one-side

Fig. 12

Microstructure of carbonitrided case on specimen

made of carbonitrided 18HGT-grade steel. Etched

with nital. Original magniﬁcation: 500·

Fig. 13

Microstructure of core of specimen made of carbo-

nitrided 18HGT-grade steel. Etched by nital. Orig-

inal magniﬁcation: 500 ·

Fig. 14

Plot of static bending test of carbonitrided 18HGT-

grade specimen

Fig. 15

Plot of static tensile test of carbonitrided 18HGT-

grade specimen

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bending, simpliﬁed Smith curves were plotted

for the heat-treated-only material (Fig. 16) and

for the carbonitrided material (Fig. 17). To plot

the chart, values of unlimited fatigue resistance

were used from the Wo

hler curves. The upper

limit of the chart for the heat-treated-only

material is the yield strength obtained from the

bending test.

The Smith curve for materials after thermo-

chemical treatment differs from that for the

reference heat-treated-only material, because its

upper limit is determined by the bending yield

strength, R

(Fig. 17). The designer of the

component, basing his design on the presently

available tables containing data of the ultimate

properties of the steel after hardening and fati-

gue properties for alternating stresses, creates a

design that consumes large amounts of material.

As the result of using values of s

1

taken from

catalogues, the strength of the assembly is

compromised. The values for fatigue resistance,

, are much higher, which can be seen from

the Smith plot (Ref 11).

Based on the results of fatigue resistance tests

for carbonitrided 18HGT steel, shown for com-

parison in Table 6, it can be concluded that

carbonitriding ensures good strength properties.

Summarizing the results of the tests presented

in the form of Smith plots, the designer, using

the characteristics of the steel achieved after

thermochemical treatment, will be able to

reduce the amount of material used and to

choose an optimal technological version, thus

ensuring high parameters and longer life of the

designed component.

Summary

Testing of properties of structural materials

is essential for development and manufacturing

Fig. 16

Simpliﬁed Smith plot for 18HGT-grade steel after

normalizing

Fig. 17

Simpliﬁed Smith plot for 18HGT-grade steel after

carbonitriding

Table 6 Comparison of fatigue properties of

18HGT-grade steel after different types of thermal

and thermochemical treatment

Strength parameter

Heat Treatment

Normalizing Carburizing Carbonitriding

Yield strength

), MPa

430 ... ...

Tensile strength

), MPa

599.8 1302.3 1303.2

Relative elongation

), %

30.45 ... ...

Necking (Z), % 70.06 ... ...

Bending yield strength

g0.2

), MPa

822.8 ... ...

Bending strength (R

MPa

... 2604.1 2889.8

Bending fatigue limit

1

), MPa

358.0 745.0 887.1

Surface-strengthening

coefﬁcient, m

1 2.08 2.48

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as well as for the practice of design and

construction of machines. A large number of

assessment criteria for materials properties, as

well as methods and testing equipment, stem

from the multitude of different mechanisms for

failure of structural materials from which com-

ponents, assemblies, and whole machines are

made. Among the most important of these are

failures due to the action of static loading. There

is, however, an entire spectrum of different types

of dynamic loading, as well as volume fatigue,

impact loading, contact stresses, destruction by

wear of mating surfaces in friction, and others

that affect the performance of engineering

components.

Processes connected with the calculation and

design of machine components and assemblies

call for a database of materials properties.

Modern computational methods and their con-

stant development force the necessity of deter-

mining an ever growing number of parameters

that describe the properties of materials. A good

example of this is the attempt to describe the

mechanism of material failure through the

coefﬁcient of stress intensity (K

), both when

the failure takes place under variable loads

(fatigue) as well as when it occurs due to wear in

processes involving friction. Computation of the

life of machine components in conditions of

variable loading calls for information not only

about the value of the fatigue limit but also about

the angle of inclination of the straight line in the

range of limited fatigue strength, and also about

the parameters of the bend point of the fatigue

curve.

Modern structural material does not need to

be homogeneous throughout its section. A great

number of steels, plastics, and other metallic

materials call for enhancement of the surface,

due to the constant quest for decreasing material

and energy consumption as well as increasing

properties. Surface layers are, in the majority of

cases, superﬁcially hardened layers formed by

thermal and thermochemical treatment or other

enhancement technologies, such as surface work

hardening and anticorrosion coatings.

Testing of materials properties after heat

treatment shows that the achievement of desired

service properties is connected with the appro-

priate selection of parameters not only in the

ﬁnal thermochemical treatment but also in the

prior volume heat treatment. In the case of

nitriding of machine components, this technol-

ogy is usually preceded by quenching and tem-

pering at a minimum temperature 20



C above

the subsequent nitriding temperature. Initial

hardening by quenching and tempering is cri-

tical to core hardness and to the properties of the

nitrided case and affects the fatigue resistance of

the material after nitriding.

An analysis of fractured surfaces of nitrided

specimens, exposed to service in conditions of

rotational bending, revealed that the weakest

location on the specimen cross section is the

zone of transition of the nitrided case to core.

The method of designing surface cases enables

an explanation of the root cause of fatigue crack

initiation under the nitrided case. The fatigue

limit in the cross section of the specimen was

described as a function of microhardness and

residual stresses. The initiation of fatigue cracks

takes place in the location where stresses from

extraneous sources exceed the value of the

fatigue limit, which is obviously in agreement

with conditions of strength. The favorable effect

of core hardness on fatigue resistance was

observed.

The investigations showed good fatigue

properties of cases obtained by carbonitriding,

as well as a lowering of ductility of these cases.

Results of investigations, presented in the form

of Smith plots, conﬁrm the necessity of further

pursuing investigations in this ﬁeld. In designing

practice, the application of obtained results is the

least expensive method of lowering material

consumption and enhancing the life of machine

components.

It was established that fatigue resistance is

signiﬁcantly affected not only by compressive

stresses but also by tensile stresses.

Among the parameters describing the state of

residual stresses, the distribution of stresses was

of more signiﬁcance, followed by the value of

the residual stresses.

Models of surface layers described in litera-

ture are difﬁcult to implement in industrial

practice. There appears to be a need for the

creation of such a model of the surface layer.

This could be described by parameters that can

be used in strength calculations and that would

allow its application in instances of different

types of extraneous loading, depending on the

type of service of the component. This model

could become the basis for predicting the state of

the surface layer, based on required usable

properties of machine components. Work on

such a model is carried out in two directions:

 Based on experimental description of the

state of the surface layer through hardness

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traverses, residual-stress distributions, and

distributions of element concentrations, for

example, carbon and nitrogen

 Based on a description of the material

through the theory of elasticity and solving

constitutive equations by numerical methods

Surface layer design for the criterion of fati-

gue failure is based on a comparison of the local

fatigue resistance with local stresses occurring at

critical locations in the investigated component.

Contemporary machines and designs should

be characterized by required life and reliability,

featuring a sufﬁcient life between overhauls,

depending on the type of service, while at the

same time fulﬁlling the requirements for ecol-

ogy and ergonomics. Such parameters should

be attained concurrently with a reduction of

material and energy consumption during manu-

facture and service. This task may be achieved

only when modern computational methods are

implemented along with modern technology and

proper service conditions at each stage of the

product life, that is, study phase, design, manu-

facture, service, and recycling.

The implemented computational methods

enable the design of products according to

strength criteria, somewhat less often according

to tribological criteria, and least often pertaining

to corrosion.

Contemporary machine components and

assemblies are subjected in service to the joint

interaction of strength, tribological, and corro-

sion hazards. On the other hand, the implemented

computational methods enable the design of

products with one selected mode of failure.

In the construction of machine components,

there are many parts (crankshafts, threaded

joints, springs) that are concurrently exposed to

different types of failure hazards during service:

mechanical, tribological, or corrosive. Similar

elements of construction (bridges, masts, cables,

earth-moving and mining machines) are ex-

posed to concurrent hazards of fatigue-type

stresses and corrosion.

Classical strength or tribological calculations

do not take into account the factor of time.

During service, due to the processes of fatigue,

tribological, or corrosive deterioration, there

occurs a change in the properties of the system

being evaluated. Tribological and corrosive

processes cause a change in the geometry and

surface condition of the component. This, in turn,

causes a change in the state of stresses in working

systems, affecting their life and reliability.

Therefore, the development of failure criteria,

taking into account the joint effect of an accu-

mulation of damage due to the working of

alternating loads, wear by friction, and the action

of corrosion, is a very important task, because

the determination of the criteria for failure will

enable proper selection of surface layers for the

given service condition.

REFERENCES

1. A. Nakonieczny, Podwyz

szenie wytrzy-

małos

ci zme˛czeniowej cze˛s

ci maszyn

przez obro

bke˛ cieplna˛ i powierzchniowa˛

obro

bke˛ plastyczna˛ (Enhancement of Fa-

tigue Strength through Heat Treatment and

Surface Work Hardening), Proc. XXIV

Seminar IMP, XI on Metallurgy and Heat

Treatment, Oct 23–24, 1984 (Warsaw), IMP

(translated from Polish)

2. T. Babul, A. Nakonieczny, and J. Taci-

kowski, Wpływ umocnienia podłoz

ana

wytrzymałos

zme˛czeniowa˛ azotowanej

stali 40HM (The Effect of Core Strength-

ening on the Fatigue Resistance of Nitrided

40HM Grade Steel), Proc. III Polish Sci-

entiﬁc Conference on Surface Treatment,

Cze˛stochowa-Kule, Politechnika Lodz,

1996 (translated from Polish).

3. A. Nakonieczny and J. Tacikowski, Analiza

pe˛kania zme˛czeniowego stali azotowanych

(An Analysis of Fatigue Fracturing of

Nitrided Steels), Proc. First Polish

Scientiﬁc Conference on Modern Tech-

nology in Surface Engineering, Sept

1994, Politechnika Lodz (translated from

Polish)

4. A. Nakonieczny, The Effect of Residual

Stresses and Hardness on Fatigue Behavior

of Surface Treated Materials, Proc. MAT-

TEC 91, Technology Transfer Series,

A. Niku-Lari, Ed., 1991

5. B. Winderlich, Das Konzept der lokalen

Deuerfestigkeit und seine Anwendung auf

martensitische Randschichten, in benson-

dere Laserhartungsschichten, Mater. wiss.

Werkst. tech., Vol 21, 1990, p 378–389 (in

German)

6. V.P. Kogaev, N.A. Machutov, and A.P.

Gusenkov, Rasc

ety detalej mas

in i kon-

strukcij na proc

nost

i dolgovec

nost

, Mas

nostroenie, Moskva, 1985, p 150–182

(in Polish)

252 / Failure Analysis of Heat Treated Steel Components

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7. J. Tacikowski and A. Nakonieczny, Report

114,01,0163, IMP, Warsaw, 1992

8. A. Nakonieczny, Dissertation, Russian

Academy of Science, Moscow, 1991

9. W. Olszan

ski, More Important Problems

Pertaining to the Austenitic Carbonitriding

Process, XVI Seminar, VII on Metallurgy

and Heat Treatment Book 2, IMP, Warsaw,

1977

10. J. Wyszkowski, Nowoczesne tendencje w

zakresie nawe˛glania i we˛gloazotowania

gazowego, (Modern Trends in the Field

of Gas Carburizing and Carbonitriding),

IMP, Warsaw, 1974 (translated from Polish)

11. W. Olszan

ski, I. Sułkowski, J. Tacikowski,

and J. Zys

k, Obro

bka cieplno-chemiczna,

(Thermochemical Treatment) Book 5, IMP,

Warsaw, 1979

Fatigue Fracture of Nitrided Layers / 253

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