i

Nondestructive Characterization of Microstructures and Determination of Elastic

Properties in Plain Carbon Steel using Ultrasonic Measurements

Vera Lúcia de Araújo Freitas1, Victor Hugo C. de Albuquerque2, Edgard de Macedo Silva3,

Antonio Almeida Silva1, João Manuel R. S. Tavares4

1Universidade Federal de Campina Grande (UFCG), Departamento de Engenharia Mecânica

(DEM), Av. Aprígio Veloso, 882, Bodocongó 58109-970, Campina Grande-PB, BRASIL

Email: vera@dem.ufcg.edu.br, almeida@dem.ufcg.edu.br

2Universidade de Fortaleza (UNIFOR), Centro de Ciências Tecnológicas (CCT), Núcleo de

Pesquisas Tecnológicas (NPT), Av. Washington Soares, 1321, Sala NPT/CCT, CEP 60.811-

905, Edson Queiroz, Fortaleza, Ceará, BRASIL

Universidade Federal da Paraíba (UFPB), Departamento de Engenharia Mecânica (DEM),

Cidade Universitária, S/N - 58059-900 - João Pessoa/PB, BRASIL

Email: victor.albuquerque@fe.up.pt

3Centro federal de Educação Tecnológica da Paraíba (CEFET PB), Área da Indústria,

Avenida 1º de Maio, 720 - 58015-430 - João Pessoa/PB, BRASIL

Email: edgard@cefetpb.edu.br

4Faculdade de Engenharia da Universidade do Porto (FEUP), Departamento de Engenharia

Mecânica (DEMec) / Instituto de Engenharia Mecânica e Gestão Industrial (INEGI), Rua Dr.

Roberto Frias, s/n - 4200-465 Porto, PORTUGAL

Email: tavares@fe.up.pt

Corresponding author: Prof. João Manuel R. S. Tavares Faculdade de Engenharia da Universidade do Porto Departamento de Engenharia Mecânica Rua Dr. Roberto Frias, s/n 4200-465 Porto, PORTUGAL email: tavares@fe.up.pt, url: www.fe.up.pt/~tavares Phone: +351 22 5081487, Fax: +351 22 5081445

ii

Nondestructive Characterization of Microstructures and Determination of Elastic

Properties in Plain Carbon Steel using Ultrasonic Measurements

Abstract

This paper presents a reliable and fast nondestructive characterization of microstructural and

elastic properties of plain carbon steel, based on ultrasonic measurements for ultrasonic

velocity and attenuation. Microstructures considered are: ferrite, pearlite, ferrite-pearlite and

martensite. Ultrasonic velocities considered longitudinal and transverse waves and modulus of

elasticity and modulus of shear were determined by correlations between them. In carbon

steels, a lower value of ultrasonic velocity was observed for the martensite in relation to the

other microstructures, while the opposite was observed in terms of ultrasonic attenuation. The

results show that the use of ultrasonic measurements to obtain ultrasonic velocities and

attenuations, in order to correlate them with the involved microstructures, as well as to

determine the modulus of elasticity and modulus of shear, is very fast and reliable, permitting

the characterization of nondestructive microstructural and elastic properties.

Keywords: Nondestructive testing; Microstructures; Plain carbon steel; Transverse and

longitudinal wave velocities; Ultrasound; Materials characterization.

1

1. Introduction

One of the main purposes of nondestructive testing (NDT) is to ensure the

functioning of components. The most common way of doing this is by checking for

defects in components through one or a combination of different techniques of

nondestructive testing. If defects are present, they are characterized by their location,

dimension, orientation, shape and nature to define the acceptability of the component in

the provided conditions established for the correspondent operation. Besides the

characteristics of the defects, there are other parameters equally important in the

evaluation of structural integrity of components, as well as their microstructural and

mechanical properties.

Usually, microstructural analysis is carried out through metallography, while

mechanical properties are determined through mechanical tests. Often, destructive tests

are performed on test pieces with standard dimensions and shapes, based on the

assumption that they truly represent the material under analysis. Even though,

technologies used in destructive tests increasingly reproduce the conditions of use of the

component in question, the obtained results cannot truly presume how it will function in

normal conditions, due to the unpredictability of some factors, such as environmental

conditions, degradation of properties, micro-damages, residual tensions and other

factors that may have a negative influence on its service life.

Characterization of material properties through nondestructive testing takes on

an increasingly important role, especially in the industry, as it can be used to monitor

components during the manufacturing process, as well as while in operation. Some

nondestructive techniques and applications include, for example, the use of X-ray

images and CT-scan to analyze delamination defects in mixed materials [1, 2], the use

of thermographic images to analyze metals [3], the use of computer simulation and

modeling to evaluate microstructures in different classes of cast iron from

metallographic images [4, 5].

In addition to the nondestructive techniques previously mentioned, another

technique widely used to analyze and characterize materials is ultrasonic testing. In

characterizing internal structures of materials, interaction of the ultrasound signal with

microstructures can be evaluated with regards to changes in the velocity of propagation,

loss of amplitude (or attenuation) and analysis of backscattered signal [6, 7]. Therefore,

several works have been developed based on ultrasonic measurements to obtain the

sonic velocity and attenuation in order to evaluate the mechanical properties of different

plain-carbon steel microstructures. For example, in duplex stainless steel subjected to

different thermal aging conditions, the ultrasonic velocity undergoes significant

modifications as it detects changes in stages due to the aging heat treatments applied,

making it possible to follow and study the embrittlement kinetics [8, 9]. The evaluation

of water immersed specimens of En3A, En9 and En25 steel behavior at 5 MHz

ultrasound backscattered according to the Rayleigh angle has been correlated to the

microstructure features induced by heat treatment [10]. The modulus of elasticity and

internal friction of induction hardened and unhardened SAE 1050 steel at ambient

temperatures were determined in [11] by resonant ultrasonic spectroscopy, in which all

components of the internal-friction in martensite were higher than those of ferrite-

pearlite, but lower than those of α-iron. Ultrasonic longitudinal wave velocity measured

by the laser-ultrasonic technique is compared to dilatometry for the monitoring of

austenite decomposition of low alloy steel [12], in which these techniques can be

applied to monitor austenite transformation of real products in an industrial production

line that would be extremely difficult with dilatometry. The study of the influence of

steel heat treatment on ultrasonic absorption measured by laser ultrasonics is proposed

in [13], the analysis of ultrasonic attenuation and microstructural evolution in a low-

carbon steel (ASTM-A105), containing 0.21 wt.% C is performed in [14], and the

measurement of ultrasound velocities and modulus of elasticity of steel at both sub-zero

and elevated temperatures is done in [15].

The main aim of this work is to evaluate the capability of ultrasonic

measurements to characterize different kinds of plain carbon steel microstructures,

analyzing the ultrasonic velocities and attenuations, and then to obtain modulus of

elasticity and modulus of shear in AISI 1006 (with ferrite microstructure), AISI 1020

(with ferrite-pearlite microstructure), AISI 1045 (with ferrite-pearlite microstructure and

carbon content higher than that of AISI 1020, and consequently higher amounts of

pearlite in normalized samples, annealed and quenched in oil; and with martensite

microstructure when quickly quenched in water), and AISI 1080 (with pearlite

microstructure). Thus, seven microstructure variations are analyzed through ultrasonic

measurements: three of them with different carbon contents in the material - AISI 1006

with lower quantities of carbon, followed by AISI 1020, AISI 1045 and AISI 1080

respectively, and four other microstructures obtained through heat treatment on AISI

1045, provided that annealing, normalizing, oil quenching and water quenching are the

heat treatments considered. These materials were selected because of their wide use in

many industrial applications. For example, AISI 1006, which is soft and very ductile,

has been used in applications that require severe bending and welding, such as panels

for automobiles or appliances. In addition, AISI 1006 has also been used in magnetic

core applications. On the other hand, AISI 1020 responds well to cold work and heat

treatments, combines good machinability, workability and weldability, and has been

used in the manufacturing, for example, of shafts, gears, hard wearing surfaces, pins,

chains and case hardened parts where core strength is not critical. AISI 1045 steel is

valuable for induction- or flame-hardened components and suitable for most

engineering and construction applications, like shafts, pins, axles, rods, studs, machine

parts, bolts, gears, pinions, forgings and bulldozer edges. Finally, AISI 1080 has been

used to construct, for example, general-purpose tools, springs and machinery parts that

require high hardness and high resistance to wear.

This paper is organized as follows: the following section presents the materials

used, describes different heat treatments performed in order to obtain the intended

microstructures, and indicates the ultrasonic measurements applied in their

characterization. Section 3 presents the results, as well as a discussion on them. Finally,

section 4 presents conclusions on advantages of nondestructive inspection based on

ultrasonic measurements.

2. Materials and Methods

The carbon steels considered in this study were AISI 1006, 1020, 1045 and

1080, because their microstructures can be identified through metallographic analysis

by optical microscopy, which is important to evaluate the microstructures determined

by ultrasonic measurements. The selected carbon steel samples, 5 of each type of steel

analyzed, were adjusted to the following dimensions: AISI 1006 and 1080 with

50x20x12 mm3, AISI 1020 and 1045 with Ø25.4x12 mm2.

After preparation, the samples underwent austenitization in an electric resistance

furnace with a capacity of up to 1473 K (1200 °C) in order to homogenize their original

microstructures. Austenitizing temperatures were 1213 K (940 °C) for AISI 1006

samples and 1133 K (860 °C) for AISI 1020. These steel samples were later cooled in

still air. Regarding AISI 1080, the austenitizing temperature was 1053 K (780 °C), and

the samples were cooled inside the furnace to avoid the formation of undesired

microstructures such as martensite and bainite.

With respect to AISI 1045, four different kinds of heat treatment were analyzed

and 5 steel samples were subjected to each treatment. Austenitizing temperature of 1113

K (840 °C) was employed. The first sample was quenched in water (WQ) with fast

agitation in order for the whole extent, from the centre to the surface, to be formed

exclusively of martensite microstructure; the second one was quenched in oil (OQ); the

third and fourth samples were submitted to normalizing (N) and annealing (A)

treatments, and cooled in still air. The samples of AISI 1045 were austenitized for 1

(one) minute per millimeter of thickness.

After obtaining the microstructures, all the samples were examined through

conventional metallographic testing, hereby undergoing sanding, polishing with

diamond paste and chemical etching with a 3% nital, for subsequent analysis through

optical microscopy, which aimed to identify and confirm the microstructures in each

one of them. After confirming microstructures in each sample, they were first machined

with a planer to adjust to desired dimensions; next, they were arranged to ensure

parallelism between faces, eliminating roughness, visible irregularities, oxidations and

other factors that influence ultrasonic measurements, which was performed after that.

For ultrasonic characterization, the pulse echo technique and direct contact

method were used to obtain ultrasonic velocity and attenuation parameters. As coupling

material, SAE 15W40 lube oil was used for the longitudinal wave measurements while

honey was used for the transverse wave measurements. A Krautkramer ultrasound

device (GE Inspection Technologies, USA, model USD15B) was used, connected to a

100 MHz digital oscilloscope (Tektronix, USA, model TDS3012B), which transmits the

ultrasonic signals to a computer, so they can be processed. All signals were captured

with 10,000 points with a sampling rate of 1 Gs/s. After acquisition, data were properly

processed in order to determine ultrasonic velocities and attenuation involved.

Ultrasonic velocity measurements for all samples were obtained by using

commercial NDT ultrasonic transducers: three transducers for longitudinal wave

measurements, one of 4 MHz (Krautkramer, Germany, model MB4S), another one of 5

MHz (Krautkramer, Germany, model MSW-QCG) and the third one of 10 MHz

(Olympus, USA, model V112), and one transducer for the transverse wave

measurements of 5 MHz (Valpey Fisher Corporation, USA, model SF052). The choice

of these transducers was based on the authors’ previous experience in this kind of NDT

and knowledge concerning the materials understudy [8, 9, 21].

For each sample, five signals with two adjacent echoes per signal were captured

related to velocity measures. Next, the time between the first two echoes was measured

through an echo overlapping algorithm [16]. With the wave propagation time and

sample thickness values, obtained by using a micrometer at the same capture points of

the ultrasound signals, it was possible to determine the average velocity of wave

propagation through equation:

0

2 ,Xv =τ

(1)

in which X is the thickness of the sample [m] and 0τ is the time of the wave course [s]

until the two adjacent echoes ( 1B and 2B ) overlap each other, and its value is

determined considering:

1 2B (t).B (t )dt .∞

−∞

− τ∫

(2)

Although, the time measurement can be obtained directly from the oscilloscope,

as previously mentioned, the echo overlapping method was used for it provides greater

sensibility and maximum accuracy [16].

Ultrasonic attenuation was calculated from reduction of the amplitude of the

ultrasound impulse, and quantified in terms of attenuation coefficient, α , [dB/mm]

given as:

0

1

20 log ,2

Ax A

α = (3)

in which x is the sample thickness [mm], 0A is the amplitude of the first echo [dB], and

1A is the amplitude of the second echo [dB]. In order to calculate ultrasonic attenuation,

longitudinal waves with frequency of 4 and 5 MHz were considered, since the

frequency of 10 MHz presented values very close to the ones from these frequencies.

The modulus of elasticity (E) [GPa] and the modulus of shear (G) [GPa] were

calculated based on the ASTM E 494-2005 (Measuring Ultrasonic Velocity in

Materials) standard, through the equations:

( )( )2 2 2T L T

2 2L T

V 3V 4VE

V V

ρ −=

−, (4)

2 ,TG V= ρ (5)

in which LV and TV are the longitudinal and transverse wave velocities [m/s],

respectively, and ρ is the material density [g/cm3].

3. Results and Discussion

Metallographic analysis and evaluation through optical microscopy qualitatively

confirmed the microstructures of carbon steel AISI 1006, 1020 and 1080 presented in

Figures 1a), 1b) and 1c), respectively. Figures 1d), 1e), 1f) and 1g) present the

micrographs of AISI 1045 samples quenched in water, in oil, normalized and annealed,

respectively.

The micrographs presented in Figures 1a) and 1b) show typical microstructures

of hypoeutectic steel AISI 1006 and 1020, respectively. These steels at room

temperature are made up of proeutectoid ferrite and pearlite for the cooling temperature

is close to equilibrium conditions; when the carbon content in the material gets closer to

0.77 wt.% C, the higher the quantity of ferrite the lower the carbon content and the

higher the percentage of pearlite the closer it is to the eutectoid point.

The AISI 1080 eutectoid steel presented an annealed pearlite microstructure

when slowly cooled (inside the furnace), Figure 1c. Structural characteristics and

properties of pearlite, which is formed by hardened ferrite, depend on the cooling

velocity, which causes a difference in pearlite lamellar space. For this reason, pearlite is

defined as thick and thin, which interferes in ultrasonic results. Thus, the smaller the

lamellar space, the higher the value of ultrasonic velocity.

Micrographs presented in Figures 1d) to 1g) for AISI 1045 hypoeutectoid steel

samples, after heat treatment, present the expected microstructures for these steels based

on the diagram of continuous cooling transformation (CCT): martensite, thin or thick

ferrite-pearlite. The martensite presented in Figure 1d) was generated from fast cooling

in water with moderate agitation. As for its morphology, it is known that in alloys

containing less than 0.6 wt%. C, the martensite grains are formed as parallel battens

(long and thin plates) aligned in bigger structural entities called blocks. Microstructural

details of martensite formed as batten are very thin and, therefore, difficult to be seen

through optical microscopy. It is known that in a steel sample submitted to quenching

heat treatment, the microstructures can differ significantly from the outer surface to its

centre due to differences in cooling velocity, which decreases as it progresses towards

the centre. When cooling velocity is enough to cause diffusion, other microcomponents

can appear, like pearlite and bainite. In the case of the AISI 1045 sample submitted to

heat treatment and quickly cooled in water, they were only made of martensite, as

intended, Figure 1d. The microstructures expected for the samples of AISI 1045

quenched in oil, normalized and annealed are presented in Figures 1e) to 1g),

respectively. The microstructural product identified was pearlite (thin or thick) plus pro-

eutectoid ferrite. One can conclude that as the slower is the cooling, thicker is the

pearlite. This means that the sample quenched in oil presents a microstructure composed

of thin ferrite-pearlite, while in the annealed sample the microstructure is thick ferrite-

pearlite, which changes the ultrasonic velocity and attenuation values of the materials.

The obtained values of ultrasonic velocities related to longitudinal waves in 4, 5

and 10 MHz frequencies are presented in Figure 2a), and related to transverse waves in

5 MHz of frequency in Figure 2b), for the AISI 1045 microstructures resulting from

heat treatments quenched in water (WQ) and in oil (OQ), as well as normalizing (N) and

annealing (A) with cooling in the open air.

For the samples of AISI 1006, 1020, 1080 and 1045 annealed (A) and quenched

in water (WQ), the values of the average longitudinal wave velocities are presented in

Figure 3a), and the average transverse wave velocities in Figure 3b). The same

microstructural characterization trend can be observed in these figures, in other words,

the ultrasonic velocity for the sample of AISI 1045 annealed always presents the highest

values, followed by the samples of normalized 1045 steels, 1045 quenched and cooled

in oil, and finally, the sample of 1045 steel quenched and cooled in water forming a

martensite structure with lower average ultrasonic velocity.

The experimental ultrasonic velocities obtained for longitudinal and transverse

waves were sensitive to microstructural variations due to heat treatments performed on

samples of AISI 1045. However, they revealed to be minimally sensitive to variation of

carbon content in samples of AISI 1006, 1020, 1080 and 1045 annealed and quenched

in water, Figures 2 and 3. In the graphs presented in these figures, it is possible to

observe the same behavior in all frequencies used, which allows us to conclude that the

obtained results are reliable.

Regarding the stages of AISI 1045, martensite presented the lowest ultrasonic

velocity registered and thick ferrite-pearlite presented the highest. These results are in

line with those obtained by Papadakis [17], Gür and Tuncer [18], and Gür and Cam

[19]. For the other samples, the lowest velocity was seen in the AISI 1080 (pearlite) and

the highest in AISI 1006 (ferrite) and 1020 (ferrite-pearlite), whose values are slightly

higher than those found in AISI 1045 (ferrite-pearlite). Comparing ferrite (AISI 1006),

pearlite (AISI 1080) and martensite (quenched in water AISI 1045) microstructures, a

higher ultrasonic velocity for ferrite (5927.83 ± 4.12) can be observed, next for pearlite

(5916.34 ± 1.60) and finally for martensite (5878.47 ± 2.91). These measurements were

obtained by considering longitudinal waves with 4, 5 and 10 MHz of frequency, by

which a small increase in velocity for higher frequencies was verified. For transverse

waves, 5 MHz frequency was considered.

The lowest ultrasonic velocity verified for martensite can be explained by the

great quantity of internal tension it presents, resulting from crystal lattice distortions

caused by the increase in volume during the austenite-martensite transformation. The

transformation of austenite into ferrite, pearlite or bainite can also cause an increase in

volume, but this fact is not significant. Macro-tensions caused by thermal gradient are

also minor when the geometry and the small thickness of the samples are considered.

Previous studies showed that ultrasonic velocity decreases as the plastic deformation

level of the material increases, due to an increase in discrepancy density [20].

According to Gür and Tuncer [18], the ultrasonic velocity in martensite is essentially

affected by changes in the modulus of elastic of individual grains, in the crystal lattice

distortion level and in the orientation of primary austenite grains. The ferrite structure

does not have many variations in orientation of grains due to the thicker structure, and

this facilitates propagation of ultrasound in this stage. The highest ultrasonic velocity is

verified in thick ferrite-pearlite (AISI 1045 annealed (A)), due to a more ample space

between pearlite lamella and higher quantity of ferrite. This means that in thicker stages,

the velocity of ultrasound propagation will be higher.

For the materials studied and the frequencies adopted, the ultrasonic

measurements show that fine grain sizes led to lower ultrasonic velocity than coarse

grain sizes, this was also observed by Albuquerque et al. [21]. However, the opposite

behavior was reported by Palanichamy et al. [22]. Additionally, Hirsekorn in [23, 24]

showed that ultrasonic velocity is not only dependent on grain size but also on

frequency. Besides the variation in terms of the grain size, ultrasonic measurements are

also sensitive to the presence of new phases/precipitates resultant from thermal aging

treatments [8, 9]. In addition, the type of microstructure also affects the ultrasonic

measurements [11]: Martensite presents high resistance to ultrasound waves, because of

its compact and fine granulation. On the other hand, pearlite presents less resistance to

ultrasound waves in relation to martensite, since it is composed of ferrite and cementite.

In the case of this microstructure, one can also consider fine pearlite, which exhibits

small lamellar spacing, as well as the coarse pearlite that presents large lamellar spacing

and consequently is lesser resistant to ultrasound waves than the fine pearlite. Finally,

ferrite is the one that offers the least resistance to ultrasound waves as this

microstructure presents equiaxial grain size and the largest grain size, when in

comparison to martensite and pearlite. The influence of the ferrite microstructure on

ultrasonic measurements was also verified during this work.

Ultrasonic measurements are also directly related to the carbon content of the

material understudy, and it has been commonly accepted that the higher the carbon

content the lower the associate ultrasonic velocity is. Our experimental findings

confirmed this behavior (Figure 3), which was also observed by Kim and Johnson in

[11].

The average values of five ultrasonic attenuation measurements were considered

for longitudinal waves in 4 and 5 MHz of frequency. Figure 4a shows ultrasonic

attenuation results for microstructures of AISI 1045 samples after heat treatment, and

Figure 4b shows the results for annealed (A) and quenched in water (WQ) AISI 1006,

1020, 1080 and 1045 samples.

Ultrasonic attenuations for different microstructures of AISI 1045 (martensite,

thin and thick ferrite-pearlite) considering longitudinal waves in 4 and 5 MHz of

frequency are presented in Figure 4. From this figure, it can be concluded that

martensite was the most attenuating microstructure and thick ferrite-pearlite was the

least. In our findings, no evident relation between ultrasonic attenuation and carbon

content was observed, Figure 4b. The same difficulty to correlate ultrasonic attenuation

with carbon content was observed by Bouda et al. in [25, 26].

The attenuation coefficient translates the spreading intensity of ultrasonic waves

by grains in each stage, and it presented a pattern in the samples with 0.45% wt.% C,

contrary to that of ultrasonic velocity in the same samples. However, these results

cannot be compared because the materials were submitted to different heat treatments.

Nevertheless, it should be noticed that the main purpose of this study was not to

compare but to make correlations between microstructures and ultrasonic parameters.

The steels were dynamically analyzed by ultrasound in order to obtain the

associated modulus of elasticity and modulus of shear, according to the standard ASTM

E-494-2005 based on 5 MHz of frequency, Table 1. The density values used, Table 1,

are in agreement with the values found in the literature, see, for example, [27, 28, 29].

According to the aforementioned standard, the modulus of elasticity and modulus of

shear obtained, through ultrasonic measurements, 1% of tolerance in their values.

In order to measure attenuation intrinsic to the material, ultrasonic measurements

must be performed with care, as many factors can contribute to its inaccuracy, such as

beam divergence (diffraction) [7], coupling materials in the direct contact technique,

unsteady pressure applied to the transducer and roughness [29]. Physical properties of

the materials depend on the crystallographic direction in which the measurements were

taken. Since crystals in the metals are anisotropic, the modulus of elasticity can vary

substantially depending on the direction considered. α-iron, for example, according to

[6], has the following modulus of elasticity: 125.0 GPa, 210.5 GPa and 272.7 GPa for

orientations [100], [110] and [111], and consequently the following average ultrasonic

velocities 5440 m/s, 6190 m/s, and 6420 m/s, thus presenting a variation higher than

15%. According to Efunda [30], the modulus of elasticity for AISI 1006 to 1080 varies

from 190 to 210 GPa, validating the results obtained in this study through ultrasonic

measurements. The values of modulus of elasticity are also equivalent to those indicated

by Kim and Johnson [31], obtained by ultrasonic resonance spectroscopy and those by

Papadakis [17, 32], obtained through pulse echo ultrasound.

Microstructural condition determines the elastic behavior of the material, as well

as the ultrasonic velocity. A general approximation that can be used to evaluate

modulus of elasticity in materials with variations in the microstructure of the tested area

does not exist, due to the complexity of interactions among microstructural elements,

such as the size and shape of grains, precipitations, distortions in the crystallographic

lattice, pores and several types of irregularities, with ultrasonic wave propagation. The

only existent procedure is based on the experimental dependence between ultrasonic

velocities and respective microstructures, applied in representative samples as

performed in this study.

4. Conclusions

An evaluation of the potentialities of ultrasonic testing, mainly by considering

ultrasonic velocity and attenuation measurements, was presented, such as

nondestructive approach for the identification of microstructures and elastic properties

in plain steels, caused by grain nucleating and growth. After detailed analysis of the

results, it is possible to conclude:

1) The use of distinct carbon steel materials can provide a detailed analysis of the

ultrasonic beam behavior in several material stages. The results point out that the

ultrasonic parameters analyzed are sensitive to the obtained microstructures.

2) Ultrasonic velocities and attenuations indicate a good capacity to identify changes in

the microstructure produced by heat treatments, but there was a minor difference in

microstructures in terms of carbon content. For the analyzed steels, the ultrasonic

velocity, either longitudinal or transverse waves, increased from the hardest stage

(martensite) to the softest stage (ferrite) in all frequencies, while the opposite happened

in ultrasonic attenuation.

3) The elastic constants (E and G) calculated from ultrasonic measurements, showed

results coherent with those found in current literature obtained through dynamic and

static methods.

In general, the outcomes are very promising and can significantly contribute to

the field of nondestructive characterization of materials and control of their mechanical

properties through ultrasonic measurements.

Acknowledgments

The second author thanks the financial support given by CNPq - National

Counsel of Technological and Scientific Development, Brazil.

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FIGURE CAPTIONS

Figure 1: Optical micrography of AISI samples: a) 1006, b) 1020, c) 1080, and 1045

heat treated and cooled in water d) and e) cooled in oil, normalized f) and annealed,

both cooled in the open air g). (3% nital chemical etching.)

Figure 2: Average ultrasonic velocity measurements for longitudinal waves with 4, 5

and 10 MHz of frequency a), and for transverse waves with 5 MHz of frequency for

AISI 1045 under heat conditions b).

Figure 3: Average ultrasonic velocity measurements for longitudinal waves with 4, 5

and 10 MHz of frequency a), and for transverse waves with 5 MHz of frequency for

AISI 1006, 1020, 1080 and 1045 annealed (A) and quenched in water (WQ) b).

Figure 4: Averages of ultrasonic attenuation for longitudinal waves with 4 and 5 MHz

of frequency for AISI 1045 samples under different heat conditions and for AISI 1006,

1020, 1080 and 1045 annealed (A) a) and quenched in water (WQ) b).

TABLE CAPTION

Table 1: Density value, average, minimum and maximum values of modulus of

elasticity and modulus of shear of the plain carbon steels considered.

FIGURES

Figure 1

Figure 2

Figure 3

Figure 4

TABLE 1

Plain Carbon Steel Density [g/cm3]

Modulus of Elasticity [GPa]

Modulus of Shear [GPa]

AISI 1006 7.86 212.44 212.92

82.41 82.73

211.89 81.88

AISI 1020 7.84 211.51 212.01

82.10 82.41

210.98 81.97

AISI 1045 (WQ) 7.87 205.05 205.72

79.28 79.66

204.87 78.54

AISI 1045 (OQ) 7.85 210.77 211.16

81.94 82.27

210.30 81.64

AISI 1045 (A) 7.83 211.35 211.93

82.08 82.33

210.77 81.56

AISI 1045 (N) 7.84 210.81 211.26

81.79 82.09

210.51 81.25

AISI 1080 7.85 211.12 211.42

81.95 82.48

210.84 81.52