Mechanics, Materials Science & Engineering, October 2015 – ISSN 2412-5954

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Sankt Lorenzen 36, 8715, Sankt Lorenzen, Austria

Mechanics, Materials Science & Engineering Journal

October 2015

Mechanics, Materials Sciences & Engineering Journal, Austria, Sankt Lorenzen, 2015

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Mechanics, Materials Science & Engineering, October 2015 – ISSN 2412-5954

 

CONTENT

 

I. MATERIALS SCIENCE .......................................................................................................................

6

METAL MATRIX COMPOSITES REINFORCED WITH NANOPARTICLES FOR THE NEEDS OF SPACE

 

EXPLORATION .......................................................................................................................................

6

PRODUCING A615/A615M HIGH STRENGTH CONSTRUCTION RE-BARS WITHOUT USE OF

 

MICROALLOYS: PART 2.......................................................................................................................

11

THERMAL CONDUCTIVITY OF ZINCBLENDE CRYSTALS .......................................................................

28

PHOTO DEGRADATION IN DYE-SENSITIZED SOLAR CELLS..................................................................

36

II. MECHANICAL ENGINEERING .......................................................................................................

48

ANALYTICAL DESCRIPTION OF PLASTIC DEFORMATION DISTRIBUTION IN THE NECK OF A FLAT

 

TENSILE SPECIMEN .............................................................................................................................

48

COMPUTER AIDED ANALYSIS AND PROTOTYPE TESTING OF AN IMPROVED BIOGAS REACTOR FOR

 

BIOMASS SYSTEM ...............................................................................................................................

59

ON THE EVOLUTION THEORY OF IDENTIFICATION OF MATHEMATICAL MODELS OF CORROSION

 

DESTRUCTION AT THE OPTIMUM DESIGN OF STRUCTURES .................................................................

66

PROPOSED DESIGN PROCEDURE OF A HELICAL COIL HEAT EXCHANGER FOR AN ORC ENERGY

 

RECOVERY SYSTEM FOR VEHICULAR APPLICATION ...........................................................................

72

MELTING HEAT TRANSFER IN MHD BOUNDARY LAYER STAGNATION-POINT FLOW TOWARDS A

 

STRETCHING SHEET WITH THERMAL RADIATION ................................................................................

97

DYNAMIC DESIGN OF GROUND TRANSPORT WITH THE HELP OF COMPUTATIONAL EXPERIMENT ....

105

KINEMATICS AND LOAD FORMULATION OF ENGINE CRANK MECHANISM ........................................

112

SAFE SIMULATION OF THE MANIPULATOR IN THE PRESENCE OF STATIC AND DYNAMIC OBSTACLES BY

USING FUZZY SYSTEM ......................................................................................................................

124

III. MACHINE BUILDING .................................................................................................................

133

FEASIBLE WAYS TO IMPROVE THE DURABILITY OF THE PUMPS’ PARTS OPERATING WITH

 

HYDROABRASIVE MIXTURES ............................................................................................................

133

IX. ECONOMICS & MANAGEMENT .................................................................................................

138

ON RELATIONS BETWEEN DUMP TRUCK EFFICIENCY AND SERVICE FACILITIES STRUCTURE ...........

138

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Mechanics, Materials Science & Engineering, October 2015 – ISSN 2412-5954

Preface

Our company, being a classical industrial enterprise, understands that production of the high-quality product or service must meet scientific background. Only in this case, the end product will be competitive on the growing international market. Therefore, innovation projects have to be market-targeted from idea to production.

The company's management has always clearly understood and understands that it is impossible to demand from academicians fast, immediate, commercial return. Thus, we want to offer an easy to access service, which allows scientists expressing scientific thoughts and achievements.

Our Journal is intended to expand the horizons of thought, setup the dialogue between science and industry. This will allow receiving information about new theoretical and applied research, consolidate the efforts of specialists and disseminate expertise in the field of mechanics, materials science, engineering, information technology, industrial and social processes.

We hope for bilateral beneficial cooperation, authors’ support and success.

Magnolithe GmbH, Editor-in-Cheif

Mr. Peter Zisser

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Mechanics, Materials Science & Engineering, October 2015 – ISSN 2412-5954

I. Materials Science

Metal Matrix Composites Reinforced With Nanoparticles for the Needs of Space

Exploration

L.E. Agureev1a, V.I. Kostikov2, Zh.V. Eremeeva3, A.A. Barmin4, R.N. Rizakhanov5, B.S. Ivanov6

1 – Researcher, Department of Nanotechnology, Keldysh Research Center, Russia

2 – Doctor of Science, Associate Professor, Moscow State University of Steel and Alloys, Russia

3 – Doctor of Science, Associate Professor, Moscow State University of Steel and Alloys, Russia

4 – Ph.D., Leading Researcher, Department of Nanotechnology, Keldysh Research Center, Russia

5 – Ph.D., Head of Department, Department of Nanotechnology, Keldysh Research Center, Russia

6 – Engineer, Department of Nanotechnology, Keldysh Research Center, Russia

a – trynano@gmail.com

Keywords: nanometric particles, aluminum composites, PM method

ABSTRACT. Aluminum (Al) matrix composite materials reinforced with small amounts (0,01 – 0,15 % vol.) of aluminum or zirconium oxides nanoparticles were fabricated by tradition powder metallurgy (PM) techniques with cold pressing and vacuum sintering. Nanoparticles and their clusters were located on grain boundaries of a matrix. The microhardness of the produced composites was dramatically increased than bulk pure Al, by increasing the amount of nanoparticles. The tensile strength of the produced composites was dramatically increased (more than 2 times) than bulk pure Al, by increasing the amount of nanoparticles. This powder metallurgical approach could also be applied to other nanoreinforced composites, such as ceramics or complex matrix materials.

Introduction. For the development of space techniques we need lung and durable materials. As you know, reduction of weight payload per 1 kg reduces the cost of flying to 100 thousand rubles [1]. From this standpoint, aluminum based composites reinforced with nanoparticles of different refractory materials are promising materials. However, aware of the high activity of nanoparticles associated with an increased number of atoms on the surface and thus uncompensated surface energy, it is advisable to create aluminum composites with small concentrations of nano-additives (order of tenths and hundredths of a mass). In addition, according to the works of the school of Academician I.F.Obraztsov and results of empirical research under the supervision of a member-correspondent of RAS V.I.Kostikov, small additions of nanoparticles can contribute a substantial modification of the properties of interfacial layer [2, 3]. These factors can increase the mechanical properties of the composite with a metal matrix two or more times. Use of nanoparticles to reinforce metallic materials lead to the development of novel composites with unique mechanical and physical properties. In order to achieve desired mechanical properties of composites, reinforcing nanoparticles must be distributed uniformly within metal matrix of the composites. Various impact on characteristics of the baked composites is made by nanoparticles depending on the arrangement (on borders of grains or in grains) [4, 5]. Results of such influence are given in table 1, without specifying concentration. Composites on a basis "aluminum – ceramic particles" have lower density, than bronze, possess an optimum ratio

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Mechanics, Materials Science & Engineering, October 2015 – ISSN 2412-5954

of durability and plasticity and sufficient corrosion resistance in combination with high operational mechanical characteristics.

1.Experimental procedure. At least five measurements were made per sample. The microstructure of the composites was observed by optical microscopy (Zeiss Axiovert 40 MAT light microscope), high resolution cold-field emission scanning electron microscopy (FEI Quanta 600 FEG) and transmission electron microscopy (JEOL, JEM-2100). The micro-Vickers hardnesses of the composites were measured according to EN ISO 6507-1 with a load of 20 and 0.02 kg for 15 s (Micromet 5114 microhardness tester). Determination of the compressive strength, bending and stretching performed on a universal servo-hydraulic machine for mechanical testing «LF-100KN» production «Walter + Bai» (Switzerland) with maximum force in static 100kN with an external digital controller (EDC) and a universal machine for mechanical tests VakEto-TestSystems.

Table 1. Influence of an arrangement of nanoparticles on properties of composites

Nanoparticles in grain.

Nanoparticles on grain border

 

 

Reduce subgrains in grain

Reduce grain, without allowing to grow borders, increasing

 

durability

 

 

Brake diffusive creep through grain volume

Brake creep on borders of grains, being pressed into a

 

matrix and on turning at the movement

 

 

Interfere with distribution of cracks

Interfere with origin and promote annihilation of vacancies,

 

increasing creep resistance on borders of grains

Increase crack resistance at the expense of a hitch of the

 

dispersing crack passing through a nanoparticle

 

 

 

Nanopowders of Al2O3 and ZrO2 (Keldysh Research Center, purity 99.5%, d = 50-60 nm) and aluminum powder ASD-4 (SUAL, TU (Technical Specifications) 48_5_226–87, S = 0.34–0.38 m2/g, d = 2–10 μm) as a matrix were used as starting materials. The Al2O3 and ZrO2 nanoparticles were produced in an electro arc plasma reactor (the process is described in detail elsewhere [6,7]), producing an average particle size between 50 and 60 nm.

Mixing. To achieve a homogeneous material structure and mechanical properties necessary that the distribution of the components in the powder batch was uniform. As to achieve this nanosized additives is very difficult, a method of mixing the charge in several steps:

1.Deagglomeration of the matrix powder ASD-4 in the ultrasonic treatment in ethanol.

2.Preparation of nanoparticle suspension in ethanol with their deagglomeration simultaneously exposed to ultrasound.

3.Mixing ethanol aluminum nanoparticles under the action of ultrasound.

4.Drying of the slurry.

5.Averaging dried charge in the mill with cylinders of ZrO2 in the mode of transition from slide to roll.

6.Request repeated charge and its mixing in a tumbling mixer. Pressing. Compression was performed in a batch cylindrical steel molds in a press 50T "Mekamak" at pressures of 100, 200, 300, 400,

500MPa.

Sintering. Sintering is carried out in an automatic vacuum furnace VMS-22-10,5. The sintering temperature was varied from 550 to 670oC in forevacuum (5·10-2 mm Hg. V.), The sintering time is

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Mechanics, Materials Science & Engineering, October 2015 – ISSN 2412-5954

from 60 to 150 minutes. The resulting samples had a 15 mm diameter and a thickness of approximately 18 mm.

2.Results and discussions. Fig. 1 shows the microstructure of the samples with additives nanoparticles of zirconium oxide. Visible small bit elongated grains. The size of grains of pure aluminum was 7 microns. The average diameter of the grains of material with nanoparticles was 4-5 microns.

Fig. 1. Microstructure of aluminum composites with ZrO2 nanoparticles, SEM

In fig. 2 the composite microstructure removed from the transmission electronic microscope is shown. The cluster of nanoparticles of oxide of aluminum located on borders of grains of a matrix is visible. Besides, on borders of grains the set of nanodimensional films of oxide of aluminum is located.

Fig. 2. Microstructure of aluminum composites with Al2O3 nanoparticles, TEM

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Mechanics, Materials Science & Engineering, October 2015 – ISSN 2412-5954

The introduction of small amounts of nanoparticles of aluminum oxide prevents the recrystallization of aluminum grains during sintering and stores grain size in the sintered material at the particle size of the starting powder.

In fig. 3, the mechanical properties of the Al-Al2O3/ZrO2 composites resulted from microhardness test of specimens, is graphically represented.

% vol.

0,15

 

content,

0,1

0,05

Nanoparticles

0,01

 

 

0

0

0,1

0,2

0,3

0,4

0,5

Vickers microhardness, GPa

AVPP

ZrO2

Al2O3

Al

Fig. 3. Vickers microhardness of aluminum composites

In fig. 4 the mechanical properties of the Al- Al2O3/ZrO2 composites resulted from tensile test of specimens, is graphically represented in compare with the mechanical properties of the Al AVPP (Russian analogue of 6xxx (Mg+ Si)-alloys) which is a precipitation hardening aluminum alloy, containing magnesium and silicon as its major alloying elements. This alloy is widely used for construction of aerospace structures [8].

% vol.

0,15

 

content,

0,1

0,05

Nanoparticles

0,01

 

 

0

0

50

100

150

200

Tensile strength, MPa

AVPP

ZrO2

Al2O3

Al

Fig. 4. Tensile strength of aluminum composites

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Mechanics, Materials Science & Engineering, October 2015 – ISSN 2412-5954

Summary. A homogeneous distribution of the Al2O3/ZrO2 nanoparticles and clusters reinforcement phase in the Al matrix was obtained by combination of wet and dry mixing.

Characterization of the mechanically milled powders confirmed uniform distribution of the reinforcement phase. Low concentration additions of nanoparticles in Al powder leads the composite towards steady-state condition in which, all microstructure properties such as powder size, powder shape and distribution of Al2O3 within Al matrix remain fixed. An optimum concentration of nanopowders (0,1 %vol.), is established for the processing of the Al-Al2O3/ZrO2 composites, that assures mechanical strength close to those of the Al AVPP alloy.

References

[1]The piloted expedition to Mars / Under the editorship of A.S. Koroteyev, The Russian academy of astronautics of K. E. Tsiolkovsky, 2006, 320 p. [In Russian]

[2]Obrazcov I.F., Lur'e S.A., Belov P.A. “Osnovy teorii mezhfaznogo sloja”, Mehanika kompozicionnyh materialov i konstrukcij, 2004, T. 10, №3, pp. 596-612. - Obraztsov I.F., Lur'e S.A., Belov P.A., “Bases of the theory of an interphase layer”, Mechanics of composite materials and designs. 2004, T. 10, №3, pp. 596-612. [In Russian]

[3]Anisimov O.V., Kostikov V.I., Shtankin Ju.V. Sozdanie metallokompozitov na osnove aljuminija putem kristallizacii zhidkogo metalla v pole centrifug. Perspektivnye materialy. 2010, № 2, pp. 5-10. - Anisimov O. V., Kostikov V. I., Shtankin Yu.V. Creation of Metalcomposites on The Basis of Aluminium by Crystallization of Liquid Metal in the Field of Centrifuges. Perspective materials, 2010, №. 2, pp. 5-10. [In Russian]

[4]T. Ohji, Y.-K. Jeong, Y.-H. Choa, K. Niihara, “Strengtheing and toughening mechanisms of ceramic nanocomposites”, Journal of American Ceramic Society, 1998, №81, pp. 1453-1460.

[5]Chuvil'deev V.N. Neravnovesnye granicy zjoren v metallah. Teorija i prilozhenija/ V.N. Chuvil'deev –M.: FIZMATLIT, 2004. -304 s. - Chuvildeev V. N. Nonequilibrium borders of grains in metals. The theory and appendices / V. N. Chuvildeev – M.: FIZMATLIT, 2004, 304 p.

[6]Polyanskiy M.N., Savishkina S.V. “Lateral layer-by-layer nanostructuring of thermal barrier coatings of zirconium dioxide during plasma spraying”, 2014, Т. 8, № 1, pp. 144-148.

[7]Sirotinkin V.P., Shamrai V.F., Samokhin A.V., Alekseev N.V., Sinaiskii M.A. “Phase composition of Al2O3 nanopowders prepared by plasma synthesis and heat-treated. Inorganic Materials”, 2012, Т. 48, № 4, pp. 342-349.

[8]Metal:Matrix Composites. Custom-made Materials for Automotive and, Aerospace Engineering. /Ed: Karl U. Kainer. -WILEY-VCH Verlag GmbH and Go. KGaA, Weinheim. - 2006.

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Mechanics, Materials Science & Engineering, October 2015 – ISSN 2412-5954

Producing A615/A615M High Strength Construction Re-bars Without Use Of

Microalloys: Part 2

Ignatius C. Okafor1a, Kaushal R. Prayakarao2a, Heshmat A. Aglan2b

1 – Chief Metallurgist, Nucor Steel Corporation, Marion OH 43302, USA

aIgnatius.okafor@nucor.com

2 – Department of Mechanical Engineering, Tuskegee University, Tuskegee, Alabama, USA

a – Kprayakarao2649@mytu.tuskegee.edu

b – Aglanh@mytu.tuskegee.edu

Keywords: A615 high strength steel, re-bar steel (grade 60), rolling process, superheat, metallurgy, grain refinement, microalloys, economical steel.

ABSTRACT. The metallurgy of ASTM A615/A615M Gr. 60 steels made from three different chemistries was studied to suggest an economically advantageous route to produce a steel grade that saves the extra cost of alloying elements. Metallographic examinations, along with microhardness and XRD studies, were performed to rate the steel chemistries based on their superheats. This study of Theoretical calculations and experimental data allow to obtain parameters of interatomic potential which are used in theoretical evaluation of scattering matrices [16]. Lattice thermal conductivity is then obtained in the framework of the iterative approach, introducing anharmonic parameters ε and εin the three-phonon scattering probabilities. Parameters ε,ε, estimated through anharmonic Grüneisen constants, are the coupling factors in the three-phonon scattering processes that we have to consider when we are evaluate the thermal resistance to phononic transport [16]. In a three-phonon scattering process, two phonons disappear to give an emerging phonon or a phonon decays in two others. Theoretical approach [16] to three-phonon processes, assumes a phonon wave-vector q belonging to a true lattice Brillouin Zone. Momentum conservation is then rigorously treated, in normal and umklapp processes.

the steel grades revealed that producing steel for requisite standards like ASTM 615/A615M Grade 60 may not be dependent on starting superheat but on the chemistry and rolling process. Study of the three chemistries A, B and C indicated that the standards were met in all 3 chemistries; however, sample A had the lowest cost chemistry and therefore is a suggested route for this product.

1.Introduction. ASTM A615/A615M Grade 60 standard calls for a minimum 60 Ksi (420MPa) yield strength with no upper limit even on tensile strength. The standard only specifies that phosphorus (P) be no more than 0.06%. The resulting plain carbon steel is expected to have basic ferrite – pearlite microstructure with minimum grain size ASTM 5. Because every steel mill is different and processes vary, some steel mills use some microalloying to achieve fine grain size in pursuit of the aim microstructure. This process of compositional and process variations can produce yield strengths typically in the range of 350 to 700 Mpa (50 – 100 Ksi). Microalloying, which enhances physical properties through ferritic grain refinement, is often supplemented by precipitation and or dislocation strengthening. Hall-Petch type of strengthening is determined to suggest that a decrease of ferritic grain size from ASTM 6 – 8 to ASTM 12 – 13 is accompanied by an increase of 30 Ksi (210 Mpa) in yield strength. Admittedly the other good effect of fine grains besides strengthening is good ductility or toughness.

Two common microalloying elements V and Nb are used in industry to achieve this goal and several authors [1-6] have studied their use. It is known that the behavior of individual micro alloying elements classifies them as mildly carbide forming or strongly carbide forming. The two micro alloying elements (V and Nb) used in this study do qualify as strong carbide formers. They therefore stabilize the α phase. This essentially means that they reduce the γ phase field. Any of the elements

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in solid solution in α strengthen the ferrite matrix in steel. These elements differ in their contribution to hardening and the extent to which they reduce plasticity as they add a certain increment to strength.

Furthermore, compared to other microalloying elements like Nb and Ti, vanadium exhibits essential differences. The Swedish Institute of Metals Research [6] found that the solubility of vanadium carbonitrides, in particular, is much larger and the solubility of vanadium’s nitride is about two orders of magnitude smaller than its carbide, contrary to Nb but similar to Ti. Vanadium has higher solubility in austenite than niobium, and its carbonitrides [V(C,N)] dissolve more easily prior to hot rolling than NbC. Consequently, vanadium is an excellent choice for strong and easily controllable precipitation strengthening, but it is expensive.

Thermodynamically it is known that pure ferrite dissolves more N than C. Thus the total N-content of the steel is normally dissolved in the ferrite before V (C,N) precipitation, whereas only a fraction of the C-content is dissolved in ferrite. Hence the precipitation strengthening would and does increase with total C-content, an effect [6] not previously recognized.

Regarding the Nb containing steel in this study, niobium is known to have three-fold influence on the mechanical properties of steel. It facilitates grain size refinement; lowers the gamma (γ) to alpha (α) transition temperature (Ar3), and enhances precipitation hardening.

Grain refinement is the only mechanism that increases strength, toughness, and ductility all simultaneously. This makes niobium the most effective microalloying element even when small quantities are added to the steel. The mechanism for grain refinement is mainly due to delaying or preventing recrystallization in the last hot-forming (rolling) steps. Flattened grains associated with the process and the attendant dislocation density of the austenite enhance ferrite nucleation. By lowering the gamma (γ) to alpha (α) transformation temperature, niobium enhances ferrite nucleation and simultaneously reduces grain growth rate. The combined effect yields a very fine grain structure. This is, however, obtainable only when niobium is in solid solution. To achieve niobium in solid solution, an adequate furnace re-heating temperature is essential. At an elevated temperature, Nb(C,N) precipitates before rolling. More Nb(C,N) can precipitate quite easily in austenite under deformation. This is due to the well understood strain induced precipitation. The resulting particles from this process inhibit grain growth and even austenite grain recrystallization during the intermittent deformation at lower temperatures. Deformed austenite structure transforms to fine ferritic structure upon cooling, giving rise to high strength and toughness. Since the Nb carbonitrides are stable at low temperatures, more strength is accomplished as remaining niobium bearing particles precipitate during cooling.

The third steel grade in this study (Fe-Mn-C) does not contain any intentionally added alloying element. Carbon content and elements like Mn and Ni do also stabilize and lower the Ar3 - temperature. Ni content in the steels studied while not purposely added are appreciably high residuals (0.15 – 0.21Ni). Suppression of gamma to ferrite transformation temperatures is known to enhance refinement of the final structure by decreasing the growth rate of the ferrite grains. Traditionally the major difference in the steels for plate and long products lies in the higher carbon contents of the latter. Pearlite formation in long products is thus greater and does tend to develop bainitic or other acicular microstructures. Besides, the processing of long products necessitates relatively higher finishing temperatures; hence recrystallization controlled rolling (RCR, process 3 in Fig. 1 below) is used in order to obtain a most homogenous fine grain size and high strength in final product.

The purpose of this work is to study the metallurgy of ASTM A615/A615M Gr. 60 steels made from three chemistries and so suggest an economically advantageous route that saves the extra cost of alloying elements. The study is in two parts. The first (Part 1, yet to be submitted) discusses

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Mechanics, Materials Science & Engineering, October 2015 – ISSN 2412-5954

microstructure and the effect of cooling rates on the said chemistries while the second (Part 2; this paper) discusses microstructure, physical properties and centerline segregation.

Fig. 1 Thermo-mechanical controlled processes (TMCP): 1) recrystallization controlled rolling and accelerated cooling, 2) controlled rolling and accelerated cooling, and 3) recrystallization controlled rolling with air-cooling [6].

2.EXPERIMENTAL PROCEDURE

2.1.Processing of Steels

The steels (A, B, and C) used in this work were melted by an electric-arc-furnace tapped into 60 ton ladles, cast into billets, and rolled into #6 (19 mm) re-bars. The compositions are shown in Table 1. All three steels had identical carbon, manganese, and silicon contents and all other elements besides vanadium and niobium were residuals.

Steel A was specifically made without an intentional addition of vanadium or niobium. The 0.005 V in the chemistry is typical of residual vanadium content in scrap. Steel B was made with an intentional addition of 0.025 V and steel C was made with an intentional addition of 0.012 Nb.

For the purpose of this work the effect of other elements (typically residuals) were not considered.

All steels were air cooled on a hot bed at production conditions.

2.2. Tensile Strength Prediction Based on Chemistry: (Fe-C-Mn, Fe-C-Mn-Nb, and Fe-C-Mn-V)

Tensile strength for each chemistry studied was calculated using the prediction models available in the literature. The relationship of these chemistries to strength has been made by several authors [7, 8]. In his work, Pickering [1] suggested the following formula for alloys where carbon content is less than 0.25%C.

TS (MPa) = 243 + 1900C + 228(Cr+Mn) + 228Mo + 91W + 22Ni + 61Cu + 380(Ti + V)

Pickering did not suggest any contribution from silicon.

De Boer [2], however, basing his work on a carbon content of approximately 0.4%C and 1.5%Si, suggested a contribution for silicon as indicated in the following equation.

TS (MPa) = 430 + 688 +81 Si + 196Mn + 202Cr + 80Mo + 400V

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Table 1. Chemical composition of the three alloys used in the study

No Vanadium added

Vanadium Added (B)

Niobium Added (C)

 

(A)

 

 

 

 

 

 

 

 

 

 

Cast Temp- 2788℉

Cast Temp- 2865℉

Cast Temp- 2812℉

 

 

 

 

 

 

Superheat- ��℉

Superheat- ����℉

Superheat- ��℉

 

 

 

 

 

 

 

Element

 

Wt%

Element

Wt%

Element

Wt%

 

 

 

 

 

 

 

C

 

0.40

C

0.37

C

0.30

 

 

 

 

 

 

 

Mn

 

1.06

Mn

0.99

Mn

1.10

 

 

 

 

 

 

 

S

 

0.033

S

0.029

S

0.037

 

 

 

 

 

 

 

P

 

0.017

P

0.024

P

0.012

 

 

 

 

 

 

 

Si

 

0.18

Si

0.18

Si

0.24

 

 

 

 

 

 

 

Cu

 

0.48

Cu

0.31

Cu

0.36

 

 

 

 

 

 

 

Cr

 

0.22

Cr

0.23

Cr

0.16

 

 

 

 

 

 

 

Mo

 

0.06

Mo

0.08

Mo

0.05

 

 

 

 

 

 

 

Sn

 

0.013

Sn

0.011

Sn

0.018

 

 

 

 

 

 

 

Ni

 

0.21

Ni

0.17

Ni

0.15

 

 

 

 

 

 

 

Nb

 

0.000

Nb

0.000

Nb

0.012

 

 

 

 

 

 

 

V

 

0.005

V

0.025

V

0.003

 

 

 

 

 

 

 

Pb

 

0.000

Pb

0.000

Pb

0.004

 

 

 

 

 

 

 

De Boer also tested the influence of Mn (0.70 to 1.3 wt. %), Cr (0.15 to 1.5 wt. %), Mo (0.20 to 0.8 wt. %), and V (0.0 to 0.10 wt. %).

Mesplont [3] and his team, starting from De Boer’s work, modified the equation with the use of more elements and developed the following equation.

TS (MPa) = 288 + 803C + 83Mn + 178Si + 122Cr + 320Mo + 60Cu + 180Ti + 1326P + 2500Nb +

+360000B.

The authors applied this equation to 164 steels; the results are shown in Fig. 2.

Because the elemental chemical analysis of our three alloys falls into the chemistry ranges used by Mesplont and co-workers [3], we have used their equation to “predict” or verify the tensile strengths of the alloys studied.

Steel A

TS (MPa) = 288+803(0.402) +83(1.06) +178(0.18) +122(0.22) +320(0.056) +60(0.482) +180(0) +1326(0.017) + 2500(0.000) +36000(0.0). This gives an empirical tensile strength of 120 Ksi. The actual mill measurement for this heat was 110 Ksi; the difference of between 8% and 9% is certainly understandable and of no obvious concern.

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Mechanics, Materials Science & Engineering, October 2015 – ISSN 2412-5954

Steel B

Sample B calculated tensile strength is 116.6 Ksi while the actual mill result is 112.3 Ksi. As for alloy A, the difference between the theoretical value predicted by Mesplont’s’s equation and the actual is between 3.7% and 3.8%.

Fig. 2. Calculated TS (MPa) versus measured TS (MP a) [3]

Steel C

Sample C in this study has a calculated tensile strength of 106.67 Ksi while the measured (mill) tensile strength was reported as 96.4 Ksi. The difference is between 9.63 % and 10.68%.

The objective of this exercise is not to verify the accuracy or lack thereof of Mesplont’s equation but to have a common verifiable frame of reference other than mill reports to compare the tensile strengths. The maximum difference of 10 percentage points between calculated and measured values irrespective of the use of alloying elements (which we all know in metallurgy as grain refiners) is truly instructive. It is this closeness that further drove this work where we seek to minimize the use of expensive alloying elements in making some basic grades of carbon steel needed in the construction industry.

2.3. Metallography of Samples

Three sets of samples, each from all three different steels, were mounted using Buehler Simplimet 1000 with Bakelite and polished for light optical metallography, microhardness studies, and SEM work. All samples were polished to the usual mirror image and etched using 2% Nital.

Metallographic pictures obtained from the optical microscopy were then studied for microstructural variations and grain sizes were estimated from the microstructures for each steel grade.

2.4. Microhardness Tests

Microhardness measurements were made on samples that had been polished and etched to reveal microstructure. Hardness was taken for each of the phases identified in the metallography. Microhardness data were obtained from around the center line of the three steel grade studies. Particular attention was paid to the center line to determine if any differences arose from the

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