Showing 58 results for Steel
Golmahalleh O., Zarei-Hanzaki A.,
Volume 1, Issue 1 (3-2004)
Abstract
In principal, a proper combination of strength and ductility is achieved through micro component refinement in steels. This is particularly empowered with ferrite refinement down to micron sizes in ferrite pearlite engineering steels. The latter is achieved through various well-defined methods in which strain induced transformation (SIT) has shown spectacular capabilities. In the present study, to address the effect of thermo mechanical processing parameters on the (SIT) behavior, two plain carbon steels were studied through single pass rolling. This was carried out at the corresponding Ar_3 + 20°C temperature of the steels. The results indicated that the transformation behavior and ferrite morphology would be .strongly influenced by both the chemical composition (i.e., carbon content) and the amount of applied strain. Furthermore, a high volume fraction of very fine ferrite with mean grain size of less than 2 µm was obtained. This was attributed to the ferrite nucleation at deformation bands and serrated austenite grain boundaries.
Morakabati M., Arabi H., Mirdamadi Sh., Abbasi S.m.,
Volume 2, Issue 2 (6-2005)
Abstract
This study was launched to investigate the effects of heating rate and aging parameters on the kinetic of precipitation reactions in a high alloy high strength steel having Ni, Co, Mo and Ti. For this purpose, as quenched specimens were subjected to three types of aging methods with different heating rates. These methods consisted of aging in Pb bath, salt bath, and furnace at different aging cycles. The kinetic of precipitation in each method was studied by hardness measurements and was described adequately by the Johnson-mehl-Avrami equation. Remarkable increase in hardness and its rate is observed when the rate of heating increases. The substantial increase in hardness of the specimens aged rapidly in salt & Pb baths, compared with those aged normally in furnace, seemed to be due to the formation of thermo elastic stresses during sudden expansion of the substance subjected to rapid heating. According to the results obtained in this research, increase in the Avrami constants, n & k, and decrease in the start time of transformation, ts, are associated with heating rate increasing. Analysis of the observed and calculated data for hardness using Arrhenius equation, shows that for the same amount of volume fraction of precipitates, the activation energy of precipitates decreased for f=25 and 50%, while at f=90 % it increased by increasing heating rate.
Dehghan Manshadi A., Zarei Hanzaki A., Golmahalleh O.,
Volume 2, Issue 2 (6-2005)
Abstract
The presence of bainite in the microstructure of steels to obtain a proper combination of strength and toughness has always been desired. The previous works however have shown that the presence of preferred bainite morphologies in the microstructure of any steel would not be readily accessible. In addition, the appearance of different bainite morphologies in the microstructure of any steel is dictated by different factors including the steel initial microstructure, austenitization characteristics, thermomechanical processing parameters and so on. Accordingly, in the present work, the effect of prior austenite grain size and the amount of austenite hot deformation on the bainite formation characteristics were investigated in 0.12C-2.5 Ni-1.2Cr steels. The results indicated that the prior austenite grain size and the amount of deformation in the austenite no-recrystallization region resulted in significant changes of the bainite formation kinetics and morphology.
Moayed M.h.,
Volume 2, Issue 3 (9-2005)
Abstract
In this research pitting Corrosion of a sensitized 316 stainless steel was investigated employing potentiodynamic, potentiostatic techniques. Sensitization process was carried out on as-received alloy by submitting the specimen in electric furnace set at 650°Cfor five hours and then the specimen was quenched 25°C water. Potentiodynamic polarization of as received and sensitized specimens in 1M H2SO4 solution at room temperature and 70°C clearly revealed that the sensitization process has caused a magnificent change on electrochemical behavior of the specimen by changing critical current density for passivation, passivation potential and passive current density. Optical microscopy examination of the specimen surface after oxalic acid electrochemical etching also showed the deterioration of grain boundary of sensitized specimen due to chromium carbide precipitation in compared to as-received one. Several anodic potentiodynamic polarization on rode shaped working electrodes prepared from as-received and sensitized specimen in 3.5% NaCl test solution proved an average ~220 mV drop in pitting potential due to sensitization. Anodic potentiostatic polarization at 400 and 200 mV above corrosion potential also demonstrate the deterioration of pitting resistance of alloy as a result of sensitization. Scanning electron microscopy examination of anodically polarized of sensitized specimen at 700mVprior and after oxalic acid etching revealed large stable pits with lacy cover and also openpits with deep crevice for etched specimens.
Nouroozi S., Vardelle A.,
Volume 2, Issue 4 (12-2005)
Abstract
In wire arc spraying, the atomizing air pressure and applied nozzle system are important factors influencing particles characteristics and coating quality. The aim of this paper is to study how the characteristics of particles such as size, velocity and temperature are influenced by the operating conditions in wire arc spray. For that, three types of wires are tested: solid wire of stainless steel 316L, cored wires 97MXC and 98MXC. Arc spray gun is an Arc Jet 9000 manufactured by TAFA. For each condition, the particles temperature and particles velocity are measured using an imaging CCD camera, Spray Watch (Oseir Ltd). Particles size distributions are determined with a laser grain meter. The morphology and composition of particles were evaluated with SEM, EDX and X-Ray diffraction. Results induce important modifications in the particles size distributions and particles velocity. A small diameter nozzle and high atomizing air pressure resulted in a reduction in particles size distributions and an increase in particles velocity.
Arabi H., Divandari M., Hosseini A.h.m.,
Volume 3, Issue 3 (12-2006)
Abstract
In this research the influence of Ti contents on the amounts of inclusions formation and mechanical properties of a high alloy high strength steel, C300, has been investigated. For this purpose several bars were casted under the same solidification conditions, but different amounts of Ti element. All the seven casted bars were homogenized at 1200°C for a period of 2 hours. Then, they were immediately hot rolled after homogenization so that the out rolling temperature was kept in the range of 1000-1200° C. The specimens were then solution annealed at 820°C for hour and finally they were aged for a period of 3 hours at 500°C. The samples were subjected to tensile, impact and hardness tests in order to relate the variation in volume percent of inclusions due to different amount of Ti, to mechanical properties. The results showed that by increasing the amount of Ti a serious decline in toughness properties of the alloy due to increase in inclusion population occurred. So this research provides a very useful information about the relation between volume fraction of inclusions and mechanical properties of a C300 high strength steel.
Abbasi S.m., Shokouh Far A., Ehsani N.,
Volume 3, Issue 3 (12-2006)
Abstract
In this study the hot deformation behaviour of a precipitation hardened (PH) stainless steel at high strain rates has been predicted through hot compression testing. Stress-strain curves were obtained for a range of strain rates from 10-3 to 10+1 S-1 and temperatures from 850 to 1150°C. Results obtained by microstructure and stress-strain curves show that at low temperatures and high strain rates, where the Zener-Holman parameter (Z) is high, work hardening and dynamic recovery occure. By increasing temperature and decreasing strain rate, the Z parameter is decreased, so that dynamic recrystallization is the dominant softening mechanism. The results were fitted using a Log Z versus Log (sinh (a sp) diagram allowing an assessment of the behavior of the stresses measured at strain rates closer to those related to the industrial hot rolling schedules. It is clearly shown that the data collected from low strain rate testing can be fairly reasonably extrapolated to higher orders of magnitude of strain rate.
Ebrahimi A.r., Yadegari M., Khosroshahi R.a.,
Volume 3, Issue 3 (12-2006)
Abstract
In this study, commercially pure titanium/304L stainless steel explosion bonded clads have been annealed under argon atmosphere over the temperature range of 700-900°C for 1h.Microstructure of the clads have been investigated before and after anealing. X-ray diffraction studies revealed that the annealing products in the form of intermetallic phases were gradually formed at the interface of the annealed clads. It was also found that, the bonding zone width increased with temperature according to an Arrhenius type equation. On the base of this equation, the activation energy of bonding zone growth was found equal to about 66.5 kJ/mol. The bond strength of the diffusion annealed clads were evaluated stress relieved. The maximum average tensile strength of ~350MPa was obtained for the as-welded clad. It was found that the bond strength decreased with annealing at 700°C due to an increase in the width of brittle intermetallic layer.
Nosrati F., Zarei Hanzaki A.,
Volume 3, Issue 3 (12-2006)
Abstract
TRIP (TRansformation- lnduced- Plasticity) behavior is a powerful mechanism to improve mechanical properties. The basis of TRIP phenomena is the transformation of retained austenite with optimum characteristics (volume fraction, stability, size and morphology) to martensite during deformation at room temperature. Accordingly, the first requirement to obtain desired TRIP effects is to produce an appropriate microstructure. Thermo mechanical processing is an effective method to control the microstructural evolution thereby mechanical properties in TRIP steels. This work deals with a TRIP steel containing 0.2% C, evaluating the effects of straining before and during ?®a atransformation on its final characteristics, using hot compression tests. The results revealed that straining in the two phase region (dynamic transformation) not only reduces the ferrite grain size more significantly, but also increases the retained austenite volumefraction. Accordingly the final mechanical properties were also improved.
G. H. Akbari, M. A. Sheikhi,
Volume 4, Issue 1 (6-2007)
Abstract
Abstract: Ball mills are used in the last stage of ore processing for grinding raw materials. Forged
70Cr2 alloy steel and Austempered Ductile Iron (ADI) balls are materials from which grinding
balls are made for Sarcheshmeh Copper Plant (SCP) ball mills. In the present study wear and
impact properties of these two kinds of balls have been investigated. Some balls randomly were
selected as samples. They were cut to investigate the cross section under optical and scanning
electron microscopes. The microstructure of the sample balls was studied and quantitative
measurements of microstructural features were performed. The hardness of different parts of cross
sections of balls was measured. The wear resistance of the balls was measured by Pin on Disc
method. Repeated dropt test was employed to evaluate impact resistance of the balls. The
microstructure of ADI balls consisted of bianitic matrix with graphite nodules and some retained
austenite and martensite. Micro cracks and porosities in the cast structure were frequently
observed. In the case of forged steel balls the microstructure composed of tempered martensite in
outer area and bianitic structure with some tempered martensite in central areas. The wear and
impact resistance of forged steel balls were markedly higher than those of ADI balls. The
difference was consistent with the differences between the microstructures of the two kinds of balls.
Cast structure with microcracks and shrinkage porosities in ADI balls gives rise to lower impact
resistance.
A. Poladi, M. Zandrahimi,
Volume 5, Issue 3 (9-2008)
Abstract
Abstract: Austenitic stainless steels exhibit a low hardness and weak tribological properties. The
wear behaviour of austenitic stainless steel AISI 316 was evaluated through the pin on disc
tribological method. For investigating the effect of wear on the changes in microstructure and
resistance to wear, optical microscopy and scanning electron microscope were used. The hardness
of the worn surfaces was measured with a micro-hardness tester. Worn surfaces were analyzed
through X-ray diffraction. Results showed that with increasing the sliding distance and applied
load, the austenite phase partially transformed to ά martensite, and there was no trace of ε phase
detected. Due to the formation of probably hard and strong martensite phase, as the sliding
distance and applied load increased, the hardness and the wear resistance of the material was
increased. Wear mechanism was on the base of delamination and abrasion.
A.nouri, Sh.kheirandish, H. Saghafian,
Volume 5, Issue 4 (12-2008)
Abstract
Abstract: In the current work, the strain hardening behavior of dual-phase steels with different silicon content (0.34-
2.26 Wt. %) was examined using the modified Crussard-Jaoul analysis. It was shown that these dual-phase steels
deform in two stages over a uniform strain range. Each stage exhibited a different strain hardening exponent varying
with silicon content. At the first stage, work hardening exponent remind significantly constant, while during the second
stage, it decreased with increasing silicon content from 0.34% to 1.51% and then increased for the higher silicon
contents (1.51% to 2.26%). It was found that the strain hardening behavior of these steels was predominantly affected
by the volume fraction of martensite at low silicon contet and the ferrite strengthening induced by silicon at the higher
silicon content. The effect of silicon content on the volume fraction of martensite and tensile properties were also
considered.
H. Aghajani, M. Soltanieh, F. Mahboubi, S. Rastegari and Kh. A. Nekouee,
Volume 6, Issue 1 (3-2009)
Abstract
Abstract: Formation of a hybrid coating by the use of plasma nitriding and hard chromium electroplating on the
surface of H11 hot work tool steel was investigated. Firstly, specimens were plasma nitrided at a temperature of 550
°C for 5 hours in an atmosphere of 25 vol. % H2: 75 vol. % N2. Secondly, electroplating was carried out in a solution
containing 250 g/L chromic acid and 2.5 g/L sulphuric acid for 1 hour at 60 °C temperature and 60 A/dm2 current
density. Thirdly, specimens were plasma nitrided at a temperature of 550 °C for 5 and 10 hours in an atmosphere of
25 vol. % H2: 75 vol. % N2. The obtained coatings have been compared in terms of composition and hardness. The
compositions of the coatings have been studied by X-ray diffraction analysis. The surface morphology and elemental
analysis was examined by using scanning electron microscopy. The improvement in hardness distribution after third
step is discussed in considering the forward and backward diffusion of nitrogen in the chromium interlayer. Also, the
formed phases in the hybrid coating were determined to be CrN+Cr2N+Cr+Fe2-3N+Fe4N.
M. Ozve Aminian, J. Hedjazi, Y. Kharazi,
Volume 6, Issue 3 (9-2009)
Abstract
Abstract: In this research, the oxidation behaviour of high Aluminum heat resistant steel (%25Cr,%20Ni,%8Al) hasbeen evaluated at the temperature range of (1000-1300ºC).The results showed that there was no countinous healinglayer on the surface of the alloy when Al increased up to %5.5 and the oxidation resistance of steel decreased due toformation of spinel oxides on the surface.By increasing the aluminum amount to %8, only Al oxide formed due to decreasing carbon potential of thealloy,homogenity of elemental concentration in matrix and no diffusion of oxygen through oxide–metalinterface,therefore it has superior oxidation resistance. Meanwhile,oxidation tests showed that the weight gain of thesteel at high temperature oxidation even at 1300ºC was too low.
B. Mirzakhani,mohammadi, H. Arabi,s. H. Seyedein, M. R. Aboutalebi, M. T. Saleh, Sh. Khoddam,
Volume 6, Issue 3 (9-2009)
Abstract
Abstract:Optimization of specimen geometry before subjecting it to hot torsion test (HTT) is essential for minimizingnon-uniform temperature distribution and obtaining uniform microstructure thought the specimen.In the present study, a nonlinear transient analysis was performed for a number of different geometries andtemperatures using the commercial finite element (FE) package ANSYSTM. FE thermal results then were applied tooptimize HTTspecimen produced from API-X 70 microalloyed steel taking into account the microstructurehomogeneity. The thermodynamic software Thermo-calcTM was also used to analysis solubility of microalloyingelements and their precipitates that may exist at different equilibrium conditions. In addition the behavior of austenitegrain size during reheating was investigated. The results show high temperature gradient occurred in long specimens.This could lead to non homogeneous initial austenite grain size and alloying element or precipitates within the gaugesection of the specimen. The proposed optimization procedure can in general be used for other materials and reheatingscenarios to reduce temperature. This then creates more homogeneous initial microstructure prior to deformation andreduces errors in post processing of the HTTresults
Bahman Mirzakhani, Hossein Arabi, Mohammad Taghi Salehi,seyed Hossein Seyedein, Mohammad Reza Aboutalebi, Shahin Khoddam, Jilt Sietsma,
Volume 6, Issue 4 (12-2009)
Abstract
Abstract
Recovery and recrystallization phenomena and effects of microalloying elements on these phenomena are of great importance in designing thermomechanical processes of microalloyed steels. Thus, understanding and modeling of microstructure evolution during hot deformation leads to optimize the processing conditions and to improve the product properties.
In this study, finite element method was utilized to simulate thermomechanical parameters during hot deformation processes. FEM results then were integrated with physically based state variable models of static recovery and recrystallization combined with a realistic microstructural geometry. The thermodynamic software Thermo-calc was also used to predict present microalloying elements at equilibrium conditions.
The model performance was validated using stress relaxation tests. Parametric studies were carried out to evaluate the effects of deformation process parameters on the microstructure development following hot deformation of the API-X70 steel
A. Noorian, Sh. Kheirandish, H. Saghafian,
Volume 7, Issue 2 (6-2010)
Abstract
Abstract:
mechanical properties of AISIH 13 hot-work tool steel have been studied. Cast samples made of the modified new steel were homogenized and austenitized at different conditions, followed by tempering at the specified temperature ranges. Hardness, red hardness, three point bending test and Charpy impact test were carried out to evaluate the mechanical properties together with characterizing the microstructure of the modified steel using scanning electron microscope. The results show that niobium addition modifies the cast structure of Nb–alloyed steel, and increases its maximum hardness. It was found that bending strength bending strain, impact strength, and red hardness of the modified cast steel are also higher than those of the cast H13 steel, and lower than those of the wrought H13 steel.
In this research, the effects of partially replacing of vanadium and molybdenum with niobium on the
S. Ahmadi,, H. R. Shahverdi*, S. S. Saremi,
Volume 7, Issue 4 (10-2010)
Abstract
Abstract: In this research work, crystallization kinetics of Fe55Cr18Mo7B16C4 alloy was evaluated by X-ray diffraction, TEM observations and differential scanning calorimetric tests. In practice, crystallization and growth mechanisms were investigated using DSC tests in four different heating rates. Results showed that a two -step crystallization process occurred in the alloy in which - Fe phase was crystallized in the first step after annealing treatments. Activation energy for the first step of crystallization i.e. - Fe was measured to be 276 (kj/mol) according to Kissinger model. Further, avrami exponent calculated from DSC curves was 2 and a three -dimensional diffusion controlled mechanism with decreasing nucleation rate was observed in the alloy. It is also known from the TEM observations that crystalline á – Fe phase nucleated in the structure of the alloy in an average size of 10 nm and completely mottled morphology.
Dr Mohammad Reza Allazadeh,
Volume 9, Issue 3 (9-2012)
Abstract
Abstract: A combination of a finite element method (FEM) algorithm with ANSYS codes and post image processing of NDT ultrasonic images along with laboratory cooling experiments and microstructural analysis provide a guideline to determine the optimum cooling rate for any grade of steel in which the highest productivity can be achieved without any degradation of the cast steel products. The suggested FEM algorithm with ANSYS codes is introduced to develop a quasi real models to simulate quenching of as-cast steel with any cooling rate from any initial temperature below steel’s melting point. The algorithm builds a model which is capable to approximate the thermodynamic stresses generated by thermal strain and possible solid-solid phase transformation for as-cast steel with any chemical composition. The model is applicable for any casting geometry (slab, billet and bloom, bar, etc) and adaptable for any method of cooling (unidirectional or multidirectional). Cooling with any cooling agent can be simulated with the algorithm in an ideal case. The phase transformation of the steel in the algorithm can be controlled by Continuous Cooling Transformation (CCT) Diagram obtained from analytical calculation or real time-temperature-transformation experiments for the cast steel. A function for optimizing cooling rate is suggested.
Dr Mohammad Reza Sarmasti Emami,
Volume 9, Issue 3 (9-2012)
Abstract
This paper presents an experimental and theoretical investigation of the causes of corrosion of stack in a cement plant. In this paper, information related to metallic stack failures are given in the form of a case study in Neka Cement Plant, Mazandaran, Iran. Heavy corrosion attacks were observed on the samples of stack. The failure can be caused by one or more modes such as overheating, stress corrosion cracking (SCC), hydrogen embrittlement, creep, flame impingement, sulfide attack, weld attack, dew point corrosion, etc. Theoretical calculations and experimental observations revealed that, the corrosion had taken place due to the condensation of acidic flue gases in the interior of stack. Also, the chemical analysis of the corrosion deposits and condensates confirmed the presence of highly acidic environment consisting of mostly sulfate ions.
