bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxidative Plasma Treatment of Fluorocarbon Surfaces for Blood-Contacting Applications
Authors: Montaño-Machado Vanessa , Angeloni Livia , Chevallier Pascale , Klak Marie Cécile , Turgeon Stéphane , Rossi Marco , Mantovani Diego
Published: December 2018

Surgical implantation of metallic stents is today a common procedure for restoring narrowed arteries. However, main complications as in-stent restenosis, partial or total thrombosis, inflammation and devices degradation are still a serious clinical concern. The coating of stents with fluorocarbon (CFx) ultrathin films represents a valuable strategy to limit these complications. Moreover, an additional step for the modification of some key surface properties of CFx coatings could further enhance their blood compatibility. Therefore, the objective of this work was to develop an oxidation process specific to ultrathin CFx coatings based on a methanol plasma treatment to modulate their biological response. Oxidized and non-oxidized coatings were investigated by XPS, ToF-SIMS, water contact angle, SEM and AFM. Tunable oxidation of the surface of CFx coatings was obtained by methanol plasma treatment, thus producing an increase of surface wettability, without affecting morphology, roughness and adhesion of the coatings. Blood test results showed an increased hemocompatibility of the oxidized samples, confirming the hypothesis that such treatment can succeed in modulating the blood contact behavior of the CFx oxidized coatings.
Temperature Dependent Mechanical Behavior of ODS Steels
Authors: de Sanctis Massimo , Fava Alessandra , Lovicu Gianfranco , Montanari Roberto , Richetta Maria , Testani Claudio , Varone Alessandra
Published: December 2018

An oxide dispersion strengthened (ODS) ferritic steel with nanometric grain size has been produced by means of low-energy mechanical alloying (LEMA) of steel powder (Fe-14Cr-1W-0.4Ti) mixed with Y2O3 particles (0.3 wt%) and successive hot extrusion (HE). The material has equiaxed grains (mean size of 400 nm) and dislocation density of 4 x 1012 m-2, and exhibits superior mechanical properties with respect the unreinforced steel. The mechanical behavior has been compared with that of ODS steels prepared by means of the most common process, high-energy mechanical alloying (HEMA), consolidation through hot isostatic pressing (HIP) or hot extrusion (HE), annealing around 1100 °C for 1-2 hours, which produces a bimodal grain size distribution. The strengthening mechanisms have been examined and discussed to explain the different behavior.
Investigation of the Local Austenite Stability Related to Hydrogen Environment Embrittlement of Austenitic Stainless Steels
Authors: Fussik Robert , Egels Gero , Theisen Werner , Weber Sebastian
Published: December 2018

Hydrogen is increasingly considered as fuel for future mobility or for stationary applications. However, the safe distribution and storage of pure hydrogen is only possible with suitable materials. Interstitially dissolved hydrogen atoms in the lattice of numerous metals are responsible for hydrogen embrittlement (HE). If hydrogen is introduced by an external source, it is called hydrogen environment embrittlement (HEE). Commonly, steels like AISI 316L with a high resistance to HEE include a large number of alloying elements and in high amount. High alloying levels result in a decrease of cost-efficiency. Therefore, the systematic investigation of lean-alloyed austenitic stainless steels is necessary in order to understand the mechanism of HEE. For that purpose, the steel grades AISI 304L and AISI 316L are selected in this work. Tensile tests in air and 400 bar hydrogen gas atmospheres are performed. After tensile testing in H, AISI 304L revealed secondary cracks at the specimen surface, which are related to the local austenite stability, which in turn is affected by the level of micro-segregation. The microstructural investigations of the crack environment directly contribute to the understanding of the micro-mechanisms of HEE. Property-maps generated from experimentally measured distributions of alloying elements allow to correlate the impact of micro-segregations on the local austenite stability. It is shown, that local segregation-bands affect the initiation and propagation of secondary cracks. In this context, the local austenite stability which is significantly affected by the Ni distribution will be discussed in detail by comparison of the metastable austenitic steel grades AISI 304L and AISI 316L.
Numerical Simulation of Residual Stresses due to Multipass Welding in High Strength Steel Plates and Validation against Experimental Measurements
Authors: Ramard Constant , Carron Denis , Pilvin Philippe , Bridier Florent
Published: December 2018

Multipass arc welding is commonly used for thick plates assemblies in shipbuilding. Sever thermal cycles induced by the process generate inhomogeneous plastic deformation and residual stresses. Metallurgical transformations contribute at each pass to the residual stress evolution. Since residual stresses can be detrimental to the performance of the welded product, their estimation is essential and numerical modelling is useful to predict them. Finite element analysis of multipass welding of a high strength steel is achieved with a special emphasis on mechanical and metallurgical effects on residual stress. A welding mock-up was specially designed for experimental measurements of in-depth residual stresses using contour method and deep hole drilling and to provide a simplified case for simulation. The computed results are discussed through a comparison with experimental measurements.
Magnetic Barkhausen Noise Characterization of the Recrystallization of a Non-Oriented Electrical Steel after Cold Rolling at Different Angles to the Hot Rolling Direction
Authors: He You Liang , Mehdi Mehdi , Hilinski Erik J. , Edrisy Afsaneh
Published: December 2018

Non-oriented electrical steel sheets are the most commonly used material for the manufacturing of magnetic cores for electric motors and generators. The microstructure and texture of the steel after final annealing have a significant effect on the magnetic properties of the lamination core. To investigate the effect of cold rolling and annealing on the magnetic properties of the steel sheets, a 0.9 wt% Si non-oriented electrical steel was cold rolled at different angles to the hot rolling direction (HRD) and annealed at various temperatures (600°C to 750°C) to produce dissimilar microstructures. The progress of recrystallization was characterized by electron backscatter diffraction (EBSD), and the magnetic response of the steel at various stages of recrystallization was evaluated by magnetic Barkhausen noise (MBN). A number of MBN parameters, e.g. the root mean square, the smoothed envelope, the peak, the full width at half maximum (FWHM) of the envelope, the time integral of the MBN signals and the MBN energy, were analyzed with respect to the fraction of recrystallization during annealing. The results show that cold rolling at different angles to the hot rolling direction induces various deformation microstructures and stored energies, which, in turn, lead to considerably different recrystallization behaviours during annealing. The difference in recrystallization of these materials is also reflected in the MBN parameters.
Low Density Steels for Forging
Authors: Kaltzakorta Idurre , Gutierrez Teresa , Elvira Roberto , Guraya Teresa , Jimbert Pello
Published: December 2018

In the last years numerous works have been done to try to reduce car weight in order to decrease CO2 emissions. In this line, Low Density Steels can be considered as one alternative in the lightweight approximation strategy [1-2] for the automotive industry. Generally, in low density steels, a considerable amount of Aluminum is added in order to reduce the overall steel density, but high Aluminum contents lead to processing drawback, that make it difficult to bring these new/lighter steel grades into the market. In the literature, different low density steel grades can be found but most of them are aimed at structural parts of the car, whereas almost none of them is aimed at forged components. In this research, different compositions of the three families of low density steels (ferritic, duplex and austenitic) were fabricated at low scale in order to try to understand the phenomena taking place in these steels, and try to find the best candidate for getting a low density steel suitable for forging in the upcoming research.
Mechanical Behavior of High-Mn Steels Processed by Hot Rolling
Authors: Belyakov Andrey , Dolzhenko Pavel , Tikhonova Marina , Torganchuk Vladimir , Kaibyshev Rustam
Published: December 2018

The mechanical properties of Fe-28%Mn-1.5%Al and Fe-0.6%C-18%Mn-1.5%Al-0.07%Nb (all in wt.%) steels subjected to hot plate rolling at a temperature of 1423 K with a total reduction of 60% were studied. The steels exhibited quite different mechanical properties in spite of almost the same original microstructures and similar stacking fault energies. The yield strength and total elongation of the Fe-28%Mn-1.5%Al steel are about 260 MPa and 45%, respectively, whereas those properties in the Fe-0.6%C-18%Mn-1.5%Al-0.07%Nb steel comprise 350 MPa and 53%, respectively. The tensile flow stress vs strain curves of the hot rolled steel samples can be described by Ludwigson-type relations with parameters being dependent on the strengthening mechanisms. Frequent deformation twinning in the Fe-0.6%C-18%Mn-1.5%Al-0.07%Nb steel promoted the strain hardening and improved the strength and ductility.
Effect of Mo, Nb and V on Hot Deformation Behaviour, Microstructure and Hardness of Microalloyed Steels
Authors: Singh Navjeet , Kostryzhev Andrii G. , Killmore Chris R. , Pereloma Elena V.
Published: December 2018

Three novel low carbon microalloyed steels with various additions of Mo, Nb and V were investigated after thermomechanical processing simulations designed to obtain ferrite-bainite microstructure. With the increase in microalloying element additions from the High V- to NbV- to MoNbV-microalloyed steel, the high temperature flow stresses increased. The MoNbV and NbV steels have shown a slightly higher non-recrystallization temperature (1000 °C) than the High V steel (975 °C) due to the solute drag from Nb and Mo atoms and austenite precipitation of Nb-rich particles. The ambient temperature microstructures of all steels consisted predominantly of polygonal ferrite with a small amount of granular bainite. Precipitation of Nb-and Mo-containing carbonitrides (>20 nm size) was observed in the MoNbV and NbV steels, whereas only coarser (~40 nm) iron carbides were present in the High V steel. Finer grain size and larger granular bainite fraction resulted in a higher hardness of MoNbV steel (293 HV) compared to the NbV (265 HV) and High V (285 HV) steels.
Microstructure Evolution and Change in Mechanical Properties of Medium Mn Steels during Thermomechanical Processing
Authors: Hou Fei Fei , Ito Atsushi , Bai Yu , Shibata Akinobu , Tsuji Nobuhiro
Published: December 2018

Medium manganese steels are nowadays energetically investigated as the third generation advanced high strength steels (AHSS) because of their excellent balance between material cost and mechanical properties. However, the phase transformation and microstructure evolution in medium manganese steels during various heat treatments and thermomechanical processing are still unclear. The present study firstly examined kinetics of static phase transformation behavior and microstructural change in a 3Mn-0.1C medium manganese steel. Hot compression tests were also carried out to investigate the influences of high-temperature thermomechanical processing on the microstructure evolution. It was found that ferrite transformation was quite slow in static conditions but greatly accelerated by hot compression in (austenite and ferrite) two phase region. Dual phase microstructures composed of martensite and ferrite with ferrite grain sizes of 1~2 μm were obtained, which exhibited superior mechanical properties.
Design and Properties of 1000 MPa Strength Level Hot-Formed Steels Possessing Dual-Phase and Complex-Phase Microstructures
Authors: Arribas Maribel , Rana Radhakanta , Lahaije Chris , Gómez Xabier , Aranguren Iñigo , Pérez Iñaki
Published: December 2018

In cold forming for automotive lightweight design, advanced high strength steels (AHSS) lead to limited formability, high springback and press forces, low stretch flangeability, multiple operations for complex geometries and large scrap rates. Two sets of AHSS, namely ferritic-martensitic dual-phase (DP) steel and martensitic-bainitic complex-phase (CP) steel with some amounts of retained austenite (RA), were designed for the hot-forming route, which eliminates the above drawbacks and guarantees higher performance in the body-in-white (BIW). Design of four DP and four CP alloys was accomplished using JMatPro6.0 thermodynamic software and available literature. The alloys were manufactured in the laboratory in cold-rolled gauge of ~1.5 mm and subjected to hot-forming cycles including hot deformation (up to 20% strain), using a dilatometer and a Gleeble 3800 machine. The thermal cycles of the DP alloys included an intercritical reheating whereas in-situ austempering or slow continuous cooling followed by supercritical reheating was used for the CP alloys. The results showed that yield strength (YS) of 605MPa & 695MPa, ultimate tensile strength (UTS) of 1097MPa & 1242MPa with a total elongation (TE) of 12.6% & 14.1% can be achieved in the best performing DP alloys with a martensite content of 65% & 60 vol.%. The best CP alloys with austempering achieved YS of 673MPa & 699MPa, UTS of 983MPa & 1026MPa and TE of 9.2% & 13.6% with RA of 4%-12 vol.%. The continuously-cooled alloys achieved even better properties. Higher bendability at 1.0 mm gauge in the critical direction was achieved in the CP alloys (90o&107o) than in the DP alloys (73o&76o).
Effect of Different Microstructures on the Performance of Air-Cooled Forging Steel 46MnVS5 Fracture Splitting Connecting Rod
Authors: Wei Yang , Fang Wen , Zhang Chao Lei , Cai Bao Run , Liu Ya Zheng
Published: December 2018

This paper analyzed mechanical properties and splitting fracture performance of 46MnVS5 with different microstructures. It will provide support of date for new type of splitting fracture connecting rod materials. The results show that bainite has good strength and ductility, but its high ductility is bad for splitting fracture. Martensite and tempered martensite have high strength and low ductility, which is bad for using performance. Ductility of tempered sorbite is too high to meet splitting fracture performance. Tensile and yield strength, impact toughness of tempered troostite is 1569MPa, 1407MPa and 17.5J/cm2, respectively. Tempered troostite has high strength and good splitting fracture performance. Bainite+martensite and tempered troostite maybe two good choices for better splitting fracture and using performance.
Hydrogen-Assisted Fracture Mechanisms in Ultrafine-Grained CrNi Austenitic Stainless Steels with Different Initial Microstructures
Authors: Astafurov Sergey V. , Astafurova Elena G. , Moskvina Valentina A. , Maier Galina G. , Melnikov Eugene V. , Ratochka Il'ya V. , Mishin Ivan P. , Fortuna Anastasiya , Zakharov Gennady
Published: December 2018

We investigated the effect of electrolytic hydrogen-charging on regularities of plastic flow, strength and fracture mechanisms of AISI 316L and 321 austenitic stainless steels. In the steels, an ultrafine-grained structure of various morphologies was formed using methods of warm abc-pressing and thermomechanical treatment (cold rolling and annealing). Hydrogen-charging of ultrafine-grained steels reduces their yield strength and elongation. The high dislocation density and low-angle boundaries inhibit the effects of hydrogen embrittlement in 316L and 321 steels.
Evaluation of Microstructural Characteristics in Low-Cycle Fatigued Austenitic Stainless Steel Using X-Ray Line Profile Analysis
Authors: Kumagai Masayoshi , Kuroda Masatoshi , Akita Koichi , Kamaya Masayuki , Ohya Shinichi
Published: December 2018

X-ray line profile analysis was performed to evaluate the microstructural characteristics of low-cycle fatigued austenitic stainless steel, AISI 316. Strains were frequently applied to the specimens with three levels of the total strain ranges, 0.01, 0.02, and 0.03. The dislocation densities at the number of cycles for each strain condition were obtained by X-ray line profile analysis. In the case that the strain range was small, that is Δε = 0.01, dislocation densities were slightly increased until 53% of life time with the cycles, and then decreased. In the case that the strain ranges were 0.02 and 0.03, the dislocation densities were steeply increased during the first stage of the life time until around 10%. However, the variations after n/Nf ≃ 10% were different each other. In the case of Δε = 0.02, dislocation density did not increase significantly until the end of the life. But in the case of Δε = 0.03, the dislocation density monotonously increased until the end of the life. These tendencies agreed with the variations of stress amplitude. The relationship between dislocation density and stress amplitude could be expressed as Δσ/2 = 1.14ρ1/2 + 207 (Δσ [MPa], ρ1/2 [m−2]).
On the Microstructural Characteristics of UFG Microalloyed Steel Influencing the Mechanical Behavior under Dynamic Loading
Authors: Majta Janusz , Bloniarz Remigiusz , Kwiecień Marcin , Muszka Krzysztof
Published: December 2018

This paper presents a summary of a preliminary research aimed at producing ultrafine-grained (UFG) and heterogeneous microstructure in microalloyed steel and testing these materials under dynamic loading conditions (strain rates 800 s-1 and 1800s-1). The UFG and bimodal-structures, due to grain size, structural composition or morphology of structural components, were produced by an advanced thermomechanical processing, namely rolling in: hot, two-phase and cold-hot combined conditions. The advantage of bimodal microstructures is their maximization of mechanical behavior under extreme loading conditions due to promoted accumulation and interactions of geometrically necessary dislocations. The dynamic work-hardening behavior has been studied as a function of solute atoms and fine-scale, second-phase particles in the UFG and bimodal-structures. The substantial complexity of the phenomena, which occur through the evolution of microstructure and texture in response to dynamic loading, presents formidable challenges to theoretical model development of plastic deformation of UFG and bimodal-structures. Such an extraordinary work hardening provides an attractive strategy to develop optimal combination of mechanical properties i.e. strength/ductility ratio. A multi-scale analysis capable of including material behavior in different scales should be applied to discuss mechanical response of mentioned above microstructures and to help to analyze their influence on mechanical behavior under dynamic loading. The investigation was performed for a material of common application: high strength microalloyed steel X70. The experimental results show that strain rate sensitivity of the heterogeneous microstructures obtained by various thermomechanical rolling routes are significant, but not by a similar magnitude with the microstructure compositions and increasing strain rate.
An Integrated Model for Predicting Hierarchical Microstructure Evolution of Steel during Hot Rolling
Authors: Luo Chun Hui , Martin David , Pyykkönen Juha
Published: December 2018

A robust model for calculating the necessary process variables such as strain, strain rate and temperature in hot rolling of a steel plate or strip is presented in this paper. The applied approach includes a well-constructed velocity function in the deformation model that is validated using a commercial finite element solver. The developed microstructure model is then integrated into the process model and includes the most essential descriptions of restoration and austenite grain structure evolution phenomena during hot rolling. Furthermore, the concept of hierarchical grain structure evolution is described as a method track the evolution of un-recrystallized and recrystallized features of the microstructure throughout a given pass schedule. The most important outcome of this approach is that each grain size component is modelled separately based on its prior thermomechanical history. A computer implementation of these models called MICDEL is used together with a simulation example to demonstrate its capability of predicting process variables and austenite grain structure evolution in hot strip rolling of steel.
Notched Creep Damage Assessment Based on EBSD Observation for Austenitic Stainless Steel
Authors: Fujiyama Kazunari , Higashide Shuhei , Nomoto Kazuki
Published: December 2018

Creep damage processes for smooth and notched specimen of austenitic stainless steel through interrupted creep tests using multiple specimens. The material used was 18-8 stainless steel for boiler tube use. The mid-sections of interrupted creep test specimens were observed through SEM(Scanning Electron Microscope) instrumented with EBSD(Electron BackScatter Diffraction patter) equipment. IPF(Inverse Pole Figure) maps, Phase maps and GOS(Grain Orientation Spread) maps were used for investigating creep damage process. For smooth specimen, the relationship between macroscopic creep time fraction and GOS averaged for all pixels showed linearity, while the relationship between creep strain and the averaged GOS showed non-linearity regressed by Green function successfully. For notched specimen, the EBSD maps became noisy possibly due to extensive phase transformation under highly concentrated notch stress. Obtained GOS data for gamma phase only showed non-monotonic change with time and nominal strain. The evaluated local strains in the vicinity of the notch showed relatively small amount, which might cause the very long creep life compared with smooth specimen under the same nominal stress condition.
The Effect of Surface Preparation on Surface Damage and Sigma Formation in Duplex Stainless Steel
Authors: Higginson Rebecca L. , Cenci Michael , Rowlett Matthew , Kornienko Vladislav , Jepson Mark A.E.
Published: December 2018

Sigma formation in duplex stainless steels is known to be detrimental to the mechanical properties of the material and limits the alloys to low temperature applications. In this paper, the surface damage caused by grinding on different grit sizes or polishing, is assessed using EBSD. The surface finish is then related to the depth of sigma formation in the surface region with a quantification of how the surface finish effects the sigma nucleation and growth. Finally, the effect of surface finish and sigma formation on the oxidation characteristics of the material is considered.
Simulation Study on Shear Crack of Steel Plate
Authors: Zhang Suo Quan , Jiao Si Hai , Ding Jian Hua , Zhang Qing Feng , Jiang Hong Sheng
Published: December 2018

Abaqus software is used to simulate the deformation behavior of typical steel materials during the shearing process, and to analyze the displacement change of the materials during the shearing process, and to study the main causes of the steel plate shear cracks. The results show that the mechanical properties of the steel, especially the uniform elongation of the steel plate, are important factors affecting the shear crack. At the same time, the room temperature tensile curves of several typical steels are measured. The corresponding relationship between the curve characteristics and the shear cracks is in agreement with the simulation results. Keywords: shear crack, simulation, mechanical properties, uniform elongation
The Effects of Hot Deformation of Austenite on the Bainite Transformation in a Fe-C-Mn-Si-Cr Steel
Authors: Chen Shang Ping , Rana Radhakanta , Xiao Bin , Haldar Arunansu
Published: December 2018

The effects of hot deformation conditions in the stable austenite state on the transformation kinetics and morphology of bainite were examined using dilatometry, electron back scatter diffraction (EBSD) and X-ray diffraction (XRD) measurements in a carbide-free bainitic steel with a composition of Fe-0.34C-2Mn-1.5Si-1Cr (in wt.%). Both uniaxial tensile and compression tests were applied to study the effect of the deformation mode. The temperature, strain and strain rate of deformation were varied in the ranges of 820-1000 °C, 0.1-0.6 and 0.001-0.1/s respectively. It has been revealed that hot tensile deformation retards the austenite transformation to lower bainite. The overall transformation kinetics slows down and the final attained amount of bainite decreases after completion of the isothermal transformation at 350 °C. However, hot compression deformation accelerates the bainite transformation, increasing both the bainite transformation rate and the final amount of bainite formed. The total amount of bainite increases with decreasing the strain rate irrespective of the mode of deformation. The effect of the deformation temperature and strain on the bainite transformation is in a complicated manner depending on the deformation mode.
The Study in Improvement of Hole Expansibility for High-Strength Steel of 980MPa Grade
Authors: Yang Kuo Cheng , Tu J.F. , Chiang L.J. , Cheng W.J. , Huang C.Y.
Published: December 2018

Recently, due to the requirements of lightweight and safety, the grade of 980MPa high-strength steel has the demand of high hole expansibility and high yield strength. Due to the large difference of hardness between the soft ferrite and hard martensite, the traditional DP980Y dual phase steel has poor hole expansibility. In order to improve the hole expansibility of DP980Y dual phase steel, the best way is to modify the microstructure into a single-phase to eliminate the large difference of hardness. In this paper, the steel of nearly full bainite microstructure with small amount of ferrite and M/A constituents was studied. Compared to the DP980Y dual phase steel, it was found that this modified steel with a single-phase microstructure has the same grade of 980MPa of tensile strength, but can achieve the demand of higher yield strength and hole-expansion ratio. This study shows reducing the amount of ferrite can increase the homogeneity of matrix with the single phase to improve the hole expansibility. In addition, the use of lower bainite transformation temperature and lower carbon content has the higher hole-expansion ratio due to the less amount of M/A constituents.
Effect of Quenching and Partitioning Processing on Microstructure and Mechanical Properties of a Low Alloyed Steel
Authors: Pfleger Bernd , Gruber Marina , Ressel Gerald , Gruber Peter , Galler Matthew , Marsoner Stefan , Ebner Reinhold
Published: December 2018

The concept of quenching and partitioning (Q&P) is a tool to generate steels with high strength and high ductility resulting from a relatively high amount of martensite and austenite. As the parameters of the Q&P treatment influence the strength and ductility properties, the goal of this work was to analyze the effects of varying quenching and partitioning temperatures on the phase evolution, on the retained austenite phase fraction and on the mechanical properties. The phase evolution during heat treatment was analyzed by dilatometer and the microstructure after processing was characterized by light microscopy in combination with color etching according to Klemm. The austenite phase fraction and its carbon content were determined by X-Ray diffraction and the mechanical properties were evaluated by tensile tests. It is shown that the quenching temperature has a minor impact on the phase fraction of austenite as well as its stabilization by carbon and thus, also the mechanical properties. Furthermore, austenite transformation during the partitioning treatment is illustrated.
Link between Microstructure and Mechanical Behavior of Double Annealed Medium Mn Steel
Authors: Arlazarov Artem , Goune Mohamed , Hazotte Alain , Bouaziz Olivier , Kegel Frédéric
Published: December 2018

Double annealing of low carbon medium Mn steel was studied. The second intercritical annealing was done at 650°C within a range of holding time: 3min to 30h. Tensile properties of the steel were measured as a function of holding time and the relation between microstructure and mechanical behavior was analyzed. Furthermore, a model, based on the mixture law combined with the considerations of equivalent increment of work in each microstructural constituent during mechanical loading, was proposed. The individual mechanical behavior of each considered microstructural constituent was described with the approaches existing in the literature. The complete model shows a very good agreement with the experimental stress-strain curves and predicts well the optimum strength-ductility balance after 2h holding.
Plastic Deformation Simulation of Sintered Ferrous Material in Cold-Forging Process
Authors: Morokuma Yuki , Nishida Shinichi , Kamakoshi Yuichiro , Kanbe Koshi , Kobayashi Tatsuya , Shohji Ikuo
Published: December 2018

A cold forging process of Mo-alloyed sintered steel was simulated by finite element method (FEM) analysis considering density change in the process. Moreover, the effect of sintering time on the behavior of the densification and the plastic deformation of it in the cold-forging process was also investigated. Using the true stress-true strain diagram obtained by the compression test with a sintered specimen, the modified true stress-true strain diagram was derived for large plastic deformation analysis with the porous material model. The result of FEM analysis for the cold compression process of the sintered specimen revealed that the analysis can simulate the shape of the excessive metal part and density change of it. Also, it was found that local deformation becomes large and thus the excessive metal part extends with increasing sintering time although the difference in the true stress-true strain diagrams is negligible.
Effect of Heat Treatmemt in (α+γ) Range on Mechanical Properties of Austempered Spheroidal Graphite Cast Iron
Authors: Inoue Tatsuo , Torizuka Shiro
Published: December 2018

It is well known that austempered spheroidal graphite cast iron shows good tensile and elongation. And, retained austenite include in the austempered spheroidal graphite cast iron structure was known to effect for the mechanical properties when TRIP was occurred. On the other hand, fineness and homogeneity of the structure are considered to influence as a factor to improve mechanical property. In this study, the mechanical properties of spherical graphite cast iron was evaluated that it treatmented fineness prior-structure and austenitized at (α + γ) range followed by isothermal treatment at bainitic transformation temperature range. Compared the heat treatment of this study and typical austempering treatment, the mechanical properties with good balance of strength and ductility were obtained in the heat treatment of this study. But, retained austenite that it determined by x-ray diffraction was slightly changed before and after the tensile test. Therfore, it was considered that not TRIP but complex phase effect on mechanical properties.
Influence of Annealing Conditions on the Austenite Size at the End of Soaking
Authors: Salib Matthieu , de Diego Calderon Irene , Ferreira de Melo Caio , Mendonca e Silva Luiz Paulo , Arlazarov Artem
Published: December 2018

Influence of chemical composition (C, Mn and Nb) and soaking temperature on the evolution of austenite grain size from a cold-rolled microstructure was studied on several Advanced High Strength Steels. A wide range of soaking temperatures was used to perform the heat treatments. Characterization of prior austenite grain size from the annealed samples using optical and confocal microscopes, Scanning Electron Microscope and Electron Back-Scattered Diffraction. Comparison of different methods was done to validate the methodology and the results were quite satisfactory. Concomitant effects of Manganese, Niobium, Carbon and of soaking temperature on the prior austenite grain size were analyzed and discussed. Important effect of Mn and Nb was underlined.
Microstructure and Damage Mechanisms in Thermomechanically Treated Si-Solution-Strengthened Spheroidal Graphite Cast Iron
Authors: Sujakhu Surendra , Castagne Sylvie
Published: December 2018

Spheroidal Graphite Irons (SGIs) are ductile cast irons with toughness and ductility comparable to those of carbon steel. In particular, high silicon Solution Strengthened Ferritic (SSF) SGIs are developed to provide higher strength with excellent ductility suitable for structural applications. The main characteristics of these materials lie in the graphite particles inclusions whose morphology and count greatly influence the mechanical properties and more specifically the fatigue crack initiation and propagation behaviour of the SGI components. In this work, SGIs specimens have been subjected to various thermomechanical treatments in order to analyse the influence of these treatments on the microstructure of the material. Observations of degenerated forms of graphite particles alongside the spheroidal nodules in the microstructure were then used as a basis for correlation with damage mechanisms at the microscale. In static tensile testing, it was observed that the matrix-nodule interface decohesion and plastic deformation of the ferrite matrix were the dominant damage mechanisms. In separately performed fatigue crack initiation and fatigue crack propagation tests, it was confirmed that the graphite particle shape played a decisive role in crack initiation and propagation. The results of the microstructural characterization have been implemented in a computational model for further study of the influence of the microstructure on the fatigue behaviour of these materials.
Low-Temperature Fracture of Ultrafine-Grained Iron
Authors: Pakiela Zbigniew , Gizynski Maciej , Romelczyk-Baishya Barbara , Kulczyk Mariusz
Published: December 2018

Metals with a body-centered cubic structure such as iron exhibit a ductile-brittle transition which results in a brittleness below a particular temperature. This temperature depends on many factors such as strain rate, size and geometry of investigated samples or the purity of the material. Another important parameter influencing fracture mechanism is grain size. It is known that grain refinement can be an efficient way to change fracture mechanism.The goal of this study was to investigate fracture mechanisms of ultrafine-grained iron processed by hydrostatic extrusion (HE). Materials subjected to various total strain levels were tested. The average grain size of the HE-processed iron was below 350 nm. The mechanical tests were carried out at various temperatures, ranging from room temperature to liquid nitrogen temperature. It was found that the fracture mechanism depends on a density of dislocation and the loading direction. It was found that materials with the dislocation density above a certain critical value break in a ductile manner even at impact tensile test in liquid nitrogen. However, bending tests of miniature beams have shown that ductile fracture occurs only when the crack propagates along the radial direction of the extruded material, whereas, on the direction parallel to the axial direction, cleavage fracture was observed. A theoretical model explaining this phenomenon was proposed. This model is based on the Rice model and it considers the competition between two phenomena - dislocation slip in the stress field of the crack front and Griffith cleavage.
Dynamic Transformation of Austenite at Temperatures above the Ae3
Authors: Jonas John Joseph , Aranas Jr. Clodualdo , Rodrigues Samuel F.
Published: December 2018

Under loading above the Ae3 temperature, austenite transforms displacively into Widmanstätten ferrite. Here the driving force for transformation is the net softening during the phase change while the obstacle consists of the free energy difference between austenite and ferrite as well as the work of shear accommodation and dilatation during the transformation. Once the driving force is higher than the obstacle, phase transformation occurs. This phenomenon was explored here by means of the optical and electron microscopy of a C-Mn steel deformed above their transformation temperatures. Strain-temperature-transformation (STT) curves are presented that accurately quantify the amount of dynamically formed ferrite; the kinetics of retransformation are also specified in the form of appropriate TTRT diagrams. This technique can be used to improve the models for transformation on accelerated cooling in strip and plate rolling.
Induction Hardening of a 0.40 % C Novel Microalloyed Steel: Effects of Heating Rate on the Prior Austenite Grain Size
Authors: Javaheri Vahid , Khodaei Nasseh , Nyo Tun , Porter David A.
Published: December 2018

This work explores the effect of heating rate on the prior austenite grain size and hardness of a thermomechanically processed novel niobium-microalloyed 0.40 % carbon low-alloyed steel intended for use in induction hardened slurry pipelines. The aim was to identify the heating rates that lead to the maximum hardness, for high wear resistance, and minimum prior austenite grain size, for high toughness. For this purpose, a Gleeble 3800 machine has been employed to simulate the induction hardening process and provide dilatometric phase transformation data. The prior austenite grain structure has been reconstructed from the EBSD results using a MatlabR script supplemented with MTEX texture and crystallography analyses. Heating rates ranged from 1 to 50 °C/s and the cooling rate was 50 °C/s. The results show that the prior austenite grain size greatly depended on the heating rate: compared to the lower heating rates, the maximum heating rate of 50 C/s produces remarkably fine prior austenite grains and a fine final martensitic microstructure after quenching. In addition, a relation between the heating rate and the deviation from equilibrium temperature has been established.
Microstructural Evolution and Wear Behavior Involving the K-Carbides Precipitation of a Fe-25Mn-6.6Al-1.3C Austenitic Steel
Authors: Feng Yi Fan , Song Ren Bo , Pei Zhong Zheng , Li Lun
Published: December 2018

In this paper, the microstructural evolution and mechanical properties of the as-cast Fe-25Mn-7Al-1.3C austenitic steel after different heat treatment were investigated. After solution treatment and subsequent aging treatment, the κ-carbides with perovskite structure were found to precipitate coherently within the austenite matrix, which improved the initial hardness and mechanical strength. The experimental steel exhibited an optimal comprehensive performance after being solution treated at 1050 °C for 1 h and then aged at 550 oC for 2 h. The tensile strength was 751 MPa, the yield strength was 581 MPa, the elongation was 48%, the hardness was 252 HB, and the Charpy V-notch impact toughness was 168 J, respectively. The impact wear test was carried out on MLD-10 abrasive wear testing machine, and the worn out surfaces under different heat treatment were characterized by scanning electron microscopy (SEM). The results indicated that the abrasion resistance of the steel under the additional aging treatment was better than that of the as-solutionized steel. The optimal abrasion resistance was obtained after being soluted at 1050 °C for 1 h and then aged at 550 oC for 2 h. However, with the aging time increasing, the coarse κ-carbides precipitating around the grain boundaries would deteriorate toughness, which lead to increase of the abrasive wear volume loss. Besides, obvious micro-cracking and relatively larger peeling pit were observed.
Hot Straining and Quenching and Partitioning of a TRIP-Assisted Steel: Microstructural Characterization and Mechanical Properties
Authors: Echeverri Edwan Anderson Ariza , Poplawsky Jonathan , Guo Wei , Tschiptschin André Paulo
Published: December 2018

Advanced high strength steels (AHSS), with yield strengths over 300 MPa and tensile strengths exceeding 600 MPa, are becoming more noticeable in vehicle manufacturing. A novel processing route of a TRIP-assisted steel was developed. Characterization and modelling techniques were used to establish correlations between processing, microstructure and mechanical properties. Quenching and partitioning (Q&P) and a novel process of hot straining (HS) and Q&P (HSQ&P) treatments have been applied to a TRIP-assisted steel in a Gleeble ®3S50 thermo-mechanical simulator. The heat treatments involved intercritical annealing at 800 oC and a two-step Q&P heat treatment with a partitioning time of 100 s at 400 oC. The effects of high-temperature isothermal deformation on the carbon enrichment of austenite, carbide formation and the strain-induced transformation to ferrite (SIT) mechanism were investigated. Carbon partitioning from supersaturated martensite into austenite and carbide precipitation were confirmed by means of atom probe tomography (APT). Austenite carbon enrichment was clearly observed in all specimens, and in the HSQ&P samples it was slightly greater than in Q&P, suggesting an additional carbon partitioning to austenite from ferrite formed by the SIT phenomenon. By APT, the carbon accumulation at austenite/martensite interface was clearly observed. The newly developed combined process is promising as the transformation induced plasticity can contribute to the formability and energy absorption, contributing to fill the gap of the third generation of high-strength steels.
Microalloying Additions to Commodity C-Mn Structural Steels: Fundamental Strengthening Mechanisms Leading to Improvements in Mechanical Properties, Alloy Optimization, Reduced Alloy Costs and Robustness of Hot Rolling Processing
Authors: Barbosa Ronaldo , Uranga Pello , Rodriguez-Ibabe J.M. , Stahlheim Douglas , Rebellato Marcelo A. , Qiao Ming Liang , Houxin Wang
Published: December 2018

Niobium in steels can be used as substitutional solid solute or as precipitates. In solution, Nb exerts a solute drag effect delaying but usually not interrupting static recrystallization during hot rolling and increasing hardenability during post rolling cooling. Fine precipitates generated during rolling/cooling can interrupt recrystallization in finishing and precipitate in the ferrite matrix increasing strength. As a relatively fine precipitate Nb can also inhibit austenite grain growth during reheating.This paper highlights the idea that micro-additions of Nb, up to 0.02%, to ordinary commodity C-Mn structural steels can improve their strength. Industry trial results are presented giving evidence that mechanical properties can be improved, and a leaner/optimized chemistry may be used by adding these micro-quantities of Nb to otherwise ordinary commodity C-Mn steels.Microstructural analysis of a C-Mn vs. a leaner/optimized C-Mn-micro Nb steel along with austenite evolution modeling using MicroSim-PM© helped identifying which type of metallurgical mechanisms are in-play resulting in higher strengths. This alternative composition has led to lower costs, lower CE, improved microstructure and a more stable process.
Effect of Number of Roughing Passes on the Dynamic Transformation of Austenite during Simulated Plate Rolling
Authors: Rodrigues Samuel F. , Siciliano Fulvio , Aranas Jr. Clodualdo , Reis Gedeon S. , Allen Brian J. , Jonas John Joseph
Published: December 2018

When austenite is deformed within the austenite phase field, it partially transforms dynamically into ferrite. Here, plate rolling simulations were carried out on an X70 steel using rough rolling passes of 0.4 strain each. The influence of the number of roughing passes on the grain size and volume fraction of induced ferrite was determined. Up to three roughing passes applied at 1100 °C followed by 5 finishing passes at 900 °C were employed. The sample microstructures were analysed by means of metallographic techniques. Both the critical strain to the onset of dynamic transformation as well as the grain size decreased with pass number during the roughing simulations. For the finishing passes, the mean flow stresses (MFS`s) applicable to each schedule decreased when a higher number of roughing passes was applied. The volume fraction of dynamically formed ferrite retained after simulated rolling increased with the roughing pass number. This is ascribed to the increased amount of ferrite retransformed into austenite and the finer grain sizes produced during roughing. The forward transformation is considered to occur displacively while the retransformation into austenite during holding takes place by a diffusional mechanism. This indicates that both dynamic transformation (DT) and dynamic recrystallization were taking place during straining.
Effect of Heat Treatment on Impact Properties of TC10 Titanium Alloy
Authors: Qin Guihong , Yan Biao , Ji Bo , Lu Wei
Published: December 2018

The impact properties of TC10 treated with different solid solution temperature were tested. The microstructure change and fracture morphology were observed. The effect of solution temperature on the impact properties of TC10 titanium alloy was studied. The results show that with the increase of solution temperature, the primary alpha phase decreases, when the temperature reached 950 degrees, all of the primary alpha phase changed into the beta phase. From the fracture appearance, the specimen changes from ductile fracture to brittle fracture, impact properties change with the temperature increased first and then decreased, appeared in the middle of a stable maximum value.
Ultrasonic Spot Welding of an Aluminum Alloy for Automotive Applications
Authors: Peng He , Jiang Xianquan , Chen Dao Lun
Published: December 2018

To reduce fuel consumption and the resulting environment-damaging, climate-changing, costly, human death-causing emissions, lightweight aluminum alloys have been increasingly used in the transportation industry due to their low density, high specific strength, superior ductility, machinability, recyclability, and environmental friendliness. The structural applications of such aluminum alloys in the automotive industry unavoidably entail welding and joining process. While it is challenging to weld aluminum sheets via the conventional resistance spot welding developed mainly for joining steel sheets, an emerging solid-state joining technology known as ultrasonic spot welding (USW) is promising for joining aluminum alloys. This study was aimed to examine the feasibility of welding a 6022 Al alloy similarly (AA6022-to-AA6022) and dissimilarly (AA6022-to-ZEK100) in relation to welding energy. It was observed that there was a significant change in the interface grain size in the similar welding, exhibiting a characteristic fine-grained “necklace”-like structure along the welding line, while an intermetallic diffusion layer was present in the dissimilar welding of aluminum-to-magnesium alloys, and its thickness increased as the welding energy increased. The tensile lap shear strength first increased, reached its peak value at a certain energy, and then decreased with increasing welding energy. The strength of the dissimilar welded joints was about 55% of that of the similar welded joints. Three different modes of interfacial failure, nugget pull-out, and transverse through-thickness (TTT) crack growth were observed in the similar welded joints, while only interfacial failure was present in the dissimilar welded joints.