bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Prior Heat Treatment on Hardness Profile after Nitrocarburization in Medium Carbon Steel
Authors: Egashira Makoto , Nishitani Shigefumi , Yuya M. , Sano N.
Published: January 2010

Gaseous ferritic nitrocarburization is one of the major surface hardening methods to improve the fatigue strength of machinery parts made of medium carbon steels. The fatigue strength of nitrocarburized steel parts depends on the hardness profile below the surface; however, the mechanism of its evolution during nitrocarburization has not been fully understood. Recently, as-forged steels, in which thermal refining process like normalizing is omitted from the viewpoints of environmental considerations, energy savings and manufacturing cost reductions, have been widely used in the machinery parts industry. Therefore, it is important to understand the mechanism of hardness increase below the surface of the nitrocarburized steels with respect to the effect of prior refining heat treatment. In the present study, the hardness increase at the subsurface region of nitrocarburized steels containing 0.4mass%C was characterized, and the influence of prior normalizing treatment was investigated. Microstructure of both the as-forged and the normalized specimens was the ferrite/perlite mixture, while the ferrite volume fraction in the as-forged steel was smaller than the latter. These as-forged and normalized steels were gaseous nitrocarburized at 853K for 2 hours under the atmosphere of RX gas and NH3 gas mixture, and then they were oil-quenched to 373K. Overall hardness below the surface after nitrocarburization was higher for the specimen without prior normalizing treatment, although both specimens had the similar nitrogen concentration profiles and precipitation behaviors of the nitrides. However, it was found that the individual ferrite grains in the as-forged steel were more hardened than those in the normalized steel. These indicate that the most likely cause of the hardness increase near the surface after nitrocarburization is the solid solution hardening by dissolved nitrogen and that the ferrite grains of the as-forged steel were likely to soak up more nitrogen and were hardened to the higher degree since the similar amount of nitrogen were incorporated mainly within ferrite grains. Thus, the prior heat treatment strongly affects the amount of hardening through the ferrite fraction.
Effect of Grain Boundary Segregation of Phoshorus on the Hall-Petch Coefficient of Ferritic Iron
Authors: Fujihara M. , Nakada Nobuo , Tsuchiyama T. , Takaki Setsuo
Published: January 2010

In IF steel without interstitials, the Hall-Petch coefficient (ky) is low as about
100 MPa･μm1/2 but it is enhnced by adding some alloying elements. Author et al. has already reported that a small amount of carbon increases ky greatly while nitrogen does not give influence so much. On the other hand, it is already known that phosphorus has a tendency to segregate at grain boundary of polycrystalline ferritic iron and that phosphorus also gives some influence to ky. However, the effect of carbon is not considered on the evaluation of ky in steels containing phosphorus. In this study, effect of phosphorus on the ky of ferritic iron was investigated by varying the grain size in Ti bearing IF-steel with different amount of phosphorus. Besides, the concentration of phosphorus and carbon at grain boundary was estimated by the grain boundary segregation model proposed by Seah et al. and the interaction between phosphorus and carbon was discussed in connection with the change of ky.
Strengthening of Ferritic Steel by Interface Precipitated Carbides in Rows
Authors: Funakawa Yoshimasa , Seto Kazuhiro , Nakamichi Haruo
Published: January 2010

Precipitation-strengthening is widely applied to high strength steel sheet for automotive use since several strength grades are easily achieved by controlling amount of microalloyed component. Recently, finer carbide dispersion has been required to obtain higher strength by smaller addition of carbide formers like titanium and niobium. Here, interface precipitation, one of the carbide formation phenomena during γ→α transformation, can be the efficient method to promote very fine carbides by lowering precipitation temperature. This study deals with relationship between transformation temperatures and hardness of ferritic steel strengthened by carbides generated by the interface precipitation.
Two kinds of 0.04%C steels containing Ti and Nb of the same amount as carbon content in atomic were hot-rolled, followed by the soaking at various temperatures for 600s. The rapid-cooled samples before the soaking for 600s exhibited higher hardness than slow-cooled samples. Large carbides generated by interface precipitation were observed in slow-cooled Ti-bearing steel with a transmission electron microscope. In slow-cooled Nb-bearing steel, large NbC precipitated in austenite before γ→α transformation. The results are suggesting that lowering transformation temperature and suppressing carbides precipitation in austenite are important to obtain high strength by interface precipitation.
Simulation of Thermo-Mechanical Controlled Rolling and Continuous Cooling of Wire Rods
Authors: Guarnaschelli Claudio , Folgarait P. , Matera Susanna , Ripamonti Dario
Published: January 2010

In this study the effect of thermo-mechanical controlled rolling and continuous cooling of different grades of steel wire rod (e.g. high-carbon for cold drawing applications, medium-carbon micro-alloyed for cold forming) has been analysed through the application of a set of integrated mathematical models simulating hot rolling and continuous cooling, and a laboratory work involving hot rolling simulation on a pilot plant and heat treatments on a laboratory scale. The samples have been characterised by means of instrumented tensile tests, metallographic analyses including determination of pearlite interlamellar spacing, and controlled compression tests.
The results show that:
- The mechanical strength of high-carbon steel is essentially related to interlamellar pearlite spacing, and can be enhanced through the control of continuous cooling. Improvements in cold drawability can be obtained by means of prior austenitic grain size (PAGS) reduction, through the application of thermo-mechanically controlled hot deformation processes.
- In the case of medium-carbon micro-alloyed steels for cold forming, the reduced PAGS achieved by means of thermo-mechanically controlled process reflects on a closer control of as-rolled mechanical properties, avoiding hardness hot spots asking for annealing treatments before cold forming. Moreover, the finer ferrite grain size could affect the forces needed during forming at the same deformation level.
Dependence of Yield Strength on Ferrite Grain Size in Ferrite/Cementite and Ferrite/Pearlite Structures of Medium Carbon Steel
Authors: Hanamura T. , Torizuka S.
Published: January 2010

Medium carbon steels have low yield ratio (YR). In order to obtain high yield strength (YS) for them, different microstructures including ferrite(F)/cementite(C) and ferrite(F)/pearlite(P) are prepared and the microstructure for high YR as well as its mechanism is clarified. The purpose of this study is, therefore, to elucidate the effect of ferrite grain size on YS in the relationship between F/P and F/C structures having the same tensile strength (TS) level. In case of F/C, YS can be significantly improved through grain refinement with a slight decrease in ductile properties. This is particularly clear by comparison of F/C with a ferrite grain size of 0.6m and F/P, where both structures show the same TS level while the YS level is significantly different; F/P representing much smaller YS than that of F/C. It is also to be noted that F/P microstructure shows low YS compared to its high TS with a generation of dislocations at the interface between ferrite and cementite in its pearlite phase. In conclusion it is necessary to consider the difference in the YS-TS relationship between F/C and F/P in order to make the most of its forging processing.
Fatigue Performance of Laser Brazes in Advanced High Strength Steels
Authors: Janssen M.H.E. , Hermans M.J.M. , Janssen M. , Richardson I.M.
Published: January 2010

Advance high strength steels (AHSS), like dual phase (DP) and transformation induced plasticity (TRIP) steels, offer high strength and toughness combined with excellent uniform elongation. However, the higher alloying content of these steels limit their weldability and the thermal cycle of welding processes destroys the carefully designed microstructure. This will result in inferior mechanical properties of the joint. Therefore, joining processes with a low heat input, like brazing, are recommendable.
Data regarding mechanical properties of joints in DP and TRIP steel is limited, especially for brazed joints. Results with respect to the fatigue lifetime of laser brazed butt joints are presented. In DP and TRIP steel, crack initiation takes place at the braze toe. In DP steel the crack propagates through the base metal. In TRIP steel, however, the crack may either follow the interface or may continue through the steel depending on the maximum stress level. The different failure mechanisms are explained on the basis of process conditions, the microstructure and the stress state.
Effect of Si on Mechanical Property of Galvannealed Dual Phase Steel
Authors: Hironaka Satoshi , Tanaka Hiroshi , Matsumoto Takashi
Published: January 2010

The mechanical properties of galvannealed dual phase steels bearing Si were investigated, and then the effect of Si on work hardening behavior during tensile deformation was discussed. Both tensile strength and yield strength were increased with increasing Si content, especially increasing ratio of tensile strength was larger than that of yield strength. On the other hand, the decrease of uniform elongation was very small with increasing Si content. Therefore, tensile strength and total elongation balance was improved by Si addition. High Si (1.2%Si) steel exhibited higher work hardening rate than low Si (0.01%Si) steel in all strain region. Dislocation cell structures were observed at 8% tensile strain in low Si steel, while dislocation cell structures were scarcely observed and instead, tangled dislocations were dominantly observed in high Si steel. Furthermore, high Si steel exhibited higher the increasing ratio of dislocation density in ferrite during tensile deformation than low Si steel. These results indicated that the formation of dislocation cell structure was retarded by Si addition, which led to the increase of work hardening rate and resulted in the improvement of tensile strength and total elongation balance.
A Technical and Economic Analysis of Pig Iron Production
Authors: Kardas Edyta
Published: January 2010

Blast furnace work involves the flow of enormous volumes of raw materials. Modifications of the blast furmace operation parameters can bring about savings connected with materials consumption and also a reduction of production costs. The continuous technical-economic analysis of this process enables changes in the process to be observed by means of simple indexes. In this article, a technical-economic analysis of the blast furnace process is presented. It is based on the results of a Polish blast furnace with an overall capacity of 3200m3.
Action of Displacement Control on Vacuum Free Aluminum/Copper Diffusion Liquefaction Bonding
Authors: Kawakami Hiroshi , Kawabe Toshiharu , Suzuki Jippei
Published: January 2010

Quickness of fracture of Al oxide film is important especially for vacuum free Al/Cu bonding. Displacement amount and rate relate closely with fracture of oxide film and create clean surface. Displacement history during bonding process under static bonding load was measured for displacement control systematically. Displacement history under static load consists of three stages with creep and liquefaction. Higher bonding load increased displacement rate of each stage and decreased the thickness of Al oxide film grown by air heating. Suitable hearing time for bond also was shortened by increment of bonding load. Two types of displacement control were designed from these experimental results. One was the accelerated displacement rate control, another was the cyclic displacement control. Fracture of Al oxide film and liquefaction of bonding surface occurred at lower displacement than static load by each displacement control.
First-Principles Calculations and the Thermodynamics of Cementite
Authors: Jang Jae Hoon , Kim In Gee , Bhadeshia H.K.D.H.
Published: January 2010

Thermodynamic data for the substitution of silicon and manganese in cementite have been estimated using first-principles methods in order to aid the design of steels where it is necessary to control the precipitation of this phase. The need for the calculations arises from the fact that for silicon the data cannot be measured experimentally; manganese is included in the analysis to allow a comparison with its known behaviour. The calculations for Fe3C, (Fe11Si4c)C4, (Fe11Si8d)C4, (Fe11Mn4c)C4 and (Fe11Mn8d)C4 are based on the total energy all-electron full-potential linearized augmented plane-wave method within the generalized gradient approximation to density functional theory. The output includes the ground state lattice constants, atomic positions and bulk moduli. It is found that (Fe11Si4c)C4 and (Fe11Si8d)C4 have about 52 and 37 kJ greater formation energy when compared with a mole of unit cells of pure cementite, whereas the corresponding energy for (Fe11Mn4c)C4 and (Fe11Mn8d)C4 is less by about 5 kJ mol1. These results for manganese match closely with published trends and data; a similar comparison is not possible for silicon but we correctly predict that the solubility in cementite should be minimal.
Strain Hardening and Damage in 6xxx Series Aluminum Alloy Friction Stir Welds
Authors: Simar Aude , Nielsen Kim Lau , de Meester Bruno , Pardoen Thomas , Tvergaard Viggo
Published: January 2010

A friction stir weld in 6005A-T6 aluminum alloy has been prepared and analyzed by
micro-hardness measurements, tensile testing and scanning electron microscopy (SEM). The
locations of the various weld zones were determined by micro-hardness indentation measurements.
The flow behavior of the various zones of the weld was extracted using micro-tensile specimens cut
out parallel to the welding direction. The measured material properties and weld topology were then
introduced in a fully coupled micro-mechanical finite element model, accounting for nucleation and
growth of voids as well as void shape evolution. The model shows satisfactory preliminary results
in predicting the tensile behaviour of the weld and the true strain at fracture.
A View on the Strategy in the Processing of Hot Rolled Dual Phase Steels
Authors: Leysen Frans , Penning Jan , Houbaert Yvan
Published: January 2010

As already intensive studies related to the processing of hot rolled dual phase steels have been reported in the past, the aim of this particular paper is to present some details within a processing strategy, that can be considered as useful for the processing of other special steel types. It will be shown that based on fundamental dilatometric measurements performed in the laboratory, a narrow window of processing parameters can be focused at. Moreover, practical dilatometric curves are shown, taking into account the transformation heat release in the arrested cooling zone (dry section), as to be considered regarding the industrial practice.
Furthermore, by introducing a slab insert technique within the development schedule, not only time consuming research can be limited, especially main objectives can be achieved. Some of these objectives are: a) a simultaneous study of the influences of the chemical composition of the steels, b) a close control of the thermomechanical parameters encountered in the industrial environment, such as rolling reductions, strain rate and inter pass time conditions, c) a check of the homogeneity of mechanical properties versus the coil length.
Effect of Retained Austenite Stability on Mechanical Properties of 590MPa Grade TRIP Sheet Steels
Authors: Matsuda Hiroshi , Noro Hisata , Nagataki Yasunobu , Hosoya Yoshihiro
Published: January 2010

Industrial low alloy TRIP sheet steels contain blocky and lath-shaped retained austenite. In the present study, transformation behaviour of blocky and lath-shaped retained austenite during straining was investigated to clarify its effect on mechanical properties. Two types of TRIP steels containing almost the same amount but the different morphology of retained austenite were used. A steel containing large amount of lath-shaped retained austenite exhibits superior ductility, and sustains high work-hardenability in a high strain region. On the contrast, a steel containing large amount of blocky retained austenite exhibits low ductility. 　The work-hardenability increased steeply to the maximum at a low strain region, and then reduced in a high strain region. The stability of the blocky austenite has been found to be poor with respected to martensite transformation. The lath-shaped retained austenite remains until a high strain region whereas the blocky retained austenite transformed into martensite in a low strain region. Carbon content was higher in the lath-shaped retained austenite than in the blocky retained austenite. Stability of retained austenite is, however, inexplicable only by the carbon content, and would be affected by the different morphology and the resulting restraint conditions.
Successful Transition from Wrought Iron to Steel in Hot Work Processing with Mechanism Differences
Authors: McQueen H.J.
Published: January 2010

The metallurgical revolution of increased supply and decreased cost followed three stages: 1) coke use in the blast furnace, 2) puddling process for wrought iron (WI) and 3) Bessemer or Siemens processes for steel. The second gave rise to the conversion from wooden (iron-reinforced) machines to iron machines such as railroad engines, ships and long-span bridges, all hot-riveted. The self-made mechanical engineers raised the precision, scale and speed of mechanical shaping technology; this was transferred from WI to ingot steel with little difficulty for the same products with increased strength. Accurately measured mechanical properties of WI and steel were related for the first time to microstructure and processing by David Kirkaldy to improve Clyde-built ships and to propel metallurgy from artisanal to science-based.
Effects of Nb, V, Ti and Al on Recrystallisation/Precipitation Interaction in Microalloyed Steels
Authors: Gómez Manuel , Rancel Lucía , Medina Sebastián F.
Published: January 2010

Recrystallisation/precipitation interaction in four steels having Nb, V, Ti, and Al, respectively, as microalloying elements has been studied by means of hot torsion tests. Remarkable differences were found in the results obtained for each steel. Nb and V-microalloyed steels presented long inhibition plateaus, but the steel with Al displayed a very short plateau. Finally the steel with Ti did not show plateau. This means that Nb and V precipitates (nitrides and carbides) can inhibit the static recrystallization but this does not happen for Al and Ti (which form nitrides). The difference between activation energies allows to predict the efficiency of different precipitates to strengthen the austenite during hot rolling. RPTT diagrams showed the interaction between both phenomena, along with the strain induced precipitation kinetics and precipitate coarsening. It is found that AlN particles nucleate and grow faster than NbCN or VN.
Monitoring Phase Transition Kinetics in Austempered Ductile Iron (ADI)
Authors: Meier Leopold , Schaaf Peter , Cusenza S. , Höche D. , Bamberger Menachem , Amran Yogev , Weiss K. , Hofmann Michael , Hoffmann Hartmut
Published: January 2010

Austempered ductile iron (ADI) is a very attractive material for applications where high strength, good ductility, wear resistance and fatigue strength are required. Thus, it offers design engineers an alternative to steel and aluminium alloys. ADI essentially is a cast ductile iron that undergoes a specially designed austempering heat treatment, which creates a microstructure of high carbon austenite and bainitic ferrite along with graphite nodules. The final proportion of these phases (and thus the mechanical properties) depends on the phase transformation kinetics which is strongly affected by composition, as-cast microstructure and heat treatment parameters (austempering).
ADI samples were austempered (heat treated) and the phase transitions were analysed after interrupted austempering. The phase fractions (austenite, ferrite, martensite, etc.) and their relation to bulk properties, like electrical resistivity, magnetic properties and mechanical properties (e.g. strength, hardness), and others were measured using optical and electron microscopy, X-ray and neutron diffraction, Mössbauer spectroscopy, and micro hardness measure¬ment. This combination of complementary techniques allows the correlation of the phase transition kinetics with the resulting properties.
Grain Refinement Mechanisms of Plain C-Mn Steel by Super Short Interval Multi-Pass Rolling in Stable Austenite Region
Authors: Miyata Kaori , Wakita Masayuki , Fukushima S. , Tomida Toshiro
Published: January 2010

One of noble grain refinement methods to attain ferrite grain size of around 1m in plain C-Mn steel has been so-called super short interval multi-pass rolling (SSMR) process, which is characterized by finish-rolling above Ae3, extreme short interpass time and then rapid cooling. The transformation mechanisms are demonstrated by the microstructural observation of an fcc Ni-Fe model alloy and C-Mn steels. In the Ni-Fe alloy hot-rolled by SSMR, equiaxed and cellar array of dislocation walls with low and high angle misorientations are observed in shear directions without recrystallization. The average spacing between the dislocation walls in the Ni-Fe alloy is in good agreement with the ferrite grain size of the C-Mn steel by SSMR process. On the other hand, in the C-Mn steel quenched to bypass ferrite transformation, the fine ferrite nuclei have been identified along intra-granular shear directions in the quenched martensite. It is concluded that the dislocation substructure in heavily deformed austenite by SSMR process have high potency as inherited ferrite nucleation
Friction and Wear Properties of Zr and TiC-Based Cermet Specimens in a Hydrogen Gas Atmosphere
Authors: Murakami Takashi , Kaneda Katsuo , Mano Hiroki , Hata Masayuki , Sasaki Shinya , Sugimura Joichi
Published: January 2010

In this study, Zr, Ti and TiC-based cermet specimens were prepared, and their friction and wear properties in various gas atmospheres were examined. The Zr specimens exhibited the lowest friction coefficients and the smallest volume change in the H2 gas atmosphere. This reason would have been due to the formation of the -type Zr hydride, which has a layered crystal structure. The Ti specimens exhibited similar friction and wear properties, although the TiC-based cermet specimens containing small amount of Mo, Ni and W exhibited the lowest friction coefficients in air, not in the H2 gas atmosphere. The low friction coefficients of the cermet specimens in air is likely to have been due to the formation of the low friction Mo oxides and W oxides.
Influence of Strain Path on Microstructure Evolution of Low Carbon Steels
Authors: Muszka K. , Sun Lin , Wynne Bradley P. , Palmiere Eric J. , Rainforth W. Mark
Published: January 2010

Changes in strain path represent one of the most important processing parameters that characterise hot metal forming processes. In the present study, the effect of strain path change on dynamic recrystallisation, strain-induced precipitation processes and phase transformation behaviour in plain carbon and Nb-microalloyed steels was investigated. To assess the effect of strain-path change, forward/forward and forward/reverse torsion tests were conducted. It has been shown that the strain reversal delays the dynamic recrystallisation kinetics whereas its effect on strain-induced precipitation process of Nb(C,N) is rather negligible. Also the onset of austenite-ferrite transformation is delayed; its products however doesn’t change significantly. This can be due to the fact that ferrite nucleation density plays the second order role compared to the geometry of deformation.
Influence of High-Mobility Boundaries on the Selective Growth of Goss Grain in Grain-Oriented Electrical Steel
Authors: Omura Takeshi , Hayakawa Yasuyuki
Published: January 2010

Behavior of the selective growth of Goss grains in grain-oriented electrical steel was investigated by controlling the heating rate in secondary recrystallization annealing．It was clarified that the important factors on the selective growth of Goss grains were the frequency and the mobility of grain boundary. It was demonstrated that boundaries having misorientation angle between 30 degree and 35 degree had the greatest influence on the selective growth, and the change of crystal orientation of secondary recrystallized grains expected by analyzing the change of primary recrystallized texture during secondary recrystallization annealing showed good agreement with the experimental result.
High Corrosion Resistance 21%Cr-0.4%Cu Ferritic Stainless Steel Contributing to Resource Conservation
Authors: Ota Hiroki , Ishii Tomohiro , Samukawa Takashi , Ujiro Takumi , Yamashita Hideaki
Published: January 2010

With prices for metal resources such as nickel and molybdenum soaring, there is a heightened sense of crisis concerning resource scarcity. While Type304, the most common stainless steel, offers excellent corrosion resistance, its price is affected significantly by the cost of nickel because of its 8% nickel content. The stainless steel that has the same corrosion resistance as that of Type304 and does not contain nickel and molybdenum has been required. JFE Steel Corporation has developed a new 21%Cr-0.4%Cu stainless steel, the world’s first ferritic stainless steel, which offers equivalent corrosion resistance to Type304 while containing absolutely no nickel or molybdenum, two rare metals. The newly developed steel contains 21% chromium with the addition of 0.4% copper. The development of the steel is based on a new discovery that the passive films of stainless steels could be strengthened by the synergy effect of high chromium content and copper addition. Copper addition enriches the chromium content in passive films after field exposure. Newly developed 21%Cr-0.4%Cu stainless steel is adopted for many applications as a substitution for Type304, including commercial kitchenware, building materials and industrial machinery. The steel is expected to be a new standard of a ferritic stainless steel as a substitution for Type304.
Linking Crystallographic, Chemical and Nano-Mechanical Properties of Phase Constituents in DP and TRIP Steels
Authors: Rijkenberg R. Arjan , Aarnts Maxim P. , Twisk Floor A. , Zuijderwijk Marga J. , Knieps M. , Pfaff H.
Published: January 2010

This paper discusses practical EBSD strategies for identification and partitioning of phase constituents in DP and TRIP microstructures including martensite, retained-austenite, bainite, intercritical and epitaxial ferrite. EBSD data is complemented with nano-indentation analysis, providing evidence of indentation-induced phase transformation of retained-austenite in TRIP steel and micro-crack initiation at the interface between ferrite and mechanically transformed martensite.
Influence of Continuous Annealing Conditions on the Microstructure and Mechanical Properties of a C-Mn Dual Phase Steel
Authors: Rocha Roberta O. , Melo Tulio M.F. , Santos Dagoberto Brandão
Published: January 2010

The influence of continuous annealing variables on the microstructure and mechanical properties of a C-Mn Dual Phase (DP) steel was studied. The annealing cycles were simulated using a Gleeble machine. Some specimens were quenched at different stages of the annealing cycle in order to evaluate the microstructural evolution during the annealing process. Tensile tests and microstrutural analysis were carried out. The results showed that high heating rates increased the final recrystallization temperature and as a consequence the microstructure obtained was refined. Austenite grain nucleation and growth were also influenced by the heating rates. Soaking temperature was the most influent variable on the mechanical properties, i. e., the yield strength increased and the tensile strength decreased with an increase in the soaking temperature. Microstructural analysis showed that not only martensite, but also bainite and martensite-retained autenite constituent (MA) were formed. Undissolved carbides were also detected by transmission electron microscopy.
Comparison of Grain Growth between Fine-Grained and Coarse-Grained Austenite in a Nb-V-Ti Microalloyed Steel
Authors: Sha Qing Yun , Qiao Li Feng , Xu Rong Jie , Huang Guo Jian , Sun Zu Qing
Published: January 2010

Comparison of grain growth of fine-grained and coarse-grained austenite in a Nb-V-Ti microalloyed steel during reheating or equalization at the same temperature was investigated using cold-charging and hot-charging specimens respectively in this study. The results show that the different grain growth behavior appears in fine-grained and coarse-grained austenite. The uniform grain growth and lower growth rate at reheating temperature studied was found in fine-grained austenite, while partial grain growth and higher growth rate was present in coarse-grained austenite. During reheating or equalization, the slow growth rate in fine-grained austenite may be contributed to stronger pinning force of fine precipitates while higher grain growth rate in coarse-grained austenite were believed to the result of lager size difference among part of grains. Grain coarsening occurs in fine-grained austenite as result of precipitate unpinning at extending holding time, but coarse-grained austenite remained wide size distribution at the same condition and this should not be considered as grain coarsening. coarse-grained austenite remained wide size distribution at the
Alloy Constitution Dependence of Strength and Deformation in Aluminum-Titanium-Vanadium Ternary Alloys Containing Gamma+Beta Dual Phase Microstructures
Authors: Takahashi Tohru , Liu Na , Yazawa Yusuke , Nunome Takuya
Published: January 2010

Compression and compressive creep behavior was studied on Al-Ti-V ternary alloys containing gamma+beta dual phase microstructures; the gamma phase was based on an L10 face centered tetragonal lattice and the beta phase on a disordered body centered cubic lattice. Yield strength and its temperature dependence have been compared with those in the gamma and/or beta single phase materials. The ternary alloy compositions were located on one assumed conjugate line across the gamma+beta dula phase field: the terminal compositions for the gamma and beta phase constituents were Al51Ti40V9 and Al35Ti20V45, respectively (numbers in atomic %). Three other alloys were prepared that contained different fractions of the constituent gamma and beta phases. The Al47Ti35V18, Al43Ti30V27, and Al39Ti25V36 alloys contained beta phase by about 22, 57, and 76 % in their area fractions. All these alloys showed limited deformability at temperature below 900K. The 0.2% proof stresses of the alloys were described in a similar way as a combination law at the room temperature; the 0.2% proof stress increased from about 500 to 1000 MPa with increasing the vanadium content. The high strength of the alloys containing high level of vanadium retained up to 900K, but the proof stress drastically diminished as the temperature was raised above 900K. Under compressive creep tests performed at temperatures ranging from 1100 to 1200 K, the minimum creep rates were smaller in the alloys containing less vanadium, and this could be ascribed to the fact that the beta phase was much softer than the gamma phase at higher temperatures than about 1000K.
Modeling of C-Mn Chromium Containing Steel to Produce DP600 through Thin Slab Direct Rolling
Authors: Wagih M. , Shahtout M. , Kady A.
Published: January 2010

The design of new steel grades and microstructures is mostly motivated by the necessity of steel industry to process always better suited high strength steel with low production costs. Automotive customers are asking for more steel options to meet increased specifications for strength, crash worthiness, energy absorption, part complexity, and dent resistance. To meet these requirements, new developed types of steel known as Advanced High-Strength Steels (AHSS) were introduced (e.g.: DP steel "Dual Phase", TRIP steel "Transformation Induced Plasticity",…etc). This paper presents a case study for producing DP600 dual phase steel in EZDK company through building up an integrated model to predicting both final austenite grain size after finishing rolling and the final ferrite grain size after cooling.
Effect of Grain Refinement on Mechanical Properties in 25Cr-1N Austenitic Steel
Authors: Tsuchiyama Toshihiro , Onomoto T. , Tsuboi K. , Takaki Setsuo
Published: January 2010

The Fe-25Cr-1N alloy produced by solution nitriding possesses extremely high yield strength owing to the solid solution strengthening by nitrogen. However, it was found that the steel exhibited an insufficient elongation because of the brittle intergranular fracture caused during the uniform tensile deformation. This is due to the marked stress concentration at grain boundaries, which is derived from the grain coarsening caused during long time solution nitriding and the development of planar dislocation structure characteristic of high nitrogen austenitic steels. The most effective way to reduce the stress concentration at grain boundary during deformation should be grain refinement. In this study, grain refinement was attempted by the two-step heat treatment for the Fe-25Cr-1N(-Mn) alloy, and then the mechanical properties were investigated by means of tensile tests and fatigue tests. The two-step heat treatment resulted in the grain refinement of austenite to 20 microns in diameter. The intergranular fracture was greatly suppressed from 70% (as-solution-nitrided) to 10% (grain-refined) in area fraction by the grain refinement. In addition, elongation was markedly increased with local necking. The yield stress and tensile strength were also increased, and thus, the fatigue limit is also raised by more than 30%.
Precipitation Behavior of Steels with Various Copper during Continuous Cooling
Authors: Wang Xue Min , Li Chuang , Shang Cheng Jia , Zheng Chang An , He Xin Lai
Published: January 2010

The precipitation behavior of several Cu-bearing steels with various copper contents during continuous cooling has been studied. The optical microscope and HRTEM were employed to study the influence of cooling rate on the precipitation process. Also, the hardness of samples with different processes is tested. The results show that when the steels was cooled at a cooling rate between 0.1-1°C/s with the cooling rate increasing the second phase precipitates become finer but the precipitates become denser. When the cooling rate is 1°C /s the density of the second phase precipitates are the largest. When the cooling rate is quicker than 1°C /s as the cooling rate increase the precipitates become finer and fewer. The hardness tests also show that the sample will get the highest hardness. When the samples are cooled at a rate larger than 5°C /s， there is few precipitates in samples. The copper-rich second phase form by Inter-phase precipitation, and the copper-rich phase i.e. G.P zone is the main cause to strengthen the alloy. As the copper content varies from 1.5wt% to 2.5wt% the highest hardness could be obtain when the samples is cooled at a rate of 1°C /s and the density of the precipitates is the largest
Temperature Development during Step-Wise Tensile Tests on a TRIP Steel
Authors: Zhao Lie , Thomser Corinna , Schneider Kirsten , Bleck Wolfgang , Sietsma Jilt
Published: January 2010

Temperature development during plastic deformation affects the stability of retained austenite and thus the mechanical properties in transformation-induced plasticity (TRIP) steels. In this work, we used a thermo-camera to monitor the temperature development during a step-wise tensile test of an Al-containing multiphase TRIP steel. The tensile tests were performed by loading the specimen at six straining rates ranging from 5 to 30 s-1 to a stress of 700 MPa and then holding for 15 min, followed by further loading at 50 s-1 until fracture. It is found that temperature increases about 13 – 18 °C during the first loading process and drops back to room temperature with a time-constant of around 2 min. The increment of temperature increases with increasing straining rate. The temperature increases around 30 °C during the second loading process. The distribution of temperature over the specimen surface is found to be rather homogeneous along the longitudinal direction in most cases, except for the ending points of two loading processes. The measurement of temperature development is found to be consistent with previous numerical simulation on the temperature development under constant stress in TRIP steels.
Microstructure and its Formation Mechanism of Weld Metal of Al-Bearing TRIP Steel
Authors: Peng Yun , Qi Yan Chang , He Chang Hong , Tian Zhi Ling , Xiao Hong Jun
Published: January 2010

A transformation-induced plasticity steel was welded by gas tungsten arc welding. The microstructure of fusion zone was analyzed by means of optical microscopy and scanning electron microscopy with EDS. It is found that fusion zone may be classified into two zones, the completely melted zone and the partially melted zone. The microstructure of completely melted zone consists predominantly of martensite and bainite, and that of partially melted zone consists mainly of martensite, bainite and ferrite. The formation mechanism of fusion zone microstructure is analyzed. The micro-hardness distribution of the joint was measured by microhardness tester. Test results show that the partially melted zone is softened, which is resulted from the formation of 20.6% ferrite. During the bending test, crack occurred at 125 degree bending angle. It is found that the crack originates from the partially melted zone because of deformation concentration.
Transverse Surface Cracks in Continuously Cast Steel Slabs, Oscillation Marks and Austenite Grain Size
Authors: Dippenaar Rian
Published: January 2010

Transverse surface cracks in low carbon steel slabs are invariably inter-granular and follow the soft ferrite films outlining the grain boundaries of exceptionally large prior-austenite grains often found at the roots of oscillation marks in continuously cast low-carbon steel slabs. Plastic deformation is concentrated in the ferrite films and cracks initiate in the ferrite films, leading to crack propagation along the austenite grain boundaries. Hot-ductility is significantly reduced by an increase in austenite grain size and in situ observations revealed that depending on the cooling rate, austenite can nucleate and grow by diffusional mechanisms or forms by a massive type of reaction. The delta-ferrite transformation has also been studied by using neutron diffraction techniques and high-energy X-rays in a synchrotron.
Effects of Casting Flux Interaction with Steel Melt on Lubrication in CC Moulds
Authors: Senk Dieter
Published: January 2010

Lubrication in CC moulds controls the shear forces to the sensible strand surface. Since that friction forces are depending on casting speed and the flux behaviour, a study on lubrication have experimentally been carried out when the slag is in contact with liquid steel. Particularly, higher amounts of aluminium in the steel as for pure de-oxidation lead to remarkable redox-reactions and to modified casting slags for the gap between strand and mould. Friction coefficients have been determined and applied to several strand shapes and castings velocities.
Physical and Chemical Mechanisms Occuring during A-TIG Welding: Comparison between Experimental Investigations and Simulations
Authors: Berthier Anne , Carin Muriel , Pellerin S. , Valensi F. , Paillard Pascal
Published: January 2010

In the present work, TIG and A-TIG welding were compared to show the arc constriction
phenomena. A 2D axial symmetric model was developed to simulate the flow behavior in the melting
pool. These results were compared to experiments carried out on a stainless steel disc (304L) melted
by a stationary heat source. The influence of the Marangoni effect, arc constriction and type of flux is
shown. The results point to the importance of the welding parameters and the use of a flux on the
characteristics of the weld beads.
Effect of Post-Weld Heat Treatment on Nd: YAG Laser Welded Ti-6Al-4V Alloy Quality
Authors: Cao Xin Jin , Debaecker Guillaume , Jahazi Mohammad , Marya Surendar , Cuddy Jonathan , Birur Anand
Published: January 2010

The effects of post-weld heat treatment on 3.05-mm thick Ti-6Al-4V alloy were investigated using a 4 kW Nd:YAG laser. Two main defects, underfill and porosity, were observed. The use of filler wire reduced underfill defects but slightly increased porosity. No cracks were detected. The as-welded and stress-relief annealed welds had very similar microstructures, hardness, and tensile properties. However, the post-weld solution heat treatment and aging transformed the martensite in the fusion zone into a coarse interlamellar α-β structure, causing a decrease in ductility but a more homogeneous distribution in the hardness of the welds.
Friction Stir Welding of Dissimilar AA 2024-T3 to AZ31B-H24 Alloys
Authors: Cao Xin Jin , Jahazi Mohammad
Published: January 2010

As a relatively new solid-state joining process, friction stir welding (FSW) may provide a feasible approach to join dissimilar materials such as Mg to Al alloys. In this work, the effects of selected process parameters including work-piece placement, pin tilting angle, and pin location on the quality of dissimilar AA 2024-T3 to AZ31B-H24 butt joints were investigated for the first time. Sound butt joints with low distortion and no solidification cavities or cracks were successfully obtained indicating the potential of FSW to join dissimilar Al to Mg alloys.
Butt Joining of High Strength Steel Sheet and Dissimilar Metal Sheet by Shot Peening
Authors: Harada Yasunori , Uemori Takeshi
Published: January 2010

In the shot peening process, the substrate undergoes large plastic deformation near the surface due to the hit with many shots. A large plastic deformation characterized by a shear droop occurs at the edge of the substrate. When the dissimilar sheets with the edge of the notch geometry are connected without level difference and then the contact area are shot-peened, the sheets can be joined due to the plastic flow generated by a large plastic deformation during shot peening. This method is similar to joining by caulking. The aim of this paper is to investigate the butt joining of high strength steel and dissimilar metal sheets using a shot peening process. The shot velocity and the coverage were controlled in the experiment. The shots used were made of high carbon cast steel and cemented carbide with an average diameter of 0.1 mm. The sheets were high strength steel and aluminum alloys. The influences of processing conditions on the joinability were mainly examined. The joint strength increased with the kinetic energy of shots. Tensile test was also examined to evaluate bond strength. It was found that the present method can be used to enhance the butt joining of high strength steel and dissimilar metal sheets.
Effect of Oxygen Content on Toughness in High Strength Weld Metal
Authors: Nakamura Shuichi , Hasegawa Toshiei , Shimura Ryuuichi , Kimoto Isamu
Published: January 2010

The effect of oxygen content on toughness in the high strength weld metals with full martensitic microstructures was investigated for Gas Metal Arc Welding (GMAW) and Gas Tungsten Arc Welding (GTAW). Solid and Flux cored two types wires were examined for their influence on the resulting oxygen content in weld metals. It has succeeded in controlling the oxygen contents without changing welding processes. As expected, the increasing oxygen content obviously decreased the upper shelf energy (vEshelf). One of the primary reasons of this tendency is considered that the higher density of oxide makes dimples on the ductile fracture surface smaller. On the other hand, as unexpected, the oxygen content from 7 to 450 ppm had no impact on the fracture appearance transition temperature (FATT), and oxides at the brittle fracture initiation point have not been found. This result supports that the oxides in high strength full martensitic weld metals (Vickers hardness = 360 ~ 430) have no harmful effect on FATT.
Comparison of Microstructures at As Welded Zone and Reheated Zone in 9%Ni Steel Similar Composition Weld Metal
Authors: Nako Hidenori , Okazaki Yoshitomi , Takeda Hiroyuki , Suenaga Kazuyuki , Nakanishi Kojiro
Published: January 2010

9%Ni steel similar composition weld wires are applied for constructions of liquefied natural gas storage tanks by gas tungsten arc welding and the weld metals show high toughness and strength level. In this study, the microstructures of 9%Ni steel similar composition weld metals have been investigated. It was found that fine microstructure was formed at the reheated zone and contributed to the high toughness level. The nucleation rate of blocks and packets from prior-austenite grain boundaries was larger at the reheated zone than the as-welded zone and resulted in the fine microstructure of the reheated zone. Our results showed that the lowering of Ni concentration at and near the prior austenite grain boundaries by the reverse transformation caused the larger nucleation rate at the reheated zone.
Research on High Heat Input Welding of the High Strength Electro-Gas Flux-Cored Wire Used for Large Storage Tank
Authors: Qu Zhao Xia , Zhang Han Qian
Published: January 2010

Baosteel cooperated with the China’s welding consumable company and developed an electro-gas welding wire BH610-EG, which is a flux-cored welding wire and can match the high strength steel B610E. In this paper, the electro-gas welding technological tests are carried out by B610E with the thickness of 21 mm and 40 mm and BH610-EG wire with the diameter of 1.6 mm. And values of the heat input of electro-gas welding experiments are in the range of 80~100kJ/cm. The main conclusions can be obtained as follows: (1) In condition of high heat input, the electro-gas welding process using BH610-EG wire is very stable, the weld surface is good. (2) Various mechanical properties of the welded joints can meet the design requirements of the storage tanks. (3) The new developed electro-gas flux-cored welding wire BH610-EG can match with B610E steel and meet the requirement of high heat input of the crude oil storage tank.
Influence of the Hardening Model on the Predicted Welding Distortion of DP600 Lap Joints
Authors: Schenk T. , Richardson I.M. , Eßer G. , Kraska M.
Published: January 2010

The accurate prediction of welding distortion is an important requirement for the industry in order to allow the definition of robust process parameters without the need to perform expensive experiments. Many models have been developed in the past decades in order to improve prediction. Assumptions are made to make the models tractable; however, the consequences are rarely discussed. One example for such an assumption is the strain hardening model, which is often a choice between either kinematic or isotropic hardening. This paper presents the results of tensile tests for DP600 performed from room temperature up to one thousand degrees and for different strain-rates. In order to employ a mixed isotropic-kinematic hardening model, the fractions of each hardening contribution have been determined by means of bend testing. The welding distortion of a DP600 overlap joint has been simulated and it is shown that such a mixed-hardening model results in more accurate and reliable results.