Showing papers in "Journal of Iron and Steel Research International in 2012"
TL;DR: In this article, the effects of sodium carbonate dosage, reduction temperature and reduction time on the qualities of final product and phase transformations in reduction process were discussed in detail, and the results showed that the final product (mass percent), assaying Fe of 90.87% and Al2O3 of 0.95% and metallization degree of 94.28% was obtained at an overall iron recovery of 95.76% under the following conditions of adding 8% Sodium carbonate, reduction roasting at 1050 °C for 80 min and finally magnetic separation of the reduced
Abstract: Red mud is the waste generated during aluminum production from bauxite, containing lots of iron and other valuable metals. In order to recover iron from red mud, the technology of adding sodium carbonate-reduction roasting-magnetic separation to treat high-iron red mud was developed. The effects of sodium carbonate dosage, reduction temperature and reduction time on the qualities of final product and the phase transformations in reduction process were discussed in detail. The results showed that the final product (mass percent), assaying Fe of 90.87% and Al2O3 of 0.95% and metallization degree of 94.28% was obtained at an overall iron recovery of 95.76% under the following conditions of adding 8% sodium carbonate, reduction roasting at 1050 °C for 80 min and finally magnetic separation of the reduced pellets by grinding up to 90% passing 0.074 mm at magnetic field intensity of 0.08 T. The XRD (X-ray diffraction) results indicated that the iron oxides were transformed into metallic iron. Most of aluminum mineral and silica mineral reacted with sodium carbonate during the reduction roasting and formed nonmagnetic materials.
118 citations
TL;DR: In this article, an empirical relationship was developed to predict the tensile strength of friction welded AISI 1040 grade medium carbon steel and austenitic stainless steel, incorporating the process parameters such as friction pressure, forging pressure, friction time and forging time, which have great influence on strength of the joints.
Abstract: Friction welding is a solid state joining process used extensively currently owing to its advantages such as low heat input, high production efficiency, ease of manufacture, and environment friendliness. Materials difficult to be welded by fusion welding processes can be successfully welded by friction welding. An attempt was made to develop an empirical relationship to predict the tensile strength of friction welded AISI 1040 grade medium carbon steel and AISI 304 austenitic stainless steel, incorporating the process parameters such as friction pressure, forging pressure, friction time and forging time, which have great influence on strength of the joints. Response surface methodology was applied to optimize the friction welding process parameters to attain maximum tensile strength of the joint. The maximum tensile strength of 543 MPa could be obtained for the joints fabricated under the welding conditions of friction pressure of 90 MPa, forging pressure of 90 MPa, friction time of 6 s and forging time of 6 s.
65 citations
TL;DR: In this paper, a quantitative analysis method of Nb in solution and in precipitates was proposed to quantitatively measure Nb either as solute in solution or in NbC precipitates, which are thought to be effective at pinning grain boundaries.
Abstract: Nb is often considered to be a powerful alloying element for controlling the recrystallization process in microalloyed high strength steels. However, Nb can be presented either as solute in solution, where it is thought to exhibit a strong solute drag effect, or as NbC precipitates, which are thought to be effective at pinning grain boundaries. Therefore, it is very important to quantitatively measure Nb in solution or in NbC precipitates. A quantitative analysis method of Nb in solution and in precipitates was proposed. The test procedure involved chemical dissolution, filtration and inductively coupled plasma atomic emission spectroscopic (ICP-AES) analysis. The amount of Nb in solution in Nb-microallyed steels under different treatment conditions was evaluated. The results show that the niobium and carbon contents in steels have a great effect on niobium dissolution kinetics. The solute Nb is more effective to retard dynamic recrystallization, while the NbC precipitates are more effective to inhibit static recrystallization. The results may help to comprehend effect of Nb in steels, and provide some guides in the design of new high strength Nb-bearing steels.
57 citations
TL;DR: In this article, the wear properties of two different crushers used for grinding raw materials of cement industry are compared using pin-on-disk wear test, the wear test was carried out with different loads on a pin.
Abstract: Wear properties of two different crushers used for grinding raw materials of cement industry are compared using pin-on-disk wear test. The wear test was carried out with different loads on a pin. Abrasive wear behavior of two alloys was evaluated by comparing mass loss, wear resistance, microhardness and friction coefficient. The mi-crostructure of the specimens was detected using optical microscope. The results showed that abrasive wear of high chromium cast iron is lower than that of Hadfield steel. Due to the presence of M7C3 carbides on the high chromium cast iron matrix, impact crushers exhibited higher friction coefficient.
56 citations
TL;DR: In this article, the microstructure and mechanical properties evolution of AISI 301LN metastable austenitic stainless steels during cold rolling were investigated and a wide range of cold thickness reduction (10% - 80%) was carried out in a four-high rolling mill at ambient temperature.
Abstract: The microstructure and mechanical properties evolution of AISI 301LN metastable austenitic stainless steels during cold rolling were investigated. A wide range of cold thickness reduction (10% – 80%) was carried out in a four-high rolling mill at ambient temperature. The X-ray and Feritscope MP30 were used to identify the strain-induced α′-martensite phase and its volume fraction, respectively. The microstructure was observed by optical micrograph and the mechanical properties were determined by tensile tests and microhardness. The results show that the strain-induced α′-martensite nucleated at the shear bands intersections and the growth of α′-martensite occurred by the repeated nucleation of new embryos. The volume fraction of strain-induced α′-martensite increased with increasing the cold rolling reduction. In addition, the percentage increased in the tensile strength is the same as that of hardness. The ratio between the average tensile strength and the average microhardness was found to range between 2.82 and 3.17.
42 citations
TL;DR: In this article, the relationship of time to minerals composition in sinters is investigated by mineragraphy are claritied observation and component analysis, and the effects of temperature and atmosphere on mineralization process.
Abstract: The relationship of time to minerals composition in sinters is investigated by mineragraphy are claritied observation and component analysis, and the effects of temperature and atmosphere on mineralization process. Results are obtained as follows. The initial melt forms below the eutectic temperature of CaO · Fe2O3 and CaO · 2Fe2O3, which is complex substance containing Ca, Fe, Si and Al, rather than the binary calcium ferrite melt. Minerals composition of binding phase is related to local content of silica in melt, which is influenced by temperature. Appearance of the melt promotes the transition from hematite to magnetite, which then alters the mechanism of calcium ferrite formation. Before the formation of magnetite, the contents of Fe and Ca within the multiple calcium ferrite decrease with temperature, but in the case of magnetite presence, the content of Fe increases solely with increase of temperature and decrease of oxygen potential. Temperature and atmosphere determine minerals composition together, and bring influence on sintering process in different ways. It can be deduced that temperature affects kinetics of the mineralization process, but atmosphere just plays a role in thermodynamics.
41 citations
TL;DR: In this article, microstructure evolution and mechanical properties of newly designed 0.1C-6Mn-0.5Si-1Al TRIP-aided steels under different annealing conditions and the effects of matrix micro-structure before intercritical anneal on the final microstructures were studied by means of X-ray diffraction (XRD), scanning electron microcopy (SEM), dilatometric simulation, optical microst structure (OM) and tensile testing in this work.
Abstract: Microstructure evolution and mechanical properties of newly designed 0. 1C-6Mn-0. 5Si-1Al TRIP-aided steels under different annealing conditions and the effects of matrix microstructure before intercritical annealing on the final microstructure were studied by means of X-ray diffraction (XRD), scanning electron microcopy (SEM), dilatometric simulation, optical microstructure (OM) and tensile testing in this work. The experimental results indicate that the TRIP steel with Mn of 6% could form a considerable amount of retained austenite with good TRIP effect after a simple intercritical annealing treatment, and the matrix microstructure before intercritical annealing treatment can greatly affect the final microstructure. The original microstructure of the ferritic matrix steel was eliminated, while annealed martensite was remained from the martensite matrix steel under the same intercritical annealing conditions.
40 citations
TL;DR: The solution-treated (ST) condition and aging precipitation behavior of 18Cr-16Mn-2Mo-1.1. 1N high nitrogen austenitic stainless steel (HNS) were investigated by optical microscope (OM), scanning electron microscope (SEM), and transmission electron microscopy (TEM).
Abstract: The solution-treated (ST) condition and aging precipitation behavior of 18Cr-16Mn-2Mo-1. 1N high nitrogen austenitic stainless steel (HNS) were investigated by optical microscope (OM), scanning electron microscope (SEM), and transmission electron microscope (TEM). The results show that the ST condition of 18Cr-16Mn-2Mo-1. IN HNS with wN above 1% is identified as 1 100 °C for 90 min, followed by water quenching to make sure the secondary phases completely dissolve into austenitic matrix and prevent the grains coarsening too much. Initial time-temperature-precipitation (TTP) curve of aged 18Cr-16Mn-2Mo-1. 1N HNS which starts with precipitation of 0.05% in volume fraction is defined and the “nose” temperature of precipitation is found to be 850°C with an incubation period of 1 min. Hexagonal intergranular and cellular Cr2N with >a = 0.478 nm and c = 0.444 nm precipitates gradually increase in the isothermal aging treatment. The matrix nitrogen depletion due to the intergranular and a few cellular Cr2N precipitates induces the decay of Vickers hardness, and the increment of cellular Cr2N causes the increase in the values. Impact toughness presents a monotonic decrease and SEM morphologies show the leading brittle intergranular fracture. The ultimate tensile strength (UTS), yield strength (YS) and elongation (El) deteriorate obviously. Stress concentration occurs when the matrix dislocations pile up at the interfaces of precipitation and matrix, and the interfacial dislocations may become precursors to the misfit dislocations, which can form small cleavage facets and accelerate the formation of cracks.
39 citations
TL;DR: In this paper, the authors investigated the corrosion behavior of the 110S tube steel in the environments of high H2S and CO2 content by using a high-temperature and high-pressure autoclave, and the corrosion products were characterized by scanning electron microscopy and X-ray diffraction technique.
Abstract: The corrosion behavior of the 110S tube steel in the environments of high H2S and CO2 content was investigated by using a high-temperature and high-pressure autoclave, and the corrosion products were characterized by scanning electron microscopy and X-ray diffraction technique. The results showed that all of the corrosion products under the test conditions mainly consisted of different types of iron sulfides such as pyrrhotite of Fe0.95S, mackinawite of FeS0.9, Fe0.985 S and FeS, and the absence of iron carbonate in the corrosion scales indicated that the corrosion process was controlled by H2S corrosion. The corrosion rate of the 110S steel decreased firstly and then increased with the rising of temperature. The minimum corrosion rate occurred at 110 °C. When the H2S partial pressure $$P_{H{_2}S}$$
below 9 MPa, the corrosion rate declined with the increase of $$P_{H{_2}S}$$
. While over 9 MPa, a higher $$P_{H{_2}S}$$
resulted in a faster corrosion process. With the increasing of the CO2 partial pressure, the corrosion rate had an increasing trend. The morphologies of the corrosion scales had a good accordance with the corrosion rates.
38 citations
TL;DR: In this article, the authors investigated the role of ESR in removal of oxide inclusions in die steel H13, including changes of species, morphologies, compositions, amounts and sizes, in the production of EAFLF→VD→ingot casting→electro-slag refining.
Abstract: Inclusion variations of die steel H13, including changes of species, morphologies, compositions, amounts and sizes, in the production of EAFLF→VD→ingot casting→electro-slag refining (ESR) procedure, were investigated by systematic sampling, and analyzed with scanning electron microscope (SEM), energy dispersive spectrum (EDS), and metallographic microscope. The variation mechanism was studied by comprehensive analysis of total oxygen, nitrogen, and acid soluble aluminum as well as chemical test of refining slag. Based on the investigations, technical measures for cleanness improvement were discussed. The results show that oxide inclusions in H13 steel change from irregular Al2O3→near globular CaO-MgO-Al2 O3 and CaO-Al2O3-SiO2 complex inclusions→finer CaO- Al2 O3 -SiO2 inclusions with higher CaO content→CaO-Al2 O3 -SiO2 inclusions with higher A12O3 content and irregular MgO-Al2O3 inclusions→fine irregular MgO-Al2 O3 -CaS inclusions in various steps of the production; the variations are related with changes of acid soluble aluminum content, reactions between slag and steel, re-oxidation of liquid steel during casting, and refining of ESR. It is also found that A12O3 inclusions are modified by refining slag in LF and VD refining; and ESR plays a good role in inclusion removal, especially in controlling the large linear VC-CrC- MoC inclusions distributed in grain boundaries. It is suggested that casting protection should be improved, and the basicity of refining slag and acid soluble aluminum content in steel should be raised.
37 citations
TL;DR: In this paper, TANDEM twin wire welding and twin wire gas metal arc welding (GMAW) were used to weld Q690 steel, a low-alloy high-strength structural steel used in the hydraulic support in the fully-mechanized mining face.
Abstract: Compared with using semi-automatic gas shielded arc welding, using automatic TANDEM twin wire welding and twin wire gas metal arc welding (GMAW) to weld Q690 steel, a low-alloy high-strength structural steel used in the hydraulic support in the fully-mechanized mining face, the welding speed, deposition rate, production environment and welding quality can be obviously improved. Compared with GMAW twin wire welding, a refined micro-structure in the weld and heat-affected zone (HAZ), narrow HAZ and improved joint strength were achieved with TANDEM on Q690. Also, due to the push-pull pulsed way in TANDEM welding, the droplet transfer, distribution on heat flow and interaction between two arcs were completely different from those in GMAW twin wire system. The heat input of TANDEM is only about 76.6% of GMAW, and correspondingly, the welding speed and welding seam can be obviously improved. The complete oscillation caused by TANDEM pulsed current occurred in the welding pool, which refined the grains in the microstructure. The results show that TANDEM twin wire welding is very suitable in the welding of Q690 used in the hydraulic support.
TL;DR: In this paper, the microstructure analysis and mechanical properties evaluation of laser beam welded AISI 409M ferritic stainless steel joints are investigated, and single pass autogeneous welds free of volumetric defects were produced at a welding speed of 3 000 mm/min.
Abstract: The microstructure analysis and mechanical properties evaluation of laser beam welded AISI 409M ferritic stainless steel joints are investigated. Single pass autogeneous welds free of volumetric defects were produced at a welding speed of 3 000 mm/min. The joints were subjected to optical microscope, scanning electron fractographe, microhardness, transverse and longitudinal tensile, bend and charpy impact toughness testing. The coarse ferrite grains in the base metal were changed into dendritic grains as a result of rapid solidification of laser beam welds. Tensile testing indicates overmatching of the weld metal is relative to the base metal. The joints also exhibited acceptable impact toughness and bend strength properties.
TL;DR: In this paper, the microstructure of composite was analyzed with optical microscope, SEM (scanning electron microscope)/EDX energydispersive X-ray and XRD (X-ray diffraction).
Abstract: Impact, friction and corrosion from the grinding balls and the grinding medium during the mineral processing result in liner breakage. Liner, made from Hadfield steel or alloyed steel, could not have served in wet grinding environment for more than ten months. Composite liner, made from HCWCI (high Cr white cast iron) and carbon steel, has been developed successfully with liquid-liquid composing process based on LFC (lost foam casting). The microstructure of composite was analyzed with optical microscope, SEM (scanning electron microscope)/EDX energydispersive X-ray and XRD (X-ray diffraction). According to micrograph, the combination region of two metals was staggered like dogtooth, no mixtures occurred between two liquid metals, and its interface presented excellent metallurgical bonding state. The results of mechanical property test show that, the hardness of HRC, the fracture toughness, and the bending strength are more than 61, 16.5 J/cm2 and 1 600 MPa, respectively. Comparison between liners made from bimetal composite and alloyed steel has also been investigated in industrial hematite ball mill. The results of eight months test in wet grinding environment prove that the service life of bimetal composite liner is three times as long as that of one made from alloyed steel.
TL;DR: In this article, the fracture behavior of cold sprayed 304 stainless steel coating in cold rolling process was studied and the fracture morphology was observed and analyzed, and the crack distributions along the longitudinal rolling direction of the coatings were also investigated and discussed.
Abstract: The fracture behavior of cold sprayed 304 stainless steel coating in cold rolling process was studied. The 304 stainless steel coatings were deposited on low carbon steel substrate by cold gas dynamic spray (CGDS) and then cold rolled, respectively. The fracture morphology of the coatings was observed and analyzed, and the crack distributions along the longitudinal rolling direction of the coatings were also investigated and discussed. The results showed that the cohesive strength of the cold sprayed 304 stainless steel coating was too low to be cold rolled. Microcracks were formed in the as-sprayed coatings and ran perpendicularly to the rolling direction. The spacing distance between these cracks decreased with the increase of the cold rolling reduction. In addition, it was also found that the initial crack generated at the surface of the coating and propagated from the surface to the interface along the weakly bonded particles. A theoretical analysis was developed for the coating fracture. It gave a critical minimum cohesive bonding strength of the coating for non-breaking in cold rolling process. The crack propagation manner of the cold rolled coatings was also discussed.
TL;DR: A high-manganese austenitic steel matrix (Mn13) composite reinforced with TiN ceramic particles was synthesized by means of Vacuum-Evaporation Pattern Casting (V-EPC) as mentioned in this paper.
Abstract: A high-manganese austenitic steel matrix (Mn13) composite reinforced with TiN ceramic particles was synthesized by means of Vacuum-Evaporation Pattern Casting (V-EPC). The composite microstructure and interface bonding of TiN/matrix were analyzed utilizing optical microscope (OM) and X-ray diffraction (XRD). The effects of different volume fraction of TiN on impact wear resistance were evaluated by MLD-10 impact wear test. The results showed that TiN was evenly distributed in composite layer and had a good interface bonding with matrix when the volume fractions of TiN were 27% and 36%, respectively. However, cast defects and TiN agglomeration occurred when the TiN volume fraction increased to 48%. Compared with high-manganese austenitic steel (Mn13), the impact wear resistance of the TiN-reinforced composite is better. In small impact load conditions, composite layer can effectively resist abrasives wear and TiN particles played an important role in determining impact wear resistance of composite layer. In large impact load, the synergistic roles of spalling of TiN particles and the increase of work hardening of Mn13 based material are responsible for impact wear resistance.
TL;DR: In this article, the precipitation kinetics of AlN and MnS in low carbon aluminium-killed steel was calculated. And the morphology, compositions and particle size distribution were investigated in three positions of the coil.
Abstract: The precipitation kinetics of AlN and MnS in low carbon aluminium-killed steel was calculated. Transmission electron microscopy (TEM), energy disperse spectroscopy (EDS) and phase analyses have been used to investigate the morphology, compositions and particle size distribution of AlN and MnS precipitates in three positions of the coil. The particles of AlN and MnS precipitates in the ferrite region after coiling and distributes along and adjacent to the ferrite grain boundaries. The shapes of AlN are plate-like, the precipitates size is about 10 to 60 nm; the shapes of MnS are spherical, the precipitates size is about 200 to 600 nm. The precipitation behavior of AlN is sensitive to the isothermal temperature and holding time, the precipitation quantity and particle size distribution of AlN in different positions of coil are unequal.
TL;DR: In this article, a composite silane conversion coating was developed on galvanized steel and the results showed that the surface of the composite coating was complete, consecutive and compact, and the coating could endure a neutral salt spray test for 72 hours without corrosion.
Abstract: In an aqueous solution of the mixtures of γ-amino propyl triethoxy silane and γ-glycidoxy propyl trimethoxy silane, a composite silane conversion coating was developed on galvanized steel. FESEM (field emission scanning electron microscope), XPS (X-ray photoelectron spectroscopy), ATR-FTIR (attenuated total reflection Flourier transform infrared spectroscopy) and SST (salt spray test) were used to characterize the obtained composite silane conversion coating and also the coating formation process was studied. The result showed that the surface of the composite silane conversion coating was complete, consecutive and compact. The coating could endure a neutral salt spray test for 72 h without corrosion. The result of salt spray test indicated that the composite silane conversion coating can provide a better corrosion inhibition than the coating which was composed of the single silane. Based on observation and analysis, it was proposed that the formation process of the silane coating on zinc should consist of three steps: the hydrolysis of the silane molecules, silane chemical adsorption and silane crosslinking condensation. The crosslinking reactions took place between γ-amino propyl triethoxy and γ-glycidoxy propyl trimethoxy silane during the forming process of the coating, and a high crosslinked density interpenetrating structure network was obtained, so the composite silane conversion coating could keep the corrosive substances from the zinc more effectively.
TL;DR: In this paper, warm compression tests were performed on the eutectoid steel to investigate the evolution of cementite morphology, and the results showed that the warm compression promoted the fragmentize and the spheroidization of lamellar cementites.
Abstract: The warm compression tests were performed on the eutectoid steel to investigate the evolution of cementite morphology. Several processing parameters, such as temperature, strain rate and reduction, were changed to analyze the effect of each parameter on spheroidization of cementite. The results showed that the warm compression promoted the fragmentize and the spheroidization of lamellar cementites. When the specimen was compressed with reduction of 50% at 700 °C and in the strain rate of 0. 01 s−1, the excellent spheroidized cementite was obtained. The mechanism of fragmentation and spheroidization of lamellar cementites during compression was discussed by using transmission electron microscope. The formation of spheroidized cementite was related to the time of compression process. The fragmentize of lamellar cementites was due to the extension of sub-grain boundary in the cementite. The spheroidization of cementite depended on the diffusion of carbon atoms at the tip of bended and breakup cementite.
TL;DR: In this article, the influence of rotational speed on the microstructure and mechanical properties such as hardness, tensile strength, and impact toughness of the dissimilar joints is discussed.
Abstract: Fundamental investigation of continuous drive friction welding of austenitic stainless steel (AISI 304) and low alloy steel (AISI 4140) is described. The emphasis is made on the influence of rotational speed on the microstructure and mechanical properties such as hardness, tensile strength, notch tensile strength and impact toughness of the dissimilar joints. Hardness profiles across the weld show the interface is harder than the respective parent metals. In general, maximum peak hardness is observed on the stainless steel side, while other peak hardness is on the low alloy steel side. A trough in hardness distribution in between the peaks is located on the low alloy steel side. Peak hardness on the stainless steel and low alloy steel side close to the interface increases with a decrease in rotational speed. All transverse tensile joints fractured on stainless steel side near the interface. Notch tensile strength and impact toughness increase with increase in rotational speed up to 1 500 r/min and decrease thereafter. The mechanism of influence of rotational speed for the observed trends is discussed in the torque, displacement characteristics, heat generation, microstructure, fractography and mechanical properties.
TL;DR: In this paper, a sinter pot test using blending mix was performed, and the results indicated that the ore blending scheme led to good sintering performance and sinter quality.
Abstract: In order to obtain good sintering performance, it is important to understand sintering properties of iron ores. Sintering properties including chemical composition, granulation and high-temperature behaviors of ores from China, Brazil and Australia. Furthermore, several indices were defined to evaluate sintering properties of iron ores. The results show that: for chemical composition, Brazilian ores present high TFe, low SiO 2 , and low Al 2 O 3 content. For granulation, particle diameter ratio of Brazilian ores are high; particle intermediate fraction of Chinese concentrates are low; and average particle size and clay type index of Australian ores are high. For high-temperature properties, ores from China, Brazil and Australia present different characteristics. Ores from different origins should be mixed together to obtain good high-temperature properties. According to the analysis of each ore's sintering properties, an ore blending scheme (Chinese concentrates 20% + Brazilian ores 40% + Australian ores 40%) was suggested. Moreover, sinter pot test using blending mix was performed, and the results indicated that the ore blending scheme led to good sintering performance and sinter quality.
TL;DR: The feasibility of paigeite treatment with iron nugget making process is proved in this paper, where carbon bearing pellets were made of boron containing iron concentrate and pulverized coal mainly, from 1 623 to 1 723 K with different heating time.
Abstract: The feasibility of paigeite ore treatment with iron nugget making process is proved. The isothermal reduction experiments at laboratory scale were carried out, using carbon bearing pellets which were made of boron containing iron concentrate and pulverized coal mainly, from 1 623 to 1 723 K with different heating time. The results indicated that iron nugget making process depends mainly on heating time and temperature. And the iron nugget and slag can separate in a clean manner at 1673 K for 15 min. For the iron nugget, the C content is 3. 57% (mass percent) and B is 0. 065% (mass percent). The B2O3 content of slag is 20. 01%, and the boron was concentrated into one phase which is identified as suanite (Mg2B3O5) during the solidification. With an extraction ratio of 80% under the atmospheric conditions, the activity of boron in slag is good. The boron-rich slag can be used to extract boric or boric acid and alleviate the shortage of boron resource. Through series of calculation and analysis related, it can be concluded that the recovery ratio of Fe and boron are about 98% and 97% respectively. The results show that this method is feasible and effective on the utilization of paigeite ore.
TL;DR: In this article, the kinetic curve of the high-temperature oxidation of austenitic stainless steel Cr18Ni11Cu3Al3MnNb at different temperatures was measured by weighting method.
Abstract: The kinetic curve of the high-temperature oxidation of austenitic stainless steel Cr18Ni11Cu3Al3MnNb at different temperatures was measured by weighting method. It is showed that the oxidation curves at 700 and 800 °C followed the parabolic law, and the steel presented an excellent anti-oxidation. The surface morphology and structure of the oxide film were studied by scanning electron microscopy and X-ray diffraction methods. A dense oxide film was attained at 700 and 800 °C, mainly composed of the hexagonal Al2O3, Fe2O3, and a small amount oxide of Cr at 700 °C. At 900 °C the oxide film started to delaminate, and was composed of (Cr, Fe)2O3 and the spinel CuCrMnO4 and Fe(Cr, Al)2O4.
TL;DR: In this paper, a multi-objective nonlinear programming model (MONPM) is proposed for steelmaking and continuous casting (SMCC) production process and a three-stage rescheduling method is proposed including the batches splitting (BS), forward scheduling method (FSM), and backward scheduling method.
Abstract: In the steelmaking and continuous casting (SMCC) production process, operation time delay may lead to casting break or processing conflict so that the initial scheduling plan becomes unrealizable. Existing research methods are difficult to guarantee the accuracy of the model and successful application to actual applications. The rescheduling problem in response to operation time delay is firstly analyzed. This is then followed by the establishment of a novel multi-objective nonlinear programming model (MONPM). In specifications, a three-stage rescheduling method is proposed including the batches splitting (BS), forward scheduling method (FSM) and backward scheduling method (BSM). As a result, the real-time application shows that the proposed rescheduling method efficiently ensures the continuous casting and dramatically shortens the redundant waiting time for molten steel in very short rescheduling time.
TL;DR: In this paper, energy-based models for predicting the low-cycle fatigue life of high-strength structural steels are presented, the models are based on energy dissipation during average of cycles, cycles to crack propagation and total cycles to failure.
Abstract: Energy-based models for predicting the low-cycle fatigue life of high-strength structural steels are presented, The models are based on energy dissipation during average of cycles, cycles to crack propagation and total cycles to failure, Plsstic strain energy per cycle was determined and found as an important characteristic for initiation and propagation of fatigue cracks for high-strength structural steels. Fatigue strain-life curves were generated using plastic energy dissipation per cycle (loop area) and compared with the Coffin-Manson relation. Low cycle fatigue life was found similar from both methods. The material showed Masing-type behavior. The cyclic hysterisis energy per cycle was calculated from cyclic stress-strain parameters. The fracture surfaces of the fatigue samples were characterized by scanning electron microscope and the fracture mechanisms were discussed.
TL;DR: In this article, the microstructure of the hot dip galvanizing TRIP steel consisted of ferrite, bainite, retained austenite and martensite during the short IBT time.
Abstract: Mechanical properties and microstructure in high strength hot dip galvanizing TRIP steel were investigated by optical microscope (OM), transmission electron microscope (TEM), X-ray diffraction (XRD), dilatometry and mechanical testing. On the heat treatment process of different intercritical annealing (IA) temperatures, isothermal bainitic transformation (IBT) temperatures and IBT time, this steel shows excellent mechanical properties with tensile strength over 780 MPa and elongation more than 22%. IBT time is a crucial factor in determining the mechanical properties as it confirms the bainite transformation process, as well as the microstructure of the steel. The microstructure of the hot dip galvanizing TRIP steel consisted of ferrite, bainite, retained austenite and martensite during the short IBT time. The contents of ferrite, bainite, retained austenite and martensite with different IBT time were calculated. The results showed that when IBT time increased from 20 to 60 s, the volume of bainite increased from 14.31% to 16.95% and the volume of retained austenite increased from 13.64% to 16.28%; meanwhile, the volume of martensite decreased from 7.18% to 1.89%. Both the transformation induced plasticity of retained austenite and the hardening of martensite are effective, especially, the latter plays a dominant role in the steel containing 7.18% martensite which shows similar strength characteristics as dual-phase steel, but a better elongation. When martensite volume decreases to 1.89%, the steel shows typical mechanical properties of TRIP, as so small amount of martensite has no obvious effect on the mechanical properties.
TL;DR: In this article, a numerical simulation model based on discrete element method (DEM) has been developed to analyze the burden distribution in the melter gasifier of COREX process, which is one of the earliest industrialized smelting reduction ironmaking technology.
Abstract: COREX process is one of the earliest industrialized smelting reduction ironmaking technology. A numerical simulation model based on discrete element method (DEM) has been developed to analyze the burden distribution in the melter gasifier of COREX process. The DEM considering the collisions between particles can directly reproduce the charging process. The burden trajectory, the location and the burden surface profile are analyzed in melter gasifier with a mixing charging of coal and direct reduction iron (DRI) at the same time. Considering the porosity of packed bed has an important effect on the gas flow distribution of melter gasifier, a method to calculate porosity has been proposed. The distribution of DRI and coal and the porosity in the radial direction are given under different charging patterns, which is necessary to judge the gas flow distribution and provide base data for further researching the melter gasifier for the next work in the future. The research results can be used to guide the operation of adjusting charging and provide important basis for optimizing the charging patterns in order to obtain the reasonable gas distribution.
TL;DR: In this paper, the effects of rolling and cooling conditions on microstructure and mechanical properties of low carbon cold heading steel were investigated on a laboratory hot rolling mill, and the results have shown that the mechanical properties exceed the standard requirements of ML30, ML35, ML40, and ML45 steel.
Abstract: Effects of rolling and cooling conditions on microstructure and mechanical properties of low carbon cold heading steel were investigated on a laboratory hot rolling mill. The results have shown that the mechanical properties of low carbon steels exceed the standard requirements of ML30, ML35, ML40, and ML45 steel, respectively due to thermomechanical controlled processing (TMCP). This is attributed to a significant amount of pearlite and the ferrite-grain refinement. Under the condition of relatively low temperature rolling, the mechanical properties exceed standard requirements of ML45 and ML30 steel after water cooling and air cooling, respectively. Fast cooling which leads to more pearlite and finer ferrite grains is more critical than finish rolling temperatures for low carbon cold heading steel. The specimen at high finish rolling temperature exhibits very good mechanical properties due to fast cooling. This result has great significance not only for energy saving and emission reduction, but also for low-carbon economy, because the goals of the replacement of medium-carbon by low-carbon are achieved with TMCP.
TL;DR: In this article, the performance of ORC units with dry and isentropic fluid was analyzed and an intuitive approach with simple impressions was developed to calculate the performances of the ORC unit.
Abstract: Low temperature exhaust gases carrying large amount of waste heat are released by steel-making process and many other industries, Organic Rankine Cycles (ORCs) are proven to be the most promising technology to recover the low-temperature waste heat, thereby to get more financial benefits for these industries. The exergy analysis of ORC units driven by low-temperature exhaust gas waste heat and charged with dry and isentropic fluid was performed, and an intuitive approach with simple impressions was developed to calculate the performances of the ORC unit. Parameter optimization was conducted with turbine inlet temperature simplified as the variable and exergy efficiency or power output as the objective function by means of Penalty Function and Golden Section Searching algorithm based on the formulation of the optimization problem. The power generated by the optimized ORC unit can be nearly as twice as that generated by a non-optimized ORC unit. In addition, cycle parametric analysis was performed to examine the effects of thermodynamic parameters on the cycle performances such as thermal efficiency and exergy efficiency. It is proven that performance of ORC unit is mainly affected by the thermodynamic property of working fluid, the waste heat temperature, the pinch point temperature of the evaporator, the specific heat capacity of the heat carrier and the turbine inlet temperature under a given environment temperature.
TL;DR: In this paper, a surface modified stainless steel (SS) was obtained by plasma surface alloying with Cu, which exhibits excellent antibacterial effects against E. coli and Staphylococcus aureus within 1 h.
Abstract: Stainless steel (SS) is not recommended to be used in hospital environments for work surfaces and door furniture due to the lack of antibacterial properties. To this end, a novel SS surface modified layer with both a quick bacterial killing rate and relatively thick has been obtained by plasma surface alloying with Cu. The microstructure, elements distribution and phase identification were analyzed by SEM, GDS, XRD and XPS. A spread plate method was adopted for evaluation of antibacterial property of specimens against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The experimental results demonstrate that the surface modified layer with the thickness of about 26 μm is uniform and dense. The layer is mainly composed of a mixture of pure Cu, expanded austenite phase and a few Fe3O4 phase. The Cu modified layer exhibits excellent antibacterial effects against E. coli and S. aureus within 1 h. No viable E. coli and S. aureus was found after 3 h (100% killed). The modified layer is relatively thick, hence it is expected that the Cu modified SS will have a durable antibacterial function.
TL;DR: In this article, the final temperature prediction models of molten steel in RH-TOP blowing refining process for interstitial free (IF) steel production were established under the condition of oxygen blowing and non-oxygen blowing respectively.
Abstract: In order to precisely control the final temperature of molten steel in RH (Ruhrstahl Heraeus)-TOP blowing refining, the final temperature prediction models of molten steel in RH-TOP blowing refining process for Interstitial Free (IF) steel production were established under the condition of oxygen blowing and non-oxygen blowing respectively. The results show that the beginning molten steel temperature of refining and the amount of added scrap were influential factors, the baking temperature in vacuum chamber was a factor that had small influence. When the model was operated, the hitting probability was above 95 % (under the condition of both oxygen blowing and non-oxygen blowing) of prediction deviation of ±10 °C. The accuracy is analyzed.