Influence of Thermal Homogenization Treatment on the Structure and Impact Toughness of H13 ESR Steel

 High levels of isotropy and homogeneous structure are very important criterion for high quality H13 hot work steel. In this paper, the cast microstructure of H13 ESR ingot and the influence of high temperature diffusion treatment on the structure and impact toughness have been investigated. The results show that: the dendrite arm spacing gradually becomes wide from the surface to the center of ingot and the interdendritic segregation areas always exist large primary carbides particles; by means of high temperature diffusion treatment of ingot prior to hot forging, the banded segregation is nearly eliminated, the annealed structure is more uniform and the isotropy properties have been improved remarkably.     

Effects of Si and Ni powder refining on the formation mechanism of nickel silicides induced by mechanical alloying

The synthesis of the Ni₂Si, Ni₅Si₂, and NiSi phases has been investigated by mechanical alloying (MA) of Ni-33.3 at. pct Si, Ni-28.6 at. pct Si, and Ni-50 at. pct Si powder mixtures. As-received and 60-minute premilled elemental powders were subjected to MA. The average surface area of the premilled Ni powder particles, which had a flaky shape, was 3.5 times larger than that of the as-received Ni powder particles, which had a spherical shape. The as-received Si powder was angular in shape and the mean particle size was 19.1 μm, whereas the mean particle size of the premilled Si powder was 10 μm. A self-propagating high-temperature synthesis (SHS) reaction, followed by a slow solid-state diffusion reaction, was observed to produce Ni silicide phases during MA of the elemental powders. The reactants and the product, however, coexisted for a long period of MA time. On the other hand, only the SHS reaction was observed to produce Ni silicides during MA of the premilled elemental powders, indicating that Ni silicides formed rather abruptly in a short period of MA time. The mechanisms and reaction rates for the formation of Ni silicides via MA appeared to be influenced by the elemental powder particle size and shape as well as the heat of formation of the products.     

Dispersion strengthening in a hypereutectic Al-Si alloy prepared by extrusion of rapidly solidified powder

When a hypereutectic aluminum-silicon alloy containing 16 wt pct silicon was rapidly solidified into powder using the spinning water atomization process, the individual powder grains were predominantly aluminum that was supersaturated with silicon and also contained well-dispersed 0.02-μm silicon particles. Although the silicon particles grew when the powder was extruded into a bar at temperatures from 673 to 803 K at an extrusion ratio of 4.3 and an extrusion speed of 0.9 mm/s, the average diameter was maintained on a submicron level. When the extrusion temperature was decreased from 803 to 673 K, the average diameter of the silicon particles in the extruded bar decreased from 0.8 to 0.5 μm, while the Vickers hardness (HV) and the ultimate tensile strength of the extruded bar increased from 120 to 160 (HV) and from 330 to 500 MPa, respectively. Both the hardness and the tensile strength of the extruded bars were several times higher than those of conventionally cast bars of the same alloy with cooling rates from 10⁻¹ to 10² K/s. On the other hand, the elongation decreased from 5.5 to 3.1 pct when the extrusion temperature was decreased from 803 to 673 K.     

Microstructure Variation of Pellets Containing Ferrous Dust during Carbonation Consolidation

The carbonation and microstructure characteristics of pellets containing ferrous dusts were investigated during carbonation consolidation at different reaction temperatures and CO2 partial pressures.The results indicated that green pellets had loose and network supporting structure with initial strength,and large cracks and pores existed in the pellets.The carbonation reaction was controlled by interfacial chemical reaction at the initial fast stage,which limited diffusion and thus caused the reaction rate to decrease.With increasing reaction temperature and CO2 partial pressure,the conversion rates of CaO and the number of microcrystalline CaCO3 particles increased,and the volume expansion of CaCO3 led to a decrease in the open porosity,average pore size and specific surface area of the pellets.Micro-pores were occluded,and the number of smaller pores(diameter less than 50nm)increased,thereby resulting in the more compact and uniform structure of carbonated pellets.Simultaneously,the dense structure prevented CO2 diffusion into the product layer,affecting the increase in carbonation conversion rate.     

Formation of TiN/TiC-Fe composites from ilmenite (FeTiO3) concentrate

The production of a ceramic hard material-metal composite directly from a mineral concentrate has great potential application. An homogenizing pretreatment of a mixture of ilmenite (FeTiO₃) and graphite, followed by annealing under an argon ambient, showed the formation of titanium carbide and elemental iron. Annealing of the same powder in nitrogen resulted in the formation of a composite of elemental iron and titanium nitride. The nitride was formed at a lower temperature than the carbide with almost complete conversion after 1 hour at 1000 °C. The rate of carbide formation was controlled by carbon diffusion, whereas the nitridation reaction was controlled by either oxygen or nitrogen diffusion. The TiC was found to form via TiC_0.5, which slowly increased its carbon content until near stoichiometric TiC was formed; stoichiometric TiN formed directly with no intermediate phases. Titanium carbide showed the presence of a second phase with a slightly smaller unit cell size; this was due to interdiffusion between the iron and TiC. The titanium carbide composite was found to be composed of 3 to 4 μm anhedral iron grains dispersed in the titanium-rich matrix. There was no segregation in the iron/titanium nitride composite with apparently submicron distribution.     

Conversion of induction heating temperature from ANSYS to DEFORM

In the production of hot extrusion pipes,the billet will be heated in an induction furnace,before piercing or extrusion,to a certain temperature.The induction heating temperature field profile in the billet will exert an influence on the deformation processes.The study has developed an data conversion program to convert the temperature data from induction heating by ANSYS to deformation simulation software DEFORM; therefore,not only the relatively accurate temperature field can be made available,compared with the usually assumed uniform temperature field,but also the connection between induction heating and deformation can be established,which is essential to evaluate the processing parameters.Numerical simulation of the piercing processes of different temperature fields by induction heating was carried out,and the results have shown that the different initial temperature fields in the billet can lead to different deformation curves,which indicates that the conversion program is necessary to study the production process of hot extrusion pipes.     

Healing Behavior of Micropores in Powder Metallurgy 316L Stainless Steel during Hot Forging and Heat Treatment

The healing behavior of micropores in powder metallurgy （P/M） 316L stainless steel during hot forging and subsequent heat treatment was studied. The results showed that hot forging can improve the homogeneity of the pore size and enhance the relative density of material in varying degree due to different forging temperatures. As a re- sult of deformation and diffusion bonding at high temperature, the irregular pores were spheroidized and finally turned into stable inner grain pores. The comparison of compression behavior between P/M and wrought dense mate rials has shown that the pores can either be the obstacles of dislocation movement or be the nucleation sites accelera- ting the reerystallization according to the difference of deformation temperatures.     

The incorporation of self-propagating,high-temperature synthesis-formed Fe-TiB2 into ferrous melts

Steel-matrix particulate composites were processed by direct addition of an Fe-TiB₂ master alloy powder to a BS970:080M30 medium-carbon steel. This powder was produced using a self-propagating, high-temperature synthesis (SHS) reaction and consisted of a dispersion of fine TiB₂ particles (2 to 5 μm), respectively, in an iron binder. The addition of the Fe-TiB₂ powder resulted in the formation a parasitic Fe₂B phase and TiC within the steel microstructure. In response to this, an SHS master alloy composed of Fe-(50 pct TiB₂+50 pct Ti) was manufactured, which, when added to the steel, prevented the formation of Fe₂B and resulted in a composite containing a mixture of TiB₂ and TiC particles. The effect of master alloy composition and addition level on the microstructural phases generated is discussed in detail. The response to heat treatment of composite materials manufactured in this way was also investigated. It was found that an isothermal hold at 840 °C leads to a substantial softening of the material processed using the Fe-TiB₂ additive, while at 1000 °C, a hardness level equivalent to that of the as-cast material was maintained. The same heat treatment of samples in which the formation of Fe₂B was suppressed resulted in no appreciable difference in hardness level or microstructure.     

Optimization and Model of Laminar Cooling Control System for Hot Strip Mills

The microstructure and mechanical propertiesof hot rolled strips are determined by the tempera-ture drop fromthe exit of finishing stand to the coi-ler .Laminar coolingis an effective way to make theproducts with ideal microstructure and mechanicalproperties and the coiling temperature must be con-trolled properly[1 -4]. The traditional models cannot meet the require-ment for high precision of coiling temperature . Theai m of present work was to develop a newlaminarcooling system with satisfac…     

Influences of liners and magnetic flux concentrator on induced Joule heat in hot extruded billet

In the production of pipes by hot extrusion method,billets should be heated to a certain temperature before hot extrusion by induction heating. The segmented liners in the induction furnace can possibly affect the circumferential Joule heat generation,thus leading to an uneven temperature field. The commonly used magnetic flux concentrators ( MFC) can increase the temperature on both ends of the billet. In this paper,the possible effect of liners and the factors affecting the utilization of the MFC,including the permeability,dimension and position,are all numerically studied and determined.     

Superplastic behavior of spray-deposited 5083 Al

A 5083 Al alloy was synthesized using spray deposition processing with N₂ as the atomization gas. It was noted that the grains that were present in as-spray-deposited 5083 Al were equiaxed with an average size of 15.2 μm. The matrix of the material was supersaturated with Mg and Mn. The asspray-deposited microstructure contained irregular pores with porosity in the range of 0.1 to 5.4 vol pct, depending on spatial location in the preform. The spray-deposited alloy was thermomechanically processed using extrusion and multiple-pass warm rolling to reduce grain size and close porosity. It was observed that spray-deposited 5083 Al exhibited superplasticity following thermomechanical processing by extrusion followed by rolling. Superplasticity was observed in the 500 °C to 550 °C temperature range and 3 × 10⁻⁵ to 3 × 10⁻³ s⁻¹ strain rate range. The corresponding strain-rate-sensitivity factors were in the 0.25 to 0.5 range and increased with decreasing strain rate. A maximum elongation of 465 pct was noted at 550 °C and 3 × 10⁻⁵ s⁻¹. The spray-deposited 5083 Al, thermomechanically processed by direct rolling, exhibited superplasticity in the same temperature and strain rate ranges as those for the extruded and rolled materials. The superplastic elongation of the spray-formed and rolled material was relatively low, being in the range of 250 to 300 pct. The deformation behavior is discussed in light of the presence of porosity in the microstructure.     

New Microalloyed Steels for Forgings

Microalloyed steels for forging applications have been newly developed in order to increase strength and toughness properties which thereby give the possibility for light weight constructions.The properties of these steels are set up by a controlled cooling directly from the forging heat without an additional heat treatment.This aim can be achieved on the one hand by a further development of precipitation hardening ferritic pearlitic steels (AFP-steel) due to an extended use of microalloying elements (AFP-M steel) and on the other hand by microalloyed steels which employ a bainitic microstructure (HDB steel).To adjust the targeted microstructure the temperature control has to be assured down to approx.500℃ for the AFP-M steels and down to approx.300℃ for the HDB steels.     

The microstructure and phase relationships in rapidly solidified type 304 stainless steel powders

The microstructure and relative amounts of fcc and bcc phases have been studied for rapidly solidified Type 304 stainless steel powders produced by vacuum gas atomization (VGA) and centrifugal atomization (CA). The VGA powder solidifies with a cellular microstructure while the CA powder has a dendritic microstructure. The volume fraction of fcc phase in the CA powder is found to increase from 40 Pct to 97 Pct with increasing particle size from 30 to 125 μm. In the VGA powder, the volume fraction of fcc phase is found to decrease from about 90 Pct to 77 Pct over the same range of particle sizes. The origins of the fcc and bcc phases in each powder are considered. It is concluded that bcc is present as both a primary crystallization phase in the smaller CA particles (<75 μm) and as compositionally stabilized eutectic ferrite at the cell walls of particles of both CA and VGA powders in which fcc was the primary crystallization phase.     

Three-dimensional Numerical Simulation and Experimental Analysis of Austenite Grain Growth Behavior in Hot Forging Processes of 300M Steel Large Components

The microstructure models were integrated into finite element (FE)code,and a three-dimensional (3D) FE analysis on the entire hot forging processes of 300M steel large components was performed to predict the distri-butions of effective strain,temperature field and austenite grain size.The simulated results show that the finest grains distribute in the maximum effective strain region because large strain induces the occurrence of dynamic re-crystallization.However,coarse macro-grains appear in the minimum effective strain region.Then,300M steel forg-ing test was performed to validate the results of FE simulation,and microstructure observations and quantitative analysis were implemented.The average relative difference between the calculated and experimental austenite grain size is 7.5 6%,implying that the present microstructure models are reasonable and can be used to analyze the hot forging processes of 300M steel.     

Combustion Synthesized Porous Body of Fe3O4/Al System by Controlled Microwave Heating and Heating Behavior of the Products

Microwave-induced substitutional combustion reaction was utilized to fabricate porous ceramic composite from Fe₃O₄/Al powder mixtures.The porous composite body was obtained by controlling the combustion reaction progress in a 2.45 GHz single mode applicator.Prior to the fabrication of the porous body,heating behavior of the powder mixtures were studied in the separated electric（E）and magnetic（H）fields.In addition,heating ability of the microwave fabricated porous product was also investigated.Fe₃O₄powder can be heated up easily in both maximum H and E field,but a better heating was observed in the maximum H field.Regardless of the mixtures ratio（mixing compositions）,maximum H field shows better heating characteristics.In E-field heating,temperature of the Fe₃O₄ samples decreased sharply when Al powder was added.However,the same phenomenon was not observed in the maximum H field heating.Thus,fabrication of the porous composite body was carrying out in maximum H field.Through an adequate control of the reaction progress,products with a porous structure consisting of well-distributed metal particles in the alumina and/or hercynite matrix were obtained.Consequently,heating of the fabricated porous composite body was also been successfully carried out in the maximum H field.Product phases and microstructure were the main factors influencing the heating ability of the porous composite body.     

Interfacial Microstructure of Al-Sn-Pb Alloy/Steel During Liquid-Solid Bonding Rolling

Studies were conducted on the interfacial microstructure of a steel/liquid aluminium and its evolution during the bonding rolling process. The effects of wetting time and deformation on the diffusion layer and on the bonding strength were examined. By means of electron microscopy and electron probe analysis, it was found that the diffusion layer is mainly composed of FeAI3. For a steel temperature of 250℃ and an aluminium temperature of 850 ~C, the diffusion layer was formed within 3 s, and the shear strength of the samples increased after 8 to 14 s. Although the interface was not damaged, it was deformed notably. For an aluminium temperature of 750℃ and a wetting time of 11 to 17 s, the shear strength of the interface remained high, but the interface was obviously broken during rolling, leading to reduced bonding strength.     

Synthesis of Nano-sized Yttria via a Sol-Gel Process Based on Hydrated Yttrium Nitrate and Ethylene Glycol and Its Catalytic Performance for Thermal Decomposition of NH4ClO4

Nano-sized yttria particles were synthesized via a non-aqueous sol-gel process based on hydrated yttrium nitrate and ethylene glycol. The effects of the molar ratio of ethylene glycol to yttrium ion and calcination temperature on crystallite size of the products were studied. The catalytic performance of the as-prepared yttria for the ammonium perchlorate (AP) decomposition was investigated by differential scanning calorimetry (DSC). The results indicate that the nano-sized cubic yttria particles with less than 20 nm in average crystallite size can be obtained after 2 h reflux at 70 ℃, dried at 90 ℃, forming xerogel, and followed by annealing of xerogel for 2 h, and that the addition of the nano-sized yttria to AP incorporates two small exothermic peaks of AP in the temperature ranges of 310 ～ 350 ℃ and 400 ～ 470 ℃ into a strong exothermic peak of AP and increases the apparent decomposition heat from 515 to over 1110 J·g-1. It is also clear that the temperature of AP decomposition exothermic peak decreases and the apparent decomposition heat of AP increases with the increase of the amount of nano-sized yttria. The fact that the addition of the 5 % nano-sized yttria to AP decreases the temperature of AP exothermic peak to 337.7 ℃ by reduction of 114.6 ℃ and increases the apparent decomposition heat from 515 to 1240 J·g-1, reveals that nano-sized yttria shows strong catalytic property for AP thermal decomposition.     

High Ductility and Toughness of a Micro-duplex Medium-Mn Steel in a Large Temperature Range from—196 ℃ to 200 ℃

A medium-Mn steel(0.2C5Mn)was processed by intercritical annealing at different temperatures(625 ℃ and 650 ℃).An ultrafine-grained micro-duplex structure consisting of alternating austenite and ferrite laths was developed by austenite reverse transformation(ART)during intercritical annealing after forging and hot rolling.Ultrahigh ductility with a total elongation higher than 30% was achieved in the temperature range from-196 ℃ to 200 ℃,and high impact toughness no less than 200Jat-40 ℃ was obtained.Based on the analysis of microstructure and mechanical properties,it was found that the enhanced ductility was determined by the phase transformation effect of austenite(TRIP effect),while the delayed ductile to brittle transition was controlled by austenite stability.     

Effect of Cooling Rate on the Room Temperature Microstructure Following the Intercritical Deformation of Steel S460

The effect of final hot rolling in the intercritical (α+γ) region on microstructure and properties is very specific to the individual processing conditions and the chemical composition of a steel.S460 is a plate steel processed in this way.To reproduce at the laboratory scale,a multi-stage simulation was developed which included a high temperature austenite deformation and an isothermal hold.The effect of the applied cooling rate following intercritical deformation was investigated.At 1K/s (typical industrial cooling) the microstructure was similar to the reference sample,but included an intragranular ferrite fraction.This was due to differences in processing history,and considered to be linked to a larger prior austenite grain size.At an accelerated cooling rate (15K/s),acicular ferrite formed on shear bands within the strained austenite phase.EBSD scans have been completed to provide further information about the microstructures,with band contrast able to identify the pearlite phase at the slowest cooling rate.This is a starting point from which to focus on the ferrite morphologies.     

Reduction Kinetics of Vanadium Titano-Magnetite Carbon Composite Pellets Adding Catalysts Under High Temperature

Experiments were carried out by adding CaF2 and NaF as catalysts in an Ar atmosphere to study the isothermal reduction kinetics of vanadium titano-magnetite carbon composite pellets under high temperature in the range from 1 473 to 1 673 K. The scanning electron microscope (SEM) was used to characterize the microstructure of product. By analyzing reduction mechanism, it was found that the rate controlling step was gas diffusion, and the activation energy was 178.39 kJ/mol without adding any catalysts. Adding CaF2 or NaF of 3% to vanadium titano-magnetite carbon composite pellets can decrease the apparent activation energy of reduction, and the decrease extent was 14.95 and 15.79 kJ/mol, respectively. In addition, temperature was an important factor influencing on reaction rate.