Effect of casting process on the inner-wall band segregation of high-strength antisulfur pipes

Controlling inner-wall band segregation is one of the difficulties in the production of high-strength antisulfur pipes.Comparative tests were carried out on different casting processes(superheat,mold electromagnetic stirring,end electromagnetic stirring,casting speed and soft reduction)for the smelting of high-strength antisulfur pipes.The microstructures of continuous-casting billets and hot-rolled or tempered pipes were analyzed using a metallographic microscope and scanning electron microscope.The mechanism and evolution law regarding the inner-wall band segregation of high-strength antisulfur pipes were studied,and the influence of different casting processes was explored.

Gating system optimization of high pressure die casting thin-wall AlSi10MnMg longitudinal loadbearing beam based on numerical simulation

High pressure die casting(HPDC) is a kind of near net shape manufacturing method. However, air entrapment in HPDC parts has serious effects upon the casting quality. In order to reduce the air entrapment defects in a AlSi10 MnMg alloy thin-wall longitudinal load-bearing beam produced by HPDC, different gating systems were designed and simulated by software Flow-3D to evaluate the entrapped air. Simulation results showed that when the beam is produced by the original designed gating system with a middle ingate, there exist obvious air entrapments in the critical area; the volume of air entrapment was reduced by replacing the middle ingate to an overflow well, and the filling of molten metal became more stable. When the middle ingate was removed for further improvement, the volume of air entrapment was decreased drastically. The parts with glossy surface and good microstructure have been successfully produced by using the final optimized gating system based on simulation results.

Solidification microstructure of M2 high speed steel by different casting technologies

The present work investigated the solidification microstructure of AISI M2 high speed steel manufactured by different casting technologies, namely iron mould casting and continuous casting. The results revealed that the as-cast structure of the steel was composed of the iron matrix and the M2C eutectic carbide networks, which were greatly refined in the ingot made by continuous casting process, compared with that by the iron mould casting process. M2C eutectic carbides presented variation in their morphologies and growth characteristics in the ingots by both casting methods. In the ingot by iron mould casting, they have a plate-like morphology and grow anisotropically. However, in the ingot made by continuous casting, the carbides evolved into the fiber-like shape that exhibited little characteristics of anisotropic growth. It was noticed that the fiber-like M2C was much easier to decompose and spheroidize after heated, as a result, the carbides refined remarkably, compared with the case of plate-like carbides in the iron mould casting ingot.

Influence of high pressure and manganese addition on Fe-rich phases and mechanical properties of hypereutectic Al-Si alloy with rheo-squeeze casting

The influence of high pressure and manganese addition on Fe-rich phases(FRPs)and mechanical properties of Al-14Si-2Fe alloy with rheo-squeeze casting(RSC)was investigated.The semi-solid alloy melt was treated by ultrasonic vibration(UV)firstly,and then formed by squeeze casting(SC).Results show that the FRPs in as-cast SC alloys are composed of coarseβ-Al5(Fe,Mn)Si,δ-Al4(Fe,Mn)Si2 and bone-shapedα-Al15(Fe,Mn)3Si2 phases when the pressure is 0 MPa.With RSC process,the FRPs are first refined by UV,and then the solidification under pressure further causes the grains to become smaller.The peritectic transformation occurs during the formation ofαphase.For the alloy with the same composition,the ultimate tensile strength(UTS)of RSC sample is higher than that of the SC sample.With the same forming process,the UTS of Al-14Si-2Fe-0.8Mn alloy is higher than that of Al-14Si-2Fe-0.4Mn alloy.

Determination of interfacial heat transfer coefficient and its application in high pressure die casting process

In this paper,the research progress of the interfacial heat transfer in high pressure die casting(HPDC)is reviewed.Results including determination of the interfacial heat transfer coefficient(IHTC),influence of casting thickness,process parameters and casting alloys on the IHTC are summarized and discussed.A thermal boundary condition model was developed based on the two correlations:(a)IHTC and casting solid fraction and(b)IHTC peak value and initial die surface temperature.The boundary model was then applied during the determination of the temperature field in HPDC and excellent agreement was found.

Best practices for making high integrity lightweight metal castings-molten metal composition and cleanliness control

To make high integrity lightweight metal castings,best practices are required in various stages of casting and heat treatment processes,including liquid metal composition and quality control,casting and gating/riser system design,and process optimization.This paper presents best practices for liquid metal processing and quality assurance of molten metal in both melting and mold filling.Best practices for other aspects of lightweight metal casting will be published separately.

High Cr white cast iron/carbon steel bimetal liner by lost foam casting with liquid-liquid composite process

Liners in wet ball mill for mineral processing industry must bear abrasive wear and corrosive wear, and consequently, the service life of the liner made from traditional materials, such as Hadfield steel and alloyed steels, is typically less than ten months. Bimetal liner, made from high Cr white cast iron and carbon steel, has been successfully developed by using liquid-liquid composite lost foam casting process. The microstructure and interface of the composite were analyzed using optical microscope, SEM, EDX and XRD. Micrographs indicate that the boundary of bimetal combination regions is staggered like dogtooth, two liquid metals are not mixed, and the interface presents excellent metallurgical bonding state. After heat treatment, the composite liner specimens have shown excellent properties, including hardness 〉 61 HRC, fracture toughness ak 〉16.5 J.cm2 and bending strength 〉1,600 MPa. Wear comparison was made between the bimetal composite liner and alloyed steel liner in an industrial hematite ball mill of WISCO, and the results of eight-month test in wet grinding environment have proved that the service life of the bimetal composite liner is three times as long as that of the alloyed steel liner.

Effect of vibration frequency on microstructure and performance of high chromium cast iron prepared by lost foam casting

In the present research, high chromium cast irons(HCCIs) were prepared using the lost foam casting(LFC) process. To improve the wear resistance of the high chromium cast irons(HCCIs), mechanical vibration was employed during the solidification of the HCCIs. The effects of vibration frequency on the microstructure and performance of the HCCIs under as-cast, as-quenched and as-tempered conditions were investigated. The results indicated that the microstructures of the LFC-produced HCCIs were refined due to the introduction of mechanical vibration, and the hardness was improved compared to that of the alloy without vibration. However, only a slight improvement in hardness was found in spite of the increase of vibration frequency. In contrast, the impact toughness of the as-tempered HCCIs increased with an increase in the vibration frequency. In addition, the wear resistance of the HCCIs was improved as a result of the introduction of vibration and increased with an increase in the vibration frequency.

Microstructure and Property of Hypereutectic High Chromium Cast Iron Prepared by Slope Cooling Body-Centrifugal Casting Method

In this paper, the ring-type ingot of hypereutectic high Cr cast iron was obtained by slope cooling bodycentrifugal casting method （SC-CCM）, and its microstructure and impact toughness were investigated, respectively. The results indicated that, first, the primary carbides in the microstructure are prominently finer than those in the hypereutectic high Cr cast iron prepared by conventional casting method. Second, in the ring-type ingot, the primary carbides near radial outer field are finer than those near radial inner field; furthermore, there is dividing field in the microstructure. Finally, the impact toughness values of the specimens impacted on the radial outer face and on the radial inner face are improved respectively about 36% and 138% more than that of the hypereutectic high Cr one prepared by conventional casting method.

Simulation of mold filling and prediction of gas entrapment on practical high pressure die castings

Element parameters including volume filled ratio,surface dimensionless distance,and surface filled ratio for DFDM(direct finite difference method)were proposed to describe shape and location of free surfaces in casting mold filling processes.A mathematical model of the filling process was proposed specially considering the mass,momentum and heat transfer in the vicinity of free surfaces.Furthermore,a method for gas entrapment was established by tracking flow of entrapped gas.The model and method were applied to practical ADC1 high pressure die castings.The gas entrapment prediction was compared with the fraction and maximum size of porosities in the different casting parts.The comparison shows validity of the proposed model and method.The study indicates that final porosities in high pressure die castings are dependent on both gas entrapment during mold filling process and pressure transfer within solidification period.

Design and Verification of an Auxiliary System for High Vacuum Die Casting

Vacuum die casting is the optimal method to produce high quality aluminum alloy components.At present,there are still very few systematic studies on vacuum die casting theory and equipment design.On the basis of the existing theories of the vacuum die casting pumping and venting systems,a simplified model is established in this research.The model has an aggregate unit consisted of ＂vacuum pump ＋ buffer tank＂ and a cylindrical container（including the shot sleeve,cavity and exhaust channel）.The theoretical analysis is carried out between the cavity pressure and the pumping time under different volume models.An auxiliary system for high vacuum die casting is designed based on the above analysis.This system is composed of a vacuum control machine and a new vacuum stop valve.The machine has a human-computer control mode with ＂programmable logic controller（PLC） ＋ touch screen＂ and a real-time monitoring function of vacuum degree for buffer tank and die cavity.The vacuum stop valve with the ＂compressed gas ＋ piston rod ＋ labyrinth groove＂ structure can realize the function of whole-process vacuum venting.The new system shows great advantages on vacuuming the cavity with a much faster speed by making tests on an existing die casting mold and a 250 t die casting machine.A die cavity pressure less than 10 kPa can be reached within 0.8 s in the experiment and the porosity of castings can be greatly decreased.The systematic studies on vacuum die casting theory and equipment have a great guiding significance for high vacuum die casting,and can also be applied to other high vacuum forming in related theoretical and practical research.

A study on centrifugal casting of high speed steel roll

High speed steel (HSS) rolls can replace traditional rolls such as alloyed cast iron rolls and powder metallurgical (PM) hard alloy rolls. The main reasons for the replacement are that the wear resistance of low-cost alloyed cast iron rolls is poor and the cost of high-quality PM hard alloy rolls is very high. By means of centrifugal casting, HSS rolls having excellent wear resistance have been manufactured. The hardness of the HSS roll is 6.5~67 HRC, the range of variation is smaller than 2 HRC and its impact toughness is 15 J/cm^2. The wear rate of HSS rolls used in the pre-finishing stands of high-speed hot wire-rod rolling mill reaches 2.5×10^(-4)mm per ton steel. Furthermore, the manufacturing cost of HSS rolls is significantly lower than that of PM hard alloy rolls; it is only 30 percent of that of PM hard alloy rolls.

HIGH STRAIN RATE SUPERPLASTICITY IN A SiC_w/2024Al COMPOSITE MADE BY SQUEEZE CASTING

In this paper,the superplastic characteristics of the beta-SiC whisker reinforced 2024aluminum composite, fabricated by squeeze casting and hot-rolling after extrusion were investigated. The compsite had a fine grain size of about 2μm, and exhibited a strain rate sensitivity of about 0.35 and a maximum elongation of 350% at an initial strain rate of 1.1×10-1s-1 at 803K. In addition, the superplastic deformation mechanisme of the composite were also examined.

Effects of high-pressure rheo-squeeze casting on the Fe-rich phases and mechanical properties of Al-17Si-(1,1.5)Fe alloys

The effects of high pressure rheo-squeeze casting(HPRC) on the Fe-rich phases(FRPs) and mechanical properties of Al-17 Si-(1,1.5)Fe alloys were investigated. The alloy melts were first treated by ultrasonic vibration(UV) and then formed by high-pressure squeeze casting(HPSC). The FRPs in the as-cast HPSC Al-17 Si-1 Fe alloys only contained a long, needle-shaped β-Al5 Fe Si phase at 0 MPa. In addition to the β-Al5 Fe Si phase, the HPSC Al-17 Si-1.5 Fe alloy also contained the plate-shaped δ-Al4 Fe Si2 phase. A fine, block-shaped δ-Al4 Fe Si2 phase was formed in the Al-17 Si-1 Fe alloy treated by UV. The size of FRPs decreased with increasing pressure. After UV treatment, solidification under pressure led to further refinement of the FRPs. Considering alloy samples of the same composition, the ultimate tensile strength(UTS) of the HPRC samples was higher than that of the HPSC samples, and the UTS increased with increasing pressure. The UTS of the Al-17 Si-1 Fe alloy formed by HPSC exceeded that of the Al-17 Si-1.5 Fe alloy formed in the same manner under the same pressure. Conversely, the UTS of the Al-17 Si-1 Fe alloy formed by HPRC decreased to a value lower than that of the Al-17 Si-1.5 Fe alloy formed in the same manner.

Interfacial heat transfer behavior at metal/die in finger-plated casting during high pressure die casting process

Heat transfer at the metal-die interface has a great influence on the solidification process and casting structure. As thin-wall components are extensively produced by high pressure die casting process(HPDC), the B390 alloy finger-plate casting was cast against an H13 steel die on a cold-chamber HPDC machine. The interfacial heat transfer behavior at different positions of the die was carefully studied using an inverse approach based on the temperature measurements inside the die. Furthermore, the filling process and the solidification rate in different finger-plates were also given to explain the distribution of interfacial heat flux(q) and interfacial heat transfer coefficient(h). Measurement results at the side of sprue indicates that qmax and hmax could reach 9.2 MW·m^(-2) and 64.3 kW ·m^(-2)·K^(-1), respectively. The simulation of melt flow in the die reveals that the thinnest(T_1) finger plate could accelerate the melt flow from 50 m·s^(-1) to 110 m·s^(-1). Due to this high velocity, the interfacial heat flux at the end of T_1 could firstly reach a highest value 7.92 MW·m^(-2) among the ends of T_n(n=2,3,4,5). In addition, the q_(max) and h_(max) values of T_2, T_4 and T_5 finger-plates increase with the increasing thickness of the finger plate. Finally, at the rapid decreasing stage of interfacial heat transfer coefficient(h), the decreasing rate of h has an exponential relationship with the increasing rate of solid fraction(f).

Characterization of A390 aluminum alloy produced at different slow shot speeds using vacuum assisted high pressure die casting

The effects of vacuum assistance on the microstructure and mechanical properties of high pressure die cast A390alloy at different slow shot speeds were evaluated.Plate-shaped specimens of hypereutectic A390aluminum alloy were produced on a TOYO BD?350V5cold chamber die casting machine incorporated with a self-improved TOYO vacuum system.According to the results,the vacuum pressure inside the die cavity increased linearly with the increasing slow shot speed at the beginning of mold filling.Meanwhile,tensile properties of vacuum die castings were deteriorated by the porosity content.In addition,the average primary silicon size decreased from23to14μm when the slow shot speed increased from0.05to0.2m/s,which has a binary functional relationship with the slow shot speed.After heat treatment,microstructural morphologies revealed that needle-shaped and thin-flaked eutectic silicon particles became rounded while Al2Cu dissolved intoα(Al)matrix.Furthermore,the fractography revealed that the fracture mechanism has evolved from brittle transgranular fracture to a fracture mode with many dimples after heat treatment.

Process for improving the ladle free- opening rate for high aluminum steel in continuous casting

Steel 20Mn23AlV is a type of high aluminum steel with a very low ladle free-opening rate. The aluminum composition of 20Mn23AlV ranges from 1.6% to 2.45% ,which is significantly higher than other types of steel. According to the real condition of 40 t ladle in steel-making plant of Baosteel Special Steel Company, previous works show that the key factors affecting the ladle free-opening rate of high aluminum steel in continuous casting are：sand material, accessories baking, ladle nozzle cleaning, the process and amount of adding sand, and the rate of argon stirring during refining. Therefore, improving the ladle filler sand quality, baking all of the raw materials, controlling the addition of ladle filler sand, cleaning the ladle nozzle, and optimizing argon stirring during the refining process can resolve the problem of a low ladle free-opening rate of high aluminum steel caused by the long ladle time of liquid steel.

Experimental research on electromagnetic continuous casting high-speed steel composite roll

A high speed steel composite roll billet was fabricated, which is regular in shape, smooth in surface, slight in trace, compact in internal structure, free of slag inclusion, shrinkage cavity, cracks and other flaws, and good in macro quality of junction surface using a vertical continuous casting machine. The interface zone microstructure of bimetallic in billet of high speed steel composite roll was analyzed by metallurgical microscope(OM), X-ray diffractmeter(XRD), scanning electron microscopy(SEM) and energy-dispersive X-ray analysis(EDS). The results indicate that the microstructure of roll billet is composed of chilled solidified layer, dendrite zone, interfacial zone of bimetal and core material zone. The microstructure of outer shell material is composed of martensite + bainite + residual austenite + some small labyrinth-shape, small-short lath-shape, or dollop-shape eutectic carbides. The microstructure of core material is slice-shape pearlite and a little ferrite along boundary of cells. The interface region microstructure of bimetallic composite roll consists of diffusion region, chilled solidified layer and columnar grain region.

Characteristics and distribution of microstructures in high pressure die cast alloys with X-ray microtomography:A review

Al and Mg alloy high pressure die castings(HPDC)are increasingly used in automotive industries.The microstructures in the castings have decisive effect on the casting mechanical properties,in which the microstructure characteristics are fundamental for the investigation of the microstructure-property relation.During the past decade,the microstructure characteristics of HPDC Al and Mg alloys,especially micro-pores andα-Fe,have been investigated from two-dimensional(2D)to threedimensional with X-ray micro-computed tomography(μ-CT).This paper provides an overview of the current understanding regarding the 3D characteristics and formation mechanisms of microstructures in HPDC alloys,their spatial distributions,and the impact on mechanical properties.Additionally,it outlines future research directions for the formation and control of heterogeneous microstructures in HPDC alloys.

Effect of slow shot speed on externally solidified crystal,porosity and tensile property in a newly developed high-pressure die-cast Al-Si alloy

The effect of slow shot speed on externally solidified crystal(ESC),porosity and tensile property in a newly developed high-pressure die-cast Al-Si alloy was investigated by optical microscopy(OM),scanning electron microscopy(SEM)and laboratory computed tomography(CT).Results showed that the newly developed AlSi9MnMoV alloy exhibited improved mechanical properties when compared to the AlSi10MnMg alloy.The AlSi9MnMoV alloy,which was designed with trace multicomponent additions,displays a notable grain refining effect in comparison to the AlSi10MnMg alloy.Refining elements Ti,Zr,V,Nb,B promote heterogeneous nucleation and reduce the grain size of primaryα-Al.At a lower slow shot speed,the large ESCs are easier to form and gather,developing into the dendrite net and net-shrinkage.With an increase in slow shot speed,the size and number of ESCs and porosities significantly reduce.In addition,the distribution of ESCs is more dispersed and the net-shrinkage disappears.The tensile property is greatly improved by adopting a higher slow shot speed.The ultimate tensile strength is enhanced from 260.31 MPa to 290.31 MPa(increased by 11.52%),and the elongation is enhanced from 3.72%to 6.34%(increased by 70.52%).