电渣重熔满足大型锻件的要求

 与锭模浇注出低密度、带缩孔铸锭相比,高性能铸锭材料的生产趋于用重熔设备来实现,铸锭的力学性能也会更均匀。水冷铜结晶器中重熔的铸锭具有较高的材料产出量,从而使具有相同最终外形的铸锭其单锭的质量更小,密度更接近于锻造的材料。因此,后续的锻造工艺不需要高锻造比来生产高密度铸锭。在100t以下的铸锭通常可以在固定锭模中生产,并配以外部底加热裝置,以避免可能的铸锭底部开裂;50t以上的铸锭采用高度复杂的拉锭系统配以多电极交换,在短的环形坩埚中重熔技术才是最经济的。大型的带有电极交换技术的电渣重熔炉,为生产超过钢厂中最大单个钢包浇铸质量的大尺寸铸锭提供了可能性。介绍了生产145t重铸锭的炉型设计。对于容易出现开裂的高度复杂的合金,可以通过应用隔热绝缘来生产。     

Microstructure and properties of cast ingots of Al-Zn-Mg-Cu alloys modified with Sc and Zr

The effect of combined additions of Sc and Zr on the microstructure and tensile properties of the direct chill (DC) cast ingots of developmental Al-Zn-Mg-Cu alloys has been evaluated in this work. The properties in both the longitudinal and transverse directions were determined in as-cast and cast-plus-heat-treated conditions, at room temperature (RT) and cryogenic temperature (CT). Extensive microstructural evaluation was carried out using optical microscopy and scanning electron microscopy, including orientation image microscopy (OIM) by the electron backscatter diffraction (EBSD) technique. The Sc-containing developmental cast alloys showed the tensile properties, which are much better than the properties of commercial cast Al alloys and are similar or even superior to the properties of 7075-T6 alloy forgings. The microstructural evolution, the strengthening mechanisms, the optimum content of the dispersoid-forming elements, and the processing-structure-property correlations are discussed.     

某低温风洞用高强不锈钢弯刀小试件生产实践

某低温风洞弯刀采用00Cr12Ni10MoTi马氏体时效不锈钢制造(代号:S03)。分别采用构筑成形和三联特冶(真空感应熔炼+真空自耗电弧熔炼+电渣重熔)工艺路线研究了10 t级S03钢小试件钢锭制备工艺。通过X射线衍射(XRD)、扫描电镜(SEM)和拉伸、冲击等评价方法,分别研究了冶炼和热处理工艺对S03钢组织及力学性能的影响。研究结果表明,构筑成形和三联特冶工艺均可实现10 t级S03钢锭的制备,两步750 ℃固溶和500 ℃时效工艺可实现S03钢较好的综合力学性能,工艺研究结果为某低温风洞百吨级弯刀钢锭制备提供了技术支撑。     

超声处理对2219大规格铝锭微观组织与宏观偏析的影响

在半连续铸造过程中施加超声,成功制备了φ1250 mm 2219铝合金铸锭.利用光学显微镜、扫描电镜、能谱仪及直读光谱仪等仪器对铸锭的组织与成分分布进行检测与分析,探究超声对铸锭组织与偏析的内在作用机制.研究结果表明:超声振动引起的空化和声流效应能明显均匀组织结构,细化晶粒,尤其是心部晶粒细化率达到39.6%.超声促进铸锭晶间第二相呈枝丫状断续分布,晶内析出物点状弥散分布.同时,超声有效减小近表面负偏析,降低边部与心部之间的溶质浓度差异,弱化整个横截面的浓度波动,从而改善宏观偏析.      

Properties of shaped castings made of modern cast VML18 and VML20 magnesium alloys manufactured by new methods

The methods of casting of modern magnesium alloys (corrosion-resistant Mg–Al–Zn VML18 alloy and a high-strength Mg–Zn–Zr VML20 alloy) into the temporary molds made of cold-hardening mixtures and the molds produced by 3D printing are considered. The mechanical properties (ultimate tensile strength, yield strength, impact toughness), the corrosion properties, and the microstructure of the ingots are studied. The experimental results are used to choose the molds and the methods of casting of the parts of the control system of advanced aircrafts, which are made of modern cast magnesium alloys VML18 and VML20.     

Control of grain size and -orientation in multi-crystalline silicon ingots

Two different cooling rates have been imposed during the early solidification of two multi-crystalline silicon ingots with 250mm diameter and 100mm height in a pilot scale directional solidification furnace. This has been done by opening a variable heat leak system below the crucible in order to achieve a high initial cooling rate in one of the ingots. The grain-structure and -orientation of these two ingots have been investigated by light microscopy (LM) and electron backscattered diffraction (EBSD), and their electrical properties by quasi-steady state photo-conductance (QSSPC) and surface photovoltage (SPV) method. The ingot with the high initial cooling rate shows predominantly grains which are significantly larger than what is usually found in mc-Si. The minority carrier diffusion lengths measured on the large grains in the ingot with high cooling rate show higher values than those measured on the ingot with smaller grains. These results indicate that principles of grain size and -orientation control in mc-Si ingots can be applied to a pilot scale furnace, and the potential for up-scaling to industrial ingots with improved electrical properties and, thus, higher solar cell conversion efficiency.     

铸坯取样位置对经济型双相不锈钢2101热塑性的影响

为了解大型铸锭在轧制过程中产生边裂的原因,通过对比铸坯中部和边部的成分、不同温度下相比例、两相硬度差等的变化规律,利用光学显微镜,扫描电子显微镜和电子背散射衍射观察分析试验钢的微观组织和断口形貌,分析了边部容易开裂的原因.结果表明,和中部相比,边部晶粒细小,且铁素体含量较多,但边部开裂更严重.这说明晶粒尺寸和相比例并不是影响使边部开裂严重的主要原因.而和中部比,铸锭边部试样两相硬度差较大,使两相在热变形过程中应变分配不均匀,容易在相界处产生应力集中,导致开裂.同时边部析出物较中部多,相界析出物的产生破坏了基体的连续性,容易在相界处产生显微裂纹,导致开裂.      

Microsegregation behavior during solidification and homogenization of AerMet100 steel

Cast AerMet100 exhibits mechanical properties comparable to the wrought properties of competing ultrahigh-strength steels; however, the segregation behavior had not been quantified under casting conditions. A microsegregation profile of the as-cast ingot was simulated and homogenization treatments were predicted using Thermo-Calc and DICTRA software. Experimental composition analysis confirmed the simulated microsegregation profile, and the homogenization process occurred at a slightly faster rate than predicted. The convergence of theory and experiment demonstrates the feasibility of designing cast alloy compositions assisted by computer simulation to minimize segregation without casting a large experimental matrix of test ingots.     

Melting of γ-TiAl in the alumina crucible

Titanium aluminide alloys with unique properties as well as high strength to weight ratio, excellent oxidation resistance and acceptable high temperature mechanical properties can be used as a high temperature structural material and a competitor for super-alloys. In this research, production process of Ti-48Al-2Cr (numbers indicate atomic percent) intermetallic in an induction furnace with argon atmosphere, alumina crucibles with different purities and several ingot casting time, were investigated. Microstructure of produced ingots was studied by optical microscope and scanning electron microscope (SEM) with EDX analyzer and phase analysis were studied by XRD method. Results show that microstructures are completely lamellar and by increasing cooling rate, interlamellar space will decrease. In the structure, three morphologies of alumina particles could be seen that are: spherical, cluster and lathed. Volume fraction of Al₂O₃ particles will increase by increasing the holding time of melt and crucibles with higher SiO₂ content will react more severe with melt.     

合金化Cr优化含Fe过共晶Al-Si合金显微组织及其机制

采用传统铸造工艺和喷射成形技术制备了无Cr和含Cr的含Fe过共晶Al-Si合金,并利用SEM(EDS)、XRD及DSC对其显微组织、相组成及相变过程进行了研究。结果表明:2%Cr的加入不光使铸态粗大针片状的δ-Al4FeSi2相变为"骨骼状"α-Al(Fe,Cr)Si相,而且使沉积态Al-25Si-5Fe-3Cu合金中短棒状的富铁相(～10μm左右)被尺寸小于3～5μm的颗粒状α-Al(Fe,Cr)Si相所替代,从而细化的组织更有利于合金性能的提高。等温处理实验结果显示沉积态含Cr合金具有较好的组织热稳定性,其主要归因于颗粒状α-Al(Fe,Cr)Si相自身的高温稳定性,而沉积态Al-25Si-5Fe-3Cu合金热稳定差主要由于β-Al5FeSi相的长大和A7Cu2Fe相的形成。另外,结合显微组织和喷射成形工艺特点对沉积态组织形成机制分析发现α-Al(Fe,Cr)Si相有可能通过直接从液相析出和经δ-Al(Fe,Cr)Si相转变而来。     

Material Characterization of Austempered Ductile Iron (ADI) Produced by a Sustainable Continuous Casting–Heat Treatment Process

Selecting a suitable manufacturing process is one way of achieving sustainability of a product by diminishing energy consumption during its production cycle and improving material efficiency. The article attempts to explore the new processing technology for direct manufacturing of lightweight austempered ductile iron (ADI) casting in a permanent mold. The new processing technology is based on the innovative integrated approach toward casting and heat-treatment process. In this technology, the ductile iron samples obtained using the permanent mold are first austenized immediately after solidification process followed by austempering heat treatment in the fluidized bed and then air cooled at room temperature to obtain ADI material. The influence of austempering time on the microstructural characteristics, mechanical properties, and strain-hardening behavior of ADI was studied. Optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) analyses were performed to correlate the mechanical properties with microstructural characteristics. It was observed that the mechanical properties of resulting ADI samples were influenced by the microstructural transformations and varied retained austenite volume fractions obtained due to different austempering time. The results indicate that the strain-hardening behavior of the ADI material is influenced by the carbon content of retained austenite.     

Preparation,microstructure and properties of Al-Zn-Mg-Sc alloy tubes

The Al-6.0Zn-2.0Mg-0.2Sc-0.10Zr hollow tube ingots, prepared by semi-continuous casting technology, were subjected to ho- mogenization treatment, hot extrusion, intermediate annealing, tension, solution and aging treatment. The microstructures and properties of as-cast Al-Zn-Mg-Sc alloy at different homogenization treatment conditions were studied using hardness measurement, X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. The results showed th...     

Effect of Melting Process on the Microstructure and Mechanical Properties of Fe–7 wt% Al Alloy

This article presents the effect of melting process on chemical composition, microstructure and mechanical properties of Fe–7 wt% Al alloy. The alloy ingot was prepared by air induction melting (AIM), air induction melting with flux cover (AIMFC) and vacuum induction melting (VIM) and cast into 50 mm diameter split cast iron mould. These cast ingots were hot-forged and hot-rolled at 1,373 K to 2 mm thick sheet. Hot-rolled alloys were characterized with respect to chemical composition, microstructure and mechanical properties. Ingots produced by AIM, AIMFC and VIM were free from gas porosity, however AIM ingots exhibited higher concentration of hydrogen as compared to AIMFC and VIM. The recovery of aluminium as well as reduction of oxygen during AIM is very poor as compared to AIMFC and VIM. AIMFC ingots exhibit low level of sulphur as compared to AIM and VIM ingots. The alloys produced by AIMFC and VIM exhibited superior tensile ductility compared to the alloys produced by AIM. The tensile properties of alloys produced by AIMFC are comparable to the alloys produced by VIM.     

2D70耐热铝合金铸态组织研究

利用光学显微镜、扫描电子显微镜、能谱分析、X射线物相分析、透射电子显微镜研究了2D70耐热铝合金半连续铸锭的铸态组织.研究结果表明:2D70耐热铝合金铸态组织为粗大枝晶组织,枝晶间蜂窝状共晶相为AL,A12CuMg/A12Cu,合金中含有大量块状相和条状相,能谱分析显示为含Fe,Ni相,铸态合金中Cu,Fe,Ni元素偏析严重.合金铸态相主要为а(Al),S(Al2CuMg),0(Al2Cu),Al7Cu2Fe,Al7Cu4Ni,Al9FeNi相.     

Effect of Sn Alloying on the Diffusion Bonding Behavior of Al-Mg-Si Alloys

Effect of Sn as an alloying element on the diffusion-bonding behavior of Al-Mg-Si alloy has been studied by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and mechanical testing of the diffusion-bonded joint. XRD results revealed the formation of Mg₂Sn and (Sn) phases during solidification following induction casting. DSC results showed local liquid (Sn) formation during the bonding process for Sn-containing alloys, where its amount was found to be increasing with the increasing Sn content. Results revealed that Sn addition leads to an increase in the bond shear strength of the diffusion-bonded joints and elimination of the irregularities formed on the bonded interface. Fractured surfaces showed that formation of (Sn) layer at the bonded interface causes the fracture to transform from the ductile to the mixed fracture mode.     

标准银锭熔铸工艺技术及发展

介绍了标准银锭熔铸的工艺技术,分析了四种标准银锭熔铸装备工艺技术的特点和不足。通过比较发现：中频炉和电炉熔铸银锭装备工艺技术已难以适应注册银锭外观质量要求;无火焰熔铸银锭装备工艺技术具有环境友好、自动化程度高以及产品合格率高、外观质量好的优点。无火焰熔铸工艺有隧道式和腔体式,相比较而言,腔体式更具发展优势。未来一段时期,无火焰腔体式熔铸银锭装备工艺技术将成为标准银锭熔铸的发展方向。     

Increasing the reliability and quality of important cast products made of chemically active metals and alloys

A technology is developed to produce highly thermoresistant ceramic monoxide corundum molds using investment casting and an aluminum-organic binder. This technology is a promising trend in creating ceramic molds for precision complex-shape casting of important ingots made of high-alloy steels, high-temperature and titanium alloys, and refractory metals. The use of the casting molds that have a high thermal and chemical resistance to chemically active metals and alloys under high-temperature casting minimizes the physicochemical interaction and substantially decreases the depth of the hard-to-remove metal oxide layer on important products, which increases their service properties.     

Effect of Titanium Addition on As Cast Structure and Macrosegregation of High‐Carbon High‐Chromium Steel

In casting heavy ingots of high‐chromium high‐carbon cold work steels, macrosegregation develops in the center of the ingot, causing difficulties during subsequent hot working. Heat transfer and solidification of an industrial scale high‐carbon high‐chromium steel ingot was simulated and thereafter a laboratory scale representative ingot was designed to model the solidification of the industrial scale ingot. Titanium in the range of 0.3–1% was added to the high‐chromium high‐carbon (12%Cr–2%C) steel during melting process. Microstructures, macrosegregation and phase formations were studied using optical microscopy, scanning electron microscopy, energy dispersive X‐ray spectrometry, wave dispersive X‐ray spectrometry, optical emission spectroscopy, and X‐ray diffraction. Addition of 0.3% titanium was sufficient to diminish the macrosegregation; however it did not have a significant effect on the grain size. Addition of 0.7 and 1% titanium had a substantial effect on grain size in the longitudinal direction and refined the primary carbides structure. The formation of small TiC carbides that precipitated before solidification of liquid iron acted as nuclei for primary pro‐eutectic austenite grains.     

On the Mechanism of Natural Convection and Equiaxed Structure during Dendritic Solidification Processes

A new technique has been developed to generate dendritic‐equiaxed structures in aluminium alloy casting processes, not only to improve the mechanical properties but also to study the effect of crystal structure on the chemical and physical properties of alloys to be cast. The investigation combined laboratory experimental work, metallographic examination and mathematic modelling. The laboratory experimental work involved different superheats for Al‐4.5%Cu alloy in cast ingots. Measurements of temperature distributions were conducted to verify the solidification model. A metallographic study combined macro and micro structural evolution of cast ingot samples. Two‐dimensional mathematical models of fluid flow and heat transfer were developed to characterise the natural convection streams and thermal fields. The model predictions were compared to temperature and isotherms measurements where a good agreement was found. The formation of cast structure and columnar, equiaxed transition (CET) and macro segregation phenomena were studied and discussed, based not only on the theories of nucleation but also on the thermal effects in the mushy and liquid zones.     

含银Al-4.5Zn-1.0Mg-0.5Cu合金的强化固溶行为

采用拉伸力学性能测试、金相显微观察、扫描电镜及透射电镜等分析手段,研究了Al-4.5Zn-1.0Mg-0.5Cu-0.4Ag合金的强化固溶行为。结果表明:经强化固溶处理后,合金固溶态的抗拉强度和屈服强度以及伸长率分别较常规固溶的低15 MPa、16 MPa和1.7%;峰值时效态的抗拉强度和屈服强度较常规固溶的分别高62 MPa和68 MPa,伸长率低0.8%。;强化固溶可使Al-4.5Zn-1.0Mg-0.5Cu-0.4Ag合金固溶后的第二相粒子减少,但使其时效后的强化相数量增多,密度增大。