Processing of Fe-Al-C-Ce alloys through air induction melting with flux cover (AIMFC) and electroslag remelting (ESR)

The effect of process parameters on recovery of reactive element, cerium, during air induction melting with flux cover (AIMFC) and electroslag remelting (ESR) of Fe-10.5 wt% Al-0.8 wt% C-(0.1 and 0.3) wt% Ce alloys and also the effect of melting techniques on hot workability, structure and tensile properties (at room temperature and at 873 K) of Fe-10.5 wt% Al-0.8 wt% C-0.3 wt% Ce alloy have been investigated. Good recovery of cerium was obtained by AIMFC. While conventional fluxes were found to be unsatisfactory, modified flux containing CeO₂ gave better recovery of cerium during ESR. The best recovery of cerium was achieved by using calcium as a deoxident during ESR. The combination of AIMFC and ESR yields a sound ingot of Fe-Al-C-Ce quaternary alloys free from gas and shrinkage porosity with very low oxygen, nitrogen and sulphur contents. Processing of AIMFC ingots through ESR has resulted in improved hot-workability. The ESR processed and hot-rolled alloy exhibited superior tensile elongation as compared to hot-rolled AIMFC alloy. This may be attributed to the comparatively sound, homogeneous and clean ingot, with a refined microstructure and fine uniform distribution of precipitates observed in hot-rolled ESR ingots.     

Enhanced Homogenization Strategy by Electroslag Remelting of High‐Manganese TRIP and TWIP Steels

In the production of high‐manganese TRIP and TWIP steels, significant micro‐segregation effects are observed after solidification. Homogenization can be achieved by heat treatment followed by deformation at a significant time and effort (forging, annealing, hot rolling). In an attempt to achieve the best homogeneous microstructure and reduced thermomechanical processing, the cast alloy is treated by electroslag remelting (ESR). After a simple hot rolling procedure with a thickness reduction of 90% and without further heat treatment, micro‐segregation of manganese can be reduced to about 5 wt%. There is a potential to achieve even lower values with further optimization of the ESR process and an adapted thermomechanical processing.     

真空电渣重熔的冶金特性

真空电渣重熔具有脱氧性能好,防止金属氧化等许多优异的冶金特性.本文通过对真空电渣重熔与普通电渣重熔、气体保护熔炼和真空电弧熔炼等冶金特性的分析对比,找出真空电渣重熔的冶金特性,表明发展真空电渣重熔的意义.     

Evaluation of electroslag remelting in TiC particle reinforced 304 stainless steel

This study is focused on the effect of electroslag remelting (ESR) on microstructure and mechanical properties of TiC particle reinforced 304 stainless steel synthesized by in situ reaction in vacuum introduction melting (VIM). Microstructure observations revealed that applying ESR process resulted in a more uniform distribution of TiC particles with reduced size, however, a slight aggregation with large TiC particles existed in the VIM ingot was found. Additionally, some tiny TiC precipitates with nano-scale were observed in the microstructure of the TiC reinforced steel after ESR process. Introduction of in situ TiC particles into the 304 stainless steel caused a significant increase of tensile properties, creep properties and wear resistance, but a decrease in ductility. Moreover, further improvement on tensile properties, creep properties, wear resistance as well as the ductility of the steel were obtained by using ESR process successfully.     

熔速对氩气保护GH4169G合金电渣锭组织及夹杂物的影响

研究了熔速对氩气保护GH4169G电渣锭宏微观组织及非金属夹杂物的影响。结果表明:适当增加熔速有利于缩短铸锭的局部凝固时间,减小二次枝晶间距,从而细化枝晶组织,但对Nb、Ti等易偏析元素沿径向的宏观分布影响不大。熔速对GH4169G铸锭中的夹杂物类型影响较小,主要为氧化物、氟化物和氮化物三类。夹杂物在铸锭表面最多,向内部迅速减少并趋于稳态。铸锭内部夹杂物多以氧化物为核心,氮化物为次外层,碳化物为最外层的双层或三层结构。采用MeltFlow-ESR模拟方法,分析了熔速对重熔过程中夹杂物运动轨迹的影响,发现提高熔速有利于夹杂物向铸锭表面运动,降低铸锭表面夹杂物富集区的厚度和铸锭内部夹杂物的数量。此外,提高熔速有利于缩短夹杂物析出长大的时间,降低夹杂物尺寸。     

Microhardness profile prediction of a graded steel by strain gradient plasticity theory

In the present study, the Vickers microhardness profile of functionally graded steel austenitic steel produced by electroslag remelting process has been investigated. To produce functionally graded steels, two different slices from plain carbon steel and austenitic stainless steels were spot welded and used as electroslag remelting electrode. Functionally graded steel containing graded layers of austenite may be fabricated via diffusion of alloying elements during remelting stage. Vickers microhardness profile of the specimen has been obtained experimentally and modeled with mechanism-based strain gradient plasticity theory. In this regard, the density of the statistically stored dislocations and that of geometrically necessary dislocations was related to the Vickers microhardness profile of each layer. The experimental results are in good agreement with those obtained from the theory.     

Structure and Mechanical Properties of Refined Ferrochrome

We studied the chemical composition, structure, and some mechanical characteristics of ferrochrome after complex refining with the use of electroslag remelting. Owing to electroslag remelting, the metallurgical process combines both the stage of refining and the stage of removal of refining products into slag.     

The electroslag remelting of high-nitrogen steels

Steels containing nitrogen at levels which are at or above the 1Bar saturation solubility limit in the liquid at the liquidus temperature offer considerable metallurgical property advantages in many respects. For example, when nitrogen is used as a substitute for carbon in stainless grades, the alloys have superior corrosion properties especially in biomedical applications: nitrogen as a strengthening element in tool steels offers advantages in freedom from carbide particles which affect the polishability. Most of the steels grade of interest require electroslag remelting to control segregation without loss of nitrogen and the behaviour of nitrogen during this process is the subject of this work. It is concluded that the required process pressures are closely related to the alloy composition and that to prevent porosity in the product the ESR step must be carried out at an appropriate overpressure of either nitrogen or argon. The addition of nitrogen during ESR is also discussed and it is shown that this is possible only through solid additives.     

Alloying of steel with a superequilibrium amount of nitrogen from a gaseous atmosphere in the process of electroslag remelting

Conclusions We designed the structure of and manufactured an installation for electroslag remelting under elevated pressure in a gaseous atmosphere, which enables one to obtain ingots 10 kg in weight under a pressure of up to 10 MPa. We showed the fundamental possibility of alloying steel with nitrogen from a gaseous phase in the process of electroslag remelting. For the remelting of 20KhN3A steel under a nitrogen pressure of 5 MPa, we obtained a sevenfold increase in the concentration of nitrogen (from 0.0166 to 0.1081 mass %). For alloying with silicon nitride, hardness remains on the level of the hardness of the parent metal (HRC 27-32). For gaseous alloying with nitrogen, hardness increases to HRC 47–50. Gaseous alloying has the following advantages: (a) the absence of a change in the chemical composition of metal due to admixtures contained in the nitrated alloying composition; (b) a considerable reduction in the cost of nitrous metal due to the elimination of nitrated ferroalloys (ferromanganese, ferrochrome, ferrosilicon, etc.) from the technological process. In the case of alloying of 20KhN3A steel by using a superequilibrium content of nitrogen, structural changes manifest themselves in the formation of white interlayers along grain boundaries, increase in the thickness of grain boundaries, and change in the density, morphology, and mutual orientation of rejections of the needle-type phase. We recorded a decrease in the lattice parameter and the appearance of the line of austenite. The addition of activation admixtures to fluxes leads to a sharp increase in the ability of metal to adsorb nitrogen in the process of electroslag remelting. At a pressure of gas-like nitrogen of 0.1 MPa, its concentration in metal increases by a factor of 4.5. This means that, in some cases, nitration is possible even without the use of expensive high-pressure equipment. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 36, No. 3. pp. 115–117, May-June, 2000.     

Effect of Al and C on structure and mechanical properties of Fe–Al–C alloys

Abstract

Effect of aluminium and carbon content on the microstructure and mechanical properties of Fe–Al–C alloys has been investigated. Alloys were prepared by combination of air induction melting with flux cover (AIMFC) and electroslag remelting (ESR). The ESR ingots were hot forged and hot rolled at 1373 K. As rolled alloys were examined using optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to understand the microstructure of these alloys. The ternary Fe–Al–C alloys containing 10·5 and 13 wt-%Al showed the presence of three phases: FeAl with disordered bcc structure, Fe₃Al with ordered DO₃ structure and Fe₃AlC_0·5 precipitates with L′1₂ structure. Addition of high concentration of carbon to these alloys resulted in excellent hot workability and superior tensile at room temperature as well as tensile and creep properties at 873 K. An increase in Al content from 9 to 13 wt-% in Fe–Al–C alloys containing the same levels of carbon has no significant influence on strength and creep properties at 873 K, however resulted in significant improvement in room temperature strength accompanied by a reduction in room temperature ductility.     

Characterisation of the structure and thermophysical properties of solid electroslag remelting slags

The solid structure and thermophysical properties of three electroslag remelting (ESR) slags were characterised. Samples from ESR trials performed by Special Metals Corporation in Burnaugh, KY, were compared to samples solidified in a vacuum induction melter. The microstructures were characterised using a combination of optical and electron microscopy, X-ray diffraction, energy-dispersive spectroscopy and a serial sectioning technique to quantify porosity. The thermophysical properties were measured using differential scanning calorimetry and laser flash diffusivity testing at Thermophysical Property Measurement Laboratory, Inc. in West Lafayette, IN. The two processing routes were found to produce similar phase fractions, but resulted in different properties as a function of phase morphology and porosity content. These results suggest that future modelling and property measurement efforts must account for both the structure and composition of the slags.     

Evaluation of the Electroslag Remelting Process in Medical Grade of 316LC Stainless Steel

This study is focused on the effects of electroslag remelting by prefused slag(CaO,Al2O3,and CaF2)on macrostructure and reduction of inclusions in the medical grade of 316LC(316LVM)stainless steel.Analysis of the obtained results indicated that for production of a uniform ingot structure during electroslag remelting, shape and depth of the molten pool should be carefully controlled.High melting rates led to deeper pool depth and interior radial solidification characteristics,while decrease in the melting ra...     

Effect of cerium and thermomechanical processing on microstructure and mechanical properties of Fe-10·5Al-0·8C alloy

The effect of cerium content and thermomechanical processing on structure and properties of Fe-10·5 wt.%Al-0·8 wt%C alloy has been investigated. Alloys were prepared by a combination of air induction melting with flux cover (AIMFC) and electroslag remelting (ESR). The ESR ingots were hot-forged and hot-rolled at 1373 K as well as warm-rolled at 923 K and heat-treated. Hot-rolled, warm-rolled and heat treated alloys were examined using optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction to understand the microstructure of these alloys. The ternary, Fe-10·5 wt.%Al-0·8 wt.%C alloy showed the presence of two phases; Fe-Al with bcc structure, and large volume fraction of Fe₃AlC_0·5 precipitates. Addition of cerium to Fe-10·5 wt.%Al-0·8 wt.%C alloy resulted in three phases, the additional phase being small volume fraction of fine cerium oxy-carbide precipitates. Improvement in tensile elongation from 3–6·4% was achieved by increasing the cerium content from 0·01–0·2 wt.% and further improvement in tensile elongation from 6·4–10% was achieved by warm-rolling and heat treatment.     

Oxidation of Alloying Elements during ESR of Stainless Steel

The oxidation of alloying elements duringthe ESR of stainless steel has been studied.The model previously developed by WEI and Mitchellfor the chemical reactions and mass transferprocesses during ESR was applied to the remeltingof the high Cr steel 1Cr18Ni9(Ti).The laboratorydata for the unsteady state A.C.ESR were analyzedand dealt with by the model.When the remeltingprocess reached a steady state,an oxidant(Fe_2O_3powder)or a deoxidant(Ca-Si powder or metallicCa)was added to the slag bath.The resultsshowed that this model is applicable to theremelting of stainless steel rather precisely,and it is expected that the model may offera reliable basis for the control of compositionduring practical ESR of high alloy steel.Also,the oxidation of Cr in the steel mustbe noticed when its content is high;but itis entirely possible to adjust the Cr contentof ingot within a considerable range,usinga special technique by means of the slag-metalreactions during the remelting.     

J-integral evaluation of austenitic-martensitic functionally graded steel in plates weakened by U-notches

In this paper, a numerical method for J-integral evaluation of plates weakened by U-notches for brittle or quasi-brittle functionally graded steel (FGS) has been proposed. The material contains austenite phase in addition to martensite layer produced by electroslag remelting (ESR). The Young’s modulus and the Poisson’s ratio have been assumed to be constant, while other mechanical properties vary exponentially along the specimen width. The effect of notch depth on the J-integral and the critical fracture load has been studied. A comparison of the J-integral between functionally graded and homogeneous steels was made, where the notch tip in the functionally graded steel is situated in a layer with same mechanical properties as the homogeneous steel.     

Effect of electroslag refining on the fracture toughness and fatigue crack propagation rates in heat treated AISI 4340 steel

The AISI 4340 steel has been electroslag refined and the improvement in mechanical properties has been assessed. Electroslag refining (ESR) has improved tensile ductility, plane strain fracture toughness, Charpy fracture energy, and has decreased fatigue crack growth rates. The K_IC values for the ESR steel are nearly twice those estimated in the unrefined steel and higher than those obtained in the vacuum arc remelted steel. Fatigue crack growth rates in region I and in region III are found to be decreased considerably in the ESR steel, while they are unaffected in region II. Measurements on heat treated samples have shown that the ESR steel has a better response to heat treatment. Both the suggested heat treatments namely austenitizing at 1140–1470 K as well as the conventional heat treatment of austenitizing at 1140 K have been followed. The improvement in the mechanical properties of ESR steel has been explained on the basis of removal of nonmetallic inclusions and reduction in sulfur content in the steel.     

Comparative cavitation erosion test on steels produced by ESR and AOD refining

Cavitation erosion studies of steels produced by Electroslag Refining (ESR) and Argon Oxygen Decarburization (AOD refining) have been carried out. The experiments were conducted using the modified ultrasonically induced cavitation test method. Erosion rates were measured and the morphology of damages under cavitation action was studied by scanning electron microscopy and optical microscopy techniques. The present work is aimed at understanding the cavitation erosion behaviour of electroslag refined steel (ESR) compared with the steel produced by Argon Oxygen Decarburization (AOD refining), commonly used in the production of hydraulic machinery parts (Pelton blades). The results exhibited lower cavitation rate of ESR steel compared with AOD steel, as a consequence of its better mechanical properties and homogeneous and fine-grained microstructure.     

Refinement of Fe4Al13 in Al–Fe alloys by plasma remelting process

Abstract

Refinement of the Fe₄Al₁₃ phase in Al–Fe (wt-%) alloys has been achieved by a plasma remelting process. The refinement effect is enhanced by increases of discharge current and argon flux. The average size of the Fe₄Al₁₃ is 40 µm in Al–1Fe alloy melted using an electric resistance furnace. This can be reduced to 0.4 µm by a plasma remelting process. Similarly, the average size of the Fe₄Al₁₃ in Al–5Fe alloy can be decreased from 60 to 3 µm by plasma remelting. The refinement is considered to be an effect of the decrease of cluster size retaining genetic information in the Al–Fe alloy melt, the homogenisation of microstructure in the melt, and the increased undercooling during solidification.     

铸锭BFe30-1-1锻造性能的研究

研究了氧含量、夹杂物、宏观组织、拉制速度和电渣重熔等因素对BFe10 1 1合金铸锭锻造性能的影响,结果表明:氧含量、夹杂物对锻造性能影响不大,铸锭中的粗大晶粒及存在的缺陷将会降低锻造性能,而斜向生长的柱状晶区有利于锻造的质量控制,慢速停拉式铸造和合理的电渣重熔工艺对发挥合金的可锻性有利。     

Creep of an electroslag refined aluminium alloy

The creep resistance ofelectroslag refined aluminium alloyRR 58 has been studied in the temperature range 450-485°C and compared with that ofpermanent-mould cast, unrefined alloy. The electroslag refined RR 58 had a greater creep resistance than the unrefined alloy; this improvement has been attributed to the reduction in hydrogen content, macroporosity and microporosity, the removal ofoxide inclusions and the fine an uniform dispersion ofsecond phase precipitates in refined alloy. From the estimated activation energy for high temperature creep deformation (155 ^kJ mol_-1), a self-diffusion mechanism has been identified as rate controlling for both refined and unrefinedRR 58. The rate equation ?= A¹[sinh (ασ)]_nexp(–Q/RT] has been found to be applicable for RR 58 deformed under creep conditions in the range oftemperatures and strain rates studied