Effect of annealing treatment on microstructures and properties of austenite-based Fe-28Mn-9Al-0.8C lightweight steel with addition of Cu

The mechanical properties of an austenite-based Fe-Mn-Al-C lightweight steel were improved by co-precipitation of nanoscale Cu-rich and κ-carbide particles.The Fe-28Mn-9Al-0.8C-(0,3)Cu (wt.%) strips were near-rapidly solidified and annealed in the temperature range from 500 ℃ to 700 ℃.The microstructure evolution and mechanical properties of the steel under different annealing processes were studied.Microstructural analysis reveals that nanoscale κ-carbides and Cu-rich particles precipitate in the austenite and ferrite of the steel in this annealing temperature range.Co-precipitation of nanoscale Cu-rich particles and κ-carbides provides an obvious increment in the yield strength.At the annealing temperature of 600 ℃,both the yield strength and ultimate tensile strength of Fe-28Mn-9Al-0.8C-3Cu (wt.%) steel strip are the highest.The total elongation is 25%,which is obviously higher than that of Cu-free steel strips,for the addition of Cu reduces the large sized κ-carbides precipitated along austenite/ferrite interfaces.When the annealing temperature rises to 700 ℃,the strength and ductility of the two steel strips deteriorate due to the formation of massive intergranular κ-carbides precipitated along austenite/ferrite interfaces.It can be concluded that a proper co-precipitation of Cu-rich particles and κ-carbides would improve the properties of austenite-based Fe-Mn-Al-C steel.

Effects of hot top pulsed magneto-oscillation on solidification structure of steel ingot

Achieving a uniform structure with few defects in heavy steel ingot is of high commercial importance. In this present work, in order to verify the potential of pulsed magneto-oscillation(PMO) applied in the production of heavy ingot, an induction coil was located at the hot top of the steel ingot to develop a novel technique, named hot top pulsed magneto oscillation(HPMO). The influences of HPMO on the solidification structure, macro segregation and compactness of a cylindrical medium carbon steel ingot with the weight of 160 kg were systematically investigated by optical microscope(OM) and laser induced breakdown spectroscopy original position metal analyzer(LIBSOPA-100). The results show that HPMO not only causes significant grain refinement and promotes the occurrence of columnar to equiaxed transition(CET) but also can homogenize the carbon distribution and enhance the compactness of the steel ingot. Therefore, HPMO technique has the potential to be applied in the production of heavy steel ingots on an industrial scale.

Grain refinement of commercial pure Al treated by Pulsed Magneto-Oscillation on the top surface of melt

Commercial pure Al can be refined by Pulsed Magneto-Oscillation(PMO) treatment applied via a plate induction coil above the top surface of the melt. The proportion of the equiaxed zone area increases with decreasing Height to Diameter(H/D) ratios from 3.5 to1.8 and further to 1.0. Meanwhile, it increases and then decreases with increasing peak current for the three kinds of ingots with H/D ratios of 3.5, 1.8 and 1.0, respectively. However, when the H/D ratio decreases to 0.44, the area proportion of equiaxed zone can reach the maximum value with a lower peak current. FEA software simulation indicates that smaller H/D ratio results in larger current density, electromagnetic force and convection on the top surface of the melt, favoring nucleation and subsequent grain formation. Through evaluating Joule heating effect by PMO, it was found that the proper amount of Joule heating benefits grain refinement. Excessive Joule heating can reduce the size of the equiaxed zone and change the growth morphology of the grains.

Effect of cooling rate and forced convection on as-cast structure of 2205 duplex stainless steel

To forecast the as-cast structure and ferrite-austenite phase ratio of 2205 duplex stainless steel(DSS), the effects of cooling rate and forced convection were observed in a high-vacuum resistance furnace in which the forced convection was created by the rotation of the crucible. The as-cast structure of all 2205 DSS samples is full equiaxed grains, and the microstructure consists of a great amount of desirable intra-granular austenite inside the continuous ferrite grain matrix, besides Widmanstatten austenite and grain boundary austenite. The ferrite grain size decreases gradually with the increase in the cooling rates(20 to 60 oC·min-1) or the forced convection, while the ferrite grains of the samples solidified with a strong convection are barely changed when the cooling rate is below 50 oC·min-1. Moreover, a small grain size is beneficial for the austenite formation but the influence is not very obvious under the cooling rates in the range of 5 to 50 oC·min-1. Compared with grain size, the cooling rate has a greater influence on the final ferrite content. A model based on the experimental results is established to predict the ferrite content, which could be approximated by δ(%) = 20.5·exp(c/80.0) + 0.34 d +34.1, where cis the cooling rate in oC·min-1 and d is the grain size in mm. By using this model, the dependence of the final ferrite content on cooling rate and grain size is well described.

Solidification characteristics of Fe-Ni peritectic al oy thin strips under a near-rapid solidification condition

This paper is an experimental investigation of the structure evolution and the solute distribution of 2 mm thick strips of Fe-(2.6, 4.2, 4.7, 7.9wt.%)Ni peritectic alloy under a near-rapid solidification condition, which were in the regions of δ-ferrite single-phase, hypo-peritectic, hyper-peritectic and γ-austenite single-phase, respectively. The highest area ratio of equiaxed grain zone in the hyper-peritectic of Fe-4.7wt.%Ni alloy strip was observed, while other strips were mainly columnar grains. The lowest micro-segregation was obtained in the Fe-7.9wt.%Ni alloy strip, while micro-segregation in the Fe-4.7wt.%Ni alloy was the highest. As opposed to the microsegregation, the macro-segregation of all the Fe-Ni strips was suppressed due to the rapid solidification rate. Finally, the structure formation mechanism of Fe-Ni alloy strips was analyzed.

An accelerated aging assisted by electric current in a Fe-Mn-Al-C low-density steel

An aging method assisted by electric current was applied to a Fe-18Mn-9Al-1C(wt.%)low-density steel.It improves the microstructure and therefore significantly increases both the yield strength and ductility of the steel.This current-assisted aging method can increase the yield strength by 178 MPa and elongation by 1.16 times in only 0.5 min at 450℃.However,the yield strength is increased only 90 MPa by the traditional aging method(heat conduction)at 450℃ for 180 min,and the elongation is even decreased from 42.0%to 31.6%.The obvious improvement in yield strength by the current-assisted aging for a short time is resulted from the fact that the current-assisted aging promotes a rapid precipitation of nano-scaleκ-carbides inγ-austenite by reducing the thermodynamic barrier and accelerating the atomic diffusion.This work demonstrates that this current-assisted aging method is significantly time saving and cost-effective for low-density steels,with potential for various industrial applications.

Preparation and nucleation of spherical metallic droplet

The preparation and solidification of metallic droplets attract more and more attention for their signiifcance in both engineering and scientiifc ifelds. In this paper, the preparation and characterization of Sn-based al oy droplets using different methods such as atomization and consumable electrode direct current arc （CDCA） technique are reviewed. The morphology and structure of these droplets were determined by optical microscopy, X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The solidiifcation behavior of single droplet was systematical y studied by means of scanning calorimetry （DSC）, and the nucleation kinetics was also calculated. In particular, the development of fast scanning calorimetry （FSC） made it possible to investigate the evolution of undercooling under ultrafast but control able heating and cooling conditions. The combination of CDCA technique and FSC measurements opens up a new door for quantitative studies on droplet solidiifcation, which is accessible to demonstrate some theories by experiments.

Effect of wide-spectrum pulsed magnetic field on grain refinement of pure aluminium

A wide-spectrum pulsed magnetic field(WSPMF)was obtained by adjusting the number of current pulses and the pulse interval between adjacent pulses.The effect of WSPMF on the grain refinement of pure aluminium was studied.The distribution of electromagnetic force and flow field in the melt under the WSPMF was simulated to reveal the grain refining mechanism.Results show that the grain refinement is attributed to the combined effect of the melt flow and oscillation under a WSPMF.When the pulse interval is 5 ms,the extreme value of electromagnetic force is the highest,and the size of the crystal nucleus is 0.35 mm.In the case of similar flow rates,the grain size gradually decreases as the pulse interval increases.The range of the harmonic frequency of the magnetic field gradually expands with the increase of the pulse interval,which can provide more energy for nucleation at the solid-liquid interface and promote nucleation.

nfluences of superheat and cooling intensity on macrostructure and macrosegregation of duplex stainless steel studied by thermal simulation

The influences of superheat and cooling intensity on macrostructure and macrosegregation of one new kind duplex stainless steel(DSS)were studied.Thermal simulation equipment was applied to prepare samples,which could reproduce the industrial processes of DSS manufactured by a vertical continuous slab caster.Macrostructure and macrosegregation were analyzed using the digital single lens reflex and laser-induced breakdown spectroscope(LIBSOPA-200),respectively.The percentage of both chill zone and center equiaxed zone increases with the superheat decreasing,while that of the columnar zone decreases.There is only equiaxed grain existing as the superheat is 10 and 20℃.The lower the superheat is,the coarser the gain size is.High cooling intensity in mold could remarkably decrease the chill zone length and refine the grains in chill zone and center equiaxed zone.The influences of cooling intensity on macrosegregation are greater than those of superheat.The macrosegregation of Si,Mn and Cr is slightly dependent on superheat,while that of Cu,Mo and Ni changes greatly with superheat increasing.

Influence of pulse magneto-oscillation on the efficiency of grain refiner

Solidification experiments were carried out in Al-Cu （w（Cu） = 5%） alloy to investigate the influence of pulse magneto-oscillation （PMO） on the efficiency of the Al3Ti1B refining agent at high superheat. The experimental solidification results show that the degree of superheat has remarkable influence on the efficiency of the grain refiner. However, the application of PMO has the potential to reduce the influence of superheat variation on the efficiency of the grain refiner. Finally, the mechanism underlying this phenomenon is discussed by performing a numerical simulation to show the forced flow inside the melt caused by PMO.

Distribution of nonmetallic inclusions in molten steel under hot-top pulsed magneto-oscillation treatment

To control the distribution of nonmetallic inclusions in molten developed method, hot-top pulsed magneto-oscillation （HPMO）, steel is of highly commercial importance. A newly was employed to control nonmetallic inclusions in a medium-carbon steel ingot. The experimental results present that the position of nonmetallic inclusions of spinel （Al-Mg-O） and Mn-S inclusions is significantly influenced by HPMO. The number of nonmetallic inclusions gradually increased from the lateral wall to the center of ingot along the radial direction under the impact of HPMO treatment, whereas this distribution trend cannot be observed in the reference sample without HPMO treatment. In addition, the number of inclusions along vertical direction is proportional to the height of ingot, especially for the inclusions with the size of larger than 10 pro. It indicates that the application of HPMO can push away inclusions from lateral to center, and then the expelled inclusions aggregate and rise up to the top of ingot.

Influence of electromagnetic parameters on solidification structure of pure AI in the case of identical power

Pulsed magneto-oscillation （PMO） as a new electromagnetic technology to generate the grain refinement in metals and alloys was significantly developed in recent years. The influence of electromagnetic parameters on the grain size reduction in pure AI was investigated under the application of PMO with a constant inputting power. The experimental results show that the grain refinement degree could be improved with the increase in the current intensity in the case of the identical power. Moreover, through analysing the electromagnetic force and resistance force applied on the nucleus, a criterion of the nucleus detached from the mould wall was constructed. Based on the criterion, the detachment of nuclei with finer radius could cause better effect of the grain refinement, when applying a higher current peak. The movement of the detached grains was considered by analysing the influence of electromagnetic force and forced flow.

Influence of pulsed magneto-oscillation on microstructure and mechanical property of rectangular 65Mn steel ingot

The pulsed magneto-oscillation （PMO） technique has the potential to be applied in the production of heavy steel ingot. In order to confirm it and achieve more insights, the solidification of rectangular 65Mn steel ingot with the size of 220 mm×220 mm × 1000 mm was investigated under the impact of PMO. Experimental results present that PMO treatment can remarkably refine the solidified microstructure of 65Mn steel ingot in comparison with the reference ingot without PMO. The application of PMO not only significantly reduces the grain size, but also promotes the morphology transition of equiaxed grains from well-developed dendritic structures to globular structures. And the resulted globular morphology is mainly due to the fact that the PMO-induced forced flow enhances the stability of crystal growth. As a consequence, the average tensile strength of as-cast samples is enhanced from 643.4 to 762.9 MPa under the application of PMO.

Distributions of Electromagnetic Fields and Forced Flow and Their Relevance to the Grain Refinement in Al–Si Alloy Under the Application of Pulsed Magneto-Oscillation

Distributions of electromagnetic fields and induced forced flow inside a metal melt are crucial to understand the grain refinement of the metal driven by pulsed magneto-oscillation(PMO).In the present study,PMO-induced electromagnetic fields and forced flow in Ga-20 wt%In-12 wt%Sn liquid metal have been systematically investigated by performing numerical simulations and corresponding experimental measurements.The numerical simulations have been confirmed by magnetic and melt flow measurements.According to the simulated distribution of electromagnetic fields under the application of PMO,the strongest magnetic field,electric eddy current and Lorentz force with inward radial direction inside the melt are concentrated adjacent the sidewall of cylindrical melt at the cross section of middle height of coil.As a result,a global forced flow throughout the whole cylindrical column filled with Ga-20 wt%In-12 wt%Snmelt is initiated with a flow structure of two pair of symmetric vortexring.The PMO-induced electromagnetic fields and forced flow in Al-7 wt%Si melt have been numerically simulated.The contribution of electromagnetic fields and forced flow to the grain refinement of Al-7 wt%Sialloy under the application of PMO is discussed.It indicates that the forced flow may play a key role in the grain size reduction.

Improving the Solidified Structure by Optimization of Coil Configuration in Pulsed Magneto-Oscillation

Using both numerical and experimental methods, we studied the effect of coil configuration of pulsed magneto-oscillation（PMO） on distribution of electromagnetic field, flow field and solidification structure with the same pulse currentparameters in A1 ingots. We designed and constructed three types of coils： surface pulsed magneto-oscillation, hot-toppulsed magneto-oscillation （HPMO） and combined pulsed magneto-oscillation （CPMO）. PMO treatment refined thesolidification structure in all the ingots. The configuration of the PMO, however, introduced differences in magnetic fieldintensity, electromagnetic force, Joule heat, flow field, equiaxed grain zone, grain size and growth direction of columnargrains. The largest equiaxed grain zone was found in CPMO treated ingot, and the smallest grain size was found in bothHPM0 and CPMO treated ingots. Numerical simulation indicated that difference in electromagnetic field and flow fieldresulted in differences in solidification structure. HPMO is more advantageous over others for large ingot production.

Microstructure and mechanical behavior of a low-density Fe-12Mn- 9Al-1.2C steel prepared using centrifugal casting under near-rapid solidification

It is vital for emission reduction and energy saving to lighten the weight of automobile. Low-density Fe-Mn-Al-C steels with high strength and excellent ductility have become a promising type of material in the automotive industry. Thus, a new approach was proposed by using centrifugal casting to produce the low-density Fe-12Mn-9Al-1.2C steel with high performance under near-rapid solidification in a near-net shape. The produced steel strips, with a thickness of 2.5 mm and a density of 6.89 g/cm3, were examined for their microstructures and mechanical properties. The results showed that mechanical properties of as-cast steel strip reached 1182 MPa in ultimate tensile strength and 28.1% in total elongation. Aging treatment at 400 or 600℃ for 3 h enhanced tensile strength of the steel strips, while aging at 800℃ dramatically decreased its elongation. Moreover, Young＇ s modulus of the steel strip improved with the increment of aging temperature. The relationship between the mechanical properties and the microstructures was discussed. The results demonstrated that advanced low-density steels with promising mechanical properties could be directly produced from liquid by this simple process.

Effect of cooling rate on microstructure and inclusion in non-quenched and tempered steel during horizontal directional solidification

In order to investigate the relationship between microstructure and MnS inclusion in non-quenched and tempered steel, and cooling rate during horizontal directional solidification, 49MnVS steel was used to conduct the experiments with a selfdesigned device. The mathematical effect of cooling rate on dendritic arm spacing and mean diameter of MnS particles (dMnS) were determined by using linear regression method. The results show that the length of dendrite from solid–liquid interface to end-solidification decreased with increasing the withdrawal velocity (#). dMnS has a similar value in the area of the steady directional solidification;the value of dMnS was 4.1, 3.6, 3.3, 2.8 and 2.3 lm at withdrawal velocity of 50, 75, 100, 150 and 200 lm/s, respectively. dMnS increased with reducing # or RC (interface cooling rate). MnS precipitated in the gaps between dendrites and was influenced by secondary dendritic arm spacing. Besides, a new concept of the ‘Precipitation Unit Space’(PUS) was proposed and the relationships between dMnS, VPUS (volume of PUS) and RC were obtained.

Corrosion mechanism research and microstructure analysis of Baosteel No.3 blast furnace hearth

Baosteel No.3 blast furnace hearth was divided into tuyere area,taphole area,taphole upper side wall and taphole lower side wall according to different working situations.Through chemical composition analysis,scanning electron microscopy,X-ray diffraction,energy dispersive spectrometry and other means,chemical composition and microstructure of different parts of hearth carbon brick were analyzed and markedly different corrosion mechanisms of these areas were found.Zn element in form of ZnO mainly deposited on the hot side of carbon brick.There was no obvious evidence that Zn permeates into carbon bricks and erodes them.Except for taphole area,K,Na,and Fe contents from hot side to cold side gradually rise and fall,resulting in the decrease of apparent porosity,the increase of density and the higher thermal conductivity compared with those of new carbon brick.The higher content of Fe in carbon brick leads to more serious erosion because Fe has greatly changed the physical properties of carbon brick.In the taphole area,the contents of Si and Al present obvious concentration gradient because of the mechanical souring of molten iron and slag.The SiO;and Al;O;particles that have different expansion factors with carbon brick damaged the carbon substrate because of temperature fluctuation.The graphitized carbon found on H4 where is the most serious corrosion site means that the carbon brick ever directly contacts with molten iron.

Molybdenum alloying in cast iron and steel

Metal casting is an important manufacturing technology for efficiently producing massive components with complex shape.A large share of industrial castings is made from iron and steel alloys,combining attractive properties and low production cost.Upgrading of properties in cast iron and steel is mainly achieved by alloying and in fewer cases by heat treatment.Molybdenum is an important alloying element in that respect,increasing strength,hardness and toughness.It also facilitates particular heat treatments such as austempering.The paper describes the metallurgical functionality of molybdenum alloying in iron-based castings and demonstrates its effectiveness for applications in the automotive and mining industry.

Effects of pulse magneto-oscillation on GCr15 bearing steel continuous casting billet

Pulse magneto-oscillation(PMO)added during solidification could affect the solidification structure and macrosegregation.A modified thermal simulation equipment was applied to prepare GCr15 bearing steel continuous casting billets with different PMO peak currents.Then,metallographic analysis,component analysis and numerical simulation were adopted to study the influence of PMO peak current and its mechanism.The sample with 150 K_(I)A PMO peak current treatment has little difference with the samples without PMO treatment on solidification structure and macrosegregation.As the peak currents are 250 and 350 K_(I)A,the columnar zone increases and macrosegregation aggravated.When 450 K_(I)A peak current is selected,the equiaxed grain ratio is enlarged,and the dendritic grains are refined,and the macrosegregation of C,Cr,Si and Mn is decreased significantly.By analyzing,different convections induced by PMO with various peak currents are the key factor to change the solidification structure and macrosegregation.