Antibacterial and corrosive properties of copper implanted austenitic stainless steel

Copper ions were implanted into austenitic stainless steel （SS） by metal vapor vacuum arc with a energy of 100 keV and an ions dose range of （0.5-8.0）× 10^17 cm^-2. The Cu-implanted SS was annealed in an Ar atmosphere furnace. Glancing X-ray diffraction （GXRD）, transmission electron microscopy （TEM） and Auger electron spectroscopy （AES） were used to reveal the phase compositions, microstructures, and concentration profiles of copper ions in the implanted layer. The results show that the antibacterial property of Cu-implanted SS is attributed to Cu9.9Fe0.1, which precipitated as needles. The depth of copper in Cu-implanted SS with annealing treatment is greater than that in Cu-implanted SS without annealing treatment, which improves the antibacterial property against S. aureus. The salt wetting-drying combined cyclic test was used to evaluate the corrosion-resistance of antibacterial SS, and the results reveal that the antibacterial SS has a level of corrosion-resistance equivalent to that of un-implanted SS.

Effect of slag composition on the cleanliness of 28MnCr5 gear steel in the refining processes

The equilibrium reaction between CaO-Al2O3-SiO2-MgO slag and 28MnCr5 molten steel was calculated to obtain the suitable slag composition which is effective for decreasing the oxygen content in molten steel. The dissolved oxygen content [O] in molten steel un- der different top slag conditions was calculated using a thermodynamic model and was measured using an electromotive force method in slag-steel equilibrium experiments at 1873 K. The relations among [O], the total oxygen content （T.O）, and the composition of the slag were investigated. The experimental results show that both [O] and T.O decrease with decreasing SiO2 content of the slag and exhibit different trends with the changes in the CaO/Al2O3 mass ratio of the slag. Increasing the CaO/Al2O3 mass ratio results in a decrease in [O] and an in- crease in T.O. To ensure that T.O ≤ 20 ppm and [O] ≤ 10 ppm, the SiO2 content should be controlled to 〈5wt%, and the CaO/AI203 mass ratio should be in the range from 1.2 to 1.6.

Mechanism research on arsenic removal from arsenopyrite ore during a sintering process

The mechanism of arsenic removal during a sintering process was investigated through experiments with a sintering pot and arsenic-bearing iron ore containing arsenopyrite; the corresponding chemical properties of the sinter were determined by inductively coupled plasma atomic emission spectrometry(ICP-AES),X-ray diffraction(XRD),and scanning electron microscopy(SEM) coupled with energy-dispersive X-ray spectroscopy(EDS). The experimental results revealed that the reaction of arsenic removal is mainly related to the oxygen atmosphere and temperature. During the sintering process,arsenic could be removed in the ignition layer,the sinter layer,and the combustion zone. A portion of Fe As S reacted with excess oxygen to generate Fe AsO_4,and the rest of the Fe As S reacted with oxygen to generate As_2O_3(g) and SO_2(g). A portion of As_2O_3(g) mixed with Al_2O_3 or CaO,which resulted in the formation of arsenates such as AlAsO_4 and Ca_3(AsO_4)_2,leading to arsenic residues in sintering products. The Fe As S component in the blending ore was difficult to decompose in the preliminary heating zone,the dry zone,or the bottom layer because of the relatively low temperatures; however,As_2O3(g) that originated from the high-temperature zone could react with metal oxides,resulting in the formation of arsenate residues.

Photocatalytic activity of ferric oxide/titanium dioxide nanocomposite films on stainless steel fabricated by anodization and ion implantation

A simple surface treatment was used to develop photocatalytic activity for stainless steel. AISI 304 stainless steel specimens after anodization were implanted by Ti ions at an extracting voltage of 50 kV with an implantation dose of 3 × 10^15 atoms.cm-2 and then annealed in air at 450℃ for 2 h. The morphology was observed by scanning electron microscopy. The microstructure was characterized by X-ray diffraction and X-ray photoelectron spectroscopy. The photocatalytic degradation of methylene blue solution was carried out under ultraviolet light. The corrosion resistance of the stainless steel was evaluated in NaCl solution （3.5 wt%） by electrochemical polarization curves. It is found that the Ti ions depth profile resembles a Gaussian distribution in the implanted layer. The nanostructured Fe203/TiO2 composite film exhibits a remarkable enhancement in photocatalytic activity referenced to the mechanically polished specimen and anodized specimen. Meanwhile, the annealed Ti-implanted specimen remains good corrosion resistance.

Mechanisms of interfacial reactions between 316L stainless steel and MnO-SiO_(2) oxide during isothermal heating

Diffusion couple experiments were performed to study the thermodynamic and kinetic mechanisms of interfacial reactions between the 316L stainless steel and the composite MnO-SiO_(2) oxide during isothermal heating at 1473 K(1200℃)for 1,3,5,and 10 h and at 1173,1273,1373,1473,and 1573 K(900,1000,1100,1200,and 1300℃)for 3 h.Compositional variations in the 316L stainless steel and the composite MnO-SiO_(2) oxide in the vicinity of the steel-oxide interface in each diffusion couple specimen were determined.Before and after isothermal heating,thermodynamic equilibria between the oxide and steel at the interface were estimated in accordance with the calculation of the Gibbs free energy change in the interfacial steel-oxide reactions.The diffusion coefficients of Mn,Cr,and Si in 316L stainless steel under different experimental conditions were quantitatively acquired.The results showed that solid-state interfacial reactions occurred between the Cr in the 316L stainless steel and composite MnO-SiO_(2) oxide during isothermal heating,which resulted in the depletion of Cr and accumulation of Si and Mn in the steel in the vicinity of the steel-oxide interface.The widths of the Crdepleted zone,Mn-accumulated zone and Si-accumulated zone all showed increasing trends with increasing isothermal heating temperature and time.The average values of the diffusion coefficients of Mn,Cr,and Si in the steel at 1473 K(1200℃)were 1.21×10^(^(-14))±2.96×10^(-15),1.69×10^(-14)±2.54×10^(-15),and 1.00×10^(-14)±1.96×10^(-15) m^(2)s^(-1),respectively,and they continued to increase with increasing isothermal heating temperature.

Formation of free-surface vortex and vortex suppression by rotating stopper-rod at end of tundish casting

A rotating stopper-rod technique was proposed to suppress the formation of free-surface vortex in the tundish.The large eddy simulation model coupled with volume of fluid model was developed to study the steel–slag–gas three-phase flow behavior.The critical slag entrapment height of the free-surface vortex and mass of residual steel were predicted at different rotating speeds(30,60,90 and 120 r/min)of the rotating stopper-rod.The numerical model was verified by water model experiment.The results showed that by rotating the stopper-rod in the opposite direction of the vortex above the submerged entry nozzle,the formation of vortex can be effectively disturbed and the critical height of the free-surface vortex can be reduced.Particularly for the 2nd strand,when the rotating speeds are 30,60,90 and 120 r/min,the critical height of the free-surface vortex above the 2nd strand is 7.3,4.7,6.3 and 7.4 cm,respectively.A reasonable rotating speed should be 60 r/min,which can reduce about 2 tons of residual steel.Other rotating speeds just can reduce about 1.6 tons of residual steel.

Improving cleanliness of 30Cr2Ni4MoV low-pressure rotor steel by CaO-SiO_(2)-MgO-Al_(2)O_(3) slag refining

The optimal composition of a CaO-SiO_(2)-Al_(2)O_(3)-MgO slag in the ladle furnace refining process was investigated to precisely control the contents of[0]and[Si]and improve the cleanliness of 30Cr2Ni4MoV steel.The iso-[O]lines and iso-[Si] lines of the equilibrium between the CaO-SiO_(2)-Al_(2)O_(3)-MgO refining slag and 30Cr2Ni4MoV steel at 1873 K were calculated by the thermodynamic software FactSage 7.3,and the activities of SiO_(2),Al_(2)O_(3)and CaO in the refining slag were discussed to achieve the optimal composition range of the refining slag.Finally,combined with high-temperature"slag-steel"equilibrium experiments,the effects of different refining slags on the oxygen contents,chemical composi-tions,quantities and sizes of inclusions in steels were studied,and then the thermody namic formation mechanism of MgAl_(2)O_(4) inclusions in 30Cr2Ni4MoV steel was discussed.The results showed that the contents of dissolved[O]nd[Si]in steel can be controlled below 10 × 10^(-6)and 0.05%.respectively;when the slag basicity is above 7.the CaO/Al_(2)O_(3)ratio is above I.and the mass fraction of SiO_(2)in the slag docs not cxcced 7%.The chemical composition of the slag has a great influence on the removal and composition of inclusions.The assessed stability phase diagrams of MgO.Al_(2)O_(3)and MgOAl_(2)O_(3) inclusion formation in the Fe-Al-Mg-O system calculated by FactSage 7.3 show good agreement with the experimental results.

Morphological transformation of elongated MnS inclusions in non-quenched and tempered steel during isothermal heating

Elongated MnS inclusions in rolled non-quenched and tempered steel tend to cause the mechanical anisotropy of steel,deteriorate the mechanical properties and degrade the quality and service life of the steel products.To reveal the mechanisms of morphological transformation of strip-shaped MnS inclusions during isothermal heating,the effects of heat treatment time and temperature on the morphology,number density and size distribution of elongated MnS inclusions were systematically studied and discussed.A diffusion couple experiment was also conducted to clarify the diffusion mode of MnS inclusions.The experimental results showed that with the increase in isothermal heating time(from 0 to 10 h at 1473 K)and temperature(from 1173 to 1573 K for 3.0 h),the number density and average aspect ratio of MnS inclusions generally showed an increase and decrease trend,respectively,while the area fraction remained stable and only slightly fluctuated around 0.4%.In the diffusion couple,after the isothermal heating at 1473 K for 3.0 h,the elements Mn and S in the steel near the steel-MnS interface were very stable without any concentration gradient.The morphology change sequence of the elongated MnS inclusions in the rolled non-quenched and tempered steel during the isothermal heating was strip→cylinderization→spindle→spheroidization.Relationship between the diameter of MnS inclusion and the spacing between two MnS inclusions after splitting,and the fitting goodness of different n values under different experimental time and temperature confirmed that the driving force for the transformation of MnS inclusions during the isothermal heating was surface diffusion,instead of volume diffusion.

Transformation of nanoscale inclusions in 316L stainless steel processed by laser beam powder bed fusion during isothermal heating

Transformation mechanisms and reaction kinetics for formation of nanoscale inclusions in as-built 316L stainless steel produced by laser beam powder bed fusion(LB-PBF)during subsequent isothermal heating process were investigated and clarified experimentally and theoretically.The resulting changes in morphologies,size distributions,number densities,and chemical compositions of the inclusions were measured and discussed,along with microstructure and texture of the steel.The results showed that with increasing isothermal heating time and temperature,the columnar grains in the as-built LB-PBF 316L stainless steel transformed into equiaxed grains,which grew gradually and exhibited a large number of twins in the FCC structure.During isothermal heating,the reaction of Si in the steel with MnO–Cr_(2)O_(3)in the nanoscale inclusion resulted in a transformation from the homogeneous oxide MnO–SiO_(2)–Cr_(2)O_(3)to an inclusion with an obvious core–shell structure,and the core part was eventually rich in Si and the shell part was predominantly rich in Mn and Si,depending on the heating temperature and time.An Ostwald ripening model used for predicting the growth of nanoscale inclusions during isothermal heating verified that the observed effects of isothermal heating time and temperature were predicted for Si diffusion control.

Thermodynamic analysis of improvement of converter gas by injecting pulverized coal into vaporization cooling flue

In order to improve the calorific value and the recovery yield of converter gas during the steelmaking process, a novel and thermodynamically admissible process was proposed. This method involved injecting pulverized coal into the vaporization cooling flue of a converter, and the approach was developed based on an industrial 30 t converter. The effects of temperature, O2 content, and the volumetric ratio of CO to CO2 on the conversion of the mixed components of gas were analyzed using thermodynamic calculations. Furthermore, the effect of the injection rate on the quality and quantity of gas was investigated. The results show that the O2 and CO2 components of flue gas decrease as the injection rate increases, whereas the CO and H2 components synchronously increase. With the injection rate of 30 kg min-1, the 02 and CO2 components of the gas decreased by 64.12 and 41.19%, respectively, while the CO and H2 increased by 20.09 and 236.84%, respectively, and the recovery time of gas increased by 11.61%, compared to non-injection.

Evolution of MnS inclusions in Ti-bearing X80 pipeline steel

Studies show that manganese sulfide （MnS） inclusions in pipeline steel affect the lateral performance of steel in its rolling deformation, as well as the hydrogen induced cracking and sulfide stress corrosion cracking resistance performance. To inhibit the precipitation of MnS and its effect on pipeline steel, a quenching experiment and a diffusion couple experiment, which investigated the evolution of MnS inclu sions in Ti bearing X80 pipeline steel, were conducted. The experimental results show that the transfor marion of the MnS inclusions during solidification is as follows： MnS→titanium sulfide （TiS） →Ti4 C2S2. The transition temperatures of MnS to TiS and TiS to Ti4C2S2 are 1673 and 1273 K, respectively, and the overall size of the sulfide decreased as well. Thermodynamic calculation results confirm that the transi tion temperatures of MnS to TiS and TiS to Ti4C2S2 are 1 623 and 1 203 K, respectively. When the sulfur content in the X80 pipeline steel is 0. 0015%, all the sulfur in the steel can be converted into Ti4C2S2 with a titanium content of more than 0.02%.

Effect of vanadium on modification of inclusions in Mn-and Si-deoxidized steel during heat treatment at 1 473 K

The effect of vanadium （V） on the modification of oxide inclusions in steels with different concentra- tions of Mn, Si, and V was determined before and after heat treatment at 1473 K. Changes in the morphology, size, and composition of these inclusions were analyzed. Equilibrium relations between the inclusions and steels at 1873 K and 1473 K were calculated using available thermodynamic data to roughly approximate the stable oxide inclusions in the steels, The results revealed that the concentra- tions of V and Si in the steel are critical for controlling the modification of the inclusions during heat treatment at 1473 K. MnO-SiO2-type oxide inclusions gradually transformed into MnO-V2O3-type or Mn-SiO2- and MnO-V2 O3-type inclusions in low Si high-V steels heat-treated for 60 min, In addi- tion, the morphology of the inclusions changed from spherical to irregular. A Si-accumulated zone and a V-depleted zone formed close to the interface in the steel matrix. The experimental and calcula- tion results indicated that, during the heat treatment, an interface chemical reaction occurred be- tween the Fe-Mn-Si-V steel and the MnO-SiO2 type oxide inclusion.

Effect of process parameters on dry centrifugal granulation of molten slag by a rotary disk atomizer

Dry centrifugal granulation(DCG)experiments for blast furnace slag(BFS)were performed by means of a rotary disk atomizer since water quenching method can create a series of problems.The results showed that the DCG method can granulate the BFS,but the results are easily affected by the slag flow rate,disk rotating speed,disk radius,disk material and slag falling height.The granulating parameters with an excessive flow rate,low rotating speed,SiN–SiC disk,stainless steel disk and low slag falling height are detrimental to the granulation process.The most suitable parameters for granulation are a slag flow rate of 5.1×10^(−5) m^(3)/s,a disk rotating speed of 1500–2300 r/min,a slag falling height of 0.8 m and a smooth graphitic disk with the radius of 0.1 m.In the absence of an off-center flow,the overall best granulating effect produces round particles with mean diameter of 3.43 mm without creating slag fiber.The vitreous content of the BFS particles granulated by graphite disks is 92%,which meets the requirements of cement raw materials.The Bond work index of dry granulated BFS is 18.4 kWh/t,and the grindability of dry granulated slag and water-quenched slag is similar.

Preparation of stainless steel mesh-supported ZnO and graphene/ZnO nanorod arrays with high photocatalytic performance

A series of zinc oxide(ZnO)nanorods arrays with different morphologies are synthesized on stainless steel mesh via a facile electrodeposition method.The influences of electrodeposition parameters on the diameter,length,density and morphology of obtained ZnO nanorods are investigated systematically.The results indicate that the electrodeposition potential is the key factor for the morphology of the obtained ZnO nanorods,which further showed the effect on the photocatalytic property of the obtained samples.Meanwhile,the prepared ZnO nanorods array exhibits an excellent photocatalytic activity for methylene blue(MB)in ultraviolet light.The degradation efficiency for MB solution reaches 95.1%under the irradiation of ultraviolet light for 120 min.In addition,the photocatalytic property of the prepared ZnO nanorods can be extended to the visible light region after the modified with graphene oxide(GO).The obtained GO/ZnO composite also shows remarkable photocatalytic activity and photostability.The photodegradation efficiency for MB is 83.6%,and the catalytic performance retains 97.3% of its initial photocatalytic activity after five cycles.

Separation and comprehensive utilization of valuable elements in Ti-bearing electric arc furnace molten slag

A novel route to comprehensive utilization of valuable elements such as Ti, A1, Si and Mg in Ti-bearing electric arc furnace molten slag （Ti-bearing EAF slag） was proposed. The route can be expressed as a three-step process including alkali fusion, water leaching and acidolysis. Following these processes under the optimum conditions, the recovery ratios of TiO2, Al2O3, SiO2 and MgO were about 97.5, 93.5, 27.9 and 53.5%, respectively. Meanwhile, nanostructured TiO2, NaA zeolite and Mg（OH）2 fire retardant were synthesized simultaneously by using Ti-bearing EAF slag as raw materials. In addition, the photocatalytic activity of prepared nanostructured TiO2 and the adsorption property of obtained NaA zeolite were investigated. The results showed that the photodegradation efficiency of as-prepared TiO2 was 80% for rhodamine B and the adsorption efficiency of NaA zeolite was 61% for Cu2＋ under the optimum conditions.