Volume 35, Issue 7 -

A new electrosilicothermic method has been proposed in the present paper to produce Ni–Cr ferroalloy, which can be used for the production of 300 series stainless steel. Based on this new process, the Ni–Si ferroalloy is first produced as the intermediate alloy, and then the desiliconization process of Ni–Si ferroalloy melt with chromium concentrate is carried out to generate Ni–Cr ferroalloy. The silicon content in the Ni–Si ferroalloy produced in the submerged arc furnace should be more than 15 mass% (for the propose of reducing dephosphorization), in order to make sure the phosphorus content in the subsequently produced Ni–Cr ferroalloy is less than 0.03 mass%. A high utilization ratio of Si and a high recovery ratio of Cr can be obtained after the desiliconization reaction between Ni–Si ferroalloy and chromium concentrate in the electric arc furnace (EAF)–shaking ladle (SL) process.

The present study compares the mechanical and electrochemical behaviour of austenitic (AISI 316L) stainless steel compacted at various pressures (200, 400 and 600 MPa) and conventionally sintered at super-solidus temperature of 1,400°C. The electrochemical behaviour was investigated in 0.1 N H 2 SO 4 solution by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The shrinkage decreased and densification has been increased with increasing pressure. The mechanical and electrochemical behaviour with pressure has been correlated with densification response and microstructure (pore type, volume and morphology). Highest densification (~92% theoretical) achieved at 600 MPa (compaction pressure) and 1,400°C (sintering temperature) resulted in excellent combination of tensile strength and ductility (456 ± 40 MPa, 25 ± 1.1%), while showing excellent corrosion resistance (0.1 mmpy or 4.7 mpy).

The formation of coarse prior austenite grain is a key factor to promote transverse crack, and the transverse crack susceptibility can be reduced by refining the austenite grain size. In the present study, the high-temperature confocal laser scanning microscope (CLSM) was used to simulate and study the effect of two γ→α phase transformation conditions on the refinement of the prior austenite grains. Under the condition of the uniform distribution of the second phase precipitation, the effect of the distribution of the proeutectoid ferrite at different cooling rates and refinement of prior austenite grain were investigated. The results indicate that, at a cooling rate of 5.0°C s –1 , the austenite grain size undergoing TH1 thermal cycle was 31% smaller than the austenite grain undergoing TH0 thermal cycle. Under TH0 cooling system, the proeutectoid ferrite was uniformly distributed in the austenite matrix; under TH1 cooling, the proeutectoid ferrite precipitated and mainly concentrated along the austenite grain boundaries to form developed-film-like ferrite, which is favorable to break the prior austenite grain boundaries. After the first phase transformation, the film-like ferrite improved the nucleation conditions of new austenite grains, thus more new austenite grains splitted the prior austenite grains, ultimately refining the prior austenite grains.

Large and hard inclusions often deteriorate the service performance and reduce the fatigue lifetime of drill rods. In this paper, the main reasons of the rupture of drill rods were analyzed by the examination of their fracture and it is found that the large inclusions were the main reason of breakage of rod drill. The inclusions were high of Ca content or Al 2 O 3 rich. Smaller and better deformability inclusions were obtained by the optimization of refining slag, calcium treatment process and the flow control devices of tundish. Results of industrial experiment after optimization show that total oxygen content of drill rods decreased by more than 50%, macro-inclusions weight fraction decreased from about 4 mg/10 kg to about 0.3 mg/10 kg and the micro-inclusions average size decreased from 6 to 3.6 μm. The average using times of drill rods after optimization were increased by about 60%.

The viscosity of experimental slag, which was mixed based on the composition of a practical blast furnace slag, was measured in this paper. The influence of Al 2 O 3 and MgO content, basicity R 2 = w (CaO)/ w (SiO 2 ) on the fluidity of slag was studied. The stepwise regression analysis in SPSS was used to reveal the relationship between sulfur distribution coefficient L S and slag composition as well as furnace temperature. The results show that increasing of MgO up to 12% can decrease the slag viscosity. The w (MgO) should be controlled below 8% when there is 20% Al 2 O 3 in the slag. Temperature of hot metal and content of CaO in slag are the two dominant factors on the desulfurization capacity of slag.

AlY coating on 1Cr18Ni9Ti stainless steel was prepared by magnetron sputtering method and some of them were pre-oxidized or vacuum diffusion annealed at 600°C, and the effect of the coating with different treatments on the oxidation behavior of the stainless steel was studied at 1,100°C in air. Results show that the order of the 24-h oxidation mass gain for the specimens is the stainless steel without coating > the stainless steel with coating but without any pre-treatment > the stainless steel with AlY coating after pre-oxidation treatment > the stainless steel with AlY coating after vacuum diffusion annealing. After oxidation, a thick and loose Fe 2 O 3 /Cr 2 O 3 film is formed on the stainless steel without coating, while thinner Fe 2 O 3 /Cr 2 O 3 film is formed on the stainless steel with AlY coating. Compared to the oxidation film formed on the steel with pre-oxidized coating, the one formed on the steel with vacuum diffusion annealed coating is thinner and denser. The rare earth Y and its oxides Y 2 O 3 in the coating produce reactive element effect and improve the ductility/adhesion of the oxide film, which enhances the oxidation resistance of the stainless steel, especially in the vacuum diffusion annealed AlY coating.

Through numerical simulation, key issues concerning the plasma jet features as well as the sizes of nozzle for supersonic atmosphere plasma spraying (SAPS) were analyzed in this paper. Numerical results were compared with the experimental measurements and a good agreement has been achieved. Due to the effect of mechanical compression, the increasing sizes of r 1 , r 2 , r 3 and r 4 ( r 1 , r 2 , r 3 and r 4 are the sizes of nozzle) lead to a decrease in temperature and velocity of plasma jet. But large size of r 5 can increase the external temperature and velocity of plasma jet, which benefit particles accelerating at the far downstream region. A new nozzle was designed based on the simulation results. Compared to the temperature and velocity of plasma jet in the original nozzle, the maximum temperature and velocity of plasma jet in new structure are increased by about 9.8% and 44.5%, which is a benefit to the particles to reach a higher speed and surface temperature.

Inconel 740H alloy is a candidate material for 700°C advanced ultra-supercritical (A-USC) coal-fired power plants application as superheater/reheater tube. In this work, oxidation behavior of Inconel 740H alloy was studied in static air at 750°C and 850°C, and in dynamic pure steam at 750°C, respectively. The alloy was oxidized approximately following a parabolic law in three test environment. In the static air, the oxidation rate at 850°C was about 50 times of that at the 750°C. More NiCrMn spinal and TiO 2 were detected after oxidation at 850°C. Cr 2 O 3 , however, was the main oxidation product at 750°C. In the pure steam, Cr 2 O 3 was still the main oxidation product. The oxidation rate was about 2.6 times of that in static air, but the surface roughness was much smaller and edges of oxide particles were more blurred. There was no evidence of cracks or spallation in three test environments.

We described a newly developed characterization technique that dislocation density could be individually determined for each texture component of plastically deformed metals by combining the line-profile analysis with the texture analysis by using X-ray diffraction. This method was applied to major texture components of cube, copper, and brass evolved in cold-rolled copper sheets. The Warren–Averbach procedure using two diffraction peaks was used for estimating the dislocation density. An increase in the dislocation density with the rolling reduction was evaluated for individual texture components. Although the individual texture components underwent the different slip paths, the dislocation densities in these texture components were almost comparable; however, the non-texture component was shown to have a higher dislocation density than the texture components. The recovery and recrystallization proceeded preferentially in the non-texture component.

In this paper, the effects of high current pulsed electron beam (HCPEB) on the microstructure evolution of casting HPb59-1 (Cu 57.1 mass%, Pb 1.7 mass% and Zn balance) alloy were investigated. The results showed a “wavy” surface which was formed with Pb element existing in the forms of stacking block and microparticles on the top surface layer after treatment. Nanocrystalline structures including Pb grains and two phases (α and β) were formed on the top remelted layer and their sizes were all less than 100 nm. The disordered β phase was generated in the surface layer after HCPEB treatment, which is beneficial for the improvement of surface properties. Meanwhile, there was a large residual stress on the alloy surface, along with the appearance of microcracks, and the preferred orientations of grains also changed.

Magnetic Co 3 O 4 nanostructures were synthesized via a facile thermal treatment method at 700°C by using trans -Na[Co(HMTA) 2 (NO 2 ) 4 ].H 2 O as a new precursor. In synthetic process Co-complex was prepared by the reaction of Na 3 [Co(NO 2 ) 6 ] and hexamethylenetetramine (HMTA). Results show that the target Co-complex was synthesized successfully and provides good conditions for preparation of magnetic nanostructures in a facile and surfactant-free method to prepare the octahedral nanostructures. Precursors and nanostructures were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), UV–visible, Fourier transform infrared (FTIR) spectroscopy and alternating gradient force magnetometer (AGFM). It is found that the Co 3 O 4 nanostructures exhibit a ferromagnetic behavior with a saturation magnetization of 8.69 emu/g and a coercivity of 305.3 Oe at room temperature.

Based on the fundamental characteristics of high chromium vanadium-titanium magnetite (HCVTM), the effects of roasting temperature and roasting time on the phase transition and oxidation consolidation during the oxidation were investigated systematically. It was shown that the oxidation of HCVTM pellet was not a simple process but complex. With increasing roasting temperature and time, the compressive strength of oxidized pellet was improved. The phase transition during oxidation was hypothesized to proceed as follows: (1) Fe 3 O 4 → Fe 2 O 3 ; (2) Fe 2.75 Ti 0.25 O 4 → Fe 9 TiO 15 + FeTiO 3 → Fe 9 TiO 15 + Fe 2 Ti 3 O 9 ; (3) Fe 2 VO 4 → V 2 O 3 → (Cr 0.15 V 0.85 ) 2 O 3 ; (4) FeCr 2 O 4 → Cr 2 O 3 → Cr 1.3 Fe 0.7 O 3 + (Cr 0.15 V 0.85 ) 2 O 3 . The oxidation consolidation process was divided into three stages: (1)oxidation below 1,173 K; (2) recrystallization consolidation at 1,173 – 1,373 K; (3) particle refining recrystallization-consolidation by the participation of liquid phase at 1,373 – 1,573 K. To obtain the HCVTM oxidized pellet with good quality, the rational roasting parameters included a roasting temperature of 1,573 K and a roasting time of 20 min.

A magnetic domain laser scribing technique of grain-oriented 3.2% silicon steel has been investigated for the direct influencing on the magnetic domain wall. The magneto-optical Kerr effect was employed to obtain a visible contrast between antiparallel domains. The effects of laser treating on domain wall were observed. The Bitter, MFM and Kerr microscope pictures showed that domain-wall positions did not repeat precisely from cycle to cycle, particularly at high inductions, and that the average domain-wall spacing decreased with increasing density of laser scribing lines. Two phenomena have been discovered that are difficult to explain (1) that the hardness decreases with increasing laser energy and (2) that the coercivity decreases with decreasing laser energy. A semi-quantitative relationship has been found between the domain patterns and used fiber laser treating method. The behavior of patterns in an applied magnetic field is shown, and based on that a two-dimensional laser lines configuration is proposed for one of the less complicated surface patterns.