Volume 37, Issue 8 -

In order to avoid the formation of crack initiation sites, inclusions in high-carbon steel for saw wire are strictly required to have excellent deformability. However, it is hard to achieve this goal with only conventional inclusion softening art, such as Si-Mn deoxidation and low basicity top slag refining. Therefore, a new method should be put forward to enhance the deformability of inclusions. Low melting temperature inclusions are widely considered to have good deformability, hence, adding K (potassium) into inclusions may become a potential new method to better enhance the deformability of inclusions due to the pronounced effect of K 2 O on lowering the melting temperature of inclusions. In the present study, the influences of Fe/K 2 CO 3 (weight ratio), K 2 CO 3 addition amount and reaction time on inclusions were investigated by using a graphite tube resistance furnace. Through this study, a solution to adding K into inclusions effectively by K 2 CO 3 addition was developed and the melting temperature of inclusions was significantly reduced. In addition, the reaction mechanism between K 2 CO 3 /slag/steel/inclusion was deduced and the relation between deformability and crystallinity of inclusions was also briefly discussed.

The relationship between MnS precipitation and induced nucleation effect of Mg-bearing inclusion has been explored through scanning electron microscope and energy dispersive spectrometer (EDS). Results indicate that MnS prefers to precipitate on Mg-bearing inclusions. Statistical analysis suggests that MgAl 2 O 4 and MgO may coexist in inclusion. After etching, it is found that Mg-bearing inclusions can induce the nucleation of intragranular acicular ferrites. Based on EDS line analysis and comparison with Al-Mn-Si-O inclusion in non-Mg-treated sample, this effect can be explained by Mn-depletion zone (MDZ), which is due to the vacancy property and crystal structure of MgAl 2 O 4 . In the same sample, similar induced nucleation effect and MDZ are not observed around pure MnS. This comparison implies that the formation of MDZ may be independent of MnS precipitation.

To investigate the mechanism by which voids form around hard inclusions, the deformations of a plastic slab with hard and soft inclusions that form inside it during the hot rolling process have been simulated with a finite element method. By comparing plastic strain distributions, the relative displacements of contact surfaces, and the deformations between hard and soft inclusions have preceded analysis of the formation mechanism of these voids. The variations of strain measurements between the matrix and hard inclusions cause relative displacement of their contact surfaces. Therefore, voids occur at the front and rear of the hard inclusions. Trials on the slab deformations using a titanium ball instead of the soft inclusion inside the slab during the hot rolling process are conducted. The simulated shapes of the soft inclusions with different reductions mostly agree with the experimental results.

Thermally induced superlow friction (0.008) of diamond-like carbon (DLC) films was achieved in ambient air in the present work. Raman and XPS (X-ray Photoelectron Spectroscopy) measurements and analyses show that superlow friction of the annealed DLC films is involved in the transformation of sp 3 to sp 2 hybridized carbon during annealing and the tribochemical reactions during sliding. The thermally activated graphitization and oxidation of the annealed DLC films in ambient air is beneficial to form the positively charged interface and achieve the stable superlow friction. A friction model was developed and applied to explain superlow friction, which is attributed to Van de Waals force between graphite layers and the repulsive force between hydroxyl group of graphite oxide and hydrogen terminated DLC films surface.

Effect of pre-oxidation on the steam oxidation of T92 heat-resistant steel at 650 °C was investigated. The results show that the mass gain and the oxide thickness of T92 sample with pre-oxidation treatment were lower than that of T92 sample after exposure in steam at 650 °C. The compact and discrete Cr-rich oxide which formed on the pre-oxidized specimen hindered ion diffusion, leading to the lower oxidation rate. The effect of pre-oxidation worked at the initial stage due to the protective Cr-rich layer formed in air gas. After a long time exposure in steam, the pre-oxidation influence decreased slowly and eventually disappeared. What’s more, the adhesion property of oxide scale was improved by pre-oxidation.

To improve the direct alloying of manganese ore in steelmaking, the decomposition and carbon reduction of manganese ore was studied using a differential thermal analyzer and resistance furnace. The remaining material after manganese ore decomposition at 1,600 °C was a mixture of 43 % MnO, 40 % MnSiO 3 and FeO, and 17 % MnSiO 3 . The remaining material after the carbon reduction of the manganese ore was a mixture of metal (30.8 % Mn 7 C 3 and 16.1 % FeC 3 ) and slag (2.5 % FeO, 5.1 % SiO 2 , and 18.8 % MnO). The high-temperature (1,200 ℃) decomposition and reduction of manganese ore produce manganese carbonate, manganese dioxide, and manganese salicylate sesquioxide. However, because it is not easy to decompose the manganese silicate in the manganese ore, the proportion of ore being reduced by carbon is small. Therefore, the increase of the manganese reduction of manganese silicate is critical to the direct alloying of manganese ore. Adding calcium oxide or magnesium oxide to the manganese ore improves the reduction of manganese ore, whereas adding slag from the initial stage or endpoint of the converter process has little effect on the manganese ore reduction.

The individual and combined effects of W and Zr additions on macrostructure, microstructure and mechanical properties of Nb have been investigated. Nb, Nb-10 wt% W, Nb-2.5 wt% Zr and Nb-10 wt% W-2.5 wt% Zr alloy ingots were prepared by electron beam drip melting using high purity Nb, W and Zr rods. Additions of W and Zr resulted in significant improvement in hardness and room temperature tensile strength. It is seen that the effect of 10 wt% W addition is more than that of 2.5 wt% Zr addition in improving room temperature strength of Nb, although on ‘per wt% addition’ basis, Zr is a more effective strengthener than W. It is also observed that the cumulative effects of 10 wt% W and 2.5 wt% Zr on grain refinement and strengthening are more than their respective individual effects.

The tin-based babbit with different layer thickness was bonded to mild steel via TIG arc brazing. The microstructure, microhardness, wear properties and phase formation mechanism near the interface of the arc brazed layer were investigated by the optical microscope (OM), X-ray diffraction (XRD), high temperature friction and wear testing machine (HTFWT), laser scanning confocal microscope (LSCM), electron microscope (SEM) and energy dispersion spectrum (EDS). It can be found that in the arc brazing seam region, the thinner layer made it possible to form larger size SbSn monotectic phase that connected together and some Fe-Sn IMCs were formed near the interface. So that when the layer thickness was 0.5 mm, the microhardness of arc brazing tin-based babbit layer was the largest and the antifriction property was the best. Moreover, on the brazing tin-based babbit interface, Fe elements were transited and diffused from mild steel into the brazing seam region. Element concentration of Fe was high near the steel interface and formed concentration gradient in the liquid metal layer, which was helpful to promote the metallurgical reaction. Phase constituents of the brazed joint interface were Fe, Fe 3 Sn, FeSn and FeSn 2 , formed in the metallurgy of Fe from mild steel and the Sn from tin-based babbit.

Autoclave molding of prepregs is an established fabrication method to produce composite components to be used in the aerospace industry and elsewhere. The process involves the excess resin to flow out and curing of the resin. The process model simulation, which is very effective to optimize the process parameters and laminate properties, requires various sub-models to account for resin flow and resin curing. This work focuses on the curing behavior and development of kinetic sub-model of a quartz fabric prepreg impregnated with cyanate ester-based resin. Differential scanning calorimetry (DSC) in both dynamic and isothermal modes has been used for the study. The dynamic study reveals that two distinct reaction mechanisms were involved during curing. The dynamic study data is used to obtain the activation energy using model-free iso-conversional method. The kinetic expression obtained using the isothermal DSC scan data is able to predict the complexity of the overall reaction which can be described by n th-order reaction kinetics for the initial phase of reaction followed by the autocatalytic reaction kinetics.

A detailed investigation concerning the formation mechanism of craters of pure metal and alloy surface after high-current pulsed electron beam (HCPEB) processing has been carried out. After HCPEB irradiation, typical craters were homogeneously distributed on the entire surface of 3Cr13 stainless steel, resulting from local sublayer melting and eruption through the solid outer surface. Comparatively, almost no craters were created of pure zirconium, which was associated with the shallow melting site and incomplete treated surface. Furthermore, a large number of ultrafine grains were formed on the irradiated surface, indicating that surface melting was the dominant interaction mechanism between HCPEB irradiation and pure zirconium. It is apparent that “crater free” phenomenon plays a dominant role in surface modification of zirconium and zirconium alloys.

The recovery of iron, chromium, and nickel from stainless steel dust (SSD) has attracted considerable attention for their utilization as secondary resources in the ever-growing field of steelmaking. This paper investigates the reduction process of SSD briquettes in iron-baths in detail in order to determine the optimum processing parameters. A novel method of analysis by studying the erosion behavior of a corundum crucible was adopted to accurately calculate the recovery rate of the metals, and the effect of the parameters on the triple metals recovery rate was determined by orthogonal testing. The results show that the most important factor for the SSD briquetting process is water, followed by sucrose, carbon, and pressure. The optimum parameters of the SSD briquetting process are 13 wt% sucrose, 13 wt% water, 11 wt% carbon, and 30 MPa pressure. The compressive intensity was found to be 27.6 MPa. When a basicity of 1.6, 17% carbon, 5 wt% ferrosilicon, and 6% CaF 2 were used in the SSD briquette reduction process, the triple metal recovery rate was in the range of 94 –100 %, 90 –100 %, and almost 100 %, respectively.