Microstructures and Mechanical Properties of a New Low Carbon Bainitic Weathering Steel

A low carbon bainitic weathering steel with Cu-P alloying was developed.The mechanical properties and hot-rolled microstructures of the new steel at different finishing temperatures were investigated.Cu-P alloying produced strong solution strengthening,delayed the transformation of austenite to bainite,thereby increased the amount of M/A islands.The interaction of phosphorous and copper atoms with dislocations inhibited the recovery process and the formation of subgrains.Low temperature rolling promoted the formation of bainite plates and reduced the size of M/A island,which were beneficial to improving the low temperature impact toughness of phosphorus-bearing low carbon bainitic steel.     

Silico-ferrite of Calcium and Aluminum (SFCA) Iron Ore Sinter Bonding Phases: New Insights into Their Formation During Heating and Cooling

The formation of silico-ferrite of calcium and aluminum (SFCA) and SFCA-I iron ore sinter phases during heating and cooling of synthetic iron ore sinter mixtures in the range 298?K to 1623?K (25?°C to 1350?°C) and at oxygen partial pressure of 5?×?10^?3 atm has been characterized using in situ synchrotron X-ray diffraction. SFCA and SFCA-I are the key bonding phases in iron ore sinter, and an improved understanding of their formation mechanisms may lead to improved efficiency of industrial sintering processes.?During heating, SFCA-I formation at 1327?K to 1392?K (1054?°C to 1119?°C) (depending on composition) was associated with the reaction of Fe₂O₃, 2CaO·Fe₂O₃, and SiO₂. SFCA formation (1380?K to 1437?K [1107?°C to 1164?°C]) was associated with?the reaction of CaO·Fe₂O₃, SiO₂, and a phase with average composition 49.60, 9.09, 0.14, 7.93, and 32.15?wt pct Fe, Ca, Si, Al, and O, respectively. Increasing Al₂O₃ concentration in the starting sinter mixture increased the temperature range over which SFCA-I was stable before the formation of SFCA, and it stabilized SFCA to a higher temperature before it melted to form a Fe₃O₄?+?melt phase assemblage (1486?K to 1581?K [1213?°C to 1308?°C]). During cooling, the first phase to crystallize from the melt (1452?K to 1561?K [1179?°C to 1288?°C]) was an Fe-rich phase, similar in composition to SFCA-I, and it had an average composition 58.88, 6.89, 0.82, 3.00, and 31.68?wt pct Fe, Ca, Si, Al, and O, respectively. At lower temperatures (1418?K to 1543?K [1145?°C to 1270?°C]), this phase reacted with melt to form SFCA. Increasing Al₂O₃ increased the temperature at which crystallization of the Fe-rich phase occurred, increased the temperature at which crystallization of SFCA occurred, and suppressed the formation of Fe₂O₃ (1358?K to 1418?K [1085?°C to 1145?°C]) to lower temperatures.     

碳含量对新型Fe-Ni-Mn-Si-C系TWIP钢组织和力学性能的影响

通过光学显微镜、X射线衍射和透射电镜等方法研究了碳含量对Fe-Ni-Mn-Si-C系合金微观组织和力学性能的影响。结果表明:Fe-Ni-Mn-Si-C系合金的主要塑性变形机制为孪生诱发塑性(TWIP)效应。碳的质量分数由0.70%增加至0.98%,合金的屈服强度和抗拉强度分别由391 MPa和860 MPa增大到458 MPa和974 MPa,伸长率由63.6%提高到69.2%。随着碳含量的提高,Fe-Ni-Mn-Si-C系合金出现明显的动态应变时效现象。Fe-15Ni-12Mn-2.5Si-XC合金具有良好的应变硬化能力,随着碳的质量分数提高至0.98%,最大应变硬化指数达到0.73。     

Investigation into the Influence of the Structure Dispersion and Homogeneity on the Properties of Powder Metastable Austenitic Carbide Steels and Diamond Tools

Diffusion and homogenization in “iron (5 μm–nickel (5 μm or 50 nm)” powder systems of various degrees of dispersion during sintering (900 and 1000°C), as well as spark plasma sintering, are investigated using the Matano–Boltzmann method. Calculated diffusivities in pairs of micron powders sintering without applying pressure (900°C, 6 h) and by the spark plasma method (900°C, 5 min) in these systems are equal to 7 × 10–10 cm2/s. It is shown that the use of nanodispersed nickel powder in diffusion pairs based on finely dispersed iron powder promotes a twofold increase in diffusivity at 900°C in contrast to the pair with the microdispersed nickel powder. Constants in the Ivensen sintering kinetics equation are calculated for the “iron–nickel” powder systems, by which the factors activating sintering of these systems are established. The dependences of the structural phase composition and physicomechanical properties of carbide steels of the Fe(base)–14 wt % Ni–8 wt % TiC system on the sintering temperature in range t = 900–1200°C and structure dispersity and homogeneity are determined. The dependences of the grain size, porosity, hardness, microhardness, fracture toughness, and bending ultimate strength on the sintering temperature are shown. Dependences of tribotechnical properties on the degree of homogeneity of the solid solution and volume of the phase transformation of metastable austenite into deformation martensite during abrasive friction turn out similar for carbide steels and diamond tools based on carbide steel. Optimal values of the variation coefficient of the nickel concentration in austenite and carbide steels of the same chemical composition but with different degrees of dispersity, which provide the maximal volume of the austenite decomposition and high values of the diamond-tool grinding coefficient, turn out equal to 5 in both systems, but the sintering parameters are different. It is shown that the physicomechanical properties of the studied systems depend on the structure porosity and dispersity, while tribotechnical properties depend on the structural homogeneity of steels.     

Friction Hydro-Pillar Processing of a High Carbon Steel: Joint Structure and Properties

Metallurgical and Materials Transactions B - A coupled experimental and theoretical study is reported here on friction hydro-pillar processing of AISI 4140 steel, which is a novel solid-state...     

The Reaction Behavior of Direct Reduced Iron (DRI) in Steelmaking Slags: Effect of DRI Carbon and Preheating Temperature

An experimental study was conducted to quantify the rate of direct reduced iron (DRI) decarburization in a steelmaking slag using the constant volume pressure increase technique. Experiments were conducted by dropping DRI pellets into molten slag at temperatures from 1773 K to 1873 K (1500 °C to 1600 °C). Subsequent experiments were carried out in which the DRI pellets were preheated while the slag temperature remained constant. The effect of the initial carbon content and the preheating temperature of the DRI on the reaction rate was investigated. The decarburization of DRI seems to comprise two stages, a reaction between the FeO and DRI followed by decarburization through the iron oxide of slag. Carbon has a significant effect on the kinetics of both stages, whereas the preheating temperature mainly influences the rate of decarburization between FeO and carbon inside the pellet.     

New insights into the widmanstätten proeutectoid ferrite transformation: Integration of crystallographic and three-dimensional morphological observations

The crystallography and three-dimensional (3-D) morphology of Widmanstätten proeutectoid ferrite precipitates are examined in an Fe-0.12 wt pct C-3.28 wt pct Ni steel isothermally reacted at 650 °C, 600 °C, and 550 °C. This article integrates new orientation mapping (OM) results with the findings of a companion article to this one on the 3-D morphology of proeutectoid ferrit^[1] and an earlier transmission electron microscopy (TEM) study which is reanalyzed here in light of the new OM and 3-D results. All of these studies were performed for the same alloy and heat treatments. The 3-D morphologies and distributions of proeutectoid ferrite precipitates are now known to often be quite different from those deduced by conventional two-dimensional (2-D) microscopy techniques. The present crystallographic studies indicate that “primary” ferrite (nucleated directly on prior austenite grain boundaries) forms monolithic single crystals and can be approximated as elongated triangular pyramids. “Secondary” ferrite morphologies can be described as laths and plates branching into the austenite from a thick and/or broad allotriomorphic ferrite base. These secondary Widmanstätten branches are composed of many misoriented crystals with ferrite: ferrite boundaries between them and appear to approach a common orientation as they extend into the austenite grain. Implications of the current findings on existing growth and crystallography models are discussed, and a preliminary hypothesis or mechanism of ferrite formation has been proposed to account for the present observations.     

在飘零中坚守:"孤儿"的寻根与救赎之旅——日据时期台湾知识分子"孤儿意识"新论

以吴浊流<亚细亚的孤儿>为代表的表现"孤儿意识"的小说,揭示了日据时期台湾知识分子在特殊历史情境下的尴尬处境和生存体验,以胡太明为典型的台湾知识分子的寻根与救赎之旅,正表现了其对于"孤儿意识"的克服,而不是如今天分离主义势力所谓的"台湾人意识",更不能成为"台独"的依据.     

Properties of circulating IgA molecules in Henoch-Sch?nlein purpura nephritis with focus on neutrophil cytoplasmic antigen IgA binding (IgA-ANCA): new insight into a debated issue. Italian Group of Renal Immunopathology Collaborative Study on Henoch-Sch?nlein purpura in adults and in children

BACKGROUND: The presence and the pathogenetic role of circulating IgA reacting with neutrophil cytoplasmic antigens (IgA-ANCA) in patients with Henoch-Sch?nlein purpura (HSP) is still debated. This study was aimed to investigate some characteristics of serum IgA and macromolecular IgA in HSP patients, focusing on IgA-ANCA. METHODS: Eighty-seven HSP patients with biopsy proved renal involvement (51 adults and 36 children) enrolled in a multicentre study of the Italian Group of Immunopathology were investigated. RESULTS: Significantly high levels of IgA immune complexes were found in both adults (P < 0.05) and children (P < 0.01), while the binding of IgA to jacalin, was significantly low in children with HSP (P < 0.01) only. Two series of ELISA were done for IgA-ANCA, in two different laboratories. Increased binding to PMN crude extracts (P < 0.01) without any modification in IgA binding to proteinase 3 was found by either specific ELISA. Conversely, the binding of IgA to myeloperoxidase (MPO) was found to be significantly (P < 0.05) increased with positive values in 25% of patients by one assay only. Three of four sera with positive IgA-MPO ANCA exhibited binding in Western-blot studies with the MPO preparation used in ELISA to a 28-kDa species. D-galactose and N-acetyl-glucosamine decreased the binding of serum IgA to MPO more in HSP than in controls (P < 0.05). CONCLUSIONS: The conflicting reports on IgA-ANCA may reflect some atypical characteristics of the reaction which can be detected only by some ELISAs. We suggest that not an antigen-antibody reaction but a lectinic interaction due to abnormal composition of IgA carbohydrate side chains may account for the IgA-ANCA reaction in patients with HSP nephritis.