Advanced Materials Research Vols. 535-537

Abstract: The paper has mainly reviewed the production process of as-cast high toughness ductile iron, analysing the effects of chemical composition, desulphurization process, nodulizing process and the craft of inoculation on the production of as-cast high toughness ductile iron.

Abstract: The influence of Sn on mechanical properties and CO2 corrosion resistance of oil tube was investigated by TEM, EBSD and electrochemical measurement. The results show that the addition of 0.05%Sn can improve the corrosion-resistance of tested steel, but decrease the elongation and impact energy. Sn affected the activity of tested steels, moved corrosion potential to negative potential and decreased corrosion current density. Consequently, the polarization resistance of electrode reaction increased and corrosion reaction was slowed down due to the effect of Sn. In addition, Sn increased the proportion of low boundary, which improved the corrosion resistance of steel, and accordingly decreased the proportion of large angle grain boundary, which contaminated the elongation and impact energy of steel. However, Sn had little influence on the microstructure, precipitates of steel. And thus the strength of steel did not change obviously.

Abstract: Using thermo-mechanical controlled process, the experiment on the yield-strength ratio of low-carbon alloy steel was carried out and the effect of ferrite grain size on the yield-strength ratio of steel was discussed. Theory analysis and the experimental results indicate that the smaller ferrite grain size is, the higher the yield-strength ratio is. In addition, the regression formulas on yield and tensile strength are also obtained.

Abstract: Nb-free and Nb-bearing medium carbon steels treated by quenching-partitioning-tempering process were investigated. The microstructural observations and hardness were analyzed by optical microscope, transmission electron microscope, X-ray diffraction and hardness test. Results show that when quenched at 210oC and partitioned at 450oC ultra fine-grained microstructures of martensite, retained austenite and carbides are obtained. The Nb-bearing steel has finer martensite lath, more volume fraction of retained austenite and higher hardness compared with that of Nb-free steel. The addition of Nb is responsible for not only the precipitation strengthening but also the more volume fraction of retained austenite during quenching-partitioning-tempering process.

Abstract: This paper deals with the numerical simulation of the new technology of gaseous fuel utilization on the sintering process of iron ore. The proposed methodology is to partially replace the solid fuel(coke breeze) by steelworks gases. A multiphase mathematical model based on transport equations of momentum, energy and chemical species coupled with chemical reaction rates and phase transformations is proposed to analyze the inner process parameters. A base case representing the actual industrial operation of a large sintering machine is used with thermocouples inserted into the sintering bed to record the inner bed temperatures and compare with model predictions in order to obtain model validation and parameters adjustment. Good agreement of the temperature pattern was obtained for the base case and thus, the model was used to predict four cases of fuel gas utilization: a) 2% of the wind boxes inflow from N01-N15 wind boxes of natural gas(NG), b) same condition with coke oven gas(COG), c) same condition with blast furnace gas(BFG) and d) mixture of 50% COG and 50% BFG. The model predictions indicated that for all cases, except only BFG, the sintering zone is enlarged and the solid fuel consumption is decreased about 8kg/t of sinter product. In order to maximize the steelworks gas utilization it is recommended the use of mixture of COG and BFG with optimum inner temperature distribution

Abstract: A failure investigation has been conducted on high carbon microalloyed steel used in engine fracture splitting con-rods. The fracture occurred when the as-rolled bars are cut down. The study involved the in-depth examination of the chemical composition, microstructures, mechanical properties and fracture morphologies of specimens from failed bars. Results indicated that the chemical composition of the as-rolled material, microstructure, and mechanical properties are within the range of the technical specification. Microstructure is ferrite-pearlite with dominance of pearlite due to the relatively high carbon content. SEM of fracture surfaces of failed as-rolled bars illustrates that the fractography is cleavage steps and river line pattern. It indicates that failure mode is brittle and the mechanism of fracture is cleavage. Microfracturography shows sulphur inclusions and oxides are the fracture initiation. The continuous network proeutectoid ferrite at the edge of fracture bar will prodigiously improve the brittleness and quickly bring stress concentration under dynamic loading conditions. Furthermore, coarseness and narrowband shape ferrite will induce to decrease toughness.

Abstract: For the characteristics of the hammer handle is under bending stress and impact constantly alternating and the the main of the hammer is Withstand strong impact and friction in use，the paper designed a new type of composite casting process of hammerhead. It has two wear block imbedding in the below of the hammer ，and it set in on both sides of the axis of the hummer wiche with Inverted trapezoidal dovetail structure. The wear block was cast by high chromium cast iron, and it is properly heat treatment and surface cleaning before casting, but Into the mold after re-heated to temperature above 600 °C，At the same time，poured into the cast high-manganese steel quickly，so the block and hammer handle fused together，the block of composite hammer does not wear off in the use, and the wear resistance of the hummer improved significantly.

Abstract: In this paper, the effect of N addition on mechanical properties of 21Cr-11Ni austenitic heat-resisting stainless steel was investigated. Scanning electron microscopy was used to study the fracture surfaces in the steels. N in 21Cr–11Ni heat-resisting steel can play a role of stabling austenite and ensuring the structure and mechanical properties in high temperatures. Fracture is changed from cleavage to ductile fracture to 21Cr–11Ni heat-resisting steel, and the strength of test steel are improved at room temperature by adding N, the tensile strength is increased by 8.33%. And the creep rupture strength is improved. The fracture time of the steel containing 0.2% N is 3.2 times higher than the steel containing 0.14% N at 1144K.

Abstract: Semi-self-fluxing iron powder is identified by self-fluxing nature or alkalinity ,they contain part of CaO and MgO. To make full use of resource and improve pellets quality,do a series of tests. The results show that semi-self-fluxing iron powder can improve pellets metallurgical properties. Put forward the appropriate mixing proportion and roasting temperature.

Abstract: The samples of 9Ni steel were treated by Quenching + Tempering (QT) and Quenching + larmellarizing + Tempering (QLT). The morphology, thermal stability and mechanical stability of the reversed austenite in 9Ni steel were studied by TEM, XRD, EBSD, subzero treatment, three-point bending, uniaxial tension and uniaxial compression. It turns out that blocky reversed austenite occurs in QT-treated steel, while blocky and filmy reversed austenite occurs in QLT-treated steel, additionally, the filmy reversed austenite distributes in the lath boundaries. Subzero treatment shows that certain amount of reversed austenite in QLT-treated samples transforms after dipping into liquefied nitrogen, but it retains a higher level of more stable austenite in QLT-treated sample than that in QT-treated sample. Both tension and compression facilitate the transformation of reversed austenite into martensite, and the retained austenite mainly locates within grains.