Advanced Materials Research Vols. 284-286

Abstract: The microstructure and properties of austempered ductile iron with carbides was studied to increase the abrasive resistance of ADI. It was proven that the austempering temperature influences greatly the microstructure, impact toughness, hardness and abrasion resistance of CADI. With increase of austempering temperature, the acicular ferrite becomes thicker and bigger, the impact toughness rises, and the hardness decreases. But there is a complicated effect of austempering temperature on wet abrasion resistance. In addition, the CADI grinding balls were cast and the field testing was performed. The CADI ball is one third of abrasion loss of low chromium cast iron, zero rate of breakage and no loosing round.

Abstract: According to the structure of purging plugs, the limit gas flow is obtained through theoretical calculation or practical test, that the minimum gas flow is 45Nm³/h and the maximum gas flow is 200Nm³/h.Different bottom blowing patterns suitable for smelting system were established based on different gas supply conditions about two and four purging plugs, at the same time, the maintenance technology of purging plug is developed under the condition of semi-steel steelmaking, these technologies are technology that is effective to improve the service life of purging plugs. A good result has been obtained after the combined blowing technology was put into production. The life of combined blown converters were greatly improved, the average life of combined blown is over 7000 heats, the life of combined blown can be the same with that of converter, the TFe in the slag is lowered by 3.25%, the [O] in steel is decreased by103PPm, the measured [C]·[O] at the end point of smelting is as high as 0.0026, the yield of alloy is increased significantly.

Abstract: The micro-mechanical behavior of inclusions in X80 pipeline steel under fatigue loading was investigated by means of SEM in situ observation. The influence of sizes and shapes of inclusion on crack initiation and propagation was analyzed. The result shows that for large-size single-particle inclusion, cracks initiate from the interior under the fatigue loading. When a certain circulation cycles are reached, cracks initiate at the matrix near the sharp corner of the inclusion. The cracks extend at the matrix during the stable extension period and unstable extension period following the crack initiation, until fracture occurred. For chain inclusion, cracks first initiate at the interface between inclusion and matrix within the chain area, and the circulation cycles needed for initiation are far less than single inclusion. Cracks steadily extend after the initiation, and then fracture after very short circulation cycles. A chain of inclusion with the shape corners is serious harmful to the fatigue properties.

Abstract: The effect of reduction on the microstructure refinement and mechanical properties of the as-hot rolled dual-phase Nb-bearing steel were studied at laboratory. It is found that the dual-phase steel displays clearly classic dual phase morphology which is ferrite and martensite or bainsite, and the fine island or lath martinsite is dispersed on the matrix of ferrite by the observation of microstructure. The grain can be refined, and the increased precipitated second particles are fined and dispersed with the increasing of reduction. The mechanical properties determination result shows that the mechanical properties have greatly improved by large reduction. The tensile strength obtained in the laboratory is up to 680MPa, the ratio of yield strength and tensile strength is low, and the elongation is better.

Abstract: This paper presents the determining method of impact toughness of drill pipe steel used in critical sour environment. Leak-Before-Break fracture principle was adopted to deduce the requirement of drill pipe with different strength grades for impact toughness, which considered both factors, such as geometry size and curvature effect. The loss law of impact toughness was also experimentally measured which could act as a good supplement for Leak-Before-Break fracture principle. Statistical data revealed that this requirement of drill pipe steel for impact toughness could be fully realized through current industrial ability.

Abstract: Influence of TiN(0.5%~2.5%) and TiO₂(1%~5%) on melting and crystalline temperature have been studied and analyzed in ferritic stainless steel containing titanium mold powder. The results show that with the increasing TiN content from 0.5% to 2.5%, the melting and crystallization temperature of mold power change between 1053~1082°C and 951~981°C respectively. With TiO₂ content from 1% to 2%, the melting temperature is lower from 1066°C to 1047°C. As the content of TiO₂ increasing to 5%, melting temperature increases obviously to 1077°C. TiO₂ has less effect on the crystallization temperature of mold power.

Abstract: Q235D is one kind of peritectic steel, so the casting production inevitably encounter the universality defects of peritectic steel casting. The bloom(250mm×280mm) of Q235D is produced by 60t consteel EBT—LF(VD)—CC process at Xining Special Steel. The main problem in the production is the transverse corner crack, finally lead to occur the cracks and “triangular gaps” at surface of round bar（Φ130mm）after rolled. In order to eliminate the defects caused by transverse corner crack of bloom, the morphology and microstructure and principle of crack formation is researched. The results showed that the crack is caused by stress along the intergranular, and no obvious segregation and particles founded around the defects. The following parameters on the continuous casting process are optimized: steel composition, superheat, the choice of a various slag, the cooling water of different section, casting speed and the electromagnetic stirring parameters. Finally the cracking defects of the bloom is eliminated, and the quality of the bar is optimized.

Abstract: Cast steel joints have been widely utilized in large-span spatial structures. Based on Ordos airport terminals engineering, the structure and design method of ribbed steel ball nodes is put forward in this essay, in which nonlinear finite element method is applied, bearing capacity and deformation capacity of ribbed steel ball nodes in the complex stress state is made a penetrating analysis to determine mechanical performance of the ribbed steel ball. Among other things, the manufacturing process and technical standards of cast steel ball nodes are elaborated.

Abstract: Effect of Ce on the strength and ductility of 1Cr18Mn8Ni5N stainless steel has been studied. The results show that the strength and ductility of 1Cr18Mn8Ni5N stainless steel are markedly improved when appropriate content of Ce is added in the steel. The 1Cr18Mn8Ni5N stainless steel with 0.016 wt.% Ce presents the best-optimized mechanical properties.

Abstract: According to the analysis of iron element purification in the current process of steel production and the study on reduction experiment of ultrafine iron ore powder, this study first summarizes and puts forward the scale effect on reduction of iron oxide. And on this basis, a new concept is proposed, named precise reduction, which includes the pre-processing—dissociation of iron oxide, preparation of ultrafine powder and the post processing—non-molten magnetic separation. Taking high phosphorus hematite, steelmaking slag and metallurgical dust as the study objects, and the better achievement shows that the low grade iron-bearing material, after precise reduction, can be transformed to the valuable resource without residue, and the process is environment friendly with low energy and material consumption, so that the zero discharge can be achieved. Not only does the steel plant be changed to be environment friendly, but also the resource is got.