Applied Mechanics and Materials Vols. 395-396

Abstract: A new technology to obtain a fine-structured and high-toughness HAZ of HSLA steel for high heat input welding is developed using metallurgical thermodynamics, physical chemistry of metallurgy and material processing methods synthetically in this study. A kind of HSLA steel is designed in this experiment. The thermal stability second phase particles which would not be dissolved or aggregated at high temperature will be expected by means of adding magnesium into the steel in the form of Mg-Zr alloy. The effect of magnesium addition on the cast microstructure of HSLA steel was analysed. The results show that The cast microstructure is mainly consist of lamellar and acicular ferrite, a small amount of pearlite and bainite. Compared with the original steel, there are acicular ferrites presenting in the experimental steel after adding 3 wt% Mg and 5 wt% Mg, which are the microstructure that we hope to get. The acicular ferrite will have a positive impact on the mechanical properties of the subsequent rolled steel.

Abstract: An Fe-3wt% Si as-cast strip was produced by twin-roll strip casting process. The as-cast strip was hot rolled at 1150°C by one pass of 20% reduction and coiled at 550°C. The tensile test was carried out and the elongation was measured. The microstructure and texture of the coiled strip and the fracture surface morphology of the tensile samples were characterized. It is found that the microstructure of the as-cast strip was characterized by columnar ferrite grains with pronounced {001}<0vw> fiber texture and martensite. The microstructure of coiled strip consisted of ferrite grains and pearlite, and the texture was mainly characterized by {001}<0vw> fiber texture. The necking was absent during the tensile test and the elongation of coiled strip was as low as 12%. The fracture surfaces of the tensile samples mainly exhibited cleavage fracture mode with coarse cleavage facets and some ligaments.

Abstract: The pile up of Magnesite Tailings cause serious environment pollution and mineral resources waste. When making the low-carbon steel or the ultra low-carbon steel in middle or small size converters, the slag superheat is always higher due to the higher tapping temperature. In order to reduce the tapping temperature, after blowing is also needed, which wil cause the contents of FeO in final slag get increased, the slag with lower viscosity, and the contens of MgO in final slag cant get saturated. So Slag Splashing should not proceed immediately that we must slag Modifiers. The modifier was synthesized by calcined magnesite and anthracite powder,modifier takes the treatment of slag. The experimental result show that the slag has a higher melting point and a suitable viscosity to achieve the requirements of slag splashing.

Abstract: This research was conducted on the influence of heat treatment parameters on the mechanical properties and abrasive wear resistance of 70Mn steel through experimental results. Orthogonal experiment was applied for designing heat treatment process and acquired optimal heat treatment parameters. The experimental results showed that the optimum heat treatment process was firstly heated to 830°C preserved for 60min, and rapidly quenched, then tempered at 200°C for 80min. Abrasive impact wear experiment was performed on MLD-10 tester, under which the wear surface and the subsurface were observed through scanning electron microscope and optical microscope. According to the experimental result, abrasive impact wear mechanism was analyzed. The results showed that plastic deformation fatigue and gouging wear were the primary mechanisms of abrasive impact wear, together with a small amount of furrow and cutting.

Abstract: The microstructure and mechanical properties of the continuous annealing DP590 steel produced by a cold rolled plant were studied by utilizing a Gleeble thermal simulator tested machine. The results show that, increasing annealing temperature can not effectively improve the martensite content in the steel and annealing temperature be set at 780 °C and 800 °C is rational. Martensite decomposition at high overaging temperature will decrease tensile strength of the samples. As the overaging temperature sets at 250 °C ~ 300 °C, the samples could achieve tensile strength more than 600 MPa, which meet the requirements of DP590.

Abstract: The electromagnetic stirring technique was used in the experiment to prepare the ingot casting. After comparing the conventional production by the means of ingot casting through electromagnetic field production, the results showed that the solidification of crystal was significantly influenced by the electromagnetic power. As the powers of the agitator increasesed from 0 KW to 20 KW, the refined grain size could be easily detected. That means, the length of the columnar crystal had shortened and isometric crystal had increased dramatically. From the phase transformation we can see that the pearlite and ferrite were distributed much more uniform than the original specimens. The results of the test showed that strengthening electromagnetic field is one of the most important methods to modify the internal crystal morphology. In conclusion, the electromagnetic stirring played a key role in ingot casting.

Abstract: The precipitation in continuously casting slabs of a Ti-Nb microalloyed steel was studied. The samples were taken from different places along cross section of slabs and the precipitations were observed by TEM. The results show that the centre area of slab contains more precipitates of Ti-Nb and carbonitrides more uniformly distribute in the centre along thickness direction. Moreover, the precipitates in the middle are more than those in the edge along width direction of slab. Some large carbonitrides exist in the middle of slab because the temperature in the middle is higher during slab cooling resulting in the large precipitates. The study provides the basis for understanding the precipitation in slabs of Ti-Nb microalloyed steels.

Abstract: In this paper, A test furnace design for use in oxygen-enriched combustion to investigate the oxide scale of steel slab. The heating time, oxygen content and temperature were investigated, and the structure of oxides formed on the slab was characterized. The results show that magnetite film formed on the slab increases in thickness with oxygen enrichment which restricts the diffusion of oxygen and make oxide scale decreased, the oxidation loss of billet has reduced by approximately 37% and the fuel has a 26% fuel savings because of the heating time is decreased

Abstract: On the basis of the thermal balance, the exergy balance of No.1 sinter machine at Baosteel was analyzed. The exergy efficiency is lower than the thermal efficiency. The main exergy loss are focused on physical water evaporation exergy of sintering mixture, chemical incomplete combustion exergy, irreversible exergy loss of ignition process, irreversible exergy loss of sintering process. The measures of saving exergy of sinter machine are proposed. The exergy efficiency can be increased by increasing the sintering material layer thickness and the temperature of the mixture, reducing the moisture of mixture, choosing the reasonable fuel particle size and particle size distribution, controlling minimum air-fuel ratio, improving material layer permeability and using hot air sintering.

Abstract: Using electron microscopy were investigated character of change microdiffraction pattern of fragmented substructure, the relationship between average size micrograins, which forming the diffraction pattern, and the point reflections number on the ring. Also the integrated degree of plastic deformation was assessed in the roll surface layers, made of steel 30CrMnSi during hot deformation. It was shown that the fragments generated during steel deformation considerably disoriented with respect to each other. Formed by heat treatment steel fragments practically is not disoriented. Found that average size of fragments to be achieved in layer at distance of 2 mm from roll surface, for anisotropic fragments amounts to 0.27×0.66 μm, for isotropic - 0.43 μm, average size of fragments - 0.44 μm. Here plastic deformation degree ε0.70. Found that in layer located at distance of 0.5 mm from roll surface, anisotropic fragments have size 0.25×0.56 μm value, for isotropic - 0.39 μm, average fragment size - 0.40 μm. Here plastic deformation degree achieved value ε0.75. It is shown that on roll surface are present only isotropic fragments with average size 0.22 μm. Corresponds to it plastic deformation degree ε0.85.