Coke properties at high temperature zones in a blast furnace play an important role for blast furnace operation. Therefore, with the advance of manufacturing technology on high strength of coke and its stability in the cold state, the interest for coke quality has been turned to that at high temperatures. This report mainly describes the behavior of coke under high temperature conditions in a lower part of blast furnace. In order to clarify the degradation behavior of coke in the blast furnace, a series of fundamental studies on the degradation of coke due to chemical, mechanical and thermal effects were carried out. At Kashima No. 1 BF the sampling of coke has been done during the scheduled time of shutdown at three levels-lower shaft, bosh, and tuyere. The movement and accumulation of fine coke and the mutual relation between coke properties and the furnace performance were examined. Based on the results of these studies and investigations, the mechanisms of degradation and disintegration of coke were discussed.
The copper partition between Na2S bearing fluxes and carbon-saturated iron melts has been measured by a chemical equilibration technique at 1473K. The results are discussed in terms of the copper capacity CCu which is defined by the following equation. CCu(copper capacity)=(%CuS0.5)/aCu(l)•P1/4S2 Of 5 sulfides of alkali and alkali-earth metals examined, the CCu value has been found to be in the order of Na2S>Li2S>BaS>K2S> CaS, With the NaS0.5-FeS system, the higher (%NaS0.5) leads to the higher CCu. The copper partition ratio LCu(=(%Cu)/[%Cu]) was 17 with [%S]-0.01 for the flux composition of 95%NaS0.5-5%FeS having the maximum CCu. Other thermodynamic properties of the sulfides and Fe-Csat.-Cu-S melts are also studied.
In the present investigation hematite samples were reduced to magnetite by a mixture of H2 and H2O at 650, 700, and 750°C. These data have been analysed with the Johnson-Mehl equation and found to fit well in the nucleation and grain growth model. Activation energy values of the reaction were calculated by different methods and have been found to match closely.
Daido Steel Co., Ltd. has developed a new non-electric scrap melting process which uses carbon powder and oxygen. The experimental furnace is called a reactor. It has a melting rate of 0.5t/h. Test melting of direct reduced iron (DRI) was performed in the reactor with emphasis on the expansion o f ferro-material sources. This paper describes the optimum operational conditions of DRI melting in the reactor with regard to thermal efficiency and iron yield. Results of the experiment are as follows: (1) In the case of a DRI mixing ratio up to 30%, the thermal efficiency of melting is comparable to that of scrap melting. (2) The iron oxide contained in DRI is reduced to iron during the melting period. The metal yield from DRI mixing heats is accordingly the same as that of scrap heats.
Surface cracking during direct rolling of continuously cast low alloy steel slabs has been investigated by means of hot tensile tests simulating the process. The hot ductility of directly cooled specimens is not reduced by high strain rate deformation corresponding to that in rolling. While, in the specimens predeformed at temperatures ranging from γ/α duplex phase to low temperature γ region at slow strain rate corresponding to that in bending and/or straightening operations of CC slabs, ductile intergranular fracture of austenite is easily induced by the subsequent deformation even at high strain rate, resulting in poor ductility. This ductility loss can be explained in terms of dynamic precipitation of carbide, nitride, or carbonitride such as AlN and/or NbC (or NbC(N)) within the matrix as well as on the γ grain boundaries during the prior slow strain rate deformation. The ductility is also influenced by the final deformation conditions because of the morphology change of the precipitates in the process, although the embrittlement mechanism is essentially the same as in the CC process.
The recrystallization behavior of low carbon steel in high speed hot rolling has been investigated in relation to the strain distribution through the thickness. Sheet specimens with the size of 2×20×250mm were rolled between 650 and 850°C at the rolling speed of 20m/s without lubrication. The rolled specimen was quenched into water with a holding time ranging from 3 to 250ms. The redundant shear strain caused by friction forms severely sheared region beneath the surface. The width of the severely sheared region decreases and the maximum shear strain increases with lowering rolling temperature. A band o f extremely fine recrystallized grains (d=2-10μm) is formed in the severely sheared region when effective strain exceeds a critical value which is dependent on rolling temperature. Recrystallized grains appear even in the sheet quenched after a short holding time of 3ms. The recrystallized grain size is strongly dependent on Zener-Hollomon parameter Z0 at the midthickness of the sheet, and is independent of effective strain and initial grain size. It can not be made clear from the present experiment whether this recrystallization occurs dynamically or statically. However, the structural features of these recrystallized grains suggest that they are dynamically recrystallized ones.
The effect of inhomogeneous shear strain on the texture variation through the thickness of hot rolled low carbon (0.006% C) Ti bearing steel sheets has been investigated. The change in texture with the progress of recrystallization has been also investigated. The steel sheets were rolled in ferritic state at a rolling speed of 20m/s to the reduction of 40% with and without lubrication, and quenched into water at an interval of 3-250ms after rolling. In unlubricated rolling, shear deformation produces a severely sheared region beneath the surface. In lubricated rolling, shear strain is negligibly small throughout the thickness. <110>||ND axis density increases and <111>||ND and <100>||ND axis density decrease with increasing shear strain in unlubricated sheets. The texture of lubricated sheet, which is identical with that at the midthickness of the unlubricated sheet, is uniform through the thickness. Recrystallization reduces <110>||ND axis density at the severely sheared region and <111>||ND at the midthickness of the unlubricated sheet. <111>||ND axis density of the lubricated sheet also decreases with recrystallization. The texture inhomogeneity through the thickness of the sheet rolled without lubrication is retained after completion of recrystallization.
Phase equilibria in the Fe rich portion of the Fe-C-B ternary system were analyzed on the basis of the solubility data on Fe-B system by Cameron and Morral. The Gibbs energy of solution phases was approximated by the interstitial model, assuming C and B to be interstitial atoms. The influence of ferromagnetism on the Gibbs energy of ferrite was also taken into account. The effect of B addition on the pure austenite field was calculated precisely, and it was confirmed that the equilibrium distribution coefficient of B between liquid and austenite is much smaller than that evaluated previously.
The effect of tellurium on the machinability of AISI 12L14+Te leaded, lowcarbon, resulfurized free-machining steel was investigated as a joint project between Inland Steel Company in the U.S.A. and Nippon Steel Corporation in Japan using two types of plunge machinability tests. The Te addition globularizes MnS inclusions and improves machinability assessed in terms of cutting force and chip breaking characteristics. However, no clear trend on the effect on surface finish was observed. More than 20% of total Te content exists in MnS inclusions as solid solution, and the rest of Te exists as compounds such as PbTe. Unlike previous observation, a phase believed to be MnTe was detected at the interface between the matrix and MnS inclusions in addition to PbTe. Enhancement of the ability of MnS inclusions to improve machinability by globularization is believed to be one of the mechanisms by which Te improves machinability, although this may not be the major mechanism in AISI 1200 series free-machining steels. Liquid metal embrittlement of PbTe or MnTe-MnS eutectic has been ruled out from the possible mechanisms when high-speed-steel tools are used because the melting points of these compounds are higher than the cutting temperature.
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