Mathematical models are proposed for analizing blast furnace preformance. High pressure operation and oxygen enriched operation are studied with the proposed models. The production rate and the fuel ratio predicted from the models agreed very well with the operation data. Also, possibility of predicting production limit is discussed.
The rate of nitrogen removal from liquid iron containing oxygen has beenstudied by blowing Argas onto the inductively stirred liquid iron at I600°C. At constant oxygen content, the rate of nitrogen removal is proportional tothe second power of the concentration of nitrogen in liquid iron. The rate is retarded markedly with increasing oxygen content. The rate constant κ(cm/wt%. sec) is inversely proportional to the concentration of oxygen contents ([%O]>0.01%), but at lower contents of oxygen the rate constant tends to approach a con-stant value. It is shown that the removal of nitrogen is controlled by the chemical reaction rate. The results are
The oxide inclusions in commercial steels consist mainly of the simple orthe complex oxides formed from the system MnO-SiO2-Al2O3. In the present investigations, the behavior of those oxide inclusions in steels during hot-rolling was observed by the same procedures as used for our previous work: that is, the steel specimens containing uniformly a certain amount of those oxide inclusions were prepared by powder metallurgy technique. These steel specimens were hot-rolled under the following conditions: the rolling temperatures were 1250-1000°C and 1000-800°C, the rolling ratio was 1/5. Then, changes of inclusions in shape, composition and crystallographic structure during hot-rolling were examined. The tensile tests of rolled steel specimens in the rolling direction were carried out to examine the influence of those inclusions on tensile strength of the steels. The main results were as follows: (I) The complex inclusions having nearly the same melting or softening points as the rolling temperature, were deformed plastically and turned into the stringer type. When both the rolling temperature and ratio are maintained to constant, the lower the melting point of inclusion and the better the homogeneity in composition of inclusion are, the larger the degree of deformation of inclusion becomes. (2) The complex inclusions formed from the system MnO-SiO2, having low melting points were softened at 1000°C. (3) When the steel specimens coexisting MnO and SiO2 of simple oxide inclusions were rolled between 1250°C and 1000°C, both inclusions were consolidated, tusned into manganese silicates whose melting points were lower, and deformed plastically. Those manganese silicates were partly crystallized into tephroite (2MnO.SiO2). (4) Those oxide inclusions in steels affected scarecely tensile strength of steels.
High Mn austenitic stainless steel has been developed for high temperature applications especially for boiler tubes. The most suitable chemical composition has been found to be 18%Cr-6%Ni-8%Mn, the structure this steel is almost wholly austenitic and its properties of creep-rupture strength, resistance to oxidation at elevated temperature and hot workability are comparable to those of type 304 steel. Small amounts of Ti and Nb have been added simultaneously to this type of steel (being called 18-6-8Ti Nb steel) to improve the elevated temperature strength. The carbon content being about 0.2%, the optimum amounts of Ti and Nb have been found to be the atomic ratio of (Ti+Nb)/C being in the range of 0.1 to 0.5. The resultant steel has considerably high creep-rupture strength in the temperature 600 to 700°C, and is believed to be very economical steel for high temperature applications. The mechanism of raising the creep-rupture strength due to the additions of Ti and Nb is considered to be to depress the coalescence of M23C6 carbides in the grains and on the grain boundaries and to make the carbides dispersing very finely within the grains during its use at high temperature. This mechanism is seemed to be the same as in the case of 18%Cr-10%Ni austenitic steel.