Practice of the application of lean coal to coal injection in large-scale blast furnaces

This study mainly introduces the technical properties of a kind of lean coal mined from Lu＇ an, a prefecture of Shanxi Province and its application to coal injection in large-scale blast furnaces（BFs） in Baosteel. China is rich in lean coal resources. The technical properties of lean coal, including ash content, sulfur content and caloricity, etc., are similar to those of anthracite coal used in Baosteel, except the fact that the volatile of lean coal is higher. Besides, the explosive property and the coking property of lean coal are suitable for the BF coal injection. In this study, lean coal was tested in the pulverized coal injection （PCI） of a BF. In the test, the blending proportion of lean coal in the coal blend was increased gradually, and the consequential production indexes were traced. All the operational indexes show that the results of the BF coal injection are good, demonstrating that lean coal can be substituted for anthracite coal in the PCI in BFs. With an abundant amount and specific utilization,lean coal is found to be of a high economic value.

Influence of cold forming on the tensile behavior and properties of low-carbon microalloyed steel

The tensile behavior and properties of cold formed low-carbon microalloyed steel with its microstmcture of all ferrite and pearlite （F ＋ P） were investigated. Bending and flattening deformations were carried out in the laboratory on hot-rolled sheets in order to simulate the cold forming process of steel sheets during pipe fabrication and sampling of high frequency straight bead welding pipes. A comparison of the tensile behavior and properties of the material made before and after cold forming indicates that cold deformation alters the tensile behavior and properties of the material to a certain degree depending on the manner of the cold deformation and the degree. The research on the Bauschinger effect indicates that for the steels investigated, when the plastic strain is small, the back stress increases rapidly with the increase of the plastic strain and then rapidly tends to saturation. The finite element analysis indicates that the change in the properties of the steel sheets due to cold forming is a result of the Banschinger effect and work hardening. The mechanism of the change in the properties is also given in this study.

Effects of strain ageing on the microstructures of microalloyed steels

This study investigates the microstructures of microalloyed steels before and after strain ageing treatment. It was found that the microstructure consisted of both lath ferrite and pearlite. Most of the carbides and/or nitrides of microalloying elements were distributed inside the grains with a small amount distributed at the grain boundaries. The precipitated phases inside the grains were much smaller in size than those at the grain boundaries. The precipitates are either circular or short bar-like,of sizes from a few nanometers to several hundred nanometers. After ageing,only carbon atoms segregate around the dislocations and nitrogen does not participate in producing the Cottrell atmosphere because it was fixed by alloying elements before ageing.