Bundles of steel bars, besides metal foams, are an example of cellular solids. Such bundles constitute a charge during the heat treatment of bars. The paper presents a mathematical model of transient heat transfer in a bundle of rectangular steel bars based on the energy balance method. The key element of this model is the procedure of determining the effective thermal conductivity using the electrical analogy. Different mechanisms of heat transfer occurring within the analysed medium (conduction in steel and contact conduction) are assigned corresponding thermal resistances. The discussed procedure involves expressing these resistances with the use of arithmetic relationships describing their changes in the temperature function. Thermal contact resistance has been described with the use of the relationships determined experimentally. As a result of the performed calculations, the influence of contact conduction between the adjacent bars and bundle arrangement on its heating time was established. The results of the calculations show that the heating time of bundles can be lowered by 5–40% as a result of a decrease in the thermal contact resistance. This effect depends on the bar size and bundle arrangement. From the practical point of view, the analysed problem is connected with the optimization of the heat treatment processes of steel bars.

The paper presents experimental studies devoted to the convection phenomenon within the steel charge of mixed porosity. Such charges constitute bundles of hollow long elements such as pipes or rectangular sections which are heat treated. A significant portion of the gas phase in the volume of the charge makes that natural convection of the gas occurring within the individual elements may have an effect on the course of heating. To the tests the Schlieren method was used which is one of the optical visualization methods applied to the analysis of the flow phenomena in the transparent and non luminous media such as air or water. The tested samples have the form of porous charge beds made from pipes and rectangular profiles. During the experiments the samples were heating up for the constant heat flux rate. The direction of flux was vertical, from the bottom to the top.

Ensuring the high quality of products and semi-finished products is a primary goal of most enterprises. The paper presents an analysis of steelmaking process quality. This analysis was carried out based on selected quality assessment measures. Numbers of complaints, of production rejects and of off-heats were considered. The analysis showed that the majority of quality problems the company had in 2010. preventive actions and corrective decreased level of quality problems to about 1% in 2012. Test the company has appointed a quality objectives for 2013. The quality targets imply lower levels of complaints and of off-heats were considered. Level defective production in recent years has significantly narrowed, and is at an acceptable level.

Before steel materials are subjected to an appropriate heat treatment, they must be preheated. During this process scale is formed, which can be a problem in the proper heat treatment of the steel charge. The preheating process of the steel charge is carried out under specific conditions – parameters. These conditions determine certain properties of scale. One of the most important issues in this context, important from the point of view of the potential removal of scale from the charge surface, is the correlation of the heating process temperature and the adherence of the scale to the steel substrate. The paper presents the results of such research and their discussion. In addition, the methodology for measuring the scale adhesion to steel substrate is presented. Mathematical relations endearing impact of heating rate on the scale adhesion have been developed.