In the state of the art of steel production, the temperature evolution of steel strips is typically controlled to regulate the phase contents indirectly and, with this, their material properties. ...This paper proposes a novel computationally efficient, real-time capable dynamic model that captures both the temperature evolution and the phase transformations in the steel strip. The steel strip is processed in a cooling section after a continuous annealing furnace. The phase transformations cover the austenite decomposition which is mainly controlled by specifically decreasing the temperature during the cooling process. For this, a phenomenological state-space model is derived, which is inspired by the Johnson-Mehl-Avrami-Kolmogorov and the Koistinen-Marburger model. Phase transformations generally change the specific latent heat of the material, which is captured in the proposed distributed-parameter model of the strip temperature by an energy balance. Lumped-parameter models are used for the temperature evolution of the wall, the rolls, and the radiant tubes. Heat transfer due to convection, radiation, and conduction couple the individual thermal submodels. A comparison of simulation results and measurements from both experimental material tests and the real plant operation demonstrate the accuracy and feasibility of the proposed model. The model is computationally inexpensive and serves as a solid basis for advanced real-time control and optimization.
•A mathematical model is proposed to describe the evolution of temperature and phases in a steel strip during cooling.•The austenite decomposition is captured by a phenomenological phase transformation model.•The model is computationally efficient and real-time capable.•The accuracy and the suitability of the proposed model is demonstrated by comparing simulation results with measurements.
In order to enhance the performance of a class of lab-scale annealing testbeds for the steel industries, this paper addresses the temperature tracking task of sheet metal specimen by invoking ...nonlinear model-based control theory. Based on an accurate mathematical model of the testbed, which uses Ohmic heating via a phase-controlled power converter, a flatness-based control approach is presented. By virtue of the parametrization of the control law in terms of physical parameters, this approach is found to significantly simplify the operation of the annealing testbed for the wide range of samples to be used, by simultaneously offering very high tracking performance for the entire domain of operation.
Molybdenum, chromium and manganese offer considerable potential as alloy elements in sintered steels, especially for PM precision parts used, for example, in automotive engines and transmissions. ...This holds in particular for recycling and health/safety aspects. Within this work, the influence of these elements as admixed alloy metals on the sintering behaviour and the properties of structural PM steels is discussed. The considerable differences in the homogenisation behaviour during sintering are described as well as the respective advantages and drawbacks. It is shown that for high density PM steels, Cr and Mo are better suited while for conventionally produced mass products Mn is attractive, its affinity to oxygen being less of a problem today than commonly assumed and since Mn addition promotes swelling, this element might be a replacement for Cu. For Mn, admixing is the more attractive route, for Cr, in contrast, prealloying offers advantages, while for Mo both alloying techniques are feasible.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Sinter brazing of ferrous PM parts involves the risk of infiltration of the porous components by the liquid filler at the expense of joint filling. This normally requires the use of expensive filler ...materials, typically complex alloyed materials e.g. based on Cu-Ni-Mn that solidify in contact with steel, thus blocking the open pores. However, these filler materials also adversely affect he corrosion and heat treating behaviour of the joint, resulting in local hardening and potentially in corrosive attack. In the present work it is shown that simple Fe-C based low-viscosity fillers can be used for sinter brazing in combination with suitable temperature-time profiles for sintering. Thus both by capillary and sandwich brazing solid joints can be obtained that do not markedly differ from the base material in composition and microstructure, except that they are fully dense, which results in even higher strength at the joint than in the base material. This means that in fact a "disappearing joint" can be attained, as typical for diffusion brazing techniques.
Sinter brazing of ferrous PM parts requires the use of special reactive filler materials to avoid infiltration of the porous components by the liquid filler at the expense of joint filling. Complex ...alloyed materials e.g. based on Cu-Ni-Mn are currently used that solidify in contact with steel, thus choking the open pores, but these filler materials also affect especially the corrosion and heat treating behaviour of the joint, resulting in local hardening and corrosive attack. In the present work it is shown that by using using an Fe-C based low-viscosity filler in combination with suitable temperature-time profiles for sintering, brazing joints can be generated, both by capillary and sandwich brazing, that do not markedly differ from the base material in composition and microstructure, except that they are fully dense, which results in even higher strength at the joint than in the base material. This means that in fact a "disappearing joint" can be attained. PUBLICATION ABSTRACT
