Heat treatment of rails

Abstract

Heat treatment is increasingly used in the heavy industry. The main advantage of this method is the achievement of the required material and mechanical properties. Heat treatment allows for a manufacturing process, which can improve product performance by increasing the steel strength, hardness and other desirable characteristics. The microstructure, grain size and chemical composition of steel affect its overall mechanical behavior. Heat treatment is an efficient way to manipulate the properties of a steel product by controlling the cooling rate. It can be expressed using the heat-transfer coefficient (HTC). The controllability of the cooling process is very important. Mist and water nozzles may provide good controllability of the HTC. An experimental stand was designed and built. The stand consists of a movable trolley with a test sample, which moves under a spray at a given velocity. Sensors record the temperature history of the tested material. This experimental stand enables simulations of a variety of cooling regimes and evaluations of the final structures of tested samples. The same experimental stand is also used for designing cooling sections in order to determine the required heat-treatment procedures and the final structures. This paper describes a cooling-section design procedure for obtaining the required structure and mechanical properties of rails. Keywords: heat transfer, heat treatment, cooling, heat-transfer coefficient, spray cooling Uporaba toplotne obdelave se v te`ki industriji pove~uje. Glavna prednost te metode je, da se dose`e zahtevane mehanske lastnosti materiala. Toplotna obdelava omogo~a postopke izdelave, ki lahko izbolj{ajo lastnosti proizvodov s tem, da pove~ajo trdnost jekla, trdoto in druge za`eljene zna~ilnosti. Mikrostruktura, velikost zrn in kemijska sestava jekla vplivajo na mehanske lastnosti. Toplotna obdelava je u~inkovita pot za vplivanje na lastnosti jeklenega proizvoda s kontroliranjem hitrosti ohlajanja. Lahko se jo izrazi z uporabo koeficienta prenosa toplote. Mo`nost kontrole postopka ohlajanja je zelo pomembna. Obvladanje procesa ohlajanja je zelo pomembno. Vodna para in vodne {obe omogo~ajo dobro kontrolo koeficienta prenosa toplote (angl. HTC). Na~rtovano in postavljeno je bilo eksperimentalno stojalo. Stojalo sestoji iz vozi~ka z vzorcem, ki se pomika pod {obe z dano hitrostjo. Senzorji bele`ijo temperaturno zgodovino vzorca. Eksperimentalno stojalo omogo~a simulacijo razli~nih re`imov ohlajanja in oceno kon~ne mikrostrukture preizku{enega vzorca. Isto stojalo je uporabno tudi kot orodje pri na~rtovanju hladilnih odsekov za dolo~anje postopka toplotne obdelave in kon~ne mikrostrukture.^lanek opisuje postopek na~rtovanja odseka za izvajanje hlajenja, za zagotavljanje`eljene mikrostrukture in mehanskih lastnosti`elezni{kih tirnic.

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