Abstract. The concepts new types of materials are, for economic reasons, focused mainly on low alloyed steels with a good combination of strength and ductility. Suitable heat and thermomechanical treatments play an important role for the utilization of these materials. Different alloying strategies are used to influence phase transformations. The quenching and partitioning process (Q-P Process) is one of the heat treatment methods which can result in a high ultimate strength as well as a good ductility. However, these good properties can be obtained only if a sufficient amount of retained austenite is stabilized. The influence of different contents of manganese, silicon and chromium on microstructural development and mechanical properties were experimentally tested. Alloying elements were used to stabilize the retained austenite in the final microstructure and also to strengthen the solid solution. Ultimate strengths of over 2000MPa with ductility over 10% were reached after the optimization of the Q-P Process. The microstructures were analyzed using several microscopic methods; mechanical properties were determined by a tensile test and the volume fraction of the retained austenite was established by X-ray diffraction phase analysis.

Typical processing routes for bearing steels include a soft annealing stage, the purpose of which is to obtain a microstructure containing globular carbides in ferritic matrix. A newly developed process called ASR cuts the carbide spheroidisation times several fold, producing considerably finer globular carbides than conventional soft annealing. The present paper explores the effect of the heating rate and temperature on the accelerated carbide spheroidisation process and on the resulting hardness. Accelerated spheroidisation was achieved by thermal cycling for several minutes around various temperatures close to the transformation temperature at various heating rates applied by induction heating.Keywords: Carbide spheroidisation, bearing steel, annealing, induction heating Proces obróbki stali łożyskowych obejmuje wyżarzanie zmiękczające, którego celem jest uzyskanie mikrostruktury zawierającej kuliste węgliki w osnowie ferrytycznej. Nowo opracowana obróbka zwana ASR polega na wielokrotnym przerywaniu procesu sferoidyzacji, co prowadzi do wytworzenia węglików kulistych o znacznie mniejszych rozmiarach w porównaniu do tych, jakie powstają w konwencjonalnym procesie wyżarzania zmiękczającego. Niniejsza praca analizuje wpływ szybkości grzania i temperatury na proces przyspieszonej sferoidyzacji węglików i na uzyskaną twardość. Przyspieszoną sferoidyzację węglików uzyskano dzięki zastosowaniu cyklicznych zmian temperatury trwających kilka minut wokół określonych temperatur bliskich temperaturze przemiany za pomocą grzania indukcyjnego z różnymi prędkościami.

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Bearings are used mostly in the quenched and tempered state, e.g., steel 100CrMnSi6-4 with a microstructure of low-tempered martensite and carbide particles undissolved during the quenching austenitization. The size and density of the particles depend on the spheroidisation annealing which is the standard operation at the beginning of the bearing manufacturing. The particles decrease the grain growth of the austenite and determine the grain size after the quenching. The process of accelerated carbide spheroidisation and refinement (ASR) was developed and is used as a replacement of the conventional spheroidisation soft annealing. The ASR process produces the structure of a ferritic matrix and fine globular carbides. The carbide size is several times smaller in comparison with the conventional soft annealing. This microstructure is better for quenching and tempering and ensures a better bearing performance. The article compares the structures and properties of the quenched and tempered 100CrMnSi6-4 steel pre-treated with the conventional soft annealing and ASR. The smaller ASR particle size allows the use of lower quenching temperatures, ensuring the desired final hardness. Samples in the hardened state were compared, considering the prior-austenite grain size, the carbide-particle size and distribution as well as the hardness. Keywords: accelerated spheroidisation, carbide-particle morphology, hardening, bearing steel Le`aji se obi~ajno uporabljajo v kaljenem in popu{~enem stanju, na primer jeklo 100CrMnSi6-4 z mikrostrukturo nizko popu{~enega martenzita in s karbidnimi delci, ki se ne raztopijo pri avstenitizaciji pred kaljenjem. Velikost in pogostost delcev je odvisna od sferoidizacijskega`arjenja, ki je standardna operacija na za~etku izdelovanja le`aja. Delci zavirajo rast avstenitnih zrn in dolo~ajo velikost zrn po kaljenju. Razvit je bil postopek pospe{ene sferoidizacije in udrobnjenja karbidov (ASR), ki je bil uporabljen namesto obi~ajnega sferoidizacijskega mehkega`arjenja. Pri ASR procesu nastane feritna osnovna mikrostruktura in drobni globularni karbidi. Velikost karbidov je nekajkrat manj{a v primerjavi z obi~ajnim mehkim`arjenjem. Taka mikrostruktura je bolj{a za kaljenje in popu{~anje in zagotavlja bolj{e lastnosti le`aja. V~lanku so primerjane mikrostrukture in lastnosti kaljenega in popu{~anega jekla 100CrMnSi6-4 predhodno mehko`arjenega in ASR. Manj{a velikost delcev pri ASR omogo~a uporabo ni`je temperature kaljenja za doseganje`eljene trdote. Vzorci v utrjenem stanju so bili primerjani z upo{tevanjem velikosti prvotnih avstenitnih zrn, velikosti in razporeditve karbidnih delcev, kot tudi trdote. Klju~ne besede: pospe{ena sferoidizacija, morfologija karbidnih zrn, kaljivost, jeklo za le`aje

Material research of the spring steels tries to meet requirements of the industry, which are mainly higher yield and tensile strength. Steel 51CrV4 is widely used for spring production. Optimization of its properties lies in tensile and yield strength enhancement without decrease in ductility in quenched and tempered state. This can be accomplished by structural refinement. One possible way to refine final quenched and tempered structure is refinement of the soft annealed structure before quenching. The article is devoted to accelerated carbide spheroidisation and refinement (ASR) and subsequent hardening of the 51CrV4 spring steel. Samples with different carbide size were prepared by conventional soft annealing in atmosphere furnace and ASR process by induction heating. Influence of the structural refinement on the properties of quenched and tempered state was studied.