Fatigue strength and fracture toughness of tempering steels

Dinamična trdnost je ena izmed najpomembnejših lastnosti, ki vpliva na življenjsko dobo strojnega delagredi hidravličnega prijemala. Predstavljena je osnovna zgradba prijemal in prikaz obravnavanega strojnega dela. V nadaljevanju so predstavljena jekla za poboljšanje, njihova kemijska sestava ter vpliv legirnih elementov na toplotno obdelavo. Predstavljen je potek toplotne obdelave tovrstnih jekel. Za tem sta predstavljena analiza trenutnega materiala ter proces izbire novega materiala za dinamično obremenjen strojni del. Pri znanih trenutnih obremenitvah je glede na izbrane parametre izbran primeren kandidat za primerjavo s trenutnim. V nadaljevanju so bili pripravljeni vzorci obeh materialov za mehanske preizkuse. Nato so bili opravljeni mehanski preizkusi dinamične trdnosti, trdote, udarne in lomne žilavosti ter analiza prelomnih površin. Na podlagi rezultatov smo oblikovali ugotovitve, kateri material naj bi bil primernejši za trenutno aplikacijo. Ugotovili smo, da ima novi material boljše vse merjene mehanske lastnosti in je primeren za testno vgradnjo. Preverili smo tudi ekonomski vidik zamenjave materiala, ki je sorazmeren z izboljšanjem mehanskih lastnosti.Fatigue strength is one of the most important properties that affect on the life of machine part. In the first part is presented the basic construction of hydraulic grapple, following is represented considered machine partshaft of hydraulic grapple. Work has focus on heat-treatment steels, their chemical composition and the influence of alloying elements on heat treatment. In work is represented process of heat treatment of low carbon steel. Afterwards is an analysis of the current material and the process of selecting a new material for a dynamically loaded machine part. For known current loads and aplication, a suitable candidate is selected for comparison with the current one. Test samples of both materials were prepared for mechanical tests. Mechanical tests of fatigue strength, hardness, impact and fracture toughness, and fracture surface analysis were then corrected. Based on the results, we make conclusions on which material is more suitable for current application. We have concluded that the new material has better all measured mechanical properties and is suitable for test installation. We also checked the economic aspect of replacing the material, which is proportional to the improvement in mechanical properties