INFLUENCE OF THERMAL TREATMENTS ON FRACTURE TOUGHNESS OF SPRING STEEL

Visoko trdnostna jekla se uporabljajo na področjih velikih dinamičnih obremenitev. Zaradi česar se proizvajalci običajno soočajo s težavami, kako zagotoviti trajno dinamično trdnost. Za njeno zagotovitev največkrat posegajo po naknadnih termičnih obdelavah. Namen diplomskega dela je tako narediti primerjalno analizo utrujenostne rasti razpoke v skladu s standardom ASTM E 1820 - 01, za termično mehko in termično obdelano vzmetno jeklo 51CrMOV4. Diplomsko delo temelji na eksperimentalnih meritvah v LSEK laboratoriju na Fakulteti za strojništvo, kjer so se izvajali lomnomehanski preizkusi z metodo mehanike loma, določevale utrujenostne rasti razpoke in materialna parametra Parisovega zakona. Obdelava podatkov je potekala v programu Microsoft Excel 2010, s katerim so tudi bili izrisani diagrami. V diplomskem delu je v splošnem opisana mehanika loma ter področje utrujanja: njeni mehanizmi za nastanek, LCF in HCF utrujanje, določevanje hitrosti rasti razpoke in razni vplivi nastanka. Kratko poglavje v diplomskem delu je namenjeno tudi pripravi upogibnih lomnomehanskih preizkušancev v skladu s standardi.High strength steels are used in fields of large dynamic loads. Leading manufacturers are usually confronted with problems like, how to ensure fatigue limit. To ensure, they mostly reach to subsequent thermal treatment. The purpose of Diploma thesis is, to make a comparative analysis of fatigue crack growth, for thermal soft and thermal treathed 51CrMOV4 spring steel in accordance with ASTM E 1820-01 standard. Diploma work is based on experimental measurements in LSEK laboratory at the Faculty of Engineering, where tests are conducted on fracture toughness with prescriptive method of fracture mechanics, determined fatigue crack growth and material parameters for Paris’ law. Processing of the data was held in Microsoft Excel 2010, with which diagrams also were drawn. The Diploma thesis described in the general field of fracture mechanics and fatigue: the mechanism for the formation, LCF and HCF fatigue, crack growth rate determination and the creation fatigue failure by various effects. A short chapter in the thesis is also intended to prepare the bending fracture toughness specimen in accordance with the standards