Žilavost feritnog reaktorskog čelika u području prelazne temperature

Abstract

Tema ove doktorske disertacije je feritni reaktorski čelik 20MnMoNi 55, konkretno njegova žilavost u području prelaznog temperaturnog režima najviše zbog njegove primene u ekstremnim uslovima, odnosno niskim temperaturama. Ispitivanja su urađena na C(T) uzorcima različitih dimenzija i tempraturama -60 i -90℃, sa ciljem dobijanja krivih verovatnoća loma cepanjem ispitivanih manjih C(T) epruveta i predikcije ponašanja većih uzoraka na ispitnim temperaturama statističkim metodama (konkretno, Vejbulovom raspodelom) obrade dobijenih rezultata. Kumulativnim raspodelama verovatnoće loma cepanjem i predikcijama ponašanja većih uzoraka u funkciji parametra mehanike loma Jc direktno je prikazan uticaj veličine uzoraka na integritet konstrukcije izrađene od ovog materijala i njegovu sposobnost ili težnju ka žilavom ili krtom lomu usled prisustva prsline. Pored šire slike ponašanja feritnog reaktorskog čelika 20MnMoNi 55 na ispitnim temperaturama -60℃ i -90℃ preko parametara Jc i drugih analiziranih relavantnih parametara, ovom disertacijom pružen je dodatni uvid uticaja dinamičkog opterećenja pripremljenih uzoraka na dobijene rezultate preko plastične zone oko vrha prsline i analizom rasipanja dobijenih rezultata. Dobijene su i analizirane određene zakonitosti uočenih pojava, poput potencijalne temperaturne zavisnosti Vejbulovih parametara kumulativne raspodele za C(T)50 uzorke na dvema ispitnim temperaturama. Skaliranjem određenih eksperimentalnih rezultata ispitivanja dobijena je empirijska zakonitost u cilju analize uticaja veličine geometrijski sličnih C(T) uzoraka na temperaturi -60℃. Cilj skaliranja je sveobuhvatno predviđanje ponašanja uzoraka većih dimenzija na osnovu ispitivanja manjih.

The topic of this doctoral thesis is ferritic reactor steel 20MnMonNi 55, i.e. its toughness in transition-temperature region, tipically used in application for structures working at low temperature. Tests were performed on the C(T) specimens with different geometry and on -60 and -90℃ in order to get cleavage fracture probabilities curves of small specimens and to predict behavior of the larger ones at specific temperatures. Method used for probability prediction is Weibull statistic method of results processing. The cumulative distributions of cleavage fracture probability, as well as obtained behaviour predictions of the larger specimens in the function of fracture mechanics parameters Jc, show the influence of specimen size effect on the integrity of real structure made of this steel, and its ability and tendency towards ductile or brittle fracture in the presence of the crack. In addition, experimental testing in this thesis provided a broad picture of ferritic reactor steel 20MnMoNi 55 behavior at temperatures -60℃ and -90℃ by analyzing Jc and other relevant parameters. This dissertation provides additional insight into the influence of dynamic loading via specimens pre-cracking and plastic strain around the specimen crack tip by analyzing the obtained scattered results and parameters. Certain relations of observed phenomena were analyzed and discussed, such as the potential temperature dependence of the Weibull parameters of the cumulative distribution for C(T)50 specimes at two temperatures. By scaling of certain experimental results with the aim of determining of size effect of geometrical similar C(T) specimens, the empirical relation for temperature of -60℃ was obtained. The goal of scaling is to comprehensively predict the behavior of larger specimens based on the examination of smaller ones.