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Vpliv toplotne obdelave jekla PK346 na prehodno temperaturo žilavosti
Šavc, Peter (Author), Nagode, Aleš (Mentor) More about this mentor... This link opens in a new window

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Abstract
Namen diplomske naloge je bil raziskati vpliv toplotne obdelave na prehodno temperaturo žilavosti nerjavnega martenzitnega izločevalnoutrjevalnega jekla PK346. Jeklo smo raztopno žarili, kalili in starali pri različnih temperaturah in časih ter merili udarno žilavost po Charpyju. Po standardu ASTM smo vizualno ocenili prelomno površino, to je delež krhkega in duktilnega preloma. Natančnejša fraktografska analiza je bila izvedena na vrstičnem elektronskem mikroskopu (SEM). S pomočjo dilatometra smo določili premenske točke AC1, AC3, Ms in Mf ter zaznali ogrobljanje bakrovih izločkov, ki vplivajo na stabilnost avstenita. Tega smo merili z rentgensko strukturno difrakcijo (XRD) pred in po staranju. Na vzorcih smo opravili tudi metalografske preiskave na svetlobnem mikroskopu in izmerili trdote po Brinellu. Ugotovili smo, da vsebnost avstenita zniža prehodno temperaturo žilavosti in trdoto jekla. Določili smo tudi najbolj optimalno toplotno obdelavo za jeklo PK346 za doseganje najnižje prehodne temperature žilavosti (–153 °C) pri udarni žilavosti (75 J). Ta sestoji iz raztopnega žarjenja pri temperaturi 1040 °C, kaljenja na zraku in dvakratnega staranja, in sicer na 760 °C/2 h ter 621 °C/4 h.

Language:Slovenian
Keywords:jeklo PK346, staranje, prehodna temperatura žilavosti, zaostali avstenit, povratni avstenit
Work type:Bachelor thesis/paper (mb11)
Organization:NTF - Faculty of Natural Sciences and Engineering
Year:2017
COBISS.SI-ID:1700447 This link opens in a new window
Views:1232
Downloads:740
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Secondary language

Language:English
Title:The effect of heat treatment on toughness transition temperature of PK346 steel
Abstract:
The purpose of the graduation thesis was to research the effect of heat treatment on toughness transition temperature of martensitic precipitation hardening stainless steel PK346. The steel was homogenized, quenched and aged at different temperatures and time periods, and impact toughness was measured using the Charpy impact test. ASTM standard was used to visually assess the fractured surface, i.e. the share of brittle and ductile fracturing. A more precise fractographic analysis was carried out with a scanning electron microscope (SEM). A dilatometer was used to determine the transformation points: AC1, AC3, Ms and Mf, and to detect the coarsening of copper precipitates, which affect the stability of austenite. The austenite was measured with the X-ray diffraction analysis (XRD) before and after the aging process. Metallographic analysis on the samples was performed using a light microscope and we also measured the hardness using the Brinell test. It was established that the content of the austenite lowers the toughness transition temperature and the hardness of steel. We also determined the optimum heat treatment for the PK346 steel to achieve the lowest toughness transition temperature (-153 °C) with impact toughness of 75 J. It consists of homogenizing at 1040 °C, air quenching and double aging at 760 °C/2 h and 621 °C/4 h.

Keywords:PK346 steel, aging, toughness transition temperature, retained austenite, reverted austenite.

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