diplomsko delo
Žiga Tome (Author), Aleš Nagode (Mentor)

Abstract

Izločevalno utrjevalna jekla so se razvila v 50. letih 20. stoletja zaradi potrebe po jeklu, ki združuje kombinacijo dobrih mehanskih lastnosti in korozijske odpornosti pri povišanih temperaturah. Toplotna obdelava izločevalno utrjevalnih jekel poteka v dveh korakih. Prvi korak je raztopno žarjenje, kjer jeklo segrejemo na temperaturno območje avstenita z namenom, da dosežemo homogeno trdno raztopino γ. Drugi korak je umetno staranje pri katerem pride do nastanka drobnih izločkov, ki povzročajo povečanje trdnostnih lastnosti. Namen diplomske naloge je bil raziskati vpliv pogojev izločevalnega utrjevanja nerjavnega jekla 17-4 PH na mikrostrukturne spremembe in trdoto. Meritve trdote smo izvedli po metodi Rockwell, mikrostrukturo jekla pa smo opazovali s pomočjo svetlobnega in vrstičnega elektronskega mikroskopa. Jeklo, ki je bilo raztopno žarjeno na temperaturi 1080 °C je imelo nekoliko višjo trdoto (35,6 HRC) po kaljenju kot jeklo, ki je bilo raztopno žarjeno na temperaturi 1000 °C (34,9 HRC). Pri štiri urnem staranju je bila najvišja trdota dosežena pri temperaturi 400 °C. Pri staranju na temperaturi 480 °C je bila največja trdota (46,6 HRC) dosežena pri jeklu, ki je bil raztopno žarjen na temperaturi 1080 °C in staran eno uro. Pri staranju na temperaturi 700 °C in dvostopenjskem staranju se trdota jekla ni bistveno spremenila glede na trdoto jekla v kaljenem stanju. Mikrostruktura jekla v kaljenem stanju je iz letvastega martenzita, jekla staranega na temperaturi 480 °C iz popuščenega martenzita in bakrovih izločkov, jekla staranega na temperaturi 700 °C pa iz martenzita in ferita. V vseh primerih smo v mikrostrukturi opazili tudi izločke NbC, ki se pri temperaturi raztopnega žarjenja niso raztopili.

Keywords

jeklo 17-4 PH;raztopno žarjenje;staranje;izločevalno utrjevanje;trdota;mikrostruktura;

Data

Language: Slovenian
Year of publishing:
Typology: 2.11 - Undergraduate Thesis
Organization: UL NTF - Faculty of Natural Sciences and Engineering
Publisher: [Ž. Tome]
UDC: 669
COBISS: 1765727 Link will open in a new window
Views: 1165
Downloads: 430
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Other data

Secondary language: English
Secondary title: ǂthe ǂeffect of heat treatment on precipitation hardening of 17-4 PH steels
Secondary abstract: The precipitation-hardened steels were developed in 1950s century for the purpose of combining good mechanical properties with corrosion resistance at high temperatures. Precipitation hardening consists of two steps. The first step is solution treatment where steel is heated to a temperature sufficient for the dissolution of any present precipitates and obtaining a homogenous austenite microstructure. The second step is artificial aging at high temperatures where numerous fine precipitates are formed which cause an improvement of mechanical properties of steel. The purpose of diploma work was to research the effect of conditions of precipitation hardening on microstructure and hardness of 17-4 PH stainless steel. Hardness measurements were taken on a Rockwell hardness tester. The microstructure was examined on a light and on a scanning electron microscope. Steel, solution treated at 1080 °C and air quenched to room temperature, had slightly higher hardness (35,6 HRC) than steel which was solution treated at 1000 °C and air quenched to room temperature (34,9 HRC). Steel aged for 4 hours had the highest hardness at temperature 400 °C. The highest hardness was measured (46,6 HRC) on steel, solution treated at 1080 °C and aged for 1 hour at 480 °C. The hardness of steel aged at 700 °C and double aged steel did not improve compared to the hardness of solution treated and quenched only steel. The microstructure of quenched steel consisted of lath martensite, the microstructure of steel aged at 480 °C consisted of tempered martensite and copper-rich precipitates while the microstructure of steel aged at 700 °C consisted of martensite as well ferrite. NbC precipitates were observed in the microstructure in all cases.
Secondary keywords: 17-4 PH steel;solution annealing;aging;precipitation hardening;hardness;microstructure;
Type (COBISS): Bachelor thesis/paper
Study programme: 0
Embargo end date (OpenAIRE): 1970-01-01
Thesis comment: Univ. v Ljubljani, Naravoslovnotehniška fak. , Odd. za materiale in metalurgijo
Pages: XII, 41 f.
ID: 10961998