Vpliv stopnje deformacije na kinetiko mehčanja jekla HSLA

Ažman, Kristjan (author), Bombač, David (mentor)

V okviru diplomskega dela so predstavljeni vplivi stopnje deformacije na kinetiko mehčanja nizko legiranega visoko trdnega jekla S690QL z uporabo dvostopenjskega tlačnega preizkusa. Konstrukcijsko jeklo z oznako S690QL je toplotno obdelano in ima minimalno napetost tečenja 690 MPa. Odlikujejo ga visoka trdnost, dobre upogibne in varilne lastnosti. Cilj diplomskega dela je primerjava vpliva stopnje deformacije na kinetiko mehčanja jekla S690QL. V teoretičnem delu so predstavljeni vplivi parametrov, kot so temperatura, velikost kristalnih zrn, zaostale napetosti in hitrost deformacije na kinetiko mehčanja. Predstavljene in diskutirane so tudi različne metode izračuna deleža mehčanja, in sicer metoda odmika, metoda ekstrapolacije krivulje tečenja ponovne obremenitve, metoda srednje napetosti tečenja in metoda sprostitve napetosti. V eksperimentalnem delu je predstavljen potek dvostopenjskega tlačnega preizkusa s simulatorjem Gleeble 1500D, s katerim lahko simuliramo vse pogoje in procese, s katerimi se srečujemo pri obdelavi in predelavi materialov. Z dvostopenjskim tlačnim preizkusom smo deformirali vzorce pri temperaturi 1050 °C pri hitrosti deformacije 1 s-1. Pri poizkusih smo spreminjali stopnjo deformacije in čas med deformacijama. Med poizkusom smo beležili vrednosti velikosti deformacije in napetosti. Iz dobljenih podatkov smo izrisali krivulje tečenja, iz katerih smo lahko kasneje določili deleže mehčanja. Rezultati tlačnih preizkusov in izračuni deležev mehčanja so predstavljeni v obliki tabel in grafov. Iz te predstavitve se jasno vidijo vplivi stopnje deformacije na kinetiko mehčanja jekla. Podatki, zbrani v okviru diplomskega dela, se skladajo z ugotovitvami predhodnih raziskav kinetike mehčanja.

• Language: Slovenian
• Keywords: jeklo S690QL, procesi mehčanja, stopnja deformacije, dvostopenjski tlačni preizkus
• Work type: Bachelor thesis/paper
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Year: 2020
• PID: 20.500.12556/RUL-120954
• COBISS.SI-ID: 34567683
• Publication date in RUL: 28.09.2020

Secondary language

• Language: English
• Title: Influence of strain on a HSLA steel softening kinetics

Abstract

The diploma work presents the effect of degree of strain on softening kinetics of S690QL steel, by using double compression test. S690QL structural steel is heat treated and has a minimum yield strength of 690MPa. It has good bending and welding properties. The goal of the diploma was to find out the effect of degree of strain on softening kinetics of S690QL steel. In the theoretical part, the influences of parameters such as temperature, grain size, residual stresses and strain rate on the softening kinetics are presented. Various methods for calculating the softening fraction are also presented and discussed. These are: offset method, back extrapolation method, mean stress method and strain recovery method. In the experimental part double compression test with a Gleeble 1500D simulator is presented, with which we can simulate all the conditions and processes we encounter in the processing of materials. The samples were deformed at a temperature of 1050°C at a deformation rate of 1s-1 by a double compression test. In the experiments, we were changing the degree of strain and the time between deformations. During the experiment, values of strain size and stress were recorded. From the obtained data, we plotted flow curves from which we could later determine the softening fraction. The results of compression tests and calculations of softening fractions are presented in the form of tables and graphs. From this presentation, the effects of the degree of strain on the softening kinetics of steel are clearly seen. The data collected in the diploma work are in line with the findings of previous research on softening kinetics.

• Keywords: S690QL steel, softening processes, strain rate, degree of strain, double compression test