Influence of free forging and heat treatment on steel properties

Ovaj diplomski rad sastoji se od teorijskog i eksperimentalnog dijela. U teorijskom dijelu dane su teorijske osnove mehanizama očvrsnuća metalnih materijala, kovanja, podjele kovačkih strojeva, toplinske obrade te mjerenja tvrdoće Vickersovom metodom. U eksperimentalnom dijelu rada na konstrukcijskom čeliku S275JR (Č.0451) trakastog oblika proveden je eksperiment slobodnog kovanja na mehaničkom kovačkom stroju s različitim brojem udaraca batom od: 2, 5, 10 i 20 puta. Dio uzoraka svakog stupnja deformiranosti podvrgnut je toplinskoj obradi koja se sastoji od zagrijavanja na 850 °C te naglog hlađenja u vodi. Nakon provedenog eksperimenta kovanja te kovanja i naknadne toplinske obrade na sabijenim uzorcima provedena je metalografska analiza te izmjerena tvrdoća Vickersovom metodom po uzdužnom presjeku kovanih traka. Provedena je analiza rezultata izmjerenih tvrdoća i metalografskih snimaka mikrostrukture, uzoraka nakon kovanja i uzoraka nakon kovanja i toplinske obrade. Zaključuje se da se povećanje tvrdoće i smanjenje veličine zrna dešava nakon kovanja i naknadne toplinske obrade s povećanjem stupnja deformiranosti.This master’s thesis consists of a theoretical and an experimental part. The theoretical section provides the theoretical foundations of the mechanisms of strengthening metallic materials, forging, classification of forging machines, heat treatment, and hardness measurement using the Vickers method. In the experimental part of the study, an experiment involving free forging was conducted on structural steel S275JR (Č.0451), in strip form, using a mechanical forging machine with varying numbers of hammer blows: 2, 5, 10, and 20 times. A portion of the samples from each level of deformation underwent heat treatment, which involved heating to 850°C followed by rapid quenching in water. After the forging experiment, as well as forging followed by subsequent heat treatment on compacted samples, metallographic analysis was performed, and Vickers hardness was measured along the longitudinal cross-section of the forged strips. An analysis of the measured hardness results and metallographic microstructure images was conducted for samples after forging, as well as samples after forging and subsequent heat treatment. It is concluded that an increase in hardness and a reduction in grain size occur after forging and subsequent heat treatment with an increase in the degree of deformation