Doctoral dissertation

Right flame cutting conditions, less waste

Tuomas Jokiaho
Flame cutting is generally applied cutting method in steel industry. However, in some occasions, it causes cracking of the plates. With right cutting parameters and plate structure, the undesirable cracking phenomenon can be avoided.
High hardness, strength, and toughness are the properties required of thick wear-resistant steel plate. To meet these requirements, special care must be taken in the manufacture of the plate.

The manufacturing steps for thick plate involve thermal cutting, such as flame cutting, which is the most generally applied cutting method for thick plate in the steel industry. Flame cutting is performed with a heating flame and oxygen jet, which creates a cut edge on the steel plate. It is a suitable method for thick steel plates and high production rates due to the exothermal reaction during the cutting process. However, flame cutting also causes problems. Due to the steep thermal gradient, a heat affected zone (HAZ) is formed at the cut edge. The HAZ includes microstructural changes and hardness variations. In addition, high residual stresses are generated in the cut edge. In the worst case, the flame cutting causes cracking of the plates.

The main purpose of this work is to identify the main contributors behind the cracking phenomenon of thick plates in flame cutting. In addition, the goal is to give guidelines for a more effective flame cut process and to determine the most suitable microstructural characteristics for thick wear-resistant steel plates and flame cutting.

To achieve these goals, a trial batch of thick wear-resistant steel plates was manufactured. The plates were flame cut with different cutting parameters and the residual stress state of the flame cut samples was measured by X-ray diffraction. In addition, both original and flame cut samples were characterized by electron microscopy and mechanical tests.

The results of this study showed that residual stress formation during flame cutting can be controlled by choosing the right cutting parameters. In addition, study shows which microstructural features are undesirable for thick plates in cracking point of view. Therefore, based on the results, study shows guidelines how to avoid the cracking.       

M.Sc. (Tech) Tuomas Jokiaho will publicly defend her doctoral thesis Residual Stress, Microstructure and Cracking Characteristics of Flame Cut Thick Steel Plates - towards Optimized Flame Cutting Practices on Friday 15th November 2019 at 12:00 noon at Tampere University in Konetalo auditorium K1702. Opponents are Emeritus Professor David Porter from University of Oulu and D.Sc. (Tech.) Taina Vuoristo from Swerim AB, Sweden. The Custos is Professor Minnamari Vippola  from the Faculty of Engineering and Natural Sciences.


The dissertation is available online at: http://urn.fi/URN:ISBN:978-952-03-1319-7

Photograph: Arto Jalonen