Characterization of Flame Cut Heavy Steel: Modeling of Temperature History and Residual Stress Formation
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ME cutting is a thermal cutting method generally used by steel manufacturers. It is an effective method for cutting thick wear-resistant steel plate, unlike mechanical cutting, which is both difficult and too slow for high production rates. Flame cutting is an exothermal process, which provides an advantage over other thermal cutting methods, because the heat generated from the cutting process supports the continuation of the flame cutting.[1] The flame cutting process consists of three steps. Firstly, the steel is heated locally to its ignition temperature using a flame obtained from the combustion of a specific fuel gas mixed with oxygen. Secondly, the heated spot is burnt with a jet of pure oxygen, which creates a
T. JOKIAHO, A. LAITINEN, S. SANTA-AHO, M. ISAKOV, P. PEURA, A. LEHTOVAARA, and M. VIPPOLA are with the Tampere University of Technology, Laboratory of Materials Science, P.O. Box 589, FI-33101 Tampere, Finland. Contact e-mail: tuomas.jokiaho@tut.fi T. SAARINEN is with the SSAB Europe Oy, Rautaruukintie 155, 92101 Raahe, Finland and also with the Sandvik Mining and Construction Oy, Pihtisulunkatu 9, 33330 Tampere, Finland. Manuscript submitted March 31, 2017.
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continuous chemical reaction between the oxygen and the steel. Thirdly, the oxygen jet not only burns the steel but also blows away the iron oxide that is formed during the cutting process.[2] However, the flame cut edge is prone to cracking, which makes cutting of thick steel plate problematic. It has been shown[3] that an increase in both the hardness and thickness of the plate enhances the cracking tendency. Flame cutting produces a heat-affected zone (HAZ) at the cut edge of steel plate due to the generation of a steep thermal gradient during the cutting process. For example, Martı´ n-Meizoso et al.[4] have reported that microstructural changes and hardness variations occur in the HAZ. Hardness values have been observed to be higher closer to the cut edge and decrease over a short distance from the cut edge.[5] In addition, the width of the HAZ decreases with increasing cutting speed.[6] Thomas et al.[7] found that flame cutting produces a martensitic layer on the steel edge. The thickness of the martensitic layer and the HAZ were observed to be dependent on the plate thickness and flame cutting speed. The flame cutting process results in the formation of residual stresses in the cut edge of the steel. It has been reported[3] that high residual stresses in the cut edge promote crack formation. Residual stresses are formed by uneven plastic strains in the material which cause
elastic strains. These elastic strains maintain the dimensional continuity in the vicinity of the plastically deformed regions.[8] The elastic strains and hence the residual stresses can be either compressive or tensile. Generally, residual compressive stresses are beneficial because they reduce the probability of cracking, whereas residual tensile stresses are unfavorable because they enhance it. Large thermal gradients produced by flame cutt
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