The Characterization of Flame Cut Heavy Steel – The Residual Stress Profiling of Heat Affected Surface Layer

Abstract

Flame cutting is commonly used thermal cutting method in metal industry when processing thick steel plates. Cutting is performed with controlled flame and oxygen jet, which burns steel and forms cutting edge. Flame cutting process is based on controlled chemical reaction between steel and oxygen at elevated temperature. Flame cutting of thick wear-resistant steels is challenging while it can result in cracks on and under the cut edge. Flame cutting causes uneven temperature distribution in the plate, which can introduce residual stresses. In addition, heat affected zone (HAZ) is formed and there both volume and microstructural changes as well as hardness variations are taking place. Therefore flame cutting always causes thermal stress, shape changes and consequently residual stresses to the material. Material behaviour under thermal and mechanical loading depends on the residual stress state of the material. Due to this, it is important to be able to measure the residual stresses. The aim of this study was to examine residual stresses on the cutting edge as a function of different flame cutting parameters. Also resulting microstructures and hardness values were verified. Varying parameters were the cutting speed, preheating and post heating procedures. Flame cut samples were investigated with X-ray diffraction method to produce residual stress profiles of the heat affected surface layer. Results indicated that different cutting parameters provide different residual stress profiles and that these profiles can be modified by changing the cutting speed and pre-or post-treatment procedures. Cutting parameters also affect the depth of the reaustenized region in the surface. The results correlate well with the actual industrial flame cutting and thus they provide an effective tool for optimizing the flame cutting process parameters.

Role of Steel Plate Thickness on the Residual Stress Formation and Cracking Behavior During Flame Cutting

“…It was also noted that a slower cutting speed and flame cutting with preheating produce a lower residual stress state in the cut edge. Similar results were obtained in other studies [13,14] by the author; the residual stress formation during flame cutting can be affected by the size of the sample and cutting parameters. In addition, preheating not only decreases the residual stresses in general but also increases the compressive stress region close to the surface by shifting the tensile stress region deeper into the subsurface.…”

“…This study is a continuation for previous studies by the current author. The first study [14] confirmed that the residual state of the flame cut edge can be affected by variating the cutting parameters. In another study, [13] a model was developed to investigate the flame cut process and residual stress formation.…”

“…[16] The residual measuring method is described in more detail in previous studies. [9,13,14] The examination locations and directions of the residual stress measurements are described in Figure 1. As shown in the figure, measurements were performed at the centerline of the samples (where the cracks are mostly formed during flame cutting) in two perpendicular measurement directions: the rolling direction (0 deg) and the thickness direction (90 deg).…”

Cracking and Failure Characteristics of Flame Cut Thick Steel Plates

“…[8] Transformation stresses arise from different microstructural transformations, which are accompanied by volume changes. [8] Previous studies [6,7,[9][10][11] have shown that flame cutting causes both residual compressive stress and high-tensile stress in the cut edge of the steel plate. The compressive stress is produced in the martensite region close to the cut edge and it is followed by high-tensile stress region in the tempered region.…”

“…The compressive stress is produced in the martensite region close to the cut edge and it is followed by high-tensile stress region in the tempered region. [7] The magnitude of the stresses and the width of these regions can be affected by the flame cutting parameters, [9,10] grain structure, [7] and the thickness of the plate. [6] In the worst case, flame cutting causes cracking of the cut edge.…”