Segregation in carbon steels

• Main Author: Liong, Wei Hao.
• Other Authors: Tan Ming Jen
• Format: Final Year Project
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Materials::Testing of materials
• Online Access: http://hdl.handle.net/10356/16213
• Institution: Nanyang Technological University

In the shipping industry, carbon steel is widely used to build ship decks and oil rigs. Carbon steel is able to withstand heavy load but due to the segregation problem, it causes delamination. Cracks can be easily initiated and propagated along regions with high level of segregation. Segregation is a manufacturing problem that is very difficult to avoid. It is caused by the non-uniformity of chemical composition within metals and alloys during solidification. From a commercial point of view, when segregation centerline (high level of segregation at center region) is detected, it will be costly to replace the whole component. Therefore heat treatment process will be carried out on the carbon steel to eliminate the segregation problem. The author hopes the information will aid the metallurgists and engineers when performing heat treatment on carbon steel. In this project, the carbon steel, EH36, is worked under various temperatures and holding times. Therefore, this report aims to investigate the optimum conditions that will eliminate the segregation problem. Subsequently, the impact strength, the hardness and ductility of the material heated statically was also examined. In conducting the literature review, the author gives an overview about heat treatment process, properties of carbon steel, especially medium carbon steel and the causes and effects of segregation in carbon steel. The techniques used to remove the segregation centerline are mentioned in greater detail as well. The series of tests and observations to determine the tensile strength, hardness and removal of segregation centerline include the Tensile Test, Brinell Hardness test and Charpy Impact test, their principles and results analyzed. For large metal pieces that cannot be cut into smaller pieces for experimental purposes, the Ultrasound test is used to determine the defect in the metal. The occurrence of an optimum temperature at which the segregation centerline is removed and the minimal loss of strength is discussed. In the concluding segment, a general overview of analysis is given and possible recommendations are proposed as well.