Thread Content
Oxidation and decarburization are two important concepts in materials science, particularly significant in metal processing and heat treatment processes. I. Definition of oxidation: Oxidation is a reaction in which reactants lose electrons during a chemical reaction; it is also a chemical reaction between a substance and oxygen. In organic reactions, the process of introducing oxygen into an organic compound or removing hydrogen from it is also called oxidation. Depending on the reaction, oxidation can be divided into slow oxidation and vigorous oxidation (such as combustion). Feature: Metal undergoes a chemical reaction with oxygen during heating, resulting in the formation of oxides (i.e., scale). This oxide scale not only causes the metal surface to change color and lose its luster, but it can also affect the mechanical properties of the metal. During oxidation, the oxidation state of a substance increases as it loses electrons. Slow oxidation, such as metal rusting and biological respiration, is a slow reaction that releases heat but does not produce light. Intense oxidation, such as combustion, occurs rapidly and produces light and heat. Impact: For steels processed by cold pressure methods (such as cold rolling and drawing), as well as steel sheets used for coating, the presence of scale (i.e., metal oxides) affects the surface quality of the finished products and increases tool wear. In chemical industry production, oxidation reactions play an important role, being used in the synthesis of many compounds, such as the oxidation of iron sulfide to sulfur dioxide followed by the production of sulfuric acid. II. Definition of decarburization: Decarburization refers to the phenomenon where all or part of the carbon in the surface layer of steel and iron-based alloy materials or components is lost; it is a defect characterized by a reduction in the carbon content on the surface of steel. Cause: Decarburization tends to occur when steel is heated to too high a temperature or remains at such high temperatures for too long. Carbon in steel reacts with oxygen, carbon dioxide, and hydrogen in the air to produce carbon monoxide or methane, causing carbon in the surface layer of the metal to escape. Impact: The strength of the steel decreases and it softens after decarburization, which has an adverse effect on the material’s properties. For steels that require quenching, decarburization reduces the carbon content in their surface layer, resulting in either no martensitic transformation or an incomplete transformation after quenching, and thus the desired hardness cannot be achieved. Decarburization on the surface of bearing steel can lead to quenching soft spots, making it prone to contact fatigue damage during use ； Surface decarburization of high-speed tool steel reduces its red hardness. Characteristics of the decarburized layer: In carbon-containing metals such as steel, decarburization may occur during heating. That is, carbon in the metal reacts with gases such as oxygen and carbon dioxide to produce gases like carbon monoxide or methane, which escape from the metal surface, resulting in a decrease in the carbon content in the surface layer of the metal. Decarburization affects the mechanical properties and heat treatment effects of metals. The decarburized layer has a lower carbon content than normal tissue due to the oxidation of carbon. As reflected in the metallographic structure, the amount of cementite (Fe3C) is lower than in normal structures. In terms of mechanical properties, its strength or hardness is lower than that of normal tissue. Summary: Oxidation and decarburization are phenomena that require close attention during the processing and heat treatment of materials. By controlling the heating temperature and time, as well as employing appropriate protective measures such as gas shielding, oxidation and decarburization can be effectively reduced, ensuring the performance and quality of the material.