Oxidation Defects and Quality Control

Hot-rolled steel plays a vital role in modern industry, it is widely used in construction, manufacturing, transportation and other fields. However, hot rolled steel often faces a challenge in the production process: oxidation defects. These defects can affect the quality, reliability and performance of the steel. In order to better understand and solve the problem of oxidation defects in hot-rolled steel, this article will delve into its causes and introduce some key technical measures to ensure high quality hot-rolled steel production.

The Oxidation Principle of Hot Rolled Steel

Basic concept of oxidation principle

To understand the oxidation defects of hot-rolled steel, it is first necessary to understand the oxidation principle. Oxidation is the process by which metals react with oxygen to form oxides. For steel, this process is particularly pronounced at high temperatures. During the hot rolling process, the billet is heated at high temperatures and reacts chemically with the surrounding oxygen to form an oxide layer. This oxide layer is usually in the form of iron oxide (Fe2O3), commonly known as "rust".

Factors of Loud Oxidation

The oxidation of hot-rolled steel is affected by many factors:

  • Temperature: High temperature accelerates the oxidation reaction. At high temperatures, metal grains absorb oxygen more easily, thus promoting the rate of oxidation. Therefore, the high temperature environment during hot rolling is one of the main reasons for oxidation.
  • Material composition: The composition of steel also has a significant effect on the oxidation reaction. Steel with a high carbon content is more likely to be oxidized because carbon combines with oxygen to form carbon oxides. In addition, the content and proportion of other alloying elements also affect the oxidation characteristics.
  • Time: The longer the exposure to high temperatures, the greater the depth and thickness of the oxide layer. Therefore, the treatment time of hot-rolled steel is also one of the important factors affecting the degree of oxidation.

Oxidation Defect of Hot Rolled Steel

After understanding the oxidation principle, we can discuss the oxidation defects of hot-rolled steel more deeply. These defects can be divided into four broad categories:

  • Classification defects: Classification defects are caused by inclusions or impurities in the raw material reacting with oxygen at high temperatures. These inclusions may form holes, bubbles and uneven inclusions in the steel, reducing the quality of the steel.
  • Temperature defects: Temperature defects are related to the time and conditions of steel exposure at high temperatures. The formation and penetration of oxide layer will affect the toughness of steel, and may lead to brittle fracture, uneven grain growth and other problems.
  • Descaling defects: In the manufacturing process of hot-rolled steel, a scale-like oxide is usually formed, which is called descaling. These scales may fall off during subsequent treatment, resulting in uneven surfaces and even holes.
  • Roll defects: The oxide layer on the roll surface may be transmitted to the steel surface during contact, resulting in holes, scratches and other defects, reducing the surface quality of the steel.

Application of Oxide Control Technology

In order to solve the oxidation defect problem of hot-rolled steel, the steel industry has adopted a variety of technical measures:

  • Sand-free steel: Sand-free steel is a steel with improved oxide layer control. By optimizing the smelting process and reducing the content of non-metallic inclusions and impurities, the steel with low oxidation property was prepared. This steel not only reduces the surface oxidation reaction, but also reduces the risk of osmotic oxidation and improves product quality.
  • Easy pickling steel: Easy pickling steel is a special steel that removes the surface oxide layer by pickling process. Pickling can effectively remove oxides, make the steel surface more flat, clean, and reduce the scale defects. This technology helps to improve the workability and corrosion resistance of steel.
  • Controlling the oxidation environment: The risk of oxidation defects can be reduced by controlling the oxidation environment during the production process. One common approach is to reduce oxygen exposure. This can be achieved by creating a reducing atmosphere inside the furnace or by using nitrogen or other inert gases. These methods help to slow down the rate of oxidation, thereby reducing the formation of oxide layers.
  • Surface treatment: For steel that already has an oxide layer, surface treatment methods can be used to repair or reduce defects. Methods such as pickling, belt grinding and polishing can help remove oxide and scale, improving the surface quality of the steel.
  • Material selection: Selecting the type of steel suitable for a specific application is also an important way to control oxidation defects. Certain types of steel themselves have higher oxidation resistance and are therefore more suitable in some high temperature or corrosive environments.

The oxidation defect of hot-rolled steel is a problem that needs attention, which is directly related to the quality and properties of steel. Understanding the principle of oxidation and the causes of defects is the first step in solving this problem. By adopting advanced oxide layer control technology and material selection, the steel manufacturing industry is constantly improving product quality, increasing production efficiency, and meeting market demand. As technology continues to advance, we can expect more high-quality and reliable hot-rolled steels to play an important role in future applications.

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