Semi-continuous Annealing of Hot Rolled Steel by RH and RH-KTB/PB Methods
1. Introduction
The annealing process has a long history and is an impo~tant hot-working process. It is a continuous or semi-continuous heat treatment of steel, usually at high temperatures to improve its mechanical properties, such as strength and ductility. The working temperature for annealing is usually higher than the recrystallization temperature. In general, higher temperatures need to be used and annealing cycles are shorter as compared to conventional methods. The choice of annealing method depends on the intended use of the steel. Two important methods of annealing that have been developed and used in the metal industry are Radiant Heating (RH) and Radiant Heat-KTB/PB (RH-KTB/PB) methods. These two annealing methods have different types of heat transfer, which affect the annealing process and the resulting microstructure and mechanical properties of the annealed steel.
2. The RH Method
The RH method uses radiant heat to anneal steel. The radiant heat sources in these methods are usually infrared lamps, induction coils, or other electrically heated bodies. The energy from these sources is transferred to the steel in the form of infrared radiation, which heats the steel quickly for proper annealing. The RH method is essentially a type of batch annealing and is used for high quality steels.
The advantages of using the RH method include: increased productivity, improved mechanical properties, uniform heat distribution throughout the steel and improved surface finish. The temperature of the steel is also controllable, which ensures a homogeneous product. Furthermore, energy consumption is lower than conventional batch annealing methods.
3. The RH-KTB/PB Method
The RH-KTB/PB annealing method is a semi-continuous process. The term KTB stands for Kolb Thermal Blanket and PB stands for Precise Blanket. The KTB is a type of insulating material placed around the steel product to transfer heat more quickly. The PB is a type of thermally resistant material that is used to improve the distribution of heat throughout the steel product.
The advantages of the RH-KTB/PB method include: improved production rate, uniform heating, improved mechanical properties, improved surface finish, and lower energy consumption. The RH-KTB/PB method is also more efficient than batch annealing and is usually used for medium to low quality steels.
4. Comparison Between RH and RH-KTB/PB
The RH method and RH-KTB/PB method have different characteristics and advantages. The RH method is a batch annealing method, which can provide excellent mechanical properties and improved surface finish. However, it does require higher energy consumption and the annealing temperature is not controllable.
The RH-KTB/PB method is a semi-continuous method and is used for low to medium quality steels. The PB insulating material helps to improve the heat distribution throughout the steel product and the KTB insulating material helps to reduce the overall energy consumption. Furthermore, the annealing temperature is more controllable and uniform as compared to the RH method.
5. Suitable Steels for RH and RH-KTB/PB Methods
The RH method is suitable for use with high quality steels with a low carbon content and good hardenability, such as stainless steels. The RH-KTB/PB method is suitable for use with medium to low quality steels, such as low carbon steel and some high strength low alloy (HSLA) steels.
6. Conclusion
The RH and RH-KTB/PB methods are two important annealing methods used by the metal industry. The RH method is suitable for high quality steels and is a batch annealing method that requires higher energy consumption. The RH-KTB/PB method is suitable for low to medium quality steels and is a semi-continuous process. Both methods have advantages and disadvantages, but each is suitable for different types of steels.
