Cr12(D3) is a heat-resistant ferritic stainless steel whose main alloying elements are chromium, tungsten and vanadium. It is widely used in the oil, chemical and mining industries for its high temperature and corrosion resistance. Apart from its excellent properties, Cr12(D3) can also be heat treated to improve its mechanical properties and enhance its corrosion resistance.
Heat treatment consists of subjecting the steel to a heating and cooling cycle that alters the microstructure of the material. In the case of Cr12(D3) three processes are typically employed: annealing, tempering and hardening. Each of these techniques produces a different microstructure and hence different properties.
Annealing is used to soften the steel by removing internal stresses, reduce its hardness and increase its ductility. It is usually carried out at temperatures between 700 and 900°C, followed by slow cooling. This process produces a refined and homogeneous grain structure and improves toughness and corrosion resistance.
Tempering is a process in which the steel is heated up to a temperature below the austenitizing temperature, before being quenched in oil or water. The main aim of this process is to improve the ductility and toughness of the steel while retaining its strength. Temperatures can range between 150 and 550°C depending on the microstructures desired.
Finally, hardening is a process where the steel is heated to a temperature above its austenitizing temperature and then quenched in oil or water. The aim of the process is to increase its strength and wear resistance. Depending on the desired properties, this process can be achieved at temperatures ranging from 1000 to 1200°C.
These processes can have a profound impact on the microstructure and properties of Cr12(D3), as shown in the micrograph below.
The bars in the diagram represent the presence of different microstructures within the steel. On the left we can see the influence of heat treatment on the hardness and resistance of the material. The annealed sample (light blue) has a relatively soft structure, whereas the tempered (green) and hardened samples (purple) have much greater hardness and resistance. On the right we can see the influence of heat treatment on the amount of carbon present in the steel. Carbon has a significant impact on the strength, wear resistance and corrosion resistance of the steel, so the amount of carbon in the steel determines the properties of the material. The annealed sample has the highest amount of carbon, whereas the tempered and hardened samples have less.
In conclusion, heat treatment is an essential step in the processing of Cr12(D3) as it improves the properties of the steel and ensures it is fit for use in demanding environments. An understanding of the microstructure and the effects of different heat treatments is essential for engineers looking to get the most out of their material.
