Influence of cooling rate on microstructure of NM400 wear-resistant steel under different conditions
NM400 wear-resistant steel is usually processed by quenching and tempering (Q&T) heat treatment. Quenching is the process of quickly cooling a heated material from its austenitizing temperature in order to produce a martensitic microstructure. While tempering is then used to reduce hardness and improve toughness. The cooling rate during quenching and tempering treatment is an essential parameter for controlling microstructure and properties of NM400 wear-resistant steel. Generally, the cooling rate of Q&T affects the lattice stability, grain size, microstructure stability and grain morphology.
Different cooling rates can lead to different microstructures of NM400 wear-resistant steel. For example, with a slow cooling rate, the austenited microstructure takes longer to reach room temperature, leading to a larger grain size due to grain coarsening and recrystallization. On the other hand, with a fast cooling rate, fine microstructure can be achieved with a refined grain size. This process is often accompanied by incomplete martensitic transformation and formation of bainitic and/or martensitic-austenite structures. The finer grain size and better dispersion of carbides achieved with a fast cooling rate decrease the hardness, but also increase its wear-resistance due to enhanced carbide formation.
The cooling rate of Q&T also has different effects on NM400 wear-resistant steel under different conditions. When it is quenched and tempered in water, a fast cooling rate is generally recommended due to the cooling power and the cost-effectiveness of water. Under this condition, a faster cooling rate helps to achieve a finer microstructure with a finer grain size and better dispersion of carbides. However, when quenching and tempering in oil, transforming the microstructure to martensitic structure requires a low cooling rate to avoid hardening and cracking. In addition, when quenching and tempering in air or other atmosphere, different cooling rates may need to be used for different circumstances in order to obtain an appropriate microstructure and lattice stability.
In conclusion, cooling rate is an important parameter that affects the microstructure and properties of NM400 wear-resistant steel during quenching and tempering. Different cooling rates can lead to different microstructures, which can in turn result in varying performance of the finished product. Factors such as quenching medium, temperature and atmosphere all need to be taken into consideration when selecting a suitable cooling rate. In addition, an accurate and systematic understanding of the influence of cooling rate on the microstructure of NM400 wear-resistant steel is necessary in order to maximize its efficiency and performance.
Conatct us
