Disadvantages Of Quenching In Steel

Introduction

Quenching is one of the most important heat treatment process to attain desirable properties, for example strength and hardness. Quenching means to rapidly cool a material. But this rapid cooling can cause some serious distortions in the material. In steels, the transformation phases and thermal gradients are the main causes of this distortion. It has become an industry objective to reduce this distortion caused by heat treatments. Ideally, controlling the quenching process by changing the heat boundaries to minimize the distortion with the additional aim of satisfying residual stress and surface hardness distribution. (Heat treating)

This experiment will be conducted on quenched, zinc coated steels. Knowledge of the phases of the carbon steels and knowing the properties of the different steels can be very beneficial in manipulating the heat treatment process to best suit what is desired. There are several impacts that should be noted about quenching a material. First, the impact on microstructure can wholly depend on the quenching process and how long it was held at certain temperatures. The percentage carbon in the steel can also impact on the time needed to obtain different forms of the steel. At 0.8% carbon, there is 100% pearlite in the microstructure. In terms of isothermal transformation, the steels heated to above 723°C

This is because the steel is hard but brittle and has internal stresses. The solution to this is by tempering to increase toughness, reduce the brittleness but in turn reduces hardness. Tempering a steel heats up the steel to temperatures ranging from 200-500°C depending on the desired mechanical properties. Heating after the quenching allows the carbon to diffuse into the martensite to relieve internal stresses. The end result would be the shock absorption capability which depends on the tempering temperature (higher the temperature, higher the shock