From a heat treater’s perspective, the purpose of adding alloying elements to steel is to enhance the material’s response to heat treatment, which in turn results in improvement of the mechanical and physical properties of the steel. Alloying additions are made for one or more of the following reasons:
  • To increase hardenability
  • To produce a finer grain size
  • To help control part distortion
  • To improve tensile strength without appreciably lowering ductility
  • To avoid quench cracking
  • To gain toughness
  • To achieve better wear resistance
  • To improve hot hardness
  • To achieve better corrosion resistance
With this disclaimer in mind, it is time to talk about the element manganese (Mn). We know that the effect of a particular alloying element on either the steelmaking process, the response to heat treatment and the properties achievable depends on the effects of both the element in question and on the (complex) interactions with other elements, either individually or collectively.

The role manganese plays in deoxidation of steel and modification of sulfides presents it is a major alloying element. It has complex interactions with carbon and is used to control inclusions. Manganese is beneficial to surface quality in all carbon ranges with the exception of rimmed steels (< 0.15%C) and is particularly beneficial in high-sulfur steels. Manganese contributes to strength and hardness, but to a lesser degree than carbon. The increase depends on the carbon content – higher-carbon steels being affected more by manganese. Higher manganese in steels lowers ductility and weldability (but to a lesser extent than carbon). Manganese also increases the rate of carbon penetration during carburizing.

Next time, we will look at some of the 50 ways manganese affects steel.