Advantages: versatility, cost-effectiveness, good weldability and toughness
Typical applications: Mechanical engineering, offshore constructions, vehicle components, railway engineering, defense industry, agricultural equipment, mining equipment
Effects of molybdenum: increases hardenability, promotes consistent strength throughout components
Steel castings are manufactured over a large variety of alloy compositions used in a multitude of applications. A high degree of specialization is involved with steel foundries. Steel castings are preferred where manufacturing of a component starting from a wrought or rolled steel semi-product is too costly or too difficult. The different steel casting alloys are distinguished according to the following application areas:
- General applications (unalloyed C-Mn-Si steel)
- Improved weldability and toughness for general purposes
- High pressure purposes for use at low temperatures
- High pressure purposes for use at room temperature and elevated temperatures
- Heat resistant steel castings
- Corrosion resistant steel castings
- Wear resistant steel castings
The base composition of steel castings consists of carbon, manganese, and silicon. Depending on the area of application, additional alloying elements such as chromium, molybdenum and nickel are required. In contrast to rolled steel grades, cast steels cannot be thermo-mechanically processed and must fully rely on heat treatments for developing a suitable microstructure providing high-performance properties.
Molybdenum is used at levels up to 0.4% to give additional solid solution strengthening and, particularly, to increase hardenability when heat treating heavy sections. Nickel is added for solid solution strengthening and when good low-temperature toughness is required. Chromium further increases hardenability. Microalloying elements such as niobium and vanadium are typically added to control grain size and to provide precipitation strengthening. The heat treatment of HSLA cast steels is often carried out in three stages: homogenization, austenitizing prior to normalizing or quenching, and tempering or ageing.
Table: Specified compositions and mechanical properties of cast HSLA steel for structural and offshore applications