This thesis describes a research project on the development of a new grade of low cost spring steel with exceptional mechanical properties on the basis of a complete understanding and quantification of the metallurgical processes taking place during the various stages of the heat treatment. The new composition in combination with a new 2-step tempering treatment resulted in a steel with a tensile strength in excess of 2400 MPa and a reduction of area for quasi-static tensile fracture of more than 20%.