Considered in particular were the toughness requirements at low temperatures, the safe weldability, and the minimum sensitivity against temper embrittlement at stress-relieving temperatures of Steel 20 MnMoNi 5 5, corresponding to ASTM A 508 Class 3. High-temperature tensile and creep properties up to 450°C had to be met.

These targets were achieved by applying the production steps as follows: 1. The steelmaking was done according to the Buderus calcium-argon blowing (CAB) process. The low sulfur contents of 0.002% and lower and the special pouring technology to achieve low segregation rates are the basic reasons for the outstanding toughness and the isotropy of the material properties. 2. The forging technology, in particular the temperature range and the deformation rate, was designed to produce fine-grain structure already in the as-forged condition. 3. A newly developed, three-step, quality heat treatment is most important for the hardening through and the toughness level of the heavy section. 4. The report submits a discussion of the dimensional limits for 20 MnMoNi 5 5 forgings produced according to different technologies.