Overcoming the Limitations of Conventional Carburizing Steels

The development program was driven by the need to overcome the limitations of conventional carburizing steels like 20MnCr5, particularly their susceptibility to IGO and reliance on post-treatment processes such as grinding and shot peening to achieve their required mechanical properties. The result is 20NiMo9-7 (158Q), alloyed with nickel (Ni) and molybdenum (Mo), elements with low oxygen affinity and strong hardenability contributions, while minimizing the presence of silicon (Si), manganese (Mn), and chromium (Cr)—see Table 1. This composition suppresses IGO and enables the formation of a fully martensitic surface layer with high compressive residual stresses, even under standard atmospheric carburizing conditions, see Figure 2. Additionally, this steel is produced via a premium production process (IQ-Steel), which ensures low levels of detrimental non-metallic inclusions. This ensures that steel cleanness is not the limiting factor for the fatigue properties.

The result is a steel that delivers high fatigue strength directly after carburizing, reducing or eliminating the need for post-processing. This makes 158Q particularly suitable for complex or small gear geometries where grinding or shot peening are impractical, offering a streamlined, cost-effective, and sustainable manufacturing route.