The introduction of direct injection turbocharged engines has increased the need for higher performance connecting rods, able to withstand higher compressive loads in operation. In this respect, new materials with high compressive yield strength and fatigue performance for powder-forged connecting rods, such as HS150, HS160, and HS170M, were developed and successfully introduced in production. Among them, HS170M, currently used to manufacture connecting rods for several high performance engines, not only has exceptional strength, but less variation in mechanical properties as a function of its chemical composition variation within the specified limits compared to other powder-forged materials. Furthermore, recent strength tests conducted at engine operating temperatures on specimens machined from connecting rods have shown some very interesting results: despite the fact that the mechanical properties of most steels decrease at higher temperatures, the strength of Cu-rich HS materials increases due to second phase strengthening provided by nano size Cu precipitates. For this reason, powder-forged connecting rods manufactured with HS170M are stronger than their drop-forged counterparts manufactured with micro alloyed steels. Additionally, advancements in design and manufacturing, such as design optimization, post-delubrication shot peening, enhanced shot peening, etc., have resulted in higher performance powder-forged connecting rods and, as a result, in mass reductions, thus further contributing to fuel economy and reduced emissions.
