Air-Hardening Die-Forged Con-Rods—Achievable Mechanical Properties of Bainitic and Martensitic Concepts

Abstract

Three air-hardening forging steels are presented, concerning their microstructure and their mechanical properties. The materials have been produced industrially and achieve either bainitic or martensitic microstructures by air-cooling directly from the forging heat. The bainitic steels are rather conservative steel concepts with an overall alloy concentration of approximately 3 wt.%, while the martensitic concept is alloyed with 4 wt.% manganese (and additional elements), and therefore belongs to the recently developed steel class of medium manganese steels. The presented materials achieve high strengths (YS: 720 MPa to 850 MPa, UTS: 1055 MPa to 1350 MPa), good elongations (Au: 4.0 MPa to 5.9 MPa, At: 12.3 MPa to 14.9 MPa), and impact toughnesses (up to 37 J) in the air-hardened condition. It is shown that air-hardened steels achieve properties close to standard Q + T steels, while being produced with a significantly reduced heat treatment.

Air Cooling Martensites—The Future of Carbon Neutral Steel Forgings?

“…From those ingots, different steel components were produced and consecutively analyzed. [2,21] The larger components, like axle journals of 30 kg, did not show fully martensitic microstructures, which leads to unfavorable impact toughness. The reason for the reduced mechanical properties is the gradients within the microstructure.…”

“…Mechanical properties for two different trials forgings produced from AHD steels. [2,21] Component YS Figure 5. Visualization of the LCA-results [25] obtained for the spring Ubolt.…”