Copper brazing response of some advanced high strength steel grades

Sheet steels are commonly used in automotive powertrain applications wherein formed and assembled components undergo a copper brazing operation as part of the manufacturing process. For high performance applications including transmission pump housings and turbines, specially processed microalloyed steels have been developed and specified in order to develop the desired mechanical properties after exposure to brazing temperatures of ∼1100 °C. New families of advanced high strength steel (AHSS) sheet are currently being developed and implemented. These are typified by increased alloy levels and exhibit unique property combinations that are particularly suited to auto body applications requiring the dual characteristics of high formability and high strength. Here it is considered that such grades may also be suited to powertrain components requiring high initial formability coupled with high final strength after copper brazing. That is, transformation strengthening during cooling after brazing is envisioned as a potential strengthening mechanism available with these new steels. In this work, initial screening results are reported to elucidate the response of some experimental AHSS to a simulated copper brazing operation during which the steels are taken into the austenitic temperature range and subsequently cooled at moderate rates to ambient conditions.