The development and manufacture of Ultra-Thin Cast Strip steel products with high residual element levels via the CASTRIP® process

A range of Ultra-Thin Cast Strip (UCS) sheet steels with elevated residual levels was produced via the CASTRIP twin drum casting method at Nucor Steel, Indiana. This paper examines the influence of elevated levels of copper, chromium, nickel, and phosphorous on mechanical properties, surface quality, processing, and weldability of UCS sheet steel products produced by the CASTRIP process. Increased levels of copper and phosphorous were found to strengthen UCS sheet steel due to solid solution strengthening but chromium and nickel did not. At lower coiling temperatures and low hot reductions, where processing conditions promote microstructural strengthening, copper and chromium further enhanced strength via increased hardenability. The presence of elevated residual levels of copper is known to potentially lead to hot shortness, unless expensive counter measures are employed, such as nickel additions. Due to the unique solidification and thermal history conditions of the CASTRIP process, higher levels of copper can be tolerated without hot shortness or loss of surface quality. The CASTRIP process is capable of utilizing increased levels of scrap containing higher residual levels, such as post-consumer shredded material. These elevated levels of residual elements can be utilized as a strengthening agent in the finished sheet. Alternatively, this influence on strength can be mitigated when desired through the choice of processing parameters. Additionally, the elevated residual content did not influence either the surface quality or the weldability of the steel