What is NUCu Steel?

A copper-precipitation-hardened, high-performance Grade 70 weathering steel, NUCu 70W (Northwestern University Cu-Precipitation-Strengthened) steel, now standardized as ASTM A710 Grade B, was developed at Northwestern University with the support of the Federal Highway Administration, the Illinois Department of Transportation, and Northwestern University’s Infrastructure Technology Institute.

The steel was designed to achieve a minimum of 70 ksi yield strength on air cooling from hot rolling without quenching and tempering (Q&T), accelerated cooling or thermomechanically-controlled processing (TMCP). This allows for elimination of alloying elements needed for hardenability as well as a low carbon content, resulting in a very low carbon equivalent for welding. As a result, its processing cost is less than for Q&T or TMCP steels. For steelmakers, this means that special equipment for Q&T or TMCP is not required.

NUCu 70W (ASTM A710 Grade B) steel possesses high Charpy absorbed impact fracture energies at very low temperatures. By adding titanium (up to 0.1%) which combines with interstitial atoms, the absorbed impact fracture energy further increases. This addition lowers the yield stress to 60 Ksi minimum but increases the Charpy Absorbed Impact Fracture Energy to more than 265 ft-lbs at -80^oF.

Due to its very low carbon equivalent, NUCu 70W (ASTM A710 Grade B) steel generally does not require pre-heat or post-heat during welding with matching welding consumables. Weatherability of NUCu 70W (ASTM A710 Grade B) steel is better than that of any other commercially available weathering steel. Paint on this steel resists degradation much better than on other weathering steels.

NUCu steel does not contain intentional additions of chromium. This is of interest because of health and environmental hazards due to formation of carcinogenic Cr⁺6 during welding.

The combination of these properties can result in significant cost savings when NUCu steel is used instead of other structural steels.