2¼Cr-1Mo steel is uniquely suited for heavy-walled steel castings because of its outstanding quenching and tempering characteristics, good impact properties, and ease of processing. This steel has been recently accepted in numerous specifications, for example, ASTM A 217, ASTM A 356, and DIN 17245. This contribution should be viewed in conjunction with the paper “Internal Properties of 2¼Cr-1Mo Cast Steel for Heavy Castings” by H. C. Lueling, Karl Achtelik, and J. M. Motz, in this publication. The present paper makes a contribution to the relatively sparse documentation regarding the core properties of large cast sections. The primary topic is the determination of the relation between primary and secondary structures and the toughness characteristics or transition temperatures. This is accomplished by comparing the test results on specimens taken from different casting sections with the results of separately heat-treated samples from the same casting using the actual cooling curves. In addition, continuous cooling diagrams and typical microstructures for selected casting sections were determined to demonstrate the segregation effect. This work was augmented with Pellini and FATT 50 percent testing together with elevated-temperature tension tests. Extended weld procedure investigations with matching electrodes were conducted on plates of 100 mm thickness. All results confirm that 2¼Cr-1Mo cast steel when oil quenched and tempered will show very homogeneous strength and toughness characteristics in wall thicknesses up to 500 mm (20 in.). The properties of weld joints made with matching electrodes are also uniform. This material performance makes this steel particularly well suited for heavy-walled components subjected to pressure.