The tensile strength S-t of grey cast iron can be calculated from measurement of wedge strength S-c by using a linear relation between both variables: S-t=AS(c)-B. The coefficients A and B depend on the casting process, the geometry of wedge penetration tool and specimen, and also on the device used to perform the wedge penetration test. Low alloyed grey cast irons of FL15, FL20, FL25 and FL30 basic materials have been cast in shell and sand moulds, at two different pouring temperatures and with and without inoculation. These changes in the process produce large variations in the structure and mechanical strength of the materials. Although these variations are important, the relationship between tensile and wedge strengths can be well described by an equation of the above mentioned type with a unique pair of values for coefficients A and B. (C) 2003 Maney Publishing.164441450