The 4340 steel has the composition: Fe - 0.4 %C, 0.7 %Mn, 0.2% Si, 1.8%Ni, 0.8% Cr, 0.25% Mo. The alloy may not contain more than 0.04% of either 
S or P. The material has a tensile strength between 980 and 1960 MPa, a yield stress of 895 to 1570 MPa, and an elongation to fracture between 21 and 11%.