4140 plate is a kind of alloy steel plate, according to ASTM A29.

The the 4140 plate alloy steel has chemical composition as below:

Standard Grade C Mn P S Si Cr Mo
ASTM A29 4140 0.38-0.43 0.75-1.00 0.035 0.040 0.15-0.35 0.8-1.10 0.15-0.25