Q345 Steel Specification and Equivalent Standard. Q345 steel specification Q345 steel belongs to 16Mn steel grade, usually it is produced in hot rolled state, hot rolled steel plate, hot rolled steel coil/sheet, it has comprehensive mechanical and welding property, as it shows good performance in structural purposes, it is widely used as welding structural part in manufacturing of ship stanag?4569?2 class stab proof steel plate equvalentss540 h beam application - Steel SupplierSS540 Steel Angle - Higher Strength for Lower Weight. JIS G3101:2004 SS540 structural steel angle contains 0.30% carbon and 1.60% manganese, which of them greatly improves its strength. Compared with SS400 & SS490, SS540 has much higher strength - 400 MPa yield strength and 540 MPa tensile strength. High strength makes it popular for applications where need strength but weight is an issue.