JIS G3106 SM41B

SM41B is the former JIS designation for rolled steel for welded structures now standardized as SM400B under JIS G3106. The 400 (old 41) denotes 400 to 510 MPa tensile strength; minimum yield is 245 MPa for thin plate, falling with thickness. The B suffix grades the notch toughness, a Charpy V-notch test of 27 J minimum at 0 C, against grade A (no impact requirement) and grade C (minus 5 C). Carbon is capped near 0.20 percent for weldability. SM400B is a general structural and shipbuilding mild steel; for classed hull structure it maps to normal-strength grade A or B under IACS UR W11.