Low Alloy Steel Plate

Q355B/Q355D Low Alloy Steel Plate

GB Q355B/Q355C/Q355D high strength low alloy steel plate with optional Z15/Z25/Z35 through thickness properties for welded structures.

Q355 took over from Q345 in the 2019 revision of GB/T 1591 and is now the standard Chinese high-strength low-alloy structural plate: 355 MPa minimum yield, good weldability, and a real Charpy guarantee instead of a letterhead promise. We stock B and D grades, and Z15/Z25/Z35 through-thickness guarantee for heavy welded box columns.

Grades and Equivalents

  • GB/T 1591: Q355B (20 deg C impact), Q355C (0), Q355D (-20), Q355E (-40)
  • Close matches: S355 (EN 10025-2), A572 Gr.50 (ASTM), ST52-3 (old DIN)
  • Z-direction grades per GB/T 5313 for thick welded joints

Sizes and Supply

  • Thickness 6-200 mm as rolled or normalized; stock normally 6-80 mm
  • Widths 2000-2500 mm, lengths to 12000 mm
  • Cut-to-size, beveling and drilling before shipment

Delivery Condition and Testing

Most stock ships as-rolled; normalized or TMCP delivery for thicker or impact-critical orders. Every plate carries an EN 10204 3.1 MTC with the actual Charpy results, and ultrasonic testing to GB/T 2970 can be added for thick sections.

Where This Plate Goes

  • Welded structural frames, cranes and booms
  • Bridges, trailers and transport equipment
  • Machinery bases and heavy equipment components

Questions Buyers Ask

Q: Is Q355D interchangeable with S355J2? A: Functionally close - both guarantee 27 J at -20 deg C - but your design code decides, not the mill. We supply whichever certificate your project needs.
Q: When do I need a Z-grade? A: Thick, highly restrained welded joints (think box columns over 40 mm) where through-thickness tearing is a risk. Tell us the joint design and we will advise.
Send sizes and impact requirement with the RFQ; stock positions come back the same day.