Hot rolled steel plate remains one of the most widely used materials in construction, shipbuilding, pressure vessel manufacturing, and general fabrication. The hot rolling process shapes steel at temperatures above its recrystallization point, resulting in plates that are easy to form, weld, and cut. For buyers, the more difficult task is choosing the right grade. This article reviews several common hot rolled steel plate grades and the situations where each is most appropriate.

What hot rolling means for properties

During hot rolling, the steel slab is reheated and passed through roughing and finishing mills. The process refines grain structure but leaves a characteristic surface scale. Tolerance, surface finish, and flatness are generally less refined than cold rolled products, but ductility and toughness are usually better. Hot rolled plates are therefore preferred when plates will be bent, welded, flame-cut, or used in load-bearing structures.

The elevated rolling temperature allows large reductions in thickness in a single pass, so hot rolled plate is available in heavy gauges that would be difficult or expensive to produce by cold rolling. Residual stresses are also lower than in cold worked material, which reduces distortion during subsequent cutting and welding.

Common Chinese grades

Among Chinese standards, Q235 and Q345 are the grades most frequently stocked. Q235B offers a balanced combination of strength, weldability, and cost. It is used for platforms, walkways, brackets, and general building frames. Q345B provides a higher yield strength and is selected for crane booms, bridges, and heavy equipment bases where weight reduction or higher load capacity is required. Hot rolled steel coil Q345 is also supplied to processors who slit or level the material into sheets and smaller plates.

Q215 is a lower-strength grade with excellent formability. Hot rolled steel plate Q215 is useful for cold-formed sections, light structural parts, and applications where extensive bending or drawing is needed before welding. The reduced carbon content improves weldability and lowers the risk of brittle fracture in cold weather.

Hot rolled steel plate 16Mn is another high-strength low-alloy grade often used in pressure vessels, storage tanks, and line pipe fittings. Its manganese content raises strength without making welding difficult, and it performs well in moderately low temperatures. Many buyers specify 16Mn when the design calls for thinner sections that still meet load requirements.

International equivalents

ASTM A36 is the North American equivalent of Q235B and is probably the most exported structural steel grade worldwide. A36 plate is used in building frames, machinery bases, and ornamental structures. Its chemical composition limits are broad, so mechanical properties can vary slightly by mill. When tighter chemistry or improved toughness is needed, A572 Grade 50 or A588 weathering steel become more suitable.

For European projects, S235JR and S355JR correspond roughly to Q235B and Q345B. Japanese standards use SS400 and SM490. JIS SS400 is common for general structural work in Asia, while SM490 is chosen for welded bridges and ships. ST37-2 is the German designation frequently encountered in machinery and automotive applications. Knowing these equivalents helps procurement teams substitute material when a specific standard is temporarily unavailable.

Structural shapes from hot rolled material

Hot rolled plate is not the only product derived from the process. Structural shapes such as hot rolled H-beams are produced from blooms and billets in the same family of mills. H-beams carry heavy vertical loads across long spans and are widely used in multi-story buildings, industrial sheds, and infrastructure projects. A closely related product is the SS400 Q235B Q345B I beam, which is used for lighter framing, purlins, and support members where the wide flange of an H-beam is not necessary.

Coating and protection

Bare hot rolled plate will rust quickly if exposed to humidity. Common protection methods include shop primer, hot-dip galvanizing, and painting after surface preparation. When plates are used outdoors, weathering grades with small copper, chromium, and nickel additions can develop a stable oxide layer that reduces maintenance. For marine or chemical environments, thicker coatings or alternative materials such as stainless steel should be evaluated.

Cutting and processing

Hot rolled plates are usually cut by flame, plasma, laser, or waterjet depending on thickness and edge quality requirements. Thinner plates are frequently sheared. When tight flatness or close dimensional tolerance is needed, additional leveling or machining should be specified at the time of order. Zhishang Steel provides cutting and processing services to reduce fabrication time at the customer facility.

Order considerations

When ordering hot rolled plate, clearly state the grade standard, thickness range, width, length, quantity, surface condition, and any required test reports. Mill certificates should confirm chemical composition, mechanical properties, and dimensional tolerance. For pressure vessel or offshore applications, third-party inspection and impact testing at specified temperatures are often mandatory.

Summary

Hot rolled steel plate selection is primarily a balance of strength, weldability, and cost. Q235B and A36 cover most general structural needs. Q345B, S355JR, and 16Mn add strength for heavier structures. Q215 and SS400 offer better formability for cold-formed parts. Matching the grade to the design code and environment ensures the fabricated structure performs safely throughout its intended life.