The hot rolling technoledge of JIS G 3125 SPA-H weatherproof steel plate for container

SPA-H weatherproof steel plate is a kind of weather-resistant steel plate. The steel grade adopts the Japanese steel grade SPA-H. Its chemical composition, mechanical properties, thickness, and width deviations are required to comply with the Japanese standard JISG3125-2004.

Weather-resistant steel plate SPA-H has good atmospheric corrosion resistance, and also has the characteristics of high temperature, abrasion, forming, fatigue, toughness, and ductility; it can be used in bare, thinned, or simplified coating applications.

SPA-H is rust-resistant, can make components thinner, reduce consumption, resist atmospheric corrosion, extend life, and has the characteristics of labor-saving and energy-saving, which will benefit component manufacturers and users.

The container manufacturing industry has strict requirements for the atmospheric corrosion resistance of steel materials. In recent years, the demand for JIS G 3125 SPA-H weathering steel plates has been growing rapidly. These steel plates are mainly produced by hot rolling technology.

During production, the billet for JIS G 3125 SPA-H weathering steel plate is heated and fed into a 1500 mm hot strip mill. Since the copper (Cu) content in SPA-H steel is relatively high, copper brittleness may occur during heating.

If cracks are present on the surface of the billet, they can expand and cause further cracking. Therefore, the heating process follows the principle of "high-temperature fast burning":

The billet is heated in a reducing or neutral atmosphere.

The heating speed is increased, and the temperature of the heating section is raised.

Excessive oxidation is avoided to reduce copper concentration on grain boundaries and the billet surface.

This prevents edge cracking during the rolling process and ensures stable quality. The billet temperature is controlled at 1160–1210°C, with a heating time of no less than 80 minutes.

SPA-H steel is relatively hard, and the rolling specifications of JIS G 3125 SPA-H weathering steel plates are usually thin. As a result, the finishing mill requires large rolling force and current, which may lead to accidents. To reduce risks, the thickness of intermediate billets is appropriately adjusted. Based on finished product specifications, the intermediate billet thickness is generally selected at 26–29 mm.

After strip rolling is completed, the steel plate undergoes intensive water cooling. The front section cooling is accelerated, while the rear section carefully controls the coiling temperature. The coiling temperature is maintained at 620 ± 15°C to ensure product stability.