A588 Grade B Heat Treatment Process for Weathering Steel

The process of heat treating A588 Grade B weathering steel is important to alloy in order to produce its signature rust-like color. With heat treatment, the steel develops a layer of oxide which adds to the corrosion resistance of the steel, as well as its aesthetic appeal. The heat treatment process is divided into two main steps: preheating and stress relieving.

1. Preheat: Preheat is the initial step of the heat treatment process. The preheating process is designed to bring the steel up to the correct temperature and to slow down the cooling rate of the steel in order to prepare it for stress relieving. The preheating temperature range for A588 Grade B weathering steel is between 250°F and 400°F (120°C and 204°C). For thicker sections of steel, higher preheating temperature is recommended due to the increased mass of the steel that slows down the cooling rate.

2. Stress Relieving: After the preheat step is completed, the steel is then ready for stress relieving. Stress relieving is necessary to achieve the desired oxidation pattern. Stress relieving is done at temperatures below the tempering temperatures, typically around 1000°F (538°C). The uniform heating of the steel reduces the tensile stresses of the steel that may have resulted from welding or bending. Stress relieving will produce a uniform oxide layer on the surface of the steel.

Following the stress relieving process, the steel is typically air cooled naturally, with no forced cooling. Air cooling helps to ensure that the oxide layer on the surface of the steel remains intact.

The heat treatment process is an important step in the fabrication of A588 Grade B weathering steel. Through this process, the steel is properly conditioned to achieve its desired rust-like appearance during exposure to the elements. It is imperative that the heat treatment process be done with precision and care, as variations in the process may affect the properties of the steel and its appearance.