A36 steel is a mild carbon steel with a very simple chemical structure. Because the chemical structure is so simple, the steel is cheaper to manufacture than more specialized steels, resulting in A36 being used in a wide range of industries. However, its strength and other structural properties degrade sharply at high temperatures, where a more specialized steel would not.
A36 steel has a carbon content of only .26 percent, classifying it as a low-carbon steel. Other elements in the alloy include manganese (.75 percent), sulfur (less than .05 percent) and phosphorous (less than .04 percent). This simple chemical composition translates into a steel with moderate strength and lower melting point in comparison to other steels.
Properties at High Temperature
According to a Federal Emergency Management Agency (FEMA) study, A36, while an excellent structural material, loses much of its strength, rigidity and tensile strength at high temperatures. According to graphs in the FEMA study, A36 has a maximum strain measurement of more than 70 kilograms per square inch at 200 degrees Celsius. However, at 600 degrees Celsius, still far below the melting point, the maximum stress in the steel is about 23 ksi. Yield strength and overall strength of A36 follows a similar pattern of sharp degradation at higher temperatures.
The poor high-temperature performance of A36 means it is a poor choice for structural applications where fire or high heat are a possibility, such as very large buildings. However, the properties of A36 at moderate to low temperatures means it is an excellent choice for outside applications, such as structural steel in bridges or roads, where a higher-priced steel with better performance is not necessary.