Is ASTM A36 considered an alloy steel or a carbon steel?

ASTM A36 is unequivocally classified as a carbon steel, specifically a mild or low-carbon steel. The distinction is based on its chemical composition. According to standard definitions, carbon steels are those where the specified minimum for copper does not exceed 0.40% (or 0.60% for certain elements), and no minimum content is specified for other alloying elements like chromium, nickel, molybdenum, etc. The primary alloying elements in A36-carbon and manganese-are within the limits for standard carbon steels (manganese content is below 1.65%). It does not rely on significant additions of elements like chromium or nickel to achieve its properties, which is the hallmark of alloy steels. Therefore, its strength is derived primarily from its carbon content and the hot-rolling process, not from deliberate, substantial alloying.