Có nhiều tổ chức định nghĩa khác nhau về thép carbon thấp, thép carbon cao. Mặc dù từ “thấp, cao” này nó có vẻ hơi ‘mơ hồ’ nhưng chúng ta lại thường nghe người ta nói đến trong thương mại và kỹ thuật. Khi nói tới “thấp cao” thì có lẽ người không chuyên có thể đặt ngay cây hỏi trong đầu “Thế nào là thấp, thế nào là cao?”. Bởi lẽ, mà lại có nhiều khái niệm thấp cao khác nhau thì cũng hơi khó trả lời. Tui đi dạo dạo thì thấy AISI (American Iron and Steel Institute, tạm dịch là Viện sắt thép Mỹ) có cách phân loại dưới đây, mà tui cho là đáng tin cậy hơn hết. Tui trích dán phân loại này dưới đây để ai cần thì tham khảo (NHĐ).
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Classification of Carbon and Low-Alloy Steels
The American Iron and Steel Institute (AISI) defines carbon steel as follows:
As a group, carbon steels are by far the most frequently used steels. More than 85% of the steel produced and shipped in the United States is carbon steel.
Low-carbon steels contain up to 0.30% C. The largest category of this class of steel is flat-rolled products (sheet or strip), usually in the cold-rolled and annealed condition. The carbon content for these high-formability steels is very low, less than 0.10% C, with up to 0.4% Mn. Typical uses are in automobile body panels, tin plate, and wire products.
For rolled steel structural plates and sections, the carbon content may be increased to approximately 0.30%, with higher manganese content up to 1.5%. These materials may be used for stampings, forgings, seamless tubes, and boiler plate.
Medium-carbon steels are similar to low-carbon steels except that the carbon ranges from 0.30 to 0.60% and the manganese from 0.60 to 1.65%. Increasing the carbon content to approximately 0.5% with an accompanying increase in manganese allows medium carbon steels to be used in the quenched and tempered condition. The uses of medium carbon-manganese steels include shafts, axles, gears, crankshafts, couplings and forgings. Steels in the 0.40 to 0.60% C range are also used for rails, railway wheels and rail axles.
High-carbon steels contain from 0.60 to 1.00% C with manganese contents ranging from 0.30 to 0.90%. High-carbon steels are used for spring materials and high-strength wires.
Ultrahigh-carbon steels are experimental alloys containing 1.25 to 2.0% C. These steels are thermomechanically processed to produce microstructures that consist of ultrafine, equiaxed grains of spherical, discontinuous proeutectoid carbide particles.
Source: http://steel.keytometals.com/Articles/Art62.htm
