Carbon-Manganese (CMn)

Carbon-Manganese High Strength Steel

Carbon and manganese are the two most cost-effective alloying additions to increase strength.  While effective at strengthening, these additions reduce ductility and toughness, and make welding more challenging.

The practical usage of these grades typically limits the highest strength to no more than 280 MPa.  Adding enough carbon and manganese to achieve higher strength results in a product without sufficient ductility for challenging applications, low toughness, and welding difficulty. These products sometimes are referred to as structural steels, and achieve their strength from the mechanism of solid solution strengthening.

Until the commercialization of High Strength Low Alloy steels, the CMn approach was the only option for users to obtain a high strength sheet metal.

Some of the specifications describing uncoated cold rolled Carbon-Manganese (CMn) or structural steels are included below, with the grades typically listed in order of increasing minimum yield strength and ductility. Different specifications may exist which describe hot or cold rolled, uncoated or coated, or steels of different strengths. Many automakers have proprietary specifications which encompass their requirements.  Note that ASTM terminology is based on minimum yield strength, while JIS and JFS standards are based on minimum tensile strength.  Also note that JIS G3135 does not explicitly state that these grades must be supplied with a C-Mn chemistry.  An HSLA approach is satisfactory as long as the mechanical property criteria are satisfied.

  • ASTM A1008M, with the terms Grade 25 [170], Grade 30 [205], Grade 33 [230] Type 1, Grade 33 [230] Type 2, Grade 40 [275] Type 1, Grade 40 [275] Type 2, Grade 45 [310], Grade 50 [340], Grade 60 [410], Grade 70 [480], and Grade 80 [550] A-25
  • JIS G3135 with the terms SPFC340, SPFC370, SPFC390, SPFC440, SPFC490, SPFC540, and SPFC590 J-3
  • JFS A2001, with the terms JSC340W, JSC370W, JSC390W, and JSC440W J-23