Friday, January 22, 2010

Basic Steel Grade and Structural Steel

Structural Steel includes all steels not used for the production of tools. As per DIN 17100, ordinary structural steels are basic and unalloyed high grade steels for buildings, bridges, containers, automobiles and machines on account of their tensile strength and elastic limits.

Sections, rods wire rods, flat pieces and forging made of this class of steel may be used in welded, forged and bolted structural parts. As the carbon content rises, tensile strength, hardness, harden ability and wear resistance increase. At the same time, however, breaking stretch cold formability and notch toughness decrease. Machine characteristics, weld ability and forge ability also worsen.

Quality Classes
Quality class is specified by the code number, -2 and -3 at the end of the designation code. The quality class -1, Bessemer steel (Thomas Gilchrist steel) is no longer produced.

The steel of group 3 differ from those of group 2, principally in that they must full higher standards regarding resistance to brittle fracture. The example of this kind steel are St 44-2 and St 44-3.

The impact test for quality class 2 is 275 at 0oC, whereas class 3 must fulfill this standard at -20oC. Steel of group 3 are therefore also better suited to welding failure, in turn necessitate that special requirements as to method of deoxidation, chemical composition of steel and states of metal treatment must be fulfilled for this steel. The example of these steel is St 44-2.

Method of deoxidation R, chemical composition: 0 – 0.5% P, 0.00s0% S, 0.009% N, state of treatment U. The example of this steel is St 44-3.

Method of deoxidation RR, chemical composition: 0 – 0.4% P, 0.04% S, 0.00% N, state of treatment N.

Type of Steels:


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