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Products and solutions, 2009-12-17, 03:31 PM

New steel grades from Hoesch Hohenlimburg

The family of micro-alloyed fine-grained structural steels has four new members. They are HSM 550 HD, HSM 600 HD, HSM 650 HD and HSM 700 HD. HSM stands for Hoesch Special structural steels Micro-alloyed and HD is the abbreviation for high-ductility, which means they have very good cold-forming properties. The numbers indicate the minimum yield strength in megapascals (MPa) and identify the new materials as ultra-high-strength steels.

The HD grades are used by auto manufacturers and their suppliers to make complex precision-blanked and stamped parts of optimized weight. The high strength of the materials means components can be designed with reduced wall thickness. In addition, heat treatment is no longer needed to increase strength. The HD materials are used among other things for seat back adjusters. These are precision ring gear parts which have to withstand torsion forces of around 2,000 Newton meters, show what HD grades from Hoesch Hohenlimburg are capable of.

While most of the steel materials produced today with yield strengths of 500 - 700 MPa and good forming properties are multi-phase steels, the HD grades from Hoesch Hohenlimburg are single-phase. The materials, which the company has patented, owe their superior forming properties to their virtually pearlite-free fine-grained microstructure. Compared with standard grades, their carbon content is significantly lower. The associated loss of strength is offset by micro-alloying elements such as molybdenum, niobium and titanium.

These elements develop their potential during the thermo-mechanical rolling of the steels in the narrow strip mill at Hoesch Hohenlimburg GmbH: Precise temperature control in the walking beam furnace and finely balanced rolling forces in the roughing stand and finishing trains of the narrow strip mill initiate a process which causes the micro-alloying elements to form tiny precipitations measuring just millionths of a millimeter which give the HD grades the required strength.

Hoesch Hohenlimburg supplies the HD grades as Hohenlimburg narrow strip, i.e. hot-rolled strip in widths of up to 685 millimeters and thicknesses of 1.5 - 16 millimeters. Hohenlimburg narrow strip offers exceptionally low thickness tolerances – comparable to cold strip – and optimum surface quality.

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