Utilization of high strength steels

HIGH STRENGTH STEELS

The early steels developed were classified as copper-nickel-phosphorus and chromium-silicon-copper. These elements improved corrosion resistance. Other elements, such as molybdenum, manganese, and a grain refiner enhanced their strength with minimum loss in ductility and toughness.

These steels were manufactured to 12 maximum carbon and were originally furnished as hot rolled sheets and strip. They welded very satisfactorily, oven by spot and seam welding, and could be fabricated by bending and moderate drawing. Development of these steels enjoyed such success that demand soon arose for carbon steels to meet the same strength levels where corrosion resistance was not a prime factor. High-strength low-alloy and high strength carbon steels became available in plate and structurals aswell as in sheets. Some hot rolled steels containing columbium or vanadium are available up to 65,000 psi yield strength. Further research and development have now produced weldable, quenched and tempered carbon steels with minimum yield strengths up to 80,000 psi and quenched and tempered low alloy steels with 100,000 psi minimum yield strength. These steels not only provide higher strength than the hot rolled steels, but improve toughness at low temperatures.

Round and rectangular tubular products as well as plates and bars ore available at these strength levels.

UTILIZATION OF HIGH STRENGTH STEELS

There are obvious advantages in using high strength steels for applications where pay load increase, dead weight reduction are of prime concern. There are also many instances of low ambient temperature applications where heat-treated high strength steels are needed.

Besides the economical advantage of getting more strength per pound of steel, use of high strength steels offers other advantages to the designer. For one thing, it permits designs that would otherwise not be practical, such as long-span parallel-chord trusses and uniform depth girders. It simplifies overall design and makes these structures less complicated. Although fabrication may be more involved by use of several different types of steel; overall fabrication generally is simpler because members are lighter and consist of fewer pieces. Because these structures are simpler, streamlined and less complicated, they are also more pleasant to look at and are worthy examples of the builder's art. There are a few pitfalls that must be avoided when designing with high strength steels and there must be a thorough understanding of these steels. A structure is designed against failure in one or more modes. Buckling and excessive deflection are functions of the modulus of elasticity and must be guarded against by use of low slenderness ratios and high moments of inertia. Fatigue often controls the design of structures. When stress concentrations are involved, such as at welds, fatigue strength doesn't necessarily increase in proportion to yield or tensile strength of the steel. Thus designers need to consider the ways in which high strength steels can be disposed in a structure to greatest advantage. Notch toughness, is an important factor in selecting steel for a structure subject to brittle fracture. Many of the high strength steels possess a high degree of notch toughness and are actually less apt to fail in a brittle manner than some lower strength steels. However, higher design stresses demand greater notch toughness.

manufactured, rolled sheets, strip, satisfactorily, seam welding, drawing, prime factor, tempered carbon steels, rectangular tubular products, designed,obvious advantages, heat-treated high strength steels, long-span parallel-chord trusses, streamlined, pitfalls, buckling, excessive deflection, notch toughness, brittle fracture.

tubular, loss, parallel-chord, art, ratios, ambient,

sheets, obvious, yield, originally, prime, structures