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HSLA

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HIGH strength low alloy steel
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  ã HSLA steel is specific group of steels with low alloys and has been developed to get higher mechanical ã Properties and greater corrosion resistance than conventional steels ã HSLA steels are produced in as hot rolled state withYS : 29 !  #Pa$%S : &' ! ( #paStrengthening mechanisms of HSLA steels include ã grain refinement ) ferrite* ã  precipitation ) distance between the ppts* ã dislocation substructure ã solid solution ) + #n* ã strain aging ) dislocation density*#ethods of manufacturing of HSLA steels ,alloying with small amount of strong carbide and nitride forming elements such as %i- .b- /- 0- etc ã microalloying ã controlled rolling,controlled cooling ã inclusion shape control1lassification of HSLA: ã Weathering steels : Steels which have better corrosion resistance! ã Control-rolled steels : Hot rolled steels which have a highly deformed austenite structurethat will transform to a very fine euia3ed ferrite structure upon cooling! ã Pearlite-reduced steels : Low carbon content steels which lead to little or no pearlite- butrather a very fine grain ferrite matri3! 4t is strengthened by precipitation hardening! ã Microalloyed steels : Steels which contain very small additions of niobium- vanadium-and5or titanium to obtain a refined grain si6e and5or precipitation hardening!  ã Acicular ferrite steels:  %hese steels are characteri6ed by a very fine high strengthacicular ferrite structure- a very low carbon content- and good hardenability! ã Dual-phase steels:  %hese steels have a ferrite microstruture that contain small- uniformlydistributed sections of martensite! %his microstructure gives the steels a low yieldstrength- high rate of wor7 hardening- and good formability Steels used for structural purposes must simultaneously satisfy several requirements at a competitive cost level. Several of the most important properties include:  1. Yield strength. When an external load is applied, the structure must deform elastically, that is, without permanent deformation, so that when the load is removed, the structure returns to its initialshape. Usually the maximum design load is limited to a safety factor of between 0.5 and0.8  percent of the yield strength.  2. Ductility. Ductility is a quantifiable property, normally determined by the amount of deformation prior to failure in a tensile test. f the yield strength is inadvertently exceeded, the ability of the steel to plastically deform without brea!ing is an important to avoid catastrophic failure . While the structure may no longer be functional, more serious damage, and possible loss of life, is generally avoided.  3. Toughness.  Under conditions of high impact loading and low temperatures, cracs !ay for! and propagate leading to brittle failure   little to no ductility#, an event to be avoided if at all possible.  . #eldability.  $or some structures, mechanical %oining by bolts or rivets is adequate. &owever, many structures are assembled by welding and this requires that permanent damage is not incurred during the process. Welding is a form of heat treatment, and alloying and high cooling rates e.g. by using thic! sections which allow rapid heat extraction# are generally deleterious.'lastic modulus and (oisson)s ratio are also inherent properties of structural steel and cannot be manipulated.
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