Coil spring steel

Abstract

Disclosed herein is a coil spring steel, comprising, by weight, carbon (C): about 0.51% to about 0.57%, silicon (Si): about 1.35% to about 1.45%, manganese (Mn): about 0.95% to about 1.05%, phosphorus (P): from about 0.003% to about 0.015%, sulfur (S): from about 0.003% to about 0.010%, chromium (Cr): from about 0.70% to about 0.90%, copper (Cu): from about 0.30% to about 0.40%, vanadium (V): from about 0.10% to about 0.15%, aluminum (Al): from about 0.010% to about 0.040%, titanium (Ti) from about 0.010% to about 0.033%, molybdenum (Mo): from about 0.05% to about 0.15%, nickel (Ni): from about 0.25% to about 0.35%, and a balance of iron (Fe) and inevitable impurities to form 100%.

What is claimed is: 
     
         1 . A coil spring steel, comprising, by weight, carbon (C): from about 0.51% to about 0.57%, silicon (Si): from about 1.35% to about 1.45%, manganese (Mn): from about 0.95% to about 1.05%, phosphorus (P): from about 0.003% to about 0.015%, sulfur (S): from about 0.003% to about 0.010%, chromium (Cr): from about 0.70% to about 0.90%, copper (Cu): from about 0.30% to about 0.40%, vanadium (V): from about 0.10% to about 0.15%, aluminum (Al): from about 0.010% to about 0.040%, titanium (Ti): from about 0.010% to about 0.033%, molybdenum (Mo): from about 0.05% to about 0.15%, nickel (Ni): from about 0.25% to about 0.35%, and a balance of iron (Fe) and inevitable impurities to form 100%. 
     
     
         2 . The coil spring steel of  claim 1 , having a grain size of about 29 μm or less. 
     
     
         3 . The coil spring steel of  claim 1 , wherein the coil spring steel is molded into a product that has a total decarburized layer depth of about 50 μm or less and a ferrite decarburization depth of 1 μm or less. 
     
     
         4 . The coil spring steel of  claim 1 , wherein the coil spring steel is molded into a product that has a fatigue life of about 800,000 cycles or greater and a corrosion fatigue life of about 500,000 cycles or greater. 
     
     
         5 . The coil spring steel of  claim 1 , having a tensile strength of about 2150 MPa or greater. 
     
     
         6 . The coil spring steel of  claim 2 , wherein aluminum (Al) is contained in an amount of from about 0.010% to about 0.030% to prevent a coarse inclusion from being formed and the coil spring steel is molded into a product that has a fatigue life of about 850,000 cycles or greater and a corrosion fatigue life of about 550,000 cycles or greater. 
     
     
         7 . The coil spring steel of  claim 2 , wherein titanium (Ti) is contained in an amount of from about 0.010% to about 0.030% to prevent a coarse precipitate from being formed, and the coil spring steel is molded into a product that has a fatigue life of about 850,000 cycles or greater and a corrosion fatigue life of about 550,000 cycles or greater.