High Carbon Tool Steels
Tools are implements that are used to shape, deform or cut other materials. They are largely made in steel, though other alloys have also been developed. The common tool steels contain C, W, Cr, Mo, V, Mn, Si in the range of 0.6 to 1.0%. They have hardness and wear resistance. For shock resistance C is restricted to 0.5%. W and Mo between 2 to 18% provide high temperature strength. V between 0.1 to 2% enhances hardenability while Si adds to toughness.
Though the tool and die steels are not produced in as large amount as other steels are, yet they are industrially very important. A variety of steel differing widely in composition and treatment is used for varying purposes. They are used in such operations as cutting, shearing, forming and rolling. These operations require adequate hardness, strength, toughness, wear resistance and heat resistance. For many purposes near-eutecoid and hyper-eutectoid steels have been used for metal cutting but these plain carbon steels have tendency to loose hardness through tempering when rise in temperature occurs during cutting. To overcome this problem high steep tool steel have been developed. The 18.4.1 type of high steel contains 18% W, 4% Cr and 1% V. These steels retain sufficient hardness due to carbide formation which is a complex compound Fe4W2C. A tough matrix is provided by Cr. These steel may retain hardness upto a temperature of 500oC.
When 5-12% of cobalt is also added, in addition, the hardness through a secondary hardening process is increased at temperature around 600oC.