Optimization of Mechanical Properties of High-Carbon Pearlitic Steels with SI and V Additions

continuous grain-boundary cementite can form and cause THE primary requirements for high-strength wire appliembrittlement.[4,5] Nevertheless, we have found that it is cations are tensile strength, ductility, and formability. Coldpossible to use pearlitic steels with carbon contents greater drawn plain-carbon pearlitic steels have commonly been than 0.8 wt pct without the formation of a continuous cementemployed for this purpose. The properties of such drawn ite network by the addition of silicon and vanadium wires are a function of the strength and microstructure of together.[6,7] The addition of vanadium results in the fragmenthe feedstock, the amount of reduction during drawing, and tation of the grain-boundary cementite network, and the the geometry of the dies. It is known that there are limitations presence of silicon acts as a kinetic inhibitor to cementite on the strength that can be achieved in as-patented plaingrowth during transformation. The addition of vanadium is carbon steels through changes of the heat-treatment condialso beneficial to the stability of the cold-drawn pearlite. tions, amount of cold deformation, die geometry, and temperThe interstitial atoms, especially nitrogen, dissolved in ferature of the drawn wire (dynamic aging and static aging). rite may cause a significant reduction of the ductility of Although very-fine-diameter pearlite wire has achieved very the steels because of strain aging.[8,9] By the addition of high strength,[1,2] it is difficult to draw plain-carbon steels vanadium, the nitrogen dissolved in ferrite[10] can be into wire of a strength higher than 2000 MPa with a large removed by the formation of alloy carbonitrides, and the finished diameter ( 2 mm). A relatively larger rod feedstock strain aging of the wire is minimized. diameter is necessary, and this makes it difficult to achieve The addition of alloying elements challenges the conventhe rapid transformation conditions needed to produce the tional concept in wire manufacturing that the optimum finest pearlite spacings and, hence, to obtain the highest rod microstructure for producing the highest strength in the finstrengths. Also, drawing a larger cross section rod introduces ished product by cold drawing is the finest possible interlanonuniform deformation and may even cause premature failmellar spacing in pearlite. Only a very small amount of alloy ure when processing plain-carbon steels. Similar problems addition (e.g., 0.1 wt pct vanadium) may introduce extra are also found in drawing large–cross section nonferrous strengthening features such as interphase precipitation to the composites.[3] The other method to increase the strength of lamellar structure, under certain transformation conditions.[7] the wire, if a large final cross section is required, is to Therefore, it is necessary to assess what the optimum microincrease the tensile strength of the rod prior to cold drawing. structure and heat-treatment conditions are in order to This permits a desired final wire tensile strength to be achieve the required mechanical properties in such microachieved with a smaller overall drawing strain. The most alloyed steels. efficient ways to develop such a high-strength rod from the The present work was carried out in order to identify the customary pearlite microstructure are to add alloy elements role of carbon, silicon, and vanadium on the mechanical or increase the carbon content. properties of pearlitic steels. Small, high-purity laboratory