Hard-wired Nitrogen Steel And Vanadium Microalloying And Controlled Rolling And Cooling Process Research

The demand of high performance wire rods makes micro-alloying wire rods' exploitation necessary in our country. In this paper, influences of V-N micro-alloying on hard wire rods' structure properties were researched.High-carbon steel wire rods 77B with different V-N content were made in the laboratory. The process of producing high-carbon steel wire rods controlled rolling and cooling was simulated by the Gleeble thermal simulating machine. Tension experiment in room-temperature was done, and microstructure was observed. The area percent of sorbite of test sample was analyzed by the Sisc-Ias metallurgical photos analysis machine. The interlamellar spacing of pearlite was measured by the S-4300 scanning electron microscopy. The precipitation of nitride and carbide was observed by the JEM-2000FX transmission electron microscopy. At last, the strengthen-toughening mechanism if a V-N micro-alloy hard wire rod was discussed, and influences of V-N micro-alloying on microstructure and properties of hard wire rods was researched.When the different content vanadium and nitrogen added in, austenite grain of wire rods refines, sorbite ratio rises and interlamllar spacing of pearlite reduce. Therefore, tensile strength, hardness and toughness of test samples are increased a lot. Such as, under the same process conditions compared to normal hard wire rods, tensile strength rises 60Mpa for wire rods with 0.088%Vand 0.011%N, its reduction of area rises 35%.The result of the thermal simulating experiment shows that if the roll-finishing temperature is 920℃and the cooling velocity after rolling is 15℃/S, the hardness and toughness of the hard wire rods will match each other best.It is considered that the V-N micro-alloyed high carbon wire rods obtain the high strength and toughness mainly due to grain refining and precipitation strengthening.