Vanadium-nitrogen Microalloyed Steel Microstructure And Properties Of Hard-wired 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 70# 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 of V-N micro-alloy hard wire rods 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 interlamellar spacing of pearlite reduce. Therefore, tensile strength, hardness and toughness of test samples are increased a lot. Such as, compared to normal hard wire rods, tensile strength rises 90~140Mpa for wire rods with 0.12% V and 0.02 N, its reduction of area rises 13.2~56.8%, austenite grain gradation is 9, and rises 3 gradation.It is proved that all samples' deforming ratio should be controlled to below 65% in high temperature deforming process by thermal simulating experiment. When the high temperature deforming ratio is more than 65%, although tensile strength of test sample is increased, plasticity is decreased badly. Additionally, high temperature thermal plasticity become worse for steel with high content of V (0.21%).Higher content of nitrogen is benefit for increasing strength and toughness for V-N micro-alloyed hard wire rods steel.It is considered that the V-N micro-alloy high carbon wire rods obtain the high strength and toughness mainly due to grain refining and precipitation strengthening.