Study On Microstructure And Mechanical Properties Of Heavily Cold Drawn Pearlite Steel Wires

Microstructure and mechanical properties evolution of 65Mn and SWRH82B heavily cold drawn pearlite steel wires were mainly studied in this paper. The investigation involves: (1) The drawing processes and mold distribution rules of 65Mn and SWRH82B heavily cold drawn pearlite steel wires; (2) Effect of heavily cold drawn plastic deformation on mechanical properties of 65Mn and SWRH82B pearlite steel wires, and the relationship between tensile strength and hardness; (3) The strengthening mechanism of heavily cold drawn plastic deformation of 65Mn and SWRH82B pearlite steel wires; (4) Effect of heavily cold drawn plastic deformation on microstructure of 65Mn and SWRH82B pearlite steel wires; (5) The thermodynamics and dynamics conditions of cementite dissolution in heavily cold drawn pearlite steel wires.The results show that:(1) Heavily cold drawn plastic deformation of 65Mn and SWRH82B pearlite steel wires could be realized with reasonable drawing velocity, lubrication condition and mold distribution mode. And the true strains of 65Mn and SWRH82B pearlite steel wires were respectively above 3.0 and 5.0.(2) The tensile strength and hardness of 65Mn and SWRH82B pearlite steel wires remarkably increased with cold drawn plastic deformation, and that was tied up with the strengthening mechanism of heavily cold drawn plastic deformation. The most tensile strength could respectively reach 3730MPa and 2712MPa.(3) The microstructure of 65Mn and SWRH82B pearlite steel wires can be refined gradually with cold drawn plastic deformation. Interlamellar spacing of pearlite reduced by degrees in the drawing processes. The pearlite groups rotated and tropisms tended to be consistent with the direction of the drawing axis. The lamellar cementite was broken and refined after deformations of cutting, bending and drawing, and the dissolution of cementite occurred severely with heavily cold drawn plastic deformation. The tensile strength and hardness appeared fluctuant changes because of cementite dissolution in heavily cold drawn pearlite steel wires.(4) In the end, the drive of cementite dissolution in heavily cold drawn pearlite steel wires mainly depended on three factors from thermodynamic and kinetic analysis: the first factor was the lamellar cementite thinning and instability; the second factor was the increase of dislocation density and the contact area between cemmentite and dislocations which were located mainly at the interface; the third one was the binding enthalpy of carbon and dislocation in ferrite exceeded the binding enthalpy of carbon and iron atoms in cementite, and that was one reason of cementite dissolution.