Microstructures And Mechanical Properties Of Vanadium Micro-alloyed Cold Drawn Cord Steel

The cord steel is mainly used in the skeleton of radial tires. Along with the development of the modern production technology, there are increasing demands for higher performance and production of the cord steel wires. Researchs on key process and phenomenon during cord steel drawing which cause quality problems easily are needed, such as heat treatment and cementite decomposition in heavily cold drawn steel wires. Therfore, vanadium alloyed cord steels were investigated with torsion, tensile, micro-hardness testing machine, optical microscope(OM), scan electronic microscope(SEM) and vibrating sample magnetometer (VSM) in this thesis. The microstructure evolution and property changes of the cord steel were studied after various heat treatments and drawing processes. The main research contents and results are as follows:<I> The evolvement of the interlamellar spacing, pearlite colony size and sorbite proportion for70and80-grade tire cord steel rod were studied drawn from1.13to0.205mm in diameter according to the traditional process. Variation of the cementite content and mechanical properties after severe plastic deformation (s=3.41). The results show pearlitic lamellae are straight and there is no apparent proeutectoid cementite in V added tire cord steel. Grains are refined in transverse section and tensile strength and torsion laps are increased after drawing. Cementite are bent and dissolved with strain increasing.<Ⅱ>The lab results of different austenitic and sorbitic temperature indicate that pearlite colony become larger and hardness is increased as austenitic temperature is increased; at the same austenitic temperature, hardness is higher at500℃than600℃.<III> The results of torsional test show that torsion laps are reduced with strain increasing and V addition makes torsion performance stable. The torsional property is extremely sensitive to inclusions and cracks.