Abstract: Tensile strength, chemical composition and microstructure of SWRS82B steel wire rod in the same circle were analyzed, and the reason for the large fluctuation of stensile trength was found as the presence of abnormal microstructure at the lapping point. The reason for the formation of abnormal microstructure was identified by analyzing the continuous cooling process of the SWRS82B steel wire rod through thermal simulation experiments and detecting the cooling condition of Stelmor. The results show that the addition of V element in the composition causes the separation of pearlite and bainite transformation zones. When the cooling rate is over or equals to 3 ℃/s and the temperature is below 550 ℃, the bainite transformation occurs. Due to the unreasonable set of Jialing device (a device which is installed on the Stelmor, and is used to adjust the wind distribution between the lapping point and non-lapping point) and the higher wind speed at the lapping point, the supercooled austenite undergoes a partial low-temperature transformation, and the phase transformation products are pearlite and bainite, resulting in significant fluctuations of the tensile strength in the same circle. The Jialing device and fan air volume are adjusted to reduce the cooling speed of the lapping point, the tensile strength fluctuation in the same circle is reduced from 102 MPa to within 49 MPa, and the tensile strength qualification rate is increased from 88% to 100%.

Key words: SWRS82B steel wire rod, fluctuation of tensile strength, thermal simulation test, abnormal microstructure, Jialing device, process optimization