The influence of wire rod cooling process on the performance of steel wire
Defects in mechanical properties of steel wire can be eliminated or improved by controlling cooling. In order to study the influence of the structure and mechanical properties of the wire rod on the finished steel wire, Canadian scientists and technicians adjusted the process parameters of the wire rod cooling process to improve the performance of the wire. These process parameters include:
Enough cooling capacity;
Able to maintain the high temperature during the wire rod rolling process;
Long cooling distance and flexible conveyor speed.
There are four main factors affecting the cooling of wire rod on the Steyrmore production line:
Spinning temperature affects both the composition and thickness of the scale. At about 650 degrees Celsius, FeO and Fe3O4 begin to form. FeO accounts for about 65%, Fe3O4 accounts for about 35%; at 800 to 900 degrees Celsius, FeO accounts for about 95%, Fe3O4 accounts for about 5%. After 900 degrees Celsius, as the temperature increases, the FeO content gradually decreases, and the Fe3O4 content gradually increases. At about 920 degrees Celsius, Fe2O3 begins to form. As the temperature increases, the Fe2O3 content gradually increases.
The speed of the conveyor belt determines the spacing of the coils. The speed is fast, the spacing is large, the cooling is fast, and the tensile strength is high. Cooling efficiency, fan power, and covering on the conveyor belt also have an important influence on the cooling of the wire rod.
Through the different combinations of 4 factors, two solutions of fast cooling and slow cooling can be obtained. Fast cooling is achieved by turning on all fans, the conveyor belt is fast and the cover is opened; slow cooling is achieved by stopping the fans, the conveying speed is slow, and the cover is closed.
With the introduction of electric arc furnaces, the increase of residual elements (Cu, Ni, Cr, Mo) has a significant impact on the production of high-quality products, especially for low-carbon steel, higher residual element content increases the solid solution strengthening of steel Significantly.
In order to prove that slow cooling can reduce the tensile strength of the final product, the low carbon steel with different residual element content is subjected to different cooling treatments and drawn to the same specification. The strength of the wire rod at the normal cooling speed increases by 9Ksi (1Ksi = 6.89 N/mm2).
After hot-rolled wire rods obtained with different cooling speeds are drawn to steel wires of the same diameter and spheroidizing annealing, the tensile strength of slow-cooling wire rods is 5% lower than that of fast-cooling wire rods.
For steel wires that require low tensile strength and good rust removal performance, moderate cooling can achieve a better combination of the two properties. The tensile strength of moderate cooling is 7% lower than that of rapid cooling.
The application of rapid cooling is where more uniform tensile strength is required. The application of rapid cooling to medium carbon steel may also obtain similar tensile strength of lead-quenched wire rod. The tensile strength fluctuation of the carbon steel wire rod in a circle was measured, and the results showed that the slow cooling fluctuation was 5.4%; the rapid cooling fluctuation was 1.3%; the lead quenching fluctuation was 1.9%.