Tension-tension fatigue properties of hot rolled and cold rolled strips with same contents and sizes were measured by using group test method at room temperature in air. The results showed that the fatigue properties of the hot rolled strips were obviously higher than those of the cold rolled strips. The hot rolled strips with similar or higher tensile strength exhibited superior fatigue property over the cold rolled strips. Fracture morphologies observed using scanning electronic microscope （SEM） showed that the hot rolled strips exhibited larger fracture areas, indicating a slightly lower plasticity, and more even fracture microstructure and stable properties. It is feasible and reliable to replace cold rolled strips with hot rolled strips.
LI Sheng-liLI NaPENG Xing-dongLU Xiang-yuLI Ji-guang
Low carbon steels with B and P additions were remelted by electromagnetic levitation and solidified in a vacuum drop tube. The droplet volumes were set to be 2 mm × 2 mm ×2 mm （TM） and 5 mm ×5 mm× 5 mm （FM）, respectively. The microstructure of rapidly solidified steel droplets （cooled in silicon oil） with P and both B and P addition was observed. The microstructures of B-bearing droplet samples were more uniform than those of B-free ones, for both TM and FM samples. The distribution of C and P along the diameter of each sample was detected. The well-distribution of C and P was detected in B-bearing droplet samples. So it could be deduced that B was also well distributed in the steels. It was B atoms that promoted the well-distribution of C and P, which further improved the uniformity of microstructure under the condition of rapid solidification. The micro-hardness of B- bearing samples was higher than that of B-free samples, and the hardening mechanism was discussed in detail.
Na LiJunwei ZhangQian XuLulu ZhaiShengli LiJiguang Li
