State Key Laboratory of Rolling Technology and Continuous Rolling Automation

Abstract Two kinds of offshore platform steels without rare earth elements and with trace rare earth elements lanthanum (less than 20ppm) were selected as the research objects. The corrosion of the two groups of steels was simulated by salt spray corrosion chamber. The macro/micro corrosion morphology of the two groups of steels was studied by scanning electron microscope; The periodic immersion corrosion experiment was used to accelerate the corrosion, the weight loss method was used to study the corrosion kinetics, and the morphology of corrosion rust layer was observed by scanning electron microscope; The composition and content of corrosion products were analyzed by XRD; The electrochemical behavior of the steel after corrosion was analyzed by electrochemical polarization curve and Nyquist diagram. The results show that the addition of trace rare earth elements lanthanum (less than 20ppm) can reduce the corrosion rate and corrosion current of two kinds of offshore platform steel with different strength, and the corrosion layer is more compact, which is a corrosion product with protective performance α - FeOOH increased. The addition of trace rare earth elements lanthanum (less than 20ppm) improves the corrosion resistance of two kinds of offshore platform steels with different strength.

Abstract Two groups of low carbon steel with ultra-micro amount (less than 20 ppm) rare earth lanthanum and without rare earth element were taken as experimental objects. Continuous cooling transformation curves of two kinds of low carbon steels were drawn by Formaster-F II automatic phase transformation instrument, alloy phase method and hardness method. According to the measured CCT curve, the microstructure and hardness of low carbon steel under different cooling rates were studied and analysed. The results show that the addition of ultra-trace rare earth elements can increase the A c1 and A c3 points of low carbon steel by about 20 °C; the starting temperature of martensite transformation M S point decreased by 19 °C, and the end temperature M f point decreased by 6 °C; at low cooling rate, the transformation range of ferrite is increased and that of pearlite is decreased; the starting temperature of bainite B s point increased by 20 °C, and the end temperature of bainite B f increased by 13 °C; at low cooling rate, the ferrite transformation range becomes larger, while at high cooling rate, the ferrite transformation range becomes smaller.

Abstract The effects of different cooling rates (0.05 °C s −1 , 0.1 °C s −1 , and 0.2 °C s −1 ) on the microstructure and mechanical properties of 1000 MPa grade automobile steel for cold forming after two-phase annealing were studied. The microstructure of the experimental steel was observed by SEM and TEM, and its mechanical properties were tested by a universal tensile testing machine. The results showed that by increasing the cooling rate of two-phase annealing, more massive retained austenite, more uniform and fine ferrite, better elongation and higher ultimate tensile strength of steel can be obtained, so as to obtain better production of tensile strength and total elongation (product of tensile strength and elongation, PSE). The final result shows that after the test steel is quenched at 800 °C + 10 min and annealed in the two-phase region at 690 °C + 10 min, the faster the cooling rate, the better the mechanical properties. The mechanical properties of the steel plate are the best when the cooling rate reaches 0.2 °C s −1 , and PSE can reach 27.44 GPa·%.

Abstract The friction and wear performance, wear morphology and friction-induced subsurface microstructural characteristics of 18Cr-8Ni austenitic stainless steels with coarse-grained (CG), heterogeneous ultrafine-grained (HUFG), and nano/ultrafine-grained (NG/UFG) microstructures after dry sliding wear under room temperature were studied. The results reveal that HUFG steel with a good match between hardness and plasticity exhibits the best wear performance, followed by CG steel, while NG/UFG steel with the highest hardness exhibits the poorest wear performance. From the element distribution map, the contents of O and Si in the delamination and wear debris are relatively high. O is relatively evenly distributed on the whole wear surface of HUFG steel, and there is a continuous oxide layer on its wear surface. After the wear test, the hardness increment near the wear surface of the CG sample is the largest, and the depth affected by sliding is the largest, followed by the HUFG sample, and those of the NG/UFG steel are the smallest. The repeated frictional shear stress causes the formation of cracks between the mechanical mixed layer and the plastic deformation layer, and the continuous expansion of cracks can help oxygen elements diffuse deeply, causing the deformation layer materials to fall off.

In the roll-bending forming process, the manual or open-loop control of the current roll bending machine leads to poor synchronization of rolls, and the cumulative deviation will increase over time. The distributed cooperative control of multiple rollers has become the main trend of the roll-bending process development, and the position tracking strategy of the rollers has gradually become a research hotspot in the roll-bending field. Therefore, this paper proposes a distributed position tracking strategy for multi-rollers in roll bending forming based on multi-agent cooperative control. The dynamic model of the roller is established and the position tracking error system of the roller is defined, and the distributed control method of the roller with multi-agent cooperation is proposed. The backstepping method is used to design the virtual control input and the actual control input, and an observer is designed to estimate the dynamic influence of the unmodeled dynamics. In addition, the stability and boundedness of the tracking error are proved by Lyapunov stability theory. The effectiveness of the strategy is verified by simulation result. This strategy replaces the traditional method of manually adjusting the rollers to coordinately control the relative position of each roller, so as to improve the position control accuracy and make the left and right lower rollers run more smoothly.