Experimental Study On Laser Bending Process And Material Feature In Transition Layer Of Laminated Plate

Stainless steel-carbon steel laminated plate (SCLP) is a relatively new laminate which combines carbon steel and stainless steel together by metallurgical bonging with a special preparation process. SCLP inherits merits of both materials and meets comprehensive performance requirements with a lower cost due to saving a lot of precious metal. Laser bending is a flexible shaping technique using the thermal stress caused by nonuniform temperature field to form the plates. What's more, the laser bending process has no contacts or external forces and can form prospective complex shape without using the molds.Based on 304/Q235A SCLP fabricated by explosion-rolling composite means, this paper studies the laser bending process of SCLP and the rule of the bending angle. In addition, the material properties in transition layer of the bending region are analyzed by means of electron micro probe analysis(EMPA) and scanning electron microscope(SEM). The main contents and results are as follows:(1) Laser bending experiment of different sizes. Taking 3 kinds thickness (1mm/1.5mm/2mm) and 3 kinds width (30mm/50mm/70mm) of SCLP as the main study objects, use Nd:YAG pulse solid laser and numerical control system to finish a series of bending experiment. The results shows that:With other parameter unaltered, the bending angle increases as the width increases, then reaches stability. While, the bending angle decreases obviously as the thickness of SCLP decreases and the variation of bending angle decreases gradually at the same time. More importantly, the changing rules between scanning times and bending angle of different thickness SCLP are not the same. Then, with regard to the phenomenon of edge effect, the control method of partial scanning is used to decrease it. At last, reasonable parameters are chosen to finish the forming of two-period corrugated sample and reached a limit angle 101°20'by two clamping steps.(2) The analysis of micro-structure in laser bending zone. The metallographic structure before and after laser bending of different thickness SCLP is studied by metallurgic microscope. The conclusions are as follows:The shape of bonding interface is a relatively linear structure along the rolling direction, and there is a certain limited grain growth region at the bonding interface nearby carbon steel layer. While the stainless steel layer mainly includes austenite grains which have smaller size on the whole. The interface of SCLP combines well after laser bending, thus proving the SCLP has a perfect bonding resistance performance. What's more, the grains in the bonding zone are squeezed and extended by the joint influence of thermal expansion and bonding stress.(3) Study on element diffusion and material property at transition layer in bending zone. After laser bending experiments on plates of 1 mm?1.5 mm and 2 mm, element diffusion at the transition layer of the bending zone is analyzed by means of metallographic microscope, EPMA and energy dispersive spectrometer (EDS) to demonstrate that the transition region of each plate is enlarged from a similar range to further diffusion in the thickness direction of Ni, Cr in stainless steel and Fe in carbon steel after bending with 2.5 ?m?3.5 ?m?3 ?m respectively. Meanwhile, nano-indentation tests are used to obtain the nano-hardness and elastic modulus of the transition layer. The nano-hardness in transition layer is 11% higher than the stainless steel laser duo to the plastic deformation and the appearance of special carbide, with yield strength increased accordingly. But, the elastic modulus in transition layer have no obvious change compared with other area. In summary, good material property in transition layer is ensured by element diffusion at the bending zone, making favorable metallurgical bond in laminated plate.Based on the experiment, this paper focus attention on laser bending process and the feature at transiting layer of bending zone, which are helpful for the precision laser bending. Additionally, the study of material properties in transiting layer are of great importance to finite element modeling analysis.