| Stainless steel-carbon steel laminated composite material (SSLCM) is a new material owning firm and metallurgical bonding by explosion-rolling composite means. The material not only possesses characteristics of the strength and plasticity which are the advantages of carbon steel, but also has merits of stainless steels, such as corrosion resistant, heat-resistant, wear-resistant and bright on the surface. Laser bending technology is a forming plastic forming method using the thermal stress of uneven temperature field to form the sheet. Laser bending of SSLS can promote the application of this sheet widely. More importantly it is a new application for laser bending in metal laminated sheet.This thesis takes1Cr18Ni9Ti/Q235A SSLS as the main study objects, studies the bending process and the law of the angle curve. By the help of the contrast test, studying the relationship between material properties difference and the bending angle of the two sheets. For the bending region feature, metallographic pictures, hardness distribution, defect detection and element distribution are analyzed. The bending zone thickness becomes bigger after laser bending, studying the relation between the energy parameters and the thickened value. And then three control methods are put forward. Main studying contents of this thesis are as follows:(1) Laser bending experiment. Making use of the JK701H Nd:YAG pulse solid laser, numerical control system, angle measurement system to finish a series of laser bending experiment, and obtain the angle curve. At the loading and unloading phase, the stainless-carbon laminated sheets are limited by the large rigid constraint. So the bending angle increases slowly, the whole curve present step shape. And during the bending process, because of the stress-stain wave the curve shows regular fluctuations. Besides that, The yield strength, specific heat capacity and thermal conductivity play a role in the angle difference of1Cr18Ni9Ti/Q235A laminated sheet and1Cr18Ni9Ti sheet. At last, choose reasonable parameter to form corrugated sample.(2) The study of the bending region material feature. After laser bending, the grain size of the stainless layer become bigger and the thickness increase. The organization of the carbon layer present gradation, in the order:grain deformation zone, the dynamic crystallization area, grain refining area and grain growth zone. The hardness of the stainless layer and the carbon layer is improved. When EALE=2J/mm, the max-hardness of the stainless steel layer is290HV.After laser bending, the max-hardness of the carbon steel layer has improved46HV. By the help of the electronic probe, the distribution of C, Fe, Cr, Mn, Ni, Si are studied, besides the C element, the others five elements don’t appear the macro segregation phenomenon. The C element occur cumulative phenomenon in the upper interface. In the bending process, the C element migrate from the stainless layer to the carbon layer, which makes the ferrite banding width improved to20μm, and the interface bonding strength increased.(3) Relying on Temperature Gradient Mechanism to research the thickening mechanism. The results show that the grain size becomes bigger in the heating process which means Thermal Expansion Thickening (TET). In the positive bending process grains are squeezed and extended by the bending stress, forming Extrusion Thickening (ET). TET and ET are the principal factors of thickening appearance, and TET occupies the main region. The stainless steel layer and the carbon layer become thicker, and the thickened value of the carbon layer at least account for69%. And then study the relation between the energy parameters and the thickened value. At last, three control methods are put forward.This thesis focus attention on the bending process and the bending region feature which are helpful for the understanding of the bending Mechanism. At the same time, these things are the basis of theory and experiment for better bending mould and quality. |
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