Microstructures And Corrosion Properties Of Laser Welded Joint For High-strength Steel Sandwich Panels

With the development of society, especially in recent years, the rapid development of the national economy. High speed railway, large aircraft, new energy vehicles and other modern means of transport is more and more widespread. All of these bring great convenience to people’s life. But in recent years, vehicle exhaust pollution is more and more attention. Especially in the past two years, fog and haze swept across the country, people attribute the problem to emissions. For transportation, saving resource, reducing energy consumption, reducing emissions, protecting the environment is the main problem must be solved. And from the aspects of military strategy, for example, destroyers, submarines and aircraft carriers, reduce the weight of equipment can improve the motor performance, increase the load and incerase the operational capability. So in the range of the world, reducing weight of vehicles and lightweight structure have higher requirements. Metal sandwich plate is produced under such background and requirements. High strength steel can meet the strength requirements. Sandwich structure is placed support core panel between the upper and lower face panel. Using the method of laser welding connected the hollow structure. Because there are three layers of structure, so it was named sandwich structure. Sandwich panel have some good characters such as great intensity, great specific stiffness, absorb impact energy, and it has simple structure and easy to manufacture. It Has been widely used in marine equipment. When used in marine equipment, the first problem is the seawater corrosion. The seawater is a natural strong electrolyte, it has very high salt content and high electrical conductivity. So Research the sandwich plate in the ocean corrosion resistance has the very vital significance of sandwich plate used in the ocean, In this article, through indoor simulated marine corrosion method, studied the corrosion resistance of welded joints of sandwich panels.The high-strength steel sandwich panels were welded using the high power laser welding. The microstructure of the welded joint was observed by scanning electron microscope (SEM) and optical electron microscopy. After the observation, the base material is formed by a rolling, witch was composed fine pearlite and ferrite. On the basis of the ferrite the pearlite distributed evenly. The weld was composed by the thick growth of columnar crystals. Heat affected zone is relatively narrow, but divided into coarse grain and fine grain area.The corrosion behavior of the welded joint of high-strength steel was investigated by method of potentiodynamic polarization and seawater immersion corrosion test; The welded joint stress corrosion sensitivity was investigated in simulated seawater by constant load devices. The results show that the960high strength steel’s corrosion process begins with uniform corrosion, then the corrosion products drops off and the uniform corrosion forms at the end of time. With the increase of corrosion time, The color of corrosion products getting darker, the corrosion products began to increase and start link together, and formed a uniform layer of iron oxide. As the longer corrosion time, scale began to burst loss. The metal substrate is exposed, and seawater corrosion is more serious. The metal surface is rugged and occurred general corrosion. The corrosion product is composed of y-FeOOH and few Fe2O3, Fe3O4, since y-FeOOH is loose and adhesion is not strong, therefore the corrosion products fall into the corrosive liquid. Its corrosion weightlessness rate is0.035mm/a, and belongs to corrosion-resistant steel. The vickers hardness of heat affected zone is the lowest value. The vickers hardness value after corrosion was lower than the uncorroded. This is because after corrosion, the ferrite on the surface of the metal corroded off first. And then the surface is uneven. The layer of oxide film is relatively loose so the hardness is small. Test results from the electrochemical corrosion the corrosion rate of three regions from large to small are welded metal>HAZ>base metal, and with the extension of time corrosion rate slowed down. Heat affected zone is the weak link of joint due to the coarse grain zone, so all the tensile specimens were broken in the heat affected zone. Stress corrosion reduced the tensile strength of tensile specimens by12%, and the elongation reduced by11.6%. fracture mode is ductile fracture.