Study On Microstructure And Properties Of Laser Welded Joint Of Q345B/304 Dissimilar Steel

With the advancement of science and technology and the rapid popularization of industrial intelligence,higher requirements are put forward for the comprehensive performance of equipment in various fields,especially the materials used in extreme environments,which require both high mechanical properties and high mechanical properties.Physical and chemical properties such as high and low temperature resistance and corrosion resistance are required,but it is difficult to meet these properties and requirements in one material at the same time.Even if they can be met at the same time,the price is relatively expensive.This makes the research on the welding process and mechanism of dissimilar materials become the focus of attention of domestic and foreign scholars.Welding lower-priced carbon steel and better-performing stainless steel can not only take advantage of the advantages of the two materials,but also save costs.This article takes Q345 B low-alloy high-strength steel and 304 stainless steel as the research object,uses laser self-fusion welding technology to obtain dissimilar steel welded joints.By adjusting the welding speed,defocus and laser power three process parameters,compare the welded joints under different process parameters.Surface and cross-section morphology,weld structure,hardness,tensile strength and corrosion resistance.When keeping the defocus at 0 and the laser power at 6 k W,the welding speed has a greater influence on the width of the weld and the heat-affected zone,and the weld structure is basically composed of martensite,but with the welding speed The decrease of the martensite laths in the lath bundle presented by the weld structure shows a decreasing trend.Under the condition that the laser power is 6 k W and the welding speed is 10 mm/s,the defocus is increased from-2 mm to 2 mm,the weld structure is still composed of martensite,but the beam waist of the weld The phenomenon went from weak to strong and then weaker.Under the condition that the defocus is kept at 0 and the welding speed is 10 mm/s,the laser power change has little effect on the weld structure.The weld structure is typical lath martensite,but under 6 k W There are a large number of lath bundles in the weld structure.Element distribution and phase composition analysis show that with the increase of laser power,the content of Cr and Ni elements in the weld has a significant decrease,while the content of Fe element will increase first with the increase of laser power,but then it will form For some compounds and intermediates,the content of Mn did not change significantly.In addition,by measuring the structure and material equality of Q345B/weld interface and 304/weld interface,it is shown that with the increase of laser power,the overheating zone contained in the heat-affected zone of Q345 B base metal will be significantly enlarged.The variable recrystallization zone,that is,the normalizing zone moves to the side of the base metal.When the laser power is 4 k W,5 k W,and 6 k W,the superheated zone of Q345 B presents coarse pearlite(P)and ferrite(F)structures,and The structure of the superheated zone at 7 k W is Widmanstatite.The 304/weld interface structure is mainly massive austenite,and small discontinuous ferrite is distributed on the massive austenite matrix,and with the increase of laser power,the ferrite gradually becomes vermicular,And its distribution is getting more and more disorderly.Corresponding to the above three welding process parameters,the hardness,tensile strength and corrosion resistance of the sample are as follows.As the welding speed increases from 6 mm/s to 14 mm/s,the maximum weld hardness is increasing,and the resistance There is a small increase in tensile strength.As the defocus increases from-2 mm to 2 mm,the maximum weld hardness also increases,and the tensile strength gradually increases.In the process of increasing the laser power from4 k W to 7 k W,the hardness value of the weld gradually decreases,and the tensile strength does not change significantly.When the laser power is 5 k W,the corrosion resistance of the weld is the strongest,and the corrosion resistance of the entire welded joint is in order It is 304 base material>weld seam>fusion zone>Q345B base material.