| Submerged arc welding have many advantages, for example its production efficiency is high, appearance of weld metal is good, it tends to realize welding automation, thus making it become the primary method for flat welding thick plates. When high strength steels were welded by submerged arc welding, grains size of weld metal were almost 15 times bigger than base metal, thus leading to low-temperature impact toughness of weld metal was approximately one-third lower than base metal, therefore the wide application of high strength steels by submerged arc welding were limited. Flux cored wires enabled flexibly adjustment of alloy components and have little spattering, its welded appearences were good; while solid wires have low diffusion hydrogen, high deposited efficiency and little slag-forming. These advantages of the two welding wires were adopted by metal cored submerged arc welding applied widely to welding high strength steels. Consequently, there have significant engineering points that developing metal-cored wires for submerged arc welding high strength steels, studing structural transformation of deposited metals to increase impact toughness of deposited metals.As for above problems, Metal-cored submerged arc welding wire named AWS A5.23/A5.23 M F69A4-ECM4-M4 was developed. Tensile strength of deposited metals is 733 MPa, its-40? impact absorbtion work averagely is 139 J. All of measured mechanical proprites were higher than the required values from AWSA5.23/A5.23M:2011 ? Specification of low alloy steel welding wire and flux for submerged arc welding?.Based on this, the influences of alloying element Mn, Ce and welding heat inputs on microstructures and mechanical proprites of deposited metals were deeply studied. Tensile and impact tests were performed on desopited metals to measure its mechanical properties, and its microstructures were observed by optical microscope and scanning electron microscope. Results showed that with in the tests welding parameters, with increasing the content of Mn, strength of deposited metals was improved, but the enough high content of Mn would obviously lower impact absorbtion work, so the content of Mn should be kept at 1.5%-2.5%. With increasing the content of Ce, the content of minor inclusions and nucleation particles of acicular ferrite were increased, correspondingly the proportion of acicular ferrite formed also raised. When the content of Ce was over 0.035%, the scales of inclusions were largened, thus having a bad effect on nucleation of acicular ferrite.-40? impact absorbtion work started to increase, then decreased, while strength of deposited metals changed not significantly. With in the tests conditions, with increasing welding heat inputs, strength of deposited metals were almost unchanged,-40? impact absorbtion work decreased gradually. When welding heat inputs was low,microstructures of deposited metals were mainly composed of acicular ferrite and fine lath bainite, it had little granular bainite. When welding heat inputs increased gradually, numbers of lath bainite and acicular ferrite decreased, microstructures sizes also changed from small to coarse.Inclusions in impact fracture dimples consisted of Al2O3?Si O2?Ti O2?Zr O2?Mn O?Fe O?Fe2O3 or several composite compound.Finally, welding tests were performed on deposited metals by using self-developed metal cored submerged arc welding wires named AWS A5.23/A5.23 M F69A4-ECM4-M4 and the same kinds of solid wires on market. Mechanical properties, deposited speeds, deposited efficiency of deposited metals and arc stability were compared and assessed. Results showed that all of self-developed metal cored submerged arc welding wires with different components had higher deposited speeds and deposited efficiency, good slag detachability performance, better processes properties, its mechanical properties fited the AWS standard requirements, thus satisfying the demands of real welding production. Among them, arc stability of self-developed welding wire 2# and 4# were best. Metal cored submerged arc welding wires designed had better processing properties and mechanical behaviors. |
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