Research On Closure Of Void Defects In The Large Section Mold Steel Forgings

Large forgings，the fundamental parts for heavy machine manufacturing，are veryimportant to the national economy，defense and the momentous equipments with advancedscience and technology. Their productivity and quality represent the level of nation’sindustrialization. However, void defects such as shrinkage cavities and porosity inevitablyoccur in large ingots during steel casting. The continuity of the metal is destroyed by theseinternal voids and stress concentration and crack damage are easy to form, resulting in lossof life and discarding. So it is very important to research the void defects ciousre in thelarge forgings.Due to big volume and high price of the large forgings, the paper first use718steel ofsmall cylinder to do the upsetting experiment. This paper combining numerical simulationand physical simulation, researched regularity and influence factors of forgings inner voiddefects closure, and applied the results of the study to practical production processimprovements.After cutting them, two sides diameter of center longitudinal hole forgingsare slightly reduced, and the middle diameter are expand severely. And the centerhorizontal hole are closed completely. The stress-strain curve of718steel are acquired bythe experiments, then input the data to the material lab of the finite element simulationsoftware DEFORM. By simulating the upsetting process of small cylinder forgings, theinternal distributions of stress and strain were obtained. The simulation results of theupsetting process of cylinder forgings with horizontal hole indicated the shape variation ofthe void was sphereâ†'ellipseâ†'aperture in turn and at last the closure of void. Measuredthe size of the longitudinal hole, simulation results were similar with experimental results,The maximum error were less than10%. The numerical simulation with the same sampledimensions was verified to be reasonable.For large forgings inner void defects, research it from position of void defects, shapeof void defects, height-diameter ratio of forgings, reduction ratio and width ratio. The influences of them to the void closure were obtained.Applied these simulation conclusion to improve the process of45tons of718steelingot’s inner void defects closure, the simulation results was very good, the improvementcould make the inner void defects close completely.