Numerical Simulation Of The Effect Of Welding With Rapid Cooling On Hot Cracking Susceptibility Of Nickel-base Alloys

Welding hot cracking in the joint of nickel-base alloys has been thesubject of considerable investigation and the cracking mechanism is that during the terminal stages of solidification,the liquid films aredistributed along solidification grain boundaries andinterdendriticsitesand cannot sustain the tensile strains generating in welding process,then the boundaries separate to form a crack which results in solidification cracking or liquation cracking.Besides,the ductility dip cracking forms in a temperature range lower than the melting point in which the weld metal is in low ductility and will crack under the tensile stresses in welding process.There have been plenty of study on the metallurgical mechanism of hot cracking,but the study on the control of stress in welding process to resist hot cracking is few.The group considers that the transient stress in welding process is difficult to control in conventional welding,so the rapid cooling technique was used for the purpose of reducing transient stress in welding process as well as hot cracking susceptibility of nickel-base alloys.The finiteelement method was used to investigateinto nickel-base alloys welding with rapid cooling.The effects of cooling position,cooling intensity,the distance between cooling source and heat source as well as the radius of cooling source on transient stress in welding process were investigated.The results show that the transient stress of welded joint decreases most when welding with trailing cooling source.And the transient stress decreases as the cooling intensity increases from 4000 W/m~2·K to 15000 W/m~2·K.Further increase of cooling intensity has no better effect.Besides,under the conditions of this paper,setting the distance between cooling source and heat source to 15 mm is appropriate to reduce transient stress and improve the ability of nickel-base alloys to resist hot cracking.And the transient stress decreases as the radius of cooling source increases within a certain range.On the other hand,in order to investigate the effect of cooling intensity,the distance between cooling source and heat source,the radius of cooling source and the interactions between them on the transient stress and hot cracking susceptibility in welding process of nickel-base alloys,an orthogonal test based on numerical simulation was developed.The best cooling solution of the orthogonal test is that the cooling intensity is 8000 W/m~2·K,the distance between cooling source and heat source is 15 mm and the radius of cooling source is 8 mm.Then an additional test was carried out based on this and the best cooling solution of this paper is that the cooling intensity is 15000 W/m~2·K,the distance between cooling source and heat source is 15 mm and the radius of cooling source is 12 mm,under which the stress in welding process was reduced by 58%.Based on the above results it can be found that appropriate rapid cooling methods can reduce the stress in welding process and we can get the effect that the hot cracking susceptibility of nickel-base alloys decreases.