The Effect Of External DC Magnetic Field On The Microstructure And Properties Of Plasma Arc Surfacing Layer

With the advancement of technology, fast developing industry as well as the dramatic mechanization and automatization, higher request is needed for the operational life span of the mechanical equipments and their spare parts. As one of the three main types of wear-out failure, the damage caused by abrasion is increasingly taken into account. Reducing abrasion and improving wearing resistance, therefore, means more in economic sense. Currently, electromagnectic welding technology is becoming more widespread as one of new welding technologies. The process of arc and bath's mass and heat transfer have been changed by external magnetic field, so the crystallization and nucleation of arc surfacing layer will been affected and the properties of surfacing layer will been improved.The iron-based, nickel-based and cobalt-based alloy powders were surfaced on the surface of low-carbon steel by plasma surfacing equipment under external DC transverse magnetic field or DC longitudinal magnetic field. The effect of magnetic field parameters on the properties of surfacing layer was researched by the analyzing of testing the surfacing layer's hardness and its abradability. The influence of magnetic filed parameters on the microstructure of surfacing layer was studied by the way of analyzing the microstructure of surfacing layer under different parameters with OM,SEM,XRD,EDX method. By comparative analysis, the mechanical property and the microstructure of the surfacing layers with same material but different magnetic patterns were explored and the action principle of two different magnetic fields were researched, and the optimal magnetic field would be confirmed. The main results are as follows:1. Under the DC longitudinal magnetic field, the best welding current and magnetic field current as well as the best surfacing layer's properties are as below:For iron-born alloy powder, the optimal value is obtained when welding current I=160A, magnetic field current Im=3A, which hardness is 68HRC, wear extent is 0.0117g. For nickel-born alloy powder, the optimal value is obtained when welding current I=140A, magnetic field current Im=1A, which hardness is 54.4HRC, wear extent is 0.3340g. For cobalt-born alloy powder, the optimal value is obtained when welding current I=160A, magnetic field current Im=3A, which hardness is 43.7HRC, wear extent is 0.5493g.2.Given the DC transverse magnetic field, the best welding current and magnetic field current as well as the best surfacing layer's property are as below:When Im=3A,I=160A, the best performance comes for iron-born alloy powder, which hardness is 76.3HRC and wear loss is 0.0183g; When Im= 2A,I=140A, the best performance comes for nickel-born alloy powder, which hardness is 66.3HRC and wear loss is 0.0767g; When Im=3A,I=160A, the best performance comes for cobalt-born alloy powder, which hardness is 56HRC and wear loss is 0.4442g.3. For iron-born alloy powder, the hardness of surfacing layer with transverse magnetic field is higher than longitudinal magnetic field, but the wear extent of surfacing layer with transverse magnetic field is worse than longitudinal magnetic fieldd. The reason is that, the hard phase in surfacing layer under transverse magnetic field is strip, hard phases in surfacing layers under longitudinal magnetic field is hexagon shape. The strip hard phase can improve the hardness but it not benefit for the wear extent.For nickel-born alloy powder, the effect of transverse magnetic field on properties of surfacing is better than the longitudinal magnetic field. For cobalt-born alloy powder, under proper magnetic parameters, the effect of DC transverse magnetic field on properties of surfacing is better than the longitudinal magnetic field.4.No matter what position the externally-added magnetic field is set, the interaction will arise between arc and bath, and the bath will revolve and form electromagnetic stirrint. Then, the surfacing layer's structure will been refined by electromagnetic stirring under proper magnetic field parameters, the distribution morphologies and amount of hard phases in surfacing layer will changed and the properties of surfcing layer will been improved. But, the magnetic intensity can not too large. The reason is that the electromagnetic damping makes surfacing layer's structure becoming loose, decreases on acting on surfacing layer's performance.