Experimental study and modeling of H13 steel deposition using laser hot-wire additive manufacturing

Bridging the joint gap with wire feed laser welding

The effect of combinations of several deoxidizers, i.e., Mg-Al, Mg-Ti, Al-Ti, and Ce-Al, on the solidification structure of Fe-2 mass pct Ni-1 mass pct Mn-1 mass pct Mo alloy melt was investigated using a melt sampling and quenching method. Using this method, we evaluated the catalytic potency of several complex inclusion particles by taking the inclusion evolution process into account. Fine equiaxed crystals were obtained in the Mg-Ti-deoxidized steel wherein the MgO(MgAl2O4)-TiN complex compounds formed. However, the longer the holding time at high temperatures, the larger the fraction of Ti2O3, and very fine TiN formed because of microsegregation during solidification, resulting in poor equiaxed crystals. When the steel was deoxidized with Mg-Al, the initial structure was dominantly columnar. However, the longer the holding time, the larger the fraction of MgAl2O4 spinel, resulting in the formation of fine equiaxed crystals. Ce-Al complex deoxidation provided a relatively small portion of equiaxed crystals, whereas Ti-Al deoxidation produced the fewest equiaxed crystals because of the formation of alumina. The effectiveness of each inoculant particle for the crystallization of the primary δ-iron was explained well by the lattice disregistry concept.

Effect of Complex Inclusion Particles on the Solidification Structure of Fe-Ni-Mn-Mo Alloy

Theoretical and experimental investigations have been carried out to examine the influence of laser power and on time on the weld thermal cycle and weld metal microstructure and hardness during laser spot welding of low alloy steel. A transient heat transfer model that takes into account the temperature dependence of material properties and latent heat of phase transformation is employed to simulate thermal cycles and cooling rates experienced by the material under various combinations of power and on times. Two models for predicting the microstructure and hardness of the weld pool metal from the cooling rates are used to evaluate the results.

Prediction of cooling rate and microstructure in laser spot welds

The effect of Mg–Ti deoxidation on the solidification structure of advanced high strength steel was investigated by observing the solidification structure and also the inclusion particles. The effect of precipitation of TiN, MgO, and “TiN–MgO” hybrid inclusion on the formation of fine equiaxed crystals was evaluated. The composition of inclusions was observed to change in the order of MgO  “MgO(core) + TiN(surface)”  Ti2O3 by reaction time, which corresponded to the change of solidification structure as “columnar  equiaxed  columnar.” This could be understood from the concept of lattice disregistry in between delta iron and MgO (3.97%), TiN (3.91%), and Ti2O3 (18.9%). However, even with very low disregistry between delta iron and MgO, the MgO itself did not work as an effective catalyst, indicating that there is another criterion for determining a good catalyst. The mechanism of the formation of TiN on MgO surface was schematically described. The precipitation of TiN on MgO surface was feasible although the content of Ti and N was lower than the equilibrium solubility product for the formation of TiN. Because disregistry between TiN and MgO is very low (0.05%), the precipitation of TiN on the surface of MgO is energetically more favorable.

Effect of Mg–Ti Deoxidation on the Formation Behavior of Equiaxed Crystals During Rapid Solidification of Iron Alloys

Laser beam welding of 13 mm plates of HY 80 steel resulted in different microstructures in the fusion zone depending on the welding process. Autogenous welds resulted in an untempered martensitic structure, whereas, with the introduction of a hot wire filler metal, the microstructures depended on the wire feed. A slow feed resulted in a mixed martensite–bainite microstructure and a fast wire feed resulted in a microstructure that is primarily acicular ferrite. The chemistry of the as deposited weld metals was different in each case. The thermal profiles for the autogenous weldment were calculated based on a two parameter model of laser welding that utilises the fusion zone boundary as a measure of ‘best fit’. Based on the cooling rate of the autogenous fusion zone, cooling rates for the two welds with hot wire filler metal were rationalised. Using these cooling rates, the chemistry of the weld metal and a model of microstructural development of the weld metal, a computer calculation was made which...

R. H. Phillips

Papers

Microstructures in hot wire laser beam welding of HY 80 steel