Electron beam/laser glazing of iron-base materials

Research on directed energy source processing of hard-iron base materials demonstrates the effect of environment, alloy chemistry and processing parameters on the nature of the crystal structure, distribution, and compositional variation of phases. In molybdenum high speed steels, for example, it is found that segregation resulting from convective and turbulent flow during glazing may either result in large scale phase separation or compositional variation within a phase. Another example of the importance of processing conditions is a clear demonstration of the effect of small oxide particles in inducing martensite during laser processing. A detailed analysis has been made to determine the effect of deflection coil parameters on the distortion of surface area glazing patterns. This is particularly important in developing techniques for preparing uniform rapidly solidified layers. In studying molybdenum base high speed steels the value of the carbon content is found to be important in determining delta ferrite formation and the peritectic reaction of this phase to uniform austenite and carbide phases. In contrast to M2 (where the carbon concentration is 0.85wt%) a homogeneous gamma/alpha phase mixture forms in materials with a carbon content of > or = 1wt%, i.e. the alloys M7, and M42. However in these two materials combined convective and turbulent flow during glazing results in a significant composition variation of the refractory elements. Tempering largely removes this inhomogeneity and results in the formation of a homogeneous tempered martensite structure. A most important effect observed in M2, M7, and M42 was the shift to longer tempering times of material glazed at moderate to high beam velocities.