Finite Element Analysis Of Residual Stress In Alloyed Steel Roll Subject To Laser Solidification Processing

Laser solidification process, also called the laser remelting process (LRP), can improve surface hardness, wear strength, corrosion resistance or fatigue resistance properties of treated materials and has been one of the important subjects in mechanical field. Especially with the wide-band laser beam developed lately, the high laser power, well distributed laser output mode, facular shape and large-scale processed domain can be acquired, which can especially prolong the fatigue life of metallic materials greatly. LRP has extensive applied aspect in some modern manufacturing fields such as aerospace, metallurgical, mechanical, petroleum and petrochemical industries, etc.Based on the facular morphology of the wide-band laser beam, distribution features of energy density and dimensions of the remelting strengthened layer, a wide-band heat source theory was advanced and, the created wide-band heat source model can be well used to simulate the laser material processing. The applicability and accuracy of the created heat source model were verified by experimental results of the thermodynamic data.In this paper, the three dimensional (3D) models of plate and roller were created, and characters of laser remelting process were discussed. According to the theories of heat transfer, elastic-plasticity dynamics, metal physics and mechanics, the effects of laser remelting processing on the temperature field, phase transformations, surface micro-hardness and residual stress in 42CrMo steel surface layer were analyzed. The influences of the linear energy density and overlapping ratios were studied. The experimental and theoretical analysis results indicated that LRP induced acicular martensite transformation in the surface layer. The remelting layer comprises the melt zone, transformation zone and tempered zone, the micro-hardness increased 2.5~3 times and martensite volumetric expansion resulted in high compressive residual stress in the melt zone. Laser remelting process is a simultaneous heating and fast cooling process with the maximum heating temperature gradient up to 1.3×10~4℃/s and lowest cooling temperature gradient nearly -7×10~3℃/s, most of the initial pearlite-ferrite microstructure is transformed into martensite in the melt zone, the even distributed structure, quality and favorable residual stress distribution can be acquired with the linear energy density ranges from 20.9J/mm~2 to 35J/mm~2 and the overlapping ratio has little influence on property of the remelting layer except for the softening phenomena to some extent, so the overlapping ratio should be equal to or less than 20%. The maximum residual compressive stress exists on the boundary of the melt zone and transformation zone, while the highest tensile stress and Von Mises stress existed between the transformation zone and tempered zone may cause the initiation and propagation of cracks. The comparison indicated that the simulation result has a good consistent with the measured result.