Mould steels repaired by laser welding

Abstract

Laser-deposit welding, by using Nd-YAG, is a mould repairing process, which has the advantages relatively to the traditional methods of achieving a less change of the metal composition around the repaired zone and permitting a very accurate deposition of a small volume of the filler material in the area chosen at the work-piece surface. This paper presents a fatigue study in specimens of two base materials used in mould production (AISI H13 and P20). Filler material as well as welding parameters were analysed in order to obtain better fatigue strength. The tests were carried out under constant amplitude loading, with two stress ratios R = 0 and R = 0.4. Welded specimens were prepared with V notches and filled with laser welding deposits. The fatigue results are presented in the form of S-N curves obtained in welded and non-welded conditions. Complementary measurements of hardness profiles and SEM analysis were carried out to understanding the fatigue behaviour and failure sites. The laser-deposit material was the weaker region in both steels, due to a high level of tensile residual stresses and also to some planar defects that are potential failure sites. Fatigue crack initiation is therefore reduced and the fatigue propagation life is enhanced. A significant mean stress effect in the base material was also observed in both mould steels.

Residual stresses analysis of ND-YAG laser welded joints

“…In a previous work [1,2], the authors observed (see Figs. 3 and 4) that welded specimens, tested at R = 0, present a significant lower fatigue resistance than the correspondent non-welded specimens tested for the same stress ratio.…”

“…In a previous work [1,2], the authors observed that welded specimens, tested at R = 0.4, presented a similar fatigue resistance to the correspondent non-welded specimens tested for the same stress ratio and also very close to the curve obtained with welded specimens for R = 0. Residual stresses are probably the main factor affecting this fatigue behaviour.…”

“…For the residual stress evaluation, a same mean Poisson coefficient of m = 0.29 was used for both phases, while a mean Young's modulus of 210 and 196 GPa was used, respectively, for the martensitic/ferritic steel and austenitic one. In all cases, the residual stresses were evaluated using the integral method [2]. All stress calculations were performed using the software GTRResidual Stress Group Software [6], which has been developed by our research group (CEMDRX).…”

Comportamiento Tribológico y Microestructural en Recubrimientos Aplicados por GTAW y HVOF (Proceso Térmico de Espreado) y Usado en Recuperación de Aceros Grado Herramienta AISI/SAE D2

“…Para aquéllos materiales que son sensibles al agrietamiento y cambios en la composición debidos a la formación de fases frágiles, la formación de carburos primarios y secundarios M 23 C 6 y M 7 C 6 . Debido a las condiciones del proceso, las cuales combinan una relativamente baja temperatura de flama con un bajo tiempo de exposición [4]. Este método emplea una alta presión de un combustible (propileno, acetileno, propano o gases de hidrógeno) para producir temperaturas del gas superior a los 3,029 ºK y para generar una supersónica o hipersónica velocidad del gas, de aproximadamente 2,000 m/s, más de cinco veces la velocidad del sonido [5].…”

Transformation from manufacturing process taxonomy to repair process taxonomy: a phenetic approach

“…Composite repair of thick section was carried out (Jones and Chiu 1999). Repairing of part by laser technology was carried out (Wang et al 2002;Borrego et al 2009). Non-destructive inspection techniques to detect cracks were employed (Diamanti et al 2005).…”