The fusion zone geometry and microstructure in complete-joint-penetration hybrid laser gas metal arc welds of a low-alloy steel are examined experimentally and theoretically. Weld geometry and spatially variable cooling rates are investigated using a three-dimensional heat transfer and fluid flow model. Experimentally measured microstructures are compared with those estimated from a microstructure model based on kinetics and thermodynamics of phase transformations, for a range of laser arc separation distances and heat inputs. Considerable variations in both cooling rates and microstructure were observed for the range of process parameters utilized. In fact, the experimental results and calculations show that for the same heat input, a predominantly ferritic and predominantly martensitic microstructure can be obtained, depending on the laser arc separation distance and resulting cooling rate. A process map is constructed showing the effect of welding speed, laser power, and laser arc separation distance on cooling rates and microconstituent volume fractions. The map indicates a martensite-free microstructure can be maintained over a wide range of welding parameters.
|Original language||English (US)|
|State||Published - Apr 1 2015|
All Science Journal Classification (ASJC) codes
- Mechanics of Materials
- Mechanical Engineering
- Metals and Alloys