Microstructural analysis of austenitic stainless steel welds and their modification during laser welding
The microstructure of austenitic stainless steel weld metal containing a duplex structure was fully characterized and its mode of formation explained. Four distinct ferrite morphologies were identified in type 308 stainless steel weld metal: vermicular, lacy, acicular, and globular. The first three ferrite types are related to transformations during and after solidification, and the fourth is related to the shape instability of the residual ferrite. Solidification behavior of type 308 stainless steel welds at high cooling rates was investigated with a high-power laser system. The welds were made at speeds ranging from 13 to 63 mm/s. The welds made at 13 mm/s contained microstructures ranging from a fully austenitic structure at the root of the weld to a ferrite plus austenitie duplex structure at the crown. However, the welds made at 25 and 63 mm/s contained a nearly fully austenitic structure with less than 1% ferrite, and third-phase particles rich in manganese and silicon were also found. The fully austenitic stainless steel welds were free of any cracking. The results are explained in terms of excessive undercooling at the tip of the ferrite cells at rapid solidification rates. This undercooling changes the mode of freezing from primary delta-ferrite to primary austenite.
- Research Organization:
- Oak Ridge National Lab., TN (USA)
- DOE Contract Number:
- W-7405-ENG-26
- OSTI ID:
- 5446384
- Report Number(s):
- ORNL/TM-8276; ON: DE82016036
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360101 -- Metals & Alloys-- Preparation & Fabrication
360102* -- Metals & Alloys-- Structure & Phase Studies
ALLOYS
AUSTENITIC STEELS
CHROMIUM ALLOYS
CHROMIUM STEELS
CHROMIUM-NICKEL STEELS
CORROSION RESISTANT ALLOYS
CRYSTAL STRUCTURE
ELECTRON MICROSCOPY
FABRICATION
IRON ALLOYS
IRON BASE ALLOYS
JOINING
LASER WELDING
MICROSCOPY
MICROSTRUCTURE
MODIFICATIONS
NICKEL ALLOYS
STAINLESS STEEL-308
STAINLESS STEELS
STEELS
WELDING