Laser surface melting and alloying of type 304L stainless steel: Improvement of corrosion and wear properties. Final report

Technical Report · Mon Aug 01 04:00:00 EDT 1994

OSTI ID:10188652

Inal, O T

Laser surface melting (LSM) of type 304L stainless steel and laser surface alloying (LSA) of this stainless steel with Mo and Ta have been studied to determine if corrosion and wear resistance properties can be improved. It was observed that these properties were affected by the presence of {delta}-ferrite, produced by the high cooling rate associated with LSM, as well as by compositional modifications in Mo-and Ta-alloyed layers. The {delta}-ferrite content was calculated from X-ray diffraction data to be 4.3 vol%, 77 vol% and 76 vol% for LSM, Mo-alloyed and Ta-alloyed LSA layers, respectively. Laser processing caused a lowered Mn content, by about 15%, and introduced extensive Mn-Si precipitation in the microstructure. In the LSM layer, the hardness increase was observed to be 10% due to refinement in subgrain structure. There was no martensitic transformation in the melted layer. {delta}-ferrite content was found to increase from 4.3 vol% at the surface to 9.9 vol% at the fusion line due to different cooling rates present in the melted layer. Passivation and pitting properties were seen to be enhanced with increase in {delta}-ferrite content in LSM samples. This is attributed to a primary solidification mode of {delta}-ferrite which dissolves more impurity elements, such as S, than austenite, as well as the removal and/or redistribution of inclusions in the melted layer. The stress corrosion cracking resistance of the melted layer was observed to be lowered; this is possibly because of the detriment to mechanical properties introduced by laser melting in the form of lowered ductility. The Mo-alloyed layer exhibited 50% increase in hardness, compared with the substrate, due to higher {delta}-ferrite content. It spontaneously passivated in 1N H{sub 2}SO{sub 4} solution, and there was no pit formation in 3.5 wt% NaCl and 10% FeCl{sub 3}{center_dot}6H{sub 2}O solutions.

• Research Organization: Electric Power Research Inst., Palo Alto, CA (United States); New Mexico Inst. of Mining and Technology, Socorro, NM (United States)
• Sponsoring Organization: Electric Power Research Inst., Palo Alto, CA (United States)
• OSTI ID: 10188652
• Report Number(s): EPRI-TR--104322; ON: UN95001367
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360103
360105
ANNEALING
CORROSION AND EROSION
CORROSION RESISTANCE
DUCTILITY
FERRITES
HARDNESS
LASER-RADIATION HEATING
MECHANICAL PROPERTIES
MELTING
MICROSTRUCTURE
MOLYBDENUM ALLOYS
PASSIVATION
PITTING CORROSION
STAINLESS STEEL-304L
STRESS CORROSION
TANTALUM ALLOYS
WEAR RESISTANCE