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Abstract:
The rule
of non-metallic inclusions distribution and the their sizes in HSLA
steel weld metals for flux cored wires are measured, and the chemical
composition and the figures of non-metallic inclusions in HSLA steel
weld metals are analyzed with transmission electron microscopy and X-ray
Microanalysis. The mechanisms of acicular ferrite nucleation in weld
metal are systematically studied, The suitable percent of Ni, Mn and Mo
in the weld metals can increase the percent of acicular ferrite in the
weld metals microstructure. The percentage of Ni, Mn and Mo in the weld
metals and welding energy input have little affect on the chemical
composition, sizes and figures of non-metallic inclusions in the weld
metals. The non-metallic inclusions beneficial to nucleation and growth
of acicular ferrite in weld metals are oxidation products of Ti, Mn, Si,
Al and the sulphides of Mn and Cu. As nucleation sites, the non-metallic
inclusions can reduce the nucleation energy remarkably. Besides they
have different thermal expansion coefficients than that of the substrate
metals, which will introduce a high stress-stain field around the
inclusions during the cooling process. These two factors are the main
driving forces to the nucleation and growth of acicular ferrite.
Key words:
Flux cored
wire Weld metal Non-metallic inclusion Acicular
ferrite
CLC No: TG401
Received 20001106, received in revised form 20010121
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