Effect of Cooling Rate on the Dislocation Densities of Mild Steel and High Tensile Strength Steel Weld Metals

Abstract

ransmission electron microscopic observation revealed the dislocation structure of various ferrites in mild steel and high strength steel weld metals. On the basis of these results the toughness of these steel weld metals was discussed. The main results were in the following.
(1) Dislocation density in ferrite of these weld metals increased with cooling rate of 10 to 1000°C/sec at solidification. The Dislocation densities ranged over 5.0×10⁹ to 1.5×10¹⁰/cm² for mild steel weld metal and 1.0×10¹⁰ to 3.0×10¹⁰/cm² for high strength steel weld metal.
(2) Significant decrease of dislocation densities of as-deposited weld metals was observed after the following weld pass.
(3) Brittle-ductile transition temperature of these steel weld metals depended on not only the ferrite size but also the dislocation structure in ferrites.