Mechanical Properties of Weld Metal for Fire-Resistant Steel with Large Heat Input Submerged Arc Welding.

Abstract

Large heat-input welding is increasingly employed because of its high productivity. For this welding, titanium and boron (Ti-B) bearing welding materials are suitable in acquiring high toughness at low temperatures. However, their properties at high temperatures have not been known. Preferable ductility at high temperatures is required when they are applied to the welding of fire-resistant steels. The present study examines the mechanical properties of Ti-B bearing welding materials for fire-resistant steels in large heat-input welding.Submerged arc welding with two electrodes in tandem was conducted with the heat-input of 13 kJ/mm. The mechanical and metallurgical investigation were v-notch Charpy tests, weld metal tensile tests, chemical analyses, and metallographic observation on ruptured surfaces.It was found that the addition of titanium and/or boron lowers the high temperature elongation. This reduction was caused by grain boundary fracture at the prior-austenite grain boundaries of the weld metal with titanium and boron. However, the high temperature properties were recovered in the weld metal with titanium as low as 30 ppm and nil boron, and this weld metal fractured in an intragranular mode with enough toughness.

Is low phosphorus content in steel a product requirement?

“…This is consistent with the fact that the presence of allotriomorphic ferrite in steel weld metals reduces the propensity to intergranular fracture at the prior austenite grain boundaries. 64,65 A similar phenomenon is observed during the infiltration of prior austenite grain boundaries by liquid zinc. In a study of the heat affected zone of steel welds, the susceptibility to liquid zinc embrittlement was reduced as the allotriomorphic ferrite content increased.…”

“…This is consistent with the fact that the presence of allotriomorphic ferrite in steel weld metals reduces the propensity to intergranular fracture at the prior austenite grain boundaries. 64,65…”

Advances in Physical Metallurgy and Processing of Steels. Design of Ferritic Creep-resistant Steels.

“…These prior boundaries become susceptible to impurity segregation and embrittlement, liquid zinc embrittlement, and any phenomenon able to exploit the disorder associated with these boundaries. [19][20][21][22] The disorder at the prior austenite grain boundaries is larger than that associated with martensite-martensite boundaries. This is because adjacent martensite plates have coherence with the parent austenite grain and hence a good fit with each other, whereas the orientation relationships between austenite grains can be random.…”

Martensite and Bainite in Steels : Transformation Mechanism & Mechanical Properties

“…Martensitic and bainitic steels are therefore particularly prone to temper embrittlement phenomena [7], to embrittlement by liquid zinc [8] and to failure by creep defects at the prior boundaries [9].…”