Effects of Titanium, Boron and Oxygen on Notch Toughness

Study on Notch Toughness of Weld Metal in Large Current MIG Arc Welding (Report 1)

Abstract

This paper describes the correlation between notch toughness and microsturcture of weld metal produced by the large current MIG arc welding. The single bead weldings were made in the inert gas (Ar-60% He and Ar-2-70% CO₂) shielding atomosphere by using the titanium and boron bearing consumable wires of 4 mm diameter.
The microstructure of weld metal varied significantly depending on the combined effects of titanium, boron and oxygen. When the consumable wire containing 0.11%Ti and 0.0067%B was used, the most appropriate range of oxygen content of weld metal was determined to be 210-300 ppm. In those weld metals, the coarse proeutectoid ferrite was prevented to form, resulting into the very fine acicular ferrite structure and ductile to brittle transition temperatures determined were in the range of -90--106°C.
As a result of phase analysis, a large proportion of titanium was evidenced to exist in these weld metals in the form of nonmetallic inclusions which were detected as the acid-insoluble titanium. The majority.of these .inclusions is thought to be oxides. As the oxygen contents of weld metal increased, boron as oxides also increased.
Notch toughness of weld metal depended upon the weld heat inputs. In the range of 0.010-0.037% Ti and 0-0.0021%B, ductile to brittle transition temperatures determined on the weld metal were considerably improved with increasing titanium and born contents.