高マンガン鋼のガスシールドアーク溶接(第1報)

Abstract

A series of study was carried out to realize automatic welding of austenitic manganese steel rail which had been conventionally performed by manual arc welding process.Using austenitic manganese steel as base metal, 16 Mn-16 Cr wire as electrode, and mainly CO2, A and N2 singly or mixed as shielding gas, build up welding was performed. Further, with the welding conditions varied, single bead welding was made. The mechanical properties. chemical composition and microstructure of weld metal were investigated on these welds.For any shielding gas used, the mechanical properties of deposited metal are satisfactory. Impact value is particularly good in the case of A-N2 gas;This is presumably partly due to relatively small contents of non-metallic inclusions. Among the welding defects, hardly any crack occurs, but blow holes are observed more often in N2-CO2 gas and in A-O2 gas containing considerable quantities of O2.As for the chemical composition of deposited metal, with an increased CO2 or O2 content of shielding gas the consumption of manganese in welding increases and as the result the manganese content of deposited metal decreases (transfer efficiency of manganese is about 80% for single use of CO2 gas). The decrease of chromium content is small but it shows the same tendency as manganese content. Nickel content hardly depends on the composition of shielding gas. Meanwhile, if the N2 content of shielding gas is large, the N content of deposited metal also grows large (0.49% for 20% CO2-80% N2). The deposition efficiency is high when the shielding gas is rich in A; and it is low when the gas is rich in CO2, N2 and O2.Under high arc voltage and under low welding current, the weld metal surface is liable to develop blow holes (pits), accompanied by a drop in the deposition efficiency and an increase in spattering, if the shielding gas is rich in CO2. In this case the manganese content of weld metal is lower than in others.If the welding is performed in appropriate shielding gas under appropriate welding conditions, use of 16 Mn-16 Cr welding wire will assure weld metal having high mechanical properties and almost free from any welding defects.