鉄鋼溶接部における硫化物の挙動と凝固割れ(第7報)

Abstract

Behaviour of sulphide and solidification crack susceptibility in TIG-arc weld metals of Fe-S-Mn-Niand Fe-S-Mn-C quarternary alloys have been investigated. In these alloys the sulphur contents were purposefully somewhat higher than those encountered in commercial steels. Main conclusions obtained are as follows:1) The addition of 2-..7% nickel or 0.2% carbon to the weld metals containing 1% manganese and 0.0480.086% sulphur not only causes the formation of filmlike sulphides (MnS) at the columnar grain boundaries, but also lowers the eutectic temperature at which the sulphides are formed. The increase in manganese content up to 2-..3%, however, prevents the formation of filmlike sulphides, and raise the eutectic temperature.2) The solidification crack susceptibility, which is evaluated with Trans-Varestraint test, is increased at 1 % manganese level with the increase in nickel or carbon content. The increase in manganese content up to 3%, however, lowers the susceptibility to the same degree as that of Fe-S-Mn ternary alloy whose Mn3/S is larger than 6.7.3)The general relationship between manganese and sulphur contents to prevent the detrimental effect of sulphur in Fe-S-Mn-NiandFc.S-Mn-Calloys is expected.That is, the relationship in which the solidification crack susceptibility is comparatively lowered is given as follows;Mn5/S>310-560Moreover, the relationship in which the susceptibility is lowered to the same degree as that of Fe-S-Mnalloy whose Mn3/Sis larger than6.7 is given as follows;Mn5/S=2500-3600