Study on Behaviour of Carbides and Knife Line Attack Phenomenon in Stabilized Austenitic Stainless Steels (Report 1)

Abstract

It is important to make clear how the carbides in austenitic stainless steels behave during heat treatment and especially during welding, because in these steels the behaviour of carbides heavily affects the corrosion resisting property and the other mechanical. properties.
It is main purpose to investigate fully the behaviour of carbides in stabilized austenitic stainless steels in the case of both time and temperature varying simultaneously such as weld thermal cycles.
On the other hand, knife line attack phenomenon neighbouring region to weld interface is the serious problem for these steels. Though this phenomenon is explained to be related to the behaviour of carbides in these steels, the detail in the mechanism of this phenomenon is yet unclear. Therefore, it is also the purpose of this study to make clear the mechanism and the cause of knife line attack.
In this report, it was carried out to investigate the influence of welding conditions and heat treatment conditions after welding on knife line attack and then to examine the change of corrosion resisting property in HAZ electrochemically.
The experimental results obtained in this study are as follows;
(1) Corosion rate at attacked region was little influenced by welding heat inputs, whereas much influenced by sensitizing time at 650°C.
(2) The corrosion rate increased with sensitizing time up to 50 h. However, in the case of sensitizing time being over 50 h, the corrosion rate decreased with sensitizing time.
(3) Corrosion resisting property in HAZ was closely related to the anodic current density at 900 mV (vs S.C.E.) which was, the corrosion potential in Huey test.