For most alloys, the thermal salt stress corrosion sensitive temperature range is 288-427 ℃. The corrosion tendency is related to metallurgical factors such as alloy composition and processing history, and the high alumina high oxygen alloy and the b processed or b treated coarse crystal Weil structure are more sensitive to stress corrosion.
The cause of metal embrittlement caused by hot salt stress corrosion is believed to be related to hydrogen embrittlement. Under the action of high temperature and stress, halides are hydrolyzed to form HCl gas, and HCl further interacts with titanium to form hydrogen, namely NaCl 10 H20 -- HCl 10 NaOH 2HCl 10 Ti -- TiCl2 12 2H.
In addition to hot salt stress corrosion, titanium flanges have a tendency to stress corrosion in red fuming nitric acid, N204, and methanol solution containing hydrochloric acid and sulfuric acid to a certain extent. When stress corrosion turbidity test is carried out with specimens with sharp notch, an aqueous solution containing 3.5%NaCl may reduce the corrosion rupture life.
The stress corrosion tendency of titanium flange is related to alloy composition and heat treatment. Increasing the content of aluminum, tin and oxygen can accelerate the effect of stress south corrosion. On the contrary, adding b stabilizing elements to the alloy, such as aluminum, vanadium, group, silver, etc., has the effect of alleviating stress corrosion. Titanium flanges also have a tendency of liquid metal embrittlement. For example, contact between melted cadmium and titanium will cause cadmium embrittlement, and mercury has a similar effect. Above 340℃, silver can promote corrosion cracking of alloys such as TA7.
