DAMAGE AND FAILURE PROCESSES IN STRUCTURAL 347H SS MATERIALS

The relationship between microstructure and high temperature strength of 347H SS welded joints was investigated. The materials studied corre spond to two preheated furnaces of the petrochemical industry, working at 700 degrees C and 45 atm (called furnaces A and B). Furnace A pres ented failures, hot fissure in the Heated Affected Zone, after 60 h op eration, whereas furnace B operated for 70000 h. The microstructure re search was made by a non conventional replica technique [1], which all owed more accuracy in the nature, quantity, morphology and distributio n of the different phases. The probable cause of the remarkable differ ent behaviour of the two materials, although both fulfil the A213/TB/3 47 H, ASTM standard requirements, has been discussed taking into accou nt the chemical composition of the steels, matrix characteristics, nat ure of the inclusions, carbides, intermetallic particles and N/Mn, Al/ N, C/Nb relationships.