Discussion about stress corrosion cracking of fuel spray nozzle seat
The cracking accidents of fuel spray nozzle seat manufactured with martensitic stainless steel occurred for several times during use.Moreover,the cracking positions of nozzle seat were almost same.In order to find out the cracking rea-sons,the cracked nozzle seats were examined by fracture analysis,chemical composition analysis and microscopic structure analysis.In addition,the residual stress analysis was also conducted for the same batch of valve seats.The testing results showed that the chemical composition of the cracked nozzle seats could meet the requirements,and there was no abnormali-ty in microscopic metallographic structure.However,the dendritic cracks distributed along with the grain boundary were observed around the fracture position.The fracture analysis showed that the cracking of nozzle seats was dominant in interg-ranular fracture,and the muddy patterns appeared in the fracture surface.The energy spectrum analysis indicated the pres-ence of a large quantity of chloride ions in the muddy patterns.The residual stress measurement showed that there was a certain residual compressive stress on the surface of unwelded nozzle seats,while there was obvious residual tensile stress near the cracking position of welded nozzle seats.The comprehensive analyses indicated that the cracking of fuel spray noz-zle seat belonged to stress corrosion cracking.
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