About spring fracture

[Donatas]

Does anyone has an experience in investigateing fracture of springs?
Its cylindrical spring from safe valve of ammonia tank-wagon?
Chemical content of steel is aprox Ñ-0,4%, Cr-1%, V-0,4%.
Thermal treatment chilling and annealing at 400deg. celsium accordingly.
Hardness 47-48HRC.
Has anyone experience in this field?

 

I've looked at a fair number of spring failures, but none associated with ammonia. The main idea in any failure is identify the fracture origin and then determine what happened at this origin to promote failure. Typically I would look at the fracture surface under low magnification, say 5 to 10X, with a shadowing light from the side. The aim is follow the river patterns back to the fracture origin. This works with fatigue and overload failures. Other failures (intergranular fractures, stress-corrosion cracking, etc.) may not show an origin. Is there any corrosion present? Did the corrosion occur after fracture, or does it look like it was part of the failure process? Are there any mechanical marks to indicate improper contact with mating or foreign parts? Next step would be to examine the origin (or the general fracture surface if no distinct origin) under higher power magnification in a scanning electron microscope. Fatigue, overload and corrosion failures, as examples, have different appearances in the SEM. ASM Metals Handbook has a volume on failure analysis that may help direct you as you proceed.