A grain boundary etching method for the analysis of intergranular P-segregation in iron-based alloys

The effectiveness of a grain boundary etching method for the non-destructive analysis of intergranular segregation of P in iron-based alloys was examined by using a saturated aqueous solution of picric acid containing sodium tridecylbenzene sulfonate. Among all the alloys examined only those doped with P suffered selective etching attack against grain boundaries. The degree of the etching attack in a P-doped NiCr steel was found to have a linear relation with the concentration of grain boundary P as measured by Auger electron spectroscopy. From these evidences, the grain boundary etching method was concluded to be useful as a technique analyzing the grain boundary concentration of P in NiCr steels. The application of the method was successfully made to CrMo and C-free NiCr steels which are hard to exhibit perfect intergranular fracture. The application was not successful to Fe-40 pct Ni and Fe-3 pct Si alloys whose surfaces were unstable electrochemically compared with those of NiCr and CrMo steels.