The invention discloses an etchant for displaying a 690 
nickel-base 
alloy deposited 
metal grain boundary and an 
etching method thereof. The etchant comprises 
ferric chloride, EDTA, deionized water andconcentrated 
hydrochloric acid. The surface of the 690 
nickel-based 
alloy deposited 
metal surface is successively wiped with the etchant and a 
nitric acid ethanol solution. Thus, it is possible to intuitively observe that the surface of a sample changes from bright to frosty during an 
etching process, and the 
weld bead can be clearly observed by naked eyes in order to better control the degree ofcorrosion, completely and clearly show the grain boundaries of the deposited 
metal sample grains, and avoid the covering by 
corrosion products. The etched different grains have different shades due to different orientations. The columnar 
crystal structure can be clearly observed and the grain boundaries are clear and complete. The etchant is made of simple raw materials, nontoxic, environmentallyfriendly, convenient in 
liquid waste disposal, low in cost, and stable and easy to control in a reaction process. The 
etching method is simple and easy to use, and provides detection basis for the 
process quality control, the process plan and the quality analysis of nuclear 
welding deposited layer, and has very important practical significance.