Prakt. Met. Sonderband 38 (2006) 393 
As stated above, an increase in thickness reduction caused the time of etching to reduce. 
This is basically due to increase in density of defects populations such as dislocations. 
High dislocation density provides an extra effective energy particularly for the surface 
atoms exposed directly to etchants, by which the rate and driving force of corrosion at the 
surface increase, so etching time expected to decrease. As it is shown in Figure 1, 
reduction of etching time with increasing the amount of deformation when using Fry, 
Aquaregia or Hydrochloride acid is linear, but this is not the case for Glyceregia. The rate 
of reduction of etching time with increasing deformation when Kalling used decreased in 
comparison with the above mentioned solutions. Effect of Nitric acid on the sample 8 
presented in table 5 was in such a way that the time of etching, by increasing deformation 
pm decreased approximately linear, but for sample 13 the rate of etching time decreasing was 
— in an exponential way with increasing the amount of cold work. So one may conclude that 
the amount of cold work not only affected the etching time but also the strength of the 
solution used and even the slight difference in the compositions of the samples (i.e. 
samples 8 and 13) can effect the etching time. 
The quality of the pictures obtained by optical metallography depends not only on etching 
solution and the technique used but also to composition of the steel. Slight variations in 
composition affect the microstructure clearance under an optical microscope. The 
differences in microstructure revealed by various etchants and techniques are shown in 
figure 2. Looking the revealed features one may recommend the following etchants and 
techniques for different metallographic purposes. 
Table 7: Recommended etchants and etching techniques for revelation of Sandvik 
stainless steel microstructure 
= Etchant Technique Type of Microstructure 
Aquaregia Soaking General Microstructure 
Fry Soaking Martensite 
Glyceregia ! Soaking Grain and Twin Boundaries 
Kalling Soaking Martensite 
Nitric Acid Electrolytic Grain Boundaries 
Hydrochloric Acid Electrolytic Grain and Twin Boundaries 
Orthophsphoric Acid Electrolytic Twin Boundaries 
V2A Hot Soaking General Microstructure 
4. Conclusions 
1- Increase in amount of cold work for the same samples causes the etching time to 
jum decrease. 
a 2- Thermal etching in air on Sandvik 1RK91 has no considerable results. 
3- For revelation of general microstructure of Sandvik 1RK91, etchants such as Aquaregia 
3: and V2A are effective. V2A recommends for martensitic microstructures. 
a 4- For revelation of pure grain boundaries of Sandvik 1RK91, Nitric acid is the best etchant 
while Aquaregia is effective sometimes. 
ce 5- For revelation of pure twin boundaries of Sandvik 1RK91, Orthophsphoric acid is the 
best while Hydrochloric is suitable for some compositions. 
ad in furnace 6- Martensite in martensitic microstructure revels by Fry and Kalling reagents, however 
Kalling results in better contrast.