00Cr17Ni14Mo2 (10% ammonium persulfate aqueous solution electrolytic etching) metallographic diagram

The observed microstructure of SUS316L after 10% Ammonium Sulfate (NH4 2SO4) electro-etching showed a banded-type ferrite-characteristic structure, which appear as a subset of ferrite.( Figure2). The ferrite bands were characterized by elongated grains of grains and grain sizes in the range of 2 to 50 µm. On the other hand, inert austenite grains were found in the matrix between ferrite bands. The ratio between ferrite bands and interval austenite grains were approximately 35:65. Sometimes, due to the stresses, embrittlement and phase transformation of martensite phase were observed in the grain boundary of ferrite band.

The presence of these small secondary austenite islands between ferrite bands can be attributed to the high-temperature stress relaxation during cooling. The specimens also underwent bainite transformation, causing numerous laths of very fine ferrite to form together with the ferrite bands and secondary austenite islands. All the laths (width <1 μm) of ferrite were distributed uniformly in the ferrite-austenite zones.

In addition to the presence of lath-type ferrite, martensite was also observed in the ferrite bands boundary region. The martensite had a needle shape and presented in anetopy. Martensite needles were about 1 μm in width and were arranged in an overall direction. Some needles had become broader with a width of about 10 μm, whereas some regions had almost no martensite needles present.

After NH4 2SO4 electro-etching, a small amount of delta ferrite was observed in the specimens, which was mainly present in the grain boundary region containing carbide. The delta ferrite had a fibrous crystallographically orientation, with a fine size in the range of 1 to 2 μm.

Similarly, a small amount of intermetallic compound, known as CR-Ni-Mo compound, was also observed in the specimens. This compound was mainly formed in the grain boundaries and had a cylindrical shape. The tubular and plate-shaped particles had a diameter of less than 3 μm. The presence of this intermetallic compound could be due to the difference between the rate of dissolution at the solid-liquid and grain boundary-liquid interface.

In summary, after 10% ammonium sulphate solution electro-etching, the SUS316L specimens were found to have a banded-type ferrite structure with ferrite grains, secondary austenite islands and lath type of ferrite and martensite, accompanied by a small amount of delta ferrite and intermetallic compounds, such as the CR-Ni-Mo compounds. These grains and phases provide useful information on the solidification behavior of the alloy and their interaction with the surrounding environment.

Metallographic analysis of SUS316L (10% aqueous ammonia etching)

SUS316L (10% aqueous ammonia etching) is a kind of austenitic stainless steel with a high chromium and nickel content, and is one of the most commonly used alloys today. In this analysis, we use a SEM and a standard metallography to observe its structure and composition density.

The results show that the surface of SUS316L (10% aqueous ammonia etching) smear is fine, uniform, and there is no obvious scratch marks. The microstructure consists of the typical austenitic grain structure, which is slightly enlarged and the grain boundaries are not obvious. On the basis of the observation of metallographic, it also shows that the grains are in different shape and size, with a few gaps between them. The matrix of the alloy contains austenite and a small amount of ferrite.

The austenite has a bright light-reflective color with a light yellow-gray and whitish area, a smooth and bright grains morphology, and the grains sizes are uniform. The ferrite’s color is a little darker and its edges are jagged, indicating a large grains structure. In addition, the alloy also contains a small amount of carbide, which has a black color.

The analysis states that the alloy has a good microstructure that can meet the technical requirements. Therefore, the SUS316L (10% aqueous ammonia etching) alloy can be applied in various applications with good performance.