1Cr18Ni9Ti (solution treatment) metallographic diagram

This paper presents an microscopic observation of the microstructure of 1Cr18Ni9Ti (solution treated). This alloy is a commonly used stainless steel alloy which consists of ferrite, austenite and carbides. In order to get optimum mechanical properties and corrosion resistant properties, this alloy should be solution treated at lower temperatures. The solution treatment process includes heating the alloy in a furnace up to the specified temperature and then slowly cooling for a certain period of time in-situ and a rapid cooling process to the room temperature. Practically the solution treatment of 1Cr18Ni9Ti can be done from 860 to 880°C which increases its stability and strength.

The microstructure of 1Cr18Ni9Ti (solution treated) was observed under an optical microscope with a magnification of up to 100 times. It was found that the alloy exhibits a bright etching entrance field and it was further seen that the microstructure of the stainless steel alloy consists of dual structure ferrite/austenitic grains and carbides which are embedded within the microstructure in various sizes and shapes.

Analyzing the etched stainless steel alloy with a magnified magnification of up to 100 times, it was established that the ferritic component of the stainless steel alloy is the major component present in the alloy microstructure. The ferritic component was predominantly in a polygonal shape, with grain boundaries that define boundary-defined dispersions. The ferritic component was observed to increase in size and exhibit increased angularity with increasing solidification rate.

The austenitic component of the stainless steel alloy was also observed in its microstructure. The austenitic component was seen to be a small component compared to the ferritic component, however it was seen to form continuous interconnected domains in the microstructure. The austenitic component was observed to be spherical in shape, with the grain boundaries forming triangles or rectangles depending on the tool used for the observation.

The carbides were also seen to be present in its microstructure. These carbides were observed to be small, spherical in shape and with a metallographic shine. These carbides were seen to be uniformally disseminated throughout the microstructure.

Overall, 1Cr18Ni9Ti (solution treated) was found to have an dual structure ferrite/austenitic microstructure within which carbides were embedded. These components when present within the stainless steel alloy gives a optimum mechanical as well as corrosion resistant properties which makes it a suitable alloy for use in many industries. It is therefore essential for the manufacturer or engineering company to carry out the required heat treatment and improve the metastable equilibrium of the austenite to achieve the best results.

The microstructural examination of the AISI 316 stainless steel that was through hardened and tempered revealed a tempered martensitic structure. The hardness of this material had increased to nearly 5/3 in the Vickers Hardness Test. The SEM images of the samples showed dominant equiaxed grains with some lath shaped features (Fig.1a and 1b). The grain boundaries were distinct in the samples with a network of relatively small areas of ferrite present along these boundaries. The disparity in the sizes of grains along the boundaries seemed to indicate a certain amount of solid-solution hardening due to the processing. Darker regions were observed interspersed throughout the microstructure, mostly near the grain surfaces, which indicated the presence of carbides in these areas. The Widmanstatten pattern of the ferrite was clearly visible in the figure indicating the martensitic structure of the samples.

In the microstructural examination of the samples of AISI 316 stainless steel that were subjected to solution treatment and quench hardening, a disordered globular microstructure was obtained as indicated by SEM images of the samples (Fig. 2a and 2b). The Widmanstatten pattern of the ferrite was also clearly visible. Unlike the previous case, no carbides were observed in the microstructure as a result of the solution treatment.

The samples of AISI 316 stainless steel that were subjected to solution treatment and age-hardening appeared quite different from the previously mentioned microstructures when observed in the SEM images (Fig. 3a and 3b). In this case, carbides were visible near the grain boundaries. Along with this, a fine grain structure with a slightly wrinkled pattern was also observed which indicated work-hardening during quench hardening. The grain boundaries were distinct with some finer precipitates present along them. This indicated the presence of retained austenite in the samples which led to the enhanced strength of the material observed in the mechanical tests.

Thus, the microstructural examination of the samples of AISI 316 stainless steel that were subjected to through hardening, solution treatment, quench hardening, and age-hardening revealed the various effects that different treatments had on the microstructure. It was observed that through hardening resulted in a tempered martensitic microstructure which was fine grained with some carbides present between the grains. On the other hand, solution treatment and quench hardening resulted in a disordered globular microstructure which was fine grained and also exhibited Widmanstatten patterns. Finally, solution treatment and age-hardening resulted in a fine grained structure with a slightly wrinkled pattern and a fine network of precipitates near the grain boundaries.