How can you tell the difference between Inconel and stainless steel?
What is Inconel?
Inconel alloys are a family of nickel-chromium-based superalloys that offer high corrosion resistance, oxidation resistance, high temperature strength, and creep resistance. Inconel alloys are able to withstand high temperatures and extremely corrosive environments thanks to two factors.
First, the formation of the intermetallic compound Ni3Nb in the gamma-binary phase (ɣ''). This intermetallic phase acts as a "glue" at the grain boundaries. This "glue" prevents the grains from increasing in size when heated to high temperatures (generally, smaller grains mean higher strength, while larger grains mean better ductility). Second, Inconel alloys are highly corrosion resistant due to the formation of a passive layer when heated. These two factors make Inconel alloys ideal alloys for applications ranging from hot section gas turbines to deep sea drilling. So, what are the downsides of these alloys? They are expensive, difficult to machine, and difficult to work with.
Stainless Steels
Stainless steels are characterized by a chromium content above 10.5% by weight. Stainless steels are divided into five categories:
Austenitic stainless steels
Ferritic stainless steels
Martensitic stainless steels
Duplex stainless steels
Precipitation hardening stainless steels
These stainless steels are named for the microstructures that form in their alloys. Duplex stainless steels are a mix of austenitic and ferritic microstructures, and precipitation hardening means that precipitates can form to increase the strength of these types of stainless steels. The strength and corrosion resistance of stainless steels depend on these microstructures. For example, austenitic stainless steels are the most ductile stainless steels, while also being the most corrosion resistant. Martensitic stainless steels, on the other hand, are generally stronger but less corrosion resistant. Austenitic stainless steels have a larger equiaxed grain structure, compared to the smaller lathe grain structure in martensitic stainless steels, which is what gives them these properties.
All stainless steels are more corrosion resistant than traditional steels and are used in a wide range of applications from kitchen utensils and building structures to biomedicine and food preparation.
Inconel vs. Stainless Steel: What's the Difference?
First, Inconel is much more expensive than stainless steel alloys. Inconel also offers greater corrosion resistance and strength at elevated temperatures. However, at low temperatures, steels like 17-4PH stainless steel will be stronger than Inconel. The main deciding factors when choosing between these two different alloys are cost, temperature, and strength. If a lower cost but higher strength part is required, stainless steel may be the best choice. If a part is required that has strict air requirements and requires elevated temperatures, then Inconel is the alloy that is more suitable for the application.
