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Wednesday, July 17, 2013

About Ni-Cr-Fe

The ternary diagram of Ni-Cr-Fe is one of the most used ternary diagrams in history. The two types of alloys covered here from the Ni-Cr-Fe diagram are Stainless Steel and Inconel (tm).
Stainless SteelThere are a vast number of types of Stainless steel. A metal alloy with a Chromium content greater than 11.5 % and an Iron content greater than 50 % is called a stainless steel. The stainless steels are broken into three major classes:

1. Chromium (11.5-17%) -iron alloys with carefully controlled carbon content. Can be heat treated to a magnetic martensite structure and are therefore known as martensitic stainless steels.

2. Chromium (17-27%) -iron alloys with low carbon content. Nonhardenable by heat treatment. Their crystal structure is magnetic ferrite and therefore are known as ferritic stainliess steels.

3. Chromium (16-26%) Nickel (6-22%) -iron alloys with low carbon content. Nonhardenable by heat treatment. Crystal structure of nonmagnetic austenite so are therefore called austenitic stainless steels.

The following table compares the composition and some basic properties of various types of stainless steel.

(1) Corrosion rate is in mils per year. The test was performed in 65% Nitric acid at 245 °F. (2) Table references

Types of Stainless steel and specific uses of each.
Stainless type 201, Stainless type 301, Stainless type 302, Stainless type 304, Stainless type 309

Inconel (tm)Inconel (tm) is a specialty alloy that uses higher percentages of Nickel and Chrome than Stainless steel, as well as many other elements in small quantities. It is actually a trademark name of Inco Alloys International and is in a group of metals known as the Nickel based super alloys. These small additions of other elements is solid-solution hardening. It is quite expensive and therefore usually reserved for applications when some type of stainless steel won't suffice. The following tables compare Inconels (tm) properties.

Corrosion of Inconel (tm)One outstanding characteristic of high-nickel alloys, like Inconel (tm), is their good resistance to a wide variety of corrosives. With few exceptions, high-nickel alloys do significantly better than martensitic, ferritic, and austenitic stainless steels in corrosive environments.