Any of us have been familiar with “stainless steel”. There are countless tools made of this material such as measuring tools, automotive parts, cutting tools, etc. But, do you really recognize it? Why when it comes to corrosion-proof tools, people go for items made of this metal? Here we will discover it.
What is Stainless Steel?
Stainless steel is classified as an alloy.
Alloy refers to the blend of two metals. It can be also addressed to a blend of metallic and non-metallic material.
In the case of blending iron and carbon, it generates an alloy called steel.
When it comes to stainless steel, it’s steel that has the addition of chromium.
Simply, they are:
Steel is Iron + Carbon
Stainless steel is Iron + Carbon + Chromium.
However, in order to become stainless steel, there is required for the ingredients to fulfill the percentage of carbon and chromium as this:
The chromium content is not lower than 10.5% and the carbon is not higher than 1.2%. Let the rest percentage contain iron. Some types of stainless steel get the addition of other elements such as molybdenum, nickel, etc, in a small percentage.
Due to the addition of chromium, this alloy then becomes more resistant to corrosion. The more the chromium, the more resistant it is. Moreover, stainless steel has other advantages such as poses excellent physical properties (hardness, strength, etc), bendable, weldable, stampable, etc.
Types of Stainless Steel
You need to know there are some types of stainless steel. Based on the crystalline structure, stainless steel is grouped into 4 types: Austenitic, Ferritic, Martensitic, and Duplex.
1. Austenitic St Steel
Austenitic stainless steel has a face-centered cubic (FCC) structure. It means one atom takes place at the center of each face and at each corner of the cube. This is generated from the addition of nickel ranging 8-10%, whereas the chromium element remains unchanging at 18% of the total mass of the stainless steel.
This structure allows them to be non-magnetic and corrosion-resistant. In comparison with ferritic below, austenitic is more reliable to resist corrosion. The tank is one example of how austenitic is an extremely useful material in the military.
2. Ferritic St Steel
Ferritic steels have a body-centered cubic (BCC) structure. This structure is indicated by an atom at the center of the cubic structure. This type has high chromium which could compose 10.5-27%, low carbon, and no nickel in general.
One outstanding property of ferritic stainless steel is its corrosion resistance; even though as good as austenitic. What’s more, it’s ductile. The downside of ferritic for feeler gauge is its magnetic property. Ferritic, further, can be grouped into 5 grades.
3. Martensitic St Steel
The structure of martensitic is a body-centered cubic (BCC) as well as ferritic. Therefore, it’s magnetic. The chromium composition is about 10.5-18%. In comparison with ferritic, the carbon composition is higher. In basic composition, there is no nickel addition. When it’s added nickel, it’s meant to add corrosion resistance and toughness property.
The advantage of martensitic is the capability to be hardened with heat treatment. By doing so, a specific hardness can be achieved up to 60HRC. Moreover, by the process of tempering and hardening, its anti-corrosion property can be maximized.
4. Duplex St Steel
Its name “duplex” has a meaning of two-phase structure. In other words, there contain austenitic and ferritic structures at the same stainless steel. The composition of both of them is equal.
It occurs in roughly two steps. From melting state (liquid) to solid, the ferritic structure forms. Then it cools down at room temperature, half of the ferritic structure turns to the austenitic structure.