The Function of Ferrite In Austenitic Stainless Steel

The Function of Ferrite In Austenitic Stainless Steel

Austenitic stainless steel is an important type of stainless steel welding materials. It is widely used in various fields because of its good heat resistance, corrosion resistance, low temperature resistance, good processability and weldability. And its production accounts for about 70% of the total stainless steel.

The Formation Mechanism of Ferrite

All different types of stainless steel are ion-based alloys with 12% Cr or more. The structure of stainless steel is determined by the alloying element content (also known as chromium and nickel equivalent).

For stainless steel, alloying elements can be divided into two main types---Ferrite forming elements (also known as chromium equivalent elements) and Austenite forming elements (also known as nickel equivalent elements).The balance between the two types of elements decides how much iron is in the tissue. The Austenite forming elements are mainly C, N, Mn, Ni, Cu, etc., and the Ferrite forming elements are mainly Cr, Mo, Si, NB, Al, Ti, etc.

Advantages and Disadvantages

Advantages:

1. Prevent hot cracks 

2. A small amount of ferrite can improve the corrosion resistance of welded joints

Disadvantages:

1. It is easy to produce brittle phase and reduce the toughness of the material.

 2. Excessive drop of ferrite leads to decrease of austenite resistance to pitting corrosion and special medium corrosion.

Control

In addition to the design of the weld composition, also there is the control of the welding process. 

1 The height of the arc and the type of shielding gas will have a significant impact on the N content of the deposited metal, and then affect the ferrite content of the deposited metal.

 2 The arc height and the type of shielding gas have a significant impact on the N content of the deposited metal, and the N content affects the ferrite content of the weld.