Ferrite testing, also known as a ferritescope test, is a fast and non-destructive inspection technique used to measure delta ferrite levels in austenitic stainless steel and duplex stainless steel materials. Maintaining the correct ferrite content is crucial for ensuring corrosion resistance, durability, and preventing cracks in the material. Exceeding the maximum allowable ferrite content can make stainless steel welds more prone to hot cracking.
The advantages of ferrite testing include its non-intrusive nature, leaving minimal marks on the test sample. Moreover, it offers the convenience of a portable testing device that can quickly, accurately, and efficiently determine ferrite values. To perform a proper ferrite test, specific material thicknessesโboth minimum and maximumโare necessary for the test specimen. The results are then interpreted based on customer-defined specifications and requirements.
โง๐๐ฒ๐ฟ๐ฟ๐ถ๐๐ฒ ๐๐ฒ๐๐๐ถ๐ป๐ด is an important quality control process used to determine the ferrite content in stainless steel materials, especially welds.
๏ฟซ It provides valuable information about the microstructure and predicts material behavior during fabrication and service.
โง๐ช๐ต๐ฎ๐ ๐ถ๐ ๐๐ฒ๐ฟ๐ฟ๐ถ๐๐ฒ?
๏ฟซ Ferrite is one of the major microstructural phases found in stainless steels along with austenite.
๏ฟซ It is magnetic in nature compared to non-magnetic austenite.
๏ฟซ ๐ป๐๐ ๐๐๐๐๐๐๐๐๐๐ ๐๐ ๐๐๐๐๐๐๐ ๐๐๐๐๐๐๐ ๐๐๐๐๐๐๐ ๐๐๐๐๐๐๐๐๐๐ ๐๐๐๐ ๐๐๐๐ ๐๐๐๐, ๐๐๐๐๐๐๐๐๐, ๐ ๐๐๐๐๐๐๐๐, ๐๐๐๐ ๐๐๐๐๐๐๐ ๐๐๐ ๐๐๐๐๐๐๐๐๐ ๐๐๐๐๐๐๐๐๐๐.
๏ฟซ Ferrite improves weld strength but decreases ductility and corrosion resistance.
โง๐ง๐๐ฝ๐ฒ๐ ๐ผ๐ณ ๐ฆ๐๐ฎ๐ถ๐ป๐น๐ฒ๐๐ ๐ฆ๐๐ฒ๐ฒ๐น๐:
๏ฟซ ๐ผ๐ช๐จ๐ฉ๐๐ฃ๐๐ฉ๐๐ Stainless Steels (e.g. 304, 316):
These have low ferrite content, usually < 1%. Ferrite decreases corrosion resistance.
๏ฟซ ๐ฟ๐ช๐ฅ๐ก๐๐ญ Stainless Steels (e.g. 2205, 2507):
Contain a mix of austenite and ferrite. Require 25-65% ferrite for optimal properties.
๏ฟซ ๐๐๐ง๐ง๐๐ฉ๐๐ Stainless Steels (e.g. 409, 430):
Contain up to 100% ferrite in annealed condition. Minimum 85% ferrite required.
๏ฟซ ๐๐๐ง๐ฉ๐๐ฃ๐จ๐๐ฉ๐๐ Stainless Steels (e.g. 410, 420):
Have 75-95% ferrite in annealed state. 75-90% needed for good corrosion resistance.
โง๐ง๐ฒ๐๐๐ถ๐ป๐ด ๐ ๐ฒ๐๐ต๐ผ๐ฑ๐:
1. ๐๐๐ฉ๐๐ก๐ก๐ค๐๐ง๐๐ฅ๐๐๐ ๐๐๐จ๐ฉ๐๐ฃ๐ (๐ฟ๐๐จ๐ฉ๐ง๐ช๐๐ฉ๐๐ซ๐):
Involves microscopic analysis of etched samples. Accurate but time-consuming and requires expert analysis.
2. ๐๐๐ง๐ง๐๐ฉ๐๐จ๐๐ค๐ฅ๐ ๐๐๐จ๐ฉ๐๐ฃ๐ (๐๐ค๐ฃ ๐ฟ๐๐จ๐ฉ๐ง๐ช๐๐ฉ๐๐ซ๐):
Uses magnetic induction principle to rapidly measure ferrite content. Widely used for its speed and portability.
โง๐๐ฒ๐ฟ๐ฟ๐ถ๐๐ฒ ๐๐ฐ๐ฐ๐ฒ๐ฝ๐๐ฎ๐ป๐ฐ๐ฒ ๐๐ฟ๐ถ๐๐ฒ๐ฟ๐ถ๐ฎ ๐ถ๐ป ๐ช๐ฒ๐น๐ฑ๐:
1.Austenitic steels: 4-8% (Keep > FN4.) ferrite prevents micro-cracking during solidification.
2.Duplex steels: 30-65% ferrite required for strength and corrosion resistance.
โง๐๐ผ๐ป๐๐ฒ๐ฟ๐๐ถ๐ผ๐ป ๐๐ผ๐ฟ๐บ๐๐น๐ฎ๐:
๏ฟซ Ferrite % = 0.7 x FN (for 22% Cr duplex)
๏ฟซ Ferrite % = 0.65 x FN (for 25% Cr duplex)
๏ฟซ FN = (Ferrite %) x [Formula] (for FN >10)