1.4462 | X2CrNiMoN22-5-3 Duplex with sigma phase

This austenitic-ferritic steel is a so-called duplex steel.
Duplex steels represent the link between the higher strength of ferritic chromium steels and the good corrosion resistance of austenitic Cr-Ni steels.
This sample showed a very low impact energy of 6 joules in the notched bar impact test at -40 °C. The alloy should actually achieve an impact energy of at least 40 J at -40 °C.
The following mechanical properties were determined in the tensile test:

• Rp0.2: 782 MPa
• Rm: 879 MPa
• A: 19 %
• Z: 36 %
• The tensile strength is within the target range, the elongation at break below.

The microstructure consists of austenite with delta ferrite and sigma phase and was contrasted with various etching agents, partly also electrolytically.
Sigma phase forms at the ferrite-austenite phase boundaries and grows preferentially into the ferrite.
Judging from the microstructure, the steel was held at around 850 to 900 °C for 1 to 10 hours.

• V2A pickling @ 70 °C
• 20 % NaOH 8V/3sec
• 10 % oxalic acid 2V/10sec
• 10 % oxalic acid 10V/10sec
• Groessbeck
• Bloech&Wedel 2

A scanning electron microscope examination of the fracture surface from the notched bar impact test shows brittle fracture in large parts with low ductile honeycomb fracture components.