Microstructure and Mechanical Properties of Fe-36Ni Alloy Prepared by a Two-Step Hydrogen Reduction Process

Fe-36Ni invar alloys (Invar 36 alloys), which have a low thermal expansion coefficient (CTE) and good mechanical properties, are typically produced through a high-pollution smelting process. A green and quick-process method for the two-step hydrogen reduction of a designed mixture of Fe 2 O 3 and NiO powders was developed to prepare Fe-36 wt.%Ni alloys. A dense Fe-36 wt.%Ni alloy with an oxygen content of 0.20 wt.% was successfully produced. A single γ -FeNi phase was identified at 1000°C, whereas grains and twins became more evident at 1100°C. The final alloy exhibited excellent mechanical properties at room temperature, showing a hardness of 154 HV, a tensile strength of 486 MPa, a yield strength of 251 MPa, and a fracture strain of 21%.