Startling C Behavior in Mo-Free Steel Atom Probe Tomography Volumes.

Area of Science:

• Materials Science
• Metallurgy
• Analytical Chemistry

Background:

• Atom probe tomography (APT) is a key technique for analyzing solute atom segregation at crystalline defects.
• Understanding solute segregation in industrial steels is crucial for material properties and performance.

Purpose of the Study:

• To investigate unexpected observations of carbon (C) segregation at dislocations in industrial steel grades using APT.
• To determine the influence of other elements, specifically molybdenum (Mo), on C segregation at dislocations.
• To assess the accuracy of APT measurements for carbon in iron under specific conditions.

Main Methods:

• Atom probe tomography (APT) was used to analyze solute atom distribution in steel samples.
• Transmission electron microscopy (TEM) was employed for correlative analysis of APT tips.
• Statistical analysis of carbon composition in APT volumes from molybdenum-free steels was performed.

Main Results:

• Carbon segregation at dislocations was exclusively observed in the presence of molybdenum co-segregation.
• In molybdenum-free steels, 35% of APT volumes showed carbon content in solid solution five times higher than expected.
• Correlative TEM-APT analysis confirmed the absence of carbon segregation at dislocations without molybdenum.

Conclusions:

• Atom probe tomography measurements of carbon segregation at dislocations in iron may be inaccurate.
• The high electric fields used in APT can cause dislocations to leave samples, potentially leading to erroneous carbon measurements.
• Molybdenum plays a critical role in the observed carbon segregation at dislocations during APT analysis.