Learning and research
Connect sampling, mounting, polishing and observation so learners can relate each stage to the final image. Separate changes in material condition from changes in preparation.
Learning route
State the inspection question, prepare step by step and record specimen condition and actual settings. Relate unusual observations to the process log before deciding whether to repeat or adjust preparation.
Records
Retain specimen identity, orientation, equipment, consumables, operator, settings and images. Examples do not replace laboratory procedures.
Typical inspection scenarios
Annealed 45 steel teaching specimens (equilibrium Fe-C structure observation)
- Challenge
- Teaching labs process many specimens in large batches, demanding high consistency; students are inexperienced, so the route must be simple, safe and repeatable while reliably revealing a clear ferrite-pearlite structure.
- Preparation & method
- Cut discs of about Φ25 mm on a small metallographic cut-off machine and hot mount them in phenolic resin for fast batch mounting and easy handling. Grind with SiC papers from P240 to P2000, rotating 90° between steps and proceeding only after the previous scratches are fully removed; polish to a mirror finish on a nap cloth with 1 μm alumina or diamond suspension. Etch with 4% nital for 5–10 s, observe the ferrite-pearlite structure, and rate grain size by the comparison method.
- Reference standards
- GB/T 13298 Metallographic examination methods for metals; GB/T 6394 Determination of average grain size of metals; GB/T 13299 Determination of microstructure of steel
DP600 cold-rolled dual-phase steel teaching specimen
- Challenge
- The hardness gap between ferrite (soft) and martensite islands (hard) easily produces relief and smeared island edges during polishing, undermining threshold segmentation in image analysis; quantifying the two-phase area fraction demands stable etch contrast and sufficient statistical fields, making this a model case for quantitative metallography by image analysis.
- Preparation & method
- Take a longitudinal section along the rolling direction on a precision cut-off machine and cold mount. Grind with SiC papers from P400 to P2000, polish with 3 μm then 1 μm diamond, and finish with 0.05 μm colloidal silica to remove relief. Pre-etch with 4% nital to outline the two phases, then re-tint with LePera's reagent (a mix of 1% aqueous sodium metabisulfite and 4% picral), which renders martensite white and ferrite brown with sharp contrast; acquire no fewer than 20 fields at 100×–500× under bright field and quantify the martensite volume fraction by gray-level threshold segmentation in image analysis software; measure the hardness of each phase separately by micro-Vickers (HV0.1) for comparison.
- Reference standards
- GB/T 18876.1 Determination of area percentage of inclusions or microstructure in steels by automatic image analysis; GB/T 13298 Metallographic examination methods for metals; GB/T 4340.1 Metallic materials — Vickers hardness test
Scenarios are method examples, not customer test reports; confirm the process per specimen.
MICROCRE learning notes · confirm the method for the specimen.