1. The classic sequence and what each step removes
| Step | ANSI grit | P-grade | Average particle size |
|---|---|---|---|
| Planar grinding | 240 | P280 | 52 µm |
| Fine grinding 1 | 320 | P400 | 35 µm |
| Fine grinding 2 | 400 | P800 | 22 µm |
| Fine grinding 3 | 600 | P1200 | 15 µm |
The pairs and particle sizes are from Buehler's CarbiMet paper data; Buehler's grinding guide describes 240/320/400/600 grit [P280/P400/P800/P1200] as the "traditional" fine-grinding sequence, with 120–240 grit used when the cut surface needs heavier planar grinding. Some methods add a 1000 grit [P2500] step before polishing.
2. The ANSI vs P-grade trap
Metallography papers are sold in two grading systems. US papers are usually graded to ANSI/CAMI, European and Asian papers to FEPA "P" grades — and the numbers do not match above about 220. ANSI 400 is P800, not P400; ANSI 600 is P1200. A lab that switches supplier and keeps "the same numbers" can end up skipping a step without knowing it. Always compare by P-grade or by micron size. More on the two systems in our grit to Ra guide, section 2.
3. Where to start: soft vs hard materials
| Material | Typical SiC sequence (ANSI grit) | Aim |
|---|---|---|
| Soft ferrous: low/medium carbon steel, austenitic stainless | 240, 320, 400, 600, 800, 1200 | Keep deformation shallow and protect second phases |
| Hard ferrous: high carbon, tool steel, case-hardened, martensitic stainless | 180, 240, 320, 400, 600 | Planarize, then minimize deformation |
Source: metallographic.com grinding guideline. The same guide recommends starting with the finest abrasive possible, typically 240 or 320 grit, and using coarser grit only for heavy stock removal — coarse papers put in deeper deformation that every later step has to remove.
4. Technique that makes the sequence work
- Grind wet. Water on waterproof SiC paper carries away swarf and keeps heat and surface deformation down.
- Rotate 90° between papers. The new scratches cross the old ones, so you can see when the previous pattern is completely gone.
- Grind until the old scratches are gone — then a little more. Moving on early is the most common reason a sample will not polish.
- Clean between steps. Rinse the sample and your hands; one coarse grain carried onto a fine paper leaves a scratch that survives polishing.
- Change paper when it stops cutting. SiC breaks down quickly; a worn paper smears rather than cuts.
5. Mapping the sequence onto Eagle AP806
Eagle AP806 is a silicon carbide waterproof paper graded in P-grades, with common stops at P60, P120, P240, P320, P400, P600, P800, P1200, P2000, P3000 and P10000, in sheets and in discs of 180, 200, 250, 280, 300 and 350 mm, PSA or plain backed.
| Purpose | AP806 sequence |
|---|---|
| Short sequence, most steels | P240 → P400 → P800 → P1200 |
| Full sequence, ferrous samples | P240 → P320 → P400 → P600 → P800 → P1200 |
| Extra pre-polish step | add P2000 after P1200 |
| Heavy sectioning damage | start at P120, then continue as above |
After grinding, polish on a napped cloth with diamond suspension or alumina; matching black, red and white velvet polishing discs come in the same diameters as the AP806 discs.
6. Common questions
What is the grinding sequence for metallographic samples?
A traditional sequence is 240, 320, 400 and 600 grit (ANSI), which is P280, P400, P800 and P1200, grinding wet on silicon carbide paper. Some methods add P2500 before polishing.
What grit should I start with for metallographic grinding?
Start with the finest grit that removes the sectioning damage, typically 240 or 320 grit (about P280 to P400). Use coarser paper only for heavy damage, because it adds deeper deformation.
Is 600 grit the same as P600?
No. 600 grit on the ANSI/CAMI scale is about P1200 on the FEPA P scale. Above about 220 the two systems diverge, so compare papers by P-grade or micron size.
Why rotate the sample 90 degrees between papers?
So the new scratches cross the old ones. When none of the previous scratch direction is visible, that step is finished.
Should metallographic grinding be wet or dry?
Wet. Water on waterproof SiC paper carries away swarf and keeps heat and surface deformation down.
Sources
- Buehler CarbiMet paper data (ANSI/P pairs, particle sizes): www.bergeng.com/mm5/downloads/buehler/CarbiMet%20Paper.pdf
- Buehler grinding and polishing guide, copy on Scribd (traditional sequence): www.scribd.com/document/550642144/12
- metallographic.com — abrasive grinding guideline: metallographic.com/metallographic-consumables/grinding/abrasive-grindi
- metallographic.com — SiC grit, P-grade and micron comparison: metallographic.com/Metallographic-Consumables/Metallography-SiC-Papers
- OnPoint Abrasives — wet grinding on SiC paper: onpointabrasives.com/collections/all/products/carbipro-silicon-carbide
Sources checked 2026-10. MOOSEFOS model data is from our own product pages.