Akasel publishes this route by hardness band rather than by alloy name, and most carbon and low-alloy steels sit inside it. Check your material against the band before using the figures: a case-hardened or quenched part will be harder than its core and belongs on a different sheet.

Why carbon and low-alloy steels are difficult

The route is chosen by hardness, not by name

This is the 150–400 HV method. A normalised mild steel, most structural grades and most low-alloy grades in the annealed or normalised condition fall in it. A through-hardened or case-hardened part does not, and preparing it to these figures will under-grind the hard region and over-polish the soft one. Measure, or use the band above.

Inclusions are usually the reason the sample exists

Sulphides and oxides are softer and harder than the matrix respectively, so both relieve. A sequence that runs long to chase the last scratch will pull sulphides and round oxides, and the inclusion rating that follows is then a rating of the preparation. Times are short here for that reason.

It ends on a fine diamond rather than on an oxide

Unlike the stainless route, this one finishes on 1 µm diamond. Carbon and low-alloy steels do not need chemical assistance to give up their deformed layer, and an oxide step on a plain-carbon steel mostly costs time and risks staining.

The published route

Akasel publishes this sequence for carbon and low-alloy steels. The figures are theirs. Times are quoted for a 300 mm preparation system and forces for a single 40 mm diameter sample.

Step	Surface	Abrasive or suspension	Speed	Force	Time
1 — plane grinding	Aka-Piatto 220	Water	300 rpm	30 N	Until plane
2 — fine grinding	Aka-Allegran 3	DiaUltra, 9 µm	150 rpm	35 N	4:00 min
3 — diamond polishing	Aka-Silk	DiaUltra, 3 µm	150 rpm	30 N	3:00 min
4 — final polishing	Aka-Napal	DiaUltra, 1 µm	150 rpm	20 N	1:00 min

Source: Akasel Aka-Brief #16, Materials of Hardness 150–400 HV, 2022 edition, page 1. Every figure in this table is printed on that page; none of them is ours.

Where the method and this catalogue differ

We say what the method specifies and what we list, and we do not put the nearest thing we sell in its place.

Water — no consumable — the disc runs under water.

Reading the sequence

The shape of the route says more than any single number in it. This part is our reading, not a manufacturer statement.

Three abrasive stages, each about a third of the previous grain size. 9 µm, then 3 µm, then 1 µm. Each step has to remove the damage the one before it left, and a ratio of roughly three is what makes that possible in the time quoted. Skipping a stage does not save the time it appears to: it moves the work into the next step, which is running a finer abrasive and is much slower at removing material.

The last step is one minute. That is short, and deliberately so. By 1 µm the job is removing the previous step’s scratches, not levelling; anything beyond that starts producing relief at the inclusions the sample was sectioned to show.

Etching is a separate decision. This route delivers a polished surface. Which etchant follows is a function of what you are looking for, and it is not something a consumables supplier should be prescribing.

The same sample, after each step

Akasel photographs the same specimen after every stage of this route and publishes the images on page 2 of Aka-Brief #16. We have not reproduced them here. The titanium guide shows what that sequence looks like for a material we do hold the images for.

Scaling it to your machine

Smaller platen, longer steps. The maker’s guidance is to add roughly a third to the times on a 250 mm system and to double them on a 200 mm one. The abrasive does the same work over less swept area.
Bigger samples, more force; smaller samples, less. The quoted loads are per 40 mm mount. Scale with mounted area rather than guessing, and if your machine cannot deliver the figure, extend the step instead of exceeding it.
Head speed is fixed. 150 rpm on the sample holder throughout, constant across every published method in this series.

What the route needs

5 consumables, and the sequence does not work without them:

Where these figures come from

The preparation route is Akasel’s, published in Akasel Aka-Brief #16, Materials of Hardness 150–400 HV, 2022 edition, page 1. The reading of it — why the sequence is shaped this way, what goes wrong, what to watch — is ours, and it is an interpretation rather than a manufacturer statement. We have not run this method in our own laboratory and we do not claim to have. Where the method calls for something we do not list, the guide says so above rather than substituting the nearest thing we sell.

Sources

Akasel Aka-Brief #16, Materials of Hardness 150–400 HV, 2022 edition, page 1 — every figure in the step table.
Akasel product pages and data sheets, cited row by row on each linked product page.
The reading of the method, and everything under “Why” and “Reading the sequence”: P2 Industrial.

Preparing carbon and low-alloy steels for metallography