Rotavator Blade Testing: Hardness, Chemistry, and a Third of the Blade Gone in 26 Hours

Blades are the part of a rotavator that actually meets soil, and they're the part an FMTTI test examines most forensically. Three separate measurements are taken — hardness, chemical composition and dimensional wear — and each tells a different story.

The figures below come from a September 2021 Initial Commercial Test report for a tractor-mounted, PTO-operated rotavator with hatchet (L-shape) blades.

Hardness: two zones, two targets

A rotavator blade isn't uniformly hard, and it isn't supposed to be. The edge has to resist abrasion; the shank has to survive shock loading without cracking. So the standard sets different targets.

Zone	Requirement (HRC)	Observed (HRC)	Result
Shank portion	37 to 45	38.0 to 42.7	Conforms
Edge portion	56 ± 3	56.0 to 59.0	Conforms

Both conformed, and the shank figures sat comfortably mid-range. Note the edge result: 56.0 to 59.0 against a permitted 53 to 59. The machine passed, but it was running at the top of the window rather than the middle — harder at the edge means better abrasion resistance and less toughness, which is a legitimate design choice rather than a fault, but it's the kind of thing a report makes visible.

Chemistry: a modern blade against a 1981 standard

This is where it gets genuinely interesting, and where a lot of manufacturers get an unwelcome surprise.

The blade standard in force specifies two permitted materials: carbon steel or silicon-manganese steel, each with its own composition ranges. The blade actually fitted was boron steel — a material the standard doesn't contemplate, because it was written in 1981 and reaffirmed rather than rewritten.

Measured against the two options the standard does offer, the results came out like this:

Constituent	Carbon steel range	Si-Mn steel range	Observed	Result
Carbon (C)	0.70 – 0.85	0.50 – 0.60	0.284	Does not conform
Silicon (Si)	0.10 – 0.40	1.50 – 2.00	0.196	Conforms
Manganese (Mn)	0.50 – 1.00	0.50 – 1.00	1.336	Does not conform
Sulphur (S)	0.05 max	0.05 max	0.011	Conforms
Phosphorus (P)	0.05 max	0.05 max	0.015	Conforms
Boron (B)	—	—	0.002	—

Carbon low, manganese high, and boron sitting in a row with no specified range on either side of it — because the standard has nothing to say about boron at all.

This is a standards-lag problem, not a quality problem. Boron steel is widely used for soil-engaging parts precisely because it delivers hardness with better toughness than plain high-carbon steel. The standard simply predates its adoption. If you build boron-steel blades, expect the chemistry rows to read this way, and be ready to explain it to a buyer who reads "does not conform" without context.

Wear: the number that should change how you sell

Blade width was measured at two positions — at the tip, and 65 mm from the edge — before and after field operation. The results are stark.

Dry land, over 26.0 hours of operation:

• At the tip: initial widths of roughly 80 to 83 mm reduced to roughly 53 to 60 mm
• Wear: 25.3 to 35.9 percent, or about 0.97 to 1.38 percent per hour

Wet land, over 11.0 hours of operation:

• Wear: 1.5 to 11.7 percent, or about 0.11 to 1.07 percent per hour

Read that again: a blade set lost around a third of its width in 26 hours of dry-land work. Per hour, dry-land operation was roughly four times more abrasive than puddling.

For a manufacturer this cuts two ways. It's a genuine consumable-sales insight — blade replacement is a recurring revenue line, and the wear rate tells you the realistic interval. It's also a design signal: if your blades wear at the top of that band, a customer working predominantly dry land will notice, and your competitor's report is a public document too.

For a dealer or an institutional buyer, it's the number to ask about. A machine's field efficiency is measured on fresh blades. Its efficiency at hour 200 is a different question, and the wear table is the only published clue.

What to do before your blades are tested

1. Know your material's story. If you use boron steel, expect the chemistry table to show non-conformity against a standard written for other alloys, and prepare the explanation rather than being caught by it.
2. Check hardness at both zones, and aim mid-range. Passing at the extreme of a permitted band is passing, but it leaves nothing for batch variation.
3. Measure your own wear before the institute does. Run your blades in the abrasive soil you actually sell into, measure width loss per hour, and know your number before it appears in a public report.
4. Treat the wear figure as a sales input. A realistic replacement interval, stated honestly, is more useful to a dealer than a claim that blades last.

Understanding how blade results will read — and which of them affect the verdict against which are recorded for information — is part of what test process guidance covers. AgPro doesn't run the tests; the institute's engineers and its designated laboratories do.

For how a non-conformity can appear without changing the outcome, see evaluative vs non-evaluative parameters. For the standards involved, see which IS codes apply to a rotavator test.