Most disputes over ferroalloy and metal powder supply are not really about quality. They are about ambiguity — a specification that two competent parties read differently, and a sampling clause that nobody wrote. The material arrives, it does not behave as expected, and there is no agreed basis for establishing whose analysis is right.
This guide is written from the manufacturing side of that relationship. It sets out what a complete purchase specification for a ferroalloy or metal powder actually contains, what each number means, where the standard traps are, and how to qualify a supplier so that the second container performs like the first one. It is aimed at procurement and quality managers in welding consumable manufacture, powder metallurgy, steelmaking and mineral processing — and at importers who need to specify with precision across a distance.
1. How to read a certificate of analysis
A certificate of analysis (COA), sometimes issued as a mill test certificate (MTC), is a statement about a specific batch. Reading it well means asking four questions of every number on it.
Is this a typical value or a guaranteed limit?
"Si 47%" and "Si 45% min" are completely different commitments. A typical value describes what the process usually produces; a guarantee is a contractual limit. Specifications should be written as min/max limits with a stated tolerance band, and the COA should report the actual measured value against those limits. Beware of specifications that quote a single nominal figure with no band — they leave the tolerance entirely to the supplier's discretion.
On what basis is it reported?
Dry basis or as-received? For a hygroscopic powder shipped in a humid season, this can be a meaningful difference in both chemistry and invoiced weight. State the basis explicitly, and state whether moisture is deducted from the invoiced weight.
By what method was it measured?
XRF, optical emission spectrometry, wet chemical analysis and combustion analysis do not always agree, particularly for light elements and for carbon and sulphur at low levels. Carbon and sulphur in the range that matters for low-carbon grades should be determined by combustion infrared analysis, and the method should be named on the certificate. Where a specification is critical — low carbon ferro chrome or low carbon ferro manganese for stainless or low-hydrogen consumables — name the method in the purchase order, not just the limit.
Who took the sample, and from what?
This is the question that decides disputes, and it is covered in section 4.
2. Mesh, micron and the sieve-series trap
Particle size is where more specifications go wrong than anywhere else, for two reasons.
First, "mesh" is not one system. The ASTM E11 series, the Tyler series, the British Standard series and the Indian Standard IS 460 series do not align exactly. A "100 mesh" aperture is not identical across all of them. If your supplier sieves to one series and your incoming inspection uses another, you will get disagreements that neither party can resolve. Name the series in the specification. Better still, specify in microns and let each party convert.
| Mesh | Aperture | Mesh | Aperture |
|---|---|---|---|
| 20 | 850 µm | 140 | 106 µm |
| 30 | 600 µm | 170 | 90 µm |
| 40 | 425 µm | 200 | 75 µm |
| 50 | 300 µm | 230 | 63 µm |
| 60 | 250 µm | 270 | 53 µm |
| 80 | 180 µm | 325 | 45 µm |
| 100 | 150 µm | 400 | 38 µm |
Second, a single cut point is not a specification. "−100 mesh" tells the supplier only that nothing should be retained on a 100 mesh screen. It says nothing about how much of the material is at 45 µm or below — and in a welding coating or a PM blend, that fines fraction drives surface area, reactivity, flow, packing density and dusting. Two lots that both pass "−100 mesh" can behave completely differently.
A proper size specification states:
- the sieve series in use;
- a maximum percentage retained on the top screen (oversize control);
- the target distribution across intermediate screens, reported as either discrete or cumulative — state which;
- a maximum percentage passing the bottom screen (fines control);
- the sieving method and duration, since dry sieving time affects results for cohesive powders.
3. The physical properties buyers forget to specify
Chemistry gets all the attention on a COA. In practice, the properties that halt production are usually physical.
- Apparent (bulk) density — measured by a standardised funnel method such as ASTM B212, or B417 for powders that will not flow freely. It determines die fill depth in a PM press and volumetric dosing in an electrode plant. A change between lots changes part weight or coating weight directly.
- Tap density — the density after standardised tapping. The ratio of tap to apparent density indicates how cohesive a powder is.
- Flow rate — the time for a standard mass to flow through a calibrated funnel (Hall flowmeter, ASTM B213; Carney funnel for poorly flowing powders). Directly predictive of feeder and hopper behaviour.
- Moisture — specify the maximum and the test conditions (drying temperature and time), because "moisture" measured at 105 °C and at 200 °C are different numbers.
- Oxygen content — critical for powder metallurgy, where oxide films prevent sinter bonding, and increasingly relevant to welding, where oxidised powder behaves like a lower-assay material.
- Morphology — specify the production route (atomised, milled, reduced) rather than trying to describe the shape.
- Surface treatment — stabilised or not, for ferro silicon and similar reactive powders.
4. Sampling: the clause that decides every dispute
Powders and granular ferroalloys segregate. A scoop taken from the top of a jumbo bag is not representative of the bag, and a bag taken from the door of a container is not representative of the lot. When buyer and seller analyse different samples, they get different answers, and neither is lying.
A sampling clause should specify:
- How many increments are taken and from where — sampling from a moving stream during packing is far better than sampling from static bags, because a moving stream presents the whole lot.
- How the gross sample is reduced — riffle splitting or rotary division, not coning and quartering by hand, which is operator-dependent.
- How many retained samples are prepared, and who holds them. The standard arrangement is three: one for the supplier, one shipped with the consignment for the buyer, one sealed and held in case of dispute.
- The umpire procedure — if buyer and seller results differ by more than an agreed tolerance, a named independent laboratory analyses the sealed sample, and its result binds both parties. Agreeing this in the contract costs nothing and saves a great deal later.
- Retention period — typically six to twelve months, matched to the buyer's own product warranty period.
5. Packaging, marking and moisture
For ferroalloy powders, packaging is a technical specification and not a logistics detail. Moisture that enters in transit or in store ends up as diffusible hydrogen in a customer's weld, as porosity in a sintered part, or as caking that will not disperse.
- Specify the liner, not just the bag. A woven polypropylene bag with an inner polyethylene liner, heat-sealed, is the practical minimum for hygroscopic powders. For sensitive material, aluminium-foil laminate or vacuum packing is available.
- Match the pack size to the consumption pattern. Opened packs deteriorate. A plant consuming 25 kg per shift should not be buying 1 MT jumbo bags. AIM ALLOYS supplies 25 kg bags, 50 kg bags, 100 kg drums and 1 MT jumbo bags for exactly this reason.
- Specify marking. Product name and grade, batch number, net and gross weight, date of manufacture, hazard labelling where applicable, and the purchase order number. Batch number on the pack is what makes traceability real.
- Specify palletisation and container loading. Desiccant, container liner, and stowage instructions matter for sea freight through humid conditions.
6. Documentation and compliance
A complete document set for an export shipment of ferroalloy powder normally comprises: commercial invoice, packing list, certificate of analysis per batch, safety data sheet, certificate of origin, bill of lading or air waybill, and any pre-shipment or third-party inspection certificate agreed.
Two compliance points deserve specific attention:
- Transport classification. Ferro silicon with 30% or more but less than 90% silicon is classified as UN 1408, Class 4.3 — substances which, in contact with water, emit flammable gases. Several metal powders, including aluminium powder, carry their own classifications. Declaration must be correct, and the packaging and container ventilation requirements that follow are not negotiable.
- Safety data sheets. Should be current, in the destination language where required, and specific to the grade supplied.
7. Qualifying a supplier
Chemistry can be verified on arrival. Consistency cannot — it has to be assessed at the supplier. A meaningful qualification looks at:
- Process route and control. Does the supplier manufacture, or trade and repack? Both are legitimate, but a manufacturer can change a distribution to suit you and a trader cannot.
- In-house laboratory. What instruments, what calibration regime, what participation in inter-laboratory comparison. A supplier who outsources every analysis cannot control the process in real time.
- Batch traceability. Can they trace a delivered bag back to a furnace tap or an atomising run, and forward to every other customer who received that lot?
- Change control. Is there a documented procedure for notifying customers before a process change? For qualified welding and PM formulations, this is more important than any single test result.
- Non-conformance handling. Ask about a real past failure and how it was resolved. The answer tells you more than any certificate.
- Capacity and continuity. Can they support your growth, and what happens if their furnace goes down?
Qualify on a production campaign, not a sample. A 25 kg sample tells you the chemistry. Only a full batch run through your own process tells you whether the powder flows, disperses, extrudes, presses or suspends the way you need it to. Build the trial campaign into the qualification plan and agree in advance what "pass" looks like.
8. Commercial terms that hide technical risk
- Price basis. Per tonne of alloy, or per unit of contained element? For variable-assay materials, per contained unit is the honest basis and protects both parties.
- Moisture and weight. Is the invoiced weight gross, net, or net dry? Who weighs, and is there an agreed weight tolerance?
- Incoterms. Know exactly where risk transfers, and make sure your insurance matches. Powder damaged by water ingress in transit is a claim nobody enjoys.
- Lead time and safety stock. Specialty grades — low carbon ferro chrome, ferro titanium, ferro boron, ferro vanadium — have longer and less predictable lead times than commodity grades. Plan cover accordingly and dual-source where a single grade can stop a production line.
- Rejection and remedy. What happens if a lot fails? Return, replace, rework, or price adjustment — and who bears freight? Agree it before you need it.
9. The one-page checklist
| Block | Must state |
|---|---|
| Identity | Alloy, grade, production route (atomised / milled / reduced), surface treatment (stabilised or not) |
| Chemistry | Each element as min/max with tolerance; analytical method for critical elements; reporting basis |
| Particle size | Sieve series; oversize limit; intermediate distribution; fines limit; cumulative or discrete; sieving method |
| Physical | Apparent density, flow, moisture, oxygen where relevant — each with test standard |
| Sampling | Increment scheme, sample reduction method, retained samples, umpire laboratory, retention period |
| Packaging | Pack type, liner, sealing, pack size, marking, palletisation, container protection |
| Documents | COA per batch, SDS, certificate of origin, transport classification, inspection certificates |
| Governance | Change notification clause, non-conformance procedure, qualification and re-qualification triggers |
The bottom line
A good specification is not a longer specification — it is one with no room for two honest readings. Name the form, name the method, name the sieve series, write the sampling clause, and add the change-notification requirement. Those five things will prevent most of the problems that ferroalloy and metal powder buyers actually encounter, and they cost nothing to include.