Small Heat-Treated Stainless Castings: AISI 431 vs 17-4PH

Both are hardenable stainless steels; 431 (1.4057) is a hardened-and-tempered martensitic grade, and 17-4PH (1.4542) is precipitation hardened. Either can reach high strength in a silica sol investment casting.

431 is a good fit when the part is already validated in 431 and the target is a moderate hardness range. 17-4PH is often chosen for higher strength and simpler heat treatment, but its toughness depends heavily on the ageing condition. For use down to about −20 °C, the over-aged conditions (H1100 or H1150) are the usual choice rather than peak-hardened H900. Corrosion resistance of both is good for outdoor use, but lower than 316L in salt or chlorides.

Only if the trial checks geometry alone; for strength or fatigue tests the trial parts must be in the production alloy and heat treatment. 304 cannot be hardened by heat treatment and is much weaker than hardened 431 or 17-4PH, so test results would not represent the real part.

A small pre-series in a special alloy costs more per piece, because the foundry melts a minimum charge of that alloy and runs the heat treatment for only a few parts. Ways to manage this: pour the pre-series together with another job in the same alloy, accept a pre-series surcharge, or make the pre-series slightly larger so it can also serve as test stock.

By hardening, then tempering at a temperature chosen for that hardness range, and checking hardness on parts from every heat-treatment batch. The measured values should be written on the heat-treatment record that ships with the parts.

For martensitic grades like 431, the tempering temperature should avoid the temper-embrittlement range (roughly 425–550 °C), which lowers impact toughness. If low-temperature toughness matters, say so in the RFQ so it can be considered when the heat-treatment route is chosen, and agree how hardness will be measured on a part this small (location and test method).

On small parts, JS13 is tighter than typical as-cast tolerance grades, so critical dimensions need to be reviewed one by one. For sizes up to 10 mm, JS13 (ISO 286) allows about ±0.07 to ±0.11 mm, while as-cast grades CT4–CT6 (ISO 8062) allow roughly ±0.13 to ±0.26 mm.

In practice many features still measure inside JS13 after process tuning. The ones that cannot are held by sizing, light machining or reaming. During the DFM review we mark which dimensions are as-cast and which need a secondary operation, before tooling and pricing are fixed.

Usually yes; we inspect the mould and shoot trial wax patterns before committing. We check the mould's condition, its ejection and cooling, and whether its shrinkage allowance matches our shell system and the chosen alloy.

The gating (how the pattern attaches to the wax tree) may need adapting to our process. Using an existing mould saves tooling cost and lead time, but the first trial castings must be measured before the pre-series is approved, because a mould built for another foundry can give slightly different dimensions.

For hardened stainless parts a common sequence is heat treatment, then micro bead blasting, then pickling and passivation. Passivation (for example to ASTM A967) restores the chromium oxide layer after blasting and heat treatment.

Ask for an EN 10204 3.1 material certificate (chemical analysis per heat) and a heat-treatment record with measured hardness. If you need mechanical test results (tensile, impact at −20 °C), say so in the RFQ, because test bars must be cast with the parts.

With an existing mould, a recent quote for a 7 g part was 10–12 working days for a 10-piece pre-series and 15–20 working days for production. Shipping time comes on top.

New tooling adds 5–7 business days. A pre-series in a special alloy may take longer if it has to wait for a suitable melt, so agree on that at quotation stage.

Send the 2D drawing with tolerances, the 3D model, the alloy and required hardness or mechanical properties, and the annual quantity. Also include the test plan for the pre-series, the finish sequence and the documents you need.

Tell us the delivery terms too (EXW, or delivered to your site). Annual volume matters more than one order quantity, because it decides tooling, batch size and unit price.