Stainless Steel Investment Casting

What is investment casting?

Investment casting — also known as the lost-wax process — is a near-net-shape casting method capable of producing parts with fine surface finish, intricate geometry and tight dimensional tolerances. A wax pattern of the part is built, assembled into a tree, and repeatedly dipped into a ceramic slurry to form a shell. The wax is melted out, the shell is fired, and molten stainless steel is poured into the cavity. Once cooled, the shell is broken away and the casting is cut from the runner system, ground, heat-treated and inspected.

We use the silica sol process (also referred to as silica colloidal investment casting), which produces a smoother surface finish and tighter tolerances than the water-glass process. This makes it especially well suited to stainless steel parts that will see machining, polishing or close-fit assembly, and reduces the amount of secondary stock and rework required downstream.

In-house process capability

Our partner foundry runs a fully integrated investment casting operation, with the following stages performed under one roof:

• Toolmaking and wax-injection die manufacture
• Wax-model making and tree assembly
• Silica sol shell building and de-waxing
• Melting and pouring of stainless, carbon and alloy steels
• Heat treatment, shot blasting and surface finishing
• CNC machining, turning, milling and grinding
• Wax recovery and process recycling

Vertical integration matters because it shortens lead times, keeps tolerances under one quality system, and avoids the hand-offs that often introduce defects in multi-supplier supply chains. It also lets us cost-engineer parts properly: in many cases we can redesign a fabricated or machined-from-bar component as a single casting and remove significant material and machining cost.

Stainless steel grades we cast

We routinely cast a wide range of stainless and special alloys to ASTM, EN and equivalent standards, including:

• Austenitic — 304 / 304L (1.4301 / 1.4307), 316 / 316L (1.4401 / 1.4404), CF8M / CF3M cast equivalents (1.4408 / 1.4409), 321 (1.4541), 347 (1.4550)
• Duplex and super duplex — 2205 / CD3MN (1.4462), CD3MWCuN (1.4501)
• Martensitic — 410 (1.4006), 420 (1.4021), CA-15, CA-40
• Other corrosion-resistant grades — CF8, CF3, CN7M, CK-20

Other grades and bespoke chemistries can be matched against your specification or drawing. Material is verified by spectrometer at the foundry and again on receipt where required, and full chemical and mechanical certification is supplied with every batch.

Sizes, tolerances and finish

Single-piece weight	From a few grams up to approximately 50 kg per casting
Linear tolerance	Typically CT4–CT6 (ISO 8062) on as-cast features
Surface finish	Ra 3.2 µm or better on most as-cast surfaces
Wall thickness	Down to 2 mm on suitable geometries
Machined features	Held to drawing tolerance via in-house CNC and grinding

Quality, testing and certification

Stainless steel investment castings used in pressure equipment cannot be signed off on appearance alone. Every part we ship is supported by a documented quality plan and a level of testing matched to the application. Standard capabilities include:

• ISO 9001:2015 quality management system
• PED 2014/68/EU compliance for pressure-bearing castings — PED explained →
• TÜV Rheinland (Notified Body ID-No. 0035) approval for precision steel castings up to 60 kg under Directive 2014/68/EU Annex I §4.3 and AD 2000-Merkblatt W0 — certificate no. 01 202 CHN/Q-16 0588
• Chemical analysis by optical emission spectrometer
• Mechanical testing — tensile, hardness, impact (Charpy down to -196 °C)
• Dimensional inspection on coordinate-measuring machine (CMM)
• Non-destructive testing — dye penetrant (PT), magnetic particle (MT), radiographic (RT) and ultrasonic (UT) on request
• End-of-line hydrostatic and pneumatic pressure testing
• Full material and inspection certification (3.1 / 3.2 EN 10204) supplied with every shipment — EN 10204 3.1 vs 3.2 explained →

Industries and applications

Our stainless steel investment castings are specified into demanding sectors where failure is not an option:

• Valves and flow control — bodies, bonnets, discs, wedges, balls, stems
• Pumps and rotating equipment — impellers, casings, diffusers, wear rings
• Oil, gas and petrochemical — wellhead, downhole and process components
• Marine and offshore — corrosion-resistant fittings, manifolds, brackets
• Cryogenic service — LNG, industrial gases and low-temperature instrumentation
• Food, dairy and pharmaceutical — hygienic-design components in 316L
• Architectural and structural — load-bearing fittings and decorative hardware