{"id":7769,"date":"2026-09-21T02:39:51","date_gmt":"2026-09-21T02:39:51","guid":{"rendered":"https:\/\/chinametalfoundry.com\/?p=7769"},"modified":"2026-09-21T08:24:46","modified_gmt":"2026-09-21T08:24:46","slug":"stainless-steel-investment-casting-grades","status":"publish","type":"post","link":"https:\/\/chinametalfoundry.com\/ko\/blog\/stainless-steel-investment-casting-grades\/","title":{"rendered":"\uc2a4\ud14c\uc778\ub9ac\uc2a4\uac15 \uc815\ubc00\uc8fc\uc870: \ub4f1\uae09 \ubc0f \uc6a9\ub3c4"},"content":{"rendered":"

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Stainless steel investment casting appears on more of the RFQs we review than any other alloy family, and it is also the one where a single wrong grade costs the most. A pump housing bought as CF8 instead of CF8M can pit inside a season of chloride wash-down; a bracket bought as 17-4PH without the ageing condition on the drawing can arrive 300 MPa below the strength the designer assumed.<\/p>\n<\/div>\n

This guide compares the five cast grades that cover the large majority of industrial demand \u2014 CF8 (304), CF8M (316), CB7Cu-1 (17-4PH), ASTM A995 Grade 4A (2205 duplex) and CA15 (410) \u2014 against the ASTM specifications they are actually bought to. It includes the corrosion maths, heat-treatment routes, machining behaviour and tolerance limits that separate a clean first article from a re-quote. Numbers below are ASTM minimums, standard industry practice or our own shop records \u2014 not marketing figures. For the broader process background, start with our \uae08\uc18d \uc8fc\uc870 \uac00\uc774\ub4dc<\/a>, and for independent process references see AFS<\/a> \uadf8\ub9ac\uace0 ASTM International<\/a>.<\/p>\n

\"stainless
A typical stainless steel investment casting mix: pressure-containing bodies, rotating impellers and structural brackets.<\/figcaption><\/figure>\n

What Stainless Steel Investment Casting Actually Buys You<\/h2>\n

“Stainless” is a corrosion mechanism, not a single material. Once chromium in the alloy exceeds roughly 10.5%<\/strong>, a chromium-oxide film forms on the surface and re-forms instantly when scratched in an oxygen-bearing environment. That film is why the part survives; everything else in the specification exists to protect or strengthen it.<\/p>\n

Pairing stainless with the lost-wax route buys three things at once. First, near-net shape: an as-cast surface typically lands at Ra 3.2\u20136.3 \u00b5m<\/strong>, so most non-sealing faces need no cut at all. Second, thin walls \u2014 2\u20133 mm<\/strong> is routine on small parts, which is where stainless earns its keep against sand routes. Third, detail: cored passages, logos and part numbers come out of the tool rather than off a machine. If your part is large and blocky, read our comparison of \ubaa8\ub798 \uc8fc\uc870 \ub300 \uc778\ubca0\uc2a4\ud2b8\uba3c\ud2b8 \uc8fc\uc870<\/a> before committing, because the cost curves cross surprisingly early.<\/p>\n

Where the process fits<\/h3>\n
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Investment casting covers parts from a few grams up to roughly 50 kg, with the sweet spot under 10 kg. Beyond that, shell handling and pour weight push cost up fast. Stainless is melted in an induction furnace, usually AOD-refined when low carbon is required, and poured at about 1550\u20131650\u00b0C<\/strong> into shells pre-fired to roughly 950\u20131050\u00b0C<\/strong>. Those temperatures are the reason wall thickness and gating must be settled at design stage \u2014 stainless does not feed like aluminium, and thin sections freeze quickly. Our investment casting service<\/a> team reviews this before tooling is cut.<\/p>\n

Cast Grade Equivalents for Stainless Steel Investment Casting<\/h2>\n

The most common sourcing error in stainless steel investment casting is quoting a wrought number and assuming the foundry will translate it. Cast specifications are separate documents with separate chemistries and separate mechanical minimums. ASTM A743\/A744 covers corrosion-resistant castings for general service, ASTM A351\/A351M covers austenitic castings for pressure-containing parts, and ASTM A995 covers duplex. Ask for the cast designation and the specification year \u2014 that removes most disputes later. If you are still at the alloy-family stage, our guide to choosing a casting alloy<\/a> walks through the trade-off logic.<\/p>\n\n\n\n\n\n\n\n\n\n\n\n
Cast grade (ASTM)<\/th>\nWrought analogue<\/th>\nKey chemistry<\/th>\nTensile \/ yield (min)<\/th>\nPREN (typ.)<\/th>\n<\/tr>\n<\/thead>\n
CF8 (A351\/A743)<\/td>\n304<\/td>\n18\u201321 Cr, 8\u201311 Ni, C \u22640.08<\/td>\n485 \/ 205 MPa<\/td>\n\u224820<\/td>\n<\/tr>\n
CF3 (A351\/A743)<\/td>\n304L<\/td>\n17\u201321 Cr, 8\u201312 Ni, C \u22640.03<\/td>\n485 \/ 205 MPa<\/td>\n\u224820<\/td>\n<\/tr>\n
CF8M (A351\/A743)<\/td>\n316<\/td>\n18\u201321 Cr, 9\u201312 Ni, 2\u20133 Mo<\/td>\n485 \/ 205 MPa<\/td>\n\u224827<\/td>\n<\/tr>\n
CF3M (A351\/A743)<\/td>\n316L<\/td>\n17\u201321 Cr, 9\u201313 Ni, 2\u20133 Mo, C \u22640.03<\/td>\n485 \/ 205 MPa<\/td>\n\u224827<\/td>\n<\/tr>\n
CB7Cu-1 (A747)<\/td>\n17-4PH<\/td>\n15.5\u201317.7 Cr, 3\u20135 Ni, 3\u20135 Cu, Nb<\/td>\n1310 \/ 1170 MPa (H900)<\/td>\n\u224817<\/td>\n<\/tr>\n
Grade 4A (A995)<\/td>\n2205 duplex<\/td>\n21\u201323.5 Cr, 4.5\u20136.5 Ni, 2.5\u20133.5 Mo, N 0.10\u20130.30<\/td>\n620 \/ 415 MPa<\/td>\n\u224835<\/td>\n<\/tr>\n
CA15 (A743)<\/td>\n410<\/td>\n11.5\u201314 Cr, Ni \u22641, C \u22640.15<\/td>\n620 \/ 450 MPa<\/td>\n\u224812<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\"stainless
Pre-fired ceramic shells ready for pour. Shell temperature and pour rate drive surface finish and thin-wall fill.<\/figcaption><\/figure>\n

CF8 and CF3 \u2014 the default austenitic grades<\/h3>\n
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CF8 is the workhorse grade in stainless steel investment casting. It is ductile (35% minimum elongation), non-magnetic, weldable and the cheapest of the austenitic cast grades. It handles food contact, indoor architectural hardware and general industrial atmospheres well. Its weakness is chlorides: in coastal air, bleach wash-down or brine service, CF8 will pit and stress-corrosion crack. Specify CF3 (the low-carbon version) whenever the part is welded or will see service between 425\u2013815\u00b0C<\/strong>, because that is the range where chromium carbides precipitate at grain boundaries and strip the passive film locally \u2014 the classic sensitisation failure.<\/p>\n

CF8M and CF3M \u2014 molybdenum for chlorides<\/h3>\n
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Adding 2\u20133% molybdenum is the single cheapest insurance policy in the family. CF8M resists pitting and crevice attack in marine spray, chemical processing and pharmaceutical clean-in-place cycles where CF8 fails. On most B2B projects the material premium is far smaller than the cost of a field failure or a recall. For anything welded, move to CF3M. This is the grade behind most of the marine castings<\/a> and quick-connect fittings we produce, including the camlock couplings covered in our dedicated stainless steel camlock casting<\/a> article.<\/p>\n

CB7Cu-1 \u2014 precipitation-hardening 17-4PH<\/h3>\n
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When strength-to-weight matters, 17-4PH is the usual answer in stainless steel investment casting. Solution-anneal at about 1040\u00b0C<\/strong>, then age: H900 at 482\u00b0C gives roughly 1310 MPa<\/strong> tensile and 40 HRC; H1150 at 620\u00b0C drops to about 930 MPa and 30 HRC but restores toughness and stress-corrosion resistance. Two specification traps. First, always state the ageing condition on the drawing \u2014 “17-4PH” alone is meaningless. Second, watch section size: heavy sections do not cool fast enough to reach full H900 properties through the core, so design to the through-thickness value, not the test-bar value. Corrosion resistance sits near CF8, not CF8M, so it is not a free upgrade.<\/p>\n

Grade 4A \u2014 2205 duplex<\/h3>\n
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In stainless steel investment casting, Grade 4A combines roughly equal ferrite and austenite. You get about twice the yield strength of CF8M, excellent chloride stress-corrosion cracking resistance, and better resistance to erosion-corrosion \u2014 which is why it dominates pump impellers and slurry handling. The constraint is thermal: never hold duplex between roughly 315\u2013480\u00b0C<\/strong> in service or stress relief, because sigma phase precipitates and embrittles the part. Solution-anneal at 1040\u20131150\u00b0C and water quench.<\/p>\n

CA15 \u2014 martensitic 410<\/h3>\n
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CA15 is the value option when you need hardness and abrasion resistance rather than corrosion resistance: pump wear rings, knife edges, turbine blades, valve trim. It is magnetic, hardenable by quench and temper, and machines far better than the austenitic grades. Its corrosion resistance is modest \u2014 think clean water and steam, not seawater. It is also the least forgiving in the foundry: it cracks on cooling if the section changes abruptly. Our casting defects guide<\/a> covers hot tearing and how gating design prevents it.<\/p>\n

Matching Stainless Steel Investment Casting Grades to Applications<\/h2>\n

Grade selection in stainless steel investment casting is really a service-environment decision. The table below maps the applications we see most often to the grade that usually wins and the reason it wins.<\/p>\n\n\n\n\n\n\n\n\n\n\n\n
Application<\/th>\nUsual grade<\/th>\nWhy it wins<\/th>\nWatch out for<\/th>\n<\/tr>\n<\/thead>\n
Valve bodies, pump casings<\/td>\nCF8M \/ CF3M (A351)<\/td>\nPressure-grade spec, Mo for process fluids, weldable<\/td>\nRadiographic soundness on heavy sections<\/td>\n<\/tr>\n
Marine hardware, deck fittings<\/td>\nCF8M, electropolished<\/td>\nChloride pitting resistance, cosmetic finish<\/td>\nPassivation after blasting (ASTM A967)<\/td>\n<\/tr>\n
Food, beverage, pharmaceutical<\/td>\nCF3M, Ra \u22640.8 \u00b5m after polish<\/td>\nLow carbon for welding, cleanable surface<\/td>\nCrevice-free design; no blind pockets<\/td>\n<\/tr>\n
Pump impellers, slurry parts<\/td>\nA995 Gr 4A (2205)<\/td>\nErosion-corrosion resistance, 2\u00d7 yield of CF8M<\/td>\nSigma-phase window 315\u2013480\u00b0C<\/td>\n<\/tr>\n
Aerospace brackets, defence hardware<\/td>\nCB7Cu-1 (17-4PH) H900\/H1075<\/td>\n1310 MPa tensile at low section weight<\/td>\nAgeing condition must be on the drawing<\/td>\n<\/tr>\n
Wear rings, valve trim, blades<\/td>\nCA15 (410), quenched and tempered<\/td>\nHardness and abrasion resistance at low alloy cost<\/td>\nHot tearing on abrupt section changes<\/td>\n<\/tr>\n
General industrial brackets, housings<\/td>\nCF8<\/td>\nLowest material cost, high ductility<\/td>\nPitting in any chloride environment<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Corrosion Performance: PREN, Sensitisation and Chloride Limits<\/h2>\n

Rather than argue from brand names, use the pitting resistance equivalent number: PREN = %Cr + 3.3 \u00d7 %Mo + 16 \u00d7 %N<\/strong>. It is a ranking tool, not a service prediction, but it makes grade conversations objective.<\/p>\n

Take two real chemistries. A CF8M heat at 18.5% Cr, 2.25% Mo and 0.05% N gives PREN = 18.5 + 7.4 + 0.8 = 26.7<\/strong>. A 2205 heat at 22.2% Cr, 3.1% Mo and 0.17% N gives 22.2 + 10.2 + 2.7 = 35.1<\/strong>. That gap of about eight points is the difference between a part that survives brackish cooling water and one that needs replacing. CF8, with no molybdenum, sits near 20 \u2014 fine indoors, marginal outside.<\/p>\n

Three things PREN does not capture. Temperature: pitting risk rises sharply above roughly 50\u201360\u00b0C in chloride service, whatever the grade. Stagnation: crevices and deposits create local chemistry that defeats any alloy. And surface condition: a blasted but un-passivated part will flash-rust in days. Passivate to ASTM A967<\/strong> (citric or nitric) after any abrasive or machining operation, and clean to ASTM A380 before it. Our casting surface finishing<\/a> guide sets out the blast\u2013passivate\u2013polish sequence in detail.<\/p>\n

Heat Treatment, Machining and Dimensional Reality<\/h2>\n

Heat treatment is where stainless steel investment casting quietly adds cost. CF8, CF3, CF8M and CF3M need solution annealing at 1040\u20131150\u00b0C<\/strong> followed by a rapid quench \u2014 a full furnace cycle plus water treatment, not a footnote. Duplex needs the same cycle with a strictly controlled quench. 17-4PH needs two cycles: solution anneal plus ageing. CA15 needs quench and temper. Each cycle adds energy, handling, straightening risk and scale removal. Budget for it explicitly; our \uc8fc\uc870 \uc5f4\ucc98\ub9ac<\/a> article prices the routes side by side, and our heat treatment service<\/a> runs them in-house.<\/p>\n

Machining behaviour in stainless steel investment casting separates the grades more than most buyers expect. Austenitic grades work-harden aggressively: dwell a tool on CF8M and the surface hardens under the insert, wrecking tool life and finish. Use sharp carbide, positive rake, constant feed and never let the cut rub. Typical turning speeds with carbide run around 120\u2013150 m\/min<\/strong> for CF8 and 90\u2013120 m\/min<\/strong> for CF8M; 17-4PH at H900 drops to roughly 60\u201390 m\/min, and 2205 to 70\u2013100 m\/min. CA15, in the annealed condition, is the friendliest of the set. Where a part is machining-dominated, our comparison of CNC \uac00\uacf5 \ub300 \uc8fc\uc870<\/a> shows how to split the geometry so the foundry does the shaping and the machine does only the sealing faces. Most of our stainless parts go straight to CNC \uac00\uacf5<\/a> for those final datums.<\/p>\n

On dimensions, stainless steel investment casting typically holds ISO 8062 CT5\u2013CT6<\/strong>. On a 30 mm feature that is about \u00b10.38 mm at CT5 and \u00b10.54 mm at CT6 \u2014 good enough to delete most roughing operations, not good enough to skip finish machining on a bore. Also allow roughly 2% linear shrink<\/strong> when you sanity-check a casting against your assembly model; a 200 mm flange will come out about 4 mm smaller than the tool. The full grade-by-grade breakdown is in our \uc8fc\uc870 \uacf5\ucc28 \uac00\uc774\ub4dc<\/a>.<\/p>\n

Cost Drivers on a Stainless Steel Investment Casting RFQ<\/h2>\n

Two quotes for the same stainless steel investment casting drawing can differ by 40% and both be honest. The spread comes from five places.<\/p>\n