AMS 5614C forgings (UNS S41025, 12Cr–0.5Mo)

Summary

Chemistry as listed in the AMS 5614 grade band. Size and weight figures are the tested envelopes for this grade on our own presses and ring mills at Jiangyin, Jiangsu, China.

What AMS 5614C forgings can you buy?

UNS S41025 is a made-to-order grade. The heat is bought against your specification, so the drawing and the required condition are needed at the first enquiry. Jiangyin Jiangnan Metal produces it by four routes, chosen by geometry and order size. Open-die forging covers long shafts, blocks and heavy discs. Seamless ring rolling produces rings from 200 mm to 2,500 mm outside diameter, the usual route for diaphragm and casing rings. Closed-die forging handles repeat-volume parts such as blade blanks and valve trim. Upset forging is used for short, large-section hubs and flanges. Trepanning replaces drilling on hollow parts above about 200 mm bore, and the removed core is kept for test coupons.

Near-net dies typically remove 30–50% of the rough machining on profiled parts. This is worth more on AMS 5614C than on carbon steel, because the material costs several times as much per kilogram and the machining allowance is paid for twice, once as metal and once as cutting time.

What is AMS 5614C / UNS S41025 steel?

Plain Type 410 is the least expensive hardenable stainless steel and performs well enough at room temperature. Under load in steam at 500 °C it has two weaknesses. It continues to temper in service and loses strength, and the condensate pits it. AMS 5614C addresses both by adding 0.40–0.60% molybdenum and by holding the residual elements that embrittle 12Cr steels to tight ceilings.

Three properties matter in service:

• Tempering resistance. Molybdenum slows the coarsening of carbides, so the steel holds its hardness at temperature instead of softening over thousands of hours of service. This is what allows a blade to keep its properties over a design life measured in decades.
• Creep and fatigue strength in wet steam. The usual application is a low-pressure turbine blade, which sees high-cycle fatigue, water droplet erosion and corrosion together. The 12Cr matrix provides the fatigue strength and the molybdenum provides the resistance to condensate pitting that would otherwise start a crack.
• Full hardenability in heavy section. With 12% chromium the steel air-hardens, and even a 300 mm section transforms to martensite. This gives uniform properties through the section, but it also means a forging left to cool unattended will crack if it is not tempered promptly.

The steel is ferromagnetic in every condition because the matrix is martensite. Its pitting resistance equivalent number is around 13 to 14, which places it in steam, fresh water and mild atmospheres rather than seawater or chloride service.

What are the equivalents of AMS 5614C?

This steel appears under several names. They describe the same 12Cr–Mo family and we accept orders under any of them, but their limits are not interchangeable. The molybdenum-free 410 grades in particular are a different material for this application.

Cross-references are for enquiry purposes. Matching a name here does not certify equivalence. Chemistry bands, trace element ceilings and test requirements differ. Always reference the standard revision in force at the contract date. Table compiled by Jiangyin Jiangnan Metal Co., Ltd.

What is the chemical composition of AMS 5614C?

This is the band we buy raw material against unless a drawing calls for something tighter. Chromium provides the corrosion resistance, carbon sets the attainable hardness, molybdenum is what separates this grade from plain 410, and the trace element ceilings at the foot of the table are what allow the steel to last in a steam path.

Source: AMS 5614C grade band as published by Jiangyin Jiangnan Metal Co., Ltd. Every heat ships with a ladle analysis on the mill certificate; product analysis on the finished forging is added on request. Where your purchase order states a tighter band, the order governs.

Melting route

The standard route is EAF + LF + VOD: electric arc melting, ladle refining, then vacuum oxygen decarburisation to remove carbon and gases while retaining the chromium. ESR remelting is added where the specification calls for consumable electrode quality, tighter cleanliness or higher transverse properties in heavy sections. State which route your drawing requires at enquiry stage, because it affects both price and mill lead time.

Values are the nominal grade bands used for comparison. Type 416 is included because it is sometimes offered as a free-machining substitute. Its sulphur addition makes it unsuitable for any part exposed to steam, condensate or fatigue loading.

What are the mechanical properties of AMS 5614C?

The tempering temperature controls the delivered properties. The hardening step is the same in every case; the temper decides whether the part ends up hard and strong or softer and tougher. A higher tempering temperature gives lower strength, higher elongation, higher impact energy and better resistance to stress-corrosion cracking.

Annealed condition, as normally shipped for machining

Hardened and tempered: strength against tempering temperature

The table below is the indicative production band for AMS 5614C forgings in sections up to about 200 mm, hardened from 950–1010 °C and tempered for a minimum of two hours. Use it to choose a tempering temperature. It is not a set of specification minima.

Indicative bands from Jiangyin Jiangnan Metal production experience on AMS 5614C / UNS S41025 forgings, longitudinal tests, sections to 200 mm. These are not acceptance values. The values that must appear on your certificate are those in the AMS revision, drawing or purchase specification you order to. Ask us to confirm them in writing before the drawing is released. Heavy sections, transverse test direction and sub-zero impact requirements all reduce the values that can be relied on.

How is AMS 5614C heat treated?

Four operations, of which two are compulsory and two are used where required. Section thickness sets every hold time. Allow roughly 30 minutes per 25 mm at temperature, with a one hour minimum.

1. Annealing

Full anneal at 840–870 °C, then furnace cool at 25 °C per hour or slower to 600 °C before air cooling. This gives ferrite plus spheroidised carbides at 235 HB maximum, soft enough for deep machining. A subcritical anneal at 730–790 °C followed by air cooling is quicker and sufficient when the part only needs stress relieving between machining passes.

2. Hardening

Austenitise at 950–1010 °C and quench in oil for heavy sections, or in forced or still air for thin ones. Because the steel air-hardens, air quenching still gives a fully martensitic structure and produces much less distortion than oil, so it is preferred for blades, thin rings and parts with abrupt section changes. Soaking above about 1030 °C coarsens the grain and dissolves enough carbon to leave retained austenite. Soaking below 950 °C leaves undissolved carbides and the part will not reach strength.

3. Tempering

Temper immediately after the quench, for at least two hours at temperature, then cool in air. Do not leave hardened parts overnight before tempering. Fresh martensite in a 12Cr steel cracks under its own residual stress, particularly at section changes and drilled holes.

4. Stress relief after machining

Where heavy machining follows tempering, stress-relieve at 600–650 °C, always at least 25–30 °C below the last tempering temperature, so the mechanical properties on the certificate are not disturbed.

Approximate values for the AMS 5614C chemistry band; exact critical points shift with the actual heat analysis and should be confirmed by dilatometry where a specification demands it. Compiled by Jiangyin Jiangnan Metal Co., Ltd.

What are the physical properties of AMS 5614C?

Representative published values for 12Cr martensitic stainless steel, compiled by Jiangyin Jiangnan Metal Co., Ltd. for design guidance. Where a calculation is safety-critical, use values measured on the delivered heat.

How corrosion resistant is AMS 5614C, and how hot can it run?

General corrosion resistance is that of a 12% chromium martensitic stainless steel, improved by the molybdenum. It is better than plain Type 410 in condensate and wet steam, much better than any low-alloy steel, and well below the austenitic and duplex grades. The pitting resistance equivalent number, PREN = %Cr + 3.3 × %Mo, is roughly 13.6 for mid-band chemistry. Continuous seawater immersion requires about 32, which marks the limit of what this grade can do.

Corrosion resistance also depends on heat treatment. Material tempered in the 400–550 °C range, or left as quenched, precipitates chromium carbides that locally deplete the matrix and lower pitting resistance. The best corrosion performance comes from the hardened and tempered condition above 620 °C, with a clean, descaled and passivated surface. A forging that has been ground but not pickled will pit at the embedded iron before the base metal is attacked.

Service temperature limits

Two limits apply, and the lower one governs.

• Do not run the part within 30 °C of its own tempering temperature. Service inside that margin continues the tempering reaction and the part softens permanently. Material tempered at 620 °C is limited to about 590 °C on this basis alone.
• Creep governs above roughly 480 °C. For stressed rotating or pressure-retaining parts the practical design limit is 480–540 °C, which suits intermediate and low-pressure steam paths rather than the hottest high-pressure stages.

Oxidation is not the limiting factor. The steel resists scaling in air to about 650 °C. For sustained duty above 540 °C, move to a creep-resistant 9–12Cr grade, to Inconel 718, or to another nickel alloy.

AMS 5614C against 410, 416, 431, Greek Ascoloy and 17-4PH

Type 410 costs less and is widely stocked. Greek Ascoloy is stronger and runs hotter. 17-4PH is stronger and more corrosion resistant but is limited to lower temperatures. AMS 5614C holds its properties in hot wet steam at a moderate price. Where a drawing calls for AMS 5614C and 410 is proposed to save money, the questions to answer are what temperature the part runs at and for how long.

Nominal comparison values compiled by Jiangyin Jiangnan Metal Co., Ltd. from published grade data. Cost multiples are indicative of forged bar in comparable quantities and move with the nickel and molybdenum markets.

Selection checks

1. How hot does it run, and for how long? Above about 450 °C for a design life in tens of thousands of hours, molybdenum is needed and plain 410 will lose hardness.
2. Is there wet steam or condensate? Droplet erosion and condensate pitting are the usual causes of blade failure. AMS 5614C is specified for that duty. Type 410 and 416 are not.
3. Is there a Charpy acceptance value on the drawing? If so, the trace element ceilings in AMS 5614C are what deliver it, and a commercial 410 bar containing molybdenum is not a substitute even if its chromium and molybdenum fall inside the band.

How is AMS 5614C forged, welded and machined?

Forging

Soak and forge from 1150–1200 °C, with a workable envelope of roughly 900–1200 °C. Finish above 900 °C. Below that the steel work-hardens quickly and the risk of surface cracking rises, so reheat rather than finish cold. Aim for a forging reduction of at least 4:1 from the ingot or billet to break down the cast structure and develop grain flow along the principal axis. Heat the charge slowly through 600–850 °C. A cold 12Cr ingot placed straight into a hot furnace can crack from thermal stress.

Because the steel air-hardens, a forging left to cool in still air reaches room temperature as untempered martensite. Transfer it directly to an annealing or tempering furnace, or hold it above 550 °C until the next operation. This is the most common cause of cracked 12Cr forgings.

Welding

Weldable, provided normal martensitic steel practice is followed:

• Preheat to 200–300 °C and hold the interpass temperature in the same band.
• Use a matching 12Cr filler where the joint must have parent metal strength and corrosion resistance, or an austenitic (309/310) or nickel-base filler where a softer weld metal is acceptable and post-weld heat treatment is not possible.
• Post-weld temper at 700–760 °C, and do not let the joint fall to room temperature first. Cool to about 100–150 °C to complete transformation, then transfer directly to the tempering furnace.
• Use low-hydrogen consumables, dried and stored correctly. Hard martensite and hydrogen together produce delayed cracking, sometimes days after welding.

Machining

Machine in the annealed condition wherever the tolerance stack allows. At 235 HB it cuts like a tough medium-carbon alloy steel. At 32 HRC tool life falls away quickly. Use positive rake, rigid setups, sharp edges and flood coolant, and do not let a tool dwell. 12Cr steels work-harden under a rubbing edge and glaze the surface, and the next pass then rubs instead of cutting. Chips are stringy, so pecking and chip-breaking geometry are important on deep holes.

How does AMS 5614C fail, and how do you prevent it?

What can Jiangyin Jiangnan Metal forge in AMS 5614C?

Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, operating since 2008 with 460 employees, including 9 senior and 32 intermediate engineers. The envelopes below are what we have run in this grade, not carbon-steel limits.

Which standards and certificates apply to AMS 5614C forgings?

Quality management is certified to ISO 9001:2015. Third-party witness certificates are issued through the inspection body you nominate: Lloyd’s Register, DNV, Bureau Veritas, ABS, TÜV or SGS. Customers keep an unrestricted right to witness any production stage, including chemistry, forging, heat treatment and mechanical testing.

How do you specify an AMS 5614C forging order?

1. Name the specification and the revision. Write AMS 5614C (UNS S41025). A purchase order that says only “12Cr stainless” or “410 with moly” leaves the trace-element ceilings and the melting route open.
2. State the delivery condition. Annealed for customer machining, or hardened and tempered. If tempered, give either the tempering temperature or the hardness band. “Supplied annealed” and “supplied at 25–28 HRC” are different parts, with different prices and lead times.
3. Give the mechanical acceptance values. Tensile, yield, elongation, reduction of area, impact energy and impact test temperature. State the test direction: longitudinal or transverse to grain flow.
4. Send the drawing with grain flow and machining stock. Mark the principal axis, the required grain direction, and the stock left on each surface for finish machining.
5. Define NDE and the acceptance class. For example “UT per EN 10228-3, quality class 3” or “UT per ASTM A388 with acceptance to the purchase order”. An unqualified “ultrasonic test” is not a specification.
6. Choose the certificate. EN 10204 3.1 as standard, 3.2 with a named witness where the project demands it. Say if you need cross-certification to a national standard.
7. Give quantity, date, Incoterm and destination. Below roughly 500 kg we consolidate onto a larger heat, which changes both price and schedule.

Drawing callout you can copy

MATERIAL:      AMS 5614C / UNS S41025 (12.5Cr - 0.5Mo)
MELTING:       EAF + LF + VOD  (add "+ ESR" if consumable-electrode quality required)
CONDITION:     Harden 950-1010 °C, oil or forced-air quench;
               temper 700 °C min 2 h, air cool.  Tempering below 620 °C not permitted.
HARDNESS:      22-26 HRC, verified at locations A, B and C
TENSILE:       760 MPa UTS min, 620 MPa YS min, 18% elongation, 60% RA (longitudinal)
IMPACT:        Charpy V, 3 specimens, 55 J average min at +20 °C
GRAIN FLOW:    Longitudinal, parallel to the principal axis; verify per ASTM E381
NDE:           UT per EN 10228-3 quality class 3
               MT per ASTM E1444 on all machined surfaces
CERTIFICATE:   EN 10204 3.1  (3.2 with third-party witness if stated on the PO)
SURFACE:       Descaled and passivated; Ra ≤ 1.6 µm on sealing faces
MARKING:       Heat number, condition and drawing number, low-stress stamped

Seven common ordering errors

1. Substituting plain 410 because the chromium matches. Without molybdenum the part softens in service and pits in condensate.
2. Leaving the revision letter off the order. Revisions change chemistry limits and test requirements. Cite AMS 5614C, or whichever revision your drawing invokes.
3. Specifying a tempering temperature in the 400–550 °C band to reach a hardness number. The hardness is met and the toughness is lost.
4. Giving a hardness band but no impact requirement on a part that will see shock loading or sub-zero start-up. A hardness test will not detect embrittlement.
5. Omitting the test direction on a heavy forging. Transverse values run well below longitudinal, and the certificate can pass or fail on that word alone.
6. Ordering “ultrasonic tested” with no standard or class. Each shop then applies its own acceptance level and quotations cannot be compared.
7. Treating a hardness cap as sour service compliance. It is not. See the ISO 15156 note above.

Where is AMS 5614C used?

Worked examples

Example 1: choosing a tempering temperature for a valve spindle

Given. A ø90 mm forged valve spindle in AMS 5614C, superheated steam at 480 °C, drawing requires 620 MPa minimum yield and a Charpy V of 50 J average at room temperature.

Method. Work from the service temperature first. The tempering temperature must be at least 30 °C above the service temperature, so 480 + 30 = 510 °C is the lower limit on that basis. 510 °C is inside the embrittlement band, so the effective lower limit is 620 °C. From Table 5: 620 °C gives 750–850 MPa yield but only about 40 J; 660 °C gives 690–780 MPa and about 55 J; 700 °C gives 620–700 MPa and about 70 J.

Result. Specify a temper at 700 °C. It clears the yield requirement with a margin, meets the 50 J impact requirement, and leaves 220 °C between service and tempering temperature so the spindle does not soften in service. Tempering at 620 °C would meet the yield requirement easily and fail the impact requirement, which is how this part is most often specified incorrectly.

Example 2: sizing and weighing a turbine diaphragm ring

Given. A ring, 1,400 mm outside diameter × 1,150 mm inside diameter × 260 mm high, in AMS 5614C, ultrasonic acceptance to EN 10228-3 class 3.

Method. Net volume = π/4 × (1.400² − 1.150²) m² × 0.260 m = 0.1302 m³. At 7,700 kg/m³ that is 1,003 kg net. Add 25% for machining stock and ring-rolling allowance and the rough forging is about 1,254 kg, inside both the 8,000 kg single-piece limit and the 2,500 mm ring mill envelope.

Points to settle first. A 125 mm radial wall at class 3 acceptance means the ultrasonic examination has to resolve small indications through a thick, air-hardening section. That favours ESR remelted material rather than the standard VOD route, and ultrasonic examination in the annealed condition before hardening, when attenuation is lowest. Both decisions have to be taken before the heat is bought.

Glossary

AMS 5614C frequently asked questions

References

1. SAE International, AMS 5614, Steel, Corrosion and Heat Resistant, Bars, Forgings, Forging Stock, and Rings, 12.5Cr – 0.5Mo. The governing specification for this grade; cite the revision letter in force at your contract date.
2. SAE International, AMS 2759/5, Heat Treatment of Martensitic Corrosion-Resistant Steel Parts.
3. SAE International, AMS 2300 / AMS 2301, Aircraft Quality and Premium Aircraft Quality Steel Cleanliness, referenced where a cleanliness class is invoked.
4. SAE International, AMS 2241 (bar tolerances) and AMS 2248 (chemical check analysis limits), referenced by the AMS corrosion-resistant steel family.
5. ASTM International, ASTM A276 / A479 / A473 / A182, product standards for Type 410 family bars, forgings and flanges.
6. ASTM International, ASTM A388/A388M, Standard Practice for Ultrasonic Examination of Steel Forgings.
7. CEN, EN 10228-3, Non-destructive testing of steel forgings — Ultrasonic testing of ferritic or martensitic steel forgings, and SEP 1921.
8. CEN, EN 10250-4, Open die steel forgings for general engineering purposes — Part 4: Stainless steels.
9. CEN, EN 10204, Metallic products — Types of inspection documents.
10. ISO / NACE, ISO 15156-2 and 15156-3 (NACE MR0175), Materials for use in H₂S-containing environments in oil and gas production.
11. ASM International, ASM Handbook Volume 1: Properties and Selection: Irons, Steels and High-Performance Alloys, martensitic stainless steels.
12. ASM International, ASM Handbook Volume 4D: Heat Treating of Irons and Steels, heat treating of martensitic stainless steels.
13. GB/T 1221 and GB/T 8732, Chinese standards for heat-resisting steel and steam turbine blade steel, covering 1Cr12Mo.

Standards are cited by number. Always work to the revision in force at your contract date. Test results on our certificates are independent and traceable to calibrated equipment.

About the manufacturer, and how to cite this page

Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, operating since 2008 with 460 employees, including 9 senior engineers and 32 intermediate engineers. The plant runs 1 t to 9 t open-die hammers, 4,500 t and 5,000 t hydraulic presses and radial-axial ring mills to 2,500 mm outside diameter, with heat treatment, machining, mechanical testing and non-destructive examination in house. Alongside AMS 5614C / UNS S41025 we forge carbon, alloy and tool steels, the martensitic and precipitation-hardening stainless families, duplex grades and nickel alloys. Quality management is certified to ISO 9001:2015, and material is supplied with EN 10204 3.1 certification as standard, 3.2 with third-party witness on request.

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