What is ASTM A182 F6a?

ASTM A182 Grade F6a is a 13 percent chromium martensitic stainless steel forging grade, UNS S41000, covered by ASTM A182/A182M for forged flanges, fittings, valves and parts used in high-temperature pressure service. It contains 11.5 to 13.5 percent chromium with 0.15 percent carbon maximum and 0.50 percent nickel maximum, and is supplied in four strength classes.

What is the difference between A182 F6a Class 1, 2, 3 and 4?

The four classes share one chemistry and differ only in tempering. Class 1 has 485 MPa minimum tensile strength and 143 to 207 HBW. Class 2 has 585 MPa and 167 to 229 HBW. Class 3 has 760 MPa and 235 to 302 HBW. Class 4 has 895 MPa and 263 to 321 HBW. Minimum elongation falls from 18 percent in Classes 1 and 2 to 15 percent in Class 3 and 12 percent in Class 4. Reduction of area stays at 35 percent minimum for all four classes.

What is the maximum weight of an ASTM A182 F6a forging?

Products made to ASTM A182 are limited to a maximum weight of 10,000 lb (4540 kg). For heavier forgings the specification directs users to ASTM A336/A336M for the similar ferritic and martensitic grades, and A965/A965M for austenitic grades.

Can A182 F6a flanges be machined from bar stock?

No. ASTM A182 states that flanges of any type, elbows, return bends, tees and header tees shall not be machined directly from bar stock. Cylindrically shaped martensitic stainless parts NPS 4 (DN 100) and under may be machined from forged or rolled bar without additional hot working.

How corrosion resistant is A182 F6a?

F6a is a 13 percent chromium martensitic grade with no specified molybdenum, so its pitting resistance equivalent number is around 14. It suits mild, low-chloride environments such as dry atmosphere, fresh water, steam and hot gases. It is not a replacement for duplex or austenitic grades in seawater, acid or chloride-bearing service, where A182 F51, F53, F55 or 904L are the usual choices.

ASTM A182 F6a Forgings (UNS S41000)

Q: Is A182 F6a the same as 410 stainless steel?

A182 F6a carries UNS number S41000, the same UNS number as AISI 410, and is close to EN 1.4006 / X12Cr13 and JIS SUS 410. The difference is the specification. F6a is a forging grade for pressure-containing piping components with defined classes, heat treatment and testing, while AISI 410 is a general grade designation.

Forged rings, rolled rings, flanges, shafts, discs, sleeves, bushings and bars, made to order by Jiangyin Jiangnan Metal Co., Ltd., an open-die forging works in Jiangyin, Jiangsu, China.

ASTM A182 Grade F6a is a 13 percent chromium martensitic stainless steel forging grade, UNS S41000, used for forged flanges, fittings, valve bodies and pressure parts in high-temperature service. It holds 11.5 to 13.5 percent chromium with carbon 0.15 percent max, nickel 0.50 percent max and no specified molybdenum, and comes in four strength classes from 485 MPa to 895 MPa minimum tensile strength. It corresponds to AISI 410, EN 1.4006 / X12Cr13 and JIS SUS 410.

UNSS41000

TypeMartensitic stainless

Chromium11.5 to 13.5 %

Classes1, 2, 3, 4

Tensile range485 to 895 MPa min

Weight limit per A1824540 kg

1. Chemical composition

Table 1. Chemical requirements for ASTM A182 Grade F6a (UNS S41000), percent by mass.
Limit	C	Mn	Si	P	S	Cr	Ni	Mo
Min.	–	–	–	–	–	11.5	–	–
Max.	0.15	1.00	1.00	0.040	0.030	13.5	0.50	not specified

Molybdenum is not a specified element in F6a. If the job calls for 13Cr with about 0.5 percent Mo, the grade you want is F6b. For 13Cr-4Ni soft martensitic service, see A182 F6NM.

2. Mechanical properties, Class 1 to Class 4

All four classes use the same chemistry and are separated by tempering alone. State the class on the purchase order. If you leave it open, the choice of heat treatment falls to the manufacturer.

Table 2. Tensile requirements at room temperature, ASTM A182 F6a.
Property	Class 1	Class 2	Class 3	Class 4
Tensile strength, min, ksi [MPa]	70 [485]	85 [585]	110 [760]	130 [895]
Yield strength, min, ksi [MPa]	40 [275]	55 [380]	85 [585]	110 [760]
Elongation in 50 mm or 4D, min, %	18	18	15	12
Reduction of area, min, %	35	35	35	35
Brinell hardness, HBW	143-207	167-229	235-302	263-321

Charpy V-notch testing is not a standard requirement for F6a under A182. It is ordered as a supplementary requirement, and we can supply impact results at ambient or sub-zero temperature when asked.

3. Heat treatment

After hot working, forgings are cooled below 538 °C (1000 °F) before heat treatment. Where two or more routes are listed for a class, any one of them is acceptable.

Table 3. Heat treatment requirements for ASTM A182 F6a.
Class	Heat treat type	Austenitising temperature	Cooling media	Quench cool below, °F [°C]	Tempering temperature, min, °F [°C]
Class 1	Anneal	not specified	furnace cool	–	not applicable
	Normalise and temper	not specified	air cool	400 [205]	1325 [725]
	Temper	not required	–	–	1325 [725]
Class 2	Anneal	not specified	furnace cool	–	not applicable
	Normalise and temper	not specified	air cool	400 [205]	1250 [675]
	Temper	not required	–	–	1250 [675]
Class 3	Anneal	not specified	furnace cool	–	not applicable
Class 3	Normalise and temper	not specified	air cool	400 [205]	1100 [595]
Class 4	Anneal	not specified	furnace cool	–	not applicable
Class 4	Normalise and temper	not specified	air cool	400 [205]	1000 [540]

A shop anneal for 13Cr martensitic stainless usually runs 815 to 900 °C, slow furnace cool to about 600 °C, then air cool. That cycle is normal practice, but the contractual requirement is the table above. Liquid quenching followed by tempering is permitted with the purchaser's agreement, in which case the parts are marked QT.

4. Melting practice and product limits

A182 requires stainless grades to be melted by electric furnace with optional separate degassing and refining, by vacuum furnace, or by either route followed by vacuum or electroslag consumable remelting. Our normal practice for F6a is EAF plus VOD, with ESR available where cleanliness or heavy-section soundness calls for it.

Weight ceiling of 4540 kg

Products made to A182 are limited to 10,000 lb (4540 kg). Heavier martensitic forgings are ordered to ASTM A336/A336M, and heavier austenitic forgings to A965/A965M. We forge to all three specifications.

Bar stock rule

Flanges of any type, elbows, return bends, tees and header tees must not be machined directly from bar. Cylindrical martensitic parts NPS 4 (DN 100) and under may be machined from forged or rolled bar with no further hot work.

Bars and parts from bar

For bar and products machined from bar outside the scope of A182, the companion specifications named in the standard are ASTM A479/A479M and A739.

5. Equivalent grades

Table 4. International designations close to A182 F6a.
Standard or region	Designation
UNS, USA	S41000
ASTM A182, forgings	F6a, Classes 1 to 4
ASME	SA-182 F6a
AISI grade	410
EN and DIN	1.4006, X12Cr13
JIS, Japan	SUS 410

These are close matches, not identical grades. Composition windows and test requirements differ between standards, so confirm the governing specification before substituting one for another.

6. Corrosion behaviour and service limits

F6a is a straight 13 percent chromium steel with no molybdenum, which puts its pitting resistance equivalent number at roughly 14. That suits mild, low-chloride duty: dry atmosphere, fresh water, steam, hot gases, mild alkalis and a range of food-industry work. Scaling resistance holds to about 650 °C, though strength drops well before that point.

It is the wrong grade for seawater, strong acids, sour service or chloride-bearing process streams. For those duties we forge duplex and super duplex (F51, F53, F55), 904L, and nickel alloys such as Inconel 625 and Hastelloy C-276. Tell us the medium and temperature and we will say whether F6a is a sensible choice.

7. Typical parts we forge in F6a

Valve components

Valve bodies, bonnets, stems, seat rings and plugs for gate, globe, ball and check valves. Valve work is one of the steadiest uses of this grade.

Flanges and piping parts

Weld neck, slip-on, blind and threaded flange forgings, plus forged fittings for high-temperature pressure piping within the A182 scope.

Rotating and wear parts

Shafts, spindles, sleeves, bushings, discs and gear blanks where moderate corrosion resistance has to sit alongside through-hardening strength.

Steam and hot gas duty

Parts running in steam, hot gases and dry atmospheres, including turbine and compressor hardware below the scaling limit.

8. Testing, inspection and certification

F6a is martensitic and ferromagnetic, so ultrasonic examination follows EN 10228-3, which covers ferritic and martensitic steel forgings. EN 10228-4 does not apply here, since it is written for austenitic and austenitic-ferritic forgings. We also test to ASTM A388/A388M and SEP 1921 when specified. Magnetic particle examination to ASTM A275/A275M and liquid penetrant to ASTM E165 are both available, and MPI works on this grade.

Under A182, one tension test is taken per heat in each heat treatment charge, with a relaxation to one test per heat per forging type and section size where the furnace is controlled to within 14 °C and a recording pyrometer gives a full heat treatment chart. Material that misses the mechanical requirements may be re-heat-treated and retested. Certification is issued to EN 10204 3.1, or 3.2 with third-party witness by BV, SGS, TUV, LR or DNV.

9. Common questions

Is A182 F6a the same as 410 stainless steel?

They share the UNS number S41000, and F6a lines up with AISI 410, EN 1.4006 / X12Cr13 and JIS SUS 410. The difference is contractual rather than metallurgical. F6a is a forging specification for pressure-containing piping components with defined strength classes, mandated heat treatment and set testing, while AISI 410 is a general grade designation with none of that attached.

Which class should I order?

Class 1 at 485 MPa and 143 to 207 HBW is the usual pick for flanges and general pressure parts, where ductility and machinability matter more than hardness. Classes 3 and 4, at 760 and 895 MPa, suit stems, shafts and wear parts needing up to 321 HBW, at the cost of elongation dropping to 15 and 12 percent. If your project imposes a hardness cap, check it against the class band before ordering, because the bands do not overlap.

What is the largest F6a forging you can make?

A182 itself caps products at 10,000 lb (4540 kg). Above that weight the applicable specification becomes ASTM A336/A336M for martensitic grades. As an open-die shop we produce to both, so send the finished weight and we will confirm the right specification with the quotation.

Can F6a flanges be cut from round bar?

No. A182 rules out machining flanges of any type, elbows, return bends, tees and header tees directly from bar stock. The exception is cylindrically shaped martensitic parts NPS 4 (DN 100) and under, which may be machined from forged or rolled bar without additional hot working.

Is F6a weldable?

13 percent chromium martensitic steel welds, but the heat-affected zone hardens, so preheat and post-weld heat treatment are normally needed. Where repair welding is done on ferritic grades under A182, test specimens may only be removed after PWHT unless that PWHT runs at least 30 °C below the actual tempering temperature. Send us the welding procedure before the class is fixed and we will flag any conflict.

What do you need for a quotation?

A drawing is ideal. Failing that, send outside diameter, inside diameter, height, quantity, class, finish condition and the certification level, to sales@steelforgepieces.com. Lead time depends on section size, class and whether ESR material is called for.

Request an A182 F6a quotation

Send a drawing, or just the dimensions and quantity. We quote rough forged, proof machined or finish machined, with the certification level you need.

Company: Jiangyin Jiangnan Metal Co., Ltd., open-die forging factory
Address: No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Phone: +86 189-2135-9659
Email: sales@steelforgepieces.com
Website: www.steelforgepieces.com

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Related grades

Chemistry, Class 1 to 4 mechanical values and heat treatment routes on this page follow ASTM A182/A182M, Tables 1 to 3. Standards are revised from time to time, so check the current edition before placing a contractual order. Page reviewed September 2026 by the technical sales team at Jiangyin Jiangnan Metal Co., Ltd.