Alloy Steel F91 Round Bar
➡️ Grade 91 | UNS K90901 | EN 1.4903
➡️ ASTM, EN, JIS & International Standards
➡️ Supply Conditions
➡️ Multiple Diameters & Supply Lengths
➡️ Global Export & International Delivery
Country of Origin:
Europe, Japan, USA
Material Type:
Alloy Steel
UNS Number:
K90901
Wr. No.:
1.4903
MTC Available:
EN 10204 3.1
Product Description for Alloy Steel F91 Round Bar
F91 is the ASTM A182 grade designation for modified 9% chromium, 1% molybdenum steel, UNS K90901, known throughout power generation as Grade 91. Stock is supplied to ASTM A182 / A182M with dimensions to ASTM A29 / A29M. The same alloy is P91 in ASTM A335 pipe and Grade 91 in ASTM A387 plate.
It is not a variant of F9. The additions of 0.18-0.25% vanadium, 0.06-0.10% niobium and controlled nitrogen at 0.030-0.070% produce fine, stable precipitates in a tempered martensitic matrix, and those precipitates give creep strength roughly double that of F22 at 600 C. That is what made supercritical and ultra-supercritical boiler design practical.
Bar is normalised at 1040-1080 C and tempered at 730-800 C. Both steps are mandatory and neither is negotiable. Hardness is controlled to a 190-248 HBW range.
The alloy is unforgiving of thermal mistakes. Heating above the lower transformation temperature without a full renormalising cycle produces untempered martensite. Under-tempering leaves the material brittle. Type IV cracking in the fine-grained heat-affected zone of welds is a well-documented long-term failure mode, which is why post-weld heat treatment control is so strict.
Sizes span 10 mm to 300 mm, hot-finished or cold-finished, random length or cut to order. The steel is ferromagnetic and is not stainless despite carrying 9% chromium.
Positive material identification on delivery is routinely specified, because F91 and F9 are visually identical and confusing the two has caused serious problems in power plant construction.
Typical work is supercritical boiler and steam header hardware, high-temperature piping components, valve bodies and hot bolting.
Common Applications of Alloy Steel F91 Round Bar
➡️ Machined shafts, spindles, valve stems, pump sleeves and pins for food, beverage, dairy and pharmaceutical equipment, where the passive chromium oxide film resists both product acids and caustic clean-in-place chemicals.
➡️ Fasteners, studs, bolts, threaded rod and anchor components produced from bar stock, chosen for corrosion resistance combined with the ductility needed for cold heading and thread rolling.
➡️ Chemical, water treatment and general process plant parts such as agitator shafts, flange blanks, nozzles and support components handling water, steam and mildly corrosive media free of significant chlorides.
➡️ Architectural and structural hardware including handrail stanchions, balustrade fittings, tension rods and bollards, where a bright ground or polished bar finish provides both appearance and low maintenance.
International Equivalent Grade for Alloy Steel F91 Round Bar
Standard
Country / Region
Grade
ASTM A182 / A182M
USA
Grade F91 (UNS K90901)
ASTM A335 / A335M
USA
Grade P91 (seamless pipe)
ASTM A387 / A387M
USA
Grade 91 (plate)
EN 10216-2
Europe / EU
X10CrMoVNb9-1 (1.4903)
DIN 17175
Europe / EU
1.4903 (X10CrMoVNb9-1)
Technical Specification for Alloy Steel F91 Round Bar
Specification
Value
Unit
Material
Alloy steel
-
Grade
F91 / Grade 91 / UNS K90901 / 1.4903
-
Product Form
Round bar / rod
-
Standard
ASTM A182 / A182M Grade F91
-
Diameter
10 - 300 (typical supply range)
mm
Length
3 - 6 (random), or cut to length
m
Manufacturing Process
Hot rolled or forged, normalised and tempered
-
Production Route
EAF with ladle refining and vacuum degassing for nitrogen control
-
Surface Finish
Hot-rolled, rough-turned, peeled, smooth-turned, centreless ground
-
Heat Treatment / Delivery Condition
Normalised 1040-1080 C, tempered 730-800 C
-
Tolerance Standard
ASTM A29 / A29M
-
Density
7.77 (typical)
g/cm3
Melting Range
1425 - 1510 (typical)
C
Thermal Conductivity at 100 C
28.0 (typical)
W/m.K
Coefficient of Thermal Expansion (20-100 C)
11.0 (typical)
um/m.C
Specific Heat (0-100 C)
480 (typical)
J/kg.K
Electrical Resistivity at 20 C
0.60 (typical)
uOhm.m
Modulus of Elasticity at 20 C
215 (typical)
GPa
Magnetic Properties
Ferromagnetic in all conditions
-
Maximum Service Temperature
600 (typical, continuous, up to 650 in some applications)
C
Testing / Inspection Standard
ASTM A370 for mechanical testing, hardness verification mandatory
-
Certification / Inspection Documents
EN 10204 3.1 or 3.2 mill test certificate with heat treatment records
-
Technical Specifications
Get the key technical specifications for Alloy Steel F91 Round Bar
Buy to ASTM A182 / A182M as Grade F91, with dimensional requirements from ASTM A29 / A29M.
The heat treatment is the material. Normalising at 1040-1080 C dissolves the vanadium and niobium carbonitrides and produces martensite on cooling. Tempering at 730-800 C then precipitates them as a fine, stable dispersion. Miss either step, or get the temperatures wrong, and the creep strength that justifies the alloy simply is not there, even though room-temperature tensile testing may still pass.
Hardness at 190-248 HBW is the practical check. Below 190 HBW the material has been over-tempered and the precipitates have coarsened. Above 248 HBW it has been under-tempered and retains brittle untempered martensite.
Three field problems are worth knowing. Local heating above the lower transformation temperature, from a careless flame cut or an uncontrolled preheat, forms fresh untempered martensite that only a full renormalise and temper will fix. Post-weld heat treatment below the specified range leaves brittle weld metal. And Type IV cracking, a creep failure in the fine-grained heat-affected zone, appears after years of service and has caused numerous header failures worldwide.
Positive material identification is routinely specified, since F91 and F9 look identical and are not interchangeable.
Chemical Composition for Alloy Steel F91 Round Bar
Element
Symbol
Min
Max
Unit
Carbon
C
0.08
0.12
%
Manganese
Mn
0.30
0.60
%
Silicon
Si
0.20
0.50
%
Phosphorus
P
-
0.020
%
Sulfur
S
-
0.010
%
Chromium
Cr
8.00
9.50
%
Molybdenum
Mo
0.85
1.05
%
Vanadium
V
0.18
0.25
%
Niobium
Nb
0.06
0.10
%
Nitrogen
N
0.030
0.070
%
Nickel
Ni
-
0.40
%
Aluminium
Al
-
0.02
%
Iron
Fe
Balance
-
%
Chemical Composition
View the chemical composition and applicable material limits for Alloy Steel F91 Round Bar
Vanadium at 0.18-0.25%, niobium at 0.06-0.10% and nitrogen at 0.030-0.070% are what separate this alloy from ordinary 9Cr-1Mo. Together they form fine vanadium and niobium carbonitrides that resist coarsening far better than chromium or molybdenum carbides do, and it is that stability under years of load at temperature which roughly doubles the creep strength against F22 at 600 C.
Nitrogen is a deliberate alloying element here, not a residual, and the narrow range matters. Too little and there is not enough carbonitride to strengthen. Too much and toughness suffers.
Aluminium is capped very low at 0.02% for a specific reason. Aluminium ties up nitrogen as aluminium nitride, which removes it from the carbonitride chemistry and quietly destroys the creep strength. A heat can meet every other requirement and still underperform if aluminium runs high.
Chromium at 8.00-9.50% provides oxidation and steam-side corrosion resistance, and molybdenum at 0.85-1.05% adds solid-solution strengthening.
Carbon at 0.08-0.12% is tightly controlled to balance martensite hardness against weldability.
Phosphorus at 0.020% and sulphur at 0.010% are far tighter than the older Cr-Mo grades, protecting creep ductility and weld integrity.
Mechanical Properties for Alloy Steel F91 Round Bar
Mechanical Property
Value
Unit
Tensile Strength
620
MPa (minimum)
Yield Strength 0.2% Proof
415
MPa (minimum)
Elongation in 50 mm
20
% (minimum)
Reduction of Area
40
% (minimum)
Hardness
190 - 248
HBW (specified range, mandatory)
Modulus of Elasticity
215
GPa (typical)
Mechanical Properties
Check the key mechanical properties and performance requirements of Alloy Steel F91 Round Bar
These figures are ASTM A182 / A182M requirements for Grade F91, tested to ASTM A370. Tensile, proof strength, elongation and reduction of area are minima. Hardness is a mandatory 190-248 HBW range, and for this grade it is the single most informative number on the certificate.
Below 190 HBW the material has been over-tempered. The fine vanadium and niobium carbonitrides have coarsened and the creep strength that justifies the alloy is compromised, even though room-temperature tensile results may still comfortably pass. Above 248 HBW the material has been under-tempered and retains untempered martensite, which is brittle and prone to cracking in service or during fabrication.
Room-temperature strength is only modestly above F9, at 620 MPa against 585 MPa minimum tensile. The reason to specify F91 lies entirely in creep, where its stress-rupture strength at 600 C is roughly double that of F22, which is what allowed supercritical steam conditions to become economic.
Design for elevated temperature runs on ASME BPVC allowable stresses for the grade, not the tensile figures shown here.
Charpy impact testing is commonly specified as a supplementary requirement, and heat treatment records should be requested with the certificate.
Dimension / Sizes for Alloy Steel F91 Round Bar
Dimension / Size
Value
Unit
Diameter
10 - 300
mm
Standard Length
3 - 6 (random / mill lengths)
m
Custom Length
Cut to length available on request
-
Diameter Tolerance
Per ASTM A29 / A29M, varies with size and finish
-
Length Tolerance
Per ASTM A29 / A29M or as agreed at order
-
Straightness Tolerance
Per ASTM A29 / A29M or as agreed at order
-
End Condition
Square cut, chamfered, or as ordered
-
Surface Finish
Hot-rolled, rough-turned, peeled, smooth-turned, centreless ground
-
Available Size Range
10 - 300, larger diameters by forging on enquiry
mm
Cut-to-Length Availability
Available
-
Dimensional Standard
ASTM A29 / A29M
-
Dimensions & Sizes
Explore available diameters, lengths, and dimensional requirements for Alloy Steel F91 Round Bar
Pricing for Alloy Steel F91 Round Bar
Round Bar Prices are generally quoted per kilograms or meters tonnes and can fluctuate with the global raw material and market prices. The final price will depend on a variety of factors, including the grade size, diameter, length, surface finish, the quantity and whether the bars are cut to length or in standard lengths.
For smaller quantities, we can also quote per metre or per piece basis once the required dimensions have been confirmed. Container-loads or orders that are larger in size are typically priced per tonne, based upon the specifications required and the supply conditions.
Please provide your desired dimensions, grades, length number, and end for a current quote including the lead time applicable and details for certification.
Pricing
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Why Choose Us
Euro Steel Bars is an international distributor, stockist and exporter of stainless round steel bars that cover carbon, stainless alloy, special grades. We stock a variety of sizes and grades. We guarantee every order with mill test certificates as well as full quality-assurance documentation. Our name speaks to our roots: European-sourced materials that is backed by the certificates and rigor that buyers from Asia as well as the Gulf and Africa are looking for.
Each bar we deliver is accompanied by EN 10204 3.1 mill test certificates as well as complete documentation of quality, so what you receive corresponds to what’s written in the documents. We carry a selection of sizes and grades ready for transport, and cut length upon the request of customers, which results in quicker lead times, whether you’re ordering just a one-off spec or a complete project tonnage.
We operate an actual wholesale business that is that is supported with an internationally-operated supply chain therefore we are able to serve fabricators sourcing one grade the same way in the same way as an EPC contractor who is placing a large order. Our clients include manufacturers, fabricators EPC construction companies, engineers oil and gas projects as well as construction companies. we design our inventory as well as documentation to show what buyers need to bring projects forward.
Our customers trust us across Qatar, Oman, Bahrain, Kuwait, Jordan, Malaysia, Singapore, Thailand, Taiwan, Turkey, Italy and South Africa. If you’re looking to source an Gulf energy project, or a construction project within Southeast Asia, you get the same quality of certified material, the exact documentation, and the exact delivery procedure.
Frequently Asked Questions
What is Alloy Steel F91 Round Bar?
What is the difference between F9 and F91?
Why is hardness so important for F91?
What is Type IV cracking?
What standard does Alloy Steel F91 Round Bar comply with?
What are the key mechanical properties of Alloy Steel F91 Round Bar?
Why is aluminium capped so low in F91?
What sizes and lengths are available?
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