What ASTM A131 Grade FH40 Is
ASTM A131 Grade FH40 is a high-strength hull structural steel plate covered by the ASTM A131/A131M specification for structural steel for ships. In the designation, the letter F fixes the Charpy V-notch impact test temperature at -60 °C, the letter H identifies a high-strength steel with a minimum yield strength of 390 MPa, and the number 40 refers to the 40 kgf/mm2 strength level. The plate is supplied as killed, fine-grain steel and combines low-temperature toughness, higher strength, strong corrosion resistance and dependable forming and welding behaviour.
FH40 plate serves the primary hull structure of ships with a displacement above 10,000 tonnes, ice-strengthened shell and frame areas, and ocean offshore platform structures where low-temperature toughness is a governing design requirement rather than a secondary check.
Chemical Composition of ASTM A131 Grade FH40
Ladle analysis limits for FH40 plate are summarised below. Single values are maximum limits unless a range is shown, and all figures are percentages by mass.
| Element | Requirement (%) | Element | Requirement (%) |
|---|---|---|---|
| Carbon, C | 0.16 max | Silicon, Si | 0.10-0.50 |
| Manganese, Mn | 0.90-1.60 | Phosphorus, P | 0.025 max |
| Sulphur, S | 0.025 max | Aluminium, Al (acid soluble) | 0.015 min |
| Niobium, Nb | 0.02-0.05 | Vanadium, V | 0.05-0.10 |
| Titanium, Ti | 0.02 max | Copper, Cu | 0.35 max |
| Chromium, Cr | 0.20 max | Nickel, Ni | 0.40 max |
| Molybdenum, Mo | 0.08 max | Nitrogen, N | 0.009 max |
Aluminium is added as a grain-refining deoxidiser, while niobium, vanadium and titanium are used in combination so that the strength level is reached through controlled rolling or normalising rather than through heavy alloying. Copper, chromium, nickel and molybdenum are held at low residuals, which keeps the carbon equivalent workable and the heat-affected zone tough.
Mechanical Properties of ASTM A131 Grade FH40
| Property | Requirement |
|---|---|
| Minimum yield strength | 390 MPa |
| Tensile strength | 510-650 MPa |
| Minimum elongation, 200 mm gauge length | 19 % |
| Minimum elongation, 50 mm gauge length | 22 % |
| Charpy V-notch impact energy | 37 J at -60 °C |
The 37 J impact requirement at -60 °C is what separates FH40 from the milder hull grades. It allows the plate to be used in the coldest service zones without a brittle fracture risk in the parent metal or in the weld heat-affected zone.
Classification Society Equivalent Grades
FH40 is recognised by the major classification societies for hull structural steel, and equivalent designations appear in their rule sets:
| Society | Equivalent grade | Society | Equivalent grade |
|---|---|---|---|
| DNV | NV F40 | GL | GL-F40 |
| LR | LR/FH40 | BV | BV/FH40 |
| CCS | CCS F40 | NK | K F40 |
| KR | R F40 | RINA | RI/F40 |
When a project is specified against a society rule instead of ASTM A131, the equivalent grade above can be quoted, but the impact test temperature, strength level and thickness restrictions must always match the rule edition referenced by the project specification.
Delivery Conditions and Supplementary Services
Delivery condition: as-rolled (AR), thermo-mechanical controlled processing (TMCP), normalised (N), or quenched and tempered (Q+T)
Ultrasonic examination to ASTM A435, ASTM A577 or ASTM A578 for straight-beam and angle-beam inspection
Through-thickness Z-direction testing to Z15, Z25 or Z35 for welded tee joints
Charpy V-notch impact testing at the specified test temperature, with optional testing at lower temperatures
Third-party inspection and certification through recognised classification societies
Mill test certificates to EN 10204 format 3.1 or 3.2
Shot blasting and painting, plus profile cutting and welding to suit fabrication drawings
Fabrication and Applications
Because FH40 is a 390 MPa yield steel, welding can be carried out with conventional low-hydrogen consumables, and preheat is set by plate thickness and by the actual carbon equivalent of each heat. The fine-grain structure produced by TMCP or normalising keeps the heat-affected zone tough at -60 °C, which is the reason the grade is chosen for the shell plating, deck and bulkhead of large hulls and for offshore platform structures.
Typical end uses include hull structures of large commercial vessels, ice-class shell plating, offshore platform legs and bracings, crane and deck structures, and heavy welded sections that need strength and low-temperature toughness at the same time.
FAQ
Q: What does the F in ASTM A131 Grade FH40 mean?
The F denotes that the steel is Charpy V-notch impact tested at a temperature of -60 °C, the lowest of the four impact temperature classes in the specification.
Q: What is the minimum yield strength of FH40 steel plate?
The minimum yield strength is 390 MPa, with tensile strength in the range of 510 to 650 MPa.
Q: Is FH40 the same as EH40?
No. Both are 390 MPa high-strength hull steels, but EH40 is impact tested at -40 °C and FH40 at -60 °C, so FH40 is the more demanding specification.
Q: Which classification society grades are equivalent to ASTM A131 FH40?
DNV NV F40, GL-F40, LR/FH40, BV/FH40, CCS F40, NK K F40, KR R F40 and RINA RI/F40 are the usual equivalents.
Q: What delivery conditions are available for FH40 plate?
As-rolled, TMCP, normalised and quenched and tempered plates are all produced; the choice depends on thickness, thickness-direction properties and the toughness level required by the design.
Q: Which standards are used for ultrasonic examination of FH40 plate?
ASTM A435 covers straight-beam examination, ASTM A577 covers angle-beam examination of thicker plate, and ASTM A578 covers straight-beam examination of thinner plate.
