Materials & grades
ASTM A320 Grade L7 low-temperature chromium-molybdenum bolting steel (L7M, L43)
ASTM A320 Grade L7 is a quenched and tempered chromium-molybdenum bolting steel, chemically like A193 B7, that must pass a Charpy impact test at −150 °F (−101 °C). It is the bolting grade for LNG, ethylene and cold-climate pressure piping.
Names by standard
What it is called in each region
| Region | System | Designation | मानक | Match |
|---|---|---|---|---|
| USA | ASTM A320/A320M | Grade L7Low-temperature alloy-steel bolting, 4140-type steel, quenched and tempered with a required impact test. | ASTM A320/A320M | Same material |
| ASTM A320/A320M | Grade L7MSame steel as L7, tempered to a hardness cap (235 HBW / 99 HRB) for sour and cold service. Lower strength. | ASTM A320/A320M | Closest equivalent | |
| ASTM A320/A320M | Grade L43Nickel-chromium-molybdenum grade (AISI 4340 type) for larger sections, up to 4 in. | ASTM A320/A320M | Closest equivalent | |
| AISI/SAE (steel type) | 4140 / 4142The steel family behind L7. Owned by the 4140 page. | SAE J404 | Closest equivalent | |
| UK | BS EN 10269 | 42CrMo4 (+QT with impact at low temperature)BSI adopts EN 10269, which sets impact energy at temperatures down to −100 °C for 42CrMo4. | BS EN 10269 | Closest equivalent |
| EU | EN 10027-1 name | 42CrMo4EN 10269 gives a low-temperature impact requirement for 42CrMo4 bar. The temperature and energy differ from A320. | EN 10269 | Closest equivalent |
| EN 10027-2 number | 1.7225 | EN 10269 | Closest equivalent | |
| Japan | JIS G 4053 | SCM440Steel family only. We found no JIS bolting grade with an A320-style impact requirement. | JIS G 4053 | Closest equivalent |
On equivalence
- A320 L7 is an ordering specification. The steel is 4140 or 4142 type, the same as A193 B7. The 4140 page owns the steel names.
- EN 10269 42CrMo4 is the closest European bolting steel. Two data sources list a minimum of 27 J at −100 °C for bar up to 60 mm, close to the 27 J at −101 °C of A320 L7. Size bands and test rules still differ, so check each certificate against the order, not only the steel name.
- A mill datasheet shows that one 42CrMo4 variant (Ovako 6137) is made to ASTM A320 L7 as well as ISO 898 class 10.9 up to 50 mm. Meeting both on one bar does not make the two specifications equivalent.
- India: we did not find a verified IS designation with an A320-style impact requirement. Indian projects order L7 under the ASTM name.
- Japan: no JIS bolting grade with an equivalent impact requirement was found. SCM440 is the steel family only.
- A320 requires at least 20 ft·lbf (27 J) for L7, L7M and L43. The recommended test temperature is −150 °F (−101 °C) for L7 and L43 and −100 °F (−73 °C) for L7M. Another test temperature is allowed if it is at least as low as the service temperature and the bolting is marked. Check the order and the current A320 text.
Chemical composition
Composition limits, mass %
| Element | L7USA · ASTM A320/A320M-11a Table 3, Grade L7 and L7M (4140 type) | L7USA · Ovako mill specification, variant 6137 made for A320 L7 (cast analysis) | 42CrMo4 (1.7225)EU · EN 10269 (cast analysis) |
|---|---|---|---|
| C | 0.38–0.48 | 0.38–0.45 | 0.38–0.45 |
| Si | 0.15–0.35 | 0.15–0.35 | ≤0.40 |
| Mn | 0.75–1.00 | 0.75–0.90 | 0.60–0.90 |
| P | ≤0.035 | ≤0.025 | ≤0.025 |
| S | ≤0.040 | ≤0.025 | ≤0.035 |
| Cr | 0.80–1.10 | 0.90–1.10 | 0.90–1.20 |
| Mo | 0.15–0.25 | 0.15–0.25 | 0.15–0.30 |
Mechanical properties
Strength and hardness
| Condition | Tensile strength | Yield strength | Elongation | Hardness |
|---|---|---|---|---|
| Grade L7, quenched and tempered, impact testedSpecified minimums, diameter up to 2½ in. Elongation 16%, reduction of area 50%. Charpy V-notch minimum 20 ft·lbf (27 J) at −150 °F (−101 °C).ASTM A320/A320M Grade L7, via Projectmaterials and Wermac | ≥860 MPa≥125 ksi | ≥720 MPa≥105 ksi | ≥16 % | — |
| Grade L43, quenched and tempered, impact testedSpecified minimums, diameter up to 4 in. Elongation 16%, reduction of area 50%. Charpy V-notch minimum 20 ft·lbf (27 J) at −150 °F (−101 °C).ASTM A320/A320M-11a Table 1, Table 2 and Table 4, Grade L43, confirmed by Boltport | ≥860 MPa≥125 ksi | ≥720 MPa≥105 ksi | ≥16 % | — |
| Grade L7M, quenched and tempered, impact testedSpecified minimums, diameter up to 2½ in. Elongation 18%. Hardness 235 HBW or 99 HRB maximum. Minimum tempering temperature 1150 °F (620 °C). Charpy V-notch minimum 20 ft·lbf (27 J), recommended test temperature −100 °F (−73 °C).ASTM A320/A320M-11a Table 1 and Table 4, Grade L7M, confirmed by Flange Bolt Chart and Boltport | ≥690 MPa≥100 ksi | ≥550 MPa≥80 ksi | ≥18 % | ≤235 HBW / ≤99 HRB |
| Ovako bar made for L7 (variant 6137), quenched and temperedMill specification, round bar over 22 to 90 mm. Reduction of area at least 50%. Impact at least 27 J (long) at −101 °C. Hardness 260–321 HB.Ovako 42CrMo4 material data sheet | 860–1070 MPa125–155 ksi | ≥725 MPa≥105 ksi | ≥16 % | 260–321 HB |
| EN 10269 42CrMo4, quenched and tempered (+QT)Specified, diameter up to 65 mm; yield and elongation are minimums. Reduction of area at least 50%. KV2 at least 50 J at 20 °C; 27 J at −100 °C and 40 J at −40 °C for diameters up to 60 mm (Torqbolt and Lucefin). Comparison only.EN 10269, 42CrMo4, via Torqbolt | 860–1060 MPa125–154 ksi | ≥730 MPa≥106 ksi | ≥14 % | — |
In practice
Behaviour, heat treatment and uses
Characteristics
- L7 and A193 B7 are both 4140-type steel with the same minimum tempering temperature, 1100 °F. A320 limits carbon and manganese more tightly (0.38–0.48% and 0.75–1.00%) than A193 B7 (0.37–0.49% and 0.65–1.10%). What A320 adds is a required Charpy V-notch test at −150 °F (−101 °C) for L7, so the bolt is proved tough at the low service temperature.
- A193 does not require or report impact values for B7. A joint with a design temperature below the B7 range therefore needs A320 L7, even if a B7 bolt would pass the test.
- L7M is the same steel tempered to a lower hardness (235 HBW / 99 HRB maximum) for sour service at low temperature. It gives up strength: 100 ksi tensile and 80 ksi yield.
- L43 is an AISI 4340-type nickel-chromium-molybdenum grade. A320 notes that holding the impact values at −150 °F in L43 may need lower phosphorus and sulphur than standard 4340.
- A320 also covers austenitic grades such as B8 and B8M, which keep ductility to very low temperature and need no impact test down to about −325 °F (−198 °C); below that A320 requires impact testing for them too.
- A320 requires the nut material to be impact tested. Nuts are A194 Grade 4 or 7.
- Hardenability limits the size at which the strength can be reached: A320 warns that some grades cannot meet the properties in large sections.
Heat treatment
- Bar is hot-wrought, quenched in a liquid and tempered. Heat treatment is the same as A193 B7 according to the supplier source read.
- Mill guidance for 42CrMo4 bar: harden at 840–880 °C in oil or water and temper at 540–680 °C. Tempering temperature controls the balance of strength and toughness.
- A320 lists −150 °F (−101 °C) as the recommended test temperature for L7 and L43, and −100 °F (−73 °C) for L7M. It allows another temperature if that is at least as low as the service temperature and the bolting is marked, so confirm the test temperature when ordering.
सामान्य उपयोग
- Flange and valve bolting in LNG plant and storage
- Ethylene and other cold hydrocarbon pressure piping
- Cryogenic and cold-climate pressure vessels and flanges
- Paired with A194 Grade 4 or 7 nuts
Bolting steels
Similar grades compared
| ग्रेड | C % | Mn % | Cr % | Ni % | Tensile, first listed condition |
|---|---|---|---|---|---|
| A320 L7 | 0.38–0.48 | 0.75–1.00 | 0.80–1.10 | — | ≥860 MPa |
| A193 B7 | 0.37–0.49 | 0.65–1.10 | 0.75–1.20 | — | ≥860 MPa |
| A193 B16 | 0.36–0.47 | 0.45–0.70 | 0.80–1.15 | — | ≥860 MPa |
| A193 B8 / B8M | ≤0.08 | ≤2.00 | 18.0–20.0 | 8.0–11.0 | ≥515 MPa |
| A194 2H | ≥0.40 | ≤1.00 | 0.80–1.10 | ≤0.40 | 500–650 MPa |
Composition from the US standard where one exists, otherwise the first standard listed on each grade's page. Strength conditions differ between grades; open a grade for its full table.
आपके सवालों के जवाब
Common questions
What is the difference between A193 B7 and A320 L7?
They use the same 4140-type steel and heat treatment. A320 L7 adds a Charpy V-notch impact test at −150 °F (−101 °C), with at least 20 ft·lbf (27 J). A193 B7 has no required impact test, so L7 is the grade for cold service.
What is the equivalent of A320 L7?
The nearest European steel is 42CrMo4 (1.7225) under EN 10269, which also specifies low-temperature impact energy. They are close, not identical, because the impact temperature and size bands differ. No verified Indian or Japanese bolting grade carries the same impact requirement.
What is A320 L7M?
L7M is the same chromium-molybdenum steel as L7 but tempered to a lower hardness, 235 HBW (99 HRB) maximum, for sour service. Its minimum strength is lower, at 100 ksi tensile and 80 ksi yield for sizes up to 2½ in.
What nuts go with A320 L7?
A194 Grade 4 or 7 nuts. A320 requires the nut material to be impact tested.
What is L43 in A320?
L43 is a nickel-chromium-molybdenum bolting grade of the AISI 4340 type, used for sections up to 4 in where L7 would not through-harden. It has the same 125 ksi minimum tensile strength as L7.
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Related references
References
Sources
- Wermac, ASTM A320 standard scope — A320 scope: low-temperature service, impact test at -150 F [-101 C], nuts to be impact tested.
- Projectmaterials, What is ASTM A320 — L7, L7M and L43 summary, impact energy, nut grades and typical LNG and ethylene uses.
- Ovako Steel Navigator, 42CrMo4 material data sheet — Lists ASTM A193 B7 as a similar designation; variant 6137 is made for ASTM A320 L7; quench and temper guidance.
- ASTM International, A193/A193M scope and abstract (alloy-steel and stainless steel bolting for high temperature or high pressure service) — Scope, grade families, nuts and A320 cross-reference; the full tables are paywalled.
- Standards.ie (NSAI shop), EN 10269:2013 Steels and nickel alloys for fasteners with specified elevated and/or low temperature properties — Title, scope and status of the CEN standard.
- Torqbolt, EN 10269 42CrMo4 (1.7225) — EN 10269 composition, +QT properties, elevated-temperature Rp0.2 and low-temperature impact values.
- Hex Technology, The Stud Guide: B7s, B16s and other common bolt materials — Typical service ranges, nut pairings and grade-selection notes from a fastener maker.
- Projectmaterials, What is ASTM A193 B7 — B7 steel type, tempering temperature, 2H nut and B7M summary.
- ASTM A320/A320M-11a, hosted copy of the full standard (Tables 1 to 4, sections 6, 10, 13) — L7, L7M and L43 composition, strength, hardness, 20 ft·lbf impact energy, recommended test temperatures (Table 4), nut and marking rules. 2011 edition, read by the independent checker.
- Flange Bolt Chart, ASTM A320 bolt material properties — L7, L7M and L43 strength, hardness (L7M 235 HBW or 99 HRB) and tempering temperatures.
- Boltport, ASTM A320 and Grade L43 specification pages — L7 and L7M composition, 20 ft·lbf impact energy, test temperatures −150 °F (L7, L43) and −100 °F (L7M).
- Lucefin, technical card 42CrMo4 to EN 10269 (AC:2008) — KV at +20, −40 and −100 °C for diameters up to 60 mm.
Values summarize published limits and typical data. The governing standard and the current edition control; check them before specifying.