Materials & grades
ASTM A193 Grade B7 / B7M chromium-molybdenum bolting steel (42CrMo4, SNB7)
ASTM A193 Grade B7 is a quenched and tempered chromium-molybdenum steel (AISI 4140 or 4142 type) for studs and bolts in high-pressure and high-temperature service, with a minimum tensile strength of 125 ksi up to 2½ in. Its nearest European steel is 42CrMo4 under EN 10269 and the Japanese JIS G 4107 grade SNB7 is its closest Japanese bolting steel.
Names by standard
What it is called in each region
| Region | System | Designation | Norma | Match |
|---|---|---|---|---|
| USA | ASTM A193/A193M | Grade B7Ordering grade for alloy-steel studs, bolts and bar, quenched and tempered. Marked B7 on the part. | ASTM A193/A193M | Same material |
| ASTM A193/A193M | Grade B7MSame steel as B7, tempered at a higher temperature to cap hardness at 235 HBW / 99 HRB for stress-corrosion cracking service. Lower strength than B7; needs 2HM nuts. | ASTM A193/A193M | Closest equivalent | |
| AISI/SAE (steel type) | 4140 / 4142 / 4145The grade is made from this steel family. A193 sets its own composition limits, which are wider than SAE 4140 on carbon. See the 4140 page for the steel. | SAE J404 | Closest equivalent | |
| UK | BS EN 10269 | 42CrMo4BSI adopts EN 10269. 42CrMo4 is the chromium-molybdenum steel in that standard that sits closest to B7. Property limits differ from A193. | BS EN 10269 | Closest equivalent |
| EU | EN 10027-1 name | 42CrMo442CrMo4 in the fastener steel standard EN 10269 is specified with elevated-temperature and low-temperature properties. It is not the same ordering specification as A193 B7. | EN 10269 | Closest equivalent |
| EN 10027-2 number | 1.7225 | EN 10269 | Closest equivalent | |
| Indie | IS 1367 (Part 3) | 8.8 / 10.9 (property classes)India has no separate high-temperature alloy bolting grade in this family that we could verify. IS 1367 (Part 3) is identical to ISO 898-1, and B7 lies between classes 8.8 and 10.9 in strength. Neither class is equivalent: see the equivalence notes. | IS 1367 (Part 3):2017 | Closest equivalent |
| Japan | JIS G 4107 | SNB7Alloy steel bolting material for high-temperature service under JIS G 4107. Its composition limits were found in one secondary source only, so they are not listed here. | JIS G 4107 | Closest equivalent |
| JIS G 4053 | SCM440The structural Cr-Mo steel from which SNB7 bar is related. SCM440 is not a bolting specification. | JIS G 4053 | Closest equivalent |
On equivalence
- A193 B7 is an ordering specification, not a steel grade. It sets a heat-treated condition and strength by size. The steel is chromium-molybdenum (AISI 4140, 4142 or 4145 type). 42CrMo4 and SCM440 are the same steel family, owned by the 4140 page, so they appear here as "closest".
- ISO 898-1 class 10.9 is not equivalent to B7. Class 10.9 requires 1040 MPa minimum tensile, and 940 MPa proof stress (Rp0.2), and is a room-temperature property class for finished fasteners. B7 requires 860 MPa tensile and 720 MPa yield up to M64, caps hardness at 321 HBW, requires reduction of area, and is tempered at 593 °C or more for elevated-temperature use. A 10.9 bolt can exceed the B7 hardness cap. A bar of 4140 can often meet both, but certificates refer to one specification.
- EN 10269 42CrMo4 gives a similar room-temperature strength (860–1060 MPa tensile, 730 MPa Rp0.2 up to 65 mm) and also specifies minimum Rp0.2 at elevated temperature (for example 640 MPa at 200 °C, 562 MPa at 300 °C, 475 MPa at 400 °C for diameters to 60 mm). The size bands, tests and marking differ from A193, so substitution needs approval.
- India: IS 1367 (Part 3) adopts ISO 898-1 and has no separate B7 equivalent in this family that we could verify. Indian projects normally order B7 under the ASTM name.
- Japan: JIS G 4107 SNB7 is the standard counterpart. A data page for SNB7 lists minimum tensile strengths of 690–860 MPa and minimum yields of 520–725 MPa across its diameter bands. These bracket the A193 values, which run from 690 to 862 MPa and 515 to 724 MPa. The diameter breakpoints were not available, so check JIS G 4107 before swapping.
- A193 B7 requires A194 Grade 2H nuts and B7M requires 2HM. Do not mix B7M studs with 2H nuts or vice versa without checking the design.
Chemical composition
Composition limits, mass %
| Element | B7USA · ASTM A193/A193M, Grade B7 (heat analysis) | 42CrMo4 (1.7225)EU · EN 10269 (cast analysis) |
|---|---|---|
| C | 0.37–0.49 | 0.38–0.45 |
| Si | 0.15–0.35 | ≤0.40 |
| Mn | 0.65–1.10 | 0.60–0.90 |
| P | ≤0.035 | ≤0.025 |
| S | ≤0.040 | ≤0.035 |
| Cr | 0.75–1.20 | 0.90–1.20 |
| Mo | 0.15–0.25 | 0.15–0.30 |
Mechanical properties
Strength and hardness
| Condition | Tensile strength | Yield strength | Elongation | Hardness |
|---|---|---|---|---|
| Quenched and tempered, minimum tempering temperature 1100 °F (593 °C)Specified minimums, diameter up to 2½ in (up to M64). Elongation 16%, reduction of area 50%. Hardness 321 HBW or 35 HRC maximum.ASTM A193/A193M Grade B7, via Torqbolt and Wermac | ≥860 MPa≥125 ksi | ≥720 MPa≥105 ksi | ≥16 % | ≤321 HBW / ≤35 HRC |
| Quenched and tempered, minimum tempering temperature 1100 °F (593 °C)Specified minimums, diameter over 2½ to 4 in (over M64 to M100). Elongation 16%, reduction of area 50%.ASTM A193/A193M Grade B7, via Torqbolt and Wermac | ≥795 MPa≥115 ksi | ≥655 MPa≥95 ksi | ≥16 % | ≤321 HBW / ≤35 HRC |
| Quenched and tempered, minimum tempering temperature 1100 °F (593 °C)Specified minimums, diameter over 4 to 7 in (over M100 to M180). Elongation 18%, reduction of area 50%.ASTM A193/A193M Grade B7, via Torqbolt and Wermac | ≥690 MPa≥100 ksi | ≥515 MPa≥75 ksi | ≥18 % | ≤321 HBW / ≤35 HRC |
| Grade B7M, quenched and tempered, minimum tempering temperature 1150 °F (620 °C)Specified minimums, diameter up to 4 in (up to M100). Elongation 18%, reduction of area 50%. Every bolt hardness-tested.ASTM A193/A193M Grade B7M, via Torqbolt and Wermac | ≥690 MPa≥100 ksi | ≥550 MPa≥80 ksi | ≥18 % | ≤235 HBW / ≤99 HRB |
| Grade B7M, quenched and tempered, minimum tempering temperature 1150 °F (620 °C)Specified minimums, diameter over 4 to 7 in (over M100 to M180). Elongation 18%, reduction of area 50%.ASTM A193/A193M Grade B7M, via Torqbolt and Wermac | ≥690 MPa≥100 ksi | ≥515 MPa≥75 ksi | ≥18 % | ≤235 HBW / ≤99 HRB |
| EN 10269 42CrMo4, quenched and tempered (+QT)Specified, diameter up to 65 mm; yield and elongation are minimums. Reduction of area at least 50%. Impact KV2 at least 50 J at 20 °C. Comparison only; not an A193 value.EN 10269, 42CrMo4, via Torqbolt | 860–1060 MPa125–154 ksi | ≥730 MPa≥106 ksi | ≥14 % | — |
In practice
Behaviour, heat treatment and uses
Characteristics
- B7 is the usual alloy stud for flanged pressure joints. It is a medium-carbon chromium-molybdenum steel hardened by quenching and tempered at 1100 °F (593 °C) or higher, so it keeps its strength well above room temperature.
- Strength in the specification falls as diameter rises: 125 ksi minimum tensile up to 2½ in, 115 ksi to 4 in and 100 ksi to 7 in. Elongation requirements rise from 16% to 18% across the same bands.
- A typical fastener-industry guideline is use below about 750 °F (400 °C) for B7. Beyond that, stress relaxation loses bolt load, and B16 or other bolting is chosen. The design code sets the actual limit, not the bolt grade.
- B7M is the same steel tempered at 1150 °F (620 °C) or higher to cap hardness at 235 HBW. This lowers strength to 100 ksi tensile. It suits services where hardness must stay low to avoid hydrogen or sulphide stress cracking, and A193 requires every B7M bolt to be hardness tested.
- Plain B7 can reach 35 HRC, above the 22 HRC limit used for sour service, so it does not meet that requirement. Check the sour-service rule (for example NACE MR0175) before substituting B7 for B7M.
- The steel is not corrosion resistant. Studs are supplied bare, zinc plated, hot-dip galvanized or PTFE coated; coatings usually lower the allowable temperature compared with bare studs.
- B7 bolting does not carry an impact requirement in A193. Where a minimum design temperature calls for Charpy testing, the equivalent low-temperature grade is A320 L7.
Heat treatment
- Bar is hot-wrought, then quenched in a liquid and tempered. A193 sets a minimum tempering temperature of 1100 °F (593 °C) for B7 and 1150 °F (620 °C) for B7M.
- Mill guidance for 42CrMo4 bar: harden at 840–880 °C in oil or water and temper at 540–680 °C.
- A supplementary requirement lets a purchaser order stress relieving after cold work or machining, held at 100 °F (55 °C) below the tempering temperature.
Typické použití
- Studs and bolts for pipe flanges, valves and pressure vessels in refinery, chemical and power plant
- Heat exchanger and boiler flange joints
- B7M for sour-service flanges and valves in oil and gas production
- Paired with A194 Grade 2H heavy hex nuts (B7) or 2HM nuts (B7M)
Bolting steels
Similar grades compared
| Jakost | C % | Mn % | Cr % | Ni % | Tensile, first listed condition |
|---|---|---|---|---|---|
| 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 |
| A320 L7 | 0.38–0.48 | 0.75–1.00 | 0.80–1.10 | — | ≥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.
Odpovědi na Vaše otázky
Common questions
What is the equivalent of ASTM A193 B7?
The nearest European steel is 42CrMo4 (1.7225) under EN 10269, and the nearest Japanese bolting grade is SNB7 under JIS G 4107. There is no exact Indian equivalent that we could verify, so ASTM A193 B7 is usually specified by name. All of these are close, not identical, because the size bands and test requirements differ.
What is the difference between A193 B7 and B7M?
B7M is the same steel as B7 but tempered at 1150 °F (620 °C) or higher so that hardness stays at or below 235 HBW. That lowers minimum tensile strength to 100 ksi against 125 ksi for B7 up to 2½ in. B7M is meant for services with stress-corrosion cracking risk, every bolt is hardness tested, and it takes 2HM nuts.
Is A193 B7 the same as 4140 steel?
B7 is made from 4140-type steel but is not the same thing. A193 B7 is an ordering specification for a heat-treated bolting product with set strength, hardness and tempering rules. AISI 4140 is a steel composition. Many 4140 bars can be heat treated to meet B7, but the certificate must state A193 B7.
Is B7 the same as a class 10.9 bolt?
No. Class 10.9 is an ISO 898-1 property class with 1040 MPa minimum tensile strength at room temperature. B7 up to M64 requires 860 MPa and is rated for elevated-temperature service. A 10.9 bolt can be harder than the B7 limit of 321 HBW, and it has no required tempering temperature. The two are not interchangeable without an engineering check.
Which nut goes with an A193 B7 stud?
A194 Grade 2H heavy hex nuts are the standard pairing for B7. For B7M, use 2HM nuts, whose hardness is capped at 235 HBW. The nut is made stronger than the stud so that, if overloaded, the stud yields first.
From the Corona catalog
Products listed with A193 B7
Tyče a pruty
Závitové tyče
Průměr: 1/4-2 1/2 in / M6-M60 · Délka: 3-20 ft / 1-6 m
Technické parametry
Tyče a pruty
Spínací tyče (se závitem na obou koncích)
Průměr: 1/2-2 1/2 in / M12-M60 · Délka: 3-20 ft / 1-6 m
Technické parametry
Komponenty pro uchycení potrubí
Závitové tyče / svorníky
Průměr: 1/4" - 2-1/2" / M6 – M60 · Délka: 2 ft – 19 ft (běžně 3, 6, 10, 12 ft) / 1 m – 5,8 m (běžně 1, 2, 3 m)
Technické parametryKeep reading
Related references
References
Sources
- 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.
- 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.
- Torqbolt, ASTM A193/A193M grades B7, B7M, B16, B8, B8M — Composition, strength by diameter band, minimum tempering temperature and supplementary requirements, transcribed from A193.
- Wermac, A193 B7 and A193 B7M studs — Inch-series B7 and B7M strength and hardness rows; B7M testing and nut pairing.
- Projectmaterials, What is ASTM A193 B7 — B7 steel type, tempering temperature, 2H nut and B7M summary.
- 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.
- Torqbolt, EN 10269 42CrMo4 (1.7225) — EN 10269 composition, +QT properties, elevated-temperature Rp0.2 and low-temperature impact values.
- SteelJIS, SNB7 datasheet (JIS G 4107) — SNB7 range of minimum strength values. Its composition table was not used (single secondary source).
- Aichi Steel, alloy steel bolting materials for high temperature service — Confirms JIS G 4107 as the standard for SNB7 to SNB16 bolting steels.
- T&R Fastenings, mechanical properties of steel bolts to ISO 898-1 — ISO 898-1 class 10.9 strength, elongation and hardness.
- Bureau of Indian Standards, IS 1367 (Part 3):2017, identical with ISO 898-1:2013 — Indian property classes for bolts, screws and studs are the ISO 898-1 classes.
- ASTM A193/A193M-10a, hosted copy of the full standard (Tables 1 to 3, sections 7, 10, 17, supplementary requirements) — B7 and B7M composition ranges, strength by diameter in inch and metric, tempering temperatures, B7M hardness and marking, S3, S4, S6, S12. 2010 edition, read by the independent checker.
- Wermac, A193 B7 vs A320 L7 studs — B7 composition (C 0.37–0.49, Mn 0.65–1.10, Cr 0.75–1.20, Mo 0.15–0.25) agrees with A193 Table 1.
- Lucefin, technical card 42CrMo4 to EN 10269 (AC:2008) — EN 10269 composition, +QT strength, KV at +20, −40 and −100 °C, and Rp0.2 at 50–550 °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.