Steel SNB7
SNB7 is the JIS chromium-molybdenum bolting steel of 4140 chemistry, supplied quenched and tempered to diameter-based strength classes (≤64 mm, 64-100 mm, 100-180 mm) plus the lower-hardness B7M variant, with annealed, normalized and hot-rolled bar also on file.
Reference datasheet — SNB7 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the Q&T ≤64mm condition
SNB7 tempers and conditions
SNB7 is supplied in 7 conditions, soft to hard. Q&T ≤64mm is the default FabDigit quotes; the values on this page are for it.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
soft condition for machining or cold work | Bar supplied soft for deep machining or thread rolling before final quench and temper. | 415 | 655 | 25 | 197 HB | — |
Hot rolled | Raw bar or forging stock bought for in-house heat treatment of studs and bolts. | 450 | 750 | 20 | 18 HRC | 7.8 % IACS |
Q&T 100–180 mm dia | Heavy anchor studs and large flange bolting; lowest guaranteed strength class. | 600 | 800 | 22 | 22 HRC | — |
Q&T ≤235 HB | Choose when NACE MR0175 sour-service hardness limits apply; strength is traded for SSC resistance. | 600 | 760 | 20 | 19 HRC | — |
air cooled from austenitizing, pre-machining stock | Uniform-grain intermediate condition for forgings before final Q&T; not a delivery condition for B7 fasteners. | 655 | 1,020 | 18 | 32 HRC | 7.8 % IACS |
Q&T 64–100 mm dia | Larger studs where hardenability limits properties to 655 MPa minimum yield. | 745 | 880 | 21 | 26 HRC | — |
Q&T ≤64mmDefault Q&T ≤64 mm dia | Standard stocked condition for studs, bolts and bar up to 64 mm — 720 MPa minimum yield. | 830 | 950 | 20 | 30 HRC | — |
What is SNB7?
SNB7 is the JIS chromium-molybdenum bolting steel of 4140 chemistry, supplied quenched and tempered to diameter-based strength classes (≤64 mm, 64-100 mm, 100-180 mm) plus the lower-hardness B7M variant, with annealed, normalized and hot-rolled bar also on file. It is the default material for high-temperature bolting in power plant and pressure vessel work because strength is held to 425 °C service. The reference condition gives 830 MPa yield, 950 MPa tensile, 20 % elongation and 285 HB (30 HRC). It is not intended for welding and has no corrosion resistance; use B7M where reduced hardness is required, or a stainless bolting grade for corrosive service. SNB7 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,416°C (2,581 °F). SNB7 has a yield strength of 830 MPa (120 ksi) and a tensile strength of 950 MPa (138 ksi) — stronger than 87% of steel grades. Elongation at break is 20% and the elastic modulus is 205 GPa (29.7 Msi).
What is SNB7 used for?
- high-temperature bolts
- studs
- flange fasteners
Advantages
- High strength — 830 MPa (120 ksi), better than 87% of steel grades
- Polishes to a fine finish — 65/100, better than 78% of steel grades
SNB7 properties
Typical room-temperature values for SNB7-Q&T ≤64mm; bars are the position among steel grades.
Physical3
SNB7 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,416°C (2,581 °F).
Mechanical16
SNB7 has a yield strength of 830 MPa (120 ksi) and a tensile strength of 950 MPa (138 ksi) — stronger than 87% of steel grades. Elongation at break is 20% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
SNB7 is rated for continuous service to 425°C (797 °F). It conducts heat at 42.6 W/m·K (24.6 BTU/hr·ft·°F), worse than 51% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
SNB7 conducts electricity at 7.8 % IACS, worse than 57% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of SNB7 takes about 30 MJ of energy and emits 2.3 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 30%.
Manufacturability6
SNB7's machinability is fair (50/100, worse than 53% of steel grades); weldability fair (35/100); formability poor (30/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. SNB7 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with SNB7
Is SNB7 easy to machine?
Machine in annealed condition where possible; at 28–32 HRC use rigid setups, coated carbide, ~80–120 m/min and generous coolant — thread rolling before hardening gives best fatigue life.
Can SNB7 be welded?
Not intended for welding; if unavoidable use low-hydrogen consumables, 250–350 °C preheat and 620–680 °C PWHT to avoid hard HAZ and hydrogen cracking.
Can SNB7 be formed, bent or molded?
Hot forge at 1100–1200 °C then normalize; cold forming only in the annealed state, with re-quench and temper afterwards to restore B7 properties.
SNB7 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| CJIS G4107 SNB7 0.38–0.48 | 0.37 – 0.49 | 0.42 |
| Si | 0.15 – 0.35 | 0.25 |
| Mn | 0.65 – 1.1 | 0.88 |
| P | ≤ 0.04 | |
| S | ≤ 0.04 | |
| Cr | 0.75 – 1.2 | 0.95 |
| Mo | 0.15 – 0.25 | 0.2 |
| Fe | balance |
What surface finishes work on SNB7?
Bare surfaces rust quickly — zinc plate, hot-dip galvanize (bake to relieve hydrogen), phosphate-and-oil or PTFE coat; keep plating baking cycles per ASTM F1941 to avoid hydrogen embrittlement.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Organic Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel SNB7 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- Similar grades
- 4140
How much does SNB7 cost?
SNB7 is a budget-cost steel ($), cheaper than about 90% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
SNB7 — frequently asked
What is SNB7 used for?
SNB7 is typically used for high-temperature bolts, studs and flange fasteners. In short: standard B7 bolting steel; 4140 chemistry, sized tempers; strength to 425 °C.
What is the yield strength of SNB7?
SNB7 has a typical yield strength of 830 MPa (120 ksi) and a tensile strength of 950 MPa (138 ksi) — stronger than 87% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is SNB7 easy to machine?
Reasonably — machinability is rated fair (50/100, worse than 53% of steel grades). Machine in annealed condition where possible; at 28–32 HRC use rigid setups, coated carbide, ~80–120 m/min and generous coolant — thread rolling before hardening gives best fatigue life.
Can SNB7 be welded?
With care — weldability is rated fair (35/100). Not intended for welding; if unavoidable use low-hydrogen consumables, 250–350 °C preheat and 620–680 °C PWHT to avoid hard HAZ and hydrogen cracking.
What surface finishes work on SNB7?
Bare surfaces rust quickly — zinc plate, hot-dip galvanize (bake to relieve hydrogen), phosphate-and-oil or PTFE coat; keep plating baking cycles per ASTM F1941 to avoid hydrogen embrittlement.
Can SNB7 be formed, bent or molded?
Hot forge at 1100–1200 °C then normalize; cold forming only in the annealed state, with re-quench and temper afterwards to restore B7 properties.
What is the maximum service temperature of SNB7?
SNB7 is rated for continuous use to about 425°C (797 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between SNB7 Q&T ≤64mm and SNB7-HR?
Q&T ≤64mm is the default condition — standard stocked condition for studs, bolts and bar up to 64 mm — 720 MPa minimum yield. HR: raw bar or forging stock bought for in-house heat treatment of studs and bolts. Yield strength is 830 MPa in Q&T ≤64mm versus 450 MPa in HR.
How much does SNB7 cost?
SNB7 is a budget-cost steel ($), cheaper than about 90% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- JIS G 4107 Alloy steel bolting materials for high temperature service — JSA (2019)
- ASTM A193/A193M Alloy-Steel and Stainless Steel Bolting for High Temperature Service — ASTM (2023)
- ASM Handbook Vol.1 Properties and Selection: Irons, Steels and High-Performance Alloys (4140/4142) — ASM International (1990)
- ASM Handbook Vol.16 Machining — ASM International (1989)
- GB/T 3077 (42CrMo) — SAC (2015)
- NACE MR0175 / ISO 15156 materials for H2S-containing environments — NACE/ISO (2020)
- 42CrMo — Mysteel / 1688 (2026)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.