Related Specifications
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175/ISO 15156-2
- NORSOK M-650
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
ASTM A193 Grade B16 Round Bar
Cr-Mo-V Alloy Steel Round Bar (Mill Source) for High-Temperature Fastener Production
ASTM A193 Grade B16 round bar (also written A193 B16 round bar, ASTM A193 Gr B16 round bar, SA-193 B16 round bar, UNS K14072 round bar) are chromium-molybdenum-vanadium quenched-and-tempered alloy-steel fasteners manufactured to ASTM A193 / A193M Table 2 mechanical limits and ASTM A29 / A752 mill specifications as the upstream raw-material source for downstream B16 fastener production. TorqBolt produces the full B16 round bar family from its Rajkot plant with imperial diameters from 1/4 in to 8 in and metric diameters from M6 to M200, both fine and coarse threads, in stock and on indent.
Round Bar configurations
B16 round bar are supplied in five standard configurations per ASTM A29 / A752 (general alloy steel bar specifications):
- Hot-rolled bar (HR) - lowest-cost finish, scaled surface, dimensional tolerance per ASTM A29 Table 5. Used as starting stock for forging and turning operations.
- Cold-drawn bar (CD) - drawn through a die for tighter dimensional tolerance and improved surface finish per ASTM A108. Direct-machinable.
- Peeled bar (P) - lathe-skinned surface to remove decarburised layer, improved diameter tolerance. Standard for high-integrity bolting.
- Turned and polished bar (T&P) - precision-turned surface with polish pass, h9 / h11 tolerance. Used for precision machined fasteners.
- Ground bar (G) - cylindrical-ground surface to h6 / h7 tolerance, mirror finish. Used for shafts and precision pins.
Diameter and length range
| Series | Stock diameter range | Indent diameter range | Length range (stock) | Length range (indent) |
|---|---|---|---|---|
| Hot-rolled (A29) | 1/2 in to 4 in | 1/4 in to 8 in | 2 m / 6 m stock | up to 12 m |
| Cold-drawn (A108) | 1/4 in to 2-1/2 in | 1/4 in to 4 in | 3 m / 6 m stock | up to 12 m |
| Peeled / Turned / Ground | 1/2 in to 2-1/2 in | 1/4 in to 4 in | 3 m / 6 m stock | up to 12 m |
B16 round bar material
B16 round bar is forged from AISI 4140 / 4142 chromium-molybdenum-vanadium alloy steel, conforming to the ASTM A193 Table 1 chemistry envelope. Vanadium addition of 0.25 to 0.35 % is the key differentiator from the B7 grade and is responsible for the creep and stress-relaxation resistance that justifies the B16 premium at elevated service temperatures.
| Element | Cr-Mo-V (% by mass) | Product analysis variation |
|---|---|---|
| C | 0.36 - 0.47 | 0.02 |
| Mn | 0.45 - 0.70 | 0.03 |
| P (max) | 0.035 | 0.005 |
| S (max) | 0.040 | 0.005 |
| Si | 0.15 - 0.35 | 0.02 |
| Cr | 0.80 - 1.15 | 0.05 |
| Mo | 0.50 - 0.65 | 0.03 |
| V | 0.25 - 0.35 | 0.03 |
B16 round bar mechanical properties
| Diameter, in. | 2-1/2 and under | over 2-1/2 to 4 | over 4 to 8 |
|---|---|---|---|
| Min. tempering temperature, °F | 1200 | 1200 | 1200 |
| Tensile strength, min, ksi | 125 | 110 | 100 |
| Yield strength, min, 0.2 % offset, ksi | 105 | 95 | 85 |
| Elongation in 4D, min, % | 18 | 17 | 16 |
| Reduction of area, min, % | 50 | 45 | 45 |
| Hardness, max | 321 HBW / 35 HRC | 321 HBW / 35 HRC | 321 HBW / 35 HRC |
Heat treatment
B16 round bar is supplied in the quenched-and-tempered (Q&T) condition. The standard heat-treatment route is: austenitise at 1650 to 1700 °F (900 to 925 °C), oil quench to develop a fully martensitic structure, then temper at 1200 °F (650 °C) minimum for time sufficient to meet the ASTM A193 Table 2 mechanical limits. Each heat-treat lot is tested per A193 sect 7. When Supplement S12 is invoked, stress-rupture testing at 1100 °F / 20 ksi is performed (suffix B16R). When Supplement S4 is invoked, hardness is verified on each round bar.
Downstream fastener conversion
B16 round bar is the upstream mill source for downstream B16 fastener production. TorqBolt cuts B16 bar stock into stud bolts, hex bolts, threaded rods, and anchor bolts, then re-tests the finished part per ASTM A193 sect 7 to confirm mechanical limits are retained through forging and heat-treatment. Bar customers requiring B16 raw material for their own machining are supplied with full EN 10204 3.1 mill MTC traceable to heat, ladle, and rolling-batch records.
Coatings and surface finish
B16 round bar is supplied in the following finish options:
- Plain (uncoated, as-machined) - default; protective oiling prevents shipping corrosion
- Black oxide - light protective finish for low-corrosion environments
- Hot-dip galvanised (HDG) per ASTM A153 - thick zinc coating for atmospheric service; baking required to prevent hydrogen embrittlement
- Zinc plating per ASTM B633 - thinner electroplated coating
- Cadmium plating per ASTM B766 / AMS-QQ-P-416 - aerospace and chemical-service applications
- Xylan 1424 / 1070 fluoropolymer - subsea and offshore high-temperature service
- PTFE coating (Teflon-based) - chemical-process flange bolting
- Geomet 500B / 720 - chromium-free corrosion protection for offshore
- Magni 565 / 575 - zinc-aluminium flake coating
- Phosphate and oil - shipping protection
Quality certification regime
TorqBolt supplies B16 round bar with the following certification options:
- EN 10204 Type 3.1 - default mill test certificate covering heat analysis, product analysis, mechanical-properties test, and heat traceability
- EN 10204 Type 3.2 - third-party-witnessed certificate (DNV, Lloyd’s Register, TÜV, Bureau Veritas) for offshore and pressure-vessel projects
- NORSOK M-650 qualified test record (QTR) - five-year validity, essential-variable changes trigger re-qualification
- NACE MR0175 / ISO 15156-2 sour-service certificate - project waiver required (B16 is not a default sour-service grade; B7M is)
- PED 2014/68/EC certificate - European Pressure Equipment Directive compliance for vessel-attached bolting
- API 6A / 17D PSL-3 - subsea and surface wellhead high-temperature applications
- Charpy V-notch impact test (Supplement S6) - on request, for piping below -20 °F
- Magnetic-particle examination (Supplement S7) - for refinery and offshore wellhead service
- ISO 17782 manufacturer-of-standard-fasteners certification - subsea SUBSEA+ pressure-traceability tier (offshore project requirement)
Lead time and procurement
Stock diameters (1/2 in to 4 in / M12 to M100) ship within 3 to 5 business days of order confirmation. Indent diameters (1/4 in to 1/2 in / M6 to M10 with custom length, or 4 to 8 in / M100 to M200) carry a 4 to 8 week lead time depending on heat-treatment lot consolidation and certification level (3.1 vs 3.2 vs NORSOK QTR). For NORSOK M-650 QTR-required round bar, expect 8 to 12 weeks for first-time grade qualification or 4 to 6 weeks for repeat orders under valid QTR. MOQ on stock is 5 pieces; on indent is 25 pieces per diameter / length combination.
Why engineers specify B16 round bar over forged pre-forms
B16 round bar is the upstream raw material for downstream fastener machining when the customer is a captive bolt-shop or an oil & gas EPC with in-house turning capacity. The bar-finish decision drives both cost and acceptance probability at the final machining step. Hot-rolled bar (ASTM A29 / A108) carries mill scale and a decarburised surface layer 0.1-0.3 mm deep; bolt turning must remove this layer entirely to expose the certified-chemistry core, requiring 0.5-0.8 mm rough-cut allowance per side. Cold-drawn bar is mill-pulled through a die after pickling, giving h11 tolerance and a clean surface, but cold-work residual stresses require a 1100 °F sub-critical stress-relief before final Q+T to A193 Table 2 limits. Peeled bar is lathe-skinned to remove decarb plus 0.5 mm of clean core, then ground or polished to h9-h10; default for high-integrity bolting. Per ASTM A29 supplementary S15, the bar is NOT mill-quenched and tempered – final heat treatment is the bolt-shop’s responsibility on the finished fastener.
Frequently asked questions
What is the maximum service temperature for A193 B16 round bar?
840 °F (450 °C) for continuous service per ASME B31.1 / B31.3 / B16.5 flange-bolting tables. 1100 °F (595 °C) for stress-rupture-qualified service with Supplement S12 (suffix B16R, 25 h rupture life at 20 ksi). Some industry sources cite 1000 °F as a conservative peak.
Are B16 round bar NACE-compliant for sour service?
B16 is not a default NACE MR0175 / ISO 15156-2 sour-service grade. For combined high-temperature and sour service, B16 requires a project-specific NACE waiver supported by stress-rupture and sulphide-stress-cracking testing. The default NACE sour-service A193 grade is B7M (impact-tested, hardness-controlled). For high-temperature sour service, an A193 B7M / B16 split assessment is often required.
Can B16 round bar be used at cryogenic temperature?
No. B16 has no Charpy V-notch requirement below -20 °F (-29 °C). For cryogenic service, use ASTM A320 Grade L7 (UNS G41400) which is the low-temperature counterpart of B16 with mandatory Charpy testing to -150 °F (-101 °C).
Which bar finish should I order for B16 fastener machining?
For one-shot turning to a finished stud bolt, peeled bar (P) is the default – the decarb layer is removed at the mill and the bar can go straight to the turning centre without rough-cut allowance. For high-volume cold-heading lines, cold-drawn (CD) with stress-relief is preferred for the dimensional tolerance, accepting the extra heat-treat step. Hot-rolled (HR) bar is the lowest cost but requires the full rough-cut allowance and is best suited to forging blanks rather than direct-to-stud machining. Ground bar (G) is overkill for fastener applications.
Related TorqBolt resources
- ASTM A193 Grade B16 bolting specification overview
- A193 B16 vs A193 B7 - full side-by-side comparison
- B16 hex bolts
- B16 heavy hex bolts
- B16 threaded rods
- B16 round bar (mill source)
- ASME SA-193 Grade B16 bolting specification
- B16 anchor bolts (high-temp foundation anchoring)
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