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 Chemical Composition
Chromium-Molybdenum-Vanadium Alloy Steel Chemistry per ASTM A193 / A193M-22 Table 1
ASTM A193 Grade B16 (UNS K14072) is a chromium-molybdenum-vanadium alloy steel with chemistry tightly controlled per ASTM A193 / A193M-22 Table 1. The base steel is in the AISI 4140 / 4142 family with vanadium added at 0.25 to 0.35 % as the defining microalloy.
B16 chemical composition (ASTM A193 / A193M-22 Table 1)
| Element | Composition range (% by mass) | Product analysis variation | Role in alloy |
|---|---|---|---|
| Carbon (C) | 0.36 - 0.47 | 0.02 | Hardenability + strength |
| Manganese (Mn) | 0.45 - 0.70 | 0.03 | Hardenability + S getter |
| Phosphorus (P), max | 0.035 | 0.005 | Impurity - embrittles grain boundaries |
| Sulphur (S), max | 0.040 | 0.005 | Impurity - reduces hot workability |
| Silicon (Si) | 0.15 - 0.35 | 0.02 | Deoxidiser + ferrite strengthener |
| Chromium (Cr) | 0.80 - 1.15 | 0.05 | Hardenability + creep + oxidation resistance |
| Molybdenum (Mo) | 0.50 - 0.65 | 0.03 | Creep resistance + temper embrittlement suppression |
| Vanadium (V) | 0.25 - 0.35 | 0.03 | Forms fine V4C3 carbides resisting grain coarsening at high temperature |
| Aluminium (Al) | 0.015 (footnote E) | n/a | Grain refiner |
Heat analysis vs product analysis
ASTM A193 distinguishes two chemistry tests:
- Heat (ladle) analysis - chemistry sampled and tested during steelmaking, before casting. Reported on the mill certificate as the heat analysis. Must fall within the Table 1 composition range.
- Product (check) analysis - chemistry sampled from the finished bar or bolt. May vary slightly from the heat analysis (because of segregation during solidification and rolling). The product analysis variation column above gives the allowed deviation from the Table 1 limit.
For example: heat analysis V = 0.30 % is in range (0.25 - 0.35). Product analysis V = 0.37 % is acceptable because 0.37 - 0.35 = 0.02 is within the 0.03 product analysis variation.
Why vanadium matters
The 0.25 to 0.35 % vanadium addition is the single most important chemistry difference between B16 and the sister Grade B7. During tempering at 1200 °F (650 °C) or higher, vanadium combines with carbon to form fine, coherent V4C3 carbides distributed through the matrix. These carbides:
- Pin austenite grain boundaries during reheat - prevents grain coarsening if the bolt is exposed to long-term service at elevated temperature
- Stabilise the tempered martensite structure - prevents continued tempering and softening during service
- Resist creep deformation - the dispersed carbide network impedes dislocation motion
- Enable the S12 stress-rupture qualification (25 h minimum rupture life at 1100 °F / 20 ksi) that is unique to B16 within the A193 alloy-steel grades
Chemistry comparison vs B7 and other A193 alloy grades
| Element | A193 B7 | A193 B16 | A193 B5 (5Cr-1/2Mo) |
|---|---|---|---|
| C | 0.37 - 0.49 | 0.36 - 0.47 | 0.10 max |
| Mn | 0.65 - 1.10 | 0.45 - 0.70 | 0.30 - 0.60 |
| Si | 0.15 - 0.35 | 0.15 - 0.35 | 0.50 max |
| Cr | 0.75 - 1.20 | 0.80 - 1.15 | 4.00 - 6.00 |
| Mo | 0.15 - 0.25 | 0.50 - 0.65 | 0.40 - 0.60 |
| V | not specified | 0.25 - 0.35 | not specified |
UNS designation and steel family
Grade B16 carries the UNS K14072 designation (Unified Numbering System for metal alloys). The base steel family is AISI 4140 / 4142 with vanadium microalloying. Closely related international grades:
| Standard | Grade designation |
|---|---|
| ASTM | A193 / A193M B16 (UNS K14072) |
| ASME | SA-193 / SA-193M B16 |
| EN 10269 | 21CrMoV5-7 / 21CrMoV5-11 (Werkstoff 1.7709) |
| DIN 17240 / 17243 | 21CrMoV5-7 |
| BS 1506-624 | (withdrawn, replaced by EN 10269) |
| JIS | SNB16 |
| AFNOR | 40CDV04-05 / 25CDV4 |
| GOST | 25Cr2MoV / 20CrMoV |
Certification regime for B16 chemistry
TorqBolt B16 chemistry is documented on every mill test certificate:
- EN 10204 Type 3.1 - heat analysis + product analysis as required
- EN 10204 Type 3.2 - third-party witnessed heat + product analysis (DNV, Lloyd’s Register, TÜV, Bureau Veritas)
- NORSOK M-650 QTR - heat and product analysis preserved in the qualified test record, valid 5 years
- PED 2014/68/EC - documented heat analysis under the Pressure Equipment Directive
Related TorqBolt resources
- A193 Grade B16 bolting specification (home)
- B16 stud bolts product page
- B16 vs B7 chemistry comparison
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