Zeron 100 hex bolts are super duplex stainless steel hex-head bolts (UNS S32760 / Werkstoff 1.4501) machined or hot-headed from solution-annealed bar to ASTM A479 / A276 / A1082, threaded per ASME B1.1 (UNC/UNF/8UN inch) or ISO 261 (M-series metric), and supplied with PMI on every fastener. The 25Cr-7Ni-3.5Mo-0.7Cu-0.7W-0.25N composition delivers PREN ≥ 40, the threshold for super duplex behaviour, with the 50/50 austenite-ferrite microstructure carrying ~2× the yield of 316L while resisting chloride pitting at CPT ≥ 50°C per ASTM G48 Method E.
PREN ≥ 40 · Yield ≥ 550 MPa · Hardness ≤ 28 HRC · ANSI B1.1 / ISO 261 thread tolerance
Where they earn their keep: short-grip flange and equipment fasteners where a stud bolt is overkill but stainless or duplex 2205 isn't strong / corrosion-resistant enough, pump bonnet bolts, valve body bolts, equipment frame fasteners on offshore topsides, ROV interface bolts, FGD scrubber duct fasteners, desalination membrane vessel exterior bolts, marine-piping clamp bolts. We supply SA, FG, FLT, and AFP supply states from the same heat tree as our stud bolts, one alloy, one MTC family, no galvanic mismatch when hex bolts and studs share a flange.
| Supply State | What it means | Yield (MPa, min) | Hardness (HRC, max) | Use case |
|---|---|---|---|---|
| SA | Solution Annealed (1100-1140°C, water quench) | 550 | 28 | Standard ASTM A479 hex bolts; default for most super duplex applications |
| FG | Fastener Grade (cold-worked) | 650 | 28 | NORSOK M-650 QTR'd, API 6A PSL3, sour-service where SA yield is insufficient |
| FLT | Fasteners for Low Temperature (ASTM A320 L7-equivalent) | 550 | 28 | LNG, FPSO arctic, ROV / subsea service at ≤ -46°C |
| Series | Diameter | Thread pitch | Length | Head spec |
|---|---|---|---|---|
| UNC (coarse) | 1/4 to 4 inch | 20 to 4 TPI | 1/2 to 24 inch | ASME B18.2.1 hex head |
| UNF (fine) | 1/4 to 1-1/2 inch | 28 to 12 TPI | 1/2 to 18 inch | ASME B18.2.1 hex head |
| 8UN (heavy) | 1 to 4 inch | 8 TPI | 2 to 24 inch | ASME B18.2.1 heavy hex |
| Metric coarse | M6 to M100 | 1.0 to 6.0 mm | 15 to 600 mm | ISO 4014 / 4017 / DIN 933 / 931 |
| Metric fine | M8 to M64 | 1.0 to 4.0 mm | 20 to 400 mm | ISO 8765 / 8676 / DIN 960 / 961 |
| Standard | Covers | Why it matters |
|---|---|---|
| ASTM A479 | Stainless steel bars and shapes | Source bar spec; mechanical envelope, ferrite content, intergranular-corrosion test |
| ASTM A276 | Stainless bars and shapes (alt source) | Used in some cold-finished bar specs for hex stock |
| ASTM A1082 | Stainless stud, bolt, screw, threaded rod | Fastener-spec home for super duplex hex bolts |
| ASME B18.2.1 | Square and hex bolts and screws (inch) | Hex-head dimensions, across-flats, thread length, bearing surface |
| ISO 4014 / 4017 / DIN 931 / 933 | Hex bolts (metric) | Metric hex bolt patterns, partial thread (4014/931) vs full thread (4017/933) |
| ASME B1.1 / ISO 965 | Thread tolerance class 2A / 6g | Loose-fit thread to prevent galling on duplex-on-duplex contact |
| NACE MR0175 / ISO 15156-3 | Sour-service hardness limit | Rolled-thread hardness ≤ 28 HRC required for H2S service |
| NORSOK M-650 + M-630 MDS 055 | Super duplex acceptance | QTR'd manufacturer for North Sea topside fasteners |
| API 6A PSL 3 / 3G | Wellhead and Christmas tree | Material qualification + impact test for upstream service |
| EN 10269 | Steels and Ni alloys for fasteners | European pressure equipment (PED 2014/68/EC) |
| Property | SA (typical) | FG (typical) | FLT (typical) | Test method |
|---|---|---|---|---|
| 0.2% Yield | 620-720 MPa | 700-800 MPa | 620-720 MPa | ASTM A370 |
| UTS | 800-870 MPa | 870-940 MPa | 800-870 MPa | ASTM A370 |
| Elongation | 30-38 % | 25-32 % | 30-38 % | ASTM A370 |
| Hardness (body) | 22-27 HRC | 24-28 HRC | 22-27 HRC | ASTM E18 |
| Hardness (rolled-thread root) | 25-28 HRC | 26-28 HRC | 25-28 HRC | HV converted per E140 |
| Charpy V-notch @ -46°C | 60-110 J | 50-90 J | 80-130 J | ASTM E23 |
| Ferrite | 40-52 % | 40-52 % | 40-52 % | ASTM E562 |
| CPT | ≥ 50°C | ≥ 50°C | ≥ 50°C | ASTM G48 Method E |
| Service | Recommended supply state | Why |
|---|---|---|
| Pump bonnet / casing fasteners (seawater service) | SA | PREN ≥ 40 + Cu-W reducing-acid resistance |
| Valve body / bonnet bolts (sour-service NACE) | FG (NACE-controlled) | Cold-work uplift while staying ≤ 28 HRC |
| FPSO topside equipment frame bolts (NORSOK) | FG | QTR'd manufacturer, A1082 stress envelope |
| Subsea ROV interface bolts | FLT | Charpy at -46°C exceeds 45 J for cold-water service |
| LNG cryogenic equipment fasteners | FLT | L7-equivalent low-temp toughness without using carbon steel |
| Desalination membrane vessel exterior bolts | SA | Seawater + brine + chloride mist; PREN ≥ 40 + 0.7Cu |
| FGD scrubber duct & chimney bolts | SA or AFP-coated | Wet-flue-gas chloride + sulfate; AFP for periodic disassembly |
| Repeated-makeup high-torque fasteners | AFP (Xylan / SermaGard / Dacromet) | Coating drops μ from ~0.30 to ~0.10, predictable torque-to-tension |
| Pulp & paper bleach plant equipment | SA | ClO2 + chlorine + chloride at process temp |
EN 10204 type 3.1 (in-house QC) or 3.2 (third-party witnessed by TUV / BV / DNV / Lloyd's / ABS) per buyer spec. Heat-traceable end-to-end, mill heat number flows through bar receipt, heading, threading, NDT, and packing. PMI on 100% of finished bolts against a calibrated S32760 master. Cert stack: chemistry + mechanical + Charpy + ferrite + G48 Method E + A923 sigma-phase + PMI + NDT + dimensional + MR0175 hardness + NORSOK M-650 QTR reference where applicable.
Hex bolt (ASME B18.2.1) is the general-purpose pattern with a flat-washer-face under the head. Hex cap screw (also B18.2.1) is the same dimensional family but tighter tolerance class, specify it when the joint relies on a precision bearing-face fit. Heavy hex bolt (B18.2.1 heavy series) is wider across-flats and thicker under the head, used when you'd otherwise use a stud-and-nut combination but the joint geometry forces a single-bolt solution, common on flange clamps and high-torque structural connections.
In service envelope, no, B7 is AISI 4140 alloy steel, Zeron 100 is super duplex stainless. They overlap on tensile strength (FG Zeron 100 hits A193 B7 territory) but diverge completely on corrosion. Use B7 / B7M for clean dry service inside conditioned process buildings; use Zeron 100 wherever seawater, chlorides, sour service, or dilute reducing acids are present.
Super duplex galls when interference-fit threads are torqued under high load. Class 2A (inch) and 6g (metric) provide enough thread clearance to prevent metal-to-metal lockup. For high-cycle repeated-makeup applications go AFP supply state, the coating reduces friction coefficient from ~0.30 to ~0.10, makes torque-to-tension predictable, and prevents the gall-and-tear that happens when uncoated duplex threads are repeatedly assembled.
Yes, that's where they outperform standard duplex (S31803 / 2205). PREN ≥ 40 + the 0.7% W contribution + the 0.7% Cu addition give CPT ≥ 50°C and CCT ≥ 35°C per ASTM G48 Methods E and F. Field experience: zeron 100 castings have served continuously in North Sea seawater since 1986; wrought hex bolts and pipework since 1989, nearly 4 decades of validated immersion performance.
Stock sizes ship in 5-7 working days with 3.1 MTC, 10-14 days with witnessed 3.2 MTC. NORSOK M-650 QTR'd lots take 14-21 days because of third-party witness scheduling. AFP coating adds 5-7 days post-thread-rolling. Specials cut from solution-annealed bar within 5 working days from RFQ approval.
Send the spec (size + length + thread + supply state + standards / MDS to comply with + coating if any + quantity + destination port) to info@torqbolt.com or +91-22-66157017 / WhatsApp. We reply with stock availability, mill route, lead time, MTC tier, and price within one business day (Mumbai IST).
