COMPREHENSIVE TECHNICAL ANALYSIS AND DATASHEET OF ASTM A194 GRADE 4 NUTS
ASTM A194 Grade 4 specifies high-strength, quenched and tempered carbon-molybdenum steel nuts engineered for severe high-temperature and high-pressure environments. While it shares a similar base hardness and proof load profile with Grade 2H, the critical addition of molybdenum transforms its metallurgical capabilities, significantly enhancing its creep resistance and high-temperature tensile retention.
This precisely alloyed material is designed to prevent structural relaxation (creep) under sustained massive clamping loads at elevated temperatures. Grade 4 nuts are the premier fastening solution for steam piping, power generation turbines, and advanced petrochemical processing where standard carbon steels would degrade or deform over time.
■ Product Overview & Specifications
ASTM A194 Grade 4 bridges the gap between standard carbon steels and highly alloyed stainless grades, offering superior thermal stability for critical upstream and downstream infrastructure.
| Material Classification | Quenched and Tempered Carbon-Molybdenum Steel Heavy Hex Nuts |
|---|---|
| UNS Designation | K11547 (Typical) |
| Microstructure | Tempered Martensite |
| Magnetic State | Magnetic |
| Density | ~7.85 g/cm³ (0.284 lb/in³) |
| Size Range | Metric: M6 to M100 | Imperial: 1/4" to 4" Custom oversized nuts available upon request. |
| Thread Types | UNC, UNF, 8UN, Metric Coarse, Metric Fine |
| Strengthening Method | Quenching & Tempering (Heat Treatment) |
■ Proprietary Datasheet Download (GATED)
Access professional-grade technical data for ASTM A194 Grade 4, including elevated-temperature creep thresholds, hardness parameters, and mating bolt torque charts.
ASTM A194 Grade 4 — Complete Technical Datasheet
Contains detailed proof load thresholds up to 175 ksi, dimensional tolerances for ASME B18.2.2 heavy hex profiles, and specific dry and lubricated installation torque values for high-temperature B16/Gr4 assemblies.
⬇ DOWNLOAD DATASHEET■ MTC Integration Section
Material traceability is the backbone of safety in severe-service thermal systems. Every lot shipped by Ananka is accompanied by fully authenticated documentation mapping back to raw steel mill certificates.
- EN 10204 Type 3.1: Issued by our independent quality department, providing specific heat-traceable test results (actual chemical analysis, mechanical test results, hardness, and proof load).
- EN 10204 Type 3.2: For critical infrastructure or "lethal service" applications, we facilitate third-party witness testing (e.g., TUV, BV, or SGS) to provide the highest level of material assurance.
■ Chemical Composition
Grade 4 incorporates Molybdenum (Mo) into the medium-carbon matrix. This single alloying element fundamentally alters the steel's behavior at elevated temperatures, pinning the grain boundaries to prevent creep deformation.
| Carbon (C) | Manganese (Mn) | Phosphorus (P) | Sulfur (S) | Silicon (Si) | Molybdenum (Mo) |
|---|---|---|---|---|---|
| 0.40 – 0.50 | 0.70 – 0.90 | 0.040 Max | 0.050 Max | 0.15 – 0.35 | 0.20 – 0.30 |
■ Mechanical Properties
Grade 4 is tested to the same demanding proof load stress as Grade 2H at room temperature, ensuring it handles extreme tensile loading without stripping.
| Mechanical Property | Up to 1-1/2" Diameter | Over 1-1/2" Diameter |
|---|---|---|
| Proof Load Stress (Heavy Hex) | 175 ksi (1205 MPa) | 150 ksi (1034 MPa) |
| Proof Load Stress (Standard Hex) | 150 ksi (1034 MPa) | 120 ksi (827 MPa) |
| Hardness (Rockwell C) | 24 to 35 HRC | 24 to 35 HRC |
| Hardness (Brinell) | 248 to 327 HBW | 248 to 327 HBW |
■ Equivalent Grades & Designations
| Standard / System | Designation |
|---|---|
| ASME Standard | SA194 Grade 4 |
| Common Trade Name | A194 Gr. 4 Carbon-Moly Nuts |
| European Equivalent | EN 10269 (Approximate Material Match for Cr-Mo Steels) |
■ Applications & Industries
Grade 4 nuts are specified when the operating temperature begins to exceed the safe limits of standard carbon steel (like Grade 2H), but does not yet require the extreme expense of austenitic stainless steels.
- Power Generation: Bolting for high-pressure steam lines, boiler feed pumps, and turbine housings.
- Petrochemical Processing: Catalytic cracking units, high-temperature distillation columns, and flare system flanges.
- Oil & Gas Exploration: High-temperature, high-pressure (HTHP) wellhead equipment.
- Industrial Furnaces: Structural bolting for heat treatment facilities and incinerator exhaust manifolds.
■ Compatible Fastener Assemblies
To maximize thermal performance, Grade 4 nuts are engineered to be paired with highly alloyed, high-temperature studs.
| Nuts (A194 Gr 4) | Mating High-Temp Bolts | Mating High-Temp Studs |
|---|---|---|
| Heavy Hex Nuts | ASTM A193 Grade B16 Bolts | ASTM A193 Grade B16 Studs (Cr-Mo-V) |
| Standard Hex / Jam Nuts | ASTM A193 Grade B7 Bolts | ASTM A193 Grade B7 Studs (Cr-Mo) |
■ Standards & Specifications
Manufactured to meet the most stringent international dimensional and material codes.
- ASTM A194 / ASME SA194: Standard Specification for Carbon and Alloy Steel Nuts for Bolts for High Pressure or High Temperature Service.
- ASME B18.2.2: Dimensional standard for Square and Hex Nuts (specifically Heavy Hex profiles).
- ASME B1.1: Unified Inch Screw Threads (UNC, UNF, 8UN).
- ASME B1.13M: Metric Screw Threads (M Profile).
■ Torque & Installation Guidelines (Typical B16 / Gr 4 Pairing)
The following torque values are approximate for A193 B16 studs mated with A194 Grade 4 heavy hex nuts. High-temperature anti-seize lubrication (often nickel or copper-based) is vital to prevent galling at extreme temperatures.
| Nominal Diameter | Threads Per Inch (UNC) | Target Torque — Dry (ft-lbs) | Target Torque — Lubricated (ft-lbs) |
|---|---|---|---|
| 1/2" | 13 | 90 | 65 |
| 5/8" | 11 | 180 | 130 |
| 3/4" | 10 | 320 | 230 |
| 1" | 8 | 770 | 550 |
■ Why Choose Ananka Group?
Ananka Group is a leading manufacturing-driven organization specializing in high-performance, thermally stable bolting packages for the global energy and infrastructure sectors.
- In-House Manufacturing: Complete production control from raw material selection and hot forging through to precision thread tapping and CNC machining.
- 100% Traceability: Heat numbers are stamped directly on the nuts (alongside the '4' mark) for absolute supply chain transparency.
- Custom Surface Coatings: Supplied plain, hot-dip galvanized (HDG), zinc-plated, or PTFE/Xylan coated based on specific environmental and offshore project needs.
- Certifications: ISO 9001:2015, ISO 14001:2015, and strict adherence to ASME and PED 2014/68/EU quality protocols.
■ Frequently Asked Questions
1. What is the main difference between Grade 2H and Grade 4?
While both share similar strength and hardness at room temperature, Grade 4 contains Molybdenum (Mo). This addition significantly improves the nut's resistance to creep (slow deformation under stress) at high temperatures, making it vastly superior to 2H in severe steam and thermal applications.
2. What bolts or studs are typically paired with Grade 4 nuts?
A194 Grade 4 nuts are primarily engineered to be mated with ASTM A193 Grade B16 studs (Chromium-Molybdenum-Vanadium), which are designed for identical high-temperature service. They can also be paired with ASTM A193 Grade B7.
3. What is the maximum operating temperature for Grade 4 nuts?
Due to the molybdenum alloying, Grade 4 nuts can reliably perform in environments up to approximately 482°C to 510°C (900°F to 950°F), outperforming standard Grade 2H nuts.
4. How do I identify an ASTM A194 Grade 4 nut?
Genuine Grade 4 nuts will have the manufacturer's identification mark stamped on the face, alongside the number "4" to denote the specific ASTM grade.
For project-specific technical support or to request a quote for ASTM A194 Grade 4 fasteners, please contact the Ananka Group Sales and Engineering Team at sales@anankafasteners.com or via WhatsApp at +91 86557 47687. Secure your high-pressure systems with certified components and world-class manufacturing expertise.