COMPREHENSIVE TECHNICAL ANALYSIS AND DATASHEET OF ASTM A194 GRADE 43 NUTS
ASTM A194 Grade 43 specifies premium high-strength, low-alloy steel nuts, manufactured from AISI 4340 Nickel-Chromium-Molybdenum steel. Unlike the austenitic stainless grades (such as Grade 8), Grade 43 is engineered specifically for ultra-high tensile strength and deep hardenability in severe-duty industrial applications.
To achieve its superior mechanical profile, Grade 43 undergoes a rigorous Hardening and Tempering (Quench and Temper) heat treatment process. ASTM strictly mandates a minimum tempering temperature of 595°C to ensure the martensitic microstructure is properly stress-relieved, providing an optimal balance of immense yield strength, ductility, and fatigue resistance for high-pressure piping and heavy machinery.
■ Product Overview & Specifications
| Material Classification | High-Strength Low-Alloy Steel (AISI 4340) |
|---|---|
| UNS Designation | G43400 |
| Microstructure | Tempered Martensite |
| Magnetic State | Strongly Magnetic |
| Density | ~7.85 g/cm³ (0.284 lb/in³) |
| Size Range | Metric: M6 to M100 | Imperial: 1/4" to 4" |
| Strengthening Method | Quenched and Tempered (Hardening & Tempering) |
■ Proprietary Datasheet Download (GATED)
ASTM A194 Grade 43 — Complete Technical Datasheet
Contains detailed proof load thresholds, dimensional tolerances for ASME B18.2.2 standard and heavy hex profiles, and precise thread engagement depths.
⬇ DOWNLOAD DATASHEET■ MTC Integration Section
Material traceability is the backbone of safety in high-pressure environments. 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, heat-treatment logs, and proof load tests).
- EN 10204 Type 3.2: For critical commercial, offshore, or chemical applications, we facilitate third-party witness testing.
■ Chemical Composition
Grade 43 relies on a potent blend of Nickel, Chromium, and Molybdenum. Nickel drastically improves the toughness and fatigue strength, Chromium increases the depth of hardness during quenching, and Molybdenum prevents "temper embrittlement" while allowing the steel to maintain strength at elevated temperatures.
| Carbon (C) | Manganese (Mn) | Phosphorus (P) | Sulfur (S) | Silicon (Si) | Chromium (Cr) | Molybdenum (Mo) | Nickel (Ni) |
|---|---|---|---|---|---|---|---|
| 0.38 – 0.43 | 0.60 – 0.85 | 0.035 Max | 0.040 Max | 0.15 – 0.35 | 0.70 – 0.90 | 0.20 – 0.30 | 1.65 – 2.00 |
■ Mechanical Properties
The mechanical integrity of Grade 43 is heavily dependent on precise thermal processing. The material is quenched to harden it, and then tempered at a minimum of 595°C to restore essential ductility.
| Mechanical Property | Grade 43 Limits |
|---|---|
| Hardness Limit (Rockwell) | 24 - 35 HRC |
| Minimum Tempering Temperature | 595 °C |
| Proof Load | Dependent on Size |
■ Equivalent Grades & Designations
| Standard / System | Designation |
|---|---|
| ASME Standard | SA194 Grade 43 |
| Common Trade Name | AISI 4340 Alloy Steel Nuts, High-Tensile Ni-Cr-Mo Nuts |
| European Equivalent | EN 1.6565 / 40NiCrMo6 |
■ Applications & Industries
- Oil & Gas Exploration: High-pressure blowout preventers (BOPs), wellhead assemblies, and heavy-duty drilling equipment subjected to immense cyclical fatigue.
- Heavy Machinery & Mining: Structural bolting for earth-moving equipment, rock crushers, and hydraulic press frames requiring extreme shear and tensile strength.
- Power Generation & Turbines: High-temperature, high-pressure steam line flanges where stainless steel lacks the required yield strength.
■ Compatible Fastener Assemblies
Grade 43 nuts are specifically designed to mate with ultra-high-strength alloy bolting to maintain joint integrity under massive load.
| Internal Threads (A194 Gr 43) | Typical Mating Bolts | Typical Mating Studs |
|---|---|---|
| Grade 43 Heavy Hex Nuts | ASTM A193 Grade B7 / B16 Hex Bolts | ASTM A193 Grade B7 / B16 Studs |
■ Frequently Asked Questions
1. Is Grade 43 stainless steel?
No. Grade 43 is a high-strength, low-alloy steel (AISI 4340). It will rust if exposed to the atmosphere or corrosive chemicals. If corrosion resistance is required alongside high strength, the nuts must be coated (e.g., PTFE/Xylan, Zinc Plating, or Cadmium) or an equivalent high-strength stainless/alloy grade should be selected.
2. What is the significance of the 595°C Minimum Tempering Temperature?
When alloy steel is quenched, it becomes extremely hard but very brittle. Tempering reheats the steel to soften it slightly and restore toughness. The ASTM mandates a minimum of 595°C to ensure the nut has enough ductility to stretch slightly under load (elastic deformation) rather than shattering like glass under extreme pressure.
3. Can Grade 43 nuts be welded?
Welding AISI 4340 (Grade 43) is highly complex and generally discouraged for fasteners. Because it is a high-carbon, deep-hardening alloy, the heat from welding will destroy the carefully controlled quench-and-temper microstructure, leading to severe cracking and catastrophic loss of strength unless extreme pre-heating and post-weld heat treatments are applied.