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FULLERKREG DIN 933 / GB 5783 Grade 12.9 full thread hex bolts are manufactured from ML40Cr alloy steel — a chromium-molybdenum alloyed medium carbon steel specifically engineered for ultra-high tensile fastener applications. With a minimum tensile strength of 1220 MPa (177,000 psi) and proof load of 1100 MPa, these are among the strongest standard hex bolts available, finished with a black oxide (blackening) surface treatment for corrosion inhibition and a distinctive matte black appearance. The fully threaded shank ensures maximum thread engagement and grip-length flexibility across all demanding applications. Compliant with DIN 933, GB 5783, and ISO 4017 standards.
| Property | Grade 8.8 | Grade 10.9 | Grade 12.9 — This Product |
|---|---|---|---|
| Tensile Strength (Rm) min. | 800 MPa | 1040 MPa | 1220 MPa ✅ |
| Proof Load (Sp) min. | 600 MPa | 830 MPa | 1100 MPa ✅ |
| Yield Strength (Rp0.2) min. | 640 MPa | 940 MPa | 1100 MPa ✅ |
| Elongation (A) min. | 12% | 9% | 8% |
| Hardness (HRC) | 22–32 | 32–39 | 39–44 ✅ |
| Hardness (HV) | 250–320 | 320–380 | 380–435 ✅ |
| Typical Material | Medium carbon steel | Alloy steel (quenched & tempered) | ML40Cr alloy steel (Q&T) ✅ |
| Strength vs. 8.8 | Baseline | +30% | +53% ✅ |
| Property | Details |
|---|---|
| Process | Hot alkaline blackening (chemical conversion coating) |
| Appearance | Matte black / satin black finish |
| Layer Thickness | 0.5–1.5 μm (negligible dimensional impact) |
| Corrosion Protection | Mild — suitable for indoor and dry environments; oil or wax post-treatment recommended for enhanced protection |
| Salt Spray Resistance | ~2–4 hours (bare); significantly improved with oil post-treatment |
| Light Reflection | Reduced — non-reflective matte surface |
| Dimensional Impact | Negligible — no significant change to thread tolerances |
| RoHS / REACH | Compliant — no hazardous substances |
| Hydrogen Embrittlement Risk | Lower than electroplating processes — important for Grade 12.9 high-strength bolts |
⚠️ Important: Black oxide provides only mild corrosion protection. For outdoor, wet, or corrosive environments, apply a compatible oil, wax, or additional protective coating after installation. For corrosive environments, consider zinc-plated or stainless steel alternatives.
| Property | Grade 12.9 Value |
|---|---|
| Property Class | 12.9 (per ISO 898-1 / DIN EN ISO 898-1) |
| Tensile Strength (Rm) min. | 1220 MPa (177,000 psi) |
| Proof Load Stress (Sp) min. | 1100 MPa |
| Yield Strength (Rp0.2) min. | 1100 MPa (90% of Rm) |
| Elongation (A) min. | 8% |
| Reduction of Area (Z) min. | 44% |
| Hardness min. | 39 HRC / 380 HV |
| Hardness max. | 44 HRC / 435 HV |
| Head Hardness max. | 44 HRC / 435 HV |
| Heat Treatment | Quenched & Tempered (Q&T) |
| Property | Value |
|---|---|
| Material Designation | ML40Cr (GB/T 6478 — Cold Heading Quality Alloy Steel) |
| Equivalent Grades | 40Cr (GB) / SCr440 (JIS) / 5140 (SAE/AISI) / 41Cr4 (DIN) |
| Carbon Content (C) | 0.37–0.44% |
| Chromium (Cr) | 0.80–1.10% |
| Manganese (Mn) | 0.50–0.80% |
| Silicon (Si) | 0.17–0.37% |
| Phosphorus (P) | ≤ 0.025% |
| Sulfur (S) | ≤ 0.025% |
| Density | 7.85 g/cm³ |
| Elastic Modulus | ~206 GPa |
| Hardenability | Good — Cr addition significantly improves through-hardening |
| Element | C (%) | Si (%) | Mn (%) | Cr (%) | P (%) | S (%) | Ni (%) | Cu (%) |
|---|---|---|---|---|---|---|---|---|
| ML40Cr | 0.37–0.44 | 0.17–0.37 | 0.50–0.80 | 0.80–1.10 | ≤ 0.025 | ≤ 0.025 | ≤ 0.30 | ≤ 0.25 |
| Standard | Region | Description |
|---|---|---|
| DIN 933 | Germany / Europe | Hexagon head bolts — full thread (metric) |
| ISO 4017 | International | Hexagon head screws — full thread, product grades A and B |
| GB 5783 | China | Hexagon head bolts — full thread (equivalent to DIN 933) |
| ISO 898-1 | International | Mechanical properties of fasteners — Grade 12.9 definition |
| GB/T 6478 | China | Cold heading quality steel — ML40Cr material specification |
| ISO 261 / DIN 13 | International | Metric coarse thread specification |
All dimensions in millimeters (mm). Data per DIN 933 / ISO 4017 standard.
| Thread (d) | Pitch (mm) | s — A/F (mm) | e — A/C (mm) | k — Head Height (mm) | d_w min (mm) | Length Range (mm) |
|---|---|---|---|---|---|---|
| M6 | 1.0 | 10 | 11.05 | 4.0 | 8.9 | 10 – 80 |
| M8 | 1.25 | 13 | 14.38 | 5.3 | 11.6 | 16 – 100 |
| M10 | 1.5 | 17 | 18.90 | 6.4 | 14.6 | 20 – 120 |
| M12 | 1.75 | 19 | 21.10 | 7.5 | 16.6 | 25 – 150 |
| M14 | 2.0 | 22 | 24.49 | 8.8 | 19.6 | 30 – 150 |
| M16 | 2.0 | 24 | 26.75 | 10.0 | 22.5 | 35 – 200 |
| M20 | 2.5 | 30 | 33.53 | 12.5 | 27.7 | 45 – 200 |
| M24 | 3.0 | 36 | 39.98 | 15.0 | 33.3 | 50 – 200 |
| M30 | 3.5 | 46 | 50.85 | 18.7 | 42.8 | 60 – 200 |
| M36 | 4.0 | 55 | 60.79 | 22.5 | 51.1 | 70 – 200 |
* Custom sizes and lengths available on request. Contact FULLERKREG for non-standard requirements.
Recommended tightening torques at 75% proof load for Grade 12.9 hex bolts:
| Thread | Torque (N·m) | Clamp Force (kN) |
|---|---|---|
| M6 | 14 | 18.5 |
| M8 | 34 | 35.5 |
| M10 | 68 | 57.5 |
| M12 | 117 | 83.5 |
| M14 | 185 | 114.0 |
| M16 | 290 | 151.0 |
| M20 | 570 | 236.0 |
| M24 | 985 | 340.0 |
| M30 | 1960 | 535.0 |
| M36 | 3400 | 775.0 |
* Torque values are for reference only. Actual requirements depend on friction coefficient, lubrication, joint material, and application. Always consult a qualified engineer for safety-critical applications. Grade 12.9 bolts are susceptible to hydrogen embrittlement — never use with cadmium plating or in hydrogen-rich environments without engineering review.
FULLERKREG DIN 933 Grade 12.9 Black Oxide Full Thread Hex Bolts — actual product photos:
| [Product Photo 1] | [Product Photo 2] | [Product Photo 3] | [Product Photo 4] |
Q: What does Grade 12.9 mean?
A: Grade 12.9 is a property class designation per ISO 898-1. The first number (12) indicates 1/100 of the nominal tensile strength in MPa — so 12 × 100 = 1200 MPa nominal tensile strength. The second number (9) indicates 90% of the tensile strength as the yield strength ratio — so yield strength = 1200 × 0.9 = 1080 MPa nominal. Minimum tensile strength is 1220 MPa.
Q: What is ML40Cr steel and why is it used for Grade 12.9 bolts?
A: ML40Cr is a cold-heading quality (CHQ) chromium-alloyed medium carbon steel per GB/T 6478. The “ML” prefix denotes cold heading quality with tighter chemical composition controls for consistent cold forming. The chromium addition (0.80–1.10%) significantly improves hardenability, allowing through-hardening of larger diameter bolts to achieve uniform Grade 12.9 mechanical properties after quench and temper heat treatment.
Q: What is black oxide and does it provide good corrosion protection?
A: Black oxide (blackening) is a chemical conversion coating that creates a thin (0.5–1.5 μm) magnetite (Fe₃O₄) layer on the steel surface. It provides mild corrosion inhibition and reduces light reflection. For enhanced corrosion protection, apply oil or wax after installation. Black oxide is preferred over electroplating for Grade 12.9 bolts because it eliminates the risk of hydrogen embrittlement associated with electroplating processes.
Q: Why is hydrogen embrittlement a concern for Grade 12.9 bolts?
A: High-strength steels (above ~1000 MPa) are susceptible to hydrogen embrittlement — a phenomenon where absorbed hydrogen causes sudden brittle fracture under stress. Electroplating processes (zinc, cadmium) introduce hydrogen into the steel. Black oxide avoids this risk, making it the preferred surface treatment for Grade 12.9 and other ultra-high-strength fasteners.
Q: Can Grade 12.9 bolts be reused?
A: Grade 12.9 bolts tightened to proof load or yield-point tightening should generally not be reused, as they may have experienced permanent deformation. For torque-controlled tightening below proof load, reuse may be acceptable — consult the joint design engineer for specific guidance.
Q: What nuts are compatible with Grade 12.9 bolts?
A: Use ISO 4032 / DIN 934 Grade 10 or Grade 12 hex nuts to match the strength of Grade 12.9 bolts. Using lower-grade nuts risks thread stripping before the bolt reaches its proof load. FULLERKREG supplies the complete range of compatible high-strength nuts and washers.
Q: Can I get material test reports (MTR)?
A: Yes. FULLERKREG provides material test reports and ISO 898-1 Grade 12.9 compliance certificates upon request for wholesale and OEM orders.
FULLERKREG — Precision Fasteners to ISO/DIN/GB Standards. All technical data is provided for reference. Grade 12.9 bolts must be installed by qualified personnel using calibrated torque equipment. Always verify fastener selection, torque requirements, and hydrogen embrittlement risk with a qualified engineer for structural and safety-critical applications.
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