Product Overview This product is a high-strength Dacromet-coated bolt manufactured from high-strength carbon steel or alloy steel, available in Grade 8.8, 10.9, and 12.9 strength classes. The bolts feature a Dacromet (zinc-aluminum flake) coating — a non-electrolytic, water-based inorganic coating that provides exceptional corrosion resistance without any risk of hydrogen embrittlement. This makes Dacromet the preferred surface treatment for high-strength fasteners where conventional electroplating would compromise structural integrity. The product line includes hex head bolts (DIN 931 / DIN 933), flange bolts (DIN 6921), socket head cap screws (DIN 912), and threaded rods / stud bolts, with thread sizes ranging from M6 to M36 (M42–M64 available on request) and lengths from 10 mm to 500 mm. Dacromet-coated bolts are widely specified in construction, rail transit, automotive, solar energy, wind power, marine, and petrochemical applications across the Middle East and Central Asia. Material & Strength Grades Grade Material Tensile Strength (min.) Yield Strength (min.) Hardness Typical Applications 8.8 Medium carbon steel (45#, 10B21) ≥800 MPa ≥640 MPa 250–320 HB General structural, machinery, solar mounting 10.9 Alloy steel (35CrMo, 40Cr, SCM435) ≥1,040 MPa ≥940 MPa 320–380 HV Heavy machinery, automotive, wind turbine 12.9 Alloy steel (42CrMo, SCM435) ≥1,220 MPa ≥1,100 MPa 385–435 HV Critical high-strength applications, engine fasteners Grade 8.8 bolts achieve a minimum tensile strength of 800 MPa and yield strength of 640 MPa, with the "8" representing approximately 1/100 of the minimum tensile strength in MPa and the ".8" indicating a yield-to-tensile ratio of 0.8. Grade 10.9 bolts provide 1,040 MPa minimum tensile strength and 940 MPa minimum yield strength, with surface hardness typically ranging from 320 to 380 HV. Grade 12.9 bolts achieve 1,220 MPa minimum tensile strength and 1,100 MPa minimum yield strength, with hardness of 385–435 HV. Material composition: Grade 8.8 bolts are typically manufactured from medium carbon steel (45#, 10B21) with quenching and tempering. Grade 10.9 and 12.9 bolts require alloy steel (35CrMo, 40Cr, 42CrMo, SCM435) with controlled heat treatment to achieve the specified mechanical properties while maintaining adequate toughness. Dacromet Coating Technology Dacromet (also known as zinc-chromium coating or zinc-aluminum flake coating) is a non-electrolytic, water-based inorganic coating consisting of overlapping zinc and aluminum flakes in an inorganic binder matrix. The coating is applied by dip-spin, spray, or dip-drain methods and thermally cured at approximately 300–320°C, forming a dense, multi-layered lamellar structure that provides both barrier protection and sacrificial (cathodic) protection of the steel substrate. Key technical specifications: Parameter Specification Coating Thickness 5–12 μm (Grade A: 5–8 μm; Grade B: 8–12 μm) Coating Weight Grade A: ≥24 g/m²; Grade B: ≥36 g/m² Salt Spray Resistance Grade A: ≥600 h without red rust; Grade B: ≥1,000 h without red rust Maximum Operating Temperature 250–300°C (continuous) Coefficient of Friction 0.10–0.15 (with lubricated topcoat: 0.06–0.19) Appearance Metallic silver-gray, uniform matte finish Hydrogen Embrittlement Risk None — non-electrolytic process, no acid pickling Dacromet achieves ≥1,000–1,500 hours of salt spray resistance (ASTM B117 / ISO 9227) before the appearance of red rust — approximately 7 to 10 times the performance of standard electro-galvanizing of comparable thickness. Even the Grade A specification provides ≥600 hours without red rust, significantly outperforming conventional zinc plating (typically 72–144 hours). No hydrogen embrittlement: The Dacromet process uses shot blasting only for surface preparation — acid pickling is deliberately avoided — and no electric current is passed through the component during coating application. This eliminates the hydrogen absorption that causes delayed brittle fracture in high-strength fasteners (Grade 10.9 and above). This is the critical safety advantage of Dacromet over electroplating for high-strength bolts. Thread fit preservation: The ultra-thin coating (5–12 μm) preserves thread geometry and ensures proper mating with standard nuts. Unlike hot-dip galvanizing (45–85 μm), no post-coating thread re-tapping is required, and torque-tension relationships remain consistent and predictable. Dacromet vs. Other Coatings — Performance Comparison Property Dacromet Electro-Galvanizing Hot-Dip Galvanizing Coating Thickness 5–12 μm 5–15 μm 45–85 μm Salt Spray (to red rust) ≥1,000–1,500 h 100–300 h 500–800 h Hydrogen Embrittlement None High risk Moderate risk Max. Service Temperature ~300°C ~100–150°C ~200–250°C Thread Fit Impact Minimal Low Significant (re-tapping needed) Corrosion Protection 7–10× better than electro-galvanizing Baseline 3–5× better than electro-galvanizing Dacromet outperforms hot-dip galvanizing by 2–3× in neutral salt spray tests, making it ideal for marine and high-humidity environments. While hot-dip galvanizing provides a thicker zinc layer for mechanical protection in structural applications, Dacromet is superior for precision fasteners and safety-critical high-strength bolts where thread tolerance and hydrogen embrittlement resistance are paramount. Standards & Specifications Parameter Details Product Type Hex Head Bolt / Flange Bolt / Socket Head Cap Screw / Threaded Rod Standard DIN 931 (partial thread) / DIN 933 (full thread) / DIN 6921 (flange) / DIN 912 (socket) / ISO 4014 / ISO 4017 / ASME B18.2.1 Thread Size M6, M8, M10, M12, M16, M20, M24, M30, M36 (M42–M64 on request) Thread Pitch M6×1.0, M8×1.25, M10×1.5, M12×1.75, M16×2.0, M20×2.5, M24×3.0, M30×3.5 Length Range 10 mm – 500 mm (customizable) Thread Tolerance 6g (metric) / Class 2A (imperial) Material Carbon steel: Q235, 45#, 10B21; Alloy steel: 35CrMo, 40Cr, 42CrMo, SCM435 Surface Finish Dacromet (standard); HDG, zinc plated, black oxide, Geomet available DIN 931 specifies partially threaded hexagon head bolts with a plain shank, while DIN 933 specifies fully threaded hexagon head bolts. Both standards cover metric coarse threads from M6 to M36 in product grades A and B. DIN 6921 covers hexagon flange bolts with an integrated flange under the head that distributes clamping load more evenly and eliminates the need for a separate washer. Mechanical Properties (Reference) Size Grade Tensile Strength (MPa) Yield Strength (MPa) Hardness M10 8.8 800 640 250–320 HB M12 8.8 800 640 250–320 HB M16 8.8 800 640 250–320 HB M16 10.9 1,040 940 320–380 HV M20 10.9 1,040 940 320–380 HV M24 10.9 1,040 940 320–380 HV M24 12.9 1,220 1,100 385–435 HV M30 12.9 1,220 1,100 385–435 HV Grade 10.9 bolts exhibit a yield-to-tensile ratio of approximately 0.90, while Grade 12.9 bolts achieve approximately 0.90 with significantly higher absolute strength values. The mean yield strength of 12.9 steel is approximately 17% higher than 10.9 steel, with the ultimate strength increasing by approximately 16%. Applications Dacromet-coated high-strength bolts are widely used across industries: Construction & Infrastructure — Structural steel connections, column base anchoring, bridge fasteners, precast concrete Rail Transit — Track fastening systems, rolling stock assembly, signaling equipment Automotive & Transportation — Chassis and powertrain assemblies, engine fasteners, exhaust systems Wind Power & Solar Energy — Turbine tower bolts, blade connections, solar mounting systems Petrochemical & Marine — Offshore platform fasteners, pipeline flanges, chemical processing equipment Heavy Machinery — Construction equipment, agricultural machinery, mining equipment Telecommunications — Tower and antenna fastening, grounding connections Medical Devices — Precision equipment assembly where corrosion resistance and non-magnetic properties are required The product is particularly suited for outdoor and high-humidity environments where long-term corrosion resistance is critical, including coastal, marine, and industrial installations. Surface Finish Options Finish Coating Thickness Salt Spray Resistance Recommended Environment Dacromet (Standard) 5–12 μm 600–1,500+ hours Coastal, marine, industrial, outdoor Geomet (Chrome-Free) 5–10 μm 500–1,200+ hours Environmentally sensitive projects Hot-Dip Galvanized 45–85 μm 500–800 hours Heavy structural, outdoor infrastructure Zinc Plated 8–12 μm 72–144 hours Indoor, general industrial Black Oxide 1–2 μm 24–48 hours Indoor, tooling, machinery Modern chromium-free Dacromet alternatives are available for projects requiring RoHS, REACH, and ELV compliance. These chrome-free formulations eliminate hexavalent chromium (Cr⁶⁺) while maintaining comparable corrosion performance. Packaging & Customization Export Packing: Wooden box / crate / steel pallet Domestic Packing: Corrugated carton / bundle with strapping OEM/ODM: Available — custom sizes, thread types, materials, strength grades, and surface finishes can be produced according to drawings or samples MOQ: Negotiable Quality Assurance All products are manufactured under strict quality control procedures in accordance with ISO 898-1 (mechanical properties of fasteners), DIN, ISO, GB, and ANSI/ASTM standards. The product has achieved a 100% positive review rate with a 50% repurchase rate on the platform, reflecting consistent quality and customer satisfaction. Material test certificates (EN 10204 3.1), dimensional inspection reports, hardness test reports, and third-party inspection reports (SGS, BV, CTI) can be provided upon request. For high-strength grades (10.9 and 12.9), tensile testing, hardness testing, and impact testing are performed on each production batch. Ordering Information To place an order or request a quotation, please specify: Product type — Hex head bolt / Flange bolt / Socket head cap screw / Threaded rod Standard — DIN 931 / DIN 933 / DIN 6921 / DIN 912 / ISO 4014 / ISO 4017 / ASME B18.2.1 Material — Carbon steel (Q235/45#/10B21) / Alloy steel (35CrMo/40Cr/42CrMo/SCM435) Strength grade — 8.8 / 10.9 / 12.9 Thread size and pitch — e.g., M16 × 2.0 or M20 × 2.5 Length — Specify total length and thread length if applicable Surface finish — Dacromet (standard) / Geomet / HDG / Zinc plated / Black oxide Quantity — With any tolerance for over/under shipment Certification — EN 10204 3.1 MTC / SASO conformity (for Saudi Arabia) / GOST-K (for Kazakhstan) Special requirements — Thread tolerance, marking, packaging, topcoat (lubricated/non-lubricated), etc.