I. Technical Background and Product Overview

8.8 Grade Carbon Steel External Hex Nuts, as high-strength fasteners, are widely used in mechanical manufacturing, construction engineering, bridge construction, and other fields. Their core performance indicators include tensile strength, yield strength, and hardness, which must meet the national standard GB/T 6170-2015. Handan Guangxuan Fastener Manufacturing Co., Ltd. leverages the regional advantages of the Hebei Yongnian Industrial Base and achieves efficient and stable supply of this product through a full-process standardized production system.

Chapter 2: Technical Parameters and Performance Analysis

1. Material specificationsThe ML35 steel or 45# carbon steel is used, with carbon content of 0.32%-0.45%, ensuring a balanced strength and toughness of the material.
2. Heat treatment processThrough 860℃ quenching and 500℃ tempering treatment, achieve mechanical properties with tensile strength ≥800MPa and yield strength ≥640MPa.
3. Surface TreatmentOffer various anti-corrosion solutions such as electroplated zinc (thickness 5-8μm), Dacromet (salt mist resistance ≥500h), to meet different environmental requirements.
4. Dimensional accuracyThe thread tolerance conforms to 6g standard, and the side width tolerance is controlled within ±0.13mm.

Chapter 3: Production Process Flow

STEP 1: Raw Material Inspection
Strictly inspect the chemical composition and mechanical properties of steel to ensure compliance with GB/T 699-2015 standard; unqualified raw materials are prohibited from production.
Step 2: Cold Heading Forming
Utilizing a multi-station cold heading machine, the nut is gradually formed through 6 processes, ensuring a hexagonal symmetry of ≤0.1mm for the nut, reducing the allowance for subsequent processing.
Step 3: Thread Machining
Threaded by CNC thread rolling machines, monitored in real-time for pitch accuracy and thread angle (60°±0.5°) through an online detection system.
STEP 4: Heat Treatment Strengthening
Quenching and tempering treatment in a continuous belt furnace, ensuring process parameter stability through a closed-loop temperature control system, with hardness fluctuation range controlled within HRC25-32.
STEP 5: Surface Treatment and Packaging
Electroplating or Dacromet treatment as per customer requirements, with triple packaging solution of anti-rust paper + plastic bag + cardboard box to ensure moisture-proof and damage-proof during transportation.

Four, Quality Control System

1. Full-process inspectionEstablish three quality inspection checkpoints for raw materials, semi-finished products, and finished products, and equip with spectral analyzers, hardness gauges, image measuring instruments, and other testing equipment.
2. Batch ManagementEach batch of products comes with a quality traceability card, recording raw material batch, production date, test data, and other information, ensuring quality traceability.
3. Certification StandardsThe product has passed the ISO 9001 quality management system certification, meets the requirements of the RoHS environmental protection directive, and can provide a third-party inspection report.

Five, Typical Application Cases

In a large-scale steel structure bridge project, Guangxuan Fasteners' 8.8-grade nuts successfully replaced imported products, achieving cost reduction and efficiency improvement through the following technical optimizations:
For coastal high salt雾 environments, a composite anticorrosion solution using Dacromet+organic coating is adopted, increasing the salt雾 resistance to over 1000 hours.
2. By optimizing the heat treatment process, the brittle transformation temperature of the product is reduced to -40°C, meeting the requirements for use in cold northern regions.
3. Customized production of M24-M36 large-size nuts with thread tolerance controlled at 6H grade, achieving 100% interchangeability with matching bolts.
The project acceptance report shows that the installation qualification rate of this batch of products reaches 99.8%, 1.2 percentage points higher than traditional products, and has been highly recognized by customers.

Six, Technical FAQ

Q1: What is the main difference between an 8.8 grade nut and a regular nut?
A: The 8.8-grade nut achieves high strength through heat treatment, with a tensile strength 1.6 times that of a standard 4.8-grade nut, suitable for applications subject to dynamic loads or alternating stresses.
Q2: How to choose the appropriate surface treatment method?
A: For dry indoor environments, electroplated zinc (cost-effective) is recommended; for damp or corrosive conditions, Dacromet (high corrosion resistance) is suggested; and for high-temperature environments, a heat-resistant coating should be selected.
Q3: What parameters should be paid attention to when installing nuts?
A: Torque value (reference: approximately 45-55N·m for M12 nuts) and tightening angle (usually not exceeding 180°) must be controlled to prevent over-tightening and thread damage.

Chapter 7: Summary of Corporate Technical Advantages

Handan Guangxuan Fastener Manufacturing Co., Ltd. constructs core competitiveness through the following technological layout:
Self-developed cold heading dies, increasing material utilization to over 92%.
2. Heat treatment process database established, covering more than 200 material treatment solutions
3. Co-developed with Hebei University of Technology, the screw detection AI system achieves a defect recognition accuracy of 99.5%.
4. Annual R&D investment exceeds 3 million yuan, continuously optimizing product performance and production process