I. Technical Background and Product Positioning

8.8 Grade Carbon Steel External Hex Nuts are high-strength fasteners with tensile strength ≥800MPa and yield strength ≥640MPa, widely used in scenarios requiring high bearing capacity such as tower cranes, bridges, and machinery equipment. Handan Guangxuan Fastener Manufacturing Co., Ltd. leverages the regional advantage of the Hebei Yongnian Standard Fastener Industrial Base and achieves large-scale and customized production of such nuts through a full-process standardized production system.

II. Core Manufacturing Process Analysis

STEP 1: Raw Material Selection and Pretreatment
采用ML35/45 carbon steel rods, with the composition analyzed by a spectrometer (C: 0.32-0.40%, Mn: 0.60-0.90%, Si≤0.35%), improved cutting properties through spheroidizing annealing treatment (holding at 650-680℃ for 4 hours).

Step 2: Cold Heading Technology
Using a 6-station high-speed cold heading machine, the blank of the nut is formed in one operation through multi-pass progressive shaping. Key parameters: forging ratio 1:2.5, forming speed 120 pieces/min, mold temperature controlled at 80-100℃.

Step 3: Heat Treatment Strengthening Process
Treated with a continuous belt furnace: quenching temperature 850±10℃, oil cooling time ≥15 minutes; tempering temperature 450±10℃, holding time 2 hours, ensuring hardness reaches HRC28-32.

Section 3: Quality Control System

Testing Equipment Configuration: Equipped with Rockwell hardness tester, universal material testing machine, magnetic particle inspection instrument, etc., each batch of products undergoes 100% hardness testing and 5% destructive sampling test.
2. Process Control Points: Set up 12 key control points including raw material acceptance, cold heading dimensions, heat treatment curves, surface treatment, etc., and achieve real-time traceability of production data through the MES system.
3. Certification Standards: The product complies with the GB/T 6170-2015 national standard, passes the ISO9001 quality management system certification, and can provide a third-party inspection report.

4. Typical Application Cases

In a large tower crane manufacturing project, Guangxuan Company customized M36×150 specifications of 8.8-grade nuts for the client. By optimizing the heat treatment process, the fatigue life of the product was improved by 30%, and combined with anti-loosening coating treatment, successfully resolved the vibration and loosening issues during high-altitude operations. The cumulative supply exceeded 50,000 pieces, with a defect rate controlled below 0.02%.

Section 5: Technical FAQ

Q1: What is the main difference between 8.8 and 10.9 grade nuts?
A: The main differences lie in the heat treatment process and mechanical properties. Grade 10.9 requires alloy steel material, with a higher quenching temperature (900-930℃), tensile strength ≥1040MPa, but the cost increases by about 25%.

Q2: How to determine if the nut quality meets the standard?
A: Can be inspected through three dimensions: free from cracks and burrs in appearance, hardness value within the specified range, and thread pass and stop gauge test passed. It is recommended to ask suppliers to provide material reports and inspection certificates when purchasing.

Q3: How is rust prevention treated on carbon steel nuts?
A: Common treatments include electroplated zinc (thickness 5-8μm), Dacromet (thickness 6-8μm), and hot-dip galvanizing (thickness 45-60μm). Guangxuan Company can recommend suitable solutions based on the usage environment, such as using Dacromet + sealing agent treatment for marine environments.