The production goals of cold heading wire plants depend on the quality and efficiency of spheroidizing annealing; automotive steel pipe customers require consistent performance and surface performance of each steel pipe. Both need to prevent oxidative decarburization during the annealing process, and nitrogen and hydrogen, dissociated ammonia or endothermic atmosphere are commonly used. In recent years, the main challenges for special steel companies have come from the safety control and environmental impact assessment costs of protective atmosphere media (such as methanol). The one-stop protective atmosphere solution reduces risks and costs through replacement of carrier gas and enriched gas, gas supply pipeline planning and data monitoring.
- Spheroidizing annealing: long cycle, surface decarburization directly affects cold heading cracking
- Bright annealing: the surface is not oxidized and requires a low dew point reducing atmosphere
- Atmosphere selection: nitrogen and hydrogen, dissociated ammonia, endothermic gas
- Pain points: Management of hazardous chemicals such as methanol, environmental impact assessment, and downtime risks
- One-stop solution: gas replacement + pipeline planning + data monitoring
Cold heading steel wire: spheroidizing annealing
Cold heading steel wire is used to produce bolts, screws and other fasteners. It needs to be spheroidized and annealed before cold heading to spheroidize carbides, reduce hardness and improve plasticity.
Quality points:
- Spheroidization rate and microstructure uniformity;
- Hardness and strength are within the required range;
- Surface decarburization control: Decarburization will cause cold heading cracking or insufficient surface hardness of the finished product;
- Surface oxidation affects subsequent drawing and phosphating.
Spheroidizing annealing has a long cycle and a large furnace load (often performed in a bell furnace or continuous furnace), so the long-term stability of the atmosphere is crucial.
Precision steel pipes and automotive steel pipes: bright annealing and normalizing
Automotive steel pipes (such as drive shaft pipes, shock absorber pipes, oil pipes) have high requirements on size, mechanical properties and surface quality, and customers want each pipe to be consistent.
bright annealing It is required that the surface is not oxidized and the atmosphere needs to be:
- Low dew point (less moisture);
- Sufficient reducing components (H₂ or CO);
- Appropriate carbon potential (to prevent decarburization of medium and high carbon steels).
Commonly used atmosphere solutions
| Plan | Features |
|---|---|
| Nitrogen-hydrogen mixture | Suitable for bright annealing of low carbon steel, H₂ ratio adjusted as required |
| dissociated ammonia | 75% H₂, strong reducibility, low cost |
| endothermic gas | Controllable carbon potential, suitable for preventing decarburization of medium and high carbon steel |
| Nitrogen + methanol | Flexible implementation but involves methanol storage |
Industry pain points and one-stop solutions
Gauss Control's fine wire/steel pipe industry page points out that the biggest challenges for special steel manufacturers in recent years have come from the safety control and environmental assessment of protective atmosphere media, such as the management costs caused by the storage and use of methanol. Its one-stop protective atmosphere solutions include:
- Replacement of heat treatment furnace carrier gas and enriched gas (reducing hazardous chemicals such as methanol);
- Protective atmosphere air supply pipeline design and planning;
- Factory equipment data monitoring.
The goal is to reduce hazardous chemicals control risks, production costs and downtime risks. The official website news also mentioned Ruizhi precision compressor motor annealing atmosphere modification and other projects.
Frequently asked questions
What atmosphere is best for spheroidizing annealing?
Depends on steel grade, furnace type and cost. For medium and high carbon steels that are sensitive to decarburization, it is recommended to use an atmosphere with controlled carbon potential; for low carbon steels, nitrogen and hydrogen can be used.
What is the reason for the blackening of the annealing surface of the bell-type furnace?
It may be caused by poor sealing, insufficient purging, high atmospheric dew point, or air intake during the cooling stage. Check the inner cover seal and purge procedure.
Does the steel pipe industry need CQI-9?
The heat treatment of steel pipes supplied to the automotive industry usually needs to meet the customer's heat treatment process requirements. CQI-9 also has process tables related to annealing and normalizing.