What are the factors affecting the brightness of stainless steel after annealing?
June 22 09:06:30, 2025
A Shandong-based stainless steel pipe manufacturer recently shared insights on how the luster of an annealed stainless steel tube reflects the quality of the final product. This process involves several critical factors, with five key elements being particularly significant.
Firstly, achieving the correct annealing temperature is crucial. Typically, stainless steel undergoes solution heat treatment, commonly referred to as "annealing," at temperatures ranging from 1040°C to 1120°C (as per Japanese standards). Observing through the furnace's viewing window, the stainless steel tubes inside should glow brightly without showing signs of sagging or distortion.
Secondly, the annealing atmosphere plays a vital role. Pure hydrogen is often used, with a preferred atmospheric purity of at least 99.99%. However, if other gases like inert gases are used, their purity might be slightly lower, provided they don't contain excessive oxygen or water vapor.
Thirdly, maintaining proper furnace sealing is essential. Bright annealing furnaces need to be hermetically sealed to isolate them from external air. Only one exhaust port should be present, used to vent hydrogen safely (to burn off any released hydrogen). A simple soap-water test can verify the integrity of the seals—look for bubbles forming at the joints. Areas prone to leaks include where pipes enter and exit the furnace, where sealing rings are frequently worn down. These spots require regular checks and timely replacement.
Fourthly, ensuring adequate protective gas pressure is necessary to prevent minor leaks. For hydrogen atmospheres, pressures exceeding 20 kBar are typically recommended.
Lastly, controlling furnace moisture levels is critical. First, ensure the furnace materials are thoroughly dried before use, especially during initial runs. Secondly, stainless steel tubes brought into the furnace should be free of excess moisture, particularly if they have hollow sections. Any leakage could ruin the entire furnace atmosphere.
It’s worth noting that under normal conditions, once the furnace is opened, the stainless steel tubes about 20 meters inside will start to exhibit a bright, reflective surface.
This information about stainless steel tubes was sourced from reliable industry professionals.