In the final product bundle of steel warehouse, double sampling for re-inspection is conducted. The steel cooling bed in the rolling mill production line automatically bundles and packs the steel, with each bundle weighing approximately Zt. The steel is packed in bundles and maintained at a temperature ranging from 20°C to 300°C. Once stored indoors, after seven days, the batch was double sampled in a steel library where the steel had cooled down to room temperature. Upon re-examining the mechanical properties of the steel, a significant improvement in area reduction was observed, along with a substantial decrease in hydrogen content. The average calculated area shrinkage was 28% higher than the initial test, and the hydrogen content was reduced by 47%. This indicates that during the stacking and cooling process on the cold bed, the hydrogen content in the steel can be effectively reduced.
The microstructure of the steel is not tightly centered, and the octahedral gap radius is smaller compared to face-centered cubic structures. Therefore, the solubility of hydrogen in austenite is greater than in ferrite. After the phase transformation is complete, hydrogen diffuses into the austenite with high solubility until it accumulates in the center, forming white spots. These white points typically form between 150°C and 200°C as the steel cools to room temperature. When the steel reaches the finishing platform, its temperature is usually between 200°C and 300°C. Although the core may contain some hydrogen, no white spots are formed at this stage. However, if the sample is placed separately and rapidly cooled to room temperature, excessive hydrogen may aggregate under internal stress, leading to sawtooth cracks known as white spots.
When the steel is bundled at 200°C–300°C and stacked in an indoor warehouse, it cools slowly to room temperature. This slow cooling significantly reduces internal stress, making it difficult for excess hydrogen to form white spots. Additionally, the ferrite in the steel has a body-centered cubic (BCC) structure, which is less densely packed than the face-centered cubic (FCC) structure. At temperatures between 20°C and 30°C, long-term insulation allows hydrogen atoms to diffuse out of the steel, further reducing hydrogen content. As a result, when double sampling and re-testing the finished steel products, the area shrinkage rate increases significantly, and hydrogen content drops notably.
Once a white spot forms in the steel, it results in a sawtooth crack, which is considered an irreversible defect. Unfortunately, this method cannot eliminate such defects. The company’s steelmaking process does not include a vacuum degassing system. Hydrogen content was measured at (4.0–6.5) ppm through sampling and analysis of 6osiZMn steel in the crystallizer. During the rolling process, the billet remains in a high-temperature austenite (γ) state, and as the billet size decreases, the material spreads outward. However, the unit cell structure of iron in the austenite state is face-centered cubic (FCC), which has a closely packed arrangement and large octahedral gaps, making it difficult for hydrogen to diffuse out.
Npt 1/4 Exhaust Valve,Safety Exhaust Valve,Npt Exhaust Valve,Small Pressure Relief Valve
Ningbo Wenhan Fluid Equipments Co., Ltd. , https://www.wenhanvalves.com