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摘要: 采用數學模擬方法研究鋼軌鋼連鑄坯脫氫退火行為，分析不同退火溫度、退火時間條件下連鑄坯脫氫效果，優化了脫氫退火工藝。在脫氫退火過程中，連鑄坯角部和邊部的氫含量快速降低，而連鑄坯中心氫含量在加熱段后期開始降低；隨著退火溫度的升高，連鑄坯中心脫氫的起始點明顯提前，最大脫氫速率顯著增加。隨著均熱段時間逐漸延長，連鑄坯中心氫含量明顯降低，但脫氫速率的增加幅度逐漸減小。通過優化脫氫退火工藝參數，連鑄坯中心氫的質量分數能夠降低至0.6×10?6，脫氫效果顯著。Abstract: Due to moisture in the ore, auxiliary material, and ladle refractory material, the hydrogen element is easily enriched in molten steel. In the metallurgy process, some hydrogen atoms form bubbles and are removed by gravity, whearas others solidify in the strand and remain in the produced steel. When the hydrogen content reaches a certain critical value, the enriched hydrogen atoms congregate to produce a white spot, which greatly reduces the strength and toughness of the steel product, and leads to brittle fracture during its service period. At present, the RH (Ruhrstahl–Heraeus) and VD (vacuum degasser) refining processes are commonly applied in steel plants, which can reduce the hydrogen content to less than 2×10?6. With the demand for high quality steel, the hydrogen content must be further decreased, so hydrogen diffusion in solid steel during the annealing process is gradually attracting increasing attention. In this study, a two-dimensional model was built to investigate the characteristic of dehydrogenation in the bloom annealing process of rail steel. Moreover, the effect of annealing temperature and annealing time on hydrogen diffusion were analyzed, and the annealing parameters were optimized. During the dehydrogenation annealing process, the hydrogen content at the corners and edges of the bloom are found to decrease rapidly, while that in the center of the strand begin to decrease in the later heating stage. As the annealing temperature increases, the starting point of dehydrogenation in the bloom center moves ahead and the maximum dehydrogenation rate increases significantly. With the extension of the soaking period, the central hydrogen content of bloom decreases significantly, but the increase rate of the dehydrogenation gradually decreases. By optimizing the bloom annealing parameters, the hydrogen content in the bloom can be steadily reduced to 0.6×10?6, which fully meets the requirement of high quality steel production.
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Key words:
- bloom /
- dehydrogenation /
- annealing temperature /
- annealing time /
- numerical simulation
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圖 2 連鑄坯溫度變化。（a）升溫曲線；（b）橫截面溫度場分布
Figure 2. Temperature variation of bloom: (a) heating curve; (b) temperature field in the cross section
圖 3 連鑄坯氫質量分數的變化。（a）角部、邊部、中心的氫質量分數；（b）連鑄坯寬度方向氫分布
Figure 3. Variation of hydrogen mass fraction: (a) hydrogen mass fraction in the corner, edge and center of bloom; (b) hydrogen distribution in the lateral direction
圖 5 不同溫度對連鑄坯脫氫的影響。（a）中心溫度變化；（b）中心脫氫速率變化
Figure 5. Effect of annealing temperature on dehydrogenation: (a) center temperature variation; (b) center dehydrogenation rate variation
圖 6 連鑄坯氫質量分數變化。（a）中心氫質量分數變化；（b）氫質量分數沿寬度方向分布
Figure 6. Variation of hydrogen mass fraction in bloom: (a) center hydrogen mass fraction; (b) hydrogen mass fraction in the lateral direction
圖 7 不同保溫時間條件下連鑄坯脫氫。（a）連鑄坯中心溫度；（b）中心脫氫速率變化
Figure 7. Dehydrogenation of bloom with different soaking times: (a) center temperature variation; (b) center dehydrogenation rate variation
圖 8 連鑄坯中心氫質量分數變化。（a）中心氫質量分數；（b）中心脫氫率
Figure 8. Variation of center hydrogen mass fraction: (a) center hydrogen mass fraction (b) center dehydrogenation efficiency
圖 9 不同保溫時間條件下連鑄坯脫氫。（a）橫截面氫質量分數；（b）中心氫質量分數變化
Figure 9. Dehydrogenation of bloom with different soaking times: (a) distribution of hydrogen mass fraction; (b) center hydrogen mass fraction variation
表 1 模型參數
Table 1. Physical parameter used in the model
Item Value Density/(kg?m?3) 7000 Specific heat capacity/(J·kg?1·K?1) 690 Thermal conductivity/(W·m?1·K?1) 28 Equilibrium hydrogen content/10?6 0.06 
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