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How to improve the internal quality of billet by gravity casting

2020-07-29 14:12:11

 (1) In order to reduce the internal cracks of the slab, the mold cooling and secondary cooling section can not be forced cooling, so the optimization of mold water quantity and secondary cooling water ratio is carried out.

(2) After adjusting the different tension and straightening pressure, take the corresponding low power sample, explore the best tension and straightening pressure. Considering the hydraulic condition, the red billet pressure is gradually optimized from 510mpa to 310mpa, and the hydraulic valve station is replaced to keep the red billet pressure stable.

(3) The remaining water jacket is eliminated. The wall thickness of the water jacket is changed from 6mm to 8mm, and the material is changed from carbon steel to stainless steel. This kind of water jacket is not easy to deform, the inner wall is smooth, and the water flow field in the water gap of the mold is uniform.

(4) Improve the quality of cooling water.

(5) Through precise operation, the stability of mold liquid level is determined by the condition of slag line of submerged nozzle after use. The stability of mold liquid level control is greatly improved, and the mold liquid level fluctuation is improved from ± 10 mm to ± 5 mm, so as to ensure the alignment of submerged nozzle and maintain the slag filling relatively standard.

(6) Change the status of the disorder of cooling water in continuous casting equipment, change the direction of water channel, optimize the water nozzle and water quantity, and basically reach a small amount of water flowing to the red billet.

(7) The superheat of molten steel in the central ladle should be strictly controlled. The superheat degree of molten steel in central ladle at 20-30 is relatively large, the columnar crystal of billet is relatively prosperous, and the probability of internal crack and central porosity of slab is increased. After the research of central ladle temperature, the superheat of molten steel in central ladle is strictly controlled at 15-25 ℃.

(8) Improve the purity of molten steel and Mn / s in steel. In the past, the whole process of blowing argon for mixing in the tapping process of converter, and then the soft blowing of small argon for 3 min. the optimization is that the whole process of blowing argon and mixing in the tapping process, and the small argon gas is 4 min,

The results show that the manganese content in 20MnSi and 20MnSiV products will be improved together, and the sulfur content in the products will be reduced. Therefore, the Mn / s in steel will be improved. Before optimization, Mn / s will be less than 15 for many heats, and all of them will be above 18 after optimization. The above measures will reduce the hot embrittlement tendency of sulfur in steel at grain boundaries.

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