普通热轧钢材的合理洁净度及生产工艺探讨

ECONOMICAL CLEANLINESS AND RATIONAL PRODUCTION TECHNOLOGY FOR COMMON HOT ROLLED STEEL PRODUCTS

钢凝固前、后生成的非金属夹杂物形貌和在钢中的分布特点不同,凝固前生成的夹杂物尺寸较大,在钢中随机分布,主要影响钢材的疲劳强度和延性等性能。凝固后生成的夹杂物尺寸小,主要在晶界富集析出。硅锰脱氧钢脱氧后钢液仍含有20×10-6以上溶解氧,这部分溶解氧在钢凝固后绝大多数会转变为微细的氧化物或氧硫化物夹杂。钢凝固后生成的夹杂物主要影响钢材的冲击韧性、韧-脆转换温度等性能。 对热轧长型材用普碳钢和低合金钢不必采用铁水脱硫预处理,对热轧钢板用普碳钢可采用铁水轻度脱硫预处理,对热轧钢板用低合金高强度钢可采用铁水脱硫预处理、炼钢过程抑制回硫和出钢过程脱硫的工艺。对超低硫低合金钢,在钢水炉外精炼脱硫处理过程钢-渣间须维持非常低的氧势,炉渣成分应控制在CaO:SiO2:Al2O3=60％～65％:4％-8％:30％～35％范围。 普通热轧长型材用钢脱氧后溶解氧含量可放宽至(30-50)×10-6,对中、厚板钢溶解氧含量必须较严格控制,最好采用铝脱氧将溶解氧控制在较低的水平,并将T[O]含量控制在50×10-6以下。采用降低炼钢终点钢水氧含量、出钢挡渣、CAS和CAB等较简易炉外精炼方法和防止铸坯夹渣等措施,能够生产满足普通热轧钢洁净度要求的高品质钢材。

Non - metallic inclusions, which form in liquid steel, are different from the inclusions forming in solidified steel. Inclusions forming before solidification are usually relatively larger, randomly exist in steel and mainly affect properties of fatigue strength and ductility of steel products. In contrast, inclusions forming after solidification are smaller and usually exist at grain boundaries. Si - Mn deoxidized steels contain more than 20 × 10 soluble oxygen after deoxidabon and most of the soluble oxygen will transfer into fine oxides or oxy - sulfides after solidification of the steels. Inclusions forming after solidification mainly affect properties of low temperature toughness, ductile - brittle transfer temperature, etc. of the steel. It is not necessary to adopt hot metal desulfurization pretreatment for common hot rolled long type steel products. Light desulfurization pretreatment of hot metal can be used for common carbon steel plate steels. For HSLA steel plate steels, technology of hot metal desulfurization treatment, prevent sulfur pick up in BOF steelmaking and desulfurization during tapping should be adopted. For extra low sulfur HSLA steels, very low oxygen potential between the steel and slag has to be kept in ladle desulfurization refining and the slag composition should be controlled close to the range of CaO: SiO2: A12O3 = 60-65%:4-8%:30-35%. For common long type hot rolled steel products, control of soluble oxygen content after liquid steel deoxidabon can be loosen to (30- 50) × 10-6. While, for heavy plate steels, soluble oxygen after deoxidation should be relatively strictly controlled. It is better to use Al deoxidabon to make the soluble oxygen concentration at a very low level and the total oxygen T[O] should be controlled below 50 ×10-6. By taking measures of decreasing steel oxygen content at end of BOF blowing, preventing slag carry over during BOF tapping, adopting relatively simpler secondary refining methods like CAS and CAB, preventing scum entrapment in continuous casting mold, etc. , high quality hot rolled steel products with good enough cleanliness can be produced.