大型合金钢锭内部质量控制

IMR OpenIR

	大型合金钢锭内部质量控制
	刘宏伟
学位类型	博士
导师	李殿中
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料加工工程
关键词	大型钢锭纯净化缩孔疏松宏观偏析 Huge Ingot Purifying Shrinkage Cavity And Porosity Macrosegregation
摘要	"大型锻件的生产能力与技术水平是衡量一个国家重大工业发展水平与重大装备自给能力的重要标志之一，直接影响国家重型装备制造业的发展。高质量的大型锻件需要优质的大型钢锭作为坯料。然而，钢锭的质量越大，钢锭内部的缩孔疏松缺陷、宏观偏析缺陷以及钢锭的纯净度越难控制，常常引起大型锻件直接报废。为了解决以上钢锭制备难题，本文以优质大型钢锭为研究目标，研究了钢水纯净化冶炼及浇注、钢锭凝固过程中形成的心部缩孔疏松以及宏观偏析，形成大型优质钢锭的制备技术。论文的主要研究内容和结论包括： 1) 基于高纯净大型钢锭的制备，开展了钢水深脱磷、深脱硫以及真空碳脱氧系列研究。100t 30Cr2Ni4MoV钢锭的试验结果如下：[S]≤0.002%，[P]=0.005%，锭身大部分[H]<1ppm，T[O]≈10ppm, [N]<70ppm，满足了超纯净30Cr2Ni4MoV大型钢锭成分要求。此钢锭材料的回火脆性敏感系数J=3.4，优于目前对超纯净30Cr2Ni4MoV大型钢锭材料的要求(J<10)。 2) 研究了12Cr2Mo1大型钢锭沉积锥处大型夹杂物问题。研究发现钢锭顶部包裹浮渣的凝固薄层熔化以及下落，是形成沉积锥处大型夹杂物的主要原因；通过改善钢锭顶部热条件以及控制包中残留钢水高度，可以解决沉积锥处大型夹杂物问题。 3) 基于高致密大型钢锭的制备，采用大型钢锭热切及大平面冷酸侵蚀技术，对原锭型100t 30Cr2Ni4MoV大型钢锭进行低倍检验。结果表明：钢锭心部存在严重的缩孔疏松缺陷。据此开发了多梯度稳态热冒口，并利用本课题组开发的有效判据G/R0.5＜2.5 ℃· s0.5·mm-1.5，研究不同冒口保温设计对心部缩孔疏松的影响，最终实现了新锭型100t 30Cr2Ni4MoV高致密钢锭的制备。其中，第三支钢锭经超声检测，锭身未发现超过Φ3mm当量孔洞缺陷。 4) 基于低偏析大型钢锭的制备，测定了三支100t 30Cr2Ni4MoV试验钢锭的成分分布，系统研究纯净化对钢锭宏观偏析的影响。通过纯净化控制，可以获得低偏析大型钢锭，钢锭锭身碳成分波动范围为±0.02wt%，没有发现A、V型偏析。 5) 运用连续介质模型，用Fe-C-Si-Mo四元系进行30Cr2Ni4MoV成分偏析模拟，研究了元素Si、Mo以及冒口保温对宏观偏析的影响。Si增加正偏析、Mo减轻正偏析；当冒口保温不会大幅度增加二次枝晶间距时，冒口保温有利于析出的溶质进入冒口，降低锭身正偏析；当冒口保温使锭身二次枝晶间距大幅度增加时，锭身溶质析出加剧，锭身上部正偏析增加。 6) 研究了吹氩及纯净化对钢锭中A型偏析的影响。吹氩能够使钢液中形成大量游离的晶核，细化晶粒，抑制溶质富集、流动，从而减轻或消除A型偏析。氧化物具有聚集杂质元素的能力，是A偏析形成的源。钢水纯净化能够使钢水中氧化物含量减少，且尺寸变小，分布更加均匀。由于氧化物能够作为MnS形成的核心，钢的纯净化有利于减少氧化物核心，抑制硫化物团簇在A偏析区富集并最终减轻A型偏析。"
其他摘要	"The manufacturing capability and the quality of large forgings indicate the developmental level of heavy industry and ability of self-supported for the heavy equipment, which directly affects the development of national major equipment manufacturing. Huge ingot with high quality, as the raw material, can assure heavy forging free from defects. However, with the increase of the size of ingots, the control on shrinkage cavity and porosity, macrosegregation and cleanliness becomes more and more difficult, which results in rejection about heavy forging. In order to solve these problems, investigation about melt purifying, central shrinkage cavity and porosity, macrosegregation during solidification of ingot have been done, the main contents and results are listed as follows: 1) In order to manufactue large ingots with high purification, deep dephosphorization, deep desuphurzation and vacuum carbon deoxidation in molten steel are studied. Following experimental results are achieved in 100 t 30Cr2Ni4MoV trial ingots: [S]≤0.002%, [P]=0.005% and [H]<1ppm, T[O]≈10ppm, [N]<70ppm in most positions of ingot body, which satisfies the composition requirement for super pure 30Cr2Ni4MoV steel. The value of temper embrittlement sensitivity coefficient J is 3.4 for the 30Cr2Ni4MoV steel, which is superior to the demand of J=10 for super pure 30Cr2Ni4MoV steel. 2) The large inclusions in deposit cone of 12Cr2Mo1 ingot are analyzed. The slag is wrapped into the solidified crust and drops with the molten crust together, which results in the large inclusions in deposit cone. Improving the hot condition on the hot top of ingot and controlling the height of residual liquid metal in ladle can avoid the large inclusions in bottom deposit cone. 3) In order to manufacture the large ingot with high soundness， hot cutting and the macroscopic examination on the whole longitudinal section of 100t ingot made with original mould is performed. The results show that central shrinkage cavity and porosity is the most serious defect in the ingot. Through developing the hot top of multi-grade thermal and stable insulation feeder and investigating the effect of different thermal insulation designs of hot top on central shrinkage cavity and porosity with valid criterion G/R0.5＜2.5 ℃· s0.5·mm-1.5, 100t ingots with high soundness have been finally obtained in optimized mould, with the result that the size of all shrinkage cavities in the sound ingot does not exceed Φ3mm by ultrasonic inspection. 4) In order to manufacture large ingots with low segregation，chemical compositions of three 100t ingots were tested, and the effect of steel cleanliness on the macrosegregation have been researched. Through the purification, the large ingot with low segregation can be obtained. The fluctuant range of carbon is within ±0.02wt% , and there are no A and V type macro-segretations found in the body of ingot. 5) The macro-segregation of 30Cr2Ni4MoV ingot is simulated with continuum model considering Fe-C-Si-Mo system. The effect of Si, Mo and good insulation of hot top on distribution of chemical composition are investigated. Si increases positive segregation of carbon, and Mo decreases the positive segregation of carbon. When good insulation of hot top does not induce large increase of secondary dendrite arm spacing, it is beneficial to make rejected solute into hot top, thus decreases positive segregation of ingot body. However, if it prolongs solidification time of ingot body greatly and makes secondary dendrite arm spacing bigger, positive segregation of ingot body increases because bigger secondary dendrite arm spacing can largely increase the amount of solute rejection 6) The effects of top blowing argon and purifying on A-segregation are researched. Top blowing argon can generate free nucleus in molten steel, thus can refine grain and inhibit solute enrichment and melt flow. Thus, top blowing argon can reduce or eliminate A-segregation. Oxides are the origin of A-segregation because they are capable of aborbing impurity. Purification of molten steel can greatly decrease the content of oxide and the size of inclusions, and can make inclusions distribute more uniformly. Because oxide can promote the nucleation of MnS, purification can inhibit MnS cluster enrichment in A-segregation, and finally reduce A- segregation."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64436
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	刘宏伟. 大型合金钢锭内部质量控制[D]. 北京. 中国科学院金属研究所,2012.