无孕育蠕墨铸铁壁厚敏感性研究
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摘要
采用低镧镁硅铁蠕化剂制备蠕铁铁液,探索了铸件壁厚对合金蠕化率、蠕墨和共晶团形态及基体组织的影响规律。结果表明,在无孕育工艺条件下,蠕墨铸铁的凝固组织由奥氏体枝晶、形态不规则的蠕墨/奥氏体共晶团和少量球墨/奥氏体共晶团组成,铸态组织由铁素体、珠光体和蠕虫状石墨及少量球状石墨组成。随着铸件壁厚的增大,蠕墨铸铁的蠕化率、蠕墨形态参数、蠕墨/奥氏体共晶团尺寸趋于增大,共晶团形貌团球化,而枝晶数量和珠光体数量显著减少。当铸件模数一定时,铸件边缘处的蠕化率、蠕墨形态参数和共晶团尺寸均低于心部,但枝晶析出数量高于心部。对于蠕化率较高的合金,当模数MS≥0.75 cm时,蠕化率对壁厚的变化不甚敏感,反之,敏感性较强;而对于蠕化率较低的合金,敏感性转变模数由0.75 cm降为0.5 cm。此外,无论合金蠕化率高低,其基体组织中的珠光体数量对壁厚变化均十分敏感,尤其是当铸件模数MS<0.5 cm时,珠光体数量随铸件模数的增大显著减少。
In this paper, the molten iron was treated by adding the vermicularizing ageng of low lanthanum magnesium-ferrosilicon alloy, and the influence of wall thickness on the vermicularity, the morphologies of vermicular graphite and eutectic cells, and the matrix microstructure of the vermicular graphite cast iron was investigated. The results indicate that the solidification microstructure of the vermicular graphite cast iron consists of austenite dendrites, irregular vermicular graphite/austenite eutectic cells and a small amount of spheroidal graphite/austenite eutectic cells, while the as-cast microstructure is composed of ferrite, pearlite,vermicular graphite and a small quantity of spheroidal graphite under the condition of no inoculation processing.With increasing the wall thickness of the casting, the vermicularity, the morphological parameters of the vermicular graphite and the size of the vermicular graphite/austenite eutectic cells are increased, and the morphology of eutectic cells tends to be spheroidized; conversely, the quantity of dentrites and pearlites remarkably decreases. When the wall thickness of the casting is constant, the vermicularity, the morphological parameters of the vermicular graphite and the size of eutectic cells at the external part of the sample is lower than those at the inner part of the sample, but the quantity of the dendrites at the external part of the sample is higher than that at the inner part of the sample. For the alloys with higher vermicularity, when the modulus of the casting MS≥0.75 cm, the vermicularity is not sensitive to the wall thickness of the casting; when the modulus of the casting MS<0.75 cm, the sensitivity is strong. For the alloys with lower vermicularity, the sensitivity transformation modulus will reduce from 0.75 cm to 0.5 cm. In addition, regardless of the vermicularity, the quantity of pearlites in the matrix microstructure of the vermicular graphite cast iron is very sensitive to the wall thickness of the casting. Especially when the modulus of the casting MS<0.5 cm, the quantity of pearlites decreases significantly with the increase of the modulus.
In this paper, the molten iron was treated by adding the vermicularizing ageng of low lanthanum magnesium-ferrosilicon alloy, and the influence of wall thickness on the vermicularity, the morphologies of vermicular graphite and eutectic cells, and the matrix microstructure of the vermicular graphite cast iron was investigated. The results indicate that the solidification microstructure of the vermicular graphite cast iron consists of austenite dendrites, irregular vermicular graphite/austenite eutectic cells and a small amount of spheroidal graphite/austenite eutectic cells, while the as-cast microstructure is composed of ferrite, pearlite,vermicular graphite and a small quantity of spheroidal graphite under the condition of no inoculation processing.With increasing the wall thickness of the casting, the vermicularity, the morphological parameters of the vermicular graphite and the size of the vermicular graphite/austenite eutectic cells are increased, and the morphology of eutectic cells tends to be spheroidized; conversely, the quantity of dentrites and pearlites remarkably decreases. When the wall thickness of the casting is constant, the vermicularity, the morphological parameters of the vermicular graphite and the size of eutectic cells at the external part of the sample is lower than those at the inner part of the sample, but the quantity of the dendrites at the external part of the sample is higher than that at the inner part of the sample. For the alloys with higher vermicularity, when the modulus of the casting MS≥0.75 cm, the vermicularity is not sensitive to the wall thickness of the casting; when the modulus of the casting MS<0.75 cm, the sensitivity is strong. For the alloys with lower vermicularity, the sensitivity transformation modulus will reduce from 0.75 cm to 0.5 cm. In addition, regardless of the vermicularity, the quantity of pearlites in the matrix microstructure of the vermicular graphite cast iron is very sensitive to the wall thickness of the casting. Especially when the modulus of the casting MS<0.5 cm, the quantity of pearlites decreases significantly with the increase of the modulus.
引文
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[3]张忠仇,李克锐,曾艺成.我国蠕墨铸铁的现状及展望[J].铸造,2012,61(11):1303-1307.
[4]Llorca-Isern N,Nesa D,Vicente M. Thin-wall compacted graphite cast iron for automotive applications[J]. Cast Metals,2003,16(1-3):325-328.
[5]邱汉泉.蠕墨铸铁及其生产技术[M].北京:化学工业出版社,2010.
[6]Górny M,Kawalec M,Sikora G,et al. Effect of cooling rate and of titanium additions on the microstructure of thin-walled compacted iron castings[J]. Cast Metals,2016,29(1-2):68-73.
[7]Wu K W,Liu G L,Zhang J Q,et al. Effect of vermiculizer amount on microstucture and properties of vermicular graphite cast iron[J].Chinese Rare Earths,2016,37(4):67-73.
[8]Zhang X,Zhang G,Hong X U. Homogeneity research on microstructure and properties of vermicular graphite cast iron[J]. Hot Working Technology,2014,43(13):27-30.
[9]徐锦锋,梁敬凡,邱汉泉,等.低镧镁硅铁蠕化剂的蠕化处理特性研究[J].铸造,2018(9):772-777.
[10]徐锦锋,翟秋亚,袁森,等.过共晶球铁凝固过程中奥氏体的生长方式与形貌特征[J].金属学报,2003,39(2):136-139.