加热温度和冷却速度对亚共晶高铬铸铁微观组织的影响

采用淬火变形膨胀仪测量高铬铸铁在不同冷却速度下的膨胀曲线,研究了加热温度和冷却速度对高铬铸铁热处理冷却过程中其微观组织转变的影响规律。结果表明,在较低冷速下微观组织为典型的亚共晶白口铸铁组织形态,由初生奥氏体的低温转变组织和共晶体组成;在冷却速度为3℃/s时开始出现马氏体组织,并优先在共晶奥氏体区域大量形成;随着冷却速度的增加,马氏体量逐步增多,在10℃/s冷速下为连续的马氏体基体组织和共晶碳化物。二次碳化物在初生奥氏体区大量弥散析出,而在共晶奥氏体区近共晶碳化物周边位置没有二次碳化物生成,远离共晶碳化物的区域有少量二次碳化物的析出。随着加热温度的升高和冷却速度的增加,初生奥氏体和共晶奥氏体区的珠光体片层间距均逐渐减小。     

淬火工艺对Cr26高铬耐磨铸铁组织与硬度的影响

利用光学显微镜、洛氏硬度计等研究了不同淬火工艺对Cr26高铬耐磨铸铁组织与硬度的影响。结果表明:铸态Cr26高铬铸铁组织主要由初生奥氏体和碳化物组成。经980~1060 ℃不同温度淬火、空冷后,高铬铸铁组织中有大量二次碳化物析出。随着淬火温度的升高,析出的二次碳化物先增加后减少,试样硬度先升高后降低。1020 ℃淬火试样硬度达到峰值,为65.7 HRC。1020 ℃淬火高铬铸铁,经空淬、油淬和水淬不同方式冷却,随着冷却速度的增大,高铬铸铁组织中碳化物颗粒、碳化物比例逐渐增大,硬度逐渐增大,其中水淬高铬铸铁试样硬度最大,达到68.2 HRC。     

Si/C和冷却速度对中铬铸铁铸态组织性能的影响

研究了Si/C和冷却速度对中铬铸铁铸态组织和性能的影响规律。试验表明 :在一定限度内提高Si/C能改变碳化物的类型和分布 ,使冲击韧性大幅提高 ;增加冷速使组织明显细化 ,特别是使奥氏体的一次、二次枝晶臂间距显著减小 ,综合力学性能得到改善     

冷却速度对铬系铸铁凝固过程中碳化物析出特征的影响

通过改变冷却条件,探讨冷却速度的变化对Cr含量分别为9%、17%的铬系铸铁凝固过程中碳化物形核、长大的热力学驱动力条件及原子扩散移位动力学条件的影响,揭示碳化物类型及尺寸、形貌的变化特征。结果表明:对于Cr含量为9%铸铁,砂型冷却下凝固组织中的碳化物是M3C、M3C7两种类型,呈大块状,尺寸较大;在金属型冷却下碳化物尺寸较砂型有所减小;水冷条件下组织中碳化物的连续性变弱,尺寸明显变小,呈长条状排列。相较于铬含量9%的铸铁,当Cr含量为17%时,砂型冷却下凝固组织中只有M3C7型碳化物,且碳化物尺寸减小,形态呈棒状;在金属型冷却时,碳化物形貌变化程度较Cr含量为9%时从砂型到金属型的变化要小;但在快速水冷下碳化物间距显著变窄,长度尺寸明显变小,分布更加均匀。     

RE对高铬铸铁定向凝固组织和力学性能的影响

采用液态金属冷却的高温度梯度定向凝固设备,研究了RE对高铬铸铁定向凝固组织和力学性能的影响.研究表明,稀土主要位于高铬铸铁的基体组织中,随凝固速度的增加,稀土在基体中的含量增加;稀土对高铬铸铁定向凝固组织中的碳化物具有细化作用,并随凝固速度的增加,定向凝固高铬铸铁组织细化程度提高,同时稀土的加入使高铬铸铁的抗拉强度明显提高.     

含硅量和冷却速度对中铬铸铁碳化物的影响

对金属型和砂型铸造的含硅量不同的2．79％C-7.17％Cr-0.48％Mn中铬铸铁试样进行了显微组织研究和热分析,结果表明：(Fe,Cr)7C3碳化物量随含硅量的增加和冷却速度的降低而增加。因此,为了增加中铬铸铁显微组织中(Fe,Cr)7C3碳化物的量,应增加化学成分中硅的含量,并控制和降低冷却速度。     

冷却速度对高铬铸铁热处理过程中组织转变的影响

研究了冷却速度对高铬铸铁热处理冷却过程中其微观组织转交的影响,并观察其微观组织.结果表明,在较低冷速下微观组织为典型的亚共晶白口铸铁组织形态,由初生奥氏体的低温转变组织和共晶体组成;在冷却速度为3℃/s时开始出现马氏体组织,并优先在共晶奥氏体区域大量形成;随着冷却速度的增加,马氏体量逐步增多,在10℃/s冷速下为连续的马氏体基体组织和共晶碳化物.二次碳化物在初生奥氏体区大量弥散析出,而在共晶奥氏体区没有二次碳化物生成.随着冷速的增加,初生奥氏体和共晶奥氏体区的珠光体片层间距均逐渐减小.     

冷却速度变化对12Cr铸铁碳化物的影响

采用砂型、金属型、水冷浇注制备含Cr量为12%的过共晶铸铁。研究冷却速度变化对Cr12铸铁凝固组织中碳化物形成特征及碳化物类型转变的影响,探讨了碳化物类型发生转变的原因。结果表明:冷却速度对碳化物尺寸和碳化物类型有很大影响。在砂型和金属型冷却试样中,凝固组织的组成和初生碳化物的形貌没有明显变化,凝固组织均由块状的M7C3型初生碳化物和菊花状的共晶团(M7C3+奥氏体)所组成。金属型冷却试样的碳化物尺寸和共晶团尺寸比砂型试样的细小。水冷条件下,凝固组织中的碳化物有明显的方向性,碳化物尺寸明显减小,凝固组织中出现了M3C+M7C3混合型碳化物,冷却速度的差异改变了碳化物的类型。     

过共晶离铬铸铁的定向凝固

本文通过定向凝固试验,研究过共晶高铬铸铁的凝固过程和凝固组织,并分析了初晶碳化物的生长过程和分布状态。结果表明,过共晶高铬铸铁中初晶碳化物和共晶碳化物均为(Fe·Cr)7C3型碳化物:初晶碳化物以包抄方式生长,其横截面呈六角形块状;随着凝固速度增加,初晶碳化物的平均直径和片间距均减小。     

冷却速度对稀土中锰白口铸铁组织和性能的影响

研究了冷却速度对稀土中锰白口铸铁组织、机械性能和耐磨性的影响。结果表明,随着冷却速度增加,合金组织中的碳化物数量增加,尺寸减小,分布呈现出明显的方向性,铸件缩松减少,韧性略有降低,耐磨性提高了44．2%。     

复合变质剂对中铬铸铁组织和性能的影响

探讨了在相同试验条件下，变质剂种类及其加入量对中铬铸铁组织和性能的影响。结果表明，由低碳铬铁和稀土硅铁组成的复合变质剂的变质效果最佳，变质后可获得高硬度、高韧性和高耐磨性的中铬铸铁；低碳铬铁和稀土硅铁的变质效果次之。     

微量元素对大断面球铁组织与性能的影响

在实验室条件下,研究了添加一定量的合金A和合金B对φ590 mm×800 mm大断面球铁件组织和性能的影响,结果显示:当合金A的加入量(质量分数)为0.03%时,抑制大断面球铁件中石墨畸变的效果最佳;同时发现:强制冷却能进一步改善大断面球铁件的石墨形态和基体组织。     

灰口铸铁件残余应力的测量与消除

铸件的残余应力影响其尺寸稳定性和性能,甚至会导致铸件失效.采用盲孔法测定铸态、退火态和铸造后砂型保温的灰口铸铁件试样的残余应力.试验结果表明,砂型保温工艺和退火处理一样,能有效地降低铸铁件的残余应力,而且该法工艺简单、成本较低.     

铸态铁素体排气管壳型背丸工艺实践

介绍了壳型背丸工艺生产表面光洁、内部组织致密的排气管铸件的铸造方法.实践表明:在壳型背丸工艺铸型冷却较快的条件下,调整C、Si含量并强化孕育处理能获得基体组织铁素体大于-95％的康明斯排气管铸件.     

The relationship between cooling rate and the structure and properties of hypo-eutectic cast iron

The aim of the present work is to make a correlation between the cooling rate of grey cast iron during solidification and the resulting structure, phases and mechanical properties. Liquid cast iron with a carbon equivalent of 3.92% was cast in sand moulds. Different cooling rates were obtained by changing the casting shape and thickness.

The cooling curves were recorded using a data acquisition system in order to determine the solidification parameters. Some samples were reheated to a temperature above solid state transformation—austenitised (1118 K) and then quenched.

The microstructure was studied in order to determine the phases formed such as graphite, pearlite, ferrite and cementite. Their shape, size and volume fractions were studied. The formation of these phases was correlated with the cooling and solidification parameters. Some mechanical properties, namely hardness and tensile properties, were measured.

Correlation between these properties cooling rate and microstructure parameters are presented.     

Effect of Cooling Rate on Microstructure and Mechanical Properties of Thin-Walled Ductile Iron Castings

This article addresses the effect of cooling rate on microstructure and mechanical properties as determined by changing molding media and section size. The research was conducted for thin-walled iron castings with 2-5-mm wall thickness and for the reference casting with 13-mm wall thickness, using different molding materials (silica sand and insulating sand “LDASC”) to achieve various cooling rates. Thermal analysis was performed to determine the real cooling rate at the beginning of the graphite eutectic solidification. In general, it was found that the predictions based on theoretical analysis of the solidification process of ductile iron are in good agreement with the experimental outcomes. Finally, the present study provides insights into the effect of cooling rate on the graphite nodule count, the ferrite fraction and mechanical properties of thin-walled ductile iron castings. The study shows that the cooling rate of thin-walled castings varies in a wide range (80-15 °C/s) when changing the wall thickness from 2 to 5 mm, accompanied by significantly changing the mechanical properties of ductile iron. The cooling rate can be effectively reduced by applying an insulating sand to obtain the desired properties of thin-walled castings practically in the whole range of ductile iron grades in accordance with the ASTM Standard.     

微量Sn对灰铸铁组织和性能的影响

Sn作为一种合金化元素,在灰铸铁中既可强烈促进珠光体的生成,又可细化珠光体.在实际生产中,由于某些生铁中含有过量的Sn,铸件易产生裂纹或显微裂纹,导致铸件报废.制备了不同Sn含量的铸件试样,并测定了其抗拉和抗弯强度,用金相显微镜观察不同Sn含量对铸件的石墨形态和基体组织的影响,同时详细考察了其铸造性能.结果表明:适量的Sn会促进珠光体基体的形成、细化共晶团,而对石墨的组织和形态无明显的不良影响.同时微量的Sn溶于奥氏体中,降低了发生先共析铁素体和珠光体的温度范围,使收缩率降低.但过量的Sn增加碳化物和磷共晶的数量,同时使灰铸铁的白口宽度增加,使铸件产生硬脆性,从而导致热裂和冷裂,这是铸件产生裂纹的主要原因.在生产中,应采取措施使铸铁中Sn含量控制在0.102％以下,并结合孕育处理等措施改善铸件的组织,提高力学性能.     

Effects of slope plate variable and reheating on semi-solid structure of ductile cast iron

Semi-solid metal casting and forming are known as a promising process for a wide range of metal alloys production. In spite of growing application of semi-solid processed light alloys, a few works have been reported about semi-solid processing of iron and steel. In this research inclined plate was used to change dendritic structure of iron to globular one. The effects of length and slope of plate on the casting structure were examined. The results show that the process can effectively change the dendritic structure to globular. In the slope plate angle of 7.5° and length of 560 mm with cooling rate of 67K·s^-1 the optimum nodular graphite and solid globular particle were achieved. The results also show that by using slope plate inoculant fading can be prevented more easily since the total time of process is rather short.
In addition, the semi-solid ductile cast iron prepared by inclined plate method, was reheated to examine the effect of reheating conditions on the microstructure and coarsening kinetics of the alloy. Solid fraction at different reheating temperatures and holding time was obtained and based on these results the optimum reheating temperature range was determined.     

Effects of forced cooling on mechanical properties and fracture behavior of heavy section ductile iron

To develop materials suitable for spent-nuclear-fuel containers, the effect of forced cooling on mechanical properties and fracture toughness of heavy section ductile iron was investigated. Two cubic castings with different cooling processes were prepared: casting A was prepared in a totally sand mold, and casting B was prepared in a sand mold with two chilling blocks placed on the left and right sides of the mold. Three positions in each casting with different solidification cooling rates were chosen. In-situ SEM tensile experiment was used to observe the dynamic tensile process. Fracture analysis was conducted to study the influence of vermicular and slightly irregular spheroidal graphite on the fracture behavior of heavy section ductile iron. Results show that the tensile strength, elongation, impact toughness and fracture toughness at different positions of the two castings all decrease with decreasing cooling rate. With the increase of solidification time, the fracture mechanism of conventional casting A changes from ductile fracture to brittle fracture, and that of casting B with forced cooling changes from ductile fracture to a mixture of ductile-brittle fracture.