The influence of nickel and copper on the austempering of ductile iron

In the present investigation, the effect of alloying elements on the austempering process, austempered microstructure, and structural parameters of two austempered ductile irons (ADI) containing 0.6% Cu and 0.6% Cu/1.0% Ni as the main alloying elements was investigated. The optical metallography and x-ray diffraction were used to study the changes in the austempered structure. The effect of alloying additions on the austempering kinetics was studied using the Avrami equation. Significantly more upper bainite was observed in the austempered Cu-Ni alloyed ADI than in Cu alloyed ADI. The volume fraction of retained austenite (X _γ), the carbon level in the retained austenite (C _γ), and the product X _γ C _γ in an austempered structure of Cu-alloyed ADI are higher than in Cu-Ni-alloyed ADI. The austempering Kinetics is slowed down by the addition of Ni.     

两相区部分奥氏体化对连续退火双相钢相变过程的影响

将连续退火双相钢部分奥氏体化与完全奥氏体化后的CCT曲线进行对比分析,讨论了部分奥氏体化的影响。结果表明:部分奥氏体化后,该钢铁素体和贝氏体转变区的范围扩大,珠光体转变受到抑制且晶粒尺寸减小,马氏体转变的开始温度从368℃下降到349℃;部分奥氏体化时马氏体的转变温度区域大于完全奥氏体化时的。     

Impact Properties of Copper-Alloyed and Nickel-Copper Alloyed ADI

The influence of austenitization and austempering parameters on the impact properties of copper-alloyed and nickel-copper-alloyed austempered ductile irons (ADIs) has been studied. The austenitization temperature of 850 and 900 °C have been used in the present study for which austempering time periods of 120 and 60 min were optimized in an earlier work. The austempering process was carried out for 60 min for three austempering temperatures of 270, 330, and 380 °C to study the effect of austempering temperature. The influence of the austempering time on impact properties has been studied for austempering temperature of 330 °C for time periods of 30-150 min. The variation in impact strength with the austenitization and austempering parameters has been correlated to the morphology, size and amount of austenite and bainitic ferrite in the austempered structure. The fracture surface of ADI failed under impact has been studied using SEM.     

Effects of Cold-Rolling Reduction on Microstructure,Thickness, Surface Roughness of AS20/20 and on Bending Toughness of AS20/20-Coated Press-Hardened Steel

The tailor-rolling blanks based on Al–Si-coated press-hardened steel (PHS) have attracted much attention along with the development of lightweight vehicles. The properties of Al–Si-coated PHS with single surface weight of 20 g m⁻² change after cold-rolling and then austenitization, which are little studied. Herein, the effects of cold-rolling reduction ratio on the microstructure, thickness, and roughness of AS20/20 coatings, and on the bending toughness of AS20/20-coated PHS, are explored. The overall continuity of the coatings is unchanged as the reduction ratio increases. When the reduction ratio is 30% or above, rapid diffusion channels are formed at the cracks of Al-filled intermetallic compound layer. Meanwhile, the thickness and surface roughness of the coatings are stable and do not decrease. After austenitization, the coatings are structurally consistent with the increase of the reduction ratio. When the reduction ratio is 30% and above, the thickness and surface roughness of the coatings are stable and do not decrease. The rapid diffusion channels lead to an increment in the proportion of FeAl phase to above 96% after austenitization, which makes the bending angle further increase. The bending angle is enlarged by 44% when the reduction ratio is 50%.     

基于ABAUQS-Matlab对42CrMo钢表面感应淬火奥氏体化参数的研究

目的 确定42CrMo钢感应淬火过程的奥氏体相变动力学参数,并验证其可靠性。方法 根据不同加热速率下42CrMo钢奥氏体膨胀曲线,基于经典JMAK（Johnson-Mehl-Avrami-Kolmogorov）模型和Kissinger方法,确定了42CrMo钢奥氏体化相变动力学的参数。建立ABAQUS局部移动式感应淬火模型,选取淬火区域加热过程中点的温度变化曲线作为验证奥氏体化模型的对象。基于Scheil法则和JMAK相变动力学模型,采用文中求解得到的奥氏体化参数,采用Matlab对42CrMo连续转变过程离散为每个时间间隔的等温相变并求解,并对照相关学者采用的扩展解析动力学模型和JAMK模型,加以验证。结果 根据上述方法,得到的42CrMo奥氏体相变动力学参数为：激活能Q为2.04×106 J/mol,指前因子lnk0的值取230.78,Avrami指数n取0.427。将淬火加热过程离散为数量很大的均匀时间间隔,并以求解的动力学模型在每个间隔内进行对应温度条件下奥氏体体积分数的求解并顺次叠加,以模拟得到的奥氏体转变时间和转变温度等作为依据,该模型有良好的表现性。结论 对42CrMo非等温且加热速度不恒定的连续奥氏体转变过程,JAMK模型拟合表现良好,采用文中求解的参数组对表面感应淬火的奥氏体转变历程进行仿真预测是可行的。     

70Cr3Mo钢大型支承辊淬火加热计算机模拟

７０Ｃｒ３Ｍｏ钢大型支承辊最终热处理淬火后辊颈和辊身需得到不同的硬度,因此采用辊颈包覆耐火纤维的加热方法。本文以非线性有限元法为基础,为加热过程了计算机模拟,实现了温度场和相变的耦合计算。比较几种不同情况的计算结果,认为利用原有的台车炉进行差温加热能满足要求,但辊身两端包裹耐火纤维对辊身的加热温芳场影响很大,导致奥氏体层分布不理想,根据模拟结果提出了改进辊颈包覆耐火纤维的方案。     

Formation kinetics of austenite in pearlitic ductile iron

This work evaluated the isothermal transformation of austenite in unalloyed pearlitic ductile iron and drew the isothermal phase diagram of austenitization in the ductile iron. Austenite forms at grain boundaries and then grows up to graphite regions during austenitiza-tion. The formation kinetics of austenite complies with the Avrami equation, in which the parameter (n) ranges from 4.71 to 4.99. The start time and finish time of transformation can be calculated at each temperature using the Avrami equation.     

钢的感应脉冲加热奥氏体均匀化

在高能量密度条件下，对亚共析钢实行感应脉冲淬火。借助电子探针等手段研究了钢的快速加热奥氏体转变动力学，导出了奥氏体均匀化动力学方程     

Carbide Dissolution during Intercritical Austenitization in Bearing Steel

In order to investigate the carbide dissolution mechanism of high carbon-chromium bearing steel during the intercritical austenitization, the database of TCFE7 of Thermo-calc and MOBFE of DICTRA software were used to calculate the elements diffusion kinetic and the evolution law of volume fraction of carbide. DIL805 A dilatometer was used to simulate the intercritical heat treatment. The microstructure was observed by scanning electron microscopy(SEM), and the micro-hardness was tested. The experimental results indicate that the dissolution of carbide is composed of two stages: initial austenite growth governed by carbon diffusion which sharply moves up the micro-hardness of quenched martensite, and subsequent growth controlled by diffusion of Cr elements in M3 C. The volume fraction of M3 C decreases with the increasing holding time, and the metallographic analysis shows a great agreement with values calculated by software.     

奥氏体化时间与冷却速率对超高碳钢组织影响的EBSD研究

本文借助EBSD技术研究了一种超高碳钢在不同奥氏体化时间和冷却速率条件下原奥氏体晶粒和珠光体团簇尺寸的变化规律。实验结果表明：原奥氏体晶粒随奥氏体化时间延长而显著增大;与传统的热蚀法相比。EBSD重构法可以获得更加准确的原奥氏体晶粒尺寸。珠光体团簇尺寸随奥氏体化保温时间延长略微增大,随冷却速率减小而明显增大;与Channel5自动截线法相比,手动截线法可获得更准确的团簇尺寸结果。