铸铁的激冷试验

激冷试验是评价铸铁石墨化倾向的一种方法。当铸铁迅速凝固或通过快速冷却被故意激冷时就形成白口而成为硬的白口铸铁。铸件截面中形成的白口数取决于铸件截面尺寸、铸铁化学成分和生产因素,如孕育工艺和过热程度。用于测定特定铸铁中白口数的激冷试样,也可用     

含Al铸铁的金属型铸造

1、绪言一般来说,在高温范围,铸铁的利用受到限制。主要原因在于因加热导致抗拉强度等物理性质恶化及生长性和氧化性。笔者等报导了引人注目的金属型微细共晶状石墨铸铁的耐生长性与高强度,以及用添加Al的方法增加基体耐氧化性能可以制造新的耐热材料。另外找出这种铸铁材料是根据Al的石墨化促进作用能制造出来的不孕育、不刷涂料、没有激冷的金属型铸铁这是个非常有趣的结果。本文报导使C、Si及Al的组成变化,在不孕育,不刷底层涂料的金属型中浇注,然后根据铸铁组织的观察来探索为获得无激冷铸铁的最适合的Al添加量,同时也对含Al无激冷铸铁的机械性能进行了探讨。     

EQ153汽车凸轮轴石墨层的形成机理探讨

分析了激冷铸铁EQ153汽车凸轮轴中石墨层的金相组织及成分分布，认为石墨层的产生是由于铁水在结晶过程中产生成分偏析的结果。     

孕育剂加入量对激冷铸铁凸轮轴组织性能的影响

在激冷铸铁凸轮轴生产过程中，适当地加入孕育剂可以有效减小桃尖处白口深度。鉴于此，研究了孕育剂量对凸轮轴组织性能的影响。结果显示，在轴颈部位碳化物≤15％的条件下，降低孕育剂量可有效减少激冷层的石墨数量，提高激冷层的硬度；同时，可增加铁液激冷敏感性，有利于凸轮轴的生产控制。     

铸铁凸轮轴的激冷与性能研究

研究了 EQ140激冷铸铁凸轮轴的激冷方式及铸造工艺、合金成分对激冷层硬度、激冷深度及金相组织的影响。试验表明,激冷铸铁凸轮轴具有良好的耐磨和抗擦伤性能。     

热处理工艺参数对激冷铸铁组织性能的影响

通过改变激冷铸铁的热处理工艺,研究淬火加热温度、保温时间对其白口层中石墨含量变化的影响,以及对硬度和耐磨性的影响.     

一种新型铸铁热分析试样的激冷剂材料配比和加入方法

在试样白口化前提下，研究了一种新的铸铁热分析试样激冷剂的配比、与冷却曲线上相变段倾角的关系。结果表明，能使相变段倾角最小的激冷剂材料配比，能够提高对铸铁成分的热分析精度。     

石墨形状沿层深依次变化的铸铁玻璃模具的试验研究

本文总结了在实验室条件下石墨形状沿截面变化的铸铁玻璃模具的试验研究结果。表明,影响最显著的工艺因素是铁水的球化处理程度和铸件凝固速度(本试验条件下主要指冷铁芯的厚度)。通过对模拟罐头瓶模具的试验已能获得在内腔激冷面有5～8mm厚球墨层其余为蜗墨和片墨层的铸件。     

硫对熔融铸铁中未溶解石墨的石墨核生成及成长的影响

1、序言铸铁在感应炉熔化中,适当提高含S量后,若在后期添加增碳剂,激冷急剧减少。其理由可认为是,S延迟了增碳剂在铁水中的分散和溶解,凝固时残存的未溶解石墨成为析出石墨核生成及成长基底。关于S对增碳剂的溶解延迟作用已经报导过,故本文论述未溶解石墨与石墨核生成及成长有关的实验结果。     

稀土La对激冷铸铁凸轮轴组织性能的影响

在激冷铸铁凸轮轴生产过程中适当地加入孕育剂可以有效减小桃尖处白口深度。研究了稀土La对凸轮轴组织性能的影响。实验结果显示,稀土La能有效减小白口深度,提高铸件的力学性能;在轴颈部位碳化物≤15%的条件下,随着稀土La加入量的增加,形成石墨能力越来越强,石墨长度也增加,并且以A型石墨为主;同时,增加稀土La加入量能降低铁液激冷敏感性,不利于凸轮轴生产控制。     

Mathematical model for austenitization kinetics of ductile iron

A mathematical model was developed in the current study to understand the progress of austenitization process in ductile irons. The austenitization time required to produce homogeneous austenite in a two-phase region of austenite and graphite has been estimated in terms of (a) time required for transformation of matrix to austenite and (b) time required for dissolution of graphite in austenite to attain uniform carbon content, which remains in equilibrium with graphite. The time required been related to the structural parameters of cast ductile iron-like radius of graphite nodule, radius of austenite cell, volume fraction of graphite, volume fraction of ferrite in cast matrix, and diffusion constant. The model was used to determine the minimum austenitization time required to achieve homogeneous austenite in three commercial ductile irons when austenitized at a temperature of 900 °C. The results were compared with those obtained. The uniformity of the carbon content in austenite of ductile iron was verified indirectly by measuring microhardness.     

等温淬火球墨铸铁的滑动磨损

研究了奥贝球铁、下贝球铁及与其基体组织相同的钢的滑动磨损性能。实验结果表明 :在一定条件下 ,石墨对等温淬火球铁耐磨性无补而有损。由于奥贝球铁的转折载荷随摩擦速度的提高而增大 ,当转速为 980r/min ,载荷 >6 8 6N时 ,等温淬火球铁的耐磨性优于钢     

Precipitation and evolution of nodular graphite during solidification process of ductile iron

The quantity and morphology of spheroidal graphite have an important effect on the properties of ductile iron,and the characteristics of spheroidal graphite are determined by the solidification process.The aim of this work is to explore the precipitation and evolution of graphite nodules in hypoeutectic,eutectic,and hypereutectic ductile irons by thermal analysis,liquid quenching and metallographic technique.Results show that hypoeutectic ductile iron has the longest solidification time and the lowest eutectic temperature;eutectic ductile iron has the shortest solidification time;hypereutectic ductile iron has the highest eutectic temperature.After solidification is completed,hypoeutectic ductile iron has the lowest nodule count,nodularity and graphite fraction;eutectic ductile iron has the highest nodule count,nodularity and the smallest nodule diameter;hypereutectic has the highest nodule diameter and graphite fraction.The nucleation and growth of graphite nodules in hypereutectic ductile iron starts before bulk eutectic crystallization stage,however,the precipitation and evolution of graphite nodules of hypoeutectic and eutectic ductile irons mainly occur in the eutectic crystallization stage.The graphite precipitated in eutectic crystallization of hypoeutectic,eutectic,and hypereutectic ductile irons,are 61%,68% and 43% of total graphite volume fraction,respectively.Simultaneously,there are plenty of austenite dendrites in hypoeutectic and hypereutectic ductile irons,which are prone to shrinkage defects.Therefore,the eutectic ductile iron has the smallest shrinkage tendency.     

合金元素对铸铁共析转变的影响

介绍了铸铁共析转变的概念、特点和转变产物;说明了没有其他合金的铸铁共析转变时,奥氏体中富余碳的去向问题;阐明了合金元素对铸铁共析转变温度、转变产物的影响情况和珠光体形成与生长机理;提出了降低铸件断面敏感性的途径.     

过共晶球铁凝固过程中奥氏体的生长方式与形貌特征

采用着色腐蚀技术显示出过共晶球铁中的高温凝固组织，观察分析过共晶球铁凝固过程中奥氏体的生长方式与形持征。结果表明：在非平衡凝固条件下，过共晶球铁凝固时通常会析出初生枝晶和晕圈枝晶，其形成条件主要与冷却速率和熔体的过冷有关。随铸件模数Mc增大，枝晶数量减少，二次臂间距显著增大，形态趋于不发达，由初生枝晶向晕圈枝晶过渡。当Mc≤0.3cm时，二次臂间距的实测值与理论预测值基本吻合。初生石墨球周围往往形成环状封闭奥氏体壳；共晶前期石墨球周围形成封闭或不封闭的框架奥氏体壳；共晶后期石墨球往往被周边生长着的共晶奥氏体所包覆，最终成为共晶奥氏体的一部分。     

Characteristics of the Transformation of Retained Austenite in Tempered Austempered Ductile Iron

Controlling the amount of retained austenite is a concern in austempered ductile iron formation. Retained austenite has a strong influence on austempered ductile iron properties, such as hardness and wear resistance. In this research, the characteristics of the transformation of retained austenite were investigated as a function of the number of tempering cycles. The hardness of the austempered ductile iron samples was measured, and the specific amount of retained austenite was analyzed by x-ray diffraction (XRD). Wear tests were conducted on a ball-on-flat sliding fixture. The tempering process was found to have no effect on the hardness of the austempered ductile iron samples. This may be due to retained austenite being partially converted into brittle quenched martensite during the tempering process. However, tougher tempered martensite was also formed from existing martensite. The two effects seemed to offset each other, and no significant differences occurred in overall hardness. XRD analysis showed that under the same austempering temperature and holding time, the amount of retained austenite decreased with additional tempering cycles. Also, with the same holding time and tempering cycles, less retained austenite was contained in the matrix at higher austempering temperatures. This was due to more high carbon content austenite and needle-like ferrite being present in the austempered ductile iron matrix. In addition, tempered austempered ductile iron exhibited significantly higher wear resistance as compared to traditionally treated ductile iron.     

大断面球铁件电炉熔炼工艺及石墨畸变机理研究

探讨了大断面QT600-3球铁件电炉熔炼生产工艺的技术要点,检测了试生产条件下球铁单铸试块与本体试块的化学成分、金相组织与力学性能,基于石墨结晶核心和石墨形态的分析,探讨了石墨畸变机理。生产试验结果表明:炉外增Si预处理增加铁液成核,轻、重稀土混合使用作为球化剂,侧重后期孕育,适当降低浇注温度,合理使用Cu元素,是电炉熔炼工艺生产大断面球铁件的重要环节;采用电炉熔炼工艺生产大断面球铁件,球化等级与化学成分稳定控制有关,抗拉强度、伸长率等力学性能与化学成分、基体组织有关;Y在铁液中形成高熔点Y2O3作为石墨析出的核心,可获得良好石墨形态;大断面球铁件中,Ti、Cu元素的偏析和球化元素Mg或稀土(Y、La、Ce)的氧化,破坏了奥氏体壳的稳定性,是造成石墨畸变的主要原因。     

高镍球铁同质电焊条焊缝组织形成规律

针对铸铁在焊接过程中焊缝易产生白口、裂纹和淬硬组织等技术难题.采用自制高镍球铁同质电焊条,探索了高镍球铁同质焊缝组织形成规律及其与接头力学性能的相关性.结果表明,焊缝组织由分枝细小的柱状奥氏体枝晶+球状石墨+少量晶间碳化物组成.焊接电流的增大使焊缝中柱状晶变得粗壮,石墨球化率升高,晶间碳化物数量增多.当焊接电流一定时,随着预热温度的增大,石墨形态变差,碳化物数量增多,接头抗拉强度减小而硬度增大.采用大电流不预热焊接工艺可以获得综合性能优良的铸铁同质焊缝.     

球墨铸铁件铁素体与珠光体形成的数值模拟

通过对球墨铸铁件共析转变的分析,改进了球铁件中铁素体与珠光体形成的数学模型。其中提出了合金影响因子,考虑了合金元素对铁素体生长的影响。对实际汽车制动臂球铁件进行模拟,并取样进行定量金相实验分析,对模拟结果进行验证。结果表明,改进的模型可以更准确地预测球铁中铁素体和珠光体的数量,能够准确地体现共析阶段过冷情况和共晶球墨数对珠光体数量的影响。     

高强高韧合成球墨铸铁的组织及力学性能

以废钢为主要原材料(20%生铁+20%回炉料+60%废钢),使用中频感应电炉熔炼,采用中间加入和镜面加入联合增碳方式,制备了合成球墨铸铁QT450-23铸件。合成铸铁球化级别1级,球化率95%,石墨圆整,球径10～20μm,基体为100%铁素体。合成铸铁抗拉强度为450MPa,伸长率为23.3%。在高温组织中,奥氏体枝晶发达,显著提高材料的冲击韧性,V型缺口冲击试样常温冲击韧性为18.4 J/cm2,是相同成分和工艺条件下,传统生铁为主配方球铁的2倍。