工艺因素对球铁曲轴疲劳性能的影响

对经正火、气体氮化、圆角滚压三种工艺的球墨铸铁曲轴进行弯曲疲劳试验，测出其疲劳极限M-1(50％)分别为1471、1935和3010N-m。说明了采用气体氮化工艺的球铁曲轴疲劳强度比正火态提高31％；而采用圆角滚压工艺的球铁曲轴疲劳强度比正火态提高104％。     

我国等温淬火球铁的生产现状及发展前景

介绍我国等温淬火球铁的生产现状、存在问题和发展前景：我国与美国、芬兰一样，从上世纪60年代开始等温淬火球铁的试验研究。目前主要应用于：(1)ADI齿轮：与钢齿轮相比，ADI齿轮成本降低15％，噪声降低1．5～5.3dB，质量降低约10％，接触疲劳强度高，安全系数高，耐磨性高；(2)ADI曲轴：性能明显高于正火球铁曲轴，可以取代合金钢曲轴，满足发动机强化后对曲轴性能的要求；(3)铁道车辆耐磨件，载重汽车弹簧支架，效果明显优于铸钢件；(4)等淬球铁凸轮轴和各种抗磨件。但目前我国ADI产量仍较低，重要领域应用较少，能稳定生产ADI的工厂还不多。主要原因是：①宣传不够和缺乏标准；②球铁铸件生产技术水平满足不了ADI生产要求；③缺乏可靠的热处理设备和专业热处理厂。     

X105系列柴油机球铁曲轴的热应力强化

本文介绍了利用热胀冷缩原理,在球铁曲轴轴颈表层获得压应力,提高曲轴的疲劳强度的热应力强化工艺。对球铁曲轴经热应力强化处理后,残余应力的稳定性、疲劳强度的提高和曲轴的变形等进行了分析讨论。弯曲疲劳试验的结果表明,X105系列柴油机曲轴,经过热应力强化处理,其弯曲疲劳强度可提高50％。由此,我们认为热应力强化法是一种新的有效的球铁曲轴强化方法。     

用非表面强化方法提高铸态球铁曲轴的可靠性

在不采用圆角滚压等表面强化处理的条件下，为使铸态球铁曲轴的弯曲疲劳强度和耐磨性达到技术要求，采取了三个措施：（1）通过合金化和优化铸造工艺，使强度和韧性达到最佳匹配；（2）加大连杆轴颈与曲柄臂的过度圆角；（3）增大曲柄臂的厚度，曲轴弯曲疲劳弯曲强度对比试验和300h台架可靠性试验以及25000km道路试验均证明，采用上述措施制造铸态球铁曲轴的方案既降低曲轴成本，又能使曲轴具有足够的弯曲疲劳强度。     

大排量柴油机曲轴以铁代钢

目前世界上大排量柴油机曲轴多采用钢材，因为其工况条件要求高强度耐疲劳性能。日本马自达公司首先在２．５L排量的高压缩比柴油机曲轴上采用球铁材料，并投入批量生产。采用金属型覆砂无冒口铸造工艺，开发了防粘砂专用型砂。采用圆角滚压工艺提高抗弯曲疲劳强度２倍以上。采用喷丸表面强化处理工艺使扭转疲劳强度提高１５％以上。采用超声发射检测法检验曲轴产品。与钢曲轴相比，成本降低了２％，质量减轻７％。已在商用车上应用。大排量柴油机曲轴以铁代钢     

ADI的疲劳性能

发动机曲轴和齿轮的失效形式属于疲劳失效,因此,疲劳性能是应用ADI曲轴、齿轮首先要考虑的性能.根据破坏原因,曲轴的疲劳强度计算应当是计算连杆轴颈圆角处的最大疲劳强度.齿轮的疲劳强度计算则有两种：齿根部弯曲疲劳强度计算和齿面接触疲劳强度计算.球铁的旋转弯曲疲劳强度随抗拉强度提高而增加,但不呈线性关系.奥氏体-贝氏体型球铁的疲劳强度达到或接近部分碳钢、合金钢经调质处理后的疲劳强度.喷丸处理可以提高ADI的各种疲劳强度.为了提高疲劳强度,抗拉强度与伸长率应合理地配合.     

完善理化检测体系,提高球铁曲轴质量

通过实地调查,理化检测和断裂曲轴分析发现,在球铁曲轴的生产呼环节中,必须充分重视并合理开展理化检测工作,尤其应主重圆角处的质量,避免“〖凭经验生产”;许多曲轴的失效,与理化检测工作开展得不合理有关,加强和完善理化检检测体系,在生产过程中合理地开展理化检测工作,对提高球铁曲轴的质量具有重要意义。     

稀土对曲轴金相组织和力学性能的影响

在用球铁生产曲轴的过程中，采用冲天炉保温炉双联熔炼，严格控制原铁液含硫量≤0.020％t同时在铁液中加入不同量的Cu—Mg型球化剂，进行球化孕育处理后，从本体取样研究残留稀土对曲轴金相组织和力学性能的影响。结果表明：随着残留稀土的增加，曲轴的球化级别逐渐变差、抗拉强度和延伸率也逐渐降低。     

铸态高强韧球铁曲轴材质的开发

在江铃4JB1铸态球铁曲轴的研制中，分析明确了富Si夹杂物是造成曲轴铸件磁痕缺陷的主要原因，采用自制的定量过滤注装置，解决了磁痕缺陷难题；通过在球化剂中加入适量Sb的反应试验，确认了微合金化是提高铸态球铁曲轴韧塑性的有效办法，建立和有效运行质量管理体系是生产合格曲轴的保证。     

高综合性能球铁的研制

通过选用合理的化学成分，严格控制铁液硫、磷的含量，在铁液中适当加入Cu、Mo合金元素，选用低稀土球化剂．并使用盖包法球化处理工艺，采用复合孕育处理工艺，进行部分奥氏体化热处理，成功研制出高强度且具有较高韧性的球铁曲轴。     

我国等温淬火球铁(ADI)生产应用及发展前景

概述了我国等温淬火球铁的生产应用情况,指出我国等淬球铁主要用于三个方面:1)普通抗磨零件,如磨球、衬板、锤头、锤片等;2)承载构件,如斜楔、销套、小型柴油机曲轴等;3)高性能、高精度要求的重要构件,如多缸柴油机曲轴和各类齿轮等。分析了我国等淬球铁扩大应用和工业化生产发展缓慢的主要原因是:1)对等淬球铁的优异性能宣传不够,没有相应的标准提供给设计者;2)大部分球墨铸铁生产厂不能稳定地提供符合等淬球铁要求的球铁铸件;3)缺乏专业的等淬球铁热处理厂和性能先进、稳定的等淬热处理装备。预测了我国等淬球铁的发展前景并对今后工作提出了建议。     

Fatigue Failure of Ductile Iron Crankshafts

Abstract

Automobile crankshafts can be produced as either steel forgings or ductile-iron castings. In the latter case, because of the high structure-sensitivity of fatigue strength, mechanical test requirements must be very specific. A detailed investigation of two series of crankshafts produced from pearlitic nodular-graphite iron, grade SG 60, is described. Normal tensile tests and microstructural examinations were supplemented by determination of fatigue life and fatigue limit. Fatigue tests under axial bending conditions were carried out on segments taken from two series (I, II) of machined crankshaft castings. Satisfactory bending moment and performance data were obtained for one series of samples. In the other series, sub-surface microporosity in the cast structure was exposed during subsequent machining and led to premature fatigue failure after less than 2 × 10⁵ cycles of testing.     

FATIGUE PROPERTIES OF AUSTEMPERED DUCTILE IRON （ADI） IN WATER ENVIRONMENT

The acicular ferrite in austempered ductile iron (ADI) matrix around graphite was corroded preferentially in wet condition, promoting crack origination and propagation and resulting in the disappearance of ADI fatigue limit. ADI fatigue strength was gradually reduced with increasing the time of test and was reduced by 50% in wet condition at 10^7 cycles compared with the fatigue limit in dry condition.The fatigue strength variation of ferritic ductile iron in wet condition was similar to that of ADI.The ferritic ductile iron, however, has better corrosion resistance so that the fatigue strength was lowered only by 10^7 in wet condition at 10^7 cycles compared with the fatigue limit in dry condition. On the other hand, the fatigue limits of ADI and ferritic ductile iron were dropped by 32% and 25% in tap water dipping 480h/dry condition respectively compared with those in dry condition.The reduction of fatigue limit was attributed to corrosion pits formation correlated with stress concentration, resulting in origination and propagation of fatigue crack.     

Oil quenched malleable iron,the strength of an old material in a “green cast” development and a new future

Malleable iron lost the interest and the development stopped in the turbulent seventies of tremendous developments of new technologies.The personal computer,emission spectrometer,thermal analysis,cold-box core system and automatic vertical moulding were introduced into the foundry industry.Experience shows that these new technologies do not always match up with malleable iron.Solidification and mould filling simulation programs are not always capable to handle a low carbon equivalent iron like malleable iron.Recent developments show however by using these new technologies and combined with practical experience,it is possible to increase the casting yield of malleable iron to the same level as ductile iron.The mechanical properties,especially the yield strength of malleable iron according to the standard are equivalent to those of ductile iron,however the yield strength of oil quenched malleable iron is significantly higher than that of ductile iron.An extensive investigation is made between ductile iron,air quenched and oil quenched malleable irons based on the properties of more than 350 test bars produced under the same conditions.The results are compared with the existing international standards and discussed.Other properties like fatigue strength and response to surface treatments as induction hardening are also discussed.The costs of malleable iron are reviewed and compared with other ferro alloys.These recent developments in increasing the casting yield,the understanding of the strength,makes malleable iron competitive with ductile iron and cheaper than the first grade of ausferritic ductile iron,or steel qualities.It is possible to design lighter and save weight which is essential in the automotive industry.An example of"green cast"development for typical applications,used in automotive transmissions and engines are shown.     

压缩机曲轴铸件水冷金属型铸造工艺

介绍空调压缩机球墨铸铁曲轴水冷金属型铸造工艺,提出了水冷金属型铸造工艺参数的控制范围,认为金属型生产过程中严格控制铁液质量和浇注工艺参数是减少铸造缺陷的有效措施。通过对化学成分、球化处理、随流孕育、铸型涂料、铸件热处理等方法进行了综合技术工艺设计与控制,在消除白口组织、获得珠光体球墨铸铁曲轴方面取得     

Effect of C and Si on mechanical properties of austempered ductile iron

It is well known that ductile cast iron can be strengthened and toughened by austempering. The tensile strength and the fatigue strength of austempered ductile iron (ADI) are equal to those of forged steel. Previous studies have been aimed at establishing a suitable process to obtain both strength and toughness in ADI.^1,2 These studies focused on the effect of alloying such as Mo, Ni, Mn, Cu, etc. and the austempering conditions such as temperature and holding time. In this study, a new type of ADI with higher toughness and higher elongation was developed as compared with conventional ADI. A new type of ADI with a low carbon content was achieved by reducing the initial carbon content, long annealing and ordinary austempering. The suitable silicon content was found to be 2.5% and effective alloying was 0.25% Mo and 0.7% Cu to obtain maximum impact energy and elongation.     

奥-贝球铁疲劳损伤过程的在线跟踪分析

应用系统分析的方法，通过三点弯曲疲劳试验，跟踪监测了奥-贝球铁试样的疲劳损伤过程。实验结果表明，在循环加载过程中，奥-贝球铁中石墨球与基体组织间的界面首先发生疲劳损伤开裂，在多数情况下疲劳裂纹并不在界面开裂处萌生，进一步的疲劳损伤是由于界面的开裂不同程度影响了基体组织内的滑移等塑性变形，并在基体内萌生疲劳裂纹。试验表明奥-贝球铁中石墨球与基体组织间的界面具有一定的疲劳强度。