Microstructure and mechanical properties of Hadfield steel matrix composite reinforced with oriented high-chromium cast iron bars

To obtain a compatible material of high hardness and high toughness, Hadfield steel matrix was reinforced by oriented high-chromium cast iron bars. The mechanical behaviors of the as-cast and water-quenched composites were comparatively studied with a Hadfield steel substrate. The experimental results showed that the alloy powders inside the flux-cored welding wires could be melted by the heat capacity of Hadfield steel melt and became high-chromium cast iron bars. The impact toughness of the water-quenched composite was higher than that of the as-cast composite and lower than that of the Hadfield steel. The wear rate of the water-quenched composite was 1.23 mg/h m² at 0.3 kg and 2.93 mg/h m² at 1.2 kg, which was lower compared with those of the as-cast composite and Hadfield steel. The impact toughness and wear resistance of the water-quenched composite were related not only to the combining actions of the Hadfield steel matrix and high-chromium cast iron bars but also to the effect of heat treatment. The wear behavior of the water-quenched composite was industrially tested as pulverizer plate.     

Microstructure and wear resistance of spray formed and conventionally cast high‐chromium white iron

A billet of hypoeutectic high‐chromium white iron (19% Cr, 2.5% C) was spray formed using Gas‐to‐Metal Ratios (GMR) of 0.9, 1.0, and 1.1. Microstructural studies and dry sand rubber wheel abrasion tests were carried out, on the one hand, to compare between the spray formed and conventionally cast material and, on the other hand, to investigate the relationship between gas‐to‐metal‐ratio, eutectic carbide morphology and abrasion resistance. The spray formed material was characterized by a considerably finer carbide morphology (max. ?30 μm) than the conventionally cast material (max. 100–200 μm). The coarser carbide morphology is believed to be responsible for the superior abrasion resistance of the conventionally cast material. Although the carbide morphology of the spray formed material was only moderately influenced by the changes in the gas‐to‐metal‐ratio, there was a clear improvement in the abrasion resistance with decreasing gas‐to‐metal‐ratio. The improvement correlated with a decrease in the fraction of very fine (<1.5 μm) carbides, rather than with an increase in the mean carbide size.     

16Cr2Mo1Cu高铬铸铁在亚临界处理中硬化行为研究

研究了亚临界处理对16Cr2Mo1Cu高铬铸铁的组织转变和性能的影响,并利用X射线衍射分析、磁性法和硬度测定法分析了硬化机制.研究表明:16Cr2Mo1Cu高铬铸铁的铸态组织由残余奥氏体、马氏体和M7C3型共晶碳化物组成,其相对含量分别为77.0%,7.2%和15.8%;在亚临界处理过程中,基体组织中的残余奥氏体析出二次碳化物并在冷却过程中转变为马氏体,使该合金在560～600℃的亚临界处理过程中出现二次硬化;在适当的处理温度和保温时间下,16Cr2Mo1Cu高铬铸铁可得到最高的硬度.     

Electron microscopy and hardness study of a semi-solid processed 27 wt%Cr cast iron

A semi-solid processed 27 wt%Cr cast iron was studied by electron microscopy and its microstructure was related to the hardness. In the as-cast condition, the primary proeutectic austenite was round in shape while the eutectic M₇C₃ carbide was found as radiating clusters mixed with directional clusters. Growth in the [0 0 1]M₇C₃ with planar faces of {0 2 0}M₇C₃ and was usually observed with an encapsulated core of austenite. Destabilisation heat treatment followed by air cooling led to a precipitation of secondary M₂₃C₆ carbide and a transformation of the primary austenite to martensite in the semi-solid processed iron. Precipitation behaviour is comparable to that observed in the destabilisation of conventional cast iron. However, the nucleation of secondary M₂₃C₆ carbide on the eutectic M₇C₃ carbide was observed for the first time. Tempering after destabilisation led to further precipitation of carbide within the tempered martensite in the eutectic structure. The maximum hardness was obtained after destabilisation and tempering heat treatment due to the precipitation of secondary carbides within the martensite matrix and a possible reduction in the retained austenite.     

The thermal fatigue resistance of vermicular cast iron coupling with H13 steel units by cast-in process

This paper focuses on improving the thermal fatigue resistance on the surface of vermicular cast iron coupling with inserted H13 steel blocks that had different cross sections, by cast-in processing. The microstructure of bionic units was examined by scanning electron microscope. Micro-hardness and thermal fatigue resistance of bionic samples with varied cross sections and spacings were investigated, respectively. Results show that a marked metallurgical bonding zone was produced at interface between the inserted H13 steel block and the parent material – a unique feature of the bionic structure in the vermicular cast iron samples. The micro-hardness of the bionic samples has been significantly improved. Thermal resistance of the samples with the circular cross section was the highest and the bionics sample with spacing of 2 mm spacing had a much longer thermal fatigue life, thus resulting in the improvement for the thermal fatigue life of the bionic samples, due to the efficient preclusion for the generation and propagation of crack at the interface of H13 block and the matrix.     

Nondestructive evaluation of cementite content in steel and white cast iron using inductive Barkhausen noise

A nondestructive testing method for the determination of the cementite content in iron-carbon steel and white cast iron is presented. The method is based on micromagnetic measuring parameters derived from inductive Barkhausen noise measurements taken under room temperature and with temperatures above the Curie temperature. The influence of different cementite contents and cementite modifications on the micromagnetic measuring quantities for steels with ferritic, pearlitic, martensitic annealed and martensitic soft annealed microstructure states and for white cast iron was determined. Cementite actively produces its own inductive Barkhausen noise and also influences the Barkhausen noise of the iron matrix both as a foreign body and by its stress fields of the second kind. Each influence has a different effect on steel and on white cast iron. It was shown that parameters derived from the Barkhausen noise can be used for determining the cementite content if the microstructure state is known. Moreover, when the steel grade is known, the microstructure state can be detected from the pattern of the Barkhausen noise curve by means of simple pattern recognition.This paper is dedicated to Prof. Dr. phil. Paul Hoeller ( Feb. 21, 1996), former director of the IZFP. Prof. Hoeller supported especially the scientific research work described in this article.     

两种高铬铸铁在热强碱中受冲刷时的腐蚀行为

为考察不同材料在热强碱中的腐蚀和磨损腐蚀行为,用电位线性扫描方法测定了Cr13和Cr26两种高铅铸铁在静态和动态的模拟介质中的极化曲线．研究结果表明：动态条件下的腐蚀电流密度比静态条件下约大两个数量级;在动态冲刷条件下,铸铁材料的表面始终处于活化状态,磨损腐蚀速率远大于纯腐蚀速率;Cr26抗磨损腐蚀的性能优于Cr13．     

铸铁电火花沉积WC-8Co超细涂层的组织及性能

采用电火花沉积技术,在铸铁表面制备WC-8Co沉积涂层。利用XRD、SEM、显微硬度计、摩擦磨损试验机研究了涂层的微观组织及耐磨性能。结果表明,通过优化的沉积工艺参数可以获得组织均匀、致密且与基体呈冶金结合的沉积层。沉积层主要由Co3W3C、Fe3W3C、W2C和Fe7W6相组成;沉积层中弥散分布有大量的超细碳化物颗粒。沉积层的最高硬度为1512.1Hv,其耐磨性能是基体的2.3倍;沉积层的磨损机制主要是磨粒磨损和疲劳磨损。涂层中弥散分布的超细硬质相是沉积层硬度及耐磨性能提高的主要因素。     

微米、亚微米高铬铁基纤维的结构和热稳定性

研究了热处理对高铬铁基纤维样品的结构和磁性的影响.微米级、亚微米级高铬铁基纤维由Cu-11Fe-4Cr原位复合丝材硝酸法萃取得到.采用X-射线衍射和扫描电镜观察分析了样品的结构和形貌,采用振动样品磁强计测试了样品的磁性,利用热重-差热分析比较了不同变形量的高铬铁基纤维在空气中的热稳定性.结果表明,在空气中低于400 ℃加热1 h后,高铬铁基纤维保持BCC结构不变,样品的饱和磁化强度均大于103 A·m2·kg-1;经800 ℃加热1 h后,由铁磁性的α-(Fe,Cr)固溶体转变为顺磁性的(Fe,Cr)2O3,样品的饱和磁化强度显著下降.随着变形量增大,较细的高铬铁基纤维的热稳定性较差.微米级、亚微米级高铬铁基纤维的热稳定性显著高于微米级多晶铁纤维.     

灰铸铁表面高功率CO2激光硬化行为的研究

利用正交试验法研究了高功率ＣＯ２激光工艺参数对灰铸铁硬化效果的影响。通过扫描电镜观察了熔化处理试样在熔池不同部位的组织特征，利用显微硬度计测定了硬化层硬度的分布规律。采用计算机回归处理分析得出了Ｐ、Ｄ、Ｖ、Ｅ对硬化层面积大小因子ｔＢ影响的表达式，并讨论了熔池各部位组织的成因。研究结果为高功率ＣＯ２激光强化处理大尺寸灰铸铁模具提供了一定的依据。     

Fracture toughness and growth of short and long fatigue cracks in ductile cast iron EN‐GJS‐400‐18‐LT

Heavy components of ductile cast iron frequently exhibit metallurgical defects that behave like cracks under cyclic loading. Thus, in order to decide whether a given defect is permissible, it is important to establish the fatigue crack growth properties of the material. In this paper, results from a comprehensive study of ductile cast iron EN‐GJS‐400‐18‐LT have been reported. Growth rates of fatigue cracks ranging from a few tenths of a millimetre (‘short’ cracks) to several millimetres (‘long’ cracks) have been measured for load ratios R=?1, R= 0 and R= 0.5 using a highly sensitive potential‐drop technique. Short cracks were observed to grow faster than long cracks. The threshold stress intensity range, ΔK_th, as a function of the load ratio was fitted to a simple crack closure model. Fatigue crack growth data were compared with data from other laboratories. Single plain fatigue tests at R=?1 and R= 0 were also carried out. Fracture toughness was measured at temperatures ranging from ?40 °C to room temperature.     

Dual metal crankshaft for heavy‐duty engines by cast‐joining of DCI and forged steel

An alternative design of a crankshaft applicable for heavy‐duty diesel engines up to 5000 horsepower has been introduced to achieve cost effectiveness and manufacturing efficiency simultaneously not sacrificing its reliability. Because it is expensive and time consuming to make full‐scale prototype and run a test, analytical feasibility study has been made in this paper. From the point of material, cast‐joined dual metal for a crankshaft is totally unprecedented and will be realized by virtue of the latest dual metal cast joining of ductile cast iron (DCI) and forged steel, which consequently reduces the manufacturing lead time dramatically. The strength of the dual metal interface is experimentally investigated to make sure its possibility and soundness. The key features of the new crankshaft include crankpins and journals made of forged steel and crankwebs of DCI. Prior to actual manufacturing of the new conceptual crankshaft, the design is analytically examined to verify its reliability in an existing heavy‐duty engine. Both conventional and the new dual metal crankshafts are investigated and compared to each other in terms of the stress and fatigue using comprehensive multi‐body dynamic analysis. The results demonstrate that the new dual metal approach is likely to provide higher reliability than the conventional monometallic crankshafts. In addition, it is shown that the inferior mechanical properties of DCI for a crankweb are effectively countered by the superior characteristics of forged steel for a crankpin and journal in the dual metal crankshaft.     

1010‐cycle fatigue properties of 1800 MPa‐class JIS‐SUP7 spring steel

10¹⁰‐cycle fatigue tests were conducted at 100 Hz for three years and at 20 kHz for one week on 1800 MPa‐class JIS‐SUP7 spring steel. Uniaxial tests up to 10⁸ cycles were also conducted at 120 and 600 Hz. The 120 Hz tests had larger control volumes. The fatigue limit at 10¹⁰ cycles was lower than at 10⁸ cycles, and any frequency effect was shown to be negligible. A size effect was found; the tests with larger control volumes showed results of lower fatigue strength.     

Mechanical,Chemical and Tribological Properties of the Nickel‐free High‐Nitrogen Steel X13CrMnMoN18‐14‐3 (1.4452)

Mechanische, chemische und tribologische Eigenschaften des Ni‐freien, hoch stickstoffhaltigen Stahls X13CrMnMoN18‐14‐3 (1.4452) Aufgrund der Probleme mit möglichen Ni‐Allergien besteht in der Medizintechnik die Forderung nach Ni‐freien Werkstoffen. Neben den bekannten Co‐ und Ti‐Basis Legierungen bieten die Ni‐freien hochstickstoffhaltigen Stähle eine kostengünstige Alternative. Der Stahl X13CrMnMoN18‐14‐3 (1.4452) ist ein Vertreter aus dieser Gruppe und wird in diesem Beitrag im lösungsgeglühten Zustand auf seine Korrosions‐, Ermüdungs‐ und Verschleißeigenschaften in Ringer Lösung untersucht und diskutiert. Im Vergleich zum üblichen medizinischen Edelstahl X2CrNiMo18‐15‐3 zeigt der 1.4452 unter allen Beanspruchungen bessere Eigenschaften. Das günstigere Ermüdungsverhalten wird durch die niedrige Stapelfehlerenergie bestimmt, während die besseren Korrosionseigenschaften auf den gelösten N zurückzuführen sind. Das sehr gute Gleitverschleißverhalten im artgleichen Kontakt wird durch das Zusammenwirken von beiden erreicht. Berücksichtigt man weiterhin das nicht‐zytotoxische Verhalten, kann man den Stahl 1.4452 als tauglich für medizinische Anwendungen bezeichnen.     

Non‐destructive evaluation of fatigue damage and fatigue crack initiation in type 316 stainless steel by positron annihilation line‐shape and lifetime analyses

Rotating bending fatigue tests were conducted using type 316 stainless steel. The fatigue tests were periodically terminated, and fatigue damage and fatigue crack initiation were non‐destructively and sequentially evaluated by positron annihilation line‐shape and lifetime analyses. The counter‐jig and anticoincidence methods were used for positron annihilation line‐shape and lifetime analyses, respectively, to enhance the analytical precision. The fatigue crack lengths were monitored by a plastic replication technique, and related to the parameters in both analyses. S‐parameter obtained in the line‐shape analysis increased with increasing fatigue damage, while it was difficult to detect fatigue crack initiation and subsequent small fatigue crack growth. That was because the precision of line‐shape analysis was limited. On the other hand, both fatigue damage and fatigue crack initiation were successfully detected by lifetime analysis. Positron annihilation lifetime also increased with increasing fatigue damage, and lifetime was longer at the notch root with fatigue crack than at the smooth section without crack. It was considered that the precision of lifetime analysis was high enough to detect high dislocation density areas at the fatigue crack tips.     

Effects of type of shielding gas upon local mechanical properties of laser welded joint in heat‐treatable steel

Small additions of oxygen or carbon dioxide to argon shielding at laser beam welding can increase welding speed and productivity and decrease the mechanical properties of welded joints. The effect of the type of active shielding gas mixtures based on argon with additions of oxygen and/or carbon dioxide upon the local mechanical properties of laser welded joints of heat‐treatable steel 25 CrMo 4 was studied. Microshear test method has been used to investigate the local mechanical properties of welded joints, including microshear strength, microshear plasticity and microshear thoughness. The obtained data were statistically processed, and a mathematical modeling of mechanical properties applying the method of response surfaces was carried out. The analysis revealed that the impact of the used shielding gas mixtures upon the local mechanical properties of the joint is not very significant. The results indicate that the microshear test can be used successfully for estimation of the local mechanical properties distribution of laser welded joints.