Effect of non-zero mean stress bending-torsion fatigue on fracture surface parameters of 34CrNiMo6 steel notched bars

Modern methods of testing materials require the use of the latest technologies and combining measurement and calculation methods. It is important to find a quantitative way of describing, among other things, the failures so that it can help to design with high accuracy. This paper studies loading orientations on crack shape and fracture surface changes. The advantage of the entire fracture surface method is simplicity and applicability in studies on other materials, shapes and loadings. A higher values of fracture surface parameters (Sx, Vx) was observed in failure specimens with lower σ/τ (B/T) ratios. It has been observed that largest crack lengths with a small number of cycles occur for loading combinations different then B=T. As well as analyzed surface parameters Sx, Vx, are higher for larger number of cycles to crack initiation (Ni) values.

Metallurgical Characterization and Kinetics of Borided 34CrNiMo6 Steel

Boriding of 34CrNiMo6 steel was performed in a solid medium consisting of Ekabor-II powders at 1123, 1173 and 1223 K for 2, 4 and 6 h. Morphological and kinetic examinations of the boride layers were carried out by optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The thicknesses of the boride layers ranged from 22±2.3 to 145±4.1 depending on boriding temperature and time. The hardness of boride layer was about 1857 HV0.1 after boriding for 6 h at 1223 K, while the hardness of the substrate was only around 238 HV0.1. Growth rate constants were found to be between 1.2×10−13 – 9.8×10−13 m2/s depending on temperature. The activation energy for boron diffusion was estimated as 239.4±8.6 kJ mol−1. This value was comparable to the activation energies reported for medium carbon steels in the literature.

Analysis of the Effect of Temperature Differences on Surface Hardness and FeB Diffusion Process on DIN 34CrNiMo6 Steel Material Through the Boriding Process

The availability of materials that meet production needs is sometimes not easy to obtain. Material properties must meet the standards are physical properties, including violence. One method is to increase the value of the surface hardness of the material by the boriding process. Boriding is a surface hardening process through the process of diffusion of the substrate, thereby causing the material hardness to increase. The results showed the temperature in the boriding process of DIN 34CrNiMo6 material was proven to affect the surface hardness of the material. The FeB diffusion process begins to form at temperatures of 850°C and 950°C. The optimal temperature for the boriding process is at a temperature of 950°C. Ketersediaan material yang memenuhi kebutuhan produksi terkadang tidak mudah untuk didapatkan. Sifat material harus memenuhi standar adalah sifat fisik material, diantaranya adalah kekerasan. Salah satu metode untuk meningkatkan nilai kekerasan permukaan material dengan proses boriding. Boriding merupakan suatu proses surface hardening melalui proses difusi terhadap substrat sehingga menyebabkan nilai kekerasan material tersebut mengalami kenaikan. Hasil penelitian menunjukkan temperatur pada proses boriding terhadap material DIN 34CrNiMo6 terbukti dapat mempengaruhi kekerasan permukaan material. Proses difusi FeB mulai terbentuk pada temperatur 850°C dan 950°C. Temperatur optimal untuk proses boriding adalah pada temperatur 950°C

Research of Tribological Properties of 34CrNiMo6 Steel in the Production of a Newly Designed Self-Equalizing Thrust Bearing

There are many cases when in large power equipment (such as a turbine or compressor) asymmetrically loading on bearings due to thermal deformations, production inaccuracies, or simple deflection of the shaft occurs. This asymmetrically loading means misalignment of rotor against stator in angle more than several tenths of a degree and it has an influence on a journal and thrust bearings. Over the last few years, thanks to increasingly precise manufacturing, solutions that can eliminate this phenomenon have been revealed. In the case of the thrust bearing, it is a system of very precise manufactured levers, which are in close contact each to other, so they have to be not only properly designed from the geometrical point of view but the important role plays a quality of the functional surfaces of these levers. The article deals with the surface treatment effect on tribological properties of 34CrNiMo6 steel used for the production of bearing levers, which are the critical parts of a newly developing self-equalizing thrust bearing. The samples with cylindrical and plate shapes were produced from 34CrNiMo6 steel as representatives of the most suitable geometries for contact surfaces. All samples were heat-treated. The surfaces of some samples were treated by electroless nickel plating or nitriding, some of the samples were treated by tumbling. Gradually, the surface roughness, microhardness, metallographic analysis and the influence of selected types of surface treatments on the wear for individual samples were evaluated within the research presented in the article. As the testing methods for evaluation of tribological properties were selected Pin-on-disc test and frequency tribological test. The results showed that the best tribological properties achieved samples treated by electroless nickel plating compared with the nitrided or only heat-treated samples.

Effect of Rare Earth Ce on the Microstructure and Mechanical Properties of 34CrNiMo6 Steel for Wind Turbine Main Shaft

The effect of rare earth Ce on mechanical properties is studied by investigating the precipitates evolution during heat treatment of 34CrNiMo6 steel. Five different rare earth Ce contents are carried out with the same holding time 3 hours. Then, the mechanical properties of 34CrNiMo6 steel are obtained under steady state conditions and impact conditions, respectively. The strength decreases while the elongation after breakage increases with the rare earth Ce content increasing. The impact absorbing energy at 20°C and −40°C increases with the rare earth Ce content increasing. Based on the experimental results, the recommended rare earth Ce content is 0.05 wt.%. The differences in mechanical properties among the different rare earth Ce contents may be the nucleation rate and growth of precipitates under different conditions. The spherification degree of cementite is more complete with rare earth Ce content, resulting in the decrease of mechanical properties and improvement of ductility.

The Comparison Research of Plasma Surface Hardening of 34CrNiMo6 Steel Produced on Direct and Reversed Polarity Current

Many product parameters are basically determined by the state of the surface layer of the material from which it is produced. Increasing the hardness of the surface layer with unique core characteristics will significantly improve the performance characteristics of products and expand field of application of 34CrNiMo6 steel. The paper presents the results of a study of the surface plasma hardening of 34CrNiMo6 steel on direct and reversed polarity current. Studies of four possible variants of plasma surface quenching, including processing with scanning and processing in closed arc mode were carried out. The results of measuring geometric characteristics and hardness of the produced hardened layers are given. The possibility of producing hardened layers with a hardness up to 52 HRC is shown. The macro-and microstructure of the produced hardened layers using light microscopy was studied. The features of structure formation in layers hardened in different variants are analyzed. It is shown that it is possible to produce hardened layers with a depth of 1.7 mm and a width of up to 24 mm in the finishing plasma treatment without significant changes in the surface roughness.