Nodular cast iron (GJS) represents one of the most widely used materials for vehicle, energy and heavy machinery industry. Nevertheless, foundries struggling with the influence of local material ...defects in GJS like pores, shrinkages and dross often leading to a locally reduced fatigue strength of the entire component. One measure to tackle those negative effects is the welding of the affected areas. This measure is then successful when locally achieved material strengths and surface qualities are higher than the component with the casting defect. Unfortunately, data for the lifetime and fatigue assessment of welded GJS are not present right now. Thus, the research project »nodularWELD« assessed the local stress- and strain-based fatigue data of different thick-walled GJS grades for building a basis for a successful usage even of defect affected components. So, three ferritic and pearlitic GJS grades were investigated in the heat-affected zone, the base material, the welding filler and more over in an integral material state comprising all those three aforementioned states based on axial and bending investigations. Additionally metallographic and fractographic analysis were conducted.
This research investigates the nickel content added by 1.1wt%, 2.2wt%, 3.7wt% and 4.5wt% on the microstructure and mechanical properties in the nodular cast iron. The results demonstrate that the ...microstructure of nickel addition consists of nodule graphite, ferrite and pearlite phase while nickel was added to 4.5 wt% the microstructure becomes ferrite transform to fully pearlite phase. In addition the ductile iron has the highest nodularity (0.79%), followed by 1.1%Ni (0.75%), 2.2%Ni (0.71%), 3.7%Ni (0.69%) and 4.5%Ni (0.58%). The hardness and tensile strength increase when increasing the nickel content. Elongation is enhanced with nickel increasing and reaches a maximum of 12% at 1.1 wt% Ni, then decreases with the further increase of nickel.
This study deals with the evaluation of corrosion resistance and other utility properties of selected austenitic nodular cast irons and their comparison with other (non-austenitic) nodular cast ...irons. For the investigations, two types of austenitic nodular cast iron were selected: nickel-manganese nodular cast iron EN-GJSA-XNiMn13-7 and nickel-chromium nodular cast iron EN-GJSA-XNiCr20-2. Basic mechanical properties, such as yield strength, tensile strength, elongation, absorbed energy and hardness, were evaluated using mechanical tests. The fatigue limit was determined using low-frequency fatigue tests. Corrosion properties, such as average corrosion rate, corrosion potential and corrosion current density, were determined by the exposure immersion test and the electrochemical potentiodynamic polarisation test. Both corrosion tests were performed in a 3.5% NaCl solution (to simulate seawater) at room temperature. The results of mechanical, fatigue and corrosion tests show that austenitic nodular cast irons have lower strength and fatigue properties but significantly higher plastic properties and corrosion resistance compared to non-austenitic nodular cast irons.
In this article, the influence of plasma nitriding on the fatigue behavior and fracture mechanisms of the GJS700 nodular cast iron has been investigated. Factors contributing to this influence, which ...included the microstructure, the phase detection, the surface roughness, and the hardness of the plasma‐nitrided specimens were discussed. Moreover, rotating‐bending high‐cycle fatigue testing was also done on standard samples, and then the field‐emission scanning electron microscopy was also utilized to find the failure mechanism on fracture surfaces. Obtained results demonstrated that the average surface roughness and the Vickers micro‐hardness increased by plasma nitriding, compared to the base material. However, fatigue lifetimes decreased in plasma‐nitrided samples due to the increase in the surface roughness and the formation of a compound layer. On the fracture surface, micro‐cracks, cleavage planes, and fatigue striations were observed. Debonding of the graphite from the matrix in all specimens was a dominant cause of the failure.
Nodular cast iron (GJS) represents one of the most widely used materials for vehicle, energy and heavy machinery industry. Nevertheless, foundries struggling with the influence of local material ...defects in GJS like pores, shrinkages and dross often leading to a locally reduced fatigue strength of the entire component. One measure to tackle those negative effects is the welding of the affected areas. This measure is then successful when locally achieved material strengths and surface qualities are higher than the component with the casting defect. Unfortunately, data for the lifetime and fatigue assessment of welded GJS are not present right now. Thus, the research project nodularWELD assessed the local stress- and strain-based fatigue data of different thick-walled GJS grades for building a basis for a successful usage even of defect affected components. So, three ferritic and pearlitic GJS grades were investigated in the heat-affected zone, the base material, the welding filler and more over in an integral material state comprising all those three aforementioned states based on axial and bending investigations. Additionally metallographic and fractographic analysis were conducted
•·Microstructure are generated based on quantitative data from experiments.•·Plasticity of graphite particle material as well as debonding of the interfaces are considered.•·Position and size of ...graphite particles have important effects on the stress and strain evolution in the cutting process.•·Simulation results are verified by experiments.
Nodular cast iron (NCI), also known as particulate metal matrix composites (PMMCs), is extensively utilized in the manufacturing of pistons for high-power engines. However, poor machinability is a significant problem due to the inherent microstructural inhomogeneity of the NCI. Therefore, this study aims to investigate influence of graphite particle distribution and size on the machinability of NCI. Microstructure of NCI is experimentally examined and quantitatively analyzed, and NCI is treated as a three-phase composite (i.e., matrix-interface-graphite particles). Graphite particles are considered as a plastic material, and debonding of interfaces is taken into account. Based on average particle size and volume fraction of graphite nodules, four microstructural models with different particle sizes and distributions are discussed, and turning experiments are conducted to validate simulation results. The findings reveal that graphite particles of different sizes and distributions affect stress–strain distribution in the cutting region of the material. As the distance between the graphite particles and the cutting tool increases, their influence on the stress–strain distribution becomes less significant. Furthermore, random distribution of graphite particles is more likely to result in complex crack initiation and expansion, leading to more pronounced serrated chips. The distribution of graphite particles has a more significant impact on the stability of cutting forces compared to the particle size. Both experiments and simulation results show that cavities and burrs are appeared along the cutting path because of graphite nodules, which reduces the surface quality and affects the subsequent use of the parts. On the one hand, the present work provides guidance for the finite element modelling of NCI, which is helpful to improve the precision of cutting simulation. On the other hand, by integrating advanced manufacturing technology to regulate the microstructure and cutting parameter of NCI, the present study can provide data basis and numerical analysis support for improving the machinability of NCI.
Large cast components made of nodular cast iron for heavy industry and wind energy turbines are usually not completely free of local material defects. In the case those material defects occur locally ...and near the component's surface this will lead to negative effects on lifetime, when high surface stresses and sharp notches or stress gradients are present and interact. One measure to bring the components into usage for foundries is to determine the defect characteristics and remove the defect by a defined manufacturing and a subsequent welding process. Nevertheless, repair welding is not accepted by certification bodies due to a lack of knowledge of the cyclic material behavior of repair welded nodular cast iron.
Within the research project “nodularWELD” the possibilities for welding thick-walled nodular cast iron are investigated on ferritic, ferritic silicon solid-solution strengthened and pearlitic cast iron grades. Afterwards the welded cast materials are subjected to cyclic stress based fatigue tests to determine the influence of the welding in comparison to the base material.
Particularly, in the presented paper a comparison of the resulting fatigue strength of ferritic EN-GJS-400-18LT, ferritic silicon solid-solution strengthened EN-GJS-450-18 and EN-GJS-700-2 is conducted. The comparison is done for the base material and the welded condition by the help of axial and bending specimens. For the investigated material conditions, the results show reduction in the fatigue strength for axial loading for EN-GJS-400-18LT and EN-GJS-700-2 by about 30 % while the silicon solid-solution strengthened EN-GJS-450-18 dropped down to around 25 % of the fatigue strength of the base material.
Martensitic nodular cast irons (MNCIs) with different graphite sizes and number densities are produced through continuous casting and cyclic heat treatments to refine their microstructures and to ...obtain a hardness of 60 HRC, and their rolling contact fatigue (RCF) properties, fractography, and subsurface microstructures have been investigated in the present study. RCF tests show that the RCF life is mainly determined by the applied Hertzian stress. Based on the calculation of characteristic parameter size and the analysis of stress concentration factor, it is found that the lower nodularity rate of graphite brings about the larger stress concentration at matrix‐graphite interfaces. This stress concentration induces a debonding of the matrix and graphite, cracks, deformation, and carbon redistribution in a local volume, which results in the formation of a white etching area. The present study indicates that MNCIs are a potential material for lubricant‐free bearings after chemical homogenization, microstructure refinement, and hardness enhancement.
Highlights
The experimental material is nodular cast iron with a martensitic matrix.
The influence of graphite on fatigue life is analogous to that of inclusions.
The lower nodularity rate of graphite, the larger stress concentration factor.
The martensitic nodular cast irons are a potential material for bearings.
Nodular cast irons have been mainly used in automobile components exposed to large forces like brake pads, suffering from abrasion against recently developed lightweight Al2O3-containing brake rotors ...during operation. Besides, aqueous corrosion (rain, snow, and chlorides) can cause these brake pads to wear out faster. This study examined the wear and corrosion properties of the V-alloyed nodular cast irons as a function of V content (0, 0.25, 0.5, 0.75, and 1 wt%). The samples were tested against an Al2O3 ball to simulate more severe abrasive conditions, whereas the electrochemical corrosion behavior was investigated in a 3.5 wt% NaCl solution. It was revealed that wear resistance increased with increasing V up to 0.50 wt%, but higher V caused a reduction due to the heavily branched eutectic carbide formation. Wear losses increased with the applied load, whereas sliding speed had no significant effect. The samples experienced uniform and graphitic corrosion in a 3.5 wt% NaCl environment. Increasing V improved their corrosion resistance to 0.75 wt% V due to the precipitated spherical vanadium carbides. The 1 wt% V-alloyed sample failed both wear and corrosion tests because of increased metastable eutectic carbides.
•V addition above 0.5% reduced wear resistance due to eutectic carbide formation.•In dry sliding conditions, the predominant mechanisms were abrasion and adhesion.•Wear losses increased with the applied load and slightly changed with sliding speed.•Increasing eutectic carbides lowered both wear and corrosion resistance.•V-alloyed ductile irons suffered from galvanic corrosion in the marine environment.
