Laser Processing of Cast Iron for Enhanced Erosion Resistance

The surfaces of nodular and gray cast iron specimens have been modified by CO₂ laser processing for enhanced hardness and erosion resistance. Control of the near-surface microstructure was achieved primarily by controlling resolidification of the laser melted layer through variations in laser beam/target interaction time and beam power density. Typical interaction times and power densities used in this study were 5 msec and 500 kW/cm². Analysis of the laser melted surface showed a dramatic increase in hardness and a greatly refined microstructure. Depending on the processing parameters, two basic kinds of microstructure can be produced in the laser hardened layer—a feathery microstructure with a very high hardness (up to 1245 HV) and a dendritic microstructure with a metastable, fully austenitic matrix and a lower hardness (600 to 800 HV). Erosion testing was done in a rotating paddle device using slurries of SiO₂ or SiC in water. Weight loss and crater profile measurements were used to evaluate the erosion characteristics of the various microstructures. Both ductile and gray cast iron showed marked improvement in erosion resistance after laser processing.     

Effect of inoculating addition on machinability of gray cast iron

Gray cast irons were inoculated with FeSi75+RE and FeSi75+Sr inoculants. The changes of apex angle of the drills before and af-ter being used were used to evaluate machinability of gray cast irons. Effect of FeSi75+RE and FeSi75+Sr inoculants on mechanical proper-ties, machinability and sensibility of gray cast iron used in cylinder block were investigated. Experimental results showed that gray cast iron treated with 60%FeSi75+40% RE inoculants exhibited tensile strength consistently at about 295 MPa along with good hardness and im-proved metallurgical quality. While gray cast iron inoculated with 20%FeSi75+80% Sr inoculants exhibited the best machinability, the low-est cross-section sensibility and the least microhardness difference. The tool flank wear of the drill increased correspondingly with the in-crease of the microhardness difference of the matrix, indicating the great effect of homogeneity of the matrix on the machinability of gray cast iron.     

Mathematical modeling of microstructural development in hypoeutectic cast iron

A mathematical heat-transfer/microstructural model has been developed to predict the evolution of proeutectic austenite, white iron eutectic, and gray iron eutectic during solidification of hypoeutectic cast iron, based on the commercial finite-element code ABAQUS. Specialized routines which employ relationships describing nucleation and growth of equiaxed primary austenite, gray iron eutectic, and white iron eutectic have been formulated and incorporated into ABAQUS through user-specified subroutines. The relationships used in the model to describe microstructural evolution have been adapted from relationships describing equiaxed growth in the literature. The model has been validated/fine tuned against temperature data collected from a QuiK-Cup sample, which contained a thermocouple embedded approximately in the center of the casting. The phase distribution predicted with the model has been compared to the measured phase distribution inferred from the variation in hardness within the QuiK-Cup sample and from image analysis of photomicrographs of the polished and etched microstructure. Overall, the model results were found to agree well with the measured distribution of the microstructure.     

Effect of graphite morphology on modulus of elasticity of low carbon equivalent ductile iron

The modulus of elasticity (Young’s Modulus) of cast irons is known to be a function of graphite volume fraction in the microstructure. Low carbon equivalent ductile iron is a low carbon cast iron in which, carbon is present as graphite in nodular form. It is observed that the modulus of elasticity of these irons is higher than that of conventional ductile iron. In the present investigation, an interrelationship of modulus of elasticity with graphite nodule counts, nodule size and graphite volume has been investigated. A significant relationship is observed between the modulus of elasticity and the above mentioned morphological characteristics of graphite.     

Imposed Thermal Fatigue and Post-Thermal-Cycle Wear Resistance of Biomimetic Gray Cast Iron by Laser Treatment

The present study aims to create coupling biomimetic units on gray cast iron substrate by laser surface treatment (LST). LSTs for single-step (LST1) and two-step (LST2) processes, were carried out on gray cast iron in different media (air and water). Their effects on microstructure, thermal fatigue, and post-thermal-cycle wear (PTW) resistance on the specimens were studied. The tests were carried out to examine the influence of crack-resistance behavior as well as the biomimetic surface on its post-thermal-cycle wear behavior and different units, with different laser treatments for comparison. Results showed that LST2 enhanced the PTW behaviors of gray cast iron, which then led to an increase in its crack resistance. Among the treated cast irons, the one treated by LST2 in air showed the lowest residual stress, due to the positive effect of the lower steepness of the thermal gradient. Moreover, the same specimen showed the best PTW performance, due to its superior crack resistance and higher hardness as a result of it.     

Modeling of microstructure and residual stress in cast iron calender rolls

A comprehensive mathematical model based on the commercial finite-element (FE) code ABAQUS has been developed to predict the evolution of temperature, microstructure, and residual stresses in cast iron castings. The thermal component of the model, applied in stage one of the analysis, is capable of simulating the formation of microstructure over a broad range of cooling conditions, including the formation of columnar white iron as well as equiaxed gray iron. To test the model, it has been evaluated against thermocouple and microstructural data collected from a reduced-scale calender roll test casting. The model has been demonstrated to be able to predict the transition from columnar white iron to equiaxed gray iron which occurs approximately 20 mm below the outside surface of the roll test casting. In addition, the model is shown to be able to satisfactorily reproduce the evolution of temperature recorded from thermocouples embedded at various locations in the test casting. An elastic-plastic stress analysis, applied in the second stage of the analysis, was performed using the temperature history and the volume fraction of white and gray iron obtained with the thermal/microstructural model. The results were verified against residual stress measurements made at various locations along the outer-diameter (OD) surface of the roll. The elastic-plastic model accounts for the temperature-dependent plastic behavior of white and gray iron and the thermal dilatational behavior of white and gray iron, including volumetric expansion due to austenite decomposition and dilatational anisotropy in columnar white iron. The results of the mathematical analysis demonstrate that the residual stress distribution in full-scale calender thermorolls cannot be deduced simply from knowledge of the microstructural distribution and basic dilatometric considerations, as is currently the practice in industry.     

Laser-beam surface transformation hardening of hypoeutectoid Ck-60 steel

A carbon dioxide laser with a power of 1.5 KW was employed for surface hardening of a hypoeutectoid Ck-60 steel. The microstructures and hardness profiles were determined as a function of power density and laser beam travel speed. The microstructure in the laser-beam hardened zone depended on power density and consisted of plate martensite (for high power density) or autotempered martensite (for low power density). In the transition zone of the laser-beam treated specimens, martensite and ferrite were observed. Case depth and maximum hardness were found to depend on power density and travel speed. A simple one-dimensional heat flow model has been used for the selection of process parameters and for the prediction of case depth. Calculated and experimentally determined case depths are in good agreement for medium values of power density.     

Nb合金化对高Cr铸铁轧辊组织的影响

微合金化是细化高Cr铸铁轧辊的凝固组织、提高轧辊的性能和使用寿命重要手段。研究了Nb微合金化对高Cr铸铁轧辊组织和硬度的影响,并采用Thermo-Calc软件分析了Nb对高Cr铸铁凝固组织的细化机制,结果表明,Nb合金化能够显著细化高Cr铸铁的轧辊的凝固组织,提高轧辊的硬度。Nb微合金化对高Cr铸铁的组织改善作用取决于MC型碳化物析出温度及其对奥氏体和共晶M₇C₃碳化物的形核的促进作用。当Nb质量分数为0.5%时,高Cr铸铁轧辊硬度最大;进一步提高Nb含量能显著细化高Cr铸铁轧辊组织,但使硬度降低。     

还原铁粉对Fe-1.1Ni-0.5Mo-0.5Cr合金组织与性能的影响

在惰性气体雾化法制备的Fe-1.1Ni-0.5Mo-0.5Cr预合金粉末中添加1.5％的Cu粉和0.6％的C粉(均为质量分数)以及还原铁粉(添加量分别为0、10％、20％和30％),混合均匀后在600 MPa压力下模压,在1 180℃烧结1h.烧结合金经180℃/1h回火处理后,进行密度、硬度、拉伸力学性能检测以及显微...     

Effect of boron on the manufacturing process and final properties of ductile iron pipes (DI pipes)

The present work concerns an assessment of the influence of boron addition in spheroidal graphite iron (SG iron) melt on the manufacturing process and final properties of DI pipes. To elicit the effect of boron addition on the final properties of DI pipe, initially laboratory scale trials were conducted. The exercise includes studying the evolution of microstructure and mechanical properties of DI pipes with different level of boron addition. The results indicate that the presence of B in the melt does not have any perceptible deleterious effect on the performance of DI pipes in general, until the limit goes beyond 200?ppm. Later on, pilot trials were conducted in a plant facility. This trial comprises addition of boron at different levels in SG iron melts and studying effect on the overall manufacturing process of DI pipe production and corresponding microstructure and mechanical properties of the final product (i.e. DI pipes). The result of the plant-level trial is found in agreement with the laboratory scale trial, confirming the fact that presence of boron up to 200?ppm level in SG iron melt used for DI pipe manufacturing does not induce any deleterious effect on manufacturing process as well as product properties. Also, it reveals that the boron-added (up to 200?ppm) DI pipes show better machinability with a favourable combination of strength, ductility and hardness compared to the boron-free DI pipes.     

Investigation into the Microstructure and Mechanical Properties of Thin Wall Austempered Gray Cast Iron (TWAGI)

The main aim of this investigation is to assess the mechanical properties of thin wall (3 mm thickness) copper alloyed gray cast iron. Thin wall alloyed gray cast iron specimens are subjected to austempering heat treatment at six different temperatures for four different time periods. As a result, these samples develop an ausferrite matrix with excellent mechanical properties. The resulting microstructures have been evaluated and characterized by means of optical microscope and scanning electron microscope (SEM) and X-Ray diffraction analysis. The hardness and tensile properties of all these specimens are determined and correlated with the microstructure. The hardness, tensile strength and ductility initially increase, and thereafter it decreases on longer periods of austempering. On the other hand, hardness and tensile strength decreases with increasing austempering temperature, while ductility increases.     

Dissipative processes during cyclic hardening of spheroidal graphite cast iron

The hardening of spheroidal graphite cast irons alloyed by vanadium via chemical dispersion has been studied. Strain hardening is experimentally found to effectively occur in a cast iron with a relatively low vanadium content (0.5 wt %). Dissipative processes in cast irons with dispersed vanadium carbide inclusions are analyzed. An increase in the degree of dispersion of vanadium carbide inclusions is shown to favor more complete dissipation of the supplied energy into heat and decreases the level of damage in the material.     

Influence of rare earth nanoparticles and inoculants on performance and microstructure of high chromium cast iron

The high chromium cast irons (HCCIs) with rare earth (RE) nanoparticles or inoculants were fabricated in the casting process. The phase compositions and microstructure were analyzed by X-ray diffraction (XRD) and optical microscopy (OM), respectively. The hardness and impact toughness were tested by Rockwel-hardmeter and impacting test enginery. And then, the morphology of fracture was researched by scanning electron microscopy (SEM). The results demonstrated that the phase compositions of HCCIs with addition of RE nanoparticles or inoculants which were M7C3 carbides + α-Fe did not change obviously. However, the prime M7C3 carbides morphology had great changes with the increase of RE nanoparticles, which changed from long lath to granular or island shape. When the content of RE nanoparticles was 0.4 wt.%, the microstructure of high chromium cast iron was refined greatly. The microstructure of carbides was coarser when the addition of RE nanoparticles was higher than 0.4 wt.%. The hardness and impact toughness of HCCIs were improved by addition of RE nanoparticles or inoculants. The impact toughness of HCCIs was increased 36.4% with RE nanoparticles of 0.4 wt.%, but the hardness changed slightly. In addition, the adding of RE nanoparticles or inoculants could reduce the degree of the brittle fracture. Fracture never seemed regular, instead, containing lots of laminates and dimples with the increase of the RE nanoparticles. The results also indicated that the optimal addition amount of the RE nanoparticles was 0.4%, under this composition, the microstructure and mechanical property achieved the best cooperation. In addition, through the study of erosion wear rate, when adding 0.4% RE nanoparticles into the HCCIs, the erosion wear rate got the minimum 0.32×10-3 g/mm2, which could increase 51.5% compared with that without any RE nanoparticles.     

Microstructure Aspects of a Newly Developed, Low Cost, Corrosion-Resistant White Cast Iron

The purpose of this work is to study the influence of heat treatment on the corrosion resistance of a newly developed white cast iron, basically suitable for corrosion- and wear-resistant applications, and to attain a microstructure that is most suitable from the corrosion resistance point of view. The composition was selected with an aim to have austenitic matrix both in as-cast and heat-treated conditions. The difference in electrochemical potential between austenite and carbide is less in comparison to that between austenite and graphite. Additionally, graphitic corrosion which is frequently encountered in gray cast irons is absent in white cast irons. These basic facts encouraged us to undertake this work. Optical metallography, hardness testing, X-ray diffractometry, and SEM–EDX techniques were employed to identify the phases present in the as-cast and heat-treated specimens of the investigated alloy and to correlate microstructure with corrosion resistance and hardness. Corrosion testing was carried out in 5 pct NaCl solution (approximate chloride content of sea water) using the weight loss method. In the investigated alloy, austenite was retained the in as-cast and heat-treated conditions. The same was confirmed by X-ray and EDX analysis. The stability and volume fraction of austenite increased with an increase of heat-treated temperature/time with a simultaneous decrease in the volume fraction of massive carbides. The decrease in volume fraction of massive carbides resulted in the availability of alloying elements. These alloying elements, on increasing the heat treatment temperature or increasing the soaking period at certain temperatures, get dissolved in austenite. As a consequence, austenite gets enriched as well as becomes more stable. On cooling from lower soaking period/temperature, enriched austenite decomposes to lesser enriched austenite and to a dispersed phase due to decreasing solid solubility of alloying elements with decreasing temperature. The dispersed second phase precipitated from the austenite adversely influenced corrosion resistance due to unfavorable morphology and enhanced galvanic action. Corrosion rate and hardness were found to decrease with an increase in heat treatment temperatures/soaking periods. It was essentially due to the increase in the volume fraction and stability of the austenitic matrix and favorable morphology of the second phase (carbides). The corrosion resistance of the investigated alloy, heat treated at 1223 K (950 °C) for 8 hours, was comparable to that of Ni-Resist iron. Thus, a microstructure comprising austenite and nearly spherical and finer carbides is the most appropriate from a corrosion point of view. Fortunately, the literature reveals that the same microstructure is also well suited from a wear point of view. It confirms that this investigated alloy will be suitable for corrosive-wear applications.     

The Effect of Graphite Fraction and Morphology on the Plastic Deformation Behavior of Cast Irons

The plastic deformation behavior of cast irons, covering the majority of graphite morphologies, has not been comprehensively studied previously. In this investigation, the effect of graphite morphology and graphite fraction on the plastic deformation behavior of pearlitic cast irons has been evaluated. The investigation is based on tensile tests performed on various different cast iron grades, where the graphite morphology and volume fraction have been varied. Pearlitic steel with alloying levels corresponding to the cast irons were also studied to evaluate how the cast iron matrix behaves in tension without the effects of the graphite phase. It is concluded that as the roundness of the graphite phase increases, the strain hardening exponent decreases. This demonstrates that the amount of plastic deformation is higher in the matrix of lamellar cast iron grades compared to compacted and nodular cast iron grades. Furthermore, this study shows that the strength coefficient in flake graphite cast irons increases as the graphite fraction decreases due to the weakening effect of the graphite phase. This study presents relationships between the strain hardening exponent and the strength coefficient and the roundness and fraction of the graphite phase. Using these correlations to model the plastic part of the stress-strain curves of pearlitic cast irons, we were able to calculate curves in good agreement with experimentally determined curves, especially for gray cast irons and ductile iron.     

Optimising grey iron powder compacts

Abstract

The grey iron microstructure Fe–2C–2Si powder based compact is tailored by different kinds of in situ and post sintering processing. This has been achieved by combining thermodynamic and kinetics modelling of microstructure development with sintering and controlled heat treatment experiments of tensile test specimens die compacted at 600 MPa. Applying optimised sintering conditions led to a grey iron like microstructure with 95% relative sintered density. Sinter hardening the compacts led to 500 MPa in yield strength and 600 MPa in ultimate tensile strength in combination with ductile fracture. Quenched and tempered condition showed the same strength values, but combined with brittle fracture due to martensitic structure. Pore rounding and partial pore filling by graphite were obtained by austenising isothermal hold during the cooling of the sintering cycle.     

Effect of liquid zinc on Armco iron with relevance to pots used in galvanizing

The present investigation deals with the comparative study of liquid zinc attack on Armco iron and Tisco A grade iron within a temperature range of 450°C to 550°C. The effect of variables, e.g. time of contact, temperature, on weight loss of iron for a similar geometry of specimens has been studied and discussed. The maximum weight loss of iron has been found at 500°C for both the irons. It has been observed that even a slight variation in silicon content (on increase) appreciably increases the rate of attack on iron.     

Effects of heat treatment and counterface on the wear behaviour of Cr21 cast iron

The unlubricated sliding wear test of high chromium white cast irons (HCCIs) was conducted using a pin-on-disc configuration under different heat treatments and different hardnesses of the counterface. With the increase of counterface hardness (20?HRC–47?HRC–54?HRC), the mass loss of the sample first increases then decreases. When the counterface hardness is 20?HRC, adhesion wear mainly takes place between the high chromium cast iron and the surface of 1045 steel. When the hardness is 47 or 54?HRC, first HCCI’ matrix wear takes place, then carbide bump flakes under alternating stress. The mass loss of the counterface decreases with the increase of hardness for the same sample. The mass loss of quenching, once tempering and twice tempering sample decreases gradually for the same counterface hardness, but fluctuation of the samples’ surface increased. The disc material is always softer than the pin material and results in a severe wear regime operation.