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The so-called Modified Martempering discussed in this work differs from the standard martempering by that the temperature of the quenching bath is below the Ms point. In spite of the fact the lower temperature increases the severity of quenching, this also usually avoids the bainite formation, and by this reason, it is possible to make a fair comparison between different processes, which result in different microstructures. The present study shows the results in terms of mechanical properties, impact resistance in special of a cold work tool steel class, after being heat treated by the isothermal modified martempering process, as well as a comparison with the conventional quenching and tempering process and the austempering as well.

Modern SI engines focusing on CO2 emission reduction has been applying flex fuel technology to enable burning biomass fuels. The prime route is the use of ethanol fuel on these engines. The action of designing an engine to run with ethanol and gasoline (Flex-Fueled Engines) affects powercell components in different ways. The mechanical loads are higher to ethanol fuel. The combustion pressure can be increased without the risk of knocking for ethanol while for gasoline the compression rate of the piston is limited due to knocking occurrence. The spark time also occurs earlier which impacts components lubrication once the maximum load happens near the top dead center (TDC) where the sliding speed is lower and consequently there is lower oil film thickness. Such combination of spark time and sliding speed may also affect dynamics which can affect inertia and load composition of engine components.

The exhaust gases emission regulations, with very restrictive limits, have imposed the need of developments in other areas, among them, in the internal components developments. The necessary maintenance of low levels of oil consumption for long periods of engine use, leads to the development of components with higher wear resistance and higher efficiency. Among these components, the piston rings and the cylinders play an important role in the oil consumption control and also in the engine service life. This paper presents the results of engine tests run to compare the components wear (piston rings and cylinders) when using different types of lubricant oils.

The components of the piston/ring/liner system must have their wear resistance increased to meet the new engine requirements. The engine operating conditions can be even worse if corrosive wear in the engine is expected to occur. This paper presents a study to improve the wear resistance of piston ring coatings and liner materials by the addition of chromium carbide and carbide forming alloying elements, respectively. The engine tests were run with high sulfur fuel (about 1.0 wt%) and lubricant with low total base number (TBN) with the objective of increasing the corrosive conditions. The results show the improvement of the ring coatings wear resistance with the increase of the chromium carbide content. The cylinder liner materials also presented lower wear rates when they had hard particles, mainly due to the addition of niobium, vanadium and titanium.

The tempering effect on as-quenched compressive residual stress of commercial carburized samples is the main objective of this work. The compressive residual stress developed during the quenching process of carburized parts is fairly well known. The study was performed using SAE 4120 RH steel samples with two different diameters of 15 and 38 mm, which resulted in different cooling rates, with a direct effect on the core microstructure. The carburized surface microstructures were considered similar. The smaller diameter core microstructures were predominantly martensitic however bainitic in the larger bars samples. The as-quenched surface compressive residual stress was lower in the smaller diameter samples. The 15 mm diameter samples showed two different types of behavior, i.e., the compressive stress for lower temperatures during tempering process was reduced, whereas the values were increased at higher temperatures.

One of the problems related to the gray cast iron cylinder liner, and others materials, transportation is the possibility of the surface corrosion due to a non-controlled environment. The manufacturer has the responsability to guarantee the product free of corrosion up to the opening at final destination. Aiming to evaluate the liners transportation, regarding the corrosion potential during the transportation cycle, Magneti Marelli Cofap did experiments where the atmospheric conditions inside the pallets were measured. Using a special device it was possible to check the temperature, absolute humidity and relative humidity variations at every step, which were pre-set by using an specific software. The main reason for variations that might happen at the liner surface are related to transportation and storage. The corrosion rate will be determined by physical and chemical atmospheric conditions.

Metal in general presents two distinct regions in tension by deformation curves, one elastic and other plastic. At the elastic region, there is a direct proportionality between applied load and correspondent deformation. This can be called an elastic linear behavior of the material. Considering graphite content cast iron with lamellar morphology this behavior does not follow the same pattern. Since the beginning of the loading those materials present non-linear behavior with the load applied. In this report will be presented microstructure analysis, micro and macro hardness tests and a precise determination of tension versus deformation curves of perlitic gray cast iron with predominant Type A graphite to get the real tension profile developed when flexion loads are applied.

With the current use of bio-renewable fuel, the application of Ethanol in Flex-Fuel vehicles presents a very low CO2 emission alternative when the complete cycle, from plantation, fuel production, till vehicle use, is considered. In Brazil more than 80% of the car production is composed of Flex-Fuel vehicles. Due to the lower heating content of the Ethanol, more aggressive combustion calibrations are used to obtain the same engine power than when burning gasoline. Such Ethanol demands, associated with the continuous increase of engine specific power has lead to thermo-mechanical loads which challenges the tribology of piston rings. The ethanol use brings also some specific tribological differences not very well understood like fuel dilution in the lube oil, especially on cold start, corrosive environment etc. Under specific driving conditions, incipient failures like spalling on nitrided steel top rings have been observed.

This paper presents some definitions about the bore surface finishing and its influence on the piston rings performance. The surface finishing of a cylinder is in most of cases obtained by a machining process called honing. In recent years, developments and innovations to the honing process have been implemented. These new surface finishings are being implemented in order to improve the working condition of the system. Some of these developments are presented. This paper also presents some benchmarking of bore finishing for SI engines and case studies showing the influence of the surface finishing on the rings performance, regarding wear, friction and lube oil consumption. The results showed that smoother bore surfaces presented lower friction coefficient and also lower wear on the rings and bores. Finally a recommendation for bore finishing and its evaluation for modern SI engines is given.

The piston rings are responsible for maintaining some engine functioning parameters in an acceptable range, mainly the lubricant oil consumption and the blow-by gases flow from the combustion chamber to the crankcase. The wear resistance of these components is related to their capacity of properly exerting these functions during the whole engine life. In Diesel engines, all the rings have a wear resistant coating applied to their contact face with the cylinder wall. However, the chrome plating of the second groove compression ring is a conservative solution with the possibility of the development of lower cost alternatives. This paper presents the results of engine tests that compare the wear resistance of second groove rings with chrome plating and rings made of nitrited gray cast iron. Test results with similar gray cast iron rings are also analyzed to infer the influence of the nitriding treatment on the wear resistance of this material.

The evolution of internal combustion engines has led to friction reduction as well as to gaseous emissions reduction, demanding the use of narrower rings. Nodular cast iron is used satisfactorily for compression piston rings, with wear resistant coatings to improve their durability. However, for more severe applications and rings narrower than 1.2mm, even the nodular cast iron mechanical resistance is not enough. In this way, the use of steel is recommended, which may have its tribological properties improved by the nitriding thermochemical treatment. This paper presents the characteristics of the materials and of the nitriding process of compression and oil control rings as well as bench and dynamometric test results run during the development of these products.

Engine developments have led to higher mechanical and thermal loads on the components, at the same time that lower friction losses are also sought. Therefore, the development of better materials and of surface treatments has received great emphasis. This paper presents the results of dynamometric engine tests with a proposed piston ring pack, composed of a gas nitrided steel top ring, a nitrided gray cast iron second ring and a normal production chrome plated oil ring. The proposed pack showed very low wear when applied to a medium duty diesel engine, besides being a cost-effective alternative to the conventional pack with moly coated and chrome plated (respectively in the top and second) rings. The proposed pack also caused very low wear on the cylinder bore, specially near the TDC, where the bore wear is usually maximum.

The market has recently required the bearings to operate under intermittent or occasionally boundary lubrication conditions through requirements guided basically by CO₂ reduction: flex-fueled engines, stop-start operation, specification of low viscosity oils, extension of high speed regimes with low stiffness conrods and crankshafts. The sensitivity of the oil film rupture, higher loads and the robustness of operation required the development of low friction coatings or overlays with improved wear resistance. MAHLE response to these requirements has been addressed through a newly developed product assigned as polymer-coated bearing. The polymeric overlay has a proprietary low friction solid blend and it is sprayed onto premium bimetallic bearings. In this paper it is shown that these bearings run at lower temperature, with lower friction and can support higher loads than the conventional bimetallic bearing.

The first groove piston rings are highly loaded due to the combustion chamber nearness. They support high pressure against the cylinder wall, high working temperature and low lubricant level. In critical working condition, it could be used flame sprayed molybdenum coating the rings from 99.9% purity wires. The wire flame spray process limitation is the deposition of only one material. Here it is presented a new concept for getting wear resistant coatings on first groove piston rings, by flame spraying, by applying simultaneously materials with different characteristics from wires. Comparative results between the proposal (Moly + Inox) and the conventional (Moly) coating are presented. The simultaneous application of stainless steel and molybdenum decreases the first groove piston rings wear without loss of scuffing resistance.

This work presents an experimental study to analyze the influence of surface finishing on engine journal bearing performance. Bimetallic bearings were manufactured with two bored finishings, one called conventional and another microprofiled. Microprofiled bearings have a potential advantage due to the higher conformability of these parts under the engine operational conditions. Bench tests and engine test were conducted in order to check the loading carrying capacity (LCC) until seizure occurrence; the temperature was evaluated at the steel back of the tested parts. Surface of the parts was evaluated after the tests. The results showed that microprofiled bearings presented slightly lower temperature at steel back during the bench tests than the conventional bearings. The loading carrying capacity for both parts was similar, due to the relatively low speed test.

The use of Biodiesel is one of the main drivers behind biomass fuels for diesel engine use. This paper compares the performance of powercell components after 100 thousand km field tests using different fuel variants. The tested engine was a 3.0L High Speed Diesel with 120kW @ 3800rpm. Two variants of B5 fuels were tested: one with oil from Soy Bean and other from Castor Bean. Each type of fuel, including regular Diesel, was tested twice. Compared to regular Diesel, the engines tested with B5 presented similar performance [1]. The evaluated powercell parts were: piston, rings, bearings, and cylinder bores. The parts were evaluated in terms of wear, seizure and corrosion. The parts from the B5 tests presented similar visual characteristics after test compared with regular Diesel. A slight wear increase was observed on the parts that ran with the B5 variants. In the case of bearings, corrosion residues were observed with B5 from Castor oil.

The higher load in heavy duty Diesel engines and the use of piston ring coatings with higher wear resistance cause more severe working conditions to the cylinder liners. In some cases, high localized wear occurs at the top dead center (TDC) of the first groove ring, where the loads and lubrication conditions are critical. It was studied the effect of the addition of hard particles on cylinder liner materials. The presence of these particles was obtained through the use of small quantities of strong carbide forming alloying elements: Vanadium, Niobium and Titanium. Cylinder liners with hard particle addition were tested in comparison to regular liners. This test used high sulfur fuel (> 1.0 wt %) and low additivation lubricant oil, maintaining the same ring pack configuration for both liners. The results showed sensible liner wear reduction at the TDC of the first ring without compromising the ring pack performance.

The demand for higher output performance engines has lead to the increase of PCP (Peak Cylinder Pressure) and more aggressive engine designs for cylinder liners, mainly for new heavy duty engines developments where low cost components are been introduced. Such trends have generated demands to adequate the liner design by improving its material properties by changing its chemical composition, new materials data or even by introducing more accurate casting manufacturing process. Therefore, there is a clear tendency to development more and more alternative solutions that combine a certain technical high-value added and low cost. The most important material properties for cylinder liners are the ultimate tensile strength (UTS) and the fatigue tensile strength. Both parameters confer to the cylinder liners, especially for wet top flanged designs, the ability to survive under high mechanical and thermal load conditions even with reduced wall thickness.

The nitriding process improves in some applications the fatigue resistance of mechanical components. There is a lack of information about the nitriding process effect on the toughness of components. It is well known that the austempering heat treatment improves the toughness of the nodular cast iron. Some efforts have been made to find a compromise between the toughness of the bainitic structure of nodular cast iron and the high wear resistance undertaken by the nitriding process. Nitriding causes smaller dimensional problems if compared with other termochemical processes in steel and cast iron, but during exposure to the nitriding temperature the stabilized austenite of the nodular cast iron bainite may decompose, and induce component distortion. It is well known that the stabilized austenite is responsible for high toughness of the nodular cast iron.

Recent developments of diesel engines have aimed the improvement of their durability as well as cost optimizations. Although these tendencies seem to be contradictory, many technologies have been applied with results that are very satisfactory. The development of components, specially the piston rings, has led to solutions with optimized performance of service life as well as of functional characteristics of oil consumption control, blow-by control and friction reduction. The use of nitrided piston ring packs allows the maximization of the system performance without compromising the cylinder bore wear, as the tribological pair is very compatible. This paper presents the results of tests with nitrided first and second groove rings for medium and heavy-duty diesel engines.