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Technical Paper

The Modified Martempering and its Effect on the Impact Toughness of a Cold Work Tool Steel

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.
Technical Paper

The Effect of Core Microstructural Stability associated with the transformation occurred in the Carburized Surface on Residual Stress Evolution during Tempering

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.
Technical Paper

Preliminary study to data adequation to use engineering tooling in perlitic matrix gray cast iron

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.
Technical Paper

Study of Sea Transportation Effects on Corrosion of Cast Iron Cylinder Liners

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.
Technical Paper

A Comparative Study Between Salt Bath and Plasma Nitrocarburizing Processes for Application in Piston Rods

The quality of the nitrocarburized layer has a decisive influence in the service life of components with pistons that work together with polymeric seals, since it interferes in the abrasion and wear mechanisms of the involved materials. Thus it is necessary to select the most adequate process to apply in a given component aiming for a quality improvement and warranty costs reduction. The literature offers a great volume of information about the different nitriding processes, but there are few reports comparing them. In this paper the salt bath and plasma processes are discussed concerning the white layer metallography, roughness and the process effect on corrosion resistance of gas spring rods manufactured with SAE 1040 steel.
Technical Paper

Effect of the Nitriding Process on Impact Resistance of Austempered Cast Irons and Quenched and Tempered Ones

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.
Technical Paper

Bead Weld Cold Plastic Deformation Effects on AISI 409 Ferritic Stainless Steel, Ti and Nb Stabilized

The automotive industry has been increasing stainless steel consumption daily. Some important parts of a car should keep using carbon steel, however, the exhaust system must use stainless steel tubes since the gas from engine cannot corrode those tubes, avoiding catalytic conversor contamination. Among stainless steel groups, ferritic has been choosing due to costs and strong high temperatures resistance. This report starts studying ferritic stainless steel welded tubes mechanical properties (ABNT 409 stabilized), raw material for exhaust systems. Some welded tubes have been produced with internal bead rollers, to compare, afterwards, with tubes which were produced without bead hardening. The results shows that hardening induced by bead rolling causes material elongation reduction, that could lead problems on the tube forming operation during exhaust system production. Those materials have been analyzed by optical and electronic microscopy, Vickers micro hardness and tensile test.
Technical Paper

The Effect of the Addition of Hard Particles on the Wear of Liner and Ring Materials Running with High Sulfur Fuel

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.
Technical Paper

Nitrited Steel Piston Rings for Internal Combustion Engines

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.
Technical Paper

Nittred Gray Cast Iron Piston Rings

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.
Technical Paper

Development Of Nitrided Oil Control Rings With Contoured Rails

The application of multipiece oil control rings (two segments or rails and one expander) to Otto engines is very efficient and has been used for many years. However, development work to improve their performance, durability and manufacturing costs is desirable. The contoured segment is an alternative to reduce the variation of oil ring unit pressure during engine life. This paper shows the results of engine tests with this component, where nitrided segments with regular stainless steel expanders and nitrided expanders were used. The results showed satisfactory behaviour, with low wear between segments and nitrided expanders as well as between segments and the cylinder wall.
Technical Paper

Improvement Of Cylinder Liner Materials Wear Resistance.

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.
Technical Paper

New Concept For Wear Resistant Coatings For Piston Rings.

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.
Technical Paper

Configurations and Materials of Oil Control Rings to Meet the New Internal Combustion Engines Requirements

The fuel economy and gaseous emissions features have led the engine developments for the last few years. Various actions taken to meet these objectives imposed the necessity of components, in this case oil control rings, with higher mechanical resistance, durability and efficiency during the engine life. A new nodular cast iron alloyed with Niobium was developed. The presence of Niobium carbides raises significantly the wear resistance of this material. New configurations of oil control rings with taper faces or barrel faces showed a better performance if compared with two-piece conventional rings. The contact surface height variation during the engine life (and also the mean specific contact pressure variation in the ring land and cylinder wall contact) brings benefits in the oil consumption reduction without compromising the durability of rings and cylinders.