D.K. Tanaka

Corrosion–erosion of nitrogen bearing martensitic stainless steels in seawater–quartz slurry

AISI 410S stainless steel was nitrided at 1473 K in N2 atmosphere, direct quenched and tempered at temperatures between 473 and 873 K. Martensitic cases with circa 0.52 wt.% N at the surface were obtained. Corrosion–erosion tests were carried out in slurries composed by quartz particles and tap or substitute ocean water. The concentration of solids, the impact angle and the pH of solution were fixed, while the temperature, surface changes and mass losses were monitored during the tests. Quenched and tempered AISI 410 and 420 stainless steels were used as comparison materials. The results showed that the erosion resistance and the corrosion–erosion resistance of the nitrided steel tempered at 473 K were higher than those of the AISI 410 and 420 steels tempered at the same temperature. This behavior was due to the higher hardness and better intergranular, pitting and generalized corrosion resistance of the nitrided alloy. The synergism between corrosion and wear was more important in the AISI 410 and 420 samples.

The particle size effect on abrasive wear of high-chromium white cast iron mill balls

Granite grinding tests, under dry and wet conditions, were performed to assess the influence of abrasive particle size to the wear behavior of martensitic high-chromium white cast iron mill balls. The tests were performed, at first, using raw granite particle sizes between 0.074 and 19.1 mm, and then with coarse and fine granite fractions obtained after screening the raw granite in a 3.36 mm sieve. It is demonstrated that the relative particle/ball size relationship is the determining parameter to ball wear. The highest ball wear rates were observed for fine granite grinding under dry (120 mg/cycle) and wet (129 mg/cycle) conditions. The lowest wear rate (ca. 50 mg/cycle) was observed for coarse granite grinding (dry and wet). These different results were attributed to the different size relationships between grinding body diameter and granite particles size. For wet-grinding of raw granite, the mineral components may influence significantly the wear behavior. Feldspar can act as a bonding agent, gluing fine quartz particles to the coarse granite and to the balls surface and turning the dependence of the relationship between the relative sizes of ball and granite particle less important to the wear process. This explains why wet-grinding of raw granite results in a ball wear two times greater (106 mg/cycle) than dry-grinding (51 mg/cycle).

Correlation between microstructure and cavitation–erosion resistance of high-chromium cast steel—preliminary results

Abstract Cavitation–erosion is a complex and highly localized phenomena involving mechanical, chemical and metallurgical parameters. The development of new materials depends on the understanding of the relationship between microstructure and cavitation–erosion. This paper investigates the role played by the microstructure on cavitation–erosion rates of 35Cr–25Ni–3Mo and 35Cr–8Ni–3Mo–2Nb, with and without tungsten addition in the as-cast condition. The difference in the microstructures was a consequence of distinct cooling rates due to the casting mold geometry. Metallographic techniques were used to reveal the microstructure. Cavitation tests were made by means of a vibratory apparatus. The performance of the alloys is compared with AISI 304 austenitic stainless steel. All alloys tested presented an improved performance when compared with the AISI 304. Alloys solidified with a high cooling rate presented best results and this behavior is attributed to the differences in the microstructure. For high-chromium cast steel, the increase of the austenite content decreases cavitation resistance. It was also observed that finer carbide particle morphology has a beneficial effect on the cavitation resistance of these materials.

Consideration of stribeck diagram parameters in the investigation on wear and friction behavior in lubricated sliding

This paper deals with an experimental study of both wear and friction responses of lubricated sliding tests, considering both responses in Stribeck diagram. Analyses concerning the wear coefficient by Archard equation were also done. Tests were oil-bath lubricated, performed through a machine with devices for rotating pin-on-disk and reciprocating pin-on-plate tests. Tested specimens were pins of AISI52100 steel and counter-bodies of AISI8640 steel. Presence of additives and contamination in lubricant oil was investigated under two mechanical loading levels, determined by the velocity/load ratio. Wear was studied by means of optical microscope and dimensional analysis of the worn surfaces. The use of a wear coefficient similar to that of Archard equation for characterizing sliding wear behavior is discussed. Differences were observed in the wear trend of the rotating and the reciprocating tests in terms of Stribeck parameters considerations.

The effect of load and relative humidity on friction coefficient between high density polyethylene on galvanized steel—preliminary results

This paper presents the influence of applied load and relative humidity (RH) in the friction coefficient of high-density polyethylene (HDPE) pin on hot dip galvanized steel disc. The experimental results showed that friction coefficient is proportional to the applied load. The measured friction coefficient was affected by environment RH depending on applied load. For low applied load, the friction coefficient varies following humidity alteration of testing environment, i.e., increase in humidity increases the friction coefficient, while for high applied load, there was observed no variation on friction coefficient. The wear rate of HDPE pin in 10 and 20 N applied load range suggests changes in the wear regime, from mild to severe.

Influence of loading, contamination and additive on the wear of a metallic pair under rotating and reciprocating lubricated sliding

This paper deals with an experimental study of wear and friction responses from lubricated sliding. Tests were carried out using a tribometer having devices for both continuous and reciprocating motion. The tested specimens were pins of AISI 52100 steel and counter-faces of AISI 8640 steel. The lubricant was paraffin mineral oil, VI 100. The presence of additives and contamination in the lubricant was investigated under two mechanical loading levels, determined by the velocity/load relation. Wear was evaluated in terms of morphology of the worn surfaces and by dimensional analysis of worn area of the pins. It was possible to obtain a ranking of influences on wear of mechanical loading, mechanical motion, oil additive and contamination presence in oil. Keywords : Wear, paraffin oil, abrasive contaminant, rotating motion, reciprocating motion, mechanical loading, mixed lubrication

Wear and Corrosion Evaluation of Electric Fuel Pumps with Ethanol/Gasoline Blends

The automotive electrical fuel pumps for gasoline and alcohol fueled vehicles engines are lubricated by the fuel itself. The new flexible fuel engine technology, specially in Brazil, the fuel pump is designed to be lubricated by gasohol (E22) or strait hydrated ethanol fuel but it is also exposed to the variable gasoline/alcohol blends in the flex-fuel engines. This paper presents the influence of different fuel blends, ethanol and gasohol, to the fuel pump wear and corrosion behaviors. The tested fuel pumps were designed for gasohol only engines. The fuel pumps were tested in a bench device, which simulates the vehicle fuel circuit, using gasohol (E22), hydrated ethanol (E100) or 60 % in volume ethanol-gasoline mixture (E60). The scanning electron microscopy examinations and roughness measurements were performed for tribological analysis of fuel pump gears. The observed wear and/or other deterioration mechanisms were mainly due to the abrasion and corrosion. The tests showed that abrasion mechanisms were more pronounced in the E22 fuel and the corrosion mechanisms were more damaging in the E60 and E100 fuels. The fuel pumps gears lubrication regime was calculated and the tested fuels lubricities were also measured.

A New Method for the Evaluation of Wear Damage in Dry Rolling Contact by Sound Intensity Level and Residual Stress Measurements

The contact fatigue wear of rolling surfaces is associated with the behavior of dislocations located at the specimen surface and subsurface. This behavior depends on the Hertzian Pressure and specimen shear strength, which affect the residual stress fields developed during cyclic loading. This work describes a new nondestructive method to evaluate changes on the residual stress fields and wear damage in dry rolling contact. A disc-disc testing machine was used into a semi-anechoic chamber to evaluate the audible sound signal (noise intensity level) continuously generated by the mechanical contact. Pairs of discs of heat treated DIN 100Cr6 (AISI 52100) steel were tested under Hertzian nominal pressures from P o = 1.5 GPa to P o = 2.5 GPa, at velocities of 40±0.5 m/s. The sound signals were later distributed into box-and-plot graphics which indicated four percentile groups (quartiles) and revealed the main tendency and dispersion of these signals. An XRD analysis, using the sin 2 ψ technique was applied to measure the residual stresses and to associate them with the noise intensity level quartiles at different stages of testing. Microstructural analyses of tested disc surfaces and resulting debris, using a Scanning Electron Microscope (SEM), showed a relation between the different noise levels and surface damage mechanisms, such as microspalling, micropitting, plastic deformation, delamination and brittle fracture.

Audible Noise, Contact Temperature, Life and Microfracture of Dry Rolling Surfaces Using DIN 100Cr6 Steel

Abstract. It was developed an approach to associate the load, life, temperature and audible acoustic emission to rolling contact fatigue wear of heat treated (OQT, Oil Quenching and Tempering, and SBQT, Salt Bath Quenching and Tempering) DIN 100Cr6 steel surfaces submitted to an hydrostatic stress field under dry rolling by friction at a disc-disc testing machine. A dynamic sensor was utilized as the stopping criteria. The material response to rolling contact fatigue was investigated and results of a canonical correlation analysis are presented.