Abstract
In this study, the sliding wear of a DIN 18MnCrSiMo6-4 continuous cooling bainitic steel plasma nitrided with a nitrogen rich gas composition was investigated. To evaluate the influence of processing time and temperature on mechanical and microstructural characteristics of nitrided layer, the samples were nitrided at 400, 450, 500 and 550 °C for 3, 6 and 9 h. The produced nitrided layers were characterized concerning the microstructure, phase composition, microhardness and surface roughness. The samples were tested by ball-on-flat reciprocating dry sliding for friction coefficient and wear analysis. The tests were stopped after a given damage criteria involving the rapid growth of the friction coefficients and wear. The correlation of the different treatment parameters and resulting case depths and surface hardness with sliding distance at the time of microcracks formation or delamination of the surface layer was evaluated statistically by the analysis of variance (ANOVA). The plasma nitrided samples at 550 °C showed better wear performances in the ball-on-flat tests than the other groups investigated, since these samples have a thicker compound layer and diffusion zone higher than the other conditions investigated. In general, the beginning wear is slower because of the hardest region of the compound layer.
Highlights
Continuous cooling bainitic steel has an increasing use in industrial processes owing to its excellent outstanding combination of yield strength and toughness[1,2,3], the possibility to reduce the process chain and reduced energy consumption[4,5,6,7]
In the case of continuous cooling bainitic steels there is no annealing treatment applied as the microstructure was obtained directly after hot rolling and controlled cooling
The surface treatment was carried out in a plasma nitriding furnace equipped with a DC power supply which was developed by the Technology Center and Metallurgy Department of Federal University of Rio Grande do Sul
Summary
Continuous cooling bainitic steel has an increasing use in industrial processes owing to its excellent outstanding combination of yield strength and toughness[1,2,3], the possibility to reduce the process chain and reduced energy consumption[4,5,6,7]. Their surface properties are acceptable for many purposes[8,9,10,11], surface hardness and wear resistance are insufficient for some highly loaded automotive components as gears for example. Since long nitriding times can have a detrimental effect on the mechanical properties of steel, the treatment temperature should be carefully selected
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