Abstract
The present paper addresses experimentally the high temperature fatigue of 40CrMoV13.9 steel and the effect of surface roughness on fatigue strength and crack initiation. The 40CrMoV13.9 steel is widely used in different engineering high temperature applications among which hotrolling of metals, where, in order to assure a constant temperature, the rolls are provided with cooling channels. These are the most stressed zone of the rolls where cracks systematically initiate. In order to completely characterize the high temperature behaviour of this steel, firstly uniaxial-tension load controlled fatigue tests have been conducted at different temperatures up to 650°C. Two geometries are considered: plain specimens and plates weakened by symmetric V-notches. Subsequently, with the aim to investigate the influence of the cooling channels roughness on the high temperature behaviour and the cracks initiation, uniaxial-tension load controlled fatigue tests have been conducted on plate with central hole at the service temperature of 650°C varying the surface roughness. After a brief review of the recent literature, the experimental procedure is described in detail and the new data from un-notched and notched specimens are summarized in terms of stress range, at the considered temperatures. Finally, fatigue data from un-notched and notched specimens are re-analysed by means of the mean value of the Strain Energy Density (SED) approach extended at high temperature.
Highlights
H ot-rolling process is increasingly required for higher mechanical performances, fatigue strength and quality of laminated products
Influence of surface roughness on high temperature fatigue and crack initiation The 40CrMoV13.9 steel is widely used in different engineering high temperature applications among which hot-rolling of metals, where, in order to assure a constant temperature, the rolls are provided with cooling channels
The present paper addresses experimentally the high temperature fatigue of 40CrMoV13.9 steel and the effect of surface roughness on fatigue strength and cracks initiation
Summary
H ot-rolling process is increasingly required for higher mechanical performances, fatigue strength and quality of laminated products. On the basis of numerous feedbacks, the cooling channels are the most stressed zone of the rolls and cracks initiate systematically from these areas For these reasons, it becomes very interesting to investigate this kind of steel, with the aim to characterize its fatigue behaviour at high temperature, considering for example notch effects and/or the influence of. With the aim to define the influence of the rolls cooling channels roughness on the high temperature behaviour and the cracks initiation, uniaxial fatigue tests have been conducted on plate with central hole at the service temperature of 650°C, varying the surface finishes. A final synthesis of the present results together with previous data from multiaxial tests (at room temperature) on the same material [13] is carried out by means of the Strain Energy Density (SED) approach, as recently made for Cu-Be alloys [8] and a Titanium Grade 2 [9], at high temperature. It is evident that the microstructure is homogenous along all the directions, through the specimen thickness, due to the austenitizing and annealing processes
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