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Abstract

In the work was presented the results of studies concerns on the destructive mechanisms for forging tools used in the wheel forging process as well the laboratory results obtained on a specially constructed test items for testing abrasive wear and thermal fatigue. The research results of the forging tools shown that the dominant destructive mechanisms are thermal fatigue occurring in the initial the exploitation stage and abrasive wear, which occurs later, and is intensified effects of thermo-mechanical fatigue and oxidation process. In order to better analysis of phenomena associated with destructive mechanisms, the authors built a special test stands allow for a more complete analysis of each of the mechanisms separately under laboratory conditions, which correspond to the industrial forging processes. A comprehensive analysis of the forging tools confirmed by laboratory tests, showed the interaction between the thermal fatigue and abrasive wear, combined with the oxidation process. The obtained results showed that the process of oxidation and thermal fatigue, very often occur together with the mechanism of abrasive wear, creating a synergy effect. This causing the acceleration, the most visible and easily measurable process of abrasive wear.
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Abstract

The study presents a durability analysis of dies used in the first operation of producing a valve-type forging from high nickel steel assigned to be applied in motor truck engines. The analyzed process of producing exhaust valves is realized in the forward extrusion technology and next through forging in closed dies. It is difficult to master, mainly due to the increased adhesion of the charge material (high nickel steel) to the tool’s substrate. The mean durability of tools made of tool steel W360, subjected to thermal treatment and nitriding, equals about 1000 forgings. In order to perform a thorough analysis, complex investigations were carried out, which included: a macroscopic analysis combined with laser scanning, numerical modelling by FEM, microstructural tests on a scanning electron microscopy and light microscopy (metallographic), as well as hardness tests. The preliminary results showed the presence of traces of abrasive wear, fatigue cracks as well as traces of adhesive wear and plastic deformation on the surface of the dies. Also, the effect of the forging material being stuck to the tool surface was observed, caused by the excessive friction in the forging’s contact with the tool and the presence of intermetallic phases in the nickel-chromium steel. The obtained results demonstrated numerous tool cracks, excessive friction, especially in the area of sectional reduction, as well as sticking of the forging material, which, with insufficient control of the tribological conditions, may be the cause of premature wear of the dies.
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