Abstract
The study performs an analysis as well as makes a comparison of the durability of forging tools used in the die forging process made of high-strength steel Unimax. For tool steel WCL (1.2343 according to DIN), which has been applied so far, the obtained average durability has been at the level of about 6000 forgings. Additionally, in order to increase the durability of the Unimax material, two surface treatment variants were applied: in the form of ion nitriding (for nitrides A) and gas nitriding together with a PVD-Alvin coating, which were compared with the results for an insert without surface treatment. For each variant, three tools were produced, in order to obtain repeatable and verified results. In the first place, an analysis of the working conditions of the tools was performed through thorough observations of the industrial forging process, particularly the tribological conditions, including the manner of lubrication as well as the temperature distributions, by means of, among others, thermovisual examinations. Additionally, numerical modeling of the process was carried out with the purpose of a more accurate analysis of the tool work in contact. Next, a detailed analysis of the exploitation of the worn tools was performed, including a macroscopic and geometrical analysis through 3D scanning, microscopic optical, and SEM tests as well as microhardness measurements. The obtained results demonstrated that only the application of the new material, Unimax, itself caused a durability increase by 2.5 times with regard to the WCL steel used so far. In turn, with the application of additional surface engineering techniques, Unimax tools characterized in better operational properties (high thermal and abrasive wear resistance at elevated temperatures), which made it possible to forge over four times more forgings, i.e., 26,000 items, after nitriding with a PVD-Alvin coating had been applied to the tool.
Highlights
The durability of forging tools is an important as well as difficult issue in both the scientific and economical aspect, in the case of plants producing forgings [1, 2]
The utilitarian aim of the study was to determine the effect of the applied tool material—Unimax—(after different treatment variants with the use of surface engineering techniques), in respect of the 1.2344 steel tool for hot operations used so far, on the increase of the hardness of forging tools
The analysis of the industrial forging process supported by temperature measurements as well as numerical modeling enabling the determination of many difficult, or even impossible to establish by other methods, parameters made it possible to point to the key process parameters, which decides about the wear
Summary
The durability of forging tools is an important as well as difficult issue in both the scientific and economical aspect, in the case of plants producing forgings [1, 2]. Among the most important ones, we can name thermo-mechanical fatigue, plastic deformation, abrasive wear, and oxidation (Fig. 1) All these factors simultaneously contribute to the wear of forging tools, while the share of the effect of the particular factors is different depending on the type of the tool (its size, shape, and production manner) as well as on the operation conditions (type of the forging aggregate, pressures, process temperature, etc.) [8]. Depending on the forging process and its conditions, one can observe a secondary fatigue crack network originating from both thermal fatigue [13,14,15] and, intensifying the degradation process, mechanical fatigue [16] as a result of high forming forces All this causes rapid and accelerated wear as well as tearing-off of increasingly bigger particles of the material, in which case, abrasive wear is not necessarily the dominant phenomenon [3]. The selected improvement manner has to be justified economically, and it should be analyzed whether the gain resulting from an increase of tool life will be higher than the sum of the expenses (material, machining, thermal and thermo-chemical treatment) [38]
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