Selection of Casting Materials for Working Parts of Machines for The Forestry Sector

The article was created as a result of the work of the TECHMATSTRATEG 1 “Modern Material Technologies” Program as part of the project with the acronym INNOBIOLAS entitled “Development of innovative working elements of machines in the forestry sector and biomass processing based on high-energy surface modification technologies of the surface layer of cast elements”; agreement No. TECHMATSTRATEG1/348072/2/ NCBR/2017. The article discusses the procedure for selecting casting materials that can meet the high operational requirements of working tools of mulching machines: transfer of high static and dynamic loads, resistance to tribological wear, corrosion resistance in various environments. The mulching process was briefly described, then the alloys were selected for experimental tests, model alloys were made and per-form material tests were carried out in terms of functional and technological properties. The obtained results allowed to select the alloy whereof the test castings were made.


Introduction
According to accepted international standards, the forest area in Poland is over 9.35 million hectares. In recent years, both in Poland and in the European Union countries, the need for new afforestation and wasteland reclamation processes has been increasing. This is due to the need to care for the natural environment, to reduce the greenhouse effect, as well as to further improve life, especially in urbanized areas [1]. Proper management of forest resources requires the use of specialized equipment and devices with a service life significantly exceeding the standards for other machines. In particular, it is necessary to significantly increase the quality and durability of the working elements of these devices. Tools of the forestry sector should be characterized by high strength and plastic parameters, especially high impact toughness, as well as excellent tribological properties and corrosion resistance.
The aim of the project is to use casting technology in combination with the technology of surfacing the working layer in the production of tools for the forestry sector. One of the most important forest work is mulching. Mulching is a conservation procedure aimed at protecting the soil against degradation and maintaining its productivity by creating the so-called mulch, i.e. a protective soil cover placed on its surface in order to reduce the adverse impact of climatic factors [2]. This article discusses the selected casting alloys as part of the implementation of joint research and development projects.
The works described in this article relied on selecting, producing and testing modern casting materials in terms of optimizing their technological and functional properties. Obtaining a casting alloy in terms of its application for the new tools implemented in the project required at the initial stage of implementation to conduct research on alloys previously used for this type of tools.

Selection of Alloys for Tests
The selection of casting material for elements of various machines and devices has been the subject of research work carried out for many years in Lukasiewicz -Krakow Institute of Technology (formerly the Foundry Research Institute). Examples of such activities related to the constructional and material-technological conversion have been described, inter alia, for alloys for elements operating under conditions of high-temperature wear in publications [12][13][14][15][16], and for alloys exposed to tribological wear, which are the subject of the research of the INNOBIOLAS project, in [1 3-7&17].
Realizing this project, the mechanical properties of 15 different grades of steels resistant to tribological wear from the most common groups of alloys for this purpose were analyzed: Roex, Hardox and SAAB Boner. On the basis of the normative mechanical prop-erties of these materials (yield point, elongation, hardness and impact tough-ness), it was found that the most favorable parameters for working of abrasive wear in impact conditions has Hardox 450 steel [1], which was assumed as a reference for the selection of appropriate alloy cast grades.
According the intentions and aim of the project, the developed tools are cast tools. By analyzing the relevant Polish and European standards for abrasion-resistant cast steel grades, 11 such alloys were selected for the evaluation of their properties. Carrying out the evaluation of these materials similar to that described in [1] in the case of standardized steel grades, two grades of cast steel Their chemical composition was analyzed using the Thermo Scientific NITON XL3t 900S GOLDD device, and the average results obtained from this analysis are presented in Table 2.

Material Research
In the following part of the work, model melts of selected test alloys were made in laboratory conditions. These melts were per- formed in an open RADYNE induction furnace with a crucible capacity of 40 kg of metal charge and an inert crucible lining. The received chemical composition of the performed heats is compared in Table 3.      Table   4. Mechanical properties were also tested on the reference material taken from the purchased mulcher flail hammers, and the results are presented in Table 5.
The manufactured alloys were subjected to laboratory corrosion and tribological tests [17] and thermal characteristics of thermophysical properties [9] necessary for numerical analysis of pouring and solidification processes in the virtual development of the casting technology of the implemented tools were prepared.
Based on the results of the laboratory tests, the 30MCDB64-M-I cast steel was selected for techno-logical tests.

Numerical analysis
Within the project, the construction of many types of the mulching hammerhead, forestry mulchers was developed. Six of them were selected for realization and implementation, as shown in Figure 4.    In the case of the RM4 mulcher, two technological concepts were analyzed, for three and four models in the gating system, shown later in the article in Figure 9. The only detail that differs in shape from the others is the tool marked RB OTL, characterized by a wide base. Two possible concepts of its casting technology were analyzed: one or four castings in a set. The concept of one casting is dictated by the fact that the casting cross-section requires an appropriate feeding of the casting.
The second concept is more economical, but technologically more At the end of (thin walled) zone is occurring in the tendency to form an increased amount of perlite as shown in Figure 7. The hammer blade has a very thin wall at the end of the tool. This can cause the formation of carbides, which will greatly increase strength, but will significantly reduce plasticity. The heat treatment compensates for such large differences in properties in the cross-section of the casting.
The performed numerical analysis on the example of the RM4 mulcher casting also allowed for a virtual evaluation of the size and  Visualization of stress simulation results shows the areas ex-posed to excessive stress concentration. Simulations A1 and B1 show the picture of reduced stress (Von Mises) for two technological concepts. In the case of the A concept, these stresses do not exceed 37 MPa, which for the analyzed alloy is significantly below its yield point. For the B concept, this value reaches a much higher value, i.e. 100 MPa, but it still does not affect the formation of cracks, because the material has a much higher yield point.
Another feature presented in Figure 9 is the distribution of ten-    Perform the operation of removing the gating system will reduce the value of residual stress-es, i.e. those arising in the technological process. The application of heat treatment will cause relaxation and elimination of stresses arising after the solidification casting process (stresses resulting from the essence of the solidification process and the resistance of the ceramic mould).
Control castings made according to the developed technology

Conclusions
a. Realizing the project work described in the article, the main goals were achieved, namely: 1. An analysis of the design and operational requirements for foundry materials for the production of new tools for the for- c. Measurements of the geometry of selected hammer heads showed that the stresses that arise during the solidification and cooling process for the analyzed manufacturing concepts of the implemented tools are below the yield point of the material used and do not cause its de-formation.