Deceased 26th November 2016
The paper presents the characterization results of various types of steel component at the end of product life with the unknown chemical composition, mechanical properties and previously implemented thermo–mechanical treatment. This study was done aiming to examine the possibilities for reuse of some end–of–life agricultural and industrial steel products in order to obtain blades for knives in non–industrial conditions with appropriate and acceptable properties. Demanded shapes of the blades were obtained by applying various types of thermo–mechanical treatment. Chemical analysis of the investigated steel components was done using the energy–dispersive spectrometer. The microstructure was analyzed using optical and scanning electron microscopy. Hardness of analyzed steel scrap and obtained blades was measured using Rockwell C scale. The hardness values of the obtained blades (with optional quenching or not) indicate to a good selection of the steel end–of–life products for this purpose.
Steels refer to alloys of iron with up to approximately 2 wt. % of carbon, very complex by structure, and widely used as engineering materials because of high iron content in the Earth’s crust, very good features and low price (Zeng
Any steel product has its own life cycle consisting of ore extraction, production, processing and finishing, product use, recycling or withdrawal at the end of its life cycle (Morfeldt
Steel production can be divided into two techniques: primary and secondary production techniques which use iron ore or steel scrap, respectively, as a ferrous resource. Steel primary production requires high process energy and large amounts of coal, resulting in high CO2 emissions (steel production is the major source of carbon dioxide emissions). Secondary production technique has a lower energy requirement (about one–third of the energy for primary production) and CO2 emissions (less than one–quarter of the emissions during the primary production) (Oda
During the exploitation and maintenance of agricultural and industrial machineries, certain amount of steel scrap is being produced. The maintenance of these machineries, among other things, includes consumable machinery components replacement at the end of their useful life. Therefore, agricultural and industrial steel scrap is of a great environmental and economic potential (Pacelli
For the experimental research, four different steel components were selected, which represent consumable parts (at the end of their life) of the agricultural and industrial machineries with the unknown chemical composition, previously implemented thermo–mechanical treatment and mechanical properties. The labels of the steel scrap (SS1, SS2, SS3 and SS4) and a pre–given purpose of these components at the end of their life are listed in
Labels and pre–given purpose of the investigated steel scrap
Label | Pre–given purpose of steel scrap |
---|---|
SS1 | Hacksaw |
SS2 | Steam turbine moving blade |
SS3 | Sword of a chainsaw |
SS4 | Rototiller hoe |
Macrophotographs of the investigated steel scrap.
Knives as the final products made from different steel scrap: (a) SS1 – hacksaw; (b) SS2 – steam turbine moving blade; (c) SS3 – sword of a chainsaw; and (d) SS4 – rototiller hoe.
The samples of the initial steel scrap, obtained blades and blades made of SS2 and SS3 after oil quenching were subjected to hardness measurement using the WPM Leipzig Rockwell C hardness tester. The hardness of the blades was measured at five points, depending on the distance from the cutting edge. The average value was taken for further analysis. The microstructure of the initial steel scrap was analyzed after standard procedure for microstructural preparation (grinding, polishing and etching with 2% solution of nital). Only the sample SS2 was etched using a solution prepared by mixing 15 ml HCl, 5 ml HNO3, and 80 ml H2O. Microstructure was analyzed using Carl Zeiss Jena Epityp 2 optical microscope (OM) and Tescan Vega 3LMU scanning electron microscope (SEM). Oxford Instruments X – Act energy–dispersive spectrometer (EDS) was used to determine the chemical composition of the initial steel scrap samples and the element distribution maps of the sample SS4.
In
SEM – EDS results of the steel scrap SS1: (a) SEM microphotograph; (b) EDS spectrum of the area in the microphotograph in
SEM – EDS results of the steel scrap SS2: (a) SEM microphotograph; and (b) EDS spectrum of the area in the microphotograph in
SEM microstructure of the steel scrap SS3 is shown in
SEM – EDS results of the steel scrap SS3: (a) SEM microphotograph; and (b) EDS spectrum of the area in the microphotograph in
SEM – EDS results of the steel scrap SS4: (a) SEM microphotograph; and (b) EDS spectrum of the area in the microphotograph in
Distribution map of elements in the scanning region in
The optical microphotographs of the initial steel scrap are given in
Optical microphotographs of the starting steel scrap: (a) SS1; (b) SS2; (c) SS3; and (d) SS4.
The microstructure of the steel scrap SS2 is shown in Figs.
SEM and optical microphotographs of the steel scrap SS3 are shown in
Hardness values (HRC) of steel scrap SS1, SS2, SS3, and SS4; blades made of SS1, SS2, SS3, and SS4; and blades made of SS3 and SS4 after oil quenching.
The hardness value of the scrap SS1 is 63 HRC, while the blade made of this steel scrap only by using mechanical treatment (cutting, grinding and polishing) shows the same hardness value.
The steel scrap SS2 has a significantly lower value of hardness of about 19 HRC. The blade made of this type of steel scrap has a slightly higher hardness value of about 22 HRC, as a result of the applied thermo–mechanical treatment in order to shape scrap to final blade. This blade was further quenched from the austenitization temperature, which additionally increased its hardness value to 34 HRC.
Steel scrap SS3 has a hardness value of about 43 HRC. The performed thermo–mechanical treatment has not affected the hardness value. However, quenching of the obtained blade in oil caused a significant increase in hardness, up to 64 HRC.
Steel scrap SS4 has a similar hardness value (about 41 HRC) as steel scrap SS3. Applied mechanical treatment, which was aimed to form steel scrap into blade, had no effect on the hardness value.
Various end–of–life agricultural and industrial steel products are very valuable for reusing. Therefore, this paper studies the possibilities of reusing of some end–of–life agricultural and industrial steel products in order to obtain blades. The characterization of chosen steel scrap showed that the initial materials were very different in structural, chemical and mechanical properties. The blades obtained in non–industrial conditions, using four different steel scrap as initial materials, had a wide range of hardness values (from 22 HRC to 64 HRC) depending on the type of steel scrap and implemented thermo–mechanical treatment. The blade made from steel scrap SS1 showed the highest value of hardness, which was achieved without further quenching, only by mechanical shaping of the starting steel scrap. The same hardness value was obtained on the blade made of steel scrap SS3 after thermo–mechanical treatment followed by quenching. The hardness values of blades made of steel scrap SS2 and SS4 were lower, 34 HRC and 43 HRC, respectively. By reusing steel scrap for different purposes various benefits can be achieved (reduction costs, saving energy, less raw material usage and decrease in waste disposal costs), which is in accordance to the basic requirements of the European Union waste management strategy (Vehlow
The research results were developed under the projects TR34023, TR34003 and OI172037 for which the funds were provided by the Ministry of Education, Science and Technological Development of the Republic of Serbia. The authors would like to thank Prof. Dr. Svetlana Nestorović (deceased in 2015) and Igor Kalinović for their help.