PROSPECTS FOR RECYCLING SOLID METALL WASTE

ABSTRACT

This article explores – Re expanding capabilities use of waste and unsuitable lump waste from high-speed steels. This task is achieved by the fact that in the known method of producing high-speed steel from lump waste of worn cutting tools from high-speed steels using the electroslag remelting method, in which the consumable electrode is made by remelting of this waste, according to the proposed method, the lumpy waste is pre-sorted and the tail parts are cut off, if necessary, before melting. From the obtained samples, milling cutters were made for processing parts with medium hardness, meeting the requirements for woodworking tools.

АННОТАЦИЯ

В данной статье рассматривается одна из расширенных возможностей использования отработанных и непригодных кусковых отходов из быстрорежущих сталей. Поставленная задача достигается тем, что в известном способе получения быстрорежущей стали из кусковых отходов изношенного режущего инструмента из быстрорежущих сталей методом электрошлакового переплава, при котором расходуемый электрод изготавливают путем переплава этих отходов, согласно предлагаемому способу, кусковые отходы предварительно перед плавлением сортируют и, при необходимости, обрезают хвостовые части. Из полученных образцов были изготовлены фрезы для обработки деталей средней твердости, отвечающие требованиям, предъявляемым к деревообрабатывающим инструментам.

Keywords: Lump waste, high-speed steel, cutting tools, electro slag remelting.

Ключевые слова: Кусковые отходы, быстрорежущая сталь, режущий инструмент, электрошлаковый переплав.

Introduction

A used tool is a valuable secondary raw material because it contains rare, expensive materials: tungsten, vanadium, cobalt, molybdenum, etc.

Organization at large metalworking plants of the process of remelting worn-out tools from high-speed steel using an electroslag remelting (ESR) installation makes it possible to obtain a large economic effect by reducing the cost of purchasing high-speed steel. [1]

The rational use of waste generated in industrial plants is a major problem. At the same time, of the total amount of waste arriving at secondary ferrous metals bases, up to 10% is expensive high-quality steel. The cost of 1 kg of secondary metal is $0.27 (US), when alloy high-speed steel costs $7 (US) per 1 kg; this necessitates the effective use of the resulting lump and chip waste for the production of grade metal.

The existing technology for processing lump and chip waste of tool steels is multi-stage and is associated with high energy costs:

An analysis of currently used methods for the production of high-alloy steels, such as induction and electric arc melting, electroslag remelting, indicates the advantages of the latter method, which can provide:

- Insignificant waste of the main alloying elements of high-speed steels, eliminating additional alloying during remelting of metal of final chemical composition;

- Defect-free surface of ingots that does not require cleaning before deformation;

- High chemical and structural homogeneity of the metal with a low content of impurities and gases;

- A better complex of physical and mechanical properties compared to conventionally smelted metal. [2]

High-speed steel of electroslag smelting, due to its fine microstructure and uniform distribution of the carbide phase, chemical homogeneity and purity, has higher ductility than conventional steel.

The described advantages of ESR tool steels apply only to the use of compact (cast or deformed) consumable electrodes.

The ESR process is used to produce high-quality steel by removing sulfur, non-metallic inclusions and gases from the metal. The oxygen content decreases by 1.5-2 times, sulfur by 2-3 times. The ingot is distinguished by a dense, uniform structure over its entire cross-section, good surface quality, and high mechanical properties. [3]

There is a known method for producing high-speed steel from waste of worn cutting

tool using the ESR method, in which this waste pre-cast in induction or arc furnaces is used as a consumable electrode [4].

When high-speed steel waste is remelted in an electric arc or induction furnace, expensive alloying elements such as tungsten, vanadium, molybdenum, cobalt, chromium, etc. are partially burned out. Then the finished steel is poured into a chill mold and the resulting rods are used as consumable electrodes when remelting them in the installation ESR.

There is a known method for producing a steel ingot when a composite electrode is used for electroslag remelting. This method can be used to produce, for example, high-speed steel ingots. According to this method, the electrode is welded from pieces of the same grade, for example, high-speed steel, and after ESR, metal of the same steel grade as the original electrode is obtained. This method narrows the possibilities of using available lump waste from various grades of high-speed steel, since it allows, after remelting, to obtain an ingot of only the grade of steel that was used in the manufacture of the electrode. [5]

The operating principle of the ESR furnace used in this study is that the power source is connected on the one hand to the consumable electrode and on the other hand to the forming electrode. The consumable electrode is melted by passing electricity through the molten slag in a pre-calculated ratio, and the ingot is poured into a prepared mold, in the form of a rod with a circle at the base, water-cooled by a gradual solidification method in a stack. Since molten steel, passing through the slag, quickly solidifies in a water-cooled crystallizer, while retaining all alloying elements. The remelted electrode is welded from recycled high-speed steel tool waste, i.e., from raw materials of the highest quality, already meeting technical requirements for purity. Therefore, during the remelting process there is no need to increase the voltage and current in order to enhance the refining effect of the slag bath during the remelting process. [7]

Materials and methods

60 kg of used drills of steel grade R6M5 (HSS-G) were collected after cutting off the tail parts, the weight of the required scrap was 32 kg. The process of recycling high-speed steel scrap consisted of 3 stages (Figure 1-3): obtaining an electrode from lamp; Manufacturing of blanks for rods; Receiving cutters as the final product. At each stage of the work, chemical analyzes of the components of the resulting product were carried out (Table 1). After heat treatment of metal materials at high temperatures in chemically active environments, the percentage of chemical elements decreases. This is explained by dissociation, adsorption, diffusion and phase transformations. One of the reasons for the decrease in percentages is the burnout of elements. In this case, as previously described, the elements burned out after each heat treatment; melting on an induction furnace, electroslag remelting, forming-forging, calibration-forging.

Table 1.

Chemical analyzes of the components

A steel electrode (at a pouring temperature of 1550 ℃) with a diameter of Ø 130 mm and a height of 175 mm was produce using an IMF-160/150 induction furnace. The work piece turned on a lathe to a diameter of Ø 125 mm to obtain chips. (Figure 1)

Figure 1. Electrode manufacturing process (A - used drills, B - melting on an induction furnace, C - finished electrode)

On the ESR installation 3.0 kA to obtain a workpiece with a diameter of Ø 295 mm, a height of 30 mm, with a remelting speed of 1200 A. 2 kg of previously obtained chips and 2 kg of ANF-6-1 flux in addition to the electrode were poured onto the crystallizer. After cooling, the workpiece was cut and forged on a forging machine at a temperature of 1060 – 1100℃ to dimensions h -25, b -25, l -500 mm. (Figure 2)

Figure 2. ESR process (A - Crystallizer, B - melting at the ESR installation, C - finished workpiece)

The production of cutters as a final product was carried out; First, the workpieces were subjected to additional forging, at a temperature of 1000 - 1100 ℃, to bring the workpiece into a cylindrical profile from a square one. The blanks were turned on a SCHNEBERGER machine. (Figure 3)

Figure 3. Milling cutter manufacturing process (A - sample pieces, B - forged square sample C - finished cutter)

Based on the obtained chemical results, the manufactured cutters contain Mo -1.78%, W -2.61%, Cr -1.83%, which is comparable to the content of the main alloying elements of steel grades O7 and 107WCr5 according to UNS T31507. The resulting material has improved (compared to alloyed tool steel) cutting properties. It is possible to process parts at temperatures up to 400–500 °C and operating speeds of 25–30 m/min, which meets the requirements of woodworking tools.

Results and discussion

The resulting alloy is characterized by the absence of defects of liquation origin, a dense defect-free macrostructure, microcrystalline structure and structural homogeneity.

Thus, the proposed method of electroslag remelting of used drills makes it possible to obtain tool steel that fully meets all the requirements for serial tool products.

The material for the manufacture of cutters must have the following characteristics:

• Hardness exceeding that of the processed products;
• High wear resistance;
• Mechanical strength.

Traditionally, carbon tool steels, high-speed steels, hard alloys, ceramics, artificial and natural diamonds are used to produce cutting tools.

The following metals can contribute to achieving the above characteristics:

Tungsten (W) even in small quantities increases the hardness, tensile strength and improves the cutting properties of steel without reducing its ductility. Tungsten helps produce fine-grained steel and improves its heat resistance.

Molybdenum (Mo) is equivalent in properties to tungsten, but its effect is more pronounced; its content in steel in small quantities increases cutting properties and hardness without reducing ductility. Molybdenum prevents cracks.

Chromium (Cr) is an additive widely used in the production of tool steel to improve its tensile strength, elastic limit, hardness and wear resistance. [6]

Steel grades O7 and 107WCr5 are used for the production of slotted, shaped and end mills. This material has improved (compared to carbon steel) cutting properties. It is possible to process parts at temperatures up to 400–500 degrees and operating speeds of 25–30 m/min. (Table 2)

Table 2.

Characteristics of steel grades O7 and 107WCr5, compatible with the chemical composition of the resulting sample

Conclusions

A method for producing high-speed steel from lump waste of worn cutting tools from high-speed steels using the ESR method, including the manufacture of a consumable electrode by melting the said waste, characterized in that the lump waste is pre-sorted and before melting, the tail parts are cut off as a result of remelting the final high-speed steel ingot with a predetermined chemical composition, which is different from the chemical composition of the original lumpy waste.

Method for smelting tool steel ingot from tool waste production, characterized by the remelting of waste consisting 100% of lump scrap and high-speed steel shavings, while the remelting of lump high-speed steel scrap is carried out in an induction furnace to obtain consumable electrodes, which are then remelted in an electroslag remelting installation.

Based on the obtained chemical results, the manufactured cutters contain Mo -1.78%, W -2.61%, Cr -1.83%, which is comparable to the content of the main alloying elements of steel grades O7 and 107WCr5 according to UNS T31507 and EU 96. The resulting material has improved (compared to alloyed tool steel) cutting properties. It is possible to process parts at temperatures up to 400–500 °C and operating speeds of 30–25 m/min, which meets the requirements of woodworking tools.

Now, the experiments are ongoing, the method of obtaining cutters by pouring onto ready-made molds after melting solid waste is being considered, the purpose of this solution is to preserve burnt-out elements and reduce production costs.

References:

1. Ivanov, V.G., Perevyazko, A.T., Chuiko, N.M. et al. Remelts of high-speed-steel chips. Metallurgist 19, 264–266 (1975). https://doi.org/10.1007/BF01226284.
2. Stroganov, A.I., Pyl'nev, Y.A., Chernyshev, E.Y. et al. Losses of tungsten during melting of high-speed steels. Metallurgis 15, 38–40 (1971). https://doi.org/10.1007/BF01087112.
3. L. D. Moshkevich, and S. I. Tishaev, “Electroslag remelted high-speed steel quality” Stal’, No. 3, 219 – 222 (1977).
4. Ivanov, I.I., Petrov, P.P. (2010). Method for making high-quality instrument steels from wastes of instrument manufacture. RU2405843C1.
5. Hoyle, G. (1983) Electroslag Processes, Principles and Practice. Applied Science Publishers, London/New York.
6. F. A. KIRK, “Materials for metal cutting” (Iron and Steel Institute, London, 1970) p. 48.
7. T. MATTAR "Production of tool steels", Ph.D. thesis, Chemistry Dept., Faculty of Science, Helwan University, Cairo, Egypt, June 1996.