INVESTIGATION OF THE POSSIBILITY OF INCREASING THE DURABILITY OF STEEL CASTINGS 110Г13Л

ABSTRACT

The study of the structure and properties of modern steels for cast parts of mining equipment showed that high-manganese austenitic steels 110Г13Л (Hadfield steel) remain promising for their manufacture. The purpose of this work is to analyze the technology for the production of cast linings for ore-grinding equipment from this steel grade. The results of factography, macro- and microstructural analysis of the alloy structure, carried out at Production Association “Navoi Machine-Building Plant”, showed that porosity and voids are formed in the central part of the casting, and microporosity - along the entire section of the casting, including in thin sections. This will make it possible to adjust the technology for producing castings from 110Г13Л steel. Microstructural analysis carried out by specialists of Production Association “Navoi Machine-Building Plant” showed that in the cast state for steel 110Г13Л, the desired steel structure is the dendritic structure of austenite grains, in the body and along the grain boundaries of which excess carbides are located. The modification helps to reduce the grain size of the austenite. Heat treatment helps to relieve casting stresses and obtain a homogeneous austenitic structure by dissolving excess carbides. The most desirable structure after heat treatment is an austenitic structure, with martensite on the surface of the casting resulting from a high cooling rate.

АННОТАЦИЯ

Изучение структуры и свойств современных сталей для литых деталей горнорудного оборудования показало, что высокомарганцевые аустенитные стали 110Х13Х (сталь Хадфилда) остаются перспективными для их изготовления. Целью данной работы является анализ технологии производства литых футеровок для рудоразмольного оборудования из данной марки стали. Результаты фактографии, макро- и микроструктурного анализа структуры сплава, проведенного на Производственном объединении “Навоийский машиностроительный завод”, показали, что пористость и пустоты образуются в центральной части отливки, а микропористость - по всему сечению отливки, в том числе в тонких сечениях. Это позволит скорректировать технологию производства отливок из стали 110Х13М. Микроструктурный анализ, проведенный специалистами Производственного объединения “Навоийский машиностроительный завод”, показал, что в литом состоянии для стали 110Х13Х желаемой стальной структурой является дендритная структура.

Keywords: mill linings; crusher linings; mining equipment; steel; Foundry; chemical composition; mechanical properties; carbides, structure; modification; heat treatment.

Ключевые слова: футеровки мельниц; футеровки дробилок; горное оборудование; сталь; литейное производство; химический состав; механические свойства; карбиды, структура; модификация; термическая обработка.

INTRODUCTION

With the development of the mining industry in the Republic of Uzbekistan, in the 60s, the Navoi Mechanical Repair Plant (now the Production Association "Navoi Machine-Building Plant") was built. The development of castings from high-manganese wear-resistant steel 110Г13Л at this plant began immediately after its launch, since wear-resistant steels have already firmly established themselves in this industry [6, 9, 10]. Today, they are used to manufacture linings for ore grinding mills, caterpillar tracks, excavator bucket teeth, tooth crowns, incl. lining of the bowl and cones for crushers MP - 1000, weighing 6.4 and 7.3 tons, respectively. To date, the volume of production of 110Г13Л steel castings at the plant is more than 250 tons. in year.

Failure of the above units and mechanisms, caused by their breakdown or rapid wear, is the main factor determining the overhaul life of equipment, and leads to a reduction in ore extraction, reduces productivity and production efficiency.

Parts operating under conditions of shock-abrasive wear are traditionally made of steel 110Г13Л. This is due to the operational properties of this steel, in particular, its high resistance to impact and abrasive wear.

The chemical composition and mechanical properties of 110Г13Л steel are regulated by ГОСТ 977-78 (see Table 1). However, the wide range of concentrations of carbon, silicon and manganese, all other things being equal, do not guarantee the constancy of mechanical and operational properties even for parts of the same purpose. Insignificant deviations of chemical elements (C, Si, S) from the requirements of ГОСТ 977-78 and insignificant changes in the melting conditions of steel 110Г13Л lead to inconsistency in the mechanical properties of the alloy with the requirements of regulatory and technical documentation [1, 2, 9, 10].

Today, there are various ways to improve the quality of 110Г13Л steel. One of the promising methods is alloy modification. Modification makes it possible to qualitatively change the technology for producing castings. However, the widespread use of modification in the practice of foundry production is hindered by the instability of the achieved effect due to the sensitivity of the process to the conditions of melting, pouring and uniform distribution of modifiers in the volume of the melt [3, 4, 9, 10]. Creation and application of ultradispersed (fraction sizes up to 1000 nm) and nanodispersed (fraction sizes up to 100 nm) modifiers will provide changes in the structure of liquid melts, increasing the properties of castings.

Microstructures of 110Г13Л steel samples obtained according to the existing technology and after the introduction of a modifier of the "MS" type produced according to TU 1760-001-64101572-2011 were investigated at PO "Navoi Machine-Building Plant".

Analysis of the results of metallographic studies showed that the modification of the melt of steel 110Г13Л made it possible to reduce the amount of non-metallic inclusions, improve the homogeneity of the structure, refine the grain size of austenite, and reduce the number of gas pockets, which, in turn, led to an increase in the density of castings. This improves the operational characteristics of castings - uniformity of load distribution, a decrease in the likelihood of cracking under shock loads, the formation of gas pores, thereby reducing the number of chips on castings [4, 5, 7, 8].

The purpose of this work is to analyze the technology for the production of cast linings for the MP-1000 crusher.

METHODIC

The studies were carried out with the use of the equipment "TEKHNOPARKA" of the Navoi State Mining Institute and the Central Laboratory of the Production Association NMP.

Models, molds, melting and knocking out of experimental casts of lining of the crusher MR - 1000 were produced in the foundry of PO NMP using the following equipment: mixer 1504M; shaking pneumatic casting molding machine with a transfer table, model 234MK; three-phase arc furnace ДСП-6 and knock-out grate model 31215.

To determine the chemical composition of the steel, a SPECTROMAX optical emission spectrometer (made in Germany) was used.

Determination of hardness is carried out on a TSh-2M hardness tester (TOCHPRIBOR, Russia).

The microstructure of the steel was studied using an MMP-4 metallographic microscope (LOMO, Russia).

Mechanical properties were determined on a R-50 tensile testing machine (Russia) with a force of 500 kN.

For the experiments, 110Г13Л steel was taken, the chemical composition of which is shown in Table 1.

Table 1.

Chemical composition of steel 110Г13Л 

RESULT AND DISCUSSIONS

The results of studies of the macro- and microstructure are shown in Fig. 12.

The microstructure of 110Г13Л steel in the cast state is coarse-grained austenite and carbides located in the body and along the grain boundaries of austenite (Fig. 1a).

Figure 1. Micrograph of a 110Г13Л steel sample before (a) and after (b) heat treatment, x100

During quenching, carbides located in the body and along the boundaries of austenite grains are completely dissolved. After quenching, the microstructure of the steel is coarse-grained austenite (Figure 1b).

The study of the fracture surface of the witness specimens cast together with the linings was carried out using an MB-8 microscope. The macrostructures of the samples before (in the cast state) and after quenching are shown in Fig. 2.

Figure 2. View of the fracture of the cast witness specimen (a) and the witness specimen after heat treatment (b)

In Fig. 2a, an uneven structure of the cast sample is observed, the fracture of the cast sample is brittle-ductile. After heat treatment, the austenite grain is crushed (Fig. 2b), the value of the viscous component is greater than in the as-cast state, less shiny crystals indicate a higher toughness of the alloy.

The mechanical properties of 110Г13Л steel in the cast state and after heat treatment were determined on a R-50 tensile testing machine with a force of 500 kN. The research results are presented in table. 2.

Table 2.

Mechanical properties of samples 

Brinell hardness as cast HB 231-246, after heat treatment (austenitization) HB 187-193. On the surface of the sample, due to the high cooling rate, martensitic regions with a hardness of HB 250 are observed.

The conducted studies of the structure and properties show that this steel can be used for the manufacture of linings operating for impact-abrasive wear. However, during the operation of the linings, the cases of their premature destruction became more frequent (see Fig. 3). To establish the causes of the breakage, a macrostructural and microstructural analysis of the lining fracture was carried out.

Macrostructural analysis of the lining fracture showed that over the entire surface of the casting there are micropores, porosity and voids (casting cavities) are also present in the central part of the casting, see Fig. 3. Visual inspection of the fracture was carried out using a magnifying glass x6 and x10 times.

Samples from the broken part of the lining for metallographic studies were cut out on a MECATOME T330 cutting machine (made in France), using a coolant. The preparation of the microsection was carried out on the NERIS grinding and polishing machine (made in Latvia).

In fig. 4 shows a diagram of cutting out samples for studying the microstructure. Porosity and voids are observed in the central part of the casting, and microporosity is observed throughout the entire section of the casting. An accumulation of gas pores is visible on the surface of the lining with the naked eye.

Numerous pores and non-metallic inclusions observed at small (X30 -50) magnifications in all microsections (see Fig. 7 - 12) are the result of poor-quality charge or insufficient deoxidation of the metal during smelting.

Figure 3. Lining failure surface

 Figure 4. Scheme of cutting out samples for metallographic studies

A schematic of cutting out samples for metallographic studies is shown in Fig. 4.

Figure 5. Micrographs of image No. 1 before (a) and after (b) etching, magnification x50 and x100.

From the provided micrographs of sample No. 1, it can be seen that micropores are observed over the entire surface of the sample, porosity and voids (casting cavities) are also present in the central part of the casting, see Fig. 5.

Manganese oxide is observed on the surface of sample No. 2 along the grain boundaries of austenite. Figure 6 shows the location of manganese oxide. An un-etched section is characterized by the presence of a black eutectic, which stretches along the grain boundaries of austenite. Etching of a thin section for the detection of manganese oxide with a 10% solution of hydrochloric acid in alcohol causes almost complete etching of the eutectic (Fig. 6b). This allows us to state that the above eutectic mainly consists of manganese oxide. There is an inverse relationship between the tensile strength, the narrowing of the cross-section, the relative elongation, the impact toughness of the steel and the content of manganese oxide in it, i.e. with an increase in the amount of manganese oxide in the metal, the above properties decrease. The concentration of manganese oxide in manganese steel varies widely and ranges from 0.01 - 0.15%. With an increase in the content of manganese oxide in the metal, its relative wear increases. Consequently, a decrease in the content of manganese oxide in manganese steel is one of the effective factors that provides a significant increase in the wear resistance of castings. The nature of the effect of manganese oxide in steel on the wear resistance of the latter can be explained by the fact that manganese oxide is located at the grain boundaries of austenite, see Fig. 6.

Figure 6. Micrographs of image # 2 x100, before etching (a) and after etching (b) at x300 magnifications

Figure 7. Micrograph of sample No. 3:

a - after etching, grains and dendrites of austenite are observed, x100; b - non-etched microsection, gas pores and non-metallic inclusions are observed over the entire surface of the microsection, x50.

Figure 8. Micrographs of samples No. 4 and No. 5:

Grains and dendrites of the solid solution of austenite, non-metallic inclusions and micropores are observed along the entire plane of the microsection. Increase. X100.

Thus, the analysis of the reasons that caused the destruction of the lining showed:

1. The surface of the fracture is non-common and on the surface of the fracture, with the naked eye, an accumulation of non-metallic inclusions is observed. Gas pores are observed over the entire fracture surface.

2. The microstructure shows the presence of non-metallic inclusions, obviously associated with poor quality charge or insufficient metal deoxidation during smelting.

3. Refined results of macro- and microstructural analysis showed that steel requires more thorough deoxidation.

In world practice, to improve the quality of steel, methods of out-of-furnace treatment by modification with the help of modifiers in the form of powders are widely used. The positive effect of modification on the macrostructure, grain size and a decrease in the number of non-metallic inclusions and on their shape is noted [5, 6, 9, 10, 11]. Considering the above, for industrial testing and study of the effect of the modifier on the structure of steel 110Г13Л, an experimental set of cone and bowl linings weighing 6.4 and 7.2 tons, respectively, for the MP-1000 crusher was made. A comparative study of the microstructure of castings obtained by the existing technology PO "NMZ" (pl. B103) and after the introduction of the modifier of the type "MS" according to TU 1760-001-64101572-2011 (pl. B106).

The chemical composition of the experimental castings is shown in table. 3.

Table 3.

Chemical composition of experimental melting

One of the promising ways to improve the quality of castings is to modify them with ultradispersed (fraction size up to 1000 nm) and nanodispersed (fraction size up to 100 nm) powdered materials. This direction allows you to qualitatively change the very technology of modification.

The introduction of the modifier was carried out by loading the modifier to the bottom of the ladle, the movement was carried out due to the energy of the falling stream of molten metal. The filling was carried out at a temperature of 1430 +/- 10 С

After the modification of 110Г13Л steel, samples were taken to study the macro- and microstructure and to test them for mechanical properties.

 To study the microstructure of modified alloys, microsections were made on a NERIS grinding and polishing machine (Kaunas, Latvia). To reveal the structure, a 4% alcoholic solution of nitric acid was used.

The structure of 110Г13Л steel in the cast state is a dendritic structure of austenite grains, with the location of excess carbides (Mn, Fe) C in the body and along the boundaries of austenite grains (Fig. 28a, b).

Figure 9. Microstructure of a cast steel 110Г13Л without modifier (a) and with modifier MS (b), magnification x100.

The micrographs show that the modification contributed to a decrease in the size of the austenite grain.

Figure. 10. Micrographs of the unmodified (a) and modified (b) reference specimen, which underwent heat treatment, magnification x100

Carbides in the body of the grain and along the grain boundaries of aussenite are neutralized by subsequent heat treatment (quenching). Micrographs of witness specimens that have undergone heat treatment are shown in Fig. 10.

As a result of the study of the samples without the use of the modifier, the microstructure of the samples was austenite with a value of "-1" points (according to ГОСТ 5939-78) with non-metallic inclusions along the boundaries and in the body of the grain (Fig. 9a). Also, when cutting the samples, gas pores and excess carbides are observed, which reduce the strength and toughness of the steel. The microstructure of the modified samples was austenite, grain size 3 points according to ГОСТ 5639-78, and minor non-metallic inclusions along the boundaries and in the body of austenite grain, see Fig. 9b.

CONCLUSION

The results of research and experimental industrial tests of the microstructure of high-manganese steel samples revealed the effect of the modifier on the microstructure of the samples in comparison with melts obtained using the existing technology, namely: modification of the melt of 110Г13Л steel made it possible to significantly improve the uniformity of the steel structure, reduce the size of the austenite grain, the number of gas pores, the number and size of nonmetallic inclusions, which in turn contributes to an increase in its density and leads to an improvement in its operational properties - it improves the uniformity of the distribution of loads, reduces cracking, the formation of pores and chips.

References:

1. Bannister, A.C. Structural integrity assessment procedures for european industry. Sintap. Sub-task 2.3: yield stress/tensile stress ratio: results of experimental programme/A.C.         Bannister, 1999. Режим доступа: http://www.eurofitnet.org/sintap_BRITISH_STEEL_BS-25.pdf.
2. Bringas, E. John Handbook of Comparative World Steel Standards / E. John Bringas // Bringas, E. John, editor. - 2nd. p.cm - (ASTM data serias; DS 67A).
3. Development of Steelmaking Processes for Producing Various High-Quality Steel Grades at Yawata Works / Shintaro Kusunoki, Ryoji Nishihara, Katsuhiko Kato, Hitoshi Sakagami, Shinichi Fukunaga, Naoki Hirashima // Nippon steel technical report, No. 104, August 2013, рр. 109-116.
4. Egamberdiev I.P., Atakulov L., Muminov R.O., Ashurov Kh.Kh. Research of Vibration Processes of Bearing Units of Mining Equipment // International Journal of Advanced Trends in Computer Science and Engineering. ‒ Volume 9, No.5, September - October 2020. – pp.7789-7793 (Scopus Base, DOI: 10.30534/ijatcse/2020/125952020).
5. Egamberdiev I.P. Spectral analysis of the oscillatory process of support assemblies on drilling machines // International Journal of Advanced Research in Science, Engineering and Technology. – National Institute of Science Communication and Information Resources– India, 2018. –Vol. 5. – Issue 5. – рр. 5958-5962.
6. Karimov N.K., Egamberdiyev I.P., Yaxshiyev Sh.N. Recommendations for improving the system of maintenance and repair of mining equipment // Сборник материалов II международной конференции на тему: «Комплексное инновационное развитие Зарафшанского региона: достижении, проблемы и перспективы». – Навои, 27-28 ноября 2019 г. – С. 551-556.
7. Медведев, В.И. Исследование, разработка и внедрение технологии изготовления отливок из комплексно-легированных сталей для быстроизнашивающихся сменных деталей горно-обогатительного оборудования / Медведев, Валерий Иванович: дис. ... канд. техн. наук - 05.16.04. - Брянск, 1999. - 149 с.
8. Сердитов, А.Е. Литые хладо- и износостойкие стали для горнодобывающей техники: дисс. ... канд. техн. наук: 05.16.01 / Сердитов Антон Евгеньевич; [Место защиты: С.-Петерб. политехн. ун-т]. - Санкт-Петербург, 2008. - 141 с.
9. Специальные стали и сплавы / А.А. Ковалева, Е.С. Лопатина, В.И. Аникина, Т.Р. Гильманшина. - Красноярск: Сиб. федер. ун-т, 2016. - 168 с.
10. Эгамбердиев И.П., Рузибаев А.Н., Туйбойов О.В., Жумаев А.А. Методика проведения производственных испытаний зубьев ковша экскаватора на карьере «МУРУНТАУ» // «Новый университет», Россия, Йошкар-ола, 2015. – №43. – С. 22-25.
11. Sh.N. Yaxshiyev, Kh.Kh. Ashurov, A.J.Mamadiyarov Dynamics of Spindle Assembly of Metal-Cutting Machine // International Journal of Engineering and Advanced Technology (IJEAT) ISSN: 2249 – 8958, Volume-9 Issue-3, February 2020. 3121-3125.