Reliable as rail steel. Rail steel and rail markings. Chemical composition and quality requirements for rail steel

20.10.2023 alternative energy

Interview: Evgeniy Shur, chief researcher of the Department of Transport Metal Science of VNIIZhT, Doctor of Technical Sciences

VNIIZhT begins testing new types of rails

– Why now is there a need to improve the quality of rails?

– In recent years, there has been a steady increase in traffic volumes on the country’s railways, freight traffic has increased, long-unit and heavy trains have been introduced, and a program has been adopted to increase traffic speeds.

Under these conditions, railway workers require new, more reliable rails capable of carrying 700–1,500 million tons of cargo under the most severe operating conditions without excessive wear and damage. For now, they are designed to carry 300–700 million tons on most road sections. That is, their resource needs to be doubled, and in a short time.

In 2007, more than 125 thousand defective rails were removed from service on Russian railways. Russian Railways spent more than 11 billion rubles last year on the purchase and replacement of faulty rails. And if we take into account that the total deployed length of our rail threads is 124 thousand km, then the requirements for the quality of products of domestic metallurgical plants should be especially high. It is no coincidence that a new standard for these metallurgical products has been in force since 2000; even more stringent requirements will be adopted in the near future.

– What do you propose to do?

– First of all, we need to increase the requirements for the quality of rails, which metallurgists must produce using the most modern technologies. Their service life needs to be increased at least twice. An equally important task is to increase the length of solid-rolled rails from 25 to 100 m (150-meter copies are already being produced abroad). After all, the fewer welded joints, the less trouble on the roads. To do this, it is necessary to quickly introduce innovative technologies that would allow domestic metallurgists to produce high-quality products that are in no way inferior to the best foreign models.

I think it’s time to expand the range of types of rails produced in our country. To organize high-speed passenger traffic in Russia at speeds of up to 350 km/h, rails of the BC category are required. To increase the speed of passenger trains to 200 km/h on a number of directions of the road network, rails for high-speed combined traffic of the SS category are needed. And for highways in Siberia and the Far North, rails of increased cold resistance and low-temperature reliability of the NK and NE categories are suitable.

In addition, for sections of the track with curves of small and medium radii, where rails especially often fail, rails of increased wear resistance and contact endurance of category I are required. Moreover, all these products must be twice as good in quality and reliability as those produced today. So far, domestic rails are inferior to the products of world leaders.

In 2007, more than 125 thousand defective rails that failed due to low quality steel were removed from service on Russian railways

– What is the reason for such a lag?

– In the early 70s of the last century, our enterprises introduced the then advanced technology for heat treatment of rails. Thanks to this method, we have produced the best products in the world for two decades. But then, due to the onset of the economic crisis, no funds were allocated for the modernization of production in our country, and foreign competitors from Japan, France and Austria, having mastered advanced technologies, took the leading positions.
True, over the past 10 years our metallurgists have managed to improve a lot. Having abandoned the production of rails from open hearth steel, they began to produce them from continuously cast oxygen-converter steel and electric steel. They began to use the continuous casting method, use furnaces to heat the workpieces before rolling, CNC roll lathes and other new products. Moreover, the improvement in the quality of rails was influenced not only by the achievements of world leaders, but also by the strict requirements of JSC Russian Railways, as well as the great work done by scientists from VNIIZhT and other institutes at the country's metallurgical plants to improve transport metal production technologies.

Although imported products are still better in many respects - geometry, straightness, quality of surface and finish, hardness, strength and wear resistance.

– What prevents domestic factories from producing rails that are not inferior to the world’s best analogues?
– First of all, there is a lack of high-quality equipment, and without a radical reconstruction and modernization of factories, success will probably not be achieved. Another equally important reason is the lack of competition. Today in Russia, only two enterprises produce rails - Nizhny Tagil and Novokuznetsk metallurgical plants, owned by the same owner - EvrazHolding LLC. But there is hope that soon the monopoly in this market will come to an end. In the coming years, high-quality rails will begin to be produced at the Chelyabinsk Metallurgical Plant, where a special workshop will be built for this purpose and the most modern equipment will be installed. In addition, next to the plant, it was decided to locate a large rail welding enterprise, where 800-meter strands for a continuous track will be welded from the 100-meter rails produced. It is also important to incentivize factories by purchasing more durable rails at a higher price.

It is important to organize serial production of a new type of rail. To do this, it is necessary to transition metallurgical plants to rolling rails in universal strands, introduce descaling technology, install equipment for automatic monitoring of the absence of defects and straightness of rails, and increase the degree of computerization of the entire production process.

– What scientific developments are metallurgists currently mastering?

– For long-term operation under conditions of large axial loads, high load intensity and curved sections of the track, rails with a carbon content in steel increased to 0.83 - 1.0% are most suitable. Tests on the Experimental Ring of VNIIZhT and trial operation on the South Ural, Oktyabrskaya and Gorky railways showed that their service life is significantly higher than that of conventional samples. Based on the results obtained, domestic metallurgical plants are already beginning to produce such rails, albeit in small quantities for now. By the way, this grade of steel, called “hypereutectoid,” was created by scientists and metallurgists in our country, but for some reason it has so far found widespread use only abroad.

In our opinion, a further increase in the performance of rails is also possible with the transition to a new structural steel base. Of the two possible options (martensite and bainite), experts prefer bainite. Currently, our metallurgists have already developed low-alloy rail steel with a bainitic structure, which makes it possible to increase the strength of the metal while simultaneously reducing the carbon content, which, in turn, will have a positive effect on its resistance to thermomechanical damage. The laboratory and bench tests carried out gave encouraging results. Now the new type of rails is to be tested at the Experimental Ring of VNIIZhT in Shcherbinka.

Interviewed by Alexander Davidyants

Until the mid-1990s, U.S. railroads purchased improved head-hardened rails from foreign suppliers, who were then the only manufacturers of these products. However, since 1994, when Pennsylvania Steel Technologies (PST) began producing rails from high-quality steel at a rebuilt plant in Steelton, the modernization of which cost $40 million, the situation began to change. PST's example was followed in 1996 by CF&I Steel with a refurbished plant in Pueblo.

At first, it began to produce rails with a volume-hardened head of type DHH 370 (the number indicates the hardness of the steel in Brinell units), and in 1997 it switched to rails of type DHH 390. Improving the quality of rail steel, bringing its hardness to 390 units. according to Brinell, was achieved through cooperation with the Japanese company Nippon Steel, which made it possible to use the technology of this company, which is the world's largest manufacturer of rails. According to the technical requirements of the American Railroad Engineering Association (AREA), the hardness of rails must be at least 341 units. according to Brinell, so CF&I exceeded this figure by 14%. Another manufacturer of improved rails in the United States in the near future may be Stafford Rail Steel. Currently, North American railroads consider U.S.-made rail steel to be the best.

Foreign companies continue to produce high quality rails, which differ from those manufactured in the United States mainly in their sulfur content. In North America, substantially higher sulfur content is allowed in rail steel because it is believed to reduce the likelihood of hydrogen flocs. Abroad, in particular in Japan, they are trying to reduce the sulfur content, since they believe that over time it contributes to the formation of vertical fatigue cracks in the head and accelerates wave-like wear due to the occurrence of gaps between sulfur inclusions. The sulfur content of rail steel is the subject of ongoing debate. Proponents of higher sulfur content argue that a lack of sulfur can increase the risk of hydrogen embrittlement if the hydrogen content of steel is not controlled. Proponents of less believe that the introduction of new technologies such as induction mixing and vacuum degassing eliminates the need for sulfur. In any case, in North America, according to metallurgical experts, the situation in the field of rail steel can be considered unprecedentedly favorable.

However, while steel with a hardness of 350-400 units. According to Brinell, it meets the requirements of modern railways in terms of use for the manufacture of rails laid on haul and station tracks, for special places on the track, such as turnouts and blind intersections, other requirements. So, for crosspieces you need rail steel with a hardness of 450-500 units. according to Brinell.

Currently, the prevailing opinion is that pearlitic rail steel is apparently not suitable for operation under high axial loads. Even if its hardness can be increased to the required value, the pearlite microstructure can only bring the Rockwell index to C-40, since the risk of destruction further increases. A problematic mixture of pearlite and bainite structures can give a Rockwell index of C-40 to C-45. In the C-45-C-50 zone, the desired result is possible with a predominantly bainitic structure (Table 3.1). Bainite is much harder than pearlite and provides better wear resistance.

Table 3.1 - Chemical composition of rails in America

The Oregon State Institute, in collaboration with AAR, conducted research showing that there are two approaches to obtaining a bainitic microstructure. One of them involves isothermal processing of ordinary carbon rail steel to a Rockwell hardness of the order of C-45-C-50. Another approach uses carbon steel with reduced amounts of carbon, increased amounts of silicon, chromium, manganese, medium molybdenum, and low amounts of boron. After quenching in water, low-carbon steel becomes very strong and relatively tough. Research has confirmed the promising properties of bainitic steels, and recent advances in manufacturing technology have made their production commercially viable. In preliminary tests of rails made of bainitic and tempered steel with a hardened head, it turned out that bainitic steel with a low carbon content is better weldable. When tested directly in the rail track, bainitic steel also showed better results than improved steel.

The high strength of bainitic steel gives it good resistance to chipping and flaking, as well as much better fatigue performance. Since such steel is more expensive, improved economic performance is planned for the future. The physical characteristics of next generation rail steels will become even more favorable. Conducted comparative tests of new bainitic steel grade J9 and austenitic manganese steel (AMS) in laboratory conditions for weldability, wear and deformation. The results of these tests were successful. Tests on models carried out at approximately the same time at the University of Illinois made it possible to compare these steels under contact conditions when a wheel rolled on a rail. The results obtained confirmed the clear advantage of J9 steel in terms of service life over AMS steel.

[Article] Rail steel and rail markings

Rail steel and rail markings

Rail steel

The material for the rails is rail steel. Rails are made of two groups: Group I - from mild open-hearth steel, deoxidized in a ladle with complex deoxidizers without the use of aluminum or other deoxidizers that form harmful streaked non-metallic inclusions in the steel; Group II - from mild open-hearth steel, deoxidized with aluminum or manganese-aluminum alloy.

The quality of steel is determined by its chemical composition (Table 1.2).

With an increase in carbon C in steel, the overall bending strength of the rails, hardness and wear resistance increase. Manganese Mn increases the hardness, wear resistance and toughness of rail steel, and silicon Si increases hardness and wear resistance. Phosphorus P and sulfur S are harmful impurities. At low temperatures, rails with a high phosphorus content become brittle, and sulfur - red-brittle (cracks form when the rails are rolled). Vanadium, titanium and zirconium are micro-alloying and modifying additives that improve the structure and quality of steel.

The macrostructure of modern carbon rail steel is lamellar pearlite with small ferrite veins at the boundaries of pearlite grains. Significant hardness, wear resistance and toughness of carbon steels are achieved by giving them a homogeneous sorbitol structure (using special heat treatment).

The mechanical properties of steel for rails of groups I and II during tensile tests must correspond to the data given in table. 1.3.

These data correspond to rails made of open hearth steel, not hardened along the entire length.

Steel for rails must have a clean, uniform, dense, fine-grained structure (macrostructure).

The rail manufacturing technology must guarantee the absence of flakes in them, as well as local non-metallic inclusions (alumina, titanium carbides and nitrides or alumina cemented with silicates), extended along the rolling direction in the form of tracks - lines.

The surface of the rail head at its ends is subjected to hardening by rolling or induction heating with high frequency currents.

To ensure greater wear resistance and durability, the rails are made of open-hearth high-carbon steel (types P75, P65, P50), subjecting them to hermetic treatment along the entire length by volumetric hardening in oil followed by furnace tempering (GOST 18267-82). The macrostructure of the quenched rail head metal is sorbitol quenching. The Brinell hardness on the rolling surface of the head of hardened rails should be in the range of 341-388 HB, the neck and sole - no more than 388 HB.

The mechanical properties of volume-hardened rails must be characterized by values not less than those indicated below:

Rails that fully meet technical requirements and standards are classified as 1st grade. Rails that have deviations in the chemical composition and mechanical properties are classified as 2nd grade.

Volume-hardened rails have a service life 1.3-1.5 times higher than conventional ones.

The operating conditions of rails on the roads of Siberia and the Far East are almost twice as difficult as in the European part of Russia. Therefore, rails of low-temperature reliability P65, volume-hardened of group I, manufactured from vanadium-niobium-boron-containing steel using nitrided ferroalloys for alloying have been created. These rails use electric steel, which is welded in arc furnaces.

At a temperature of minus 60 °C, electric steel rails can withstand shock loads twice as high as open-hearth steel rails.

Currently, Russian rails are among the best in the world. However, Japanese, French, Swedish and Canadian rails have significantly lower levels of self-stress and greater purity of the rail steel, as well as straightness. That is why their purchase has now begun for high-speed sections of Russian railways.

Marking, service life of rails and measures to extend them

Rails are marked to ensure their correct placement on the track and to determine the place and time of manufacture of each individual rail. It is divided into the main (permanent) one, performed during rolling by stamping in a hot and cold state (Fig. 1.2) and additional or temporary, performed with paint. The main factory marking indicates the conformity of the rails

requirements of the standards, and an additional one notes the features of each rail (shortening, grade, etc.).

The plant that produces the rails guarantees the proper service of the rails along the way during the operating period, calculated in millions of tons of gross tonnage T. Rails are removed from the track either due to head wear or defects. As a rule, vertical wear of the head does not reach the limit values at the operating rate T, at which the rails are continuously replaced due to their maximum yield for single defects.

Currently, the accepted classification of rail defects is given in Table. 1.4.

The intensity of a single output of rails depends on their operating time (the tonnage passed along them), the track design, loads on the rails from wheel pairs of circulating rolling stock, the layout and profile of the track, the type of rails, the quality of steel and other factors. In Fig. Figure 1.3 shows the growth curves averaged for the network of the former USSR for a single withdrawal of non-heat-treated rails on straight and flat curves, depending on the skipped tonnage during a link track on wooden sleepers.

Bulk-hardened rails have a significantly lower output, which can be seen, for example, in the graph in Fig. 1.4 for the line St. Petersburg - Moscow.

The largest single removal of defective rails is made due to insufficient contact fatigue strength of the metal, due to excessive lateral wear of the head in curves and due to corrosion of the rail base and corrosion fatigue cracks (defects 44, 17, 21, 14, 11 , 69 - see table 1.4).

Extending the service life of rails is currently being done through the use of resource-saving technologies; in particular, a good means of restoring the service properties of rails is their periodic grinding along the way or sharpening of old rails at rail welding enterprises. Rail grinding mechanisms and rail grinding trains with abrasive wheels are used for grinding rails.

Improving the quality of rails is carried out in three main areas: increasing the purity of rail steel; increasing the hardness of rail metal and improving its structure; increasing the straightness of rails during manufacturing. The R65sh rail is also being developed, which will have a head height reserve (6...7 mm) for subsequent grinding.

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Introduction
1. General characteristics of rail steels
2. Chemical composition and quality requirements for rail steel
3. Rail steel production technology
4. Production of rail steel using modifiers
Conclusion
List of sources used

Introduction

Rail steel is a carbon alloy steel that is alloyed with silicon and manganese. Carbon gives steel characteristics such as hardness and wear resistance. Manganese enhances these qualities and increases viscosity. Silicon also makes rail steel harder and more wear-resistant. Rail steel can be made even better with the help of micro-alloying additives: vanadium, titanium and zirconium.

The wide range of requirements imposed in this regard on the quality of railway rails requires the improvement of technological processes, the development, testing and implementation of new technologies and the use of progressive processes in the field of rail production.

The main reason for the low prevalence of production of rails from electric steel is the targeted focus of the construction of modern electric furnaces with large-capacity furnaces to utilize regional scrap resources and provide regions with metal products for industrial and construction purposes. At the same time, fairly high economic efficiency and competitiveness are achieved.

1. General characteristics of rail steels

The production of rails in our country is about 3.5% of the total production of finished steel, and the freight load on railways is 5 times higher than in the USA, and 8...12 times higher than on the roads of other developed capitalist countries. This places particularly high demands on the quality of rails and steel for their manufacture.

Rails are divided into:

- according to types P50, P65, P65K (for external threads of curved track sections), P75;

- quality categories: B - heat-strengthened rails of the highest quality, T1, T2 - heat-strengthened rails, N - non-heat-strengthened rails;

- the presence of bolt holes: with holes at both ends, without holes;

- method of steel smelting: M - from open hearth steel, K - from converter steel, E - from electric steel;

- type of initial billets: from ingots, from continuously cast billets (CCB);

- anti-floc treatment method: made of evacuated steel, subjected to controlled cooling, subject to isothermal exposure.

The chemical composition of rail steels is presented in Table 1. In steel grades, the letters M, K and E indicate the method of steel smelting, the numbers indicate the average mass fraction of carbon, the letters F, C, X, T indicate the alloying of steel with vanadium, silicon, chromium and titanium, respectively.

Table 1 - Chemical composition of rail steels (GOST 51685 - 2000)

Wide gauge railway rails of types P75 and P65 are manufactured according to GOST 24182-80 from open hearth steel M76 (0.71...0.82% C; 0.75...1.05% Mn; 0.18...0 .40% Si;< 0,035 % Р и < 0,045 % S), и более легкие типа Р50 - из стали М74 (0,69...0,80 % С). После горячей прокатки все рельсы подвергают изотермической обработке для удаления водорода с целью устранения возможности образования флокенов. Рельсы поставляют для эксплуатации на железных дорогах незакаленными (сырыми) по всей длине и термоупрочненными по всей длине. Концы сырых рельсов подвергают поверхностной закалке с прокатного нагрева или с нагрева ТВЧ. Длина закаленного слоя от торца рельса 50...80 мм, а твердость закаленной части IIB 311...401. Сырые рельсы из стали М76 должны иметь ов >Ј 900 MPa and 5 > 4%. The rail manufacturing technology must ensure that there are no lines of non-metallic inclusions (alumina) extended along the rolling direction with a length of more than 2 mm (group I) and more than 8 mm (group II), since such lines serve as a source of initiation of contact fatigue cracks during operation.

The high load intensity of railways has led to the fact that the performance of raw, non-heat-strengthened rails no longer meets the requirements of the heavy work of the railway network.

Further increase in the operational resistance of thermally strengthened rails can be achieved by alloying the rail steel. Promising is the alloying of carbon rail steel with small additions of vanadium (-0.05%), the use of alloy steels such as 75GST, 75KhGMF, etc., as well as the use of thermomechanical processing.

2. Chemical composition and quality requirements for rail steel

rail steel chemical carbon

Steels that do not have a grade or code are designated by the number (code) of the corresponding standard and the serial number in this standard. For example, steels in the US standard ASTM A1 are designated as ASTM/1, ASTM/2, etc., steels in the Canadian standard are designated as CN/1, CN/2, etc., steels in Australian standards in accordance with the code standard are designated as AS/1 (standard AS 1085 p.1) and AS/11 (standard AS 1085 p.11).

The carbon content in rail steel is determined depending on the cross-sectional dimensions of the rail. In general, the dimensions of a rail are usually characterized by the mass of its linear meter (kg/linear m). The greater the mass of a linear meter, the higher the carbon content in rail steel should be.

Manganese acts like carbon, increasing the strength and wear resistance of hot-rolled rails. In this regard, in the Australian standard AS 1085 p.1, along with the content of carbon and manganese separately, the total indicator of their content (C+Mn/5) is also standardized. In the ASTM A1 standard, with a high manganese content, the content of nickel, chromium and molybdenum is limited, which is necessary to obtain a uniform structure of rail steel by ensuring a given level of hardenability. In steel grades B, 3B and 90B (standards BS 11, ISO 5003 and UIC 860), the decrease in carbon content is compensated by an increase in manganese content.

In Russian standards (GOST 24182, 18267), in addition to the limits for the content of basic chemical elements - carbon, silicon, manganese, phosphorus and sulfur, standardized in most foreign standards, limits for the content of micro-alloying additives are established: vanadium (steel grades M76V and M74V), zirconium (grades steel M76Ts, K74Ts and M74Ts), titanium (steel grades M76T, K74T and M74T) and vanadium together with titanium (steel grade M76VT), arsenic content is limited< 0,15% для сталей из керченских руд.

Domestic rail steels are similar in the content of manganese, silicon, phosphorus and sulfur. Grades of rail steels for a certain dimensional type of rail differ in microalloying additives. Such steels are practically analogues, therefore in the Consolidated List they are placed one after another with the corresponding foreign analogues indicated in each line. The repetition of one steel grade in two or more lines of the Consolidated List is due to the fact that there is more than one analogue in the standards of one country. For example, the first line of the Consolidated List indicates the domestic steel grade M76 and its analogues: according to the US standard ASTM A1 - ASTM/1, according to the Japanese standard JIS 1124-1124, according to the Australian standard AS 1085 r.11 - AS/11, according to the Canadian standard CNR1 - CN/1 and according to the international standard ISO 5003 - 2A. The second line of the Consolidated List for the same grade of M76 steel indicates other foreign analogues: according to the US AREA standard, the steel is designated AREA/1, according to the Australian standard AS 1085 r.1 - AS/1 and according to the Canadian standard CNR12 - CN/2. Steels CN/1 and CN/2 differ in silicon content, which depends on the method of steel smelting.

A significant improvement in the purity of rail steel and an increase in its metallurgical quality in Russia was achieved as a result of the transition from ladle deoxidation of steel with aluminum to its deoxidation with complex vanadium-silicon-calcium, silicon-magnesium-titanium and calcium-zirconium alloys. Complex deoxidation of rail steel with the listed alloys without the use of aluminum made it possible to eliminate the formation of lines of alumina inclusions in the rail head, which were centers of initiation of contact fatigue damage to the rails. The absence of stitched non-metallic inclusions in the rail head has led to an increase in their operational durability.

In most current standards, the right to choose the method of steel production is given to the manufacturer, and information about the method of steel production is communicated to the consumer through special markings of the rails. There are cases when, depending on the method of casting steel, different limits for the content of chemical elements are established. Thus, in the Canadian standard, the silicon content in steel when casting into ingots is 0.10-0.25%, and during continuous casting of steel - 0.16-0.35%.

An important element of the technological chain for the production of railway rails is anti-floc treatment, which consists of a special cooling mode for heavy-type hot-rolled rails (40 kg/linear m), which ensures the removal of hydrogen. or in vacuum degassing of liquid rail metal before casting. The Canadian Government Railways standard sets the maximum permissible hydrogen content in evacuated steel.

Control of the production technology of rail steel in the hot-rolled state is carried out by determining the mechanical properties during tensile testing of samples cut from the rail head and measuring Brinell hardness. In tensile tests, in most cases, temporary tensile strength (tensile strength) and relative elongation are determined, sometimes - relative transverse contraction.

The macrostructure of hot-rolled rails is also monitored with quality assessment using specially developed macrostructure scales.

The quality of rails is also assessed by the absence or presence of signs of destruction of rail sections as a result of being hit by a falling load. The weight of the falling load (usually 1000 kg), the height of the drop of the load and the distance between the supports on which the tested section (sample) of the rail is installed in a horizontal position are specified depending on the standard size of the rail using an equation or a special table given in the relevant standard. The impact is made in the middle between the supports of the rail sample.

The properties of thermally strengthened rails are assessed in standards by mechanical characteristics: when testing tensile specimens cut from the rail head, impact strength at room and low (-40°C, -60°C) test temperatures and hardness measured by Brinell, Rockwell, Vickers and Shora. The microstructure and depth of the hardened layer are also standardized, which depend both on the chemical composition of the rail steel, which determines the level of its hardenability, and on the heat treatment technology.

3. Rail steel production technology

In top and combined blast oxygen converters, dephosphorization begins from the first minutes of purging. However, at a carbon content of about 0.6 - 0.9%, the phosphorus content in the metal stabilizes or even increases slightly. A further decrease in phosphorus concentration is observed at significantly lower carbon content. Therefore, when the phosphorus content in cast iron is high and blowing is stopped at the grade carbon content, the concentration of phosphorus in the metal is usually higher than the required content in steel.

To obtain the required phosphorus content in high-carbon steel, which is smelted with the cessation of blowing at the grade carbon content, slag renewal is used. At the same time, the productivity of steel-smelting units decreases, and the consumption of slag-forming materials and cast iron increases.

At different plants, the converter is dumped to drain the slag at a carbon content of 1.2 - 2.5%. When the phosphorus content in cast iron is 0.20 - 0.30%, the slag is renewed twice at a carbon content of 2.5 - 3.0% and 1.3 - 1.5%. After downloading the slag, freshly burnt lime is added to the converter. The FeO content in the slag is maintained within 12 - 18% by changing the level of the tuyere above the bath. To liquefy the slag, fluorspar is added during blowing in an amount of 5 - 10% by weight of lime. These measures make it possible to obtain a phosphorus concentration of no more than 0.010 - 0.020% by the time the blowing is completed to the grade carbon content in the steel.

During tapping, the metal is deoxidized in a ladle with ferrosilicon and aluminum. In this case, a mandatory operation is cutting off the converter slag. Getting it into the ladle leads to rephosphorization of the metal during deoxidation and, especially, during out-of-furnace processing under reducing slag for desulfurization.

Blowing the metal in the converter to a low carbon content allows for its deep dephosphorization. In this regard, the technology of smelting rail and cord steel in oxygen converters has become somewhat widespread, which involves the oxidation of carbon to 0.03 - 0.07% and subsequent carburization of the metal in a ladle with petroleum coke, anthracite, etc. The use of such technology requires the availability of clean materials harmful impurities and gases from carburizers. This necessitates special training, the organization of which can create significant difficulties.

Some enterprises use the technology of producing rail and cord steel in oxygen converters by smelting low-carbon metal and then carburizing it with liquid cast iron, which is poured into a steel-pouring ladle before releasing the melt from the converter. Its use requires the presence of cast iron with sufficiently pure phosphorus content. To obtain the carbon content in steel within the required limits, the final carburization of the deoxidized metal is carried out with solid carburizers during vacuum processing.

Due to the low oxygen content in high-carbon rail steel, a high degree of purity for oxide inclusions can be obtained without the use of such relatively complex types of out-of-furnace processing as vacuuming or processing at the UKP. Usually, this is achieved by blowing the metal in the ladle with an inert gas. At the same time, in order to avoid secondary oxidation of the metal, ladle slag must contain a minimum amount of iron and manganese oxides.

For this purpose, when smelting rail steel in arc steel-smelting furnaces, the design of which does not provide for a bay window release of metal, it is recommended to carry out a shortened melting recovery period. To do this, after obtaining the required phosphorus content in the metal, the slag from the oxidation period of the smelting is drained from the furnace. Preliminary deoxidation of steel is carried out with silicon and manganese, which are introduced into the furnace in the form of ferrosilicon and ferromanganese or silicomanganese. Then new slag is placed in the furnace, which is deoxidized with ground coke or scrap electrodes and granulated aluminum before release of the melt. It is also possible to use powdered ferrosilicon for this purpose. The final deoxidation of steel with silicon and aluminum is carried out in a ladle during tapping. After being released into the ladle, the metal is purged with an inert gas for homogenization and, mainly, to remove accumulations of Al2O3. During operation of rails, accumulations of Al2O3 cause delamination in the working part of the rail head. The consequence of delamination can be the complete separation of the peeled plates on the rail head and its premature failure.

A more effective way to prevent the formation of delaminations in rail steel, smelted both in converters and in arc steel-smelting furnaces, is to modify non-metallic inclusions by treating the steel with calcium. Typically, silicocalcium is used for this purpose, which is introduced into the metal as part of a flux-cored wire or blown in a stream of argon through tuyeres immersed in the melt.

4. Production of rail steel using modifiers

Rails fail due to defects of contact fatigue origin. In a single shift, up to 50% of the rails are taken out of service due to these defects. The reason for the formation of defects is high-hard non-metallic inclusions such as alumina (A12 O 3) and aluminosilicates, stretched into lines along the rolling direction. In cast metal they form clusters, which, during rolling, are crushed and stretched, forming lines whose length can reach tens of millimeters. The very size of individual inclusions of alumina (corundum) also affects the magnitude of stresses and deformations in microvolumes of metal. It has been shown that the greatest danger in rail steel is 30 micron corundum inclusions [I]. According to other data, line inclusions of corundum become dangerous, reducing fatigue properties already at a value of 7-100 micromicrons.

Therefore, all work in the production of rail steel is aimed at reducing both the size of acute-angled inclusions and finding solutions to reduce the length of their lines in the rolled metal.

To some extent, metal contamination can be reduced by blowing the metal in the ladle with an inert gas, evacuation, and using (simultaneously with blowing) the introduction of new slag with solid slag mixtures with cutoff during the release of metal from the steel-smelting unit of furnace slag [3]. However, the problem can be solved more fundamentally by using modifiers for processing rail steel.

At NTMK, in the first stages of experiments, modifiers containing calcium and zirconium were used. At the same time, on experimental melts, when filling a ladle with metal (open hearth melting 440 tons) to 1/5 of its height, FeSiCa (3.2 kg/ton) was introduced in portions, and after that SiZr was introduced in portions - 0.45 kg/ton. The supply of ferroalloys was completed when 2/3 of the ladle was filled. It was discovered that on the experimental metal there were no stitch lengths of 4 mm, on ordinary metal - more than 20% of the samples had stitches of 4-16 mm.

In the future, when using complex alloys based on silicocalcium with zirconium and aluminum, the consumption is 1.9 kg/t. The optimal composition of the modifier used is 6-7% Zr and 5-7% A1. At the same time, it was possible to ensure a level of impact strength of the rails of at least 0.25 Mg 7 / M 2, and no lines longer than 2 mm were found.

Ukrainian researchers have carried out work on testing master alloys with Mg and Ti in the smelting of rail steel in converters and open-hearth furnaces [b]. The use of alloys with Mg, Ti and A1 (55-58% Si, 4-5% Mg, 4-7% Ti) for modifying rail steel in the ladle made it possible to localize shrinkage defects in the profitable part of the ingot, to reduce the segregation of elements by 27-32 %o increase the wear resistance of the metal, but the length of the alumina lines was significant, on average 5.3 mm. After using alloys without aluminum, it was possible to reduce the number of alumina inclusions and the length of the lines. The addition of complex master alloy SmTi to a ladle without additive A1 ensured a reduction in the prevalence of rails with surface defects, mainly in films, by 5-8%, and an increase in the yield of grade 1 rails by 1.8-4.5%. The length of the lines did not reach 2 mm, the operational durability and reliability of the experimental rails were, respectively, 20-25% higher than those made from steel deoxidized with aluminum.

The next attempt to reduce the contamination of rails with streaked oxide inclusions was the use of an alloy containing barium alumina to modify steel. At the same time, a deeper deoxidation of the metal was achieved, the total oxygen content from 0.0036-0.006%o to 0.0026%o and a decrease in the anisotropy of plastic properties. The modifier was added to the ladle.

The fourth group of attempts to improve the quality of rail steel is associated with the appearance of vanadium in the composition of modifiers used for processing liquid metal in a ladle. Moreover, the metal is microalloyed with vanadium (its content is 0.005-0.01%) from containing alloys (the content of components in such alloys has not been established) and from natural cast iron alloyed with vanadium. The same work provides data on the microalloying of vanadium-containing metal with zirconium. This achieves an increase in the ultimate contact endurance of heat-strengthened rails by 7.2% and a reduction in their wear by 23%. It is noted that rails made of steel deoxidized with a calcium-containing master alloy containing vanadium have the highest reliability and durability.

The experience of using complex ferroalloys with vanadium and adding them to a ladle when producing rail steel is described in work carried out at the Kuznetsk Metallurgical Plant.

Microalloying in the ladle, due to existing and unregulated processes when introducing modifiers into the ladle (metal oxidation, temperature, additive moment), is unstable, the absorption of easily oxidized components of alloys (magnesium, calcium, zirconium, vanadium) is low, and their consumption is 3 -4 kg per ton, so a group of researchers at the Azovstal OJSC plant, when producing rail steel, changed the modification by introducing wire with a KMKT alloy (the content of elements is not reported).

Thus, the problem of increasing the absorption of easily oxidized elements introduced into liquid metal in the composition of complex alloys exists. Therefore, the development and application of new methods for introducing modifiers, in particular at casting, is of current importance.

Conclusion

The railway rail production technology used at domestic metallurgical plants ensures the required quality and durability of the product. However, for a number of reasons, rail steel in the Russian Federation is smelted in open-hearth furnaces, which limits the technological capabilities of metallurgists to significantly and dramatically improve the quality of steel used for the production of rails.

Rail steel containing 0.60 - 0.80% C and cord steel similar in composition are smelted in oxygen converters and arc steel-smelting furnaces. The most difficult task in the production of these grades of steel is to obtain a low phosphorus content in the metal when blowing is stopped at the grade of carbon content.

In arc steel-smelting furnaces, rail and cord steel are smelted using conventional technology, using measures for intensive removal of phosphorus from the metal - adding iron ore to the charge and at the beginning of a short oxidation period with continuous removal of slag and its renewal with lime additives. In this case, measures are also necessarily taken to prevent furnace slag from entering the steel-pouring ladle.

The International Union of Railways (UIC) has developed the international standard UIC 860 concerning the quality and methods of manufacturing rail steels and the conditions for acceptance of rails of different weight categories, non-heat-treated, made from ordinary and wear-resistant steels. The properties of rail steels are determined primarily by the carbon content. It was taken as the basis for determining analogues of steels in various standards.

Rail steel must have high strength, wear resistance and not have local stress concentrates of metallurgical origin. In the middle third of the width of the sole and on the upper plane of the head, single gentle stripping of pockets, nicks, scratches with a depth of up to 0 5 mm is allowed, and in other places - up to 1 mm.

List of sources used

1) Kudrin, V.A. Technology for producing high-quality steel [Text] // V.A. Kudrin, V.M. Parma. - M: Metallurgy, 1984. 320 p.

2) Povolotsky, D. Ya. Electrometallurgy of steel and ferroalloys [Text] / D. Ya. Povolotsky, V. E. Roshchin, M. A. Ryss and others - M.: Metallurgy, 1984. - 568 p.

3) Simonyan, L.M. Metallurgy of special steels. Theory and technology of special electrometallurgy: A course of lectures [Text]. / L.M. Simonyan, A.E. Semin, A.I. Kochetov. - M.: MISIS, 2007. - 180 p.

4) Kudrin, V.A. Theory and technology of steel production: Textbook for universities. - M.: “Mir”, LLC “ACT Publishing House”, 2003.- 528 p.

5) Goldstein, M.I. Special steels: textbook for universities [Text] / M.I. Goldstein, Grachev S.V., Veksler Yu.G. - M.: Metallurgy, 1985. - 408 p.

6) Paderin, S.N. Theory and calculations of metallurgical systems and processes [Text]. / S.N. Paderin, V.V. Filippov. - M.: MISIS, 2002. - 334 p.

7) Bratkovsky, E.V., Electrometallurgy of steel and special electro-metallurgy [Text] / E.V. Bratkovsky, A.V. Zavodyany. - Novotroitsk: NF MISiS, 2008.

8) Kudrin, V.A. Theory and technology of steel production: a textbook for universities [Text] / Yu.V. Kryakovsky, A.G. Shalimov. - M.: “Mir”, LLC “AST Publishing House”, 2003. - 528 p.

9) Voskoboynikov, V.G. General metallurgy: textbook for universities [Text] / V.G. Kudrin, A.M. Yakushev. - M.: ICC "Akademkniga", 2002. - 768 p.

10) Alperovich, M.E. Vacuum arc remelting and its economic efficiency / M.E. Alperovich. - M.: Metallurgy, 1979. - 235 p.

Posted on Allbest.ru

1 Creation technology

The main material for such shovels is rail steel, saturated with carbon. The material is characterized by high strength and low weight, which is the best option for a working tool. Often, old rails or rails that do not meet the necessary conditions are used for such purposes. The resulting metal is packaged, after which it undergoes processing.

1.1 Production process (video)

1.2 Advantages of a shovel made of rail steel

Among the advantages of shovels made of rail steel, the following should be noted:

High strength and balanced elasticity. These qualities are ensured by durable material and a special hardening method. Moreover, the elasticity of the metal base allows the shovel to bend slightly under load and then return to its original position. This means that such an instrument is not in danger of deformation.

Light weight. Despite the strength and density of the material, the high carbon content makes the shovel lighter than a forged steel tool. This increases comfort when working.

Resistant to wear and corrosion. Resistance to corrosion processes is ensured not only by the specifics of the material, but also by the anti-corrosion coatings that cover most rail steel shovels.

Low price indicators. Shovels made of rail steel on the market in terms of price are slightly more expensive than shovels made of forged steel and stainless steel.

Self-sharpening during operation. Shovels made of rail steel, due to their structure, do not lose their sharpness even when working with hard types of soil, roots, or frozen soil. And sharpening adjustments are carried out during operation.

2 Choosing a shovel made of rail steel

When choosing a shovel, the main points that you should pay attention to are the overall design of the blade and the ergonomics of the tool. As for the general design of the blade, it is best to select a shovel with additional stiffening ribs. Such a tool is much harder to break or bend during operation.

As for the ergonomics of the shovel, the main nuance is the ledges for the feet. They must have the correct bend angle. An edge that is raised too high will cut your leg when working, and an edge that is too low will cause your legs to slip. A convenient addition is also the handle at the end of the handle. It makes working with bulk materials or cutting roots easier.

2.1 Instrument care

Whatever the quality of the tool, in order for it to function properly over many years, it must be properly monitored and maintained:

After finishing the work, the shovel must be immediately cleaned of any remaining soil.
It is better to store the tool in dry, well-ventilated places without access to moisture.
It is better to paint the cuttings, and this should be done periodically. This will increase the service life.
Constantly monitor the quality of the connection between the handle and the working blade. Under no circumstances should it wobble. In this case, it must be immediately knocked down and secured in a new way.

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