RU2434060C2 - Procedure for production of rail steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: procedure consists in melting steel in electric furnace, in tapping metal in ladle with furnace slag cut off, in addition of slag forming mixture and ferro alloys containing silicon and manganese both during tapping and at aggregate "furnace-ladle", in micro-alloying with vanadium, in steel nitriding and modifying at aggregate "furnace-ladle" with simultaneous melt blowing with argon. Nitriding is carried out with nitrogen containing material introduced into melt in form of powder wire containing 4-34 wt % of nitrogen, and also iron and, separately or together, elements of row: manganese, silicon, vanadium and niobium. Also, nitrogen containing material is used in form of alloy or mixture of separate materials. Ratio between contents of nitrogen and vanadium is 0.2-0.47, while ratio between contents of calcium and vanadium is 0.02-0.066. At micro alloying vanadium is introduced into melt in form of powder wire, while modifying is performed with calcium, or calcium-barium material.

EFFECT: raised plastic and toughness properties of rail steel at maintaining its strength.

5 cl, 2 tbl

Description

The invention relates to ferrous metallurgy, in particular to methods for producing rail, spring, tool and other grades of steel.

A known method of producing rail steel, selected as an analogue, including filling scrap metal and lime in an electric arc furnace, melting scrap metal, pouring molten iron, oxidizing carbon with gaseous oxygen, dephosphorizing, downloading oxidative slag through the threshold of the working window, and then releasing the steel into the ladle with a cut-off furnace slag with 10-15% molten metal remaining in the furnace from the smelting mass and finishing the metal in the ladle with an additive in the ladle during the production of a slag-forming mixture of lime fluorspar in the ratio (0.8-1.2) :( 0.2-0.5) with a flow rate of 10-17 kg / t of steel, as well as ferroalloys - silicon and manganese-containing ferroalloys based on the introduction of up to 0.15 in steel % silicon and up to 0.75% manganese. Next, the steel is treated on a ladle-furnace unit by introducing into the ladle successively to the required concentrations of manganese, silicon, carbon, vanadium and calcium, and when introduced, the steel is purged through the bottom porous lance with nitrogen at a rate of up to 65 nm ³ / h with a total quantity introduced gaseous nitrogen not more than 20 nm ³ to a content of 0.020% nitrogen, the final purge is carried out with argon with a flow rate of up to 65 nm ³ / h / 1 /.

The disadvantage of this method is the low and unstable assimilation of nitrogen, which is characteristic of almost all technologies for introducing gases into the metal by blowing them. The dispersion in the nitrogen content in steel leads to a lack of dispersed nitride and carbonitride particles forming in the metal of the required size — mainly vanadium nitrides and carbonitrides — stabilizing the grain structure in the manufacture of rails and increasing their wear resistance. As a result, the grain size in steel and the number of large - more than 1 μm - non-metallic inclusions increase, which is accompanied by a decrease in the level of mechanical properties of the metal, and especially ductility and low-temperature impact strength, which leads to a reduction in the service life of rails.

Closest to the claimed one and chosen as a prototype is a method for producing rail steel, comprising smelting steel in an electric furnace without deoxidizing metal and slag, releasing metal into a ladle with furnace slag cut-off, purging metal in a ladle with nitrogen and argon, an additive during the production and purging of slag-forming mixtures of ferroalloys containing silicon and manganese, and microalloying steel at the ladle furnace with vanadium, characterized in that after microalloying the steel at ladle furnace with vanadium, it is modified by Fe a silicon alloy containing silicon, calcium, barium, in which the ratio of barium to calcium is 1.0-1.5, and their amount in the composition of the ferroalloy is 150-300 g / t steel. In addition, the installation "ladle furnace" can purge steel with argon, and vanadium is introduced in the form of nitrided ferrovanadium to provide the necessary nitrogen content in steel / 2 /.

The disadvantage of this method is the low and unstable uptake of nitrogen when it is introduced into the melt both by blowing and in the form of a piece on the ladle-furnace unit — from above through a slag layer. As a result, insufficient formation of dispersed vanadium-containing nitrides and carbonitrides leads to low stabilization of the grain structure of the metal, a decrease in its plastic and viscous characteristics, and, ultimately, to the early formation of contact-fatigue defects during the operation of rails. The prototype does not say about the necessary ratio between the content in the metal of nitrogen and vanadium, forming the number and size of dispersed particles necessary for stabilizing the structure. In addition, when using complex modifying material, the role of calcium, which differs from barium by horophilic properties, is not separately distinguished, which makes it possible to additionally affect the purity of grain boundaries and, therefore, the complex of plastic and viscous properties of rail metal.

The objective of the present invention is to increase the plastic and viscous properties of rail steel while maintaining its required strength.

The problem is achieved in that in the proposed method for the production of rail steel, including steel smelting in an electric furnace or converter, the release of metal into a ladle with a furnace slag cut-off, an additive during the production and on the ladle furnace slag-forming mixture and ferroalloys containing silicon and manganese, vanadium microalloying, nitriding and steel modification at the ladle furnace with simultaneous purging of the melt with argon, nitriding is carried out by the material introduced into the melt by flux-cored wire, and soda zhaschim 4-34 wt% nitrogen, and iron, and, separately or together, the elements from the series. manganese, silicon, vanadium, niobium. In this case, the nitrogen-containing material can be an alloy or a mixture of individual materials.

In addition, according to the method, in the steel, the ratio between the nitrogen and vanadium content is 0.2-0.47, and between the calcium and vanadium content is 0.02-0.066. During microalloying, vanadium is introduced into the melt in the form of a flux-cored wire, and the modification is carried out with calcium or calcium-barium material.

Studies conducted on the sources of patent and scientific and technical information have shown that the claimed method for the production of rail steel is unknown and does not follow explicitly from the studied prior art, i.e. meets the criteria of novelty and inventive step.

The inventive method can be implemented at any enterprise specializing in this industry, because this requires well-known materials and standard equipment, i.e. is industrially applicable.

Our studies have shown that the set of required mechanical properties of rail steel is strength, ductility, toughness, content of non-metallic inclusions, etc. - are largely determined, along with traditional technological factors (chemical composition, temperature and strain conditions of crystallization, deformation and heat treatment of the metal), the size of the austenitic and final grain, the amount of dispersed (less than 0.5-1 microns) phase and the purity of the grain boundaries from excess discharge, captivity, and segregation. With a decrease in the size of crystallites, an increase in the number of dispersed particles inhibiting grain growth throughout the technological process, and an increase in the purity of grain boundaries, the ductility and toughness of a rail metal, its ability to withstand cyclic fractures, etc. increase. The task of creating a sufficient amount of dispersed particles is solved in rail steel, mainly due to additional nitriding of the steel at the stage of after-furnace treatment, however, the effectiveness of this process depends on the method of introducing nitrogen into the melt.

The authors' long-term practice has shown that the most stable assimilation of nitrogen is achieved by introducing the latter into the melt with a flux-cored wire, the filler of which can be almost any nitrogen-containing material, and, in particular, containing up to 34% N, iron, as well as manganese, silicon, vanadium , niobium, i.e. nitrided ferromanganese, ferrosilicon manganese, ferrosilicon, ferrochrome, etc. The latter can be part of the nitrogen-containing filler separately, either together, in the form of an alloy, or a mixture of individual materials.

The assimilation of nitrogen by introducing it with flux-cored wire in our experiments, depending on the steel grade, smelting technology and the material used, was 55-85%, however, the main thing was the high stability of this process - the assimilation spread was 2-5%. The result of this treatment is the formation in the metal of the required amount of dispersed (less than 0.1-0.5 microns) nitride and carbonitride particles, which in rail steel are mainly represented by vanadium nitrides and carbonitrides.

In addition, the size and number of particles capable of stabilizing the grain structure depends on the content of vanadium and nitrogen in the steel. A lack of nitrogen leads to the absence of dispersed particles, and an excess leads to the formation of large inclusions. In both the first and second cases, the stabilization properties of this phase are insufficient. It was experimentally established that the best braking of the grain structure is achieved when the ratio between the nitrogen and vanadium content in the steel is 0.2-0.47, which corresponds to a relatively uniform distribution of crystallites in the metal - Dmax. / Dav. is 2.5-5.

It should be borne in mind that grain boundaries are objectively a zone of increased defectiveness of the crystal structure, where excessive precipitates of embrittling phases, segregation, captivity, etc., which reduce the plastic, impact, corrosion, and other properties of the metal, are concentrated. Removing such precipitates from grain boundaries and their more uniform distribution over the grain body is a reserve for increasing the plastic and impact characteristics of rail steel. A similar result can be achieved by enriching the border volumes with calcium, which has pronounced horophilic properties and, due to this, displacing embrittlement phases, segregations, and film precipitates from grain boundaries. It has been established that the improvement of the plastic and impact properties of rail metal is manifested when the ratio between the contents of calcium and vanadium in the steel is in the range 0.02-0, 066.

Microalloying vanadium steel is most effective, from the point of view of increasing and stability of assimilation of this element, to conduct also flux-cored wire. In addition, our experiments showed that the modification of the melt during out-of-furnace treatment in the case of nitriding of rail steel with flux-cored wire can be carried out with calcium or calcium-barium material, and the best plastic and impact properties of the metal are obtained if the above relations between the contents of calcium and vanadium are observed.

An example of the method

Experimental melts were carried out in electric furnaces with a main lining. Next, the steel with slag cut-off was discharged into the ladle and slag-forming and partially ferroalloys were introduced along the way, and then the metal was transferred to the ladle furnace, where the slag-forming mixture, silicon and manganese-containing ferroalloys, flux-cored wire, flux-cored wire were sequentially planted. nitrated ferroalloys (versions of the materials used are given in Table 1), as well as for modification - flux-cored wire with ferrosilicon-calcium grade SK30, or ferrosilicon barium grade SKV-10. During processing at the ladle-furnace unit, the metal was purged with argon. The amount of nitrided ferroalloys was introduced into the melt, based on the nitrogen content after the arc furnace (0.006-0.008%) to obtain 0.011-0.016% N in the metal. The filler wires used - nitrided ferrosilicon manganese, ferrosilicon, ferromanganese, ferrovanadium and ferroniobium - contained, respectively, 15, 34, 10, 10, and 9% N. In some experiments, the filler included an alloy of nitrided materials (var. 10 and 21), and in the rest, a mixture of nitrided ferroalloys. To reduce the nitrogen content in the filler to 4%, ferrosilicon manganese was used. The assimilation of nitrogen by the metal was 65 ± 3%. The change in the ratios of nitrogen / vanadium and calcium / vanadium varied between 0.2-0.53 and 0.016-0.075, respectively. A modifying wire was introduced at the rate of 180 g of calcium or the sum of calcium and barium per ton of melt.

Processing according to the prototype included smelting in electric furnaces with a main lining, metal production with slag cut-off into a ladle with a partial additive of slag-forming mixtures and ferroalloys containing silicon and manganese. Next, the metal was transferred to the ladle-furnace assembly, where the remaining slag-forming mixtures and ferroalloys containing silicon and manganese were planted, lumpy 50% ferrovanadium (var. 1, table 1) or additional nitrided ferrovanadium (var. 2, table. 1) and then a flux-cored wire filled with a ferroalloy containing 8.0% Ba and 7.8% Ca. The total consumption of barium and calcium was 270 g / t of steel.

The average values of the mechanical properties - hardness, elongation, impact strength (KCU at + 20 ° С and - 60 ° С), and N / V, Ca / V ratios in finished rails smelted by the proposed method and the prototype method are presented in table 2.

The results shown in table 1 and 2 indicate:

1. The production of rail steel according to the method specified in the prototype (var. 1 and 2), leads to the formation of a metal structure that meets the required level of strength, relative to elongation and toughness.

2. The production of rail steel of claim 1 of the formula of the proposed method, that is, in the case of modifying treatment with calcium or calcium barium ligature and nitriding of the melt with a flux-cored wire, which contains from 4% N to 34% N of all fillers, results in a rail metal having higher relative elongation and toughness (var. 3-12, 21 and 23), compared with the prototype.

3. The production of rail steel with a mixed filler from nitrided ferroalloys (var. 3-9, 11, 12, 23) or with fused nitrogen-containing filler (var. 10 and 21) provides the best complex of plastic and impact characteristics of metal, compared with the prototype - claim 2 of the formula of the proposed method.

4. The production of rail steel according to claim 3 of the formula of the proposed method, ie when the ratio in the metal of nitrogen to vanadium is in the range of 0.2-0.47, and calcium to vanadium in the range of 0.02-0.066 leads to an additional increase in the plastic and impact characteristics of the metal (var.13-20.22).

5. Microalloying the melt with a flux-cored wire with ferrovanadium in all versions of the production of rail steel led to improved mechanical properties of steel, compared with the prototype - claims 4 and 5 of the formula of the proposed method.

The proposed method for the production of rail steel can be used for smelting steel, intended for mass production of rails for various purposes in order to increase their ductility, toughness and service life.

Information sources

1. The method of producing rail steel. RF patent №2254380, cl. 7 C21C 7/00.

2. A method of producing rail steel. RF patent №2327745, cl. 7 C21C 7/00, C21C 5/52

Table 1 Composition of cored wire fillers No. p / p Mn Si N V Nb Fe 1 prototype - - - - - - 2 prototype - - - - - - 3 58 fifteen four - - ost four 12 - - 5 6 7 8 - 60 34 - - 9 70 - 10 - - 10 29th 8 eleven - - eleven - - 10 fifty - 12 46 eleven 10 - 10 13 58 fifteen 12 - - fourteen fifteen 16 17 eighteen 19 twenty 21 46 eighteen 16 - - 22 58 fifteen 12 - - 23 58 fifteen 12 - -

table 2 Effect of flux-cored wire filler composition and the content of nitrogen, vanadium and calcium in rail steel on the mechanical properties of metal Filler Option No. - Table 1 The content of elements in steel The mechanical properties of metal N, wt.% V, wt.% Ca, wt.% N / V Ca / V σ _in , MPa δ,% KCU + 20 ° C, J / cm ² KCU-60 ° C, J / cm ² one 0.010 0.05 0.002 0.20 0.04 1280 fourteen 36 28 2 0.012 0.05 0.002 0.24 0.04 1290 fifteen 36 28 3 0.012 0.05 0.002 0.24 0.04 1290 17 38 thirty four 0.016 0,03 0.002 0.53 0,066 1280 16 37 thirty 5 0.011 0.06 0.002 0.47 0,066 1280 17 38 thirty 6 0.014 0.06 0.001 0.23 0.016 1280 16 37 thirty 7 0.014 0.04 0.003 0.35 0,075 1300 17 38 29th 8 0.014 0.04 0.003 0.35 0,075 1290 17 37 29th 9 0.014 0.04 0.003 0.35 0,075 1300 16 37 thirty 10 0.014 0.04 0.003 0.35 0,075 1300 16 37 thirty eleven 0.014 0.04 0.003 0.35 0,075 1290 17 38 thirty 12 0.014 0.04 0.003 0.35 0,075 1280 17 38 29th 13 0.014 0,03 0.002 0.47 0,066 1280 21 41 32 fourteen 0.014 0.04 0.002 0.35 0.05 1280 22 43 32 fifteen 0.014 0.06 0.002 0.23 0,033 1290 twenty 40 31 16 0.011 0,03 0.002 0.36 0,066 1290 21 40 31 17 0.011 0.04 0.002 0.275 0.05 1290 21 40 31 eighteen 0.012 0.06 0.002 0.2 0,033 1300 21 41 32 19 0.012 0.05 0.001 0.24 0.02 1300 22 43 33 twenty 0.012 0.05 0.003 0.24 0.06 1290 21 43 31 21 0.014 0.04 0.003 0.35 0,075 1280 17 38 thirty 22 0.014 0,03 0.002 0.47 0,066 1280 21 41 32 23 0.016 0,03 0.002 0.53 0,066 1290 16 38 29th

Claims (5)

1. Method for the production of rail steel, including steelmaking in electric furnaces, steelmaking into a ladle with furnace slag cut-off, an additive during the production and on the ladle furnace of a slag-forming mixture and ferroalloys containing silicon and manganese, vanadium microalloying, nitriding and modification became calcium or calcium-barium material at the ladle furnace with simultaneous purging of the melt with argon, characterized in that the nitriding is carried out with a nitrogen-containing material, which is introduced into the melt in the form of powder th wire containing 4-34 wt.% nitrogen, as well as iron and separately or together elements from the series: manganese, silicon, vanadium, niobium. 2. The method according to claim 1, characterized in that the nitrogen-containing material is used in the form of an alloy or a mixture of individual materials. 3. The method according to any one of claims 1 and 2, characterized in that the ratio between the nitrogen and vanadium content in the steel is 0.2-0.47, and the ratio between the calcium and vanadium content in the steel is 0.02-0.066. 4. The method according to any one of claims 1 and 2, characterized in that during microalloying, vanadium is used as vanadium, which is introduced in the form of a cored wire. 5. The method according to claim 3, characterized in that when microalloying, vanadium is used as vanadium, which is introduced in the form of a cored wire.