Method for reducing residual stress of U76CrREH steel rail through rare earth alloy elements

Abstract

The invention discloses a method for reducing residual stress of a U76CrREH steel rail through rare earth alloy elements. The method comprises the following steps: 1) raw material selection: selecting proper iron ore and rare earth alloy elements as raw materials; ore containing rare earth elements such as cerium Ce, lanthanum La or neodymium Nd is adopted; (2) adding alloy elements: in the smelting process, adding a proper amount of vanadium V, titanium Ti, niobium Nb and chromium Cr alloy elements; and 3) a heat treatment process: heating the steel rail to an austenitizing temperature of 900-950 DEG C, performing air cooling to 700-750 DEG C, then performing pure air cooling to 560 DEG C, keeping the steel rail at the temperature section for 30 seconds as far as possible, then balancing internal temperature return and cooling strength of the steel rail, and finally completing a quenching process at 510 DEG C. By optimizing addition of alloy elements and a heat treatment process, the residual stress of the steel rail is reduced, the comprehensive performance of the steel rail is improved, and the requirements of railway transportation for high strength, high toughness and low stress of the steel rail are met.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgical materials, and in particular relates to a method for reducing residual stress of a U76CrREH rail by using rare earth alloy elements. Background Art

[0002] At present, with the development of railway transportation, the requirements for rail performance are getting higher and higher. U76CrRE rare earth rails are widely used in the field of railway transportation due to their good mechanical properties and wear resistance. However, during the production process of rails, due to uneven heat treatment, different cooling rates and uneven distribution of alloy components, large residual stresses are easily generated. These residual stresses not only affect the service life of the rails, but may also cause the rails to break or deform during operation, seriously affecting the safety and reliability of railway transportation. Therefore, how to effectively control and reduce the residual stress of U76CrRE rare earth rails has become a technical problem that needs to be solved urgently.

[0003] By adjusting the addition of rare earth alloy elements, the residual stress in the rail can be effectively controlled and reduced, and its overall performance can be improved. The present invention proposes a method for reducing the residual stress of U76CrRE rare earth rails by controlling rare earth alloy elements, so as to provide an efficient, economical and feasible technical solution. Summary of the invention

[0004] The purpose of the present invention is to provide a method for reducing the residual stress of U76CrREH rails by using rare earth alloying elements, thereby reducing the residual stress of the rails and improving their comprehensive performance by optimizing the addition of alloying elements and the heat treatment process, so as to meet the requirements of railway transportation for high strength, high toughness and low stress of the rails.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The present invention discloses a method for reducing residual stress of U76CrREH rail by using rare earth alloy elements, which is characterized by comprising:

[0007] 1) Raw material selection: Select suitable iron ore and rare earth alloy elements as raw materials; use ores containing rare earth elements such as cerium Ce, lanthanum La or neodymium Nd;

[0008] 2) Addition of alloy elements: During the smelting process, add appropriate amounts of vanadium V, titanium Ti, niobium Nb, and chromium Cr alloy elements;

[0009] 3) Heat treatment process: Heat the rail to the austenitizing temperature of 900-950℃, air cool to 700-750℃, and then cool to 560℃ with pure air, so that the rail can be kept in this temperature range for 30S as much as possible, and then balance the internal temperature return and cooling intensity of the rail, and finally complete the quenching process at 510℃.

[0010] Furthermore, the optimal microstructure is achieved by precisely controlling the mass percentages of alloying elements: 0.1-0.3% vanadium, 0.05-0.2% titanium, 0.02-0.1% niobium and 0.5-1.5% chromium are added.

[0011] Furthermore, the chemical composition of the rail in terms of mass percentage is: C 0.76%, Si 0.635%, Mn 0.908%, V 0.41%, Cr 0.25%, Ce 0.0015%, P 0.018%, S 0.001%, and the rest is iron and unavoidable impurities.

[0012] Furthermore, the chemical composition of the rail in terms of mass percentage is: C 0.761%, Si 0.640%, Mn 0.920%, V 0.41%, Cr 0.26%, La 0.0018%, P 0.017%, S 0.001%, and the rest is iron and unavoidable impurities.

[0013] Furthermore, the chemical composition of the rail in terms of mass percentage is: C 0.758%, Si 0.639%, Mn 1.01%, V 0.43%, Cr 0.26%, Nd 0.0020%, P 0.016%, S 0.001%, and the rest is iron and unavoidable impurities.

[0014] Furthermore, the Nd element has the best application effect. While the strength and hardness are increased, the toughness is also improved accordingly, and the residual stress is the lowest.

[0015] The present invention also provides the use of the rare earth alloy element Nd to increase the strength and hardness of the U76CrREH rail while improving the toughness and reducing the residual stress.

[0016] Compared with the prior art, the beneficial technical effects of the present invention are:

[0017] The invention provides a method for reducing the residual stress of a U76CrRE rare earth rail by controlling rare earth alloy elements, thereby improving the mechanical properties and service life of the rail.

[0018] The present invention significantly reduces the residual stress of the rail and improves the tensile strength, toughness and wear resistance of the rail by reasonably adding rare earth alloy elements during the steelmaking process and combining an optimized heat treatment process. DETAILED DESCRIPTION

[0019] A method for reducing residual stress of U76CrREH rail by rare earth alloy elements, the specific components of each embodiment are shown in Table 1:

[0020] Table 1 Comparison of different components during the embodiment (mass fraction) / %

[0021]

[0022] As shown in Table 1, Examples 1 to 3 are all U76CrRE rail smelting compositions within the standard composition range, wherein the contents of C, Si, Mn, Cr, V, P, and S are substantially the same, and the experimental steel smelting process, alloy grade, and alloy addition system are the same. Example 1 contains 15 PPm of rare earth Ce, Example 2 contains 18 PPm of rare earth La, and Example 3 contains 20 PPm of rare earth Nd.

[0023] Table 2 Comparison of conventional mechanical properties during the embodiment

[0024]

[0025]

[0026] As shown in Table 2, the tensile strength of Examples 1 to 3 is ≥1280MPa, the elongation after fracture is ≥10%, and the tread hardness is ≥320HBW, which meets the performance requirements for U76CrREH rails in the standard "TB / T 2344.1-2020 Rails Part 1 43kgm~75kgm Rails". Compared with Example 1, the elongation after fracture of Example 2 can reach 14%, and the elongation after fracture of Example 3 can reach 14.5%. The tensile strength of Example 3 is ≥1295MPa, and the tread hardness is ≥380HBW. Compared with Example 1, the strength and hardness of Example 3 are increased, and the toughness is also improved accordingly, and the residual stress is as low as 231MPa, indicating that the rails after alloying with rare earth neodymium (Nd) element have lower residual stress.

[0027] Usage process:

[0028] ① The rail of the present invention uses C, Mn, Si, Cr, V and Ce as main alloying elements, and the weight percentage of the chemical composition of the rail is C: 0.71-0.80%, Si: 0.50-0.80%, Mn: 0.75-1.05%, Cr: 0.25-0.35%, V: 0.04-0.12%, Ce: 0.002-0.020%, La: 0.002-0.020, Nd: 0.002-0.020%, P≤0.025%, S≤0.025%, Al: ≤0.004%, and the rest is Fe.

[0029] ② Use scrap steel, pure iron, ferroalloys, rare earth alloys, etc. as raw materials for electric furnace smelting.

[0030] ③ Scrap steel and pure iron are added into the smelting furnace, and the smelting furnace is evacuated to a vacuum degree of about 30 Pa. After the vacuum degree requirement is reached, an inert protective gas is added.

[0031] ④ Turn on the power to induction heat the melting furnace charge, induction heating for 15-20 minutes to melt the charge, first add 70-80% ferrosilicon, 90-98% metallic manganese, 50-60% ferrochrome, 75-85% ferrovanadium into the vacuum smelting furnace, heat for about 2-5 minutes, add 10-20% ferrocerium, ferrolanthanum or ferronedithium, and continue to perform electromagnetic stirring and alloy homogenization smelting. During the smelting process, the bottom blowing device can be used to stir the melt, and the forward and backward tilting operation of the tilting furnace device can also be used to tilt the crucible forward or backward, which can also achieve the purpose of stirring the melt.

[0032] ⑤ 1-2 minutes after all the alloys are added, the temperature of the molten steel reaches: 1550-1570℃. After standing for 2-5 minutes, it is poured out of the furnace. The cast steel ingot needs to be slowly cooled in the ingot mold to room temperature before being removed from the mold.

[0033] ⑥ The cast ingot is heated and rolled, the heating temperature is 1200-1250℃, the heating time is greater than 180min, the heating rate is ≤400℃ / h, the soaking temperature is 1100~1260℃, and the soaking time is greater than 40min.

[0034] ⑦ Rolling adopts reversible hot rolling experimental unit, rolling mill line speed ≤ 2m / s, maximum reduction ≤ 40%, maximum rolling force ≤ 10000KN. If the rolling temperature does not meet the requirements, the intermediate billet needs to be heated again and rolled after heating to temperature.

[0035] ⑧ Effective means should be used during rolling to remove the oxide scale on the billet, the rolling pass should be ≥5, and the billet rolling reduction ratio should be ≥9:1. The initial forming temperature is 1060-1130℃, the final forming temperature is 890-940℃, and the billet is air-cooled to room temperature after rolling.

[0036] ⑨Then carry out the air jet quenching process, air cool the rail to 756℃, use 10MPa wind pressure to carry out the air jet test, cool the rail to 550℃, maintain this temperature for 30S, wait until the temperature stabilizes to 510℃, leave the test area, and cool to room temperature.

[0037] The heat-treated U76CrREH rail finally obtained through the above smelting and rolling meets the standard composition and performance requirements, with tensile strength ≥1280MPa, tread hardness ≥370HBW, residual stress ≤250MPa, and microstructure of pearlite and a small amount of ferrite.

[0038] The present invention can obtain U76CrREH rails with higher tensile strength and toughness, meet the demand for rail use on freight lines, further improve the service safety of rails on low-temperature sections, and reduce the cost of rail maintenance on lines.

[0039] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for reducing residual stress of U76CrREH rail by rare earth alloy elements, characterized in that: include: 1) Raw material selection: Select suitable iron ore and rare earth alloy elements as raw materials; use ores containing rare earth elements such as cerium Ce, lanthanum La or neodymium Nd; 2) Addition of alloy elements: During the smelting process, add appropriate amounts of vanadium V, titanium Ti, niobium Nb, and chromium Cr alloy elements; 3) Heat treatment process: Heat the rail to the austenitizing temperature of 900-950℃, air cool to 700-750℃, and then cool to 560℃ with pure air, so that the rail can be kept in this temperature range for 30S as much as possible, and then balance the internal temperature return and cooling intensity of the rail, and finally complete the quenching process at 510℃.

2. The method for reducing residual stress of U76CrREH rail by rare earth alloy elements according to claim 1, characterized in that: The optimal microstructure is achieved by precisely controlling the mass percentages of alloying elements: 0.1-0.3% vanadium, 0.05-0.2% titanium, 0.02-0.1% niobium and 0.5-1.5% chromium are added.

3. The method for reducing residual stress of U76CrREH rail by rare earth alloy elements according to claim 1, characterized in that: The chemical composition of the rail by mass percentage is: C 0.76%, Si 0.635%, Mn 0.908%, V 0.41%, Cr 0.25%, Ce 0.0015%, P 0.018%, S 0.001%, and the rest is iron and inevitable impurities.

4. The method for reducing residual stress of U76CrREH rail by using rare earth alloy elements according to claim 1, characterized in that: The chemical composition of the rail by mass percentage is: C 0.761%, Si 0.640%, Mn 0.920%, V 0.41%, Cr 0.26%, La 0.0018%, P 0.017%, S 0.001%, and the rest is iron and inevitable impurities.

5. The method for reducing residual stress of U76CrREH rail by rare earth alloy elements according to claim 1, characterized in that: The chemical composition of the rail by mass percentage is: C 0.758%, Si 0.639%, Mn 1.01%, V 0.43%, Cr 0.26%, Nd 0.0020%, P 0.016%, S 0.001%, and the rest is iron and inevitable impurities.

6. The method for reducing residual stress of U76CrREH rail by using rare earth alloy elements according to claim 1, characterized in that: The Nd element has the best application effect. While the strength and hardness are increased, the toughness is also improved accordingly, and the residual stress is the lowest.

7. The application of rare earth alloy element Nd to increase the strength and hardness of U76CrREH rail while improving toughness and reducing residual stress.

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