Method for refining interlamellar spacing of high-carbon steel rail

Abstract

The invention discloses a method for refining the interlamellar spacing of a high-carbon steel rail, and belongs to the field of steel rail production and application. The method provided by the invention is used for treating a steel billet of a high-carbon steel rail, wherein the steel billet comprises the following chemical components in percentage by mass: 0.90-0.95% of C; 0.30% to 0.50% of Si; mn: 0.90 to 1.00%; less than or equal to 0.020% of P; less than or equal to 0.020% of S; 0.30% to 0.35% of Cr; 0.01-0.05% of Nb, and the balance Fe and inevitable impurities. The microscopic structure of the steel rail obtained through the method is a fine lamellar pearlite structure, the pearlite lamellar spacing is smaller than or equal to 100 nm, the yield strength of the steel rail is larger than or equal to 900 MPa, the tensile strength is larger than or equal to 1350 MPa, the ductility is larger than or equal to 10%, and the tread hardness is larger than or equal to 400 HBW.

Description

Technical Field

[0001] The invention belongs to the field of rail production and application, and particularly relates to a method for refining the interlayer spacing of high-carbon steel rail sheets. Background Art

[0002] The metallographic structure of high-carbon rails is primarily pearlite, and their performance is directly dependent on the interlamellar spacing. Pearlite is formed by alternating layers of ferrite and cementite. The smaller the interlamellar spacing (e.g., ≤120nm), the significantly improved mechanical properties of the rail, including yield strength, tensile strength, elongation, and hardness. The current development of high-speed and heavy-load railways has placed higher demands on rail wear resistance and peeling resistance in small-radius curves, necessitating a refined interlamellar spacing to extend rail service life.

[0003] In traditional rail production processes, lamellar spacing is primarily regulated by controlling the cooling rate. Insufficient cooling rates result in excessive lamellar spacing (150-450nm), resulting in insufficient strength and toughness. Excessive cooling rates can easily produce atypical microstructures (such as proeutectoid ferrite and reticular cementite), reducing drawability and surface quality. Existing technologies struggle to balance cooling rate and microstructure uniformity. Therefore, there is an urgent need to develop a method for refining the lamellar spacing in high-carbon steel rails. Summary of the Invention

[0004] In view of the problems existing in the prior art, one aspect of the present invention provides a method for refining the interlayer spacing of high-carbon steel rail sheets, wherein the chemical composition of the steel billet of the high-carbon steel rail is as follows by mass percentage: C: 0.90-0.95%; Si: 0.30-0.50%; Mn: 0.90-1.00%; P≤0.020%; S≤0.020%; Cr: 0.30-0.35%; Nb: 0.01-0.05%, and the remainder is Fe and unavoidable impurities;

[0005] The method comprises the following steps: heating, rolling and cooling the steel billet; wherein:

[0006] In the steel billet heating step, the heating time is ≥3.5 hours and the heating temperature is ≥1300°C;

[0007] In the rolling step, the starting rolling temperature is controlled at 1160°C ± 10°C, and after the rail undergoes plastic deformation during rolling, the finishing rolling temperature is controlled at 960°C ± 10°C;

[0008] In the cooling step, the steel is first cooled to 800° C. at a cooling rate of 0.5 to 0.6° C. / s, then cooled to 500° C. at a cooling rate of 3.0 to 3.5° C. / s, and then slowly cooled to room temperature in a room temperature environment.

[0009] In some embodiments, the billet of the high carbon steel rail has a chemical composition in mass percentage of: C: 0.90%; Si: 0.43%; Mn: 0.95%; P: 0.012%; S: 0.008%; Cr: 0.32%; Nb: 0.01%; and the balance of Fe and inevitable impurities.

[0010] In some embodiments, the billet of the high carbon steel rail has a chemical composition in mass percentage of: C: 0.92%; Si: 0.50%; Mn: 0.90%; P: 0.010%; S: 0.006%; Cr: 0.35%; Nb: 0.03%, and the balance of Fe and inevitable impurities.

[0011] In some embodiments, the billet of the high carbon steel rail has a chemical composition in mass percentage of: C: 0.95%; Si: 0.48%; Mn: 1.00%; P: 0.010%; S: 0.006%; Cr: 0.30%; Nb: 0.05%, and the balance of Fe and inevitable impurities.

[0012] In some embodiments, the high carbon steel rail has a pearlite interlamellar spacing of ≤ 100 nm, a rail yield strength of ≥ 900 MPa, a tensile strength of ≥ 1350 MPa, an elongation of ≥ 10%, and a tread hardness of ≥ 400 HBW.

[0013] Another aspect of the present application provides a high carbon steel rail obtained by the above method. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 Figure 1 is a photograph of the pearlite interlamellar spacing of the high carbon steel rail obtained by the method of Example 1. DETAILED DESCRIPTION

[0015] The present application is described in detail below by specific examples, which are intended to facilitate the understanding of the present application, and are not intended to limit the content of the present application.

[0016] The high carbon steel rail billets involved in the following examples and comparative examples are all obtained according to the smelting method well known to those skilled in the art, which mainly includes the following process steps: 1) molten iron pretreatment: the molten iron must be pretreated with desulfurization, requiring [P] ≤ 0.12%, [S] ≤ 0.0.030%, and the other raw materials meet the requirements of the corresponding standards; 2) converter smelting: the endpoint is controlled to be C ≥ 0.08%, the steel tapping temperature T> 1610 ° C, silicon manganese, ferromanganese, ferroniobium and ferrosilicon alloy are used for in-tank deoxidation and alloying, and heavy rail carburizer is used for converter carburization; 3) LF furnace Refining: After the refined slag is added, there must be sufficient heating time to ensure that the slag is completely melted and foamed slag is formed as soon as possible to realize submerged arc operation and achieve the goal of white slag operation; the slag basicity is controlled to be ≥2.0; 4) VD vacuum degassing: deep vacuum time ≥20min, vacuum degree less than 0.1Kpa, soft blowing time after vacuum treatment is greater than or equal to 20min, and the molten steel must not be exposed during the soft blowing; 5) Continuous casting: the casting process is to achieve automatic liquid level control, electromagnetic stirring is used normally, the superheat of the continuous casting molten steel is 25℃, and a constant casting speed of 0.8m / min is used for control.

[0017] Example 1

[0018] The chemical composition of the high carbon steel rail billet involved in this embodiment includes, by mass percentage, the following: C: 0.90%; Si: 0.43%; Mn: 0.95%; P: 0.012%; S: 0.008%; Cr: 0.32%; Nb: 0.01%; the remainder is Fe and unavoidable impurities.

[0019] Specific production steps:

[0020] The billet was heated for 3.6 hours at 1320°C. The rolling temperature was 1165°C. After plastic deformation during rolling, the rail was rolled to a final temperature of 956°C. The rail was then cooled to 800°C at a rate of 0.6°C / s, followed by rapid air jet cooling to 500°C at a cooling rate of 3.2°C / s. The rail was then slowly cooled to room temperature.

[0021] After the rail was cooled to room temperature, the mechanical properties were tested. The microstructure was fine lamellar pearlite + a small amount of ferrite, the pearlite lamellar spacing was 89nm, the rail yield strength was 975MPa, the tensile strength was 1435MPa, the elongation was 13.5%, and the tread hardness was 426HBW.

[0022] Example 2

[0023] The chemical composition of the steel billet of the high carbon steel rail involved in this embodiment includes, by mass percentage, C: 0.92%; Si: 0.50%; Mn: 0.90%; P: 0.010%; S: 0.006%; Cr: 0.35%; Nb: 0.03%, and the remainder is Fe and unavoidable impurities.

[0024] Specific production steps:

[0025] The billet heating time was 3.6 hours and the heating temperature was 1300℃. The rolling starting temperature was 1162℃, and after the plastic deformation of the rail by rolling, the finishing temperature was 960℃. The rail was cooled to 800℃ at a rate of 0.5℃ / s, then was rapidly air-cooled to 500℃ at a rate of 3.0℃ / s, and then was slowly cooled to room temperature.

[0026] After the rail was cooled to room temperature, the mechanical properties were tested. The microstructure was fine lamellar pearlite, the pearlite interlamellar spacing was 95nm, the yield strength of the rail was 906MPa, the tensile strength was 1389MPa, the elongation was 13.0%, and the tread hardness was 415HBW.

[0027] Example 3

[0028] The chemical composition of the billet of the high carbon steel rail involved in this example included, in terms of mass percentage: C: 0.95%; Si: 0.48%; Mn: 1.00%; P: 0.010%; S: 0.006%; Cr: 0.30%; Nb: 0.05%, and the balance was Fe and unavoidable impurities.

[0029] Specific production steps:

[0030] The billet heating time was 3.6 hours and the heating temperature was 1330℃. The rolling starting temperature was 1165℃, and after the plastic deformation of the rail by rolling, the finishing temperature was 962℃. The rail was cooled to 800℃ at a rate of 0.6℃ / s, then was rapidly air-cooled to 500℃ at a rate of 3.5℃ / s, and then was slowly cooled to room temperature.

[0031] After the rail was cooled to room temperature, the mechanical properties were tested. The microstructure was fine lamellar pearlite, the pearlite interlamellar spacing was 98nm, the yield strength of the rail was 910MPa, the tensile strength was 1358MPa, the elongation was 12.0%, and the tread hardness was 410HBW. The pearlite interlamellar spacing photograph of the rail is shown in Figure 1 .

[0032] Comparative Example 1

[0033] The billet of the high carbon steel rail involved in this comparative example 1 was the billet in Example 3.

[0034] Specific production steps:

[0035] The billet heating time was 3.6 hours and the heating temperature was 1280℃. The rolling starting temperature was 1132℃, and after the plastic deformation of the rail by rolling, the finishing temperature was 930℃. The rail was cooled to 800℃ at a rate of 0.7℃ / s, then was rapidly air-cooled to 520℃ at a rate of 2.1℃ / s, and then was slowly cooled to room temperature.

[0036] The mechanical properties of the rail after cooling to room temperature are detected, the microstructure is fine lamellar pearlite structure, the pearlite lamellar spacing is 105 nm, the yield strength of the rail is 891 MPa, the tensile strength is 1367 MPa, the elongation is 12.0%, and the tread hardness is 390 HBW.

[0037] Comparative Example 2

[0038] The steel billet of the high-carbon steel rail involved in the present comparative example 2 is the steel billet in Example 3.

[0039] Specific production steps are as follows:

[0040] The heating time of the steel billet is 3.6 hours, and the heating temperature is 1280℃. The rolling temperature is 1135℃, and the final rolling temperature is 933℃ after plastic deformation of the rail during rolling. The rail is cooled to 800℃ at a cooling rate of 0.8℃ / s, then rapidly air-cooled to 510℃ at a cooling rate of 2.5℃ / s, and then slowly cooled to room temperature.

[0041] The mechanical properties of the rail after cooling to room temperature are detected, the microstructure is fine lamellar pearlite structure, the pearlite lamellar spacing is 124 nm, the yield strength of the rail is 816 MPa, the tensile strength is 1289 MPa, the elongation is 12.5%, and the tread hardness is 355 HBW.

[0042] By comparing Examples 1-3 and Comparative Examples 1-2, the method parameters of Comparative Example 1 and Comparative Example 2 are not within the range required by the present application, and when the steel billet of the high-carbon steel rail is treated, the pearlite lamellar spacing of the rail is large, and the strength and hardness of the rail detected do not meet the requirements. The composition of the rails of Examples 1-3 and the controlled cooling process after rolling fully meet the requirements in the method of the present application, so that the pearlite lamellar spacing of the rails obtained is small, and the rails have high strength and hardness, which can prolong the service life of the rails.

[0043] Finally, it should be noted that the above description is only a preferred embodiment of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent replacements to some technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for refining the interlaminar spacing of a high-carbon steel rail, wherein the chemical composition of the steel billet of the high-carbon steel rail is as follows, by mass percentage: C: 0.90-0.95%; Si: 0.30-0.50%; Mn: 0.90-1.00%; P≤0.020%; S≤0.020%; Cr: 0.30-0.35%; Nb: 0.01-0.05%, with the remainder being Fe and unavoidable impurities; The method comprises the following steps: Billet heating, rolling and cooling; including: In the steel billet heating step, the heating time is ≥3.5 hours and the heating temperature is ≥1300°C; In the rolling step, the starting rolling temperature is controlled at 1160°C ± 10°C, and after the rail undergoes plastic deformation during rolling, the finishing rolling temperature is controlled at 960°C ± 10°C; In the cooling step, the steel is first cooled to 800° C. at a cooling rate of 0.5 to 0.6° C. / s, then cooled to 500° C. at a cooling rate of 3.0 to 3.5° C. / s, and then slowly cooled to room temperature in a room temperature environment.

2. The method according to claim 1, wherein the chemical composition of the steel billet of the high carbon steel rail is as follows by mass percentage: C: 0.90%; Si: 0.43%; Mn: 0.95%; P：0.012％； S: 0.008%; Cr: 0.32%; Nb: 0.01%; the rest are Fe and inevitable impurities.

3. The method according to claim 1, wherein the chemical composition of the steel billet of the high carbon steel rail is as follows, by mass percentage: C: 0.92%; Si: 0.50%; Mn: 0.90%; P: 0.010%; S: 0.006%; Cr: 0.35%; Nb: 0.03%, and the remainder is Fe and unavoidable impurities.

4. The method according to claim 1, wherein the chemical composition of the steel billet of the high carbon steel rail is as follows, by mass percentage: C: 0.95%; Si: 0.48%; Mn: 1.00%; P: 0.010%; S: 0.006%; Cr: 0.30%; Nb: 0.05%, and the remainder is Fe and unavoidable impurities.

5. The method according to claim 1, wherein the pearlite lamellar spacing of the high carbon steel rail is ≤100 nm, the rail has a yield strength ≥900 MPa, a tensile strength ≥1350 MPa, an elongation ≥10%, and a tread hardness ≥400 HBW.

6. A high carbon steel rail obtained by the method according to any one of claims 1 to 5.

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