Titanium microalloyed low-carbon steel as well as preparation method and application thereof

Abstract

The invention provides a preparation method of titanium microalloyed low-carbon steel, which comprises the following steps: S1) preparing a low-carbon steel casting blank which comprises the following components in percentage by mass: less than or equal to 0.09% of C, 0.30-0.50% of Si, 1.00-1.70% of Mn, 0.20-0.30% of Cr, 0.05-0.10% of V and 0.07-0.10% of Ti; and (S2) the low-carbon steel casting blank is heated and then rolled, and the titanium microalloyed low-carbon steel is obtained. The invention further provides the titanium microalloyed low-carbon steel and application thereof. According to the preparation method of the titanium microalloyed low-carbon steel, by reducing the carbon content, introducing trace titanium and combining a proper rolling process, the obtained low-carbon steel is free of widmanstatten structures as steel for a brake beam, and the low-temperature impact property is met while the mechanical property and the fatigue property are guaranteed.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, and in particular to a titanium microalloyed low-carbon steel, its preparation method and its application. Background Technology

[0002] The brake beam of a railway freight car plays a vital role in transmitting braking force during vehicle operation. It is frequently subjected to complex alternating stresses such as impact and shear, which can lead to deformation or even fracture. Therefore, the materials used for the brake beam of a railway freight car have high requirements for mechanical properties and fatigue performance. After heat treatment, the yield strength is required to be ≥460MPa, Akv (-40℃) ≥27J, and the fatigue performance is required to be 1 million cycles without cracking.

[0003] Existing technology typically uses low-alloy high-strength steel Q460E to manufacture brake beams for railway freight cars. However, in actual production, these brake beams frequently fail to meet low-temperature impact performance standards, primarily due to the presence of Widmanstätten structure in their microstructure. Research indicates that Nb-containing steels have a lower transformation temperature range and a greater tendency to form Widmanstätten ferrite. In actual production, most railway freight car brake beams using Q460E low-alloy high-strength steel are predominantly Nb-V composite steel, making them prone to Widmanstätten structure formation during processing and thus affecting their low-temperature impact performance.

[0004] Therefore, it is of great significance to provide a new steel grade suitable for the brake beams of railway freight cars to meet the requirements of low-temperature impact performance. Summary of the Invention

[0005] The technical problem solved by this invention is to provide a method for preparing titanium microalloyed low-carbon steel. The titanium microalloyed low-carbon steel prepared in this application is used in brake beams and has no Widmanstätten structure, and has good low-temperature impact performance.

[0006] In view of this, this application provides a method for preparing titanium microalloyed low-carbon steel, comprising the following steps:

[0007] S1) Prepare a low-carbon steel billet, wherein the composition of the low-carbon steel billet, by mass percentage, includes: C≤0.09%, Si 0.30%~0.50%, Mn 1.00%~1.70%, P≤0.020%, S≤0.015%, Cr 0.20%~0.30%, V 0.05%~0.10%, Ti 0.07%~0.10%, N≤40ppm, with the remainder being Fe and unavoidable impurities;

[0008] S2) The low-carbon steel billet is heated and then rolled to obtain titanium microalloyed low-carbon steel, wherein the final rolling temperature is 850-900℃.

[0009] In some specific embodiments, the method for preparing the low-carbon steel billet is as follows:

[0010] Molten iron and / or scrap steel are added to the converter, controlling the S content to ≤0.060%. When the initial steel composition reaches C≤0.06%, P≤0.010%, S≤0.010%, and the steel temperature ≥1670℃, the steel is tapped into the ladle. During tapping, aluminum-iron pre-deoxidation is first added, followed by FeSi alloy, FeMn alloy, and FeCr alloy, controlling C to 0.03%–0.07%, Si to 0.30%–0.50%, Mn to 1.00%–1.70%, and Cr to 0.20%–0.30%. Then, low-nitrogen ferrotitanium and ferrovanadium are added sequentially to obtain molten steel.

[0011] The molten steel is poured at a constant rate, and the ladle is superheated to 20-40°C to obtain a low-carbon steel billet.

[0012] In some specific embodiments, in step S2), the heating temperature is 1230-1270°C, and the heating time is t = (0.7-0.85)H, where H is the thickness of the low-carbon steel billet.

[0013] In some specific embodiments, step S2) further includes the following after heating:

[0014] The heated low-carbon steel billet is subjected to high-pressure water descaling.

[0015] In some specific embodiments, in step S2), the temperature of the final rolling is 860–880°C.

[0016] In some specific embodiments, step S2) includes cooling after rolling, the cooling rate being ≤2℃ / s, and the cooling method being natural air cooling.

[0017] This application also provides titanium microalloyed low-carbon steel prepared by the aforementioned preparation method, comprising, by mass percentage: C≤0.09%, Si 0.30%~0.50%, Mn 1.00%~1.70%, P≤0.020%, S≤0.015%, Cr0.20%~0.30%, V 0.05%~0.10%, Ti0.07%~0.10%, N≤40ppm, with the remainder being Fe and unavoidable impurities.

[0018] In some specific embodiments, the content of C is 0.05-0.09%, and / or the content of Ti is 0.08-0.09%.

[0019] This application also provides a railway freight car brake beam, which is made of low-carbon steel, wherein the low-carbon steel is prepared by the method described in the above scheme or the titanium microalloyed low-carbon steel described in the above scheme.

[0020] In some specific embodiments, the titanium microalloyed low-carbon steel further includes post-treatment, which specifically involves normalizing and tempering the titanium microalloyed low-carbon steel, wherein the normalizing temperature is 920-930°C and the tempering temperature is 480-490°C; the metallographic structure of the railway freight car brake beam does not contain Widmanstätten structure.

[0021] This application provides a method for preparing titanium microalloyed low-carbon steel. First, a low-carbon steel billet is prepared, then the billet is heated and rolled to obtain titanium microalloyed low-carbon steel. The method for preparing titanium microalloyed low-carbon steel in this application incorporates low-content carbon and trace amounts of titanium, combined with a rolling process. This allows the titanium microalloyed low-carbon steel used in railway freight car brake beams to achieve strength comparable to existing materials while avoiding the formation of Widmanstätten structure, thus improving the low-temperature impact performance of the brake beam. Detailed Implementation

[0022] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0023] In view of the requirements for mechanical properties, fatigue properties, and low-temperature impact resistance of titanium microalloyed low-carbon steel used in the braking beams of railway freight cars in the prior art, this application provides a method for preparing titanium microalloyed low-carbon steel. By reducing the carbon content, introducing trace amounts of titanium, and combining it with an appropriate rolling process, the resulting titanium microalloyed low-carbon steel, used as a braking beam steel for railway freight cars, is free of Widmanstätten structure. While ensuring mechanical and fatigue properties, it also meets the requirements for low-temperature impact resistance. Results show that after normalizing at 920℃ and tempering at 480℃, the titanium microalloyed low-carbon steel is free of Widmanstätten structure, with a yield strength ≥460MPa and Akv(-40℃) ≥27J. After being manufactured into a combined braking beam for railway freight cars, it passed a fatigue performance test of 1 million cycles according to GB / T1978 standard without cracking. Specifically, this invention discloses a method for preparing titanium microalloyed low-carbon steel, including the following steps:

[0024] S1) Prepare a low-carbon steel billet, wherein the composition of the low-carbon steel billet, by mass percentage, includes: C≤0.09%, Si 0.30%~0.50%, Mn 1.00%~1.70%, P≤0.020%, S≤0.015%, Cr 0.20%~0.30%, V 0.05%~0.10%, Ti 0.07%~0.10%, N≤40ppm, with the remainder being Fe and unavoidable impurities;

[0025] S2) The low-carbon steel billet is heated and then rolled to obtain titanium microalloyed low-carbon steel, wherein the final rolling temperature is 850-900℃.

[0026] The preparation method of titanium microalloyed low-carbon steel mainly includes a smelting process and a rolling process. The smelting process includes converter smelting, ladle refining, and continuous casting performed sequentially, specifically:

[0027] Molten iron and / or scrap steel are added to the converter, controlling the S content to ≤0.060%. When the initial steel composition reaches C≤0.06%, P≤0.010%, S≤0.010%, and the steel temperature ≥1670℃, the steel is tapped into the ladle. During tapping, aluminum-iron pre-deoxidation is first added, followed by FeSi alloy, FeMn alloy, and FeCr alloy, controlling C to 0.03%–0.07%, Si to 0.30%–0.50%, Mn to 1.00%–1.70%, and Cr to 0.20%–0.30%. Then, low-nitrogen ferrotitanium and ferrovanadium are added sequentially to obtain molten steel.

[0028] The molten steel is poured at a constant rate, and the ladle is superheated to 20-40°C to obtain a low-carbon steel billet.

[0029] The specific operating methods of the above-mentioned smelting process are carried out in a manner known to those skilled in the art, and this application does not impose any special restrictions on them.

[0030] According to the present invention, after obtaining the low-carbon steel billet, it is heated to a temperature of 1230-1270°C for a heating time t = (0.7-0.85)H, where H is the thickness of the low-carbon steel billet; specifically, the heating temperature is 1245-1265°C for a heating time of 220-270 min.

[0031] This application then rolls the heated billet. Preferably, the heated billet is descaled by high-pressure water before rolling. The final rolling temperature is 850–900°C, specifically 855–880°C, and more specifically, 857–878°C. After rolling, it is cooled by natural air cooling at a rate ≤2°C / s, specifically 1.5–2.0°C / s, and more specifically, 1.6–1.8°C / s.

[0032] Furthermore, this application also provides a titanium microalloyed low-carbon steel prepared by the above method, comprising, by mass percentage: C≤0.09%, Si 0.30%~0.50%, Mn 1.00%~1.70%, P≤0.020%, S≤0.015%, Cr0.20%~0.30%, V 0.05%~0.10%, Ti0.07%~0.10%, N≤40ppm, with the remainder being Fe and unavoidable impurities.

[0033] In the titanium microalloyed low-carbon steel provided in this application, specifically, the C content is 0.05% to 0.09%; for example, the C content in this application is 0.01%, 0.02%, 0.03%, 0.04%, 0.06%, 0.07%, and 0.08%.

[0034] The Si content is 0.30-0.50%, specifically 0.35-0.48%; for example, the Si content in this application is 0.32%, 0.37%, 0.38%, 0.40%, 0.41%, 0.42%, 0.44%, 0.45%, 0.47%, and 0.49%.

[0035] The Mn content is 1.00% to 1.70%, specifically 1.05% to 1.60%, and more specifically 1.15% to 1.45%. For example, the Mn content in this application is 1.10%, 1.18%, 1.20%, 1.21%, 1.23%, 1.25%, 1.28%, 1.30%, 1.32%, 1.35%, 1.38%, 1.40%, 1.42%, 1.45%, 1.48%, 1.50%, 1.52%, and 1.55%.

[0036] The Cr content is 0.20% to 0.30%, specifically, the Cr content is 0.23% to 0.28%; for example, the Cr content in this application is 0.21%, 0.22%, 0.24%, 0.25%, 0.26%, 0.27%, and 0.29%.

[0037] The content of V is 0.05% to 0.10%, specifically, the content of V is 0.06% to 0.08%; for example, the content of V in this application is 0.07% and 0.09%.

[0038] The Ti content is 0.07-0.10%, specifically 0.08% and 0.09%.

[0039] If the content of N is ≤40ppm, and the content of Ti and N is too high, Ti and N will combine to form coarse TiN inclusions, which will weaken the grain refinement and precipitation strengthening effect of Ti.

[0040] This application also provides a railway freight car brake beam, which is made of low-carbon steel, wherein the low-carbon steel is the same as the low-carbon steel described in the above-mentioned scheme.

[0041] In this application, the low-carbon steel used for the brake beam of the railway freight car needs to be normalized and tempered; the normalizing temperature is 920-930℃, and the tempering temperature is 480-490℃.

[0042] This application provides a titanium microalloyed low-carbon steel for brake beams with good mechanical and fatigue properties. After normalizing at 920℃ and tempering at 480℃, it has no Widmanstätten structure, yield strength ≥460MPa, Akv(-40℃) ≥27J. After being made into a combined brake beam for railway freight cars, it was tested for fatigue performance of 1 million cycles according to GB / T1978 standard and no cracks were found.

[0043] To further understand the present invention, the following detailed description, in conjunction with embodiments, illustrates the titanium microalloyed low-carbon steel provided by the present invention, its preparation method, and its applications. The scope of protection of the present invention is not limited by the following embodiments.

[0044] Example 1

[0045] (1) A 320mm×410mm billet was obtained by converter smelting, LF refining and continuous casting. The superheat of the molten steel in the ladle during the continuous casting process was 20~30℃. The chemical composition was: C 0.07%, Si 0.40%, Mn 1.25%, P 0.015%, S 0.008%, Cr 0.20%, V 0.08%, Ti 0.07%, N 35ppm, and the remainder was Fe and unavoidable impurities.

[0046] (2) The billet obtained in step (1) is heated in a heating furnace. The temperature of the soaking section of the heating furnace is 1265℃ and the heating time is 224min.

[0047] (3) The heated billet is descaled by high pressure water and then rolled into steel for the brake beam of railway freight cars. The final rolling temperature is 878℃.

[0048] (4) The rolled section steel is naturally air-cooled at a cooling rate of 1.8℃ / s to obtain titanium microalloyed low carbon steel.

[0049] The titanium microalloyed low-carbon steel used for railway freight car brake beams, prepared by the above method, exhibits no Widmanstätten structure after normalizing at 920℃ and tempering at 480℃. It has a yield strength of 472MPa and an Akv (-40℃) of 105J. After being fabricated into a combined brake beam for railway freight cars, it undergoes fatigue performance testing for 1 million cycles according to GB / T1978 standard and shows no cracks.

[0050] Example 2

[0051] (1) A 320mm×410mm billet was obtained by converter smelting, LF refining and continuous casting. The superheat of the molten steel in the ladle during the continuous casting process was 25~35℃. The chemical composition was: C 0.09%, Si 0.40%, Mn 1.50%, P 0.015%, S 0.008%, Cr 0.25%, V 0.08%, Ti 0.10%, N 38ppm, and the remainder was Fe and unavoidable impurities.

[0052] (2) The billet obtained in step (1) is heated in a heating furnace. The temperature of the soaking section of the heating furnace is 1265℃ and the heating time is 270min.

[0053] (3) The heated billet is descaled by high pressure water and then rolled into steel for the brake beam of railway freight cars. The final rolling temperature is 857℃.

[0054] (4) The rolled section steel is naturally air-cooled at a cooling rate of 2.0℃ / s to obtain titanium microalloyed low carbon steel.

[0055] The titanium microalloyed low-carbon steel used for railway freight car brake beams, prepared by the above method, exhibits no Widmanstätten structure after normalizing at 920℃ and tempering at 480℃. It has a yield strength of 495MPa and an Akv (-40℃) of 145J. After being fabricated into a combined brake beam for railway freight cars, it undergoes fatigue performance testing for 1 million cycles according to GB / T1978 standard and shows no cracks.

[0056] Example 3

[0057] (1) A 320mm×410mm billet was obtained by converter smelting, LF refining and continuous casting. The superheat of the molten steel in the ladle during the continuous casting process was 28~34℃. The chemical composition was: C 0.05%, Si 0.35%, Mn 1.45%, P 0.015%, S 0.008%, Cr 0.25%, V 0.08%, Ti 0.10%, N 36ppm, and the remainder was Fe and unavoidable impurities.

[0058] (2) The billet obtained in step (1) is heated in a heating furnace. The temperature of the soaking section of the heating furnace is 1265℃ and the heating time is 250min.

[0059] (3) The heated billet is descaled by high pressure water and then rolled into steel for the brake beam of railway freight cars. The final rolling temperature is 857℃.

[0060] (4) The rolled section steel is naturally air-cooled at a cooling rate of 2.0℃ / s to obtain titanium microalloyed low carbon steel.

[0061] The titanium microalloyed low-carbon steel used for railway freight car brake beams, prepared by the above method, exhibits no Widmanstätten structure after normalizing at 920℃ and tempering at 480℃. It has a yield strength of 465MPa and an Akv (-40℃) of 152J. After being fabricated into a combined brake beam for railway freight cars, it undergoes fatigue performance testing for 1 million cycles according to GB / T1978 standard and shows no cracks.

[0062] Comparative Example 1

[0063] (1) A 320mm×410mm billet was obtained by converter smelting, LF refining and continuous casting. The superheat of the molten steel in the ladle during the continuous casting process was 20~40℃. The chemical composition was: C 0.18%, Si 0.33%, Mn 1.48%, P 0.010%, S 0.004%, Cr 0.26%, Ni 0.25%, V 0.11%, Nb 0.036%, Ti 0.011%, N 0.0062%, with the remainder being Fe and unavoidable impurities.

[0064] (2) The billet obtained in step (1) is heated in a heating furnace. The heating furnace has a uniform heating temperature of 1215℃ and a heating time of 210min.

[0065] (3) The heated billet is descaled by high pressure water and then rolled into steel for the brake beam of railway freight cars. The final rolling temperature is 900℃.

[0066] (4) The rolled section steel is naturally air-cooled at a cooling rate of 1.8℃ / s to obtain titanium microalloyed low carbon steel.

[0067] The titanium microalloyed low-carbon steel for railway freight car brake beams prepared by the above method, after being normalized at 920℃ and tempered at 480℃, has a Widmanstätten structure of grade D, a yield strength of 473 MPa, and an AKv (-40℃) of 11 J.

[0068] Comparative Example 2

[0069] (1) A 320mm×410mm billet was obtained by converter smelting, LF refining and continuous casting. The superheat of the molten steel in the ladle during the continuous casting process was 25~40℃. The chemical composition was: C 0.17%, Si 0.30%, Mn 1.42%, P 0.011%, S 0.002%, Cr 0.26%, Ni 0.25%, V 0.12%, Nb 0.036%, Ti 0.008%, N 0.0062%, with the remainder being Fe and unavoidable impurities.

[0070] (2) The billet obtained in step (1) is heated in a heating furnace. The heating furnace has a uniform heating temperature of 1220℃ and a heating time of 234 min.

[0071] (3) The heated billet is descaled by high pressure water and then rolled into steel for the brake beam of railway freight cars. The final rolling temperature is 906℃.

[0072] (4) The rolled section steel is naturally air-cooled at a cooling rate of 1.9℃ / s to obtain titanium microalloyed low carbon steel.

[0073] The titanium microalloyed low-carbon steel for railway freight car brake beams prepared by the above method, after being normalized at 920℃ and tempered at 480℃, has a Widmanstätten structure of grade D, a yield strength of 480 MPa, and an AKv (-40℃) of 16 J.

[0074] Comparative Example 3

[0075] (1) A 320mm×410mm billet was obtained by converter smelting, LF refining and continuous casting. The superheat of the molten steel in the ladle during the continuous casting process was 28~39℃. The chemical composition was: C 0.18%, Si 0.31%, Mn 1.46%, P 0.011%, S 0.004%, Cr 0.26%, Ni 0.24%, V 0.11%, Nb 0.037%, Ti 0.008%, N 0.0093%, with the remainder being Fe and unavoidable impurities.

[0076] (2) The billet obtained in step (1) is heated in a heating furnace. The heating furnace has a uniform heating temperature of 1209℃ and a heating time of 245min.

[0077] (3) The heated billet is descaled by high pressure water and then rolled into steel for the brake beam of railway freight cars. The final rolling temperature is 910℃.

[0078] (4) The rolled section steel is naturally air-cooled at a cooling rate of 1.7℃ / s to obtain titanium microalloyed low carbon steel.

[0079] The titanium microalloyed low-carbon steel for railway freight car brake beams prepared by the above method, after being normalized at 920℃ and tempered at 480℃, has a Widmanstätten structure of grade D, a yield strength of 460 MPa, and an AKv (-40℃) of 14 J.

[0080] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0081] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing titanium microalloyed low-carbon steel, comprising the following steps: S1) Prepare a low-carbon steel billet, wherein the composition of the low-carbon steel billet, by mass percentage, includes: C≤0.09%, Si0.30%~0.50%, Mn1.00%~1.70%, P≤0.020%, S≤0.015%, Cr0.20%~0.30%, V0.05%~0.10%, Ti0.07%~0.10%, N≤40ppm, with the remainder being Fe and unavoidable impurities; S2) The low-carbon steel billet is heated and then rolled to obtain titanium microalloyed low-carbon steel, wherein the final rolling temperature is 850-900℃.

2. The preparation method according to claim 1, characterized in that, The specific method for preparing the low-carbon steel billet is as follows: Molten iron and / or scrap steel are added to the converter, controlling the S content to ≤0.060%. When the initial steel composition reaches C≤0.06%, P≤0.010%, S≤0.010%, and the steel temperature ≥1670℃, the steel is tapped into the ladle. During tapping, aluminum-iron pre-deoxidation is first added, followed by FeSi alloy, FeMn alloy, and FeCr alloy, controlling C to 0.03%–0.07%, Si to 0.30%–0.50%, Mn to 1.00%–1.70%, and Cr to 0.20%–0.30%. Then, low-nitrogen ferrotitanium and ferrovanadium are added sequentially to obtain molten steel. The molten steel is poured at a constant rate, and the ladle is superheated to 20-40°C to obtain a low-carbon steel billet.

3. The preparation method according to claim 1, characterized in that, In step S2), the heating temperature is 1230-1270℃, and the heating time is t = (0.7-0.85)H, where H is the thickness of the low-carbon steel billet.

4. The preparation method according to claim 1, characterized in that, In step S2), the heating process further includes: The heated low-carbon steel billet is subjected to high-pressure water descaling.

5. The preparation method according to claim 1, characterized in that, In step S2), the final rolling temperature is 860–880°C.

6. The preparation method according to claim 1, characterized in that, In step S2), the rolling process includes cooling, the cooling rate is ≤2℃ / s, and the cooling method is natural air cooling.

7. The titanium microalloyed low-carbon steel prepared by the preparation method according to any one of claims 1 to 6, comprising, by mass percentage: C≤0.09%, Si 0.30%~0.50%, Mn 1.00%~1.70%, P≤0.020%, S≤0.015%, Cr 0.20%~0.30%, V 0.05%~0.10%, Ti 0.07%~0.10%, N≤40ppm, with the remainder being Fe and unavoidable impurities.

8. The titanium microalloyed low-carbon steel according to claim 7, characterized in that, The content of C is 0.05-0.09%, and / or the content of Ti is 0.08-0.09%.

9. A braking beam for railway freight cars, made of low-carbon steel, wherein the low-carbon steel is prepared by the method described in any one of claims 1 to 6 or by the titanium microalloyed low-carbon steel described in any one of claims 7 to 8.

10. The railway freight car brake beam according to claim 9, characterized in that, The titanium microalloyed low-carbon steel also includes post-treatment, which specifically involves normalizing and tempering the titanium microalloyed low-carbon steel. The normalizing temperature is 920-930℃, and the tempering temperature is 480-490℃. The metallographic structure of the railway freight car brake beam does not contain Widmanstätten structure.