A production process for controlling the grain size of 45 steel

Abstract

The present application relates to a kind of production processes for controlling the grain size of 45 steel, technical route as follows: 120 tons converter smelting-deoxidation alloying (adding aluminum ingot)-LF refining-RH vacuum refining-feeding nitrogen wire-continuous casting-steel loading-heating-scaling removal-rolling-water cooling-cooling bed cooling-dimension shearing-collection-packing.The present application can fully meet the requirements of austenite grain size ≥7.0 grade and no individual large grain, ferrite grain size ≥6.0 grade and no mixed crystal by controlling appropriate acid-soluble aluminum element, controlling the nitrogen content of casting blank after vacuum degassing, optimizing heating process and adopting controlled cooling process to produce 45 steel.

Description

Technical Field

[0001] This invention relates to the field of steel rolling production technology, and in particular to a production process for controlling the grain size of 45 steel. Background Technology

[0002] As a key component of the suspension system, automotive shock absorbers are subjected to a combination of loads, including tension, compression, vibration, and inertial impact, as the working device's posture changes continuously during service.

[0003] Currently, manufacturers generally use surface medium-frequency quenching and end friction welding to manufacture piston rods. The internal parts and the end friction welding positions still retain the original state of the round steel, requiring the raw materials to have good comprehensive performance and using grain size as an evaluation parameter.

[0004] According to GB / T6394, the austenite and ferrite grain sizes across the entire cross-section must meet the following requirements: austenite grain size ≥ 7.0 with no large individual grains, and ferrite grain size ≥ 6.0 with no mixed grains. However, in actual production, factors such as equipment failure and shift changes can lead to prolonged time the billet spends in the heating furnace, making it impossible to guarantee that the austenite grain size meets the requirements. Furthermore, in the absence of an insulation cover on the cooling bed, severe mixed grain phenomena are likely to occur in actual production. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a production process for controlling the grain size of 45 steel, which can effectively solve the problems of coarse austenite and ferrite grains in 45 steel.

[0006] The technical solution adopted in this invention is as follows:

[0007] The production process for controlling the grain size of 45 steel proposed in this invention specifically includes the following steps:

[0008] S1. Converter smelting: After the steelmaking converter blowing process is completed, aluminum ingots and alloys are added during the tapping process for deoxidation and alloying.

[0009] S2, LF refining: LF refining is carried out after the converter tapping is completed;

[0010] S3, RH vacuum refining: After LF refining is completed, RH vacuum refining is carried out, followed by the feeding operation of nitrogen-coated cored wire;

[0011] S4. After continuous casting, the steel billet enters the heating furnace for heating;

[0012] S5. Steel billet is rolled after descaling;

[0013] S6. The steel billet is rolled sequentially through the roughing mill, intermediate mill and finishing mill;

[0014] S7, water-cooled; upper cooling bed reddening temperature 900℃-960℃;

[0015] S8. After being cooled on a cooling bed, the products are cut to length, collected, and packaged using a cold shearing machine.

[0016] Furthermore, in step S1, after the steelmaking converter blowing process is completed, the final carbon content is controlled at 0.08%-0.20%; after the steel is tapped, the acid-melted aluminum content is controlled at 0.032%-0.042%.

[0017] Furthermore, in step S2, after the LF refining is completed, the acid-melted aluminum content is controlled at 0.027%-0.032%.

[0018] Furthermore, in step S3, after RH refining, the acid-melted aluminum content is controlled at 0.022%-0.027%.

[0019] Furthermore, in step S3, the wire feeding rate is 180m-220m / furnace, the wire feeding speed is 2m / s-4m / s, and the nitrogen content in the steel is controlled at 40ppm-60ppm.

[0020] Furthermore, in step S4, the temperature of the preheating section in the heating furnace is 700℃-850℃, the temperature of the heating section is 1020℃-1070℃, and the temperature of the soaking section is 1030℃-1080℃.

[0021] Furthermore, in step S5, the rolling temperature is 940℃-1000℃.

[0022] Furthermore, in step S7, the reheating temperature of the steel billet on the cooling bed is 900℃-960℃.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] This invention produces 45 steel by controlling appropriate acid-soluble aluminum elements, controlling the nitrogen content of the billet after vacuum degassing, optimizing the heating process, and using controlled cooling. This effectively meets the requirements of austenite grain size ≥ 7.0 with no individual large grains, and ferrite grain size ≥ 6.0 with no mixed grains. Attached Figure Description

[0025] Figure 1 This is a magnified structural diagram of the austenite grain size in Embodiment 1 of the present invention;

[0026] Figure 2 This is a magnified structural diagram of the ferrite grain size in Embodiment 1 of the present invention;

[0027] Figure 3 This is a magnified structural schematic diagram of the austenite grain size at the edge in Comparative Example 1 of the present invention;

[0028] Figure 4 This is an enlarged structural schematic diagram of the ferrite grain size at the edge in Comparative Example 1 of the present invention. Detailed Implementation

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] The production process for controlling the grain size of 45 steel proposed in this invention is as follows: 120-ton converter smelting—deoxidation and alloying (adding aluminum ingots)—LF refining—RH vacuum refining—nitrogen feeding line—continuous casting—loading steel—heating—descaling—rolling—water cooling—cooling bed cooling—length shearing—collection—packaging.

[0031] The specific steps are as follows:

[0032] S1. Converter smelting: Steelmaking adopts a 120-ton top and bottom blowing converter. After the converter blowing is completed, the final carbon content is controlled at 0.08%-0.20%, the final phosphorus content is less than or equal to 0.015%, and the tapping temperature is 1600℃-1690℃.

[0033] Aluminum ingots and alloys are added during the tapping process for deoxidation and alloying. The specific steps are as follows: After tapping 1 / 4 of the steel, aluminum ingots (reference dosage 1.2-1.6 kg / t) and alloys such as ferrosilicon are added sequentially. The addition is completed when tapping 3 / 4 of the steel. It is not allowed to add alloys and slag to the bottom of the ladle before tapping. The double permeable bricks of the ladle are in good condition. Argon is purged throughout the entire process from tapping to hoisting the ladle.

[0034] At the end of steel tapping, the aluminum content of the acid melt should be controlled at 0.032%-0.042%.

[0035] S2, LF refining: LF refining is carried out after the converter tapping is completed. The acid melt aluminum content is controlled at 0.027%-0.032% after LF refining.

[0036] S3, RH vacuum refining: After LF refining is completed, RH vacuum refining is carried out. After RH refining, the acid melt aluminum is controlled at 0.022%-0.027%. Then, the nitrogen alloy cored wire feeding operation is carried out. The wire feeding amount is 180m-220m / furnace, the wire feeding speed is 2m-4m / s, and the nitrogen content in the steel is controlled at 40ppm-60ppm.

[0037] S4. After continuous casting, the steel billet is heated in a heating furnace; a 30.0m walking beam regenerative heating furnace is used.

[0038] The dimensions of the continuously cast steel billet are 160mm×160mm×11m;

[0039] The temperature of the preheating section inside the furnace is controlled at 700℃-850℃, the temperature of the heating section is controlled at 1020℃-1070℃, and the temperature of the soaking section is controlled at 1030℃-1080℃; the total heating time is controlled at 100min-130min.

[0040] S5. After descaling, the steel billet is rolled at a rolling temperature of 940℃-1000℃.

[0041] S6. The steel billet is rolled by a roughing mill, an intermediate mill, and a finishing mill; the roughing mill, intermediate mill, and finishing mill are all arranged alternately in a horizontal and vertical manner to reduce surface defects such as folds.

[0042] S7. After water cooling, the billet is placed on the cooling bed. The water cooling tank has three sections. The first section is used to ensure that the surface of the billet is fully heated after it is placed on the cooling bed. The red temperature of the billet on the cooling bed is 900℃-960℃.

[0043] S8. After the round steel is cooled on the cold bed, it is cut to length, collected, and packaged using a cold shearing machine.

[0044] This invention, by adding appropriate amounts of aluminum and nitrogen, enables the formation of fine aluminum nitride particles anchored at grain boundaries, preventing grain coarsening during reheating and subsequent welding. The steel rolling process utilizes a suitable heating technique based on the aluminum nitride solution temperature. Post-rolling water quenching reduces the stability of supercooled austenite, promotes pearlite formation, and precipitates fine, dispersed aluminum nitride particles to refine the grain structure, thereby significantly improving the overall performance of the steel.

[0045] The effects of the present invention will be further illustrated below through specific embodiments and comparative examples:

[0046] Example 1

[0047] The rolling process for φ22mm 45 steel includes the following steps:

[0048] Steelmaking is carried out using a 120-ton top-and-bottom blown converter, with the final carbon control at 0.10% and the final phosphorus control at 0.012%, and the tapping temperature at 1650℃.

[0049] After 1 / 4 of the steel has been tapped, 1.4 kg / t of aluminum ingots are added sequentially, and the acid melting aluminum content is controlled at 0.035% at the end of the converter tapping process.

[0050] The LF-leached aluminum content is controlled at 0.030%.

[0051] After RH refining, the acid melt aluminum content is controlled at 0.025%. Then, the nitrogen alloy cored wire feeding operation is carried out with a wire feeding rate of 200m / furnace and a wire feeding speed of 3m / s. The nitrogen content in the steel is controlled at 50ppm.

[0052] A 45 steel billet with dimensions of 160mm×160mm×11m is sent to a heating furnace for heating treatment to obtain a heated steel billet.

[0053] The heating furnace is a 30.0m walking beam regenerative heating furnace;

[0054] The preheating section of the heating furnace has a temperature control range of 729℃-781℃, the heating section has a temperature control range of 1058℃-1082℃, the soaking section has a temperature control target of 1066℃-1076℃, and the total heating time is 117min-121min.

[0055] The heat-treated steel billet is then subjected to descaling, rough rolling, intermediate rolling and finish rolling in sequence.

[0056] The initial rolling temperature is 962℃-983℃;

[0057] The roughing mill unit includes two φ650 and four φ610 short stress line continuous rolling mills;

[0058] The intermediate rolling mill unit includes two φ610 and four φ470 short stress line continuous rolling mills;

[0059] The finishing mill unit includes two φ470 and two φ380 short stress line continuous rolling mills;

[0060] After being cooled by water, it is placed on a cooling bed;

[0061] The temperature of the upper cooling bed is 935℃-950℃;

[0062] After the round steel bars are cooled on the cooling bed, they are cut to length, collected, and packaged.

[0063] like Figure 1 and Figure 2 As shown, in this embodiment, the austenite grain size is 8.5 grade and there are no individual large grains; the actual grain size is 8.5 grade, with some grains at grade 6.0.

[0064] Comparative Example 1

[0065] Rolled φ22mm 45 steel

[0066] The difference between the comparative example and the embodiment is that the acid-soluble aluminum content in the steelmaking process is low, and no nitrogen feed line is used (Als = 0.005%, N = 23ppm); the heating temperature of the steel rolling process is high and there is no controlled cooling.

[0067] Steelmaking is carried out using a 120-ton top-and-bottom blown converter, with the final carbon content controlled at 0.10% and the final phosphorus content controlled at 0.012%, and the tapping temperature at 1650℃.

[0068] After 1 / 4 of the steel has been tapped, 1.0 kg / t of aluminum ingots are added sequentially, and the acid-melted aluminum content is 0.015% at the end of the converter tapping process.

[0069] The LF-exit acid-melted aluminum content is 0.008%;

[0070] At the end of RH refining, the aluminum content in the acid melt was 0.005%, and the nitrogen content in the steel was 27 ppm.

[0071] The preheating section temperature of the heating furnace is controlled at 827℃-863℃, the heating section temperature is controlled at 1071℃-1088℃, the soaking section temperature is controlled at 1088℃-1101℃, and the total heating time is 93min-107min.

[0072] Rolling temperature: 1011℃-1026℃;

[0073] The temperature of the upper cooling bed is 991℃-997℃.

[0074] like Figure 3 and Figure 4 As shown, in the comparative example, the austenite grain size is grade 7.5, with a few grade 0 grains at the edges; the actual grain size is grade 8.0 to grade 4.0, with grade 4.0 accounting for 10% to 15% at the edges.

[0075] All matters not covered in this invention are common knowledge.

[0076] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A production process for controlling the grain size of 45 steel, characterized in that, The process includes the following steps: S1. Converter smelting: After the steelmaking converter blowing process is completed, aluminum ingots and alloys are added during the tapping process for deoxidation and alloying. S2, LF refining: LF refining is carried out after the converter tapping is completed; S3, RH vacuum refining: After LF refining is completed, RH vacuum refining is carried out, followed by the feeding operation of nitrogen-coated cored wire; S4. After continuous casting, the steel billet enters the heating furnace for heating; S5. Steel billet is rolled after descaling; S6. The steel billet is rolled sequentially through the roughing mill, intermediate mill and finishing mill; S7. After water cooling, it is placed on the cooling bed; S8. After cooling on a cooling bed, the products are cut to length, collected, and packaged using a cold shearing machine. In step S1, after the steelmaking converter blowing process is completed, the final carbon content is controlled at 0.08%-0.20%; after tapping, the acid-melted aluminum content is controlled at 0.032%-0.042%. In step S2, after LF refining, the acid-melted aluminum content is controlled at 0.027%-0.032%. In step S3, after RH refining, the acid-melted aluminum content is controlled at 0.022%-0.027%. In step S3, the wire feeding rate is 180m-220m / furnace, the wire feeding speed is 2m / s-4m / s, and the nitrogen content in the steel is controlled at 40ppm-60ppm. In step S4, the temperature of the preheating section in the heating furnace is 700℃-850℃, the temperature of the heating section is 1020℃-1070℃, and the temperature of the soaking section is 1030℃-1080℃. In step S5, the rolling temperature is 940℃-1000℃; In step S7, the reheating temperature of the steel billet on the cooling bed is 900℃-960℃.

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