Production process for controlling grain size of 45 steel

Abstract

The invention relates to a production process for controlling the grain size of 45 steel. The technical route is as follows: 120-ton converter smelting, deoxidation alloying (adding aluminum ingots), LF refining, RH vacuum refining, nitrogen wire feeding, continuous casting, steel loading, heating, descaling, rolling, water cooling, cooling bed cooling, fixed-length shearing, collecting and packaging. The 45 steel is produced by controlling proper acid-soluble aluminum elements, controlling the nitrogen content of a casting blank after vacuum degassing, optimizing a heating process and adopting a controlled cooling process, and the requirements that the austenite grain size is larger than or equal to 7.0 grade and no individual large grains exist, and the ferrite grain size is larger than or equal to 6.0 grade and no mixed crystals exist can be fully met.

Description

Technical Field

[0001] The present invention relates to the technical field of steel rolling production, and particularly relates to a production process for controlling the crystal grain size of 45 steel. Background Art

[0002] As a main component of the suspension system, an automotive shock absorber, during its service process, is subjected to the combined action of various loads such as tensile and compressive forces, vibrations, and inertial impacts as the attitude of the working device continuously changes.

[0003] Currently, manufacturing enterprises generally adopt the production process of surface intermediate frequency quenching and end friction welding to manufacture piston rods. The original state of the round steel is still retained inside and at the position of end friction welding, requiring the raw material to have good comprehensive performance and using the crystal grain size as an evaluation parameter.

[0004] According to GB / T6394, the austenite crystal grain size and ferrite crystal grain size of the entire cross-section are evaluated, and it is necessary to meet the requirements that the austenite crystal grain size ≥ 7.0 grades and there are no individual large grains, and the ferrite crystal grain size ≥ 6.0 grades and there is no mixed crystal. However, in the actual production process, due to influencing factors such as equipment failures and shift handovers, the time of the steel billet in the heating furnace is prolonged, making it impossible to ensure that the austenite crystal grain size meets the requirements; in the case of lacking a heat preservation cover on the cooling bed, serious mixed crystal phenomena are likely to occur in the actual production of crystal grain size. Summary of the Invention

[0005] Aiming at the above problems, the purpose of the present invention is to provide a production process for controlling the crystal grain size of 45 steel, which can effectively solve problems such as the coarsening of austenite grains and ferrite grains of 45 steel.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A production process for controlling the crystal grain size of 45 steel proposed by the present invention specifically includes the following steps:

[0008] S1. Converter smelting: After the blowing of the steelmaking converter ends, 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 ends;

[0010] S3. RH vacuum refining: RH vacuum refining is carried out after LF refining ends, and then the operation of feeding nitrogen-containing alloy cored wire is carried out;

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

[0012] S5. The steel billet is descaled and then rolled;

[0013] S6. The steel billet is successively rolled by a rough rolling mill set, an intermediate rolling mill set, and a finishing rolling mill set;

[0014] S7. Water cooling through the water channel; the temperature of the steel billet turning red on the cooling bed is 900°C - 960°C;

[0015] S8. After cooling on the cooling bed, it is cut to a fixed length by a cold shear, collected, and packed.

[0016] Further, in the step S1, after the blowing in the steelmaking converter is completed, the final carbon content is controlled at 0.08% - 0.20%; after the tapping is completed, the acid-soluble aluminum content is controlled at 0.032% - 0.042%.

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

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

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

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

[0021] Further, in the step S5, the rolling start temperature is 940°C - 1000°C.

[0022] Further, in the step S7, the temperature of the steel billet turning red on the cooling bed is 900°C - 960°C.

[0023] The present invention has the following beneficial effects compared with the prior art:

[0024] By controlling the appropriate acid-soluble aluminum element, controlling the nitrogen content of the continuous casting billet after vacuum degassing, optimizing the heating process, and adopting the controlled cooling process to produce 45 steel, the present invention can effectively meet the requirements that the austenite grain size is ≥7.0 grades and there are no individual large grains, and the ferrite grain size is ≥6.0 grades and there is no mixed grain. Description of the Drawings

[0025] Figure 1 It is an enlarged structural schematic diagram of the austenite grain size in Example 1 of the present invention;

[0026] Figure 2 It is an enlarged structural schematic diagram of the ferrite grain size in Example 1 of the present invention;

[0027] Figure 3 It is an enlarged structural schematic diagram of the edge austenite grain size in Comparative Example 1 of the present invention;

[0028] Figure 4 Schematic enlarged structure diagram of the grain size of the ferrite at the edge in Comparative Example 1 of the present invention. Specific embodiments

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0030] A production process for controlling the grain size of 45 steel proposed by the present invention has a technical route as follows: smelting in a 120-ton converter - deoxidation alloying (adding aluminum ingots) - LF refining - RH vacuum refining - feeding nitrogen wire - continuous casting - charging steel - heating - descaling - rolling - water cooling through the water box - cooling on the cooling bed - sizing shearing - collecting - packing.

[0031] The specific steps are as follows:

[0032] S1. Converter smelting: Steelmaking is carried out using a 120-ton top-bottom combined blowing converter. After the blowing of the steelmaking converter ends, the end-point carbon is controlled at 0.08% - 0.20%, the end-point phosphorus is less than or equal to 0.015%, and the tapping temperature is 1600°C - 1690°C;

[0033] During tapping, aluminum ingots and alloys are added for deoxidation alloying. The specific steps are as follows: After 1 / 4 of the tapping, aluminum ingots (reference dosage 1.2 - 1.6 kg / t) and alloys such as ferrosilicon are added in sequence, and the addition is completed when 3 / 4 of the tapping is reached. It is not allowed to add alloys and slag materials at the bottom of the ladle before tapping; The double porous plugs of the ladle are in good condition, and argon is purged throughout the process from tapping to lifting the ladle;

[0034] The acid-soluble aluminum at the end of tapping is controlled at 0.032% - 0.042%;

[0035] S2. LF refining: After the converter tapping ends, LF refining is carried out. The acid-soluble aluminum at the end of LF refining is controlled at 0.027% - 0.032%;

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

[0037] S4. After continuous casting, the steel billet is fed into the heating furnace for heating; A 30.0 m walking beam regenerative heating furnace is used;

[0038] The specifications of the continuously cast and drawn billet are 160mm×160mm×11m;

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

[0040] S5. After descaling the billet, rolling starts, and the rolling start temperature is 940°C - 1000°C;

[0041] S6. The billet is rolled by the roughing mill unit, intermediate rolling mill unit, and finishing mill unit; the roughing mill unit, intermediate rolling mill unit, and finishing mill unit are all arranged alternately in horizontal and vertical directions to reduce surface defects such as folding;

[0042] S7. After water-cooling through the water box, it is sent to the cooling bed. There are 3 sections in the water-cooling water box, and the first section is used. The purpose is to make the surface of the billet have sufficient reversion temperature after being sent to the cooling bed. The reversion temperature of the billet when it is sent to the cooling bed is 900°C - 960°C;

[0043] S8. After the round steel is cooled on the cooling bed, it is cut to a fixed length, collected, and packed by a cold shear.

[0044] By adding appropriate aluminum and nitrogen elements, the present invention can form fine aluminum nitride that pins at the grain boundaries and prevents grain coarsening during reheating and subsequent welding processes. The rolling mill formulates a suitable heating process according to the solid solution temperature of aluminum nitride, reduces the stability of undercooled austenite through water-cooling after rolling, promotes the formation of pearlite, and precipitates fine and dispersed aluminum nitride particles to refine the grains, thereby significantly improving the comprehensive performance of the steel.

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

[0046] Example 1

[0047] Rolling φ22mm 45 steel, the production process includes the following steps:

[0048] Steelmaking is carried out by a 120-ton top and bottom combined blowing converter. The final carbon content is controlled at 0.10%, the final phosphorus content is controlled at 0.012%, and the tapping temperature is 1650°C;

[0049] After 1 / 4 of the tapping, 1.4 kg / t of aluminum ingots are sequentially added, and the acid-soluble aluminum content at the end of the converter tapping is controlled at 0.035%;

[0050] The acid-soluble aluminum content at the LF station is controlled at 0.030%;

[0051] The acid-soluble aluminum content at the end of the RH refining is controlled at 0.025%. The operation of feeding the compound nitrogen alloy cored wire is carried out. The feeding amount is 200 m / furnace, the feeding speed is 3 m / s, and the nitrogen content in the steel is controlled at 50 ppm;

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

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

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

[0055] The heated steel billet is successively descaled, rough rolled, intermediate rolled, and finish rolled;

[0056] Among them, the rolling start temperature is 962℃-983℃;

[0057] The rough rolling mill train includes 2 φ650 and 4 φ610 short stress line continuous rolling mills;

[0058] The intermediate rolling mill train includes 2 φ610 and 4 φ470 short stress line continuous rolling mills;

[0059] The finish rolling mill train includes 2 φ470 and 2 φ380 short stress line continuous rolling mills;

[0060] After water cooling through the water box, it is sent to the cooling bed;

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

[0062] The round steel on the cooling bed is cooled and then cut to length, collected, and packaged.

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

[0064] Comparative Example 1

[0065] Rolling φ22mm 45 steel

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

[0067] In steelmaking, a 120-ton top and bottom combined blowing converter is used for smelting, the end point carbon is controlled at 0.10%, the end point phosphorus is controlled at 0.012%, and the tapping temperature is 1650℃;

[0068] After 1 / 4 of the tapping, 1.0kg / t of aluminum ingots are sequentially added, and the acid-soluble aluminum at the end of the converter tapping is 0.015%;

[0069] The acid-soluble aluminum in the LF tapping is 0.008%;

[0070] The acid-soluble aluminum at the end of RH refining is 0.005%, and the nitrogen content in the steel is 27 ppm;

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

[0072] The rolling start temperature is 1011 °C - 1026 °C;

[0073] The temperature on the cooling bed is 991 °C - 997 °C.

[0074] As Figure 3 and Figure 4 shown, in the comparative example, the austenite grain size is 7.5 grades, and there are individual 0-grade grains at the edge; the actual grain size is 8.0 grades - 4.0 grades, and the proportion of 4.0 grades at the edge is 10% - 15%.

[0075] Matters not detailed in the present invention are all well-known technologies.

[0076] The above-described embodiments are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined 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 comprises the following steps: S1. Converter smelting: After the steelmaking converter blowing is completed, aluminum ingots and alloys are added during the steelmaking process for deoxidation and alloying; S2, LF refining: LF refining is carried out after the converter steel is tapped; S3, RH vacuum refining: RH vacuum refining is carried out after LF refining, followed by the feeding operation of complex nitrogen alloy cored wire; S4, after continuous casting, the steel billet enters the heating furnace for heating; S5, rolling after descaling the steel billet; S6, the steel billet is rolled in sequence by a rough rolling mill, an intermediate rolling mill and a finishing rolling mill; S7, put on cooling bed after water cooling; S8. After cooling on the cooling bed, the products are cut to length, collected and packaged using a cold shear.

2. A production process for controlling the grain size of 45 steel according to claim 1, characterized in that: In the step S1, after the steelmaking converter blowing is completed, the final carbon is controlled at 0.08%-0.20%; after the steel is tapped, the acid-melted aluminum is controlled at 0.032%-0.042%.

3. A production process for controlling the grain size of 45 steel according to claim 1, characterized in that: In the step S2, after the LF refining is completed, the acid-melted aluminum is controlled at 0.027%-0.032%.

4. A production process for controlling the grain size of 45 steel according to claim 1, characterized in that: In step S3, after RH refining, the acid-melted aluminum is controlled at 0.022%-0.027%.

5. A production process for controlling the grain size of 45 steel according to claim 1, characterized in that: In step S3, the wire feeding amount 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.

6. A production process for controlling the grain size of 45 steel according to claim 1, characterized in that: In step S4, the temperature of the preheating section in the heating furnace is 700°C-850°C, the temperature of the heating section is 1020°C-1070°C, and the temperature of the soaking section is 1030°C-1080°C.

7. A production process for controlling the grain size of 45 steel according to claim 1, characterized in that: In the step S5, the rolling temperature is 940°C-1000°C.

8. A production process for controlling the grain size of 45 steel according to claim 1, characterized in that: In step S7, the red-hot temperature of the cooling bed on the steel billet is 900°C-960°C.

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