A method for controlling hot-rolled wire rod of easy pickling and non-annealing medium carbon cold-upset steel

Abstract

The application provides a control method for hot-rolled wire rod of easy pickling and non-annealing medium carbon cold upsetting steel, and belongs to the technical field of metallurgy. The control method comprises the steps of descaling, rolling, wire laying and cooling. In the rolling process, the temperature at the entrance of the finishing rolling is 820-880 DEG C, and the temperature at the entrance of the reducing diameter is 750-810 DEG C. In the wire laying process, the temperature is 760-800 DEG C. In the cooling process, the wire rod is naturally cooled on the cooling roller way, and when the temperature is 720-780 DEG C, the heat preservation cover is covered, and when the temperature is 630-660 DEG C, the heat preservation cover is opened, then the wire rod is naturally cooled on the cooling roller way, and the temperature of the collected coil is 450-480 DEG C. The application can reduce the thickness of the iron oxide skin of the wire rod, and the thickness of the iron oxide skin is less than or equal to 9 um, the iron oxide skin has micro-cracks, the integrity of the iron oxide skin is damaged, and the wire rod is more favorable for pickling. Meanwhile, the strength of the medium carbon steel wire rod is reduced, and the wire rod can be directly drawn and cold upsetting processed without annealing.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a method for controlling the hot-rolled wire rod of easily pickled, non-annealed medium carbon cold heading steel. Background Technology

[0002] The iron oxide scale on the surface of hot-rolled wire rod needs to be removed during downstream processing. If the iron oxide scale on cold-heading steel wire rod is not easily pickled, the iron oxide scale will still adhere to the surface of the wire rod after pickling, resulting in pickling spots and affecting the quality of subsequent surface galvanizing, thus causing scrap.

[0003] To meet the requirements for easy pickling, steel producers generally adopt low-temperature wire drawing and rapid cooling processes to reduce the thickness of the iron oxide scale. However, the rapid cooling rate increases the strength of the wire rod. Medium-carbon cold heading steel, due to its high initial strength, requires annealing before processing. Downstream users, in order to reduce production costs, prefer wire rods that can be drawn and cold-headed directly without annealing. To meet the anneal-free requirement, steel producers generally adopt high-temperature wire drawing and slow cooling with full covering to reduce the wire rod strength. Therefore, from a production process perspective, it is difficult to simultaneously achieve both easy pickling and anneal-free requirements.

[0004] Currently, there are no reports on a production technology for medium carbon steel wire rod that combines easy pickling with annealing-free processing. A new process needs to be developed that facilitates pickling and descaling of the wire rod while reducing its strength, thus meeting the requirements of users for direct drawing and cold heading. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a method for controlling the pickling and annealing-free production of medium carbon cold heading steel wire rod, reducing the thickness of the iron oxide scale on the wire rod, disrupting the integrity of the iron oxide scale, and making the wire rod more suitable for pickling. At the same time, it reduces the strength of the medium carbon steel wire rod, resulting in more easily deformable ferrite soft phase structure, making the wire rod more suitable for drawing and cold heading processes.

[0006] To solve the above-mentioned technical problems, the technical solution provided by the present invention is: a method for controlling the hot-rolled wire rod of easily pickled and non-annealed medium carbon cold heading steel, the control method including descaling, rolling, wire drawing and cooling processes; The rolling process has a finishing mill inlet temperature of 820–880°C and a sizing mill inlet temperature of 750–810°C. The spinning process is carried out at a spinning temperature of 760–800°C. In the cooling process, the wire rod is naturally cooled on the cooling roller conveyor. When the temperature reaches 720-780°C, an insulation cover is placed on top. When the temperature reaches 630-660°C, the insulation cover is opened, and the wire rod is then naturally cooled on the cooling roller conveyor. The winding temperature is 450-480°C.

[0007] In the descaling process described in this invention, the high-pressure water descaling pressure is ≥18 MPa.

[0008] In the cooling process described in this invention, the inlet speed of the Stellmore cooling line roller conveyor is 15-20 m / min, with an increment of 1 m / min. The front insulation cover is opened, and the wire rod is naturally cooled on the cooling roller conveyor. When the temperature reaches 720-780°C, the insulation cover is closed. When the temperature reaches 630-660°C, the insulation cover is opened, and then the wire rod is naturally cooled on the cooling roller conveyor. The winding temperature is 450-480°C.

[0009] The carbon content of the hot-rolled wire rod described in this invention is 0.35-0.39%.

[0010] The hot-rolled wire rod of the present invention has an iron oxide scale thickness of 6-9 μm; the iron oxide scale has a non-dense microstructure with cracks; and the wire rod has a red appearance.

[0011] The hot-rolled wire rod of the present invention has a tensile strength of 580-610 MPa.

[0012] The hot-rolled wire rod of the present invention has a metallographic structure of ferrite + pearlite, wherein the ferrite content is 52-57% and the pearlite content is 43-48%. The wire rod can be directly drawn and cold-headed without annealing.

[0013] The iron oxide scale of this invention has a thickness of 6–9 μm; the microstructure of the iron oxide scale is not dense and contains cracks; the wire rod has a red appearance. While obtaining a thin iron oxide scale, compared with the ordinary process of high-temperature wire drawing + slow cooling with full covering, the tensile strength is significantly reduced, which can reduce the tensile strength of the wire rod by 40–60 MPa.

[0014] The theoretical analysis of the component ratio and process adjustment of this invention is as follows: To simultaneously meet the requirements of both easy pickling and annealing-free processes, it is necessary to ensure complete removal of iron oxide scale in a single pass, and to design reasonable rolling and coiling temperatures. This requires increasing the cooling rate of the wire rod unwinding rollers, minimizing the residence time in the high-temperature zone of the wire rod, reducing the amount of iron oxide scale formation, controlling the Fe3O4 content in the iron oxide scale structure, and controlling the iron oxide scale thickness. Furthermore, while controlling the iron oxide scale, it is also crucial to rationally control the phase transformation process of medium carbon steel to obtain more ferrite soft phase structure and reduce the pearlite hard phase structure content, thereby lowering the tensile strength of the wire rod.

[0015] The beneficial effects of adopting the above technical solution are as follows: 1. The method for controlling the thickness of hot-rolled medium carbon cold heading steel wire rod in this invention reduces the thickness of the iron oxide scale on the wire rod, making the iron oxide scale thickness ≤9μm. The presence of micro-cracks in the iron oxide scale disrupts its integrity, making the wire rod more suitable for pickling. 2. This invention also reduces the strength of medium carbon steel wire rod, lowering the tensile strength from 640-670 MPa to 580-610 MPa, allowing the wire rod to be directly drawn and cold-headed without annealing. Attached Figure Description

[0016] Figure 1 The image shows the metallographic structure of the hot-rolled carbon cold heading steel wire rod in Example 1. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to specific embodiments.

[0018] Examples 1-5 A method for controlling the hot-rolled wire rod of easily pickled, non-annealed medium carbon cold heading steel includes descaling, rolling, wire drawing, and cooling processes. The specific control method is as follows: Descaling process: High-pressure water descaling pressure ≥18Mpa; Rolling process: Finishing mill inlet temperature 820~880℃; Reduction sizing inlet temperature 750~810℃; Silk spinning process: Silk spinning temperature 760~800℃; Cooling process: The inlet speed of the Stellmore cooling line roller conveyor is 15-20 m / min, with an increment of 1 m / min. The front insulation cover is opened, and the wire rod is naturally cooled on the cooling roller conveyor. When the temperature reaches 720-780℃, the insulation cover is closed. When the temperature reaches 630-660℃, the insulation cover is opened, and the wire rod is naturally cooled on the cooling roller conveyor. The coiling temperature is 450-480℃ when the wire rod is collected.

[0019] The process parameters for Examples 1-5 are shown in Table 1, and the iron oxide scale thickness, wire rod tensile strength, and microstructure of Examples 1-5 are shown in Table 2. Figure 1 The image shows the metallographic structure of the hot-rolled carbon cold heading steel wire rod in Example 1 (the other examples are similar and are omitted).

[0020] The wire rod obtained in this embodiment has a carbon content of 0.35-0.39%, a tensile strength of 580-610 MPa, and a metallographic structure of ferrite + pearlite, wherein the ferrite content is 52-57% and the pearlite content is 43-48%. The iron oxide scale thickness of the hot-rolled wire rod in this embodiment is 6-9 μm; the microstructure of the iron oxide scale is not dense and contains cracks; the wire rod has a red appearance and can be directly drawn and cold-headed without annealing.

[0021] Table 1. Process control parameters for hot-rolled carbon cold heading steel wire rod in Examples 1-5 Table 2 Properties of medium carbon cold heading steel hot-rolled wire rods in Examples 1-5 The above embodiments are only used to illustrate and not limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention without departing from the spirit and scope of the present invention. Any modifications or partial substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for controlling the hot-rolled wire rod of easily pickled, non-annealed medium carbon cold heading steel, characterized in that, The control method includes descaling, rolling, wire drawing, and cooling processes; The rolling process has a finishing mill inlet temperature of 820–880°C and a sizing mill inlet temperature of 750–810°C. The spinning process is carried out at a spinning temperature of 760–800°C. In the cooling process, the wire rod is naturally cooled on the cooling roller conveyor. When the temperature is 720-780°C, an insulation cover is placed on top. When the temperature is 630-660°C, the insulation cover is opened. Then, the wire rod is naturally cooled on the cooling roller conveyor, and the winding temperature is 450-480°C. The descaling process involves high-pressure water descaling at a pressure ≥18 MPa. The thickness of the iron oxide scale on the hot-rolled wire rod is 6-9 μm; the wire rod has a red appearance, and the microstructure of the iron oxide scale is not dense and contains cracks. The tensile strength of the hot-rolled wire rod is 580-610 MPa; The metallographic structure of the hot-rolled wire rod is ferrite + pearlite, wherein the ferrite content is 52-57% and the pearlite content is 43-48%.

2. The method for controlling the hot-rolled wire rod of easily pickled, non-annealed medium carbon cold heading steel according to claim 1, characterized in that, In the cooling process, the inlet speed of the Stellmore cooling line roller conveyor is 15-20 m / min, with an increment of 1 m / min. The front insulation cover is opened, and the wire rod is naturally cooled on the cooling roller conveyor. When the temperature reaches 720-780°C, the insulation cover is closed. When the temperature reaches 630-660°C, the insulation cover is opened, and then the wire rod is naturally cooled on the cooling roller conveyor. The winding temperature is 450-480°C.

3. The method for controlling the hot-rolled wire rod of easily pickled, non-annealed medium carbon cold heading steel according to claim 1, characterized in that, The carbon content of the hot-rolled wire rod is 0.35-0.39%.

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