A controlled cooling method for small-size 38crmoal wire rod non-annealing steel

Abstract

This invention belongs to the field of metallurgical technology, specifically disclosing a controlled cooling method for small-diameter 38CrMoAl wire rod without annealing. The wire rod specifications are Ф5.0-8.0mm, and the chemical composition of the steel by weight percentage is: C: 0.35%-0.42%, Si: 0.20%-0.45%, Mn: 0.30%-0.60%, Al: 0.70%-1.10%, Cr: 1.35%-1.65%, Mo: 0.15%- The composition is 0.25%, P≤0.020%, S≤0.020%, Cu≤0.20%, Ni≤0.30%, with the remainder being Fe and unavoidable impurities. The coiling temperature is controlled at 750-800℃, the Steyrmo roller conveyor inlet temperature at 700-750℃, the Steyrmo roller conveyor outlet temperature at 650-700℃, the coiling temperature at 630-650℃, the inlet temperature at 610-630℃, and the outlet temperature at 560-610℃. The microstructure of the small-gauge wire rod produced by this invention is ferrite + pearlite, without martensite, bainite, or other abnormal structures that affect drawing. By controlling the microstructure of the small-gauge wire rod to be ferrite + pearlite, downstream customers can directly draw it without annealing, eliminating the annealing process and saving 300-500 yuan / ton in costs.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology and relates to a controlled cooling method for small-diameter 38CrMoAl wire rod without annealing. Technical Background

[0002] 38CrMoAl steel is a high-quality nitriding steel with good mechanical properties. It is often used to manufacture mechanical parts that are subjected to impact loads and reciprocating wear. The processing requires a drawing process, so users have certain requirements for the drawing performance of this steel.

[0003] The current situation is that the microstructure of 38CrMoAl wire rods produced by various steel mills, with small specifications of Ф5.0-8.0mm wire rods, is ferrite + pearlite + martensite + bainite, with a small amount of abnormal structures such as martensite and bainite. Direct drawing will lead to drawing fracture and drawing cracks, and annealing is necessary before drawing. The microstructure of medium and large specifications of wire rods above 8.0mm is ferrite + pearlite, and they can be drawn directly without annealing.

[0004] 38CrMoAl is a medium-carbon alloy steel with high content of alloying elements Cr and Mo. The microstructure of small-diameter Ф5.0-8.0mm wire rod is extremely difficult to control, and abnormal structures such as martensite and bainite are easily generated. Therefore, how to effectively control the microstructure of small-diameter Ф5.0-8.0mm wire rod is an important research topic in steel rolling production. Summary of the Invention

[0005] To solve the above-mentioned technical problems, this invention provides a controlled cooling method for small-diameter 38CrMoAl wire rod without annealing. By controlling the wire drawing temperature, the temperature at which the wire enters the Steyrmo roller conveyor, the temperature at which it exits the Steyrmo roller conveyor, the coiling temperature, the temperature at which it enters the insulation corridor, and the temperature at which it exits the insulation corridor, the cooling rate at each stage after wire drawing is controlled. This ensures that the microstructure of the small-diameter Ф5.0-8.0mm wire rod is ferrite + pearlite, without abnormal structures such as martensite and bainite that affect drawing, allowing for direct drawing without annealing.

[0006] The technical solution of this invention is:

[0007] A controlled cooling method for small-diameter 38CrMoAl wire rod without annealing, with wire rod specifications of Ф5.0-8.0mm, is disclosed in the following rolling controlled cooling process: heating of 150 cubic meter continuous casting billet → high-pressure water descaling → roughing rolling → intermediate rolling → pre-finishing rolling → water cooling → finish rolling → water cooling → sizing rolling → wire drawing → Stellmore slow cooling → coiling → heat preservation corridor heat preservation slow cooling. The method is characterized by the following chemical composition by weight percentage: C: 0.35%–0.42%, Si: 0.20%–0.45%, Mn: 0.30%–0.60%, Al: 0.70%. %~1.10%, Cr: 1.35%~1.65%, Mo: 0.15%~0.25%, P≤0.020%, S≤0.020%, Cu≤0.20%, Ni≤0.30%, the remainder being Fe and unavoidable impurities; spinning temperature 750-800℃, Steyrmo roller conveyor inlet temperature 700-750℃, Steyrmo roller conveyor outlet temperature 650-700℃, winding temperature 630-650℃, inlet temperature of the insulation corridor 610-630℃, outlet temperature of the insulation corridor 560-610℃.

[0008] Furthermore, all insulation covers on the Steyrmo roller conveyor are closed, and the gaps between the insulation covers are sealed with insulation cotton cloth after the insulation covers are closed to ensure the insulation effect.

[0009] Furthermore, the Steyrmo roller conveyor speed is 0.07–0.12 m / s, and the Steyrmo roller conveyor wire cooling rate is ≤0.2℃ / s.

[0010] Furthermore, an asbestos insulation chamber is installed between the coil drum and the insulation corridor, with the temperature inside the insulation corridor at 610-630℃ and the coil cooling rate ≤0.5℃ / s.

[0011] Furthermore, heating devices are installed at the beginning, middle, and end sections of the insulated corridor. The ambient temperature inside the insulated corridor is 50-80℃, the insulation time of the insulated corridor is 2.5±0.5h, the temperature exiting the insulated corridor is 560-610℃, and the wire rod cooling rate is ≤0.2℃℃ / s.

[0012] Furthermore, the heating device is a tubular resistance heater used to control the ambient temperature inside the insulated corridor.

[0013] Furthermore, the microstructure of the 38CrMoAl wire rod is ferrite + pearlite.

[0014] Invention Principle: Using a FORMASTOR-F fully automatic phase transformation instrument, the critical phase transformation points of 38CrMoAl steel were determined to be: Ar1 620℃, Ar3 746℃, Ac1 769℃, Ac3 866℃, Ms 376℃, and Mf 150℃. When the cooling rate is less than 0.5℃ / s, the room temperature microstructure is proeutectoid ferrite + pearlite; when the cooling rate is 0.5-2.0℃ / s, the room temperature microstructure is ferrite + pearlite + bainite; when the cooling rate is 2.0-5.0℃ / s, the room temperature microstructure is bainite + martensite; and when the cooling rate is greater than 5.0℃ / s, the room temperature microstructure is martensite.

[0015] Therefore, in order to obtain wire rods with a ferrite + pearlite microstructure, it is necessary to control the cooling rate at each stage to be less than 0.5℃ / s.

[0016] The beneficial effects of this invention are:

[0017] 1. This invention controls the cooling rate at each stage after wire drawing by controlling the temperature at each key point: the temperature at the Stelmore roller conveyor entering the cover, the temperature at the Stelmore roller conveyor exiting the cover, the coiling temperature, the temperature at the insulated corridor entering the cover, and the temperature at the insulated corridor exiting the cover. This controls the microstructure of small-gauge wire rods to be ferrite + pearlite, without abnormal structures such as martensite and bainite that affect drawing.

[0018] 2. By controlling the microstructure of small-diameter Ф5.0-8.0mm wire rod to be ferrite + pearlite, downstream customers can directly draw the wire without annealing, eliminating the annealing process, saving 300-500 yuan / ton in costs, reducing production costs and improving production efficiency. Attached Figure Description

[0019] 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 only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 Metallographic structure diagram of Example 1;

[0021] Figure 2 Metallographic structure diagram of Example 2;

[0022] Figure 3 The metallographic structure diagram is for Comparative Example 1. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1:

[0025] A controlled cooling method for small-diameter 38CrMoAl wire rod without annealing. The chemical composition of the steel by weight percentage is: C: 0.36%, Si: 0.25%, Mn: 0.40%, Al: 0.85%, Cr: 1.50%, Mo: 0.20%, P: 0.010%, S: 0.012%, Cu: 0.032%, Ni: 0.018%, with the remainder being Fe and unavoidable impurities; the wire rod specification is Ф6.5mm; the rolling controlled cooling process route is: heating of 150 cubic meter continuous casting billet → high-pressure water descaling → roughing rolling → intermediate rolling → pre-finishing rolling → water cooling → finish rolling → water cooling → sizing rolling → wire drawing → Steyrmo slow cooling → coiling → heat preservation corridor heat preservation slow cooling. The process includes the following steps:

[0026] (1) All insulation covers of the Steyrmo roller conveyor are closed. The gaps between the insulation covers are sealed with insulation cotton cloth after the insulation covers are closed to ensure the insulation effect. The speed of the Steyrmo roller conveyor is controlled at 0.07-0.10m / s, the temperature of the Steyrmo roller conveyor entering the cover is controlled at 705-740℃, the temperature of the Steyrmo roller conveyor exiting the cover is controlled at 650-690℃, and the winding temperature is controlled at 630-650℃, thereby controlling the cooling rate of the Steyrmo roller conveyor wire rod at 0.15-0.2℃ / s.

[0027] (2) An asbestos insulation chamber is added between the coil and the insulation corridor to control the temperature of the coil entering the insulation corridor to 610-630℃, thereby controlling the coil cooling rate to 0.4-0.5℃ / s;

[0028] (3) Add heating devices to the head, middle and tail sections of the insulated corridor to control the ambient temperature inside the insulated corridor to 65℃, the insulation time of the insulated corridor to 2.6h, and control the temperature outside the insulated corridor to 560-600℃, thereby controlling the cooling rate of the wire rod to 0.15-0.2℃ / s.

[0029] The metallographic structure of small-diameter 38CrMoAl wire produced according to the above control methods is as follows: Figure 1 As shown, the metallographic structure is ferrite + pearlite.

[0030] Example 2:

[0031] A controlled cooling method for small-diameter 38CrMoAl wire rod without annealing. The chemical composition of the steel by weight percentage is: C: 0.38%, Si: 0.22%, Mn: 0.45%, Al: 0.88%, Cr: 1.55%, Mo: 0.22%, P: 0.012%, S: 0.010%, Cu: 0.030%, Ni: 0.021%, with the remainder being Fe and unavoidable impurities; the wire rod specification is Ф8.0mm; the controlled cooling rolling process is as follows: heating of 150 cubic meter continuous casting billet → high-pressure water descaling → roughing rolling → intermediate rolling → pre-finishing rolling → water cooling → finish rolling → water cooling → sizing rolling → wire drawing → Steyrmo slow cooling → coiling → heat preservation corridor heat preservation slow cooling. The process includes the following steps:

[0032] (1) All insulation covers of the Steyrmo roller conveyor are closed. The gaps between the insulation covers are sealed with insulation cotton cloth after the insulation covers are closed to ensure the insulation effect. The speed of the Steyrmo roller conveyor is controlled at 0.08-0.12m / s, the temperature of the Steyrmo roller conveyor entering the cover is controlled at 710-750℃, the temperature of the Steyrmo roller conveyor exiting the cover is controlled at 665-700℃, and the winding temperature is controlled at 635-650℃, thereby controlling the cooling rate of the Steyrmo roller conveyor wire rod at 0.10-0.18℃ / s.

[0033] (2) An asbestos insulation chamber is added between the coil drum and the insulation corridor to control the temperature of the coil entering the insulation corridor to 612-628℃, thereby controlling the coil cooling rate to 0.35-0.48℃ / s;

[0034] (3) Add heating devices to the head, middle and tail sections of the insulated corridor to control the ambient temperature inside the insulated corridor to 55℃, the insulation time of the insulated corridor to 2.5h, and control the temperature outside the insulated corridor to 570-605℃, thereby controlling the cooling rate of the wire rod to 0.12-0.18℃ / s.

[0035] The metallographic structure of small-diameter 38CrMoAl wire produced according to the above control methods is as follows: Figure 2 As shown, the metallographic structure is ferrite + pearlite.

[0036] Comparative Example 1:

[0037] A controlled cooling method for small-diameter 38CrMoAl wire rod without annealing. The chemical composition of the steel by weight percentage is: C: 0.38%, Si: 0.22%, Mn: 0.45%, Al: 0.88%, Cr: 1.55%, Mo: 0.22%, P: 0.012%, S: 0.010%, Cu: 0.030%, Ni: 0.021%, with the remainder being Fe and unavoidable impurities; the wire rod specification is Ф8.0mm; the controlled cooling rolling process is as follows: heating of 150 cubic meter continuous casting billet → high-pressure water descaling → roughing rolling → intermediate rolling → pre-finishing rolling → water cooling → finish rolling → water cooling → sizing rolling → wire drawing → Steyrmo slow cooling → coiling → heat preservation corridor heat preservation slow cooling. The process includes the following steps:

[0038] (1) All insulation covers of the Steyrmo roller conveyor are closed. The gaps between the insulation covers are sealed with insulation cotton cloth after the insulation covers are closed to ensure the insulation effect. The speed of the Steyrmo roller conveyor is controlled at 0.08-0.12m / s, the temperature of the Steyrmo roller conveyor entering the cover is controlled at 710-750℃, the temperature of the Steyrmo roller conveyor exiting the cover is controlled at 665-700℃, and the winding temperature is controlled at 635-650℃, thereby controlling the cooling rate of the Steyrmo roller conveyor wire rod at 0.10-0.18℃ / s.

[0039] (2) The asbestos insulation chamber between the coil drum and the insulation corridor was not closed, and the temperature inside the insulation corridor was 570-602℃, thereby controlling the coil cooling rate to 1.80-2.05℃ / s;

[0040] (3) The heating devices at the beginning, middle and end of the insulated corridor are not put into operation. The ambient temperature inside the insulated corridor is 30℃. The insulation time of the insulated corridor is 2.5h. The temperature of the insulated corridor is controlled at 510-565℃, thereby controlling the cooling rate of the wire rod at 0.42-0.56℃ / s.

[0041] The metallographic structure of small-diameter 38CrMoAl wire produced according to the above control methods is as follows: Figure 3 As shown, the metallographic structure consists of ferrite, pearlite, and martensite.

[0042] The above description is merely an embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A controlled cooling method for small-diameter 38CrMoAl wire rod without annealing, with wire rod specifications of Ф5.0-8.0mm, and a rolling controlled cooling process route: heating of 150 cubic meter continuous casting billet → high-pressure water descaling → roughing rolling → intermediate rolling → pre-finishing rolling → water cooling → finish rolling → water cooling → sizing rolling → wire drawing → Stellmore slow cooling → coiling → heat preservation corridor heat preservation slow cooling, characterized in that, The steel's chemical composition by weight percentage is: C: 0.35%–0.42%, Si: 0.20%–0.45%, Mn: 0.30%–0.60%, Al: 0.70%–1.10%, Cr: 1.35%–1.65%, Mo: 0.15%–0.25%, P≤0.020%, S≤0.020%, Cu≤0.20%, Ni≤0.30%, with the remainder being Fe and unavoidable impurities; the coiling temperature is 750–800℃, the Steyrmo roller conveyor inlet temperature is 700–750℃, the Steyrmo roller conveyor outlet temperature is 650–700℃, and the coiling temperature is 630–650℃. An asbestos insulation chamber is installed between the coil drum and the insulation corridor. The temperature inside the insulation corridor is 610-630℃, and the coil cooling rate is 0.35-0.48℃ / s. Heating devices are installed at the beginning, middle, and end of the insulated corridor. The ambient temperature inside the insulated corridor is 50-80℃, the insulation time is 2.5±0.5h, the temperature exiting the insulated corridor is 560-610℃, and the wire rod cooling rate is ≤0.2℃ / s. The Steyrmo roller conveyor speed is 0.07-0.12m / s, and the Steyrmo roller conveyor wire rod cooling rate is ≤0.2℃ / s.

2. The controlled cooling method for small-diameter 38CrMoAl wire rod without annealing as described in claim 1, characterized in that, All insulation covers on the Stellmore roller conveyor are closed, and the gaps between the insulation covers are sealed with insulation cloth after the insulation covers are closed.

3. The controlled cooling method for small-diameter 38CrMoAl wire rod without annealing as described in claim 1, characterized in that, The heating device is a tubular resistance heater used to control the ambient temperature inside the insulated corridor.

4. The controlled cooling method for small-diameter 38CrMoAl wire rod without annealing as described in any one of claims 1-3, characterized in that, The microstructure of the 38CrMoAl wire rod is ferrite + pearlite.

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