Controlled cooling method for small-specification 38CrMoAl wire annealing-free steel

Abstract

The invention belongs to the technical field of metallurgy, and particularly discloses a controlled cooling method of small-size 38CrMoAl wire annealing-free steel, the specification phi of a wire rod is 5.0-8.0 mm, and the steel comprises the following chemical components in percentage by weight: 0.35-0.42% of C, 0.20-0.45% of Si, 0.30-0.60% of Mn, 0.70-1.10% of Al, 1.35-1.65% of Cr, 0.15-0.25% of Mo, less than or equal to 0.020% of P, less than or equal to 0.020% of S, less than or equal to 0.20% of Cu, less than or equal to 0.30% of Ni and the balance of Fe and inevitable impurities. The spinning temperature is controlled to be 750-800 DEG C, the stelmor roller way cover entering temperature is 700-750 DEG C, the stelmor roller way cover exiting temperature is 650-700 DEG C, the coil collecting temperature is 630-650 DEG C, the temperature of entering a heat preservation vestibule is 610-630 DEG C, and the temperature of exiting the heat preservation vestibule is 560-610 DEG C. The microstructure of the produced small-specification wire rod is ferrite and pearlite, and abnormal structures, such as martensite and bainite, influencing drawing are avoided. By controlling the microstructure of the small-specification wire rod to be ferrite and pearlite, a downstream customer can directly perform drawing without annealing, the annealing process is omitted, and the cost is saved by 300-500 yuan / ton.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy and relates to a controlled cooling method for small-size 38CrMoAl wire annealing-free steel. Technical Background

[0002] 38CrMoAl steel is a high-quality nitrided steel with good mechanical properties. It is often used to manufacture mechanical parts that withstand impact loads and work under reciprocating wear conditions. 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 38CrMoAl wire produced by various steel mills has a small-size Ф5.0-8.0mm wire rod with a microstructure of 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 must be annealed before drawing; the microstructure of medium and large-size wire rods above 8.0mm is ferrite + pearlite, and can be directly drawn without annealing.

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

[0005] In order to solve the above technical problems, the present invention provides a cooling control method for small-size 38CrMoAl wire annealing-free steel, by controlling the spinning temperature, the Stelmor roller inlet hood temperature, the Stelmor roller outlet hood temperature, the coiling temperature, the inlet insulation corridor temperature and the outlet insulation corridor temperature, by controlling the temperature of each key point, thereby controlling the cooling rate of each stage after spinning, controlling the microstructure of the small-size Ф5.0-8.0mm wire rod to be ferrite + pearlite, without abnormal structures such as martensite and bainite that affect drawing, and can be directly drawn without annealing.

[0006] The technical solution of the present invention is:

[0007] A controlled cooling method for small-size 38CrMoAl wire annealing-free steel, with a wire rod specification of Ф5.0-8.0mm, and a rolling controlled cooling process route: 150 square continuous casting billet heating → high-pressure water descaling → rough rolling → intermediate rolling → pre-finishing rolling → water cooling → finishing rolling → water cooling → sizing reduction rolling → spinning → Stelmor slow cooling → coiling → insulation corridor insulation slow cooling, characterized in that the chemical composition of the steel 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%, the rest are Fe and inevitable impurities; spinning temperature 750-800℃, Stelmor roller inlet temperature 700-750℃, Stelmor roller outlet temperature 650-700℃, coiling temperature 630-650℃, inlet insulation corridor temperature 610-630℃, outlet insulation corridor temperature 560-610℃.

[0008] Furthermore, all the insulation covers of the Stelmo 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 Stelmor roller speed is 0.07-0.12 m / s, and the cooling rate of the Stelmor roller wire rod is ≤0.2°C / s.

[0010] Furthermore, an asbestos insulation compartment is arranged between the collecting drum and the insulation corridor, the temperature entering the insulation corridor is 610-630°C, and the cooling rate of the wire rod is ≤0.5°C / s.

[0011] Furthermore, heating devices are installed at the head, middle and tail sections of the insulation corridor, the ambient temperature in the insulation corridor is 50-80°C, the insulation time of the insulation corridor is 2.5±0.5h, the temperature out of the insulation corridor is 560-610°C, and the cooling rate of the wire rod is ≤0.2°C / s.

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

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

[0014] Principle of the invention: Through the FORMASTOR-F fully automatic phase transformation instrument, the critical points of each phase transformation of 38CrMoAl steel are tested, Ar1 is 620°C, Ar3 is 746°C, Ac1 is 769°C, Ac3 is 866°C, Ms is 376°C, and Mf is 150°C; when the cooling rate is less than 0.5°C / s, the room temperature structure is proeutectoid ferrite + pearlite; when the cooling rate is 0.5-2.0°C / s, the room temperature structure is ferrite + pearlite + bainite; when the cooling rate is 2.0-5.0°C / s, the room temperature structure is bainite + martensite; when the cooling rate is greater than 5.0°C / s, the room temperature structure is martensite.

[0015] Therefore, in order to obtain a wire rod with a structure of ferrite + pearlite, the cooling rate in each stage needs to be controlled to be less than 0.5℃ / s.

[0016] Beneficial effects of the present invention:

[0017] 1. The present invention controls the spinning temperature, the Stelmor roller inlet hood temperature, the Stelmor roller outlet hood temperature, the coiling temperature, the inlet temperature of the insulation corridor and the outlet temperature of the insulation corridor, and controls the temperature of each key point, thereby controlling the cooling rate of each stage after spinning, and controlling the microstructure of the small-sized wire rod to be ferrite + pearlite, without abnormal structures such as martensite and bainite that affect drawing.

[0018] 2. By controlling the microstructure of small-size Ф5.0-8.0mm wire rod to ferrite + pearlite, downstream customers can directly draw without annealing, eliminating the annealing process, saving 300-500 yuan / ton, reducing production costs and improving production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 This is the metallographic structure diagram of Example 1;

[0021] Figure 2 This is the metallographic structure diagram of Example 2;

[0022] Figure 3 This is the metallographic structure diagram of comparative example 1. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] Embodiment 1:

[0025] A controlled cooling method for small-size 38CrMoAl wire annealing-free steel, wherein the chemical composition weight percentage of the steel 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%, and the rest is Fe and unavoidable impurities; the wire rod specification is Ф6.5mm; the rolling controlled cooling process route is: 150 square continuous casting billet heating → high-pressure water descaling → rough rolling → intermediate rolling → pre-finishing rolling → water cooling → finishing rolling → water cooling → sizing reduction rolling → wire laying → Stelmor slow cooling → coiling → insulation corridor insulation slow cooling. The following process steps are included:

[0026] (1) All insulation covers of the Stelmor roller 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; the Stelmor roller speed is controlled at 0.07-0.10m / s, the Stelmor roller inlet cover temperature is controlled at 705-740℃, the Stelmor roller outlet cover temperature is controlled at 650-690℃, and the coiling temperature is controlled at 630-650℃, thereby controlling the cooling rate of the Stelmor roller wire rod at 0.15-0.2℃ / s;

[0027] (2) Add an asbestos insulation compartment between the collection drum and the insulation corridor, and control the temperature entering the insulation corridor to 610-630℃, thereby controlling the wire rod cooling rate to 0.4-0.5℃ / s;

[0028] (3) Heating devices are added at the head, middle and tail sections of the insulation corridor to control the ambient temperature in the insulation corridor to 65°C, the insulation time of the insulation corridor to 2.6h, and the temperature of the insulation corridor to 560-600°C, thereby controlling the cooling rate of the wire rod to 0.15-0.2°C / s.

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

[0030] Embodiment 2:

[0031] A controlled cooling method for small-size 38CrMoAl wire annealing-free steel, wherein the chemical composition weight percentage of the steel 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%, and the rest is Fe and inevitable impurities; the wire rod specification is Ф8.0mm; the rolling controlled cooling process route is: 150 square continuous casting billet heating → high-pressure water descaling → rough rolling → intermediate rolling → pre-finishing rolling → water cooling → finishing rolling → water cooling → sizing reduction rolling → wire laying → Stelmor slow cooling → coiling → insulation corridor insulation slow cooling. The following process steps are included:

[0032] (1) All insulation covers of the Stelmor roller 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; the Stelmor roller speed is controlled to 0.08-0.12m / s, the Stelmor roller inlet cover temperature is controlled to 710-750℃, the Stelmor roller outlet cover temperature is controlled to 665-700℃, and the coiling temperature is controlled to 635-650℃, thereby controlling the cooling rate of the Stelmor roller wire rod to 0.10-0.18℃ / s;

[0033] (2) Add an asbestos insulation compartment between the collection drum and the insulation corridor, and control the temperature entering the insulation corridor to 612-628°C, thereby controlling the wire rod cooling rate to 0.35-0.48°C / s;

[0034] (3) Heating devices are added at the head, middle and tail sections of the insulation corridor to control the ambient temperature in the insulation corridor to 55°C, the insulation time of the insulation corridor to 2.5h, and the temperature of the insulation corridor to 570-605°C, thereby controlling the cooling rate of the wire rod to 0.12-0.18°C / s.

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

[0036] Comparative Example 1:

[0037] A controlled cooling method for small-size 38CrMoAl wire annealing-free steel, wherein the chemical composition weight percentage of the steel 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%, and the rest is Fe and inevitable impurities; the wire rod specification is Ф8.0mm; the rolling controlled cooling process route is: 150 square continuous casting billet heating → high-pressure water descaling → rough rolling → intermediate rolling → pre-finishing rolling → water cooling → finishing rolling → water cooling → sizing reduction rolling → wire laying → Stelmor slow cooling → coiling → insulation corridor insulation slow cooling. The following process steps are included:

[0038] (1) All insulation covers of the Stelmor roller 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; the Stelmor roller speed is controlled to 0.08-0.12m / s, the Stelmor roller inlet cover temperature is controlled to 710-750℃, the Stelmor roller outlet cover temperature is controlled to 665-700℃, and the coiling temperature is controlled to 635-650℃, thereby controlling the cooling rate of the Stelmor roller wire rod to 0.10-0.18℃ / s;

[0039] (2) The asbestos insulation compartment between the collection drum and the insulation corridor is not closed, and the temperature entering the insulation corridor is 570-602°C, thereby controlling the wire rod cooling rate to 1.80-2.05°C / s;

[0040] (3) The heating devices at the head, middle and tail sections of the insulation corridor are not put into use, the ambient temperature in the insulation corridor is 30°C, the insulation time of the insulation corridor is 2.5h, and the temperature of the insulation corridor is controlled to be 510-565°C, thereby controlling the cooling rate of the wire rod to be 0.42-0.56°C / s.

[0041] The metallographic structure of small-sized 38CrMoAl wire produced according to the above control method is as follows Figure 3 As shown, the metallographic structure is ferrite + pearlite + martensite.

[0042] The above description is only an embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A controlled cooling method for small-size 38CrMoAl wire annealing-free steel, with wire rod specification Ф5.0-8.0mm, rolling controlled cooling process route: 150 square continuous casting billet heating → high-pressure water descaling → rough rolling → intermediate rolling → pre-finishing rolling → water cooling → finishing rolling → water cooling → sizing reduction rolling → wire laying → Stelmor slow cooling → coiling → insulation corridor insulation slow cooling, characterized in that: The chemical composition of the steel 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%, and the rest is Fe and inevitable impurities; the spinning temperature is 750-800℃, the Stelmor roller inlet temperature is 700-750℃, the Stelmor roller outlet temperature is 650-700℃, the coiling temperature is 630-650℃, the inlet temperature of the insulation corridor is 610-630℃, and the outlet temperature of the insulation corridor is 560-610℃.

2. The controlled cooling method of a small-size 38CrMoAl wire annealing-free steel as claimed in claim 1, characterized in that: All insulation covers of the Stelmo roller conveyor are closed, and the gaps between the insulation covers are sealed with insulation cotton cloth after the insulation covers are closed.

3. The controlled cooling method of a small-size 38CrMoAl wire annealing-free steel as claimed in claim 1, characterized in that: The Stelmor roller speed is 0.07-0.12m / s, and the cooling rate of the Stelmor roller wire rod is ≤0.2℃ / s.

4. The controlled cooling method of a small-size 38CrMoAl wire annealing-free steel as claimed in claim 1, characterized in that: An asbestos insulation compartment is set between the collection drum and the insulation corridor. The temperature entering the insulation corridor is 610-630℃, and the cooling rate of the wire rod is ≤0.5℃ / s.

5. The controlled cooling method of a small-size 38CrMoAl wire annealing-free steel as claimed in claim 1, characterized in that: Heating devices are installed at the head, middle and tail sections of the insulation corridor. The ambient temperature in the insulation corridor is 50-80℃, the insulation time of the insulation corridor is 2.5±0.5h, the temperature out of the insulation corridor is 560-610℃, and the cooling rate of the wire rod is ≤0.2℃ / s.

6. The controlled cooling method of a small-size 38CrMoAl wire annealing-free steel as claimed in claim 5, characterized in that: The heating device is a tubular resistance heater, which is used to control the ambient temperature in the insulation corridor.

7. A controlled cooling method for a small-size 38CrMoAl wire annealing-free steel as claimed in any one of claims 1 to 6, characterized in that: The microstructure of the 38CrMoAl wire rod is ferrite+pearlite.

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