A method for producing atmospheric corrosion resistant hot-rolled spring steel wire rod

Abstract

A production method of hot-rolled spring steel wire rod resistant to atmospheric corrosion, wherein the chemical composition of the steel is C=0.51%-0.59%, Si=1.30%-1.60%, Mn=0.50%-0.80%, P≤0.015%, S≤0.015%, Cr=0.50%-0.80%, N≤0.0060%, O≤0.002%, and the rest is Fe and inevitable impurities; the process steps include heating, rolling, spinning, and cooling. The method of the present invention controls the composition and density of the iron oxide scale on the surface of the wire rod by controlling the spinning temperature and the Stelmor cooling process flow, optimizes the composition ratio of the iron oxide scale on the surface of the spring steel wire rod, improves the density of the surface iron oxide scale, and prevents the surface iron oxide scale from cracking and falling off, thereby improving the atmospheric corrosion resistance of the wire rod surface, reducing the risk of pitting pits in the finished spring, and improving the surface quality and fatigue life of the finished spring.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy and relates to a surface control method for a steel material for hot-rolled oil-quenched cold-rolled springs. Background Art

[0002] Hot-rolled spring steel wire rod is the main material for processing and manufacturing automobile suspension springs. Generally, 10.0-22.0mm wire rod is drawn 1.0-1.5mm, quenched in oil or water medium, tempered, and cold rolled into springs. The finished spring has fatigue life requirements. The surface quality of the spring plays an important role in the fatigue life, so strict requirements are placed on the surface quality of the spring. If the anti-corrosion ability of the iron oxide scale on the surface of the hot-rolled spring steel wire rod is insufficient, the pitting rust pits will have a great impact on the surface quality and fatigue life of the finished spring.

[0003] Therefore, controlling the composition and density of the oxide scale of hot-rolled spring steel wire rod can improve the quality of downstream processed spring products and has practical research significance. Summary of the invention

[0004] The purpose of the present invention is to provide a method for producing hot-rolled spring steel wire rod resistant to atmospheric corrosion, which can control the surface of the oxidized iron sheet to be dense without fluffiness and microcracks, prolong the time for the hot-rolled spring steel wire rod to rust, and avoid the appearance of pitting pits on the surface of the finished spring.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A method for producing atmospheric corrosion resistant hot-rolled spring steel wire rod, wherein the chemical composition of the steel is C=0.51%-0.59%, Si=1.30%-1.60%, Mn=0.50%-0.80%, P≤0.015%, S≤0.015%, Cr=0.50%-0.80%, N≤0.0060%, O≤0.002%, and the rest is Fe and unavoidable impurities; comprising the following steps:

[0007] 1) Heating: Using a walking beam heating furnace, the furnace time is 90-150 minutes, and the temperature of the billet out of the furnace is 890-950℃;

[0008] 2) Rolling: Through rough rolling, pre-finishing rolling and finishing rolling mill, the finished wire rod is rolled to the finished wire rod size, and the temperature of the finishing mill is 800-850℃;

[0009] 3) Spinning: Adjust the water volume of the water cooling line after final rolling to 800-1200L / min and the spinning temperature to 800-830℃;

[0010] 4) Cooling: Stelmor cooling is adopted, and the air-cooled roller adopts fast cooling by fan + slow cooling + fast cooling by fan + slow cooling: turn on the cooling fan, the cooling rate in the temperature range of 700-830℃ is 4-6℃ / s, and the delayed cooling method is used to control the cooling rate to 0.5-2.5℃ in the temperature range of 600-700℃, and the hot-rolled structure is controlled to be pearlite and ferrite; turn on the cooling fan in the temperature range of 450-600℃ and control the cooling rate to 4-8℃ / s; the delayed cooling method is used to control the cooling rate to 0.5-2.5℃ in the temperature range of 300-450℃; the spring steel wire rod with hot-rolled structure of pearlite and ferrite, the outer oxide scale is dense Fe3O4, and the inner oxide scale is FeO.

[0011] Principle of the invention:

[0012] In process steps 3) and 4), the water volume of the water cooling line after final rolling is adjusted to ensure that the wire drawing temperature is in the temperature range of 800-830°C, and the cooling rate of different sections of the air-cooled roller is controlled to ensure that the wire rod metallographic structure is pearlite and ferrite, the outer layer of iron oxide is dense Fe3O4, and the inner layer of iron oxide is FeO.

[0013] Optimize the composition of iron oxide scale. The water volume of the water cooling line after final rolling is adjusted in the range of 800-1200L / min, and the wire laying temperature is adjusted in the temperature range of 800-830℃. If the wire laying temperature is too low, red rust Fe2O3 will be produced in the iron oxide scale. If the wire laying temperature is too high, the proportion of FeO layer in the iron oxide scale will increase. The wire laying temperature should be controlled to ensure that FeO / Fe3O4=1 / 1 in the iron oxide scale on the surface of the finished wire rod.

[0014] How to control the density of iron oxide scale. Stelmor air-cooled roller adopts fan rapid cooling + slow cooling + fan rapid cooling + slow cooling, and adopts delayed cooling to reduce the cooling speed of spring steel phase transformation, and controls the hot-rolled structure to pearlite and a small amount of ferrite. After the phase transformation, the cooling speed is increased to reduce the growth stress of iron oxide scale, so that the iron oxide scale structure is fine and the density of iron oxide scale is improved.

[0015] The scale structure of the hot-rolled wire rod is divided into three layers: the inner layer is a loose FeO layer, the middle layer is a black and dense Fe3O4, and the outermost layer is a red Fe2O3. Among the three-layer physical structure of the scale, the FeO layer is easy to pickle, the Fe3O4 layer is dense and has corrosion resistance, and the Fe2O3 layer is a red scale. It is required to avoid the generation of Fe2O3 during production, so the main components of the scale are Fe3O4 and FeO. The dense and relatively large Fe3O4 layer is beneficial to improving the atmospheric corrosion resistance of the wire rod. The scale remaining on the surface of the finished product is generated during the final rolling and Stelmor controlled cooling process. The present invention mainly controls the composition and density of the scale on the surface of the hot-rolled spring steel wire rod by controlling the spinning temperature and the Stelmor controlled cooling process.

[0016] The beneficial effects of the present invention are as follows: the method of the present invention controls the composition and density of the iron oxide scale on the surface of the wire rod by controlling the spinning temperature and the Stelmor cooling process flow, thereby optimizing the composition ratio of the iron oxide scale on the surface of the spring steel wire rod, improving the density of the surface iron oxide scale, and preventing the surface iron oxide scale from cracking and falling off, thereby improving the atmospheric corrosion resistance of the wire rod surface, reducing the risk of pitting pits in the finished spring, and improving the surface quality and fatigue life of the finished spring. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is an electron microscope image of the iron oxide scale on the surface of the wire rod in the original process of Example 1.

[0018] Figure 2 This is an electron microscope image of the iron oxide scale on the surface of the wire rod controlled by the process in Example 1.

[0019] Figure 3 This is an electron microscope image of the iron oxide scale on the surface of the wire rod controlled by the process in Example 2.

[0020] Figure 4 This is an electron microscope image of the iron oxide scale on the surface of the wire rod controlled by the process in Example 3. DETAILED DESCRIPTION

[0021] Example 1

[0022] A method for producing atmospheric corrosion resistant hot-rolled spring steel wire rod, wherein the chemical composition of the steel is C=0.55%, Si=1.48%, Mn=0.70%, P=0.012%, S=0.010%, Cr=0.70%, N=0.0040%, O=0.0012%, and the rest is Fe and unavoidable impurities; the process steps include:

[0023] 1) Heating: The furnace time is 120 minutes, and the billet temperature out of the furnace is 900±5℃;

[0024] 2) Rolling: Rolling to the finished wire rod size through roughing and intermediate rolling, pre-finishing rolling and finishing rolling mill, the temperature of the finishing rolling mill is 820±5℃;

[0025] 3) Spinning: Adjust the water tank flow rate after the RSM unit to 1000L / min to obtain a spinning temperature of 820±5℃;

[0026] 4) The Stelmore air cooling line increases the spacing by adjusting the speed of the rollers, and at the same time blows air upward from the bottom to increase the cooling speed of the wire rods; the Stelmore air cooling line turns off the cooling fan and the insulation cover on the rollers to slow down the cooling speed of the wire rods.

[0027] Table 1 shows the process scheme of the surface scale control technology of the hot-rolled spring steel wire rod in Example 1. The cooling speed of the spring steel wire in the 450-600°C section is adjusted from closed to open by the Stelmor roller cooling fan, and the corresponding insulation cover is adjusted from closed to open, so as to accelerate the cooling speed of the wire rod in this area, and control the cooling speed from the original process 1.2°C / s to 5°C / s; the spinning temperature is controlled to 820±5°C, and the other Stelmor fans and insulation covers are opened unchanged, and the Stelmor roller speed is unchanged, as shown in Table 1. The above test reduces the growth stress of the scale by using a fast cooling speed, thereby improving the density of the scale.

[0028] Table 2 is a comparison table of the structure and compactness of the scale oxide of the control process and the original process in Example 1. The scale oxide structure of the control process does not produce red rust Fe2O3, and FeO / Fe3O4=1 / 1, the total thickness of the scale oxide is controlled at 10.2μm, the composition ratio, thickness and compactness are all in an ideal state, which is convenient for improving the atmospheric corrosion resistance of the hot-rolled wire rod.

[0029] Table 1 Comparison between the new process and the original process in Example 1

[0030] .

[0031] Table 2 Comparison of the structure and density of iron oxide scale produced by the new process and the original process in Example 1

[0032] .

[0033] Example 2

[0034] A method for producing atmospheric corrosion resistant hot-rolled spring steel wire rod, wherein the chemical composition of the steel is C=0.55%, Si=1.48%, Mn=0.70%, P=0.012%, S=0.010%, Cr=0.70%, N=0.0040%, O=0.0012%, and the rest is Fe and unavoidable impurities; the process steps include:

[0035] 1) Heating: The furnace time is 120 minutes, and the billet temperature out of the furnace is 900±5℃;

[0036] 2) Rolling: Rolling to the finished wire rod size through roughing and intermediate rolling, pre-finishing rolling and finishing rolling mill, the temperature of the finishing rolling mill is 820±5℃;

[0037] 3) Spinning: Adjust the water tank flow rate after the RSM unit to 1000L / min to obtain a spinning temperature of 820±5℃;

[0038] 4) The Stelmore air cooling line increases the spacing by adjusting the speed of the rollers, and at the same time blows air upward from the bottom to increase the cooling speed of the wire rods; the Stelmore air cooling line turns off the cooling fan and the insulation cover on the rollers to slow down the cooling speed of the wire rods.

[0039] Table 3 shows the process scheme of the surface scale control technology of the hot-rolled spring steel wire rod in Example 2. The cooling speed of the spring steel wire in the 450-600°C section is adjusted from closed to open by the Stelmor roller cooling fan, and the corresponding insulation cover is adjusted from closed to open, so as to accelerate the cooling speed of the wire rod in this area, and control the cooling speed from the original process 1.2°C / s to 7°C / s; the spinning temperature is controlled to 820±5°C, and the other Stelmor fans and insulation covers are opened unchanged, and the Stelmor roller speed is unchanged, as shown in Table 3. The above test reduces the growth stress of the scale by using a fast cooling speed, thereby improving the density of the scale.

[0040] Table 4 is a comparison table of the structure and compactness of the scale oxide of the control process and the original process in Example 2. No red rust Fe2O3 is produced in the scale oxide structure of the control process, and FeO / Fe3O4=1 / 1, the total thickness of the scale oxide is controlled at 10.6μm, the composition ratio, thickness and compactness are all in an ideal state, which is convenient for improving the atmospheric corrosion resistance of the hot-rolled wire rod.

[0041] Table 3 Comparison of the new process and the original process in Example 2

[0042] .

[0043] Table 4 Comparison of the structure and density of iron oxide scale produced by the new process and the original process in Example 2

[0044] .

[0045] Comparative Example 3

[0046] A method for producing atmospheric corrosion resistant hot-rolled spring steel wire rod, wherein the chemical composition of the steel is C=0.55%, Si=1.48%, Mn=0.70%, P=0.012%, S=0.010%, Cr=0.70%, N=0.0040%, O=0.0012%, and the rest is Fe and unavoidable impurities; the process steps include:

[0047] 1) Heating: The furnace time is 120 minutes, and the billet temperature out of the furnace is 900±5℃;

[0048] 2) Rolling: Rolling to the finished wire rod size through roughing and intermediate rolling, pre-finishing rolling and finishing rolling mill, the temperature of the finishing rolling mill is 820±5℃;

[0049] 3) Spinning: Adjust the water tank flow rate after the RSM unit to 1000L / min to obtain a spinning temperature of 820±5℃;

[0050] 4) The Stelmore air cooling line increases the spacing by adjusting the speed of the rollers, and at the same time blows air upward from the bottom to increase the cooling speed of the wire rods; the Stelmore air cooling line turns off the cooling fan and the insulation cover on the rollers to slow down the cooling speed of the wire rods.

[0051] Table 5 shows the process scheme of the surface scale control technology of the hot-rolled spring steel wire rod in Example 3. The Stelmor roller reduces the cooling speed compared to the original process, and adjusts the roller speed corresponding to the 450-600°C section of the spring steel wire from 0.6m / s to 0.3m / s, increases the accumulation between the wire rods, and controls the cooling speed of the wire rods in this area to 0.6°C / s; the spinning temperature is controlled to be 820±5°C unchanged, the other Stelmor fans and insulation covers are opened unchanged, and the speed of the other sections of the Stelmor rollers is unchanged, see Table 5, the above test increases the growth stress of the scale by reducing the cooling speed, so as to test and observe the scale situation.

[0052] Table 6 is a comparison table of the structure, thickness and compactness of the scale oxide of the control process and the original process in Example 3. The scale oxide structure of the control process has little change, and the thickness has increased slightly. The surface of the scale oxide of the wire rod has more obvious cracks and shedding under the electron microscope, which has damaged the surface atmospheric corrosion resistance of the wire rod. It is not conducive to the anti-corrosion management of the wire rod by downstream customers before the drawing and reform.

[0053] Table 5 Comparison of the new process and the original process in Example 3

[0054] .

[0055] Table 6 Comparison of the structure and density of iron oxide scale produced by the new process and the original process in Example 3

[0056] .

Claims

1. A method for producing atmospheric corrosion resistant hot-rolled spring steel wire rod, characterized in that: The chemical composition of steel is as follows: C = 0.51% ~ 0.59%, Si = 1.30% ~ 1.60%, Mn = 0.50% ~ 0.80%, P ≤ 0.015%, S ≤ 0.015%, Cr = 0.50% ~ 0.80%, N ≤ 0.0060%, O ≤ 0.002%, and the rest is Fe and unavoidable impurities; The process steps include: 1) Heating: Using a walking beam heating furnace, the furnace time is 90-150 minutes, and the temperature of the billet out of the furnace is 890-950℃; 2) Rolling: Through rough rolling, pre-finishing rolling and finishing rolling mill, the finished wire rod is rolled to the finished wire rod size, and the temperature of the finishing mill is 800-850℃; 3) Spinning: Adjust the water volume of the water cooling line after final rolling to 800-1200L / min and the spinning temperature to 800-830℃; 4) Cooling: Stelmor cooling is adopted, and the air-cooled roller adopts fast cooling by fan + slow cooling + fast cooling by fan + slow cooling: turn on the cooling fan, the cooling rate in the temperature range of 700-830℃ is 4-6℃ / s, and the delayed cooling method is used to control the cooling rate to 0.5-2.5℃ / s in the temperature range of 600-700℃, and the hot-rolled structure is controlled to be pearlite and ferrite; turn on the cooling fan in the temperature range of 450-600℃ to control the cooling rate to 4-8℃ / s; the delayed cooling method is used to control the cooling rate to 0.5-2.5℃ / s in the temperature range of 300-450℃; the spring steel wire rod with hot-rolled structure of pearlite and ferrite, the outer oxide scale is dense Fe3O4, and the inner oxide scale is FeO, and the FeO / Fe3O4 in the oxide scale on the surface of the finished wire rod is 1 / 1.

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