A method for producing a 2100mpa spring steel wire rod

Abstract

The application discloses a production method of 2100Mpa spring steel wire rod, and chemical composition of the steel is as follows: C=0.53% to 0.56%, Si=1.45% to 1.55%, Mn=0.65% to 0.80%, P≤0.012%, S≤0.010%, Cr=0.65% to 0.80%, V=0.10% to 0.20%, Nb=0.02% to 0.05%, and the rest is Fe and inevitable impurity elements; through adding V and Nb micro-alloy strengthening, designing smelting process and continuous casting process, the high-quality continuous casting billet is obtained; through innovative controlled rolling and controlled cooling process and reasonable wire rod packaging protection measures, the 2100Mp spring steel wire rod is finally obtained, the surface quality and internal quality of the 2100Mp spring steel wire rod are excellent, the mechanical properties and fatigue performance indexes of the spring steel wire and spring are good, and the use requirements are met.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of spring steel wire rod production and relates to a production method of 2100Mpa spring steel wire rod. BACKGROUND

[0002] With the rapid development of new energy vehicles, more and more high-strength suspension spring steels are needed. In order to increase the cruising range of the vehicle, the vehicle needs to carry more weight, and the maximum design stress of the spring has reached 1300Mpa. In order to meet the spring stress requirement, the strength of the spring steel wire needs to reach more than 2100Mpa. With the continuous increase of the strength of the spring steel wire, the requirements for the internal quality and surface quality of the steel are also higher and higher, and the segregation level, the size of the inclusions and the number of the inclusions need to be extremely low. In order to meet the quality requirements of the high-stress spring, process and technical innovation needs to be made on the smelting process, continuous casting process and rolling process to produce high-quality spring steel wire rod. SUMMARY

[0003] The application aims to provide a production method of 2100Mpa spring steel wire rod, which meets the performance requirements of 2100Mpa high-stress suspension spring steel wire rod.

[0004] The technical scheme of the application is as follows:

[0005] A production method of 2100Mpa spring steel wire rod, the process flow comprises smelting, continuous casting, blooming, heating of the billet, rolling, roller cooling, hot coiling, slow cooling in the heat preservation corridor, packaging and finished product, and the chemical composition of the steel is characterized by the following weight percentage: C=0.53%~0.56%, Si=1.45%~1.55%, Mn=0.65%~0.80%, P≤0.012%, S≤0.010%, Cr=0.65%~0.80%, V=0.10%~0.20%, Nb=0.02%~0.05%, and the rest is Fe and inevitable impurity elements; and the process steps comprise the following steps:

[0006] 1) smelting: 1~1.5 tons of refining slag is added for slagging according to the weight of the converter tapping of 120 tons, low-alkalinity slag is used for smelting in the whole process of LF refining, 1~1.5 tons of special slag refining slag is added for slagging in the smelting process, the target alkalinity is 0.85~1.0, SiC is added for deoxidation, the target alkalinity of the refining slag is 0.85~1.0, the RH vacuum is maintained for 15~30 minutes, and after the air is broken, it is statically placed for 15~20 minutes, and the soft blowing time is 15~30 minutes; the ladle and the RH furnace are washed with non-Al deoxidation and without Al steel;

[0007] 2) continuous casting: the immersion depth of the nozzle is 100-130 mm, full- range protection casting; the overheat degree of the tundish is 30-45 °C; the steel amount in the ladle is not less than 6 tons; the current of the crystallizer electric stirring is 300 A, the frequency is 2.5 Hz; the current of the terminal electric stirring is 300 A, the frequency is 3 Hz; the constant pulling speed is 0.5 m / min; the specific water quantity of the secondary cooling is 0.18-0.20 L / kg; the reduction amounts of the 2nd, 3rd, 4th, 5th, 6th and 7th stands are 4 mm, 5 mm, 5 mm, 4 mm, 4 mm and 3 mm respectively;

[0008] 3) breakdown: the continuous casting billet is hot sent at 400 °C and above, the total heating time is 400-600 minutes; the cross-sectional size of the steel billet after breakdown is 180 mm x 180 mm;

[0009] 4) heating and rolling: the temperature of the preheating section is 600-800 °C, the heating time is 20-50 minutes; the temperature of the heating section is 900-1000 °C, the heating time is 20-40 minutes; the temperature of the soaking section is 1000-1020 °C, the heating time is 15-30 minutes; the total heating time is 80-120 minutes; the out-furnace temperature is 950-970 °C, the in-reducing-diameter temperature is 850-870 °C, the wire rod temperature is 870-890 °C; the wire rod specification is Φ10-25 mm;

[0010] 5) roller cooling and coiling: the roller is divided into 10 sections, the roller speed of each section is 0.45 m / s, the total length of the roller is 6-7 meters; the cooling speed before entering the heat preservation cover is controlled at 2.8-3.3 °C / s, the out-heat-preservation-cover temperature is 680-720 °C; the vertical coiling core frame is used for coiling;

[0011] 6) slow cooling: after coiling, the wire rod enters the heat preservation corridor for slow cooling, the residence time in the heat preservation corridor is not less than 1 hour, the heat preservation corridor is in full steel state at all times;

[0012] Further, in step 1) smelting: the mass percentage of the main components of the refining slag is CaO = 40%-48%, SiO2 = 45%-55%, Al2O3 = 0-0.5%, Fe2O3 = 0-0.5%, MgO = 0-3%.

[0013] Further, in step 5) roller cooling and coiling: in addition to the first section, each section corresponds to two heat preservation covers and two fans; 8-10 heat preservation covers are opened, 2-8 cooling fans are opened below the roller, the air volume of each fan is 4000-14000 Nm3 / h, the air volume is distributed by the Jialing device, the distribution ratio of the lap joint point / non-lap joint point is 6 / 4. 3

[0014] Further, in step 6) slow cooling: the heat preservation corridor is provided with a movable corridor door, a closed space is formed after the corridor door is closed, the corridor door is controlled by electrical interlocking, the corridor door is opened when the wire rod enters and exits the corridor, and the corridor door is closed immediately after the wire rod enters and exits.​

[0015] The beneficial effects of the present application are: the use of special refining slag improves the level of inclusion control, the automatic scanning detection result of inclusions is that the number is ≤5 / mm 2 , the maximum size is ≤10um; according to the size characteristics of the continuous casting billet, higher superheat casting, blooming hot charging high temperature diffusion are used, the segregation index of the continuous casting billet is 0.96~1.05, the carbon difference of the cross section is ≤0.05%; high temperature wire drawing + hot coiling + corridor slow cooling are used to improve the hot rolling performance, disc shape and iron oxide skin structure, lubricating liquid and lower baling pressure are used, the rod hot rolling strength is 950~1050Mpa, the cross section shrinkage rate is ≥45%, the rod surface damage point is ≤20 / disk; after drawing heat treatment, the tensile strength of the spring steel wire is 2100Mpa or more, the cross section shrinkage rate is 45% or more, and the spring fatigue life is 500000 times or more. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 It is a metallographic structure diagram of the rod of Example 1, and the crystal phase structure is sorbite + pearlite + ferrite.

[0017] Figure 2 It is a low-power and cross-section carbon content distribution diagram of the continuous casting billet of Example 1. DETAILED DESCRIPTION

[0018] The following will be described in combination with examples.

[0019] Example 1:

[0020] A production method of a 2100Mpa suspension spring spring steel rod, the process flow includes: smelting (hot metal pretreatment → converter → refining LF → RH vacuum treatment) → continuous casting (350mm×430mm) → blooming (180mm×180mm) → billet heating → rolling (rough to medium → medium rolling → pre-precision rolling → precision rolling → reducing sizing → water tank cooling → wire drawing) → roller cooling → hot coiling → heat preservation corridor → packaging → finished product. The chemical composition weight percentage is C=0.55%, Si=1.50%, Mn=0.70%, P=0.005%, S=0.006%, Cr=0.70%, V=0.16%, Nb=0.02%, the rest is Fe and inevitable impurity elements; including the following key steps:

[0021] 1) Smelting: 118 tons of converter tapping, 1 ton of special refining slag for slagging after tapping, low basicity slag for the whole process of LF refining, 1 ton of special slag and 260 kg of lime for slagging during smelting, the mass percentage of the main components of the special slag is 45% CaO, 50% SiO2, 0.2% Al2O3, 0.2% Fe2O3, 2% MgO. 200 kg of SiC is added for deoxidation, the refining slag basicity is 0.92. RH vacuum is maintained for 20 minutes, and after breaking the vacuum, it is placed for 15 minutes, and the soft blowing time is 16 minutes. One furnace of low Al steel is used to wash the ladle and RH furnace in advance, and low Al refractory is used.

[0022] 2) Continuous casting: the immersion depth of the lower nozzle is 110 mm, and the whole process is protected casting; the tundish superheat is 34°C; the ladle steel amount is 6 tons; the crystallizer electric stirring current is 300 A, and the frequency is 2.5 Hz; the end electric stirring current is 300 A, and the frequency is 3 Hz; the constant pulling speed is 0.5 m / min; the secondary cooling specific water quantity is 0.18 L / kg; the control is carried out on 2 / 3 / 4 / 5 / 6 / 7 racks to carry out pressing, and the pressing amounts are 4 mm / 5 mm / 5 mm / 4 mm / 4 mm / 3 mm respectively.

[0023] 3) Breakdown: continuous casting billet 480°C hot delivery, furnace time 450-460 minutes; after breakdown, the steel billet cross section size is 180 mm x 180 mm.

[0024] 4) Heating and rolling: preheating temperature 780°C, heating time 40 minutes; heating temperature 950°C, heating time 30 minutes; soaking temperature 1020°C, heating time 17 minutes; total heating time 87 minutes; discharge temperature 970°C, entry reducing temperature 855°C, wire drawing temperature 882°C; wire rod specification Φ25 mm.

[0025] 5) Roller cooling and coiling: the roller speed of each section of the air cooling line is 0.45 m / s, and the total length of the roller is 5.6 meters. The air cooling roller heat preservation cover is opened for 10, and the cooling fan under the roller is opened for 8, each fan air volume is 14000 Nm 3 / h, the air volume is distributed by Jialing device, the distribution ratio of lap joint / non-lap joint is 6 / 4. The cooling speed is controlled at 2.8°C / s, and the temperature out of the heat preservation cover is 720°C; the wire rod is coiled by vertical core frame.

[0026] 6) After coiling, the wire rod is cooled and preserved in the heat preservation corridor, the corridor door is electrically controlled in chain, the wire rod is opened when it enters and exits the corridor, and the wire rod is closed immediately after it enters and exits. The wire rod stays in the heat preservation corridor for 1 hour to ensure that the heat preservation corridor is always full of steel.

[0027] Example 2:

[0028] A kind of spring steel wire rod for 2100Mpa suspension spring and its production method, the process flow includes: smelting (hot metal pretreatment→ converter→ LF furnace refining→ RH vacuum degassing treatment)→ continuous casting (350mm×430mm)→ blooming (180mm×180mm)→ billet heating→ rolling (rough to medium→ medium rolling→ pre-precision rolling→ precision rolling→ reducing sizing→ water tank cooling→ wire drawing)→ roller cooling→ hot coiling→ slow cooling in heat preservation corridor→ packing→ finished product.The chemical composition weight percentage is C=0.54%, Si=1.50%, Mn=0.68%, P=0.08%, S=0.007%, Cr=0.72%, V=0.15%, Nb=0.03%, the rest is Fe and inevitable impurity elements;Including the following key steps:

[0029] 1) smelting: 123 tons of converter tapping, 1.05 tons of special refining slag is added after tapping, low basicity slag is used in the whole process of LF refining, 1.3 tons of special slag is added during smelting, the mass percentage of the main components of the special slag is 43%CaO, 47%SiO2, 0.4%Al2O3, 0.1%Fe2O3, 1%MgO.160 kg of SiC is added for deoxidation, the target basicity of refining slag is 0.91.RH keeps vacuum for 16 minutes, stands for 17 minutes after breaking vacuum, and soft blowing time is 20 minutes.1 furnace of low Al steel is used to wash the ladle and RH furnace in advance, and low Al refractory is used.

[0030] 2) continuous casting: the immersion depth of the lower nozzle is 120mm, and the whole process is protected casting;The tundish overheat degree is 43℃;The large ladle steel quantity is 6 tons;The crystallizer electric stirring current is 300A, and the frequency is 2.5Hz;The end electric stirring current is 300A, and the frequency is 3Hz;The constant pulling speed is 0.5m / min;The secondary cooling specific water quantity is 0.18L / kg;Control 2 / 3 / 4 / 5 / 6 / 7 racks to press down, and the press-down quantities are 4mm / 5mm / 5mm / 4mm / 4mm / 3mm respectively.

[0031] 3) blooming: the continuous casting billet is hot sent at 500~520℃, and the total heating time is 460~470 minutes.The cross-sectional size of the billet after blooming is 180mm×180mm.

[0032] 4) heating and rolling: the preheating section temperature is 720~730℃, the heating time is 47 minutes;The heating section temperature is 980℃, the heating time is 38 minutes;The soaking section temperature is 1019℃, the heating time is 29 minutes;The total heating time is 114 minutes;The discharge temperature is 966℃, the entry reducing sizing temperature is 863℃, and the wire drawing temperature is 886℃;The wire rod specification is Φ14mm.

[0033] 5) roller cooling and coiling: the roller speed of each air cooling line is 0.45m / s, and the total length of the roller is 6 meters.8 air cooling roller covers are opened, and 3 cooling fans under the roller are opened, and the air volume of each fan is 5000Nm3 / h, the air volume is distributed by the air distribution device, and the distribution ratio of the lap joint point / non-lap joint point is 6 / 4. The cooling speed before entering the heat preservation cover is controlled at 3.0 ℃ / s, and the temperature out of the heat preservation cover is 700 ℃; and the rod is collected by using a vertical rod core rack.

[0034] 6) After the collection, the rod is slowly cooled in the heat preservation corridor, the corridor door is controlled by electrical interlocking, the door is opened when the rod enters and exits the corridor, and the door is closed immediately after the rod enters and exits. The rod stays in the heat preservation corridor for not less than 1 hour, so that the heat preservation corridor is always full of steel.

[0035] Example 3

[0036] A kind of 2100Mpa suspension spring spring steel wire rod for spring and its production method, the technological process includes: smelting (hot metal pretreatment→ converter→ LF furnace refining→ RH vacuum degassing treatment)→ continuous casting (350mm×430mm)→ blooming (180mm×180mm)→ billet heating→ rolling (rough to medium→ medium rolling→ pre-precision rolling→ precision rolling→ reducing sizing→ water tank cooling→ wire drawing)→ roller cooling→ hot coiling→ slow cooling in heat preservation corridor→ packing→ finished product. The chemical composition weight percentage content is C=0.54%, Si=1.49%, Mn=0.68%, P=0.009%, S=0.005%, Cr=0.71%, V=0.12%, Nb=0.02%, the rest is Fe and inevitable impurity elements;Including the following key steps:

[0037] 1) smelting: the converter tapping weight is 126 tons, and 1.2 tons of special refining slag is added after tapping for slagging;Low basicity slag is used for smelting during the whole process of LF refining, 1 ton of special slag refining slag is added for slagging, and the basicity is 0.89;The mass percentage content of the main components of the special slag is 42%CaO, 47%SiO2, 0.3%Al2O3, 0.4%Fe2O3 and 1%MgO. Add 170 kg of SiC for deoxidation, and the target basicity of the refining slag is 0.89. RH keeps vacuum for 19 minutes, stands for 18 minutes after breaking the vacuum, and soft blowing time is 23 minutes. The ladle and RH furnace are washed with non-Al deoxidation and without Al steel in advance, and low Al refractory is used.

[0038] 2) continuous casting: the immersion depth of the lower nozzle is 110 mm, and the whole process is protected by casting;The superheat degree of the tundish is 36 ℃;The remaining steel quantity of the ladle is 6 tons;The final terminal electric stirring current is 300 A, and the frequency is 3 Hz;The constant pulling speed is 0.5 m / min;The specific water consumption of the secondary cooling is 0.18~0.20 L / kg;Control 2 / 3 / 4 / 5 / 6 / 7 racks to be pressed, and the pressing amounts are 4 mm / 5 mm / 5 mm / 4 mm / 4 mm / 3 mm respectively.

[0039] 3) Breakdown: the continuous casting billet is heated at 450℃, and the total heating time is 550 minutes. After the breakdown, the cross-sectional size of the billet is 180mm x 180mm.

[0040] 4) Heating and rolling: the preheating temperature is 690~700℃, the heating time is 43 minutes; the heating temperature is 980℃, the heating time is 33 minutes; the soaking temperature is 1010℃, the heating time is 26 minutes; the total heating time is 102 minutes; the discharge temperature is 960℃, the entry temperature of the reducing diameter is 860℃, and the wire rod temperature is 880℃; the wire rod specification is Φ10mm.

[0041] 5) Roller cooling and coiling: the roller speed of each air cooling line is 0.45m / s, and the total roller length is 6 meters. The air cooling roller heat preservation cover is opened for 8, and the cooling fan under the roller is opened for 2, each fan air volume is 4000Nm 3 / h, the air volume is distributed by the Jialing device, and the distribution ratio of the lap joint / non-lap joint is 6 / 4. The cooling speed before entering the heat preservation cover is controlled at 3.3℃ / s, and the temperature out of the heat preservation cover is 683℃; the coiling is carried out by using the vertical coil core frame.

[0042] 6) After the coiling, the wire rod enters the heat preservation corridor for heat preservation and slow cooling. The heat preservation corridor is provided with movable corridor doors, which form a closed space after being closed to ensure the heat preservation effect. The corridor door is electrically connected in a chain control mode, and is opened when the wire rod enters and exits the corridor, and is closed immediately after the wire rod enters and exits. The residence time in the heat preservation corridor is not less than 1 hour to ensure that the heat preservation corridor is always full of steel.

[0043] The performance test results of the continuous casting billet and the wire rod of the above examples are shown in Table 1.

[0044] Table 1 Performance test results of the continuous casting billet and the wire rod of the examples

[0045] .

Claims

1. A method for producing 2100Mpa spring steel wire rod, the process flow comprising smelting → continuous casting → blooming → billet heating → rolling → roller cooling → hot coiling → slow cooling in holding tunnel → packing → finished product, characterized in that: The chemical composition of the steel is C=0.53%~0.56%, Si=1.45%~1.55%, Mn=0.65%~0.80%, P≤0.012%, S≤0.010%, Cr=0.65%~0.80%, V=0.10%~0.20%, Nb=0.02%~0.05%, and the rest is Fe and inevitable impurity elements; the hot rolling strength of the rod is 950~1050Mpa, the reduction of area is ≥45%, and the surface damage of the rod is ≤20 per rod; the tensile strength of the spring wire after drawing and heat treatment is 2100Mpa or above, the reduction of area is 45% or above, and the spring fatigue life is 500,000 times or above; comprising the following process steps: 1) smelting: according to the weight of the converter tapping, 1~1.5 tons of refining slag is added for slagging after the converter tapping; low alkalinity slag is used in the whole process of LF refining, 1~1.5 tons of special slag refining slag is added for slagging during the smelting process, and the target alkalinity is 0.85~1.0; SiC is added for deoxidation, and the target alkalinity of the refining slag is 0.85~1.0; RH vacuum is maintained for 15~30 minutes, and after breaking the vacuum, it is placed for 15~20 minutes, and the soft blowing time is 15~30 minutes; the ladle and RH furnace are washed with non-Al deoxidization and without adding Al steel, and low Al refractory is used; 2) continuous casting: the immersion depth of the nozzle is 100~130mm, and the whole process is protected by casting; the superheat of the tundish is 30~45℃; the remaining steel quantity of the ladle is not less than 6 tons; The crystallizer electric stirring current is 300A, and the frequency is 2.5Hz; the end electric stirring current is 300A, and the frequency is 3Hz; the constant pulling speed is 0.5m / min; the specific water quantity of the secondary cooling is 0.18~0.20L / kg; and the control 2, 3, 4, 5, 6, and 7 frame reduction amounts are 4mm, 5mm, 5mm, 4mm, 4mm, and 3mm respectively; 3) cogging: the continuous casting billet is hot sent at 400℃ or above, and the total heating time is 400~600 minutes; the cross-sectional size of the steel billet after cogging is 180mm×180mm; 4) heating and rolling: the preheating temperature is 600~800℃, the heating time is 20~50 minutes; the heating temperature is 900~1000℃, the heating time is 20~40 minutes; the soaking temperature is 1000~1020℃, and the heating time is 15~30 minutes; the total heating time is 80~120 minutes; the discharge temperature is 950~970℃, the entering reducing temperature is 850~870℃, and the wire drawing temperature is 870~890℃; the rod diameter is Φ10~25mm; 5) Roller cooling and coiling: The roller is divided into 10 sections, the speed of each section is 0.45 m / s, the total length of the roller is 6-7 meters; in addition to the first section, each section corresponds to two heat preservation covers and two fans; 8-10 heat preservation covers are opened, 2-8 cooling fans are opened below the roller, the air volume of each fan is 4000-14000 Nm 3 / h, the air volume is distributed by the Jialing device, the distribution ratio of the lap joint point / non-lap joint point is 6 / 4; the cooling speed before entering the heat preservation cover is controlled at 2.8-3.3 ℃ / s, the temperature out of the heat preservation cover is 680-720 ℃; a vertical coil core frame is used for coiling; 6) slow cooling: after the collection, the rod is kept in the heat preservation corridor for slow cooling, and the residence time in the heat preservation corridor is not less than 1 hour, and the heat preservation corridor is always in full steel state.

2. A process for production of 2100 Mpa spring steel wire rod as claimed in claim 1 wherein Step 1) smelting: the mass percentage of the main components of the refining slag is CaO=40%~48%, SiO2=45%~55%, Al2O3=0~0.5%, Fe2O3=0~0.5%, and MgO=0~3%.

3. A process for producing a 2100 MPa spring steel wire rod as claimed in claim 1, characterized in that: Step 6) slow cooling: the heat preservation corridor is provided with movable corridor doors, and a closed space is formed after the corridor doors are closed; the corridor doors are controlled by electrical interlocking, and are opened when the rod enters or exits the corridor, and are closed immediately after the rod enters or exits.

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