An annealing-free high-strength low-carbon boron-containing cold-heading steel and its preparation method

Abstract

The present invention discloses a boron-containing cold-heading steel with high strength and low carbon without annealing and a preparation method thereof. The cold-heading steel has the following chemical components by weight percentage: C 0.12 - 0.16wt%, Si 0.06 - 0.10wt%, Mn 0.50 - 0.80wt%, P ≤ 0.012wt%, S ≤ 0.010wt%, B 0.0020 - 0.0040wt%, Cr 0.12 - 0.18wt%, Ti 0.015 - 0.030wt%, Al 0.060 - 0.080wt%, and the balance is Fe and inevitable impurity elements. The boron-containing cold-heading steel with high strength and low carbon without annealing prepared by the present invention has a tensile strength ≤ 500MPa, an elongation rate ≥ 34.0%, and a reduction of area ≥ 70%, and has excellent cold deformation ability. When using the cold-heading steel with high strength and without annealing of the present invention to process high-strength fasteners, the annealing process is eliminated, the processing cost is greatly reduced, the metal yield is increased, and the pollutant emissions are reduced at the same time, which has great economic and social benefits.

Description

Technical Field

[0001] The present invention belongs to the field of metallurgical technology, and particularly relates to an annealing-free high-strength low-carbon boron-containing cold-heading steel and a preparation method thereof. Background Art

[0002] For the manufacture of high-strength fasteners, annealing treatment is generally required before drawing and cold heading to increase plasticity and improve the deformation ability of wire rods, and to avoid cracking during material processing. However, annealing the material not only increases production costs but also causes environmental pollution. Therefore, the fastener manufacturing industry urgently hopes that steel enterprises can produce annealing-free cold-heading steel that can be directly drawn and cold headed.

[0003] The present invention aims to provide an annealing-free high-strength low-carbon boron-containing cold-heading steel with a nominal diameter of 10-20 mm and a preparation method thereof. Summary of the Invention

[0004] The first object of the present invention is to provide an annealing-free high-strength low-carbon boron-containing cold-heading steel, and the second object of the present invention is to provide a preparation method of the annealing-free high-strength low-carbon boron-containing cold-heading steel.

[0005] The first object of the present invention is achieved as follows. An annealing-free high-strength low-carbon boron-containing cold-heading steel has the following chemical components by weight percentage: C 0.12-0.16 wt%, Si 0.06-0.10 wt%, Mn 0.50-0.80 wt%, P≤0.012 wt%, S≤0.010 wt%, B 0.0020-0.0040 wt%, Cr 0.12-0.18 wt%, Ti 0.015-0.030 wt%, Al 0.060-0.080 wt%, and the balance is Fe and unavoidable impurity elements; the cold-heading steel has the following process mechanical properties: tensile strength is 410-460 MPa, elongation rate ≥34.0%, and reduction of area ≥70.0%.

[0006] The second object of the present invention is achieved as follows. The preparation method of the annealing-free high-strength low-carbon boron-containing cold-heading steel is realized according to the following steps:

[0007] A. Desulfurization of hot metal pretreatment: Transport the blast furnace hot metal to the KR hot metal pretreatment device for desulfurization treatment. The insertion depth of the stirring head is controlled at 4200-4500 mm, and a conventional CaO-based desulfurizer is added in an amount of 5.0-7.0 kg / t 钢 for desulfurization treatment, and the stirring time is controlled for 4 minutes; after the stirring is completed, slag skimming operation is carried out to ensure that the hot metal surface in the ladle is exposed by ≥5 / 6, and the desulfurization slag is completely skimmed to obtain pretreated desulfurized hot metal.

[0008] B. Steelmaking: Add the pretreated desulfurized hot metal and high-quality scrap steel at 900 kg / t respectively钢 , 160 kg / t 钢 The hot metal and scrap steel with a charging ratio of 160 kg / t are charged into the LD converter, and conventional top-bottom combined blowing is carried out. The converter smelting adopts the double slag method. In the early stage of smelting, the first batch of slag materials are added at 13 - 18 kg / t 钢 , 10 - 15 kg / t 钢 respectively for adding lime and lightly burned dolomite to make slag. After the first batch of slag materials finish making slag and the converter is tilted to pour out the slag, the second batch of slag materials are added. The second batch of slag materials are added at 10 - 12 kg / t 钢 , 8 kg / t 钢 respectively for adding lime and lightly burned dolomite to make slag again. Control the C content of the molten steel at the end point ≥ 0.07 wt% and the tapping temperature ≤ 1610 °C; before tapping, add the following slag washing desulfurizer with a mass ratio of 1.0 kg / t 钢 to the bottom of the ladle for slag washing: CaF₂ 6.5 wt%, SiO₂ 5.2 wt%, CaO 62.5 wt%, Na₂O 9.4 wt%, Al 1.9 wt%, P 0.045 wt%, S 0.055 wt%, and the rest are inevitable impurities. The whole process of bottom blowing argon technology is adopted during tapping, and the argon flow rate is controlled at 20 - 30 NL / min.

[0009] C. Deoxidation and alloying: Tap the molten steel. When the amount of molten steel in the ladle is greater than 1 / 4, in the following deoxidation and alloying sequence: ferrosilicon aluminum → low-aluminum calcium silicon barium → high-carbon ferrochrome → medium-carbon ferromanganese, add the following substances to the ladle in turn: add ferrosilicon aluminum alloy with the following mass ratio at 1.8 - 2.4 kg / t 钢 : Al 80.5 wt%, and the rest are Fe and inevitable impurities; add low-aluminum calcium silicon barium with the following mass ratio at 1.3 - 2.2 kg / t 钢 : Si 52.5 wt%, Ba 11.8 wt%, Ca 10.4 wt%, Al 0.8 wt%, and the rest are Fe and inevitable impurities; add high-carbon ferrochrome with the following mass ratio at 1.6 - 2.8 kg / t 钢 : Cr 56.7 wt%, C 7.2 wt%, and the rest are Fe and inevitable impurities; add medium-carbon ferromanganese with the following mass ratio at 5.6 - 9.7 kg / t 钢 : Mn 77.8 wt%, C 1.7 wt%, and the rest are Fe and inevitable impurities; add the above alloys when the amount of molten steel in the ladle reaches 4 / 5; after tapping is completed, lift the molten steel to the LF furnace refining process.

[0010] D. Refining of molten steel in LF furnace: After the tapping in Step C is completed, lift the molten steel to the refining station of the LF furnace, connect the argon gas belt, turn on the argon gas, and blow argon for 2 minutes with an argon gas flow rate of 10 - 15 NL / min. Then, lower the electrodes to slag-making with gears 7 - 9; after energizing for 3 minutes, lift the electrodes to observe the slag-making situation in the furnace, and then measure the temperature and take samples; if the slag condition is relatively thin, add 5.0 - 7.0 kg / t of lime 钢 and 1.0 kg / t of refining slag 钢 Adjust the slag, control the slag basicity to 4.0 - 5.0; according to the analysis results of the steel sample, add alloys and aluminum pellets 0.4 - 0.7 kg / t 钢 Adjust the composition of the molten steel, control the oxygen activity of the molten steel ≤ 5 ppm; then increase the argon gas flow rate to 30 - 40 NL / min, and add ferro-titanium with the following mass ratio at a rate of 0.8 - 1.6 kg / t 钢 : Ti 35.6 wt%, the rest is Fe and inevitable impurities, and soft blow argon for 3 minutes; then add ferro-boron with the following mass ratio at a rate of 0.10 - 0.14 kg / t 钢 : B 30.5 wt%, the rest is Fe and inevitable impurities, and soft blow argon for 2 minutes; then heat the molten steel temperature to 1610 - 1620 °C and then carry out wire feeding treatment. Feed a calcium-iron wire with the following mass ratio: Ca 92.5 wt%, the rest is Fe and inevitable impurities, the wire feeding speed is 2.5 m / s, and the wire feeding amount is 6 - 8 m / t 钢 ; after the wire feeding is completed, carry out soft blowing of the molten steel with a small argon gas flow rate of 20 - 30 NL / min for 12 minutes, and then add a molten steel covering agent with the addition amount controlled at 1.0 kg / t 钢 Finally, lift the molten steel to the casting station

[0011] E. Casting of molten steel: Under the conditions that the molten steel temperature in the tundish is 1545 - 1560 °C, the drawing speed is 1.9 - 2.1 m / min, the water volume in the mold is 155 m 3 / h, the secondary cooling specific water volume is 1.7 - 1.9 L / kg, and the current intensity of the mold electromagnetic stirring is 400 A and the operating frequency is 2.5 Hz, use an R9m straight-arc continuous straightening 7-strand rectangular billet caster to cast the molten steel into small square billets with a cross-section of 165 mm × 165 mm

[0012] F. Heating of steel billets: Send the small square billets into the heating furnace for heating, with the soaking section temperature of 1020 - 1150 °C and the starting rolling temperature of the steel billets of 980 - 1030 °C

[0013] G. Control rolling of billets: After removing the scale on the surface of the billets by a high-pressure water descaling machine, the billets are sent into a fully continuous high-speed wire rod rolling mill for control rolling. The roughing mill group performs 6 passes of rolling, with a rolling speed of 0.18 - 1.10 m / s, a rolling temperature of 960°C - 1030°C, and an elongation of 6.003; the intermediate rolling mill group performs 6 passes of rolling, with a rolling speed of 1.50 - 6.20 m / s, a rolling temperature of 900 - 960°C, and an elongation of 5.63. The pre-finishing mill group performs 2 - 6 passes of rolling, with a rolling speed of 7.90 - 22.14 m / s, a rolling temperature of 860°C - 1030°C, and an elongation of 1.59 - 3.57; the finishing mill group and the sizing and reducing mill group perform 6 passes of rolling, with a rolling speed of 12.23 - 63.80 m / s, a rolling temperature of 800°C - 850°C, and an elongation of 2.55 - 2.86, and then they are sent into a laying head to form coils.

[0014] H. Stelmor roller table cooling: The bright coil rods obtained after laying head are sent into a 122-meter Stelmor roller table for delayed cooling. 10 cooling fans are turned off, the Stelmor heat preservation cover is closed, the roller table speed is controlled at 0.30 m / s - 0.52 m / s, the laying head temperature of the coil rods is controlled at 780°C - 820°C, and the coiling temperature is controlled at 360°C - 420°C, and coil rods of Φ10mm - Φ20mm round steel are obtained after coiling.

[0015] I. Cooling on the P-F conveyor line: The round steel coil rods are sent into a 500-meter-long P-F suspension conveyor line for natural cooling, and thus an anneal-free high-strength low-carbon boron-containing cold heading steel is obtained.

[0016] During the smelting process of the anneal-free high-strength low-carbon boron-containing cold heading steel of the present invention, the mass percentages of C and Mn are reduced, the carbon equivalent is decreased, thereby improving the existing form and distribution of S in the steel and enhancing the cold forming performance of the steel. Meanwhile, element B is added, and a very small amount of B can significantly improve the hardenability of the steel; in addition, a certain content of element Ti is added to the steel, making full use of the nitrogen fixation effect of Ti to form stable TiN and reducing the generation of BN, ensuring the effective hardenability of B, and also improving the strength of the steel through the solid solution strengthening of TiC; Al is added to the steel as a deoxidizer and grain refiner to further improve the toughness and plasticity of the steel at low temperatures;

[0017] During the rolling process, through the processing method combining deformation-induced ferrite phase transformation rolling and low-temperature rolling by controlling the rolling temperature, the post-rolling cooling temperature and the cooling speed, the carbide is modified during the deformation process, and finally a structure of ferrite plus pearlite and a small amount of granular carbide is obtained, realizing the online softening of the steel wire rod, enhancing the strength and cold working performance of the steel, and thus obtaining an anneal-free low-carbon boron-containing high-strength cold heading steel, whose strength and cold forming performance are equivalent to those of medium-carbon steel or medium-carbon alloy steel after annealing, the spheroidizing annealing treatment process can be omitted, and it can be used to manufacture 10.9-grade structural fasteners.

[0018] The tensile strength of the non-annealed high-strength low-carbon boron-containing cold-heading steel prepared by the present invention is ≤500 MPa, the reduction of area is ≥70%, and it has excellent cold deformation ability. Using the non-annealed high-strength cold-heading steel of the present invention eliminates the annealing process when processing high-strength fasteners, greatly reduces the processing cost, improves the metal yield, and at the same time reduces pollutant emissions, having significant economic and social benefits. Specific embodiments

[0019] The following further illustrates the present invention in conjunction with embodiments, but does not limit the present invention in any way. Any transformation or replacement based on the teachings of the present invention falls within the protection scope of the present invention.

[0020] A non-annealed high-strength low-carbon boron-containing cold-heading steel of the present invention has the following chemical components by weight percentage: C 0.12 - 0.16 wt%, Si 0.06 - 0.10 wt%, Mn 0.50 - 0.80 wt%, P ≤ 0.012 wt%, S ≤ 0.010 wt%, B 0.0020 - 0.0040 wt%, Cr 0.12 - 0.18 wt%, Ti 0.015 - 0.030 wt%, Al 0.060 - 0.080 wt%, and the rest is Fe and inevitable impurity elements; the cold-heading steel has the following process mechanical properties: the tensile strength is 410 - 460 MPa, the elongation rate is ≥34.0%, and the reduction of area is ≥70.0%.

[0021] The present invention also provides a preparation method of the non-annealed high-strength low-carbon boron-containing cold-heading steel, which is realized according to the following steps:

[0022] A. Desulfurization of hot metal pretreatment: Transport the blast furnace hot metal to the KR hot metal pretreatment device for desulfurization treatment. The insertion depth of the stirring head is controlled at 4200 - 4500 mm, and desulfurization treatment is carried out by adding a conventional CaO-based desulfurizer in an amount of 5.0 - 7.0 kg / t, and the stirring time is controlled for 4 minutes; after the stirring ends, the post-slag skimming operation is carried out to ensure that the hot metal surface in the ladle is exposed by ≥5 / 6, and the desulfurization slag is completely skimmed to obtain the pretreated desulfurized hot metal. 钢 After the stirring ends, the post-slag skimming operation is carried out to ensure that the hot metal surface in the ladle is exposed by ≥5 / 6, and the desulfurization slag is completely skimmed to obtain the pretreated desulfurized hot metal.

[0023] B. Steelmaking: Charge the pretreated desulfurized hot metal and high-quality scrap steel into the LD converter according to the ratio of 900 kg / t 钢 and 160 kg / t 钢 of hot metal and scrap steel respectively, and carry out conventional top-bottom combined blowing. The converter smelting adopts the double slag method. In the early stage of smelting, the first batch of slag materials are respectively 13 - 18 kg / t 钢 and 10 - 15 kg / t 钢Add lime and lightly burned dolomite to make slag. After the first batch of slag-making materials finish slag-making and the furnace is tilted and slag is poured out, add the second batch of slag-making materials, and the second batch of slag-making materials is added at 10 - 12 kg / t 钢 、8 kg / t 钢 Add lime and lightly burned dolomite to make slag again, control the C content of the molten steel at the end point ≥ 0.07 wt%, and the tapping temperature ≤ 1610 °C; before tapping, add the following slag-washing desulfurizer with a mass ratio of 1.0 kg / t 钢 to the bottom of the ladle for slag washing: CaF₂ 6.5 wt%, SiO₂ 5.2 wt%, CaO 62.5 wt%, Na₂O 9.4 wt%, Al 1.9 wt%, P 0.045 wt%, S 0.055 wt%, and the rest are inevitable impurities. The whole process of bottom blowing argon technology is adopted during tapping, and the argon flow rate is controlled at 20 - 30 NL / min.

[0024] C. Deoxidation and alloying: Tap the molten steel. When the amount of molten steel in the ladle is greater than 1 / 4, add the following substances to the ladle in the following deoxidation and alloying sequence: ferrosilicon aluminum → low-aluminum calcium-silicon-barium → high-carbon ferrochrome → medium-carbon ferromanganese. Add the following substances according to the amount of 1.8 - 2.4 kg / t 钢 of ferrosilicon aluminum alloy with the following mass ratio: Al 80.5 wt%, and the rest are Fe and inevitable impurities; add the following substances according to the amount of 1.3 - 2.2 kg / t 钢 of low-aluminum calcium-silicon-barium with the following mass ratio: Si 52.5 wt%, Ba 11.8 wt%, Ca 10.4 wt%, Al 0.8 wt%, and the rest are Fe and inevitable impurities; add the following substances according to the amount of 1.6 - 2.8 kg / t 钢 of high-carbon ferrochrome with the following mass ratio: Cr 56.7 wt%, C 7.2 wt%, and the rest are Fe and inevitable impurities; add the following substances according to the amount of 5.6 - 9.7 kg / t 钢 of medium-carbon ferromanganese with the following mass ratio: Mn 77.8 wt%, C 1.7 wt%, and the rest are Fe and inevitable impurities; add the above alloys when the amount of molten steel in the ladle reaches 4 / 5; after tapping is completed, lift the molten steel to the LF furnace refining process.

[0025] D. LF furnace refining of molten steel: After the molten steel in step C is tapped, lift it to the LF furnace refining station, connect the argon belt, start argon blowing with an argon flow rate of 10 - 15 NL / min for 2 minutes, and then lower the electrode to melt the slag with gear 7 - 9; after energizing for 3 minutes, lift the electrode to observe the slag melting situation in the furnace, and then measure the temperature and take samples; if the slag condition is relatively thin, add 5.0 - 7.0 kg / t 钢 of lime and 1.0 kg / t 钢 of refining slag to adjust the slag, and control the slag basicity at 4.0 - 5.0; according to the analysis results of the steel sample, add alloys and aluminum pellets of 0.4 - 0.7 kg / t 钢Adjust the composition of the molten steel and control the oxygen activity of the molten steel ≤ 5 ppm; then increase the argon flow rate to 30 - 40 NL / min, and add ferrotitanium in an amount of 0.8 - 1.6 kg / t 钢 with the following mass ratio: Ti 35.6 wt%, the rest being Fe and inevitable impurities, and soft blow argon for 3 minutes; then add ferroboron in an amount of 0.10 - 0.14 kg / t 钢 with the following mass ratio: B 30.5 wt%, the rest being Fe and inevitable impurities, and soft blow argon for 2 minutes; then heat the molten steel temperature to 1610 - 1620 °C and perform wire feeding treatment. Feed a calcium - iron wire with the following mass ratio: Ca 92.5 wt%, the rest being Fe and inevitable impurities, at a wire feeding speed of 2.5 m / s and a wire feeding amount of 6 - 8 m / t 钢 ; after the wire feeding is completed, perform soft blowing of argon on the molten steel with a small argon flow rate of 20 - 30 NL / min for 12 minutes, then add a molten steel covering agent with an addition amount controlled at 1.0 kg / t 钢 , and finally lift the molten steel to the casting station.

[0026] E. Molten steel casting: Under the conditions that the molten steel temperature in the tundish is 1545 - 1560 °C, the drawing speed is 1.9 - 2.1 m / min, the water volume in the mold is 155 m 3 / h, the secondary cooling specific water volume is 1.7 - 1.9 L / kg, the current intensity of the mold electromagnetic stirring is 400 A, and the operating frequency is 2.5 Hz, use an R9m straight - arc continuous straightening 7 - machine 7 - strand rectangular billet caster to cast the molten steel into small square billets with a cross - section of 165 mm × 165 mm.

[0027] F. Billet heating: Send the small square billets into the heating furnace for heating, with the soaking section temperature of 1020 - 1150 °C and the billet starting rolling temperature of 980 - 1030 °C.

[0028] G. Billet controlled rolling: After removing the scale on the surface of the billets by a high - pressure water descaling machine, send the billets into a fully - continuous high - speed wire rod rolling mill for controlled rolling. The roughing mill group performs 6 passes of rolling, with a rolling speed of 0.18 - 1.10 m / s, a rolling temperature of 960 °C - 1030 °C, and an elongation rate of 6.003; the intermediate rolling mill group performs 6 passes of rolling, with a rolling speed of 1.50 - 6.20 m / s, a rolling temperature of 900 - 960 °C, and an elongation rate of 5.63. The pre - finishing mill group performs 2 - 6 passes of rolling, with a rolling speed of 7.90 - 22.14 m / s, a rolling temperature of 860 °C - 1030 °C, and an elongation rate of 1.59 - 3.57; the finishing mill group and the sizing mill group perform 6 passes of rolling, with a rolling speed of 12.23 - 63.80 m / s, a rolling temperature of 800 °C - 850 °C, and an elongation rate of 2.55 - 2.86, and then send them into a laying - head machine to form coils.

[0029] H. Stelmor conveyor cooling: Feed the as-spun bright coil wire into a 122-meter Stelmor conveyor for delayed cooling. Turn off 10 cooling fans and close the Stelmor heat preservation cover. Control the conveyor speed at 0.30 m / s to 0.52 m / s, the wire laying temperature at 780°C to 820°C, and the coiling temperature at 360°C to 420°C to obtain round steel coil wire with a diameter of Φ10mm to Φ20mm by coiling.

[0030] I. P-F transfer line cooling: Feed the round steel coil wire into a 500-meter-long P-F suspension transfer line for natural cooling to obtain non-annealed high-strength low-carbon boron-containing cold heading steel, and its process mechanical properties are shown in Table 1.

[0031] Table 1 Process mechanical properties of non-annealed high-strength low-carbon boron-containing cold heading steel produced by the present invention

[0032]

[0033] In step A, the blast furnace hot metal composition is: C 4.6 - 5.0wt%, Si 0.20 - 0.40wt%, Mn 0.15 - 0.25wt%, P 0.075 - 0.095wt%, S ≤ 0.040wt%, and the rest is Fe and inevitable impurities.

[0034] In step B, the pre-treated hot metal composition is: C 4.6 - 5.0wt%, Si 0.20 - 0.40wt%, Mn 0.15 - 0.25wt%, P 0.075 - 0.095wt%, S ≤ 0.015wt%, and the rest is Fe and inevitable impurities.

[0035] In step B, the high-quality scrap steel chemical composition is: C 0.12 - 0.20wt%, Si 0.10 - 0.30wt%, Mn 0.40 - 0.65wt%, P 0.015 - 0.035wt%, S 0.011 - 0.035wt%, and the rest is Fe and inevitable impurities.

[0036] In step I, the cooling start temperature is 280°C to 380°C.

[0037] The following further illustrates the present invention through examples.

[0038] Example 1

[0039] A. Hot metal pretreatment desulfurization: The blast furnace hot metal (chemical composition: C 4.6wt%, Si 0.20wt%, Mn 0.15wt%, P 0.075wt%, S 0.025wt%, the rest being Fe and inevitable impurities) is transported to the KR hot metal pretreatment device for desulfurization treatment. The insertion depth of the stirring head is controlled at 4200 mm, and desulfurization treatment is carried out by adding a conventional CaO-based desulfurizer in an amount of 5.0 kg / t. The stirring time is controlled at 4 minutes. After stirring, the post-slag skimming operation is carried out to ensure that the hot metal surface in the ladle is exposed by ≥ 5 / 6, and the desulfurization slag is completely skimmed off. The composition of the hot metal after pretreatment is controlled as follows: C 4.6wt%, Si 0.20wt%, Mn 0.15wt%, P 0.075wt%, S 0.008wt%, the rest being Fe and inevitable impurities. 钢 B. Steelmaking: The pretreated desulfurized hot metal from step A (C 4.6wt%, Si 0.20wt%, Mn 0.15wt%, P 0.075wt%, S 0.008wt%, the rest being Fe and inevitable impurities) and high-quality scrap steel (chemical composition: C 0.12wt%, Si 0.10wt%, Mn 0.40wt%, P 0.015wt%, S 0.011wt%, the rest being Fe and inevitable impurities) are charged into the LD converter in proportions of 900 kg / t

[0040] and 160 kg / t 钢 of hot metal and scrap steel respectively, and conventional top-bottom combined blowing is carried out. The converter smelting adopts the double-slag method. In the early stage of smelting, the first batch of slag materials is added in amounts of 13 kg / t 钢 and 10 kg / t 钢 of lime and calcined dolomite for slag formation. After the first batch of slag materials finish slag formation and the furnace is tilted and slag is poured out, the second batch of slag materials is added. The second batch of slag materials is added in amounts of 10 kg / t 钢 and 8 kg / t 钢 of lime and calcined dolomite for slag formation again. The C content of the molten steel at the end point is controlled at 0.07wt%, and the tapping temperature is 1595°C. Before tapping, the following slag washing desulfurizer with the following mass ratio is added to the bottom of the ladle in an amount of 1.0 kg / t 钢 : CaF2 6.5wt%, SiO2 5.2wt%, CaO 62.5wt%, Na2O 9.4wt%, Al 1.9wt%, P 0.045wt%, S 0.055wt%, the rest being inevitable impurities. The whole process of bottom blowing argon is adopted during tapping, and the argon flow rate is controlled at 20 NL / min. 钢

[0041] C. Deoxidation and alloying: Tapping the molten steel after the smelting in step B. When the amount of molten steel in the ladle is greater than 1 / 4, add the following substances to the ladle in the following deoxidation and alloying sequence: ferrosilicon aluminum → low-aluminum calcium silicate barium → high-carbon ferrochrome → medium-carbon ferromanganese, adding in turn: according to 1.8 kg / t 钢 of ferrosilicon aluminum alloy with the following mass ratio: Al 80.5 wt%, the rest being Fe and inevitable impurities; according to 1.3 kg / t 钢 of low-aluminum calcium silicate barium with the following mass ratio: Si 52.5 wt%, Ba 11.8 wt%, Ca 10.4 wt%, Al 0.8 wt%, the rest being Fe and inevitable impurities; according to 1.6 kg / t 钢 of high-carbon ferrochrome with the following mass ratio: Cr 56.7 wt%, C 7.2 wt%, the rest being Fe and inevitable impurities; according to 5.6 kg / t 钢 of medium-carbon ferromanganese with the following mass ratio: Mn 77.8 wt%, C 1.7 wt%, the rest being Fe and inevitable impurities; add the above alloys when the amount of molten steel in the ladle reaches 4 / 5; after tapping, lift the molten steel to the LF furnace refining process.

[0042] D. LF furnace refining of molten steel: Lift the molten steel after tapping in step C to the LF furnace refining station, connect the argon belt, turn on the argon and blow argon with a small argon flow rate (10 NL / min) for 2 minutes, then lower the electrode and use gear 8 to slag; after energizing for 3 minutes, lift the electrode to observe the slagging situation in the furnace, and then measure the temperature and take samples; if the slag condition is relatively thin, add 5.0 kg / t of lime 钢 and 1.0 kg / t of refining slag 钢 to adjust the slag, and control the slag basicity to 4.0; according to the analysis results of the steel sample, add alloys and 0.4 kg / t of aluminum pellets 钢 to adjust the composition of the molten steel and control the oxygen activity of the molten steel at 2 ppm; then appropriately increase the argon flow rate (30 NL / min), and add the following ferrotitanium with a mass ratio of 0.8 kg / t 钢 : Ti 35.6 wt%, the rest being Fe and inevitable impurities, and soft blow argon for 3 minutes; then add the following ferroboron with a mass ratio of 0.10 kg / t 钢 : B 30.5 wt%, the rest being Fe and inevitable impurities, and soft blow argon for 2 minutes; then heat the molten steel temperature to 1620 °C and perform wire feeding treatment, feeding a calcium-iron wire with the following mass ratio: Ca 92.5 wt%, the rest being Fe and inevitable impurities, the wire feeding speed is 2.5 m / s, and the wire feeding amount is 6 m / t 钢 ; after the wire feeding is completed, use a small argon flow rate of 20 NL / min to soft blow argon for the molten steel, the soft blow time is 12 minutes, and then add a molten steel covering agent, and the addition amount is controlled at 1.0 kg / t钢 , and then lift the molten steel to the casting station.

[0043] E. Molten steel casting: Under the conditions that the molten steel temperature in the tundish is 1560 °C, the drawing speed is 2.1 m / min, the water volume in the mold is 155 m 3 / h, the specific water volume in secondary cooling is 1.9 L / kg, the current intensity of the electromagnetic stirring in the mold is 400 A, and the operating frequency is 2.5 Hz, use an R9m straight-arc continuous straightening 7-strand rectangular billet caster to cast the molten steel in step D into small square billets with a cross-section of 165 mm × 165 mm.

[0044] F. Billet heating: Feed the small square billets with a cross-section of 165 mm × 165 mm in step E into the heating furnace for heating. The soaking section temperature is 1035 °C, and the starting rolling temperature of the billet is 990 °C.

[0045] G. Controlled rolling of billets: After removing the scale on the surface of the billets in step F through a high-pressure water descaling machine, feed them into the rough rolling mill for 6 passes of rolling. The rolling speed is 0.18 m / s, the rolling temperature is 1000 °C, the elongation is 6.003, 6 passes of rolling in the intermediate rolling mill, the rolling speed is 5.82 m / s, the rolling temperature is 900 °C, the elongation is 5.63, 6 passes of rolling in the pre-finishing mill, the rolling speed is 22.14 m / s, the rolling temperature is 880 °C - 1015 °C, the elongation is 3.57, 6 passes of rolling in the finishing mill and the sizing and reducing mill, the rolling speed is 63.80 m / s, the rolling temperature is 840 °C, the elongation is 2.86, and then feed them into the coiler to form coils.

[0046] H. Cooling on the Stelmor roller table: Feed the Φ10 mm bright round wire rod in step G into the 122-meter Stelmor roller table for delayed cooling. Turn off 10 cooling fans, close the Stelmor heat preservation cover. The speed of the first section of the roller table is 0.40 m / s, the speed of the last section is 0.52 m / s, the wire rod spinning temperature is 812 °C, the coiling temperature is 403 °C, and Φ10 mm round steel wire rods are obtained after coiling.

[0047] I. Cooling on the P-F conveyor line: Feed the round steel wire rods into the 500-meter-long P-F suspension conveyor line for natural cooling. The starting temperature of cooling is 332 °C. After packing and weighing, high-strength low-carbon boron-containing cold heading steel wire rods with excellent cold working performance are obtained. It has the following chemical components by weight percentage: C 0.12 wt%, Si 0.06 wt%, Mn 0.50 wt%, P 0.007 wt%, S 0.006 wt%, B 0.0020 wt%, Cr 0.12 wt%, Ti 0.015 wt%, Al 0.060 wt%, and the rest are Fe and unavoidable impurity elements. Its process mechanical properties are shown in Table 2.

[0048] Table 2 Process Mechanical Properties of Annealing-Free High-Strength Low-Carbon Boron-Containing Cold Heading Steel Produced in Example 1

[0049] Example 2

[0050] A. Hot metal pretreatment desulfurization: The blast furnace hot metal (chemical composition: C 4.8wt%, Si 0.30wt%, Mn 0.20wt%, P 0.080wt%, S 0.032wt%, the rest is Fe and inevitable impurities) is transported to the KR hot metal pretreatment device for desulfurization treatment. The insertion depth of the stirring head is controlled at 4400 mm, and desulfurization treatment is carried out by adding a conventional CaO-based desulfurizer in an amount of 6.0 kg / t. The stirring time is controlled at 4 minutes. After stirring, the post-slag skimming operation is carried out to ensure that the hot metal surface in the ladle is exposed by ≥ 5 / 6, and the desulfurization slag is completely skimmed off. The composition of the hot metal after pretreatment is controlled as follows: C 4.8wt%, Si 0.30wt%, Mn 0.20wt%, P 0.080wt%, S 0.012wt%, the rest is Fe and inevitable impurities. 钢 B. Molten steel smelting: The pretreated desulfurized hot metal from step A (C 4.8wt%, Si 0.30wt%, Mn 0.20wt%, P 0.080wt%, S 0.012wt%, the rest is Fe and inevitable impurities) and high-quality scrap steel (chemical composition: C 0.16wt%, Si 0.20wt%, Mn 0.55wt%, P 0.025wt%, S 0.022wt%, the rest is Fe and inevitable impurities) are charged into the LD converter according to the ratios of 900 kg / t of hot metal and 160 kg / t of scrap steel respectively, and conventional top-bottom combined blowing is carried out. The converter smelting adopts the double slag method. In the early stage of smelting, the first batch of slag materials is added with lime and calcined dolomite for slag formation at 15 kg / t and 13 kg / t respectively. After the first batch of slag materials is used up for slag formation and the converter is tilted and the slag is poured out, the second batch of slag materials is added. The second batch of slag materials is added with lime and calcined dolomite for slag formation again at 12 kg / t and 8 kg / t respectively. The C content of the molten steel at the end point is controlled at 0.08wt%, and the tapping temperature is 1605°C. Before tapping, the following slag washing desulfurizer with the following mass ratio is added to the bottom of the ladle at an amount of 1.0 kg / t for slag washing: CaF2 6.5wt%, SiO2 5.2wt%, CaO 62.5wt%, Na2O 9.4wt%, Al 1.9wt%, P 0.045wt%, S 0.055wt%, the rest is inevitable impurities. The whole process of bottom blowing argon is adopted during tapping, and the argon flow rate is controlled at 25 NL / min.

[0051] B. Molten steel smelting: The pretreated desulfurized hot metal from step A (C 4.8wt%, Si 0.30wt%, Mn 0.20wt%, P 0.080wt%, S 0.012wt%, the rest is Fe and inevitable impurities) and high-quality scrap steel (chemical composition: C 0.16wt%, Si 0.20wt%, Mn 0.55wt%, P 0.025wt%, S 0.022wt%, the rest is Fe and inevitable impurities) are charged into the LD converter according to the ratios of 900 kg / t of hot metal and 160 kg / t of scrap steel respectively, and conventional top-bottom combined blowing is carried out. The converter smelting adopts the double slag method. In the early stage of smelting, the first batch of slag materials is added with lime and calcined dolomite for slag formation at 15 kg / t and 13 kg / t respectively. After the first batch of slag materials is used up for slag formation and the converter is tilted and the slag is poured out, the second batch of slag materials is added. The second batch of slag materials is added with lime and calcined dolomite for slag formation again at 12 kg / t and 8 kg / t respectively. The C content of the molten steel at the end point is controlled at 0.08wt%, and the tapping temperature is 1605°C. Before tapping, the following slag washing desulfurizer with the following mass ratio is added to the bottom of the ladle at an amount of 1.0 kg / t for slag washing: CaF2 6.5wt%, SiO2 5.2wt%, CaO 62.5wt%, Na2O 9.4wt%, Al 1.9wt%, P 0.045wt%, S 0.055wt%, the rest is inevitable impurities. The whole process of bottom blowing argon is adopted during tapping, and the argon flow rate is controlled at 25 NL / min. 钢 、160 kg / t 钢 of hot metal and scrap steel are charged into the LD converter according to the ratios, and conventional top-bottom combined blowing is carried out. The converter smelting adopts the double slag method. In the early stage of smelting, the first batch of slag materials is added with lime and calcined dolomite for slag formation at 15 kg / t 钢 、13 kg / t 钢 respectively. After the first batch of slag materials is used up for slag formation and the converter is tilted and the slag is poured out, the second batch of slag materials is added. The second batch of slag materials is added with lime and calcined dolomite for slag formation again at 12 kg / t 钢 、8 kg / t 钢 respectively. The C content of the molten steel at the end point is controlled at 0.08wt%, and the tapping temperature is 1605°C. Before tapping, the following slag washing desulfurizer with the following mass ratio is added to the bottom of the ladle at an amount of 1.0 kg / t for slag washing: CaF2 6.5wt%, SiO2 5.2wt%, CaO 62.5wt%, Na2O 9.4wt%, Al 1.9wt%, P 0.045wt%, S 0.055wt%, the rest is inevitable impurities. The whole process of bottom blowing argon is adopted during tapping, and the argon flow rate is controlled at 25 NL / min. 钢 respectively. The C content of the molten steel at the end point is controlled at 0.08wt%, and the tapping temperature is 1605°C. Before tapping, the following slag washing desulfurizer with the following mass ratio is added to the bottom of the ladle at an amount of 1.0 kg / t for slag washing: CaF2 6.5wt%, SiO2 5.2wt%, CaO 62.5wt%, Na2O 9.4wt%, Al 1.9wt%, P 0.045wt%, S 0.055wt%, the rest is inevitable impurities. The whole process of bottom blowing argon is adopted during tapping, and the argon flow rate is controlled at 25 NL / min.

[0052] C. Deoxidation alloying: Tapping the molten steel after the smelting in step B. When the amount of molten steel in the ladle is greater than 1 / 4, add the following substances to the ladle in the following deoxidation alloying sequence: ferrosilicon aluminum → low-aluminum calcium silicon barium → high-carbon ferrochrome → medium-carbon ferromanganese. Add the following substances in sequence: add ferrosilicon aluminum alloy with the following mass ratio by the amount of 2.2 kg / t 钢 : Al 80.5 wt%, the rest is Fe and inevitable impurities; add low-aluminum calcium silicon barium with the following mass ratio by the amount of 1.8 kg / t 钢 : Si 52.5 wt%, Ba 11.8 wt%, Ca 10.4 wt%, Al 0.8 wt%, the rest is Fe and inevitable impurities; add high-carbon ferrochrome with the following mass ratio by the amount of 2.2 kg / t 钢 : Cr 56.7 wt%, C 7.2 wt%, the rest is Fe and inevitable impurities; add medium-carbon ferromanganese with the following mass ratio by the amount of 7.5 kg / t 钢 : Mn 77.8 wt%, C 1.7 wt%, the rest is Fe and inevitable impurities; add the above alloys when the amount of molten steel in the ladle reaches 4 / 5. After tapping, lift the molten steel to the LF furnace refining process.

[0053] D. LF furnace refining of molten steel: Lift the molten steel after tapping in step C to the LF furnace refining station, connect the argon belt, turn on the argon and blow argon with a small argon flow rate (15 NL / min) for 2 minutes, then lower the electrode and use gear 7 to melt the slag; after energizing for 3 minutes, lift the electrode to observe the slag melting situation in the furnace, and then measure the temperature and take samples; if the slag condition is relatively thin, add 6.0 kg / t of lime 钢 and 1.0 kg / t of refining slag 钢 to adjust the slag, and control the slag basicity to 5.0; according to the analysis results of the steel sample, add alloys and 0.6 kg / t of aluminum pellets 钢 to adjust the composition of the molten steel and control the oxygen activity of the molten steel at 4 ppm; then appropriately increase the argon flow rate (35 NL / min), and add ferro titanium with the following mass ratio by the amount of 1.2 kg / t 钢 : Ti 35.6 wt%, the rest is Fe and inevitable impurities, and soft blow argon for 3 minutes; then add ferro boron with the following mass ratio by the amount of 0.12 kg / t 钢 : B 30.5 wt%, the rest is Fe and inevitable impurities, and soft blow argon for 2 minutes; then heat the temperature of the molten steel to 1615 °C and then carry out wire feeding treatment, feed calcium ferro wire with the following mass ratio: Ca 92.5 wt%, the rest is Fe and inevitable impurities, the wire feeding speed is 2.5 m / s, and the wire feeding amount is 7 m / t 钢; After the wire feeding is completed, soft argon blowing is carried out on the molten steel with a small argon gas flow rate of 25 NL / min for 12 minutes. Then, a molten steel covering agent is added, and the addition amount is controlled at 1.0 kg / t. 钢 , and then the molten steel is lifted to the casting station.

[0054] E. Molten steel casting: Under the conditions that the molten steel temperature in the tundish is 1553 °C, the casting speed is 2.0 m / min, the water volume in the mold is 155 m 3 / h, the secondary cooling specific water volume is 1.8 L / kg, the current intensity of the mold electromagnetic stirrer is 400 A, and the operating frequency is 2.5 Hz. The molten steel in step D is cast into small square billets with a cross-section of 165 mm × 165 mm by using an R9m straight-arc continuous straightening 7-strand rectangular billet caster.

[0055] F. Billet heating: The small square billets with a cross-section of 165 mm × 165 mm in step E are sent into the heating furnace for heating. The soaking section temperature is 1105 °C, and the starting rolling temperature of the billets is 1016 °C.

[0056] G. Billet controlled rolling: After the billets in step F are descaled on the surface by a high-pressure water descaling machine, they are sent to the rough rolling mill for 6 passes of rolling. The rolling speed is 1.10 m / s, the rolling temperature is 985 °C, and the elongation is 6.003. They are rolled in the medium rolling mill for 6 passes, the rolling speed is 6.20 m / s, the rolling temperature is 935 °C, and the elongation is 5.63. They are rolled in the pre-finishing mill for 4 passes, the rolling speed is 13.48 m / s, the rolling temperature is 863 °C, and the elongation is 2.51. They are rolled in the finishing mill and the sizing and reducing mill for 4 passes, the rolling speed is 21.95 m / s, the rolling temperature is 833 °C, and the elongation is 2.63. Then they are sent to the coiler to form coils.

[0057] H. Stelmor roller table cooling: The Φ16 mm bright round wire rods in step G are sent to a 122-meter Stelmor roller table for delayed cooling. 10 cooling fans are turned off, and the Stelmor heat preservation cover is closed. The speed of the first section of the roller table is 0.30 m / s, and the speed of the last section is 0.48 m / s. The wire rod spinning temperature is 817 °C, and the coiling temperature is 373 °C. Φ16 mm round steel wire rods are obtained after coiling.

[0058] I. Cooling of the P-F conveyor line: The coiled round steel wire rods after controlled cooling in step H are fed into a 500-meter-long P-F hanging conveyor line for natural cooling. The starting temperature of cooling is 326 °C. After packing and weighing, steel wire rods for high-strength fasteners with excellent cold working performance are obtained. They have the following chemical composition by weight percentage: C 0.14 wt%, Si 0.08 wt%, Mn 0.65 wt%, P 0.010 wt%, S 0.008 wt%, B 0.0030 wt%, Cr 0.16 wt%, Ti 0.022 wt%, Al 0.070 wt%, and the rest is Fe and inevitable impurity elements. Their process mechanical properties are shown in Table 3.

[0059] Table 3 Process Mechanical Properties of Annealing-Free High-Strength Low-Carbon Boron-Containing Cold Heading Steel Produced in Example 2

[0060] Example 3

[0061] A. Desulfurization of hot metal pretreatment: The blast furnace hot metal (chemical composition: C 5.0 wt%, Si 0.40 wt%, Mn 0.25 wt%, P 0.095 wt%, S 0.040 wt%, and the rest is Fe and inevitable impurities) is transported to a KR hot metal pretreatment device for desulfurization treatment. The insertion depth of the stirring head is controlled at 4500 mm, and a conventional CaO-based desulfurizing agent is added in an amount of 7.0 kg / t 钢 for desulfurization treatment, and the stirring time is controlled at 4 minutes; after stirring, slag skimming operation is carried out to ensure that the hot metal surface in the ladle is exposed by ≥ 5 / 6, and the desulfurization slag is completely skimmed; the composition of the pretreated hot metal is controlled as: C 5.0 wt%, Si 0.40 wt%, Mn 0.25 wt%, P 0.095 wt%, S 0.015 wt%, and the rest is Fe and inevitable impurities.

[0062] B. Steelmaking: The pretreated desulfurized hot metal (C 5.0 wt%, Si 0.40 wt%, Mn 0.25 wt%, P 0.095 wt%, S 0.015 wt%, and the rest is Fe and inevitable impurities) in step A and high-quality scrap steel (chemical composition: C 0.20 wt%, Si 0.30 wt%, Mn 0.65 wt%, P 0.035 wt%, S 0.035 wt%, and the rest is Fe and inevitable impurities) are respectively charged at 900 kg / t 钢 、160 kg / t 钢The hot metal and scrap steel were charged into an LD converter according to the charging ratio, and conventional top-bottom combined blowing was carried out. The converter smelting adopted the double slag method. In the early stage of smelting, the first batch of slag materials were added with lime and light burned dolomite for slag making at 18 kg / t steel and 15 kg / t steel respectively. After the first batch of slag materials were finished slag making and the converter was tilted to pour out the slag, the second batch of slag materials were added. The second batch of slag materials were added with lime and light burned dolomite for slag making again at 12 kg / t steel and 8 kg / t steel respectively, and the C content of the molten steel at the end point was controlled at 0.09 wt%, and the tapping temperature was 1610 °C; before tapping, the following mass ratio of slag washing desulfurizer was added to the bottom of the ladle at a rate of 1.0 kg / t steel for slag washing: CaF₂ 6.5 wt%, SiO₂ 5.2 wt%, CaO 62.5 wt%, Na₂O 9.4 wt%, Al 1.9 wt%, P 0.045 wt%, S 0.055 wt%, and the rest were inevitable impurities. The whole process of bottom blowing argon technology was adopted during tapping, and the argon flow rate was controlled at 30 NL / min.

[0063] C. Deoxidation and alloying: Tapping the molten steel smelted in step B. When the amount of molten steel in the ladle was greater than 1 / 4, according to the following deoxidation and alloying sequence: ferrosilicon aluminum → low-aluminum calcium-silicon-barium → high-carbon ferrochrome → medium-carbon ferromanganese, the following substances were added to the ladle in turn: according to 2.4 kg / t 钢 amount, add the following mass ratio of ferrosilicon aluminum alloy: Al 80.5 wt%, and the rest are Fe and inevitable impurities; according to 2.2 kg / t 钢 amount, add the following mass ratio of low-aluminum calcium-silicon-barium: Si 52.5 wt%, Ba 11.8 wt%, Ca 10.4 wt%, Al 0.8 wt%, and the rest are Fe and inevitable impurities; according to 2.8 kg / t 钢 amount, add the following mass ratio of high-carbon ferrochrome: Cr 56.7 wt%, C 7.2 wt%, and the rest are Fe and inevitable impurities; according to 9.7 kg / t 钢 amount, add the following mass ratio of medium-carbon ferromanganese: Mn 77.8 wt%, C 1.7 wt%, and the rest are Fe and inevitable impurities; add the above alloys when the amount of molten steel in the ladle reaches 4 / 5; after tapping, lift the molten steel to the LF furnace refining process.

[0064] D. LF furnace refining of molten steel: Lift the molten steel after tapping in step C to the LF furnace refining station, connect the argon belt, turn on the argon and blow argon with a small argon flow rate (15 NL / min) for 2 minutes, then lower the electrode and use gear 9 to melt the slag; after 3 minutes of power on, lift the electrode to observe the slag melting situation in the furnace, and then measure the temperature and take samples; if the slag condition is relatively thin, add 7.0 kg / t of lime 钢 and 1.0 kg / t of refining slag 钢 to adjust the slag, and control the slag basicity at 5.0; according to the analysis results of the steel sample, add alloys and 0.7 kg / t of aluminum pellets 钢Adjust the composition of the molten steel and control the oxygen activity of the molten steel at 5 ppm; then appropriately increase the argon flow rate (40 NL / min), and add ferro-titanium in the amount of 1.6 kg / t 钢 with the following mass ratio: Ti 35.6 wt%, the rest being Fe and inevitable impurities, and soft blow argon for 3 minutes; then add ferro-boron in the amount of 0.14 kg / t 钢 with the following mass ratio: B 30.5 wt%, the rest being Fe and inevitable impurities, and soft blow argon for 2 minutes; then heat the molten steel temperature to 1610 °C and perform wire feeding treatment. Feed a calcium-ferro wire with the following mass ratio: Ca 92.5 wt%, the rest being Fe and inevitable impurities. The wire feeding speed is 2.5 m / s, and the wire feeding amount is 8 m / t 钢 ; after the wire feeding is completed, soft blow argon to the molten steel with a small argon flow rate of 30 NL / min, and the soft blow time is 12 minutes. Then add a molten steel covering agent, and control the addition amount to 1.0 kg / t of steel. Then lift the molten steel to the casting station.

[0065] E. Molten steel casting: Under the conditions that the molten steel temperature in the tundish is 1545 °C, the drawing speed is 1.9 m / min, the water volume in the mold is 155 m 3 / h, the specific water volume in secondary cooling is 1.7 L / kg, the current intensity of the mold electromagnetic stirring is 400 A, and the operating frequency is 2.5 Hz. Use an R9m straight-arc continuous straightening 7-strand rectangular billet caster to cast the molten steel in step D into small square billets with a cross-section of 165 mm × 165 mm.

[0066] F. Billet heating: Feed the small square billets with a cross-section of 165 mm × 165 mm in step E into the heating furnace for heating. The soaking section temperature is 1150 °C, and the billet starting rolling temperature is 1020 °C.

[0067] G. Billet controlled rolling: After removing the scale on the surface of the billet in step F through a high-pressure water descaling machine, feed it into the rough rolling mill for 6 passes of rolling. The rolling speed is 0.98 m / s, the rolling temperature is 1030 °C, the elongation is 6.003. Then perform 6 passes of rolling in the medium rolling mill, the rolling speed is 6.20 m / s, the rolling temperature is 960 °C, the elongation is 5.65. Perform 2 passes of rolling in the pre-finishing mill, the rolling speed is 9.87 m / s, the rolling temperature is 1028 °C, the elongation is 1.59. Perform 4 passes of rolling in the finishing mill and the sizing mill, the rolling speed is 15.59 m / s, the rolling temperature is 847 °C, the elongation is 2.55, and then feed it into the coiler to form coils.

[0068] H, Cooling on the Stelmor conveyor: Feed the Φ20mm bright coil rod in step G into the 122-meter Stelmor conveyor for delayed cooling. Shut down 10 cooling fans and close the Stelmor thermal insulation cover. The speed at the first section of the conveyor is 0.30 m / s, and the speed at the last section is 0.42 m / s. The wire rod spinning temperature is 808 °C, and the coiling temperature is 363 °C. The Φ20mm round steel wire rod is obtained after coiling.

[0069] I, Cooling on the P-F conveyor line: Feed the loose coil round steel wire rod after controlled cooling in step H into the 500-meter-long P-F suspension conveyor line for natural cooling. The starting temperature of cooling is 343 °C. After packing and weighing, a high-strength fastener steel wire rod with excellent cold working performance is obtained. It has the following chemical composition by weight percentage: C 0.16wt%, Si 0.10wt%, Mn 0.80wt%, P 0.012wt%, S 0.010wt%, B 0.0040wt%, Cr 0.18wt%, Ti 0.030wt%, Al 0.080wt%, and the rest is Fe and inevitable impurity elements. Its process mechanical properties are shown in Table 4.

[0070] Table 4 Process Mechanical Properties of the Annealing-Free High-Strength Low-Carbon Boron-Containing Cold Heading Steel Produced in Example 3

[0071]

Claims

1. A preparation method of an annealing-free high-strength low-carbon boron-containing cold-heading steel, the cold-heading steel having the following chemical components by weight percentage: C 0.12 - 0.16wt%, Si 0.06 - 0.10wt%, Mn 0.50 - 0.80wt%, P ≤ 0.012wt%, S ≤ 0.010wt%, B 0.0020 - 0.0040wt%, Cr 0.12 - 0.18wt%, Ti 0.015 - 0.030wt%, Al 0.060 - 0.080wt%, and the rest being Fe and inevitable impurity elements, the cold-heading steel having the following process mechanical properties: tensile strength of 410 - 460MPa, elongation rate ≥ 34.0%, reduction of area ≥ 70.0%; characterized in that, It is implemented according to the following steps: A. Hot metal pretreatment desulfurization: Transport the blast furnace hot metal to the KR hot metal pretreatment device for desulfurization treatment. The insertion depth of the stirring head is controlled at 4200 - 4500 mm. Add conventional CaO-based desulfurizer for desulfurization treatment according to the amount of 5.0 - 7.0 kg / t of steel, and control the stirring time at 4 minutes. After stirring, perform the operation of skimming the post-treatment slag to ensure that the hot metal surface in the ladle is exposed by ≥5 / 6, and skim off all the desulfurization slag to obtain the pretreated desulfurized hot metal; B. Molten steel smelting: Charge the pretreated desulfurized hot metal and high-quality scrap steel into the LD converter according to the ratios of 900 kg / t of steel and 160 kg / t of steel respectively for hot metal and scrap steel, and conduct conventional top-bottom combined blowing. The converter smelting adopts the double-slag method. In the early stage of smelting, add lime and calcined dolomite for slag formation according to 13 - 18 kg / t of steel and 10 - 15 kg / t of steel respectively for the first batch of slag materials. After the first batch of slag materials is finished and the furnace is tilted and the slag is poured out, add the second batch of slag materials. The second batch of slag materials adds lime and calcined dolomite for slag formation again according to 10 - 12 kg / t of steel and 8 kg / t of steel respectively, and control the C content of the molten steel at the end point ≥0.07 wt% and the tapping temperature ≤1610 °C. Before tapping, add the following slag washing desulfurizer to the bottom of the ladle according to the amount of 1.0 kg / t of steel for slag washing: CaF₂ 6.5 wt%, SiO₂ 5.2 wt%, CaO 62.5 wt%, Na₂O 9.4 wt%, Al 1.9 wt%, P 0.045 wt%, S 0.055 wt%, and the rest are inevitable impurities. The whole process of bottom blowing argon process is adopted during tapping, and the argon flow rate is controlled at 20 - 30 NL / min; C. Deoxidation alloying: Tap the molten steel. When the amount of molten steel in the ladle is greater than 1 / 4, add the following substances to the ladle in the following deoxidation alloying sequence: ferrosilicon aluminum → low-aluminum calcium silicon barium → high-carbon ferrochrome → medium-carbon ferromanganese. Add the following ferrosilicon aluminum alloy according to the amount of 1.8 - 2.4 kg / t of steel: Al 80.5 wt%, and the rest are Fe and inevitable impurities; add the following low-aluminum calcium silicon barium according to the amount of 1.3 - 2.2 kg / t of steel: Si 52.5 wt%, Ba 11.8 wt%, Ca 10.4 wt%, Al 0.8 wt%, and the rest are Fe and inevitable impurities; add the following high-carbon ferrochrome according to the amount of 1.6 - 2.8 kg / t of steel: Cr 56.7 wt%, C 7.2 wt%, and the rest are Fe and inevitable impurities; add the following medium-carbon ferromanganese according to the amount of 5.6 - 9.7 kg / t of steel: Mn 77.8 wt%, C 1.7 wt%, and the rest are Fe and inevitable impurities. Add the above alloys when the amount of molten steel in the ladle reaches 4 / 5. After tapping is completed, lift the molten steel to the LF furnace refining process; D. Refining of molten steel in LF furnace: After the tapping of molten steel in step C is completed, lift the molten steel to the refining station of the LF furnace, connect the argon gas belt, turn on the argon gas, and blow argon for 2 minutes with an argon gas flow rate of 10 - 15 NL / min. Then, lower the electrodes to slag-making in gears 7 - 9; after energizing for 3 minutes, lift the electrodes to observe the slag-making situation in the furnace, and then measure the temperature and take samples; if the slag condition is relatively thin, add 5.0 - 7.0 kg / t of steel lime and 1.0 kg / t of steel refining slag to adjust the slag, and control the slag basicity to be 4.0 - 5.0; according to the analysis results of the steel sample, add alloys and 0.4 - 0.7 kg / t of steel aluminum pellets to adjust the composition of the molten steel, and control the oxygen activity of the molten steel ≤ 5 ppm; then increase the argon gas flow rate to 30 - 40 NL / min, and add ferrotitanium with the following mass ratio in an amount of 0.8 - 1.6 kg / t of steel: Ti 35.6 wt%, and the rest is Fe and inevitable impurities, and soft blow argon for 3 minutes; then add ferroboron with the following mass ratio in an amount of 0.10 - 0.14 kg / t of steel: B 30.5 wt%, and the rest is Fe and inevitable impurities, and soft blow argon for 2 minutes; then heat the molten steel temperature to 1610 - 1620 °C and then carry out wire feeding treatment, feed a calcium-ferro wire with the following mass ratio: Ca 92.5 wt%, and the rest is Fe and inevitable impurities, the wire feeding speed is 2.5 m / s, and the wire feeding amount is 6 - 8 m / t of steel; after the wire feeding is completed, carry out soft blow argon on the molten steel with a small argon gas flow rate of 20 - 30 NL / min, and the soft blow time is 12 minutes, then add a molten steel covering agent, and control the addition amount to be 1.0 kg / t of steel, and finally lift the molten steel to the casting station; E. Molten steel casting: Under the conditions that the molten steel temperature in the tundish is 1545 - 1560 °C, the casting speed is 1.9 - 2.1 m / min, the water volume in the mold is 155 m 3 / h, the specific water volume in secondary cooling is 1.7 - 1.9 L / kg, and the current intensity of electromagnetic stirring in the mold is 400 A with an operating frequency of 2.5 Hz, a small square billet with a cross-section of 165 mm × 165 mm is cast from the molten steel by using an R9m straight-arc continuous straightening 7-strand rectangular billet caster; F. Heating of steel billets: Send the small square billets into the heating furnace for heating, the soaking section temperature is 1020 - 1150 °C, and the starting rolling temperature of the steel billets is 980 - 1030 °C; G. Controlled rolling of steel billets: After removing the scale on the surface of the steel billets by a high-pressure water descaling machine, send the steel billets into a fully continuous high-speed wire rod rolling mill for controlled rolling. The roughing mill group has 6 passes of rolling, the rolling speed is 0.18 - 1.10 m / s, the rolling temperature is 960 °C - 1030 °C, and the elongation is 6.003; the intermediate rolling mill group has 6 passes of rolling, the rolling speed is 1.50 - 6.20 m / s, the rolling temperature is 900 - 960 °C, and the elongation is 5.

63. The pre-finishing mill group has 2 - 6 passes of rolling, the rolling speed is 7.90 - 22.14 m / s, the rolling temperature is 860 °C - 1030 °C, and the elongation is 1.59 - 3.57; the finishing mill group and the sizing and reducing mill group have 6 passes of rolling, the rolling speed is 12.23 - 63.80 m / s, the rolling temperature is 800 °C - 850 °C, and the elongation is 2.55 - 2.86, and then send it into the coiler to form coils; H. Cooling on the Stelmor roller table: Send the bright coil rods obtained after coiling into a 122-meter Stelmor roller table for delayed cooling, turn off 10 cooling fans, close the Stelmor insulation cover, control the roller table speed to be 0.30 m / s - 0.52 m / s, control the coiling temperature of the coil rods to be 780 °C - 820 °C, and control the coiling temperature to be 360 °C - 420 °C, and coil to obtain round steel coil rods; I. Cooling of the P-F conveyor line: The round steel wire rod is fed into the 500-meter-long P-F hanging conveyor line for natural cooling, and thus the non-annealed high-strength low-carbon boron-containing cold heading steel is obtained.

2. The preparation method of the non-annealed high-strength low-carbon boron-containing cold heading steel according to claim 1, wherein, In step A, the chemical composition of the blast furnace hot metal is: C 4.6 - 5.0 wt%, Si 0.20 - 0.40 wt%, Mn 0.15 - 0.25 wt%, P 0.075 - 0.095 wt%, S ≤ 0.040 wt%, and the rest is Fe and inevitable impurities.

3. The preparation method of the boron-containing cold heading steel with high strength and low carbon without annealing according to claim 1, characterized in that, In step B, the chemical composition of the pre-treated desulfurized hot metal is: C 4.6 - 5.0 wt%, Si 0.20 - 0.40 wt%, Mn 0.15 - 0.25 wt%, P 0.075 - 0.095 wt%, S ≤ 0.015 wt%, and the rest is Fe and inevitable impurities.

4. The preparation method of the boron-containing cold heading steel with high strength and low carbon without annealing according to claim 1, characterized in that, In step B, the chemical composition of the high-quality scrap steel is: C 0.12 - 0.20 wt%, Si 0.10 - 0.30 wt%, Mn 0.40 - 0.65 wt%, P 0.015 - 0.035 wt%, S 0.011 - 0.035 wt%, and the rest is Fe and inevitable impurities.

5. The preparation method of the non-annealed high-strength low-carbon boron-containing cold-heading steel according to claim 1, characterized in that, In step I, the starting temperature of cooling is 280°C - 380°C.

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