Low-temperature rolled high-quality free-cutting steel and production process thereof

Abstract

The invention provides low-temperature rolled high-quality free-cutting steel and a production process thereof. The low-temperature rolled high-quality free-cutting steel comprises the following components: less than or equal to 0.10% of C, less than or equal to 0.006% of Si, 0.90-1.60% of Mn, 0.30-0.90% of P, 0.30-0.50% of S, less than or equal to 0.030% of Al, less than or equal to 0.0060% of N, less than or equal to 0.0140% of O and the balance of Fe and other inevitable impurities. Compared with the prior art, by controlling Mn / S to be 3.5-7.0, when the K value is equal to 2 * (Mn / S) + LF activity oxygen value, and K is larger than or equal to 35 and smaller than or equal to 69, the final sulfide is properly controlled. Low-temperature rolling is adopted, the sulfide hot brittleness interval is avoided, the plasticity of sulfide is relatively poor during rolling in the temperature interval, energy consumption is reduced, and meanwhile the phenomenon that the cutting performance of a finished product becomes poor due to the fact that the sulfide is lengthened in the rolling process is avoided. Finally, the high-quality free-cutting steel production process adopting low-temperature rolling is developed.

Description

Technical Field

[0001] The invention belongs to the field of free-cutting steel production, and in particular relates to low-temperature rolled high-quality free-cutting steel and a production process thereof. Background Art

[0002] With the development of high-speed, precision and automation of mechanical processing, especially the prosperity of the automobile industry, precision instrument industry and household appliance industry, end users have an increasingly strong demand for reducing processing costs by improving the machining performance of steel materials, and high-quality free-cutting steel is in urgent need of development. Free-cutting steel is mainly used to make non-load-bearing parts with low force requirements but strict requirements on size and roughness, such as instruments, watch parts, automobiles, machine tools and other various machines; standard parts with strict requirements on dimensional accuracy and roughness, but relatively low requirements on mechanical properties, such as gears, shafts, bolts, valves, bushings, pins, pipe joints, etc.

[0003] MnS is the main plastic inclusion in free-cutting steel. Its size, shape and distribution seriously affect the performance of steel and it is often used to improve the cutting performance of free-cutting steel. There are many related factors of sulfide. First of all, the source of sulfide in steel mainly comes from the original addition, and the influence of sulfur will be eliminated by manganese. Therefore, w(Mn) / w(S) is crucial. At the same time, the most significant factor affecting the morphology of sulfide is oxygen content. When the oxygen activity in steel is high, sulfide is Class I, and as the oxygen activity decreases, sulfide gradually changes from Class I to Class III. Therefore, the key to the morphology of sulfide inside the ingot is to control w(Mn) / w(S) and oxygen content. In addition to these factors, the most common method of rolling is to use high-temperature heating, with the heating temperature exceeding 1220°C. This heating temperature is to avoid the cracking of the rolling head due to the hot brittleness of the sulfide during the sulfide rolling process, and to control the sulfide morphology and avoid rolling the sulfide in a range with good plasticity, so that the sulfide morphology in the finished product tends to be elongated and the anisotropy increases. For the sulfide morphology of sulfur-containing steel, it is determined that the sulfide aspect ratio is ≤3, which is a spindle-shaped sulfide. The finished product with a high proportion of spindle-shaped sulfides has excellent cutting performance, and the factors affecting the sulfide morphology are more complicated. In addition to the steelmaking process, the selection of the continuous casting process and the formulation of the rolling conditions will affect its final form. However, the high-temperature heating energy loss is large. At the same time, the excessively high rolling heating temperature is not conducive to continuous production scheduling. Therefore, it is necessary to control the entire process of steelmaking and rolling.

[0004] The Chinese patent with publication number CN 112404126 A published on February 26, 2021, discloses a controlled rolling and controlled cooling method for improving the sulfide morphology of free-cutting steel wire rods. It mainly uses low-temperature rolling to heat and roll free-cutting steel, which not only saves energy, but also effectively avoids the problem of steel pile caused by the beginning of the rolling process. However, it is limited to the rolling area and does not involve the control of the sulfide morphology in the ingot. The method is relatively limited and has low applicability.

[0005] The Chinese patent with publication number CN 104451458 A published on March 25, 2015, discloses a free-cutting steel and its production method and application in key manufacturing. It adopts a high-temperature heating method to avoid the hot brittle sensitive temperature range of steel (850-1050°C), thus avoiding the cracking of rolled bit due to hot brittleness. However, the high-temperature heating energy consumption in its production process is large, and it is not conducive to large-scale mixed production. At the same time, long-term firing at too high a temperature reduces the life of the heating furnace.

[0006] How to reduce the occurrence of hot brittleness of steel under the condition of reducing energy consumption during rolling is a difficult problem faced by the entire industry. At the same time, how to control the sulfide morphology in the ingot and rolled product throughout the entire process is crucial to the finished product performance of free-cutting steel. Summary of the invention

[0007] The object of the present invention is to provide a low-temperature rolled high-quality free-cutting steel and a production process thereof, which is controlled from the steelmaking process, by controlling Mn / S: 3.5-7.0 and the active oxygen range of the LF furnace refining process, controlling the sulfide morphology of the ingot, optimizing the design of important parameters related to the rolling process, obtaining a low-temperature rolled high-quality free-cutting steel production process, and realizing energy-saving rolling.

[0008] The specific technical solutions of the present invention are as follows:

[0009] A low temperature rolled high quality free cutting steel comprising the following components in percentage by weight:

[0010] C≤0.09%, Si≤0.006%, Mn: 0.95~1.65%, P: 0.03~0.08%, S: 0.28~0.45%, Al≤0.030%, N≤0.0060%, O≤0.0140%, and the rest are Fe and other inevitable impurities.

[0011] The composition of the low temperature rolled high quality free cutting steel also satisfies Mn / S: 3.5-7.0;

[0012] The structure of this steel is ferrite + pearlite, in which ferrite accounts for 92-96% of the volume. This organizational feature ensures that the hardness of the steel is not too high and is beneficial to cutting. The inclusions in the steel are mainly type A MnS formed by Mn and S. MnS is also the key to the excellent cutting performance of this type of steel. The spindle-shaped sulfides have good cutting properties.

[0013] The present invention provides a production process for low temperature rolling of high quality free-cutting steel, comprising the following process flow:

[0014] Converter smelting - LF furnace refining - continuous casting - low temperature rolling;

[0015] The LF furnace refining controls the active oxygen range to be 30-55ppm;

[0016] Preferably, the active oxygen range is controlled to satisfy K value = 2×(Mn / S) + LF active oxygen value, 35≤K value≤69;

[0017] Mn / S is the ratio of the mass percentage of Mn to the mass percentage of S in the composition of the above-mentioned low-temperature rolled high-quality free-cutting steel;

[0018] The LF active oxygen value is the active oxygen in the LF furnace refining process, in ppm;

[0019] When calculating the above Y value, substitute the value before the above unit into the formula.

[0020] The continuous casting billet has a specification of 160 mm × 160 mm;

[0021] The continuous casting adopts a combined method of end electromagnetic stirring parameters and light pressure reduction for tension straightening, wherein the end electromagnetic stirring parameters are selected as current 360-380A; frequency 3.0-6.0Hz; and the total reduction rate of light pressure reduction is 15-20mm.

[0022] The continuous casting obtains a slab sulfide spindle rate of ≥50%;

[0023] The low temperature rolling, the heating soaking temperature is controlled at 900-950°C, and the heating time is ≥180min;

[0024] The low temperature rolling includes a soaking period of ≥ 80 min;

[0025] The low temperature rolling also includes a starting rolling temperature of 800-850°C and a spinning temperature of 790-830°C.

[0026] After the above-mentioned low-temperature rolling, a Φ5.5-20 mm hot-rolled wire rod is obtained, and the sulfide spindle rate in the finished wire rod accounts for ≥45%.

[0027] In order to obtain a good sulfide inclusion morphology, it is necessary to ensure a suitable [Mn] / [S] ratio and oxygen content. Compared with other elements, the S element in steel tends to form MnS with the Mn element. Therefore, the ratio of Mn and S content in steel is crucial and can affect the precipitation of MnS inclusions. The sulfide spindle rate is closely related to the manganese-sulfur ratio. At the same time, the increase in oxygen content can also make the sulfide present a thick and short spindle shape, which is beneficial to the cutting performance of the steel, but too high an oxygen content will cause defects such as subcutaneous pores to form in the final ingot. The present invention controls the oxygen content by controlling the LF active oxygen method, and the two are synergistic. Based on previous research, under the conditions defined by the present invention, when the manganese / sulfur ratio is in the range of 3.5-7.0 and when 35≤K≤69, the spindle-shaped effect of the finished sulfide is best. Low temperature rolling is adopted to avoid the hot brittle range of sulfides. The plasticity of sulfides is relatively poor during rolling in this temperature range, which reduces energy consumption and avoids the phenomenon that the cutting performance of the finished product is deteriorated due to the elongation of the sulfide rolling process.

[0028] Compared with the prior art, the present invention controls the sulfide morphology of the ingot by controlling Mn / S: 3.5-7.0 and the active oxygen range of the LF furnace refining process, wherein the K value is set to 2×(Mn / S)+LF active oxygen value as the sulfide control factor. When 35≤K≤69, the final sulfide is properly controlled. Low-temperature rolling is adopted to avoid the hot brittle range of sulfides. When rolling in this temperature range, the plasticity of sulfides is relatively poor, which reduces energy consumption and avoids the phenomenon of deterioration of the cutting performance of the finished product caused by the elongation of the sulfide rolling process. Finally, a high-quality free-cutting steel production process using low-temperature rolling is developed. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The morphology of sulfides in the ingot of Example 1;

[0030] Figure 2 This is a photo of the morphology of the finished wire rod sulfide in Example 1. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] The present invention provides a low temperature rolled high quality free-cutting steel, comprising the following components in percentage by mass:

[0033] C≤0.09%, Si≤0.006%, Mn: 0.95~1.65%, P: 0.03~0.08%, S: 0.28~0.45%, Al≤0.030%, N≤0.0060%, O≤0.0140%, and the rest are Fe and other inevitable impurities.

[0034] The composition of the low temperature rolled high quality free cutting steel also satisfies Mn / S: 3.5-7.0;

[0035] The present invention provides a production process for low temperature rolling of high quality free-cutting steel, comprising the following process flow:

[0036] Converter smelting - LF furnace refining - continuous casting - low temperature rolling;

[0037] in:

[0038] The converter smelting is mainly for deoxidation and alloying. The alloy raw materials of the steel of the present invention are mainly lime, wollastonite, aluminum iron, phosphorus iron, low carbon ferromanganese and high sulfur ferrosulfur alloy. The components C, Si, Mn, P and S are basically adjusted in place during the converter steelmaking process, and the LF is fine-tuned. The purpose of this operation is to reduce the refining time and heating steps that may be added due to the adjustment of the LF components, and reduce the risk of increased oxygen content in the steel.

[0039] The LF furnace refining: after the molten steel is seated, the molten steel is stirred by bottom blowing argon, and the argon flow rate is 700-1000NL / min; the temperature is increased according to the inlet temperature, the amount of alloy added and the outlet temperature; the refining slag is low-basicity slag, and the basicity is 2.4-2.8 to ensure the sulfur recovery rate; wherein, the whole process is controlled by the final active oxygen range of 30-55ppm, which indirectly guarantees the oxygen content in the final product. When the oxygen content exceeds, aluminum iron is used to deoxidize the molten steel, and silicon carbide is used to deoxidize the slag surface to ensure the deoxidation balance of the molten steel-slag surface; the added alloy material is ferrosulfur, ferrophosphorus, low-carbon ferromanganese, high-sulfur ferrosulfur alloy, etc., to fine-tune the alloy composition. Preferably, the active oxygen range is controlled to satisfy K value = 2×(Mn / S) + LF active oxygen value, 35≤K value≤69. (The formula mainly highlights the combined effect of two factors. The Mn / S ratio multiplied by 2 is mainly an empirical factor, and the sum of the obtained value and the LF active oxygen shows its combined effect.)

[0040] The continuous casting is to carry out continuous casting of small square billets, adopt induction heating of the tundish, control the temperature of the molten steel in the tundish to be 15-30°C above the liquidus temperature, adopt the combined process of electromagnetic stirring + light pressure reduction to improve the quality of the billet, and solve the central segregation phenomenon that is very easy to occur in this type of steel, and the specification of the continuous casting billet is 160mm×160mm 2. Specifically: the entire continuous casting process uses argon sealing to protect the casting throughout the process, the steelmaking exit temperature is adjusted according to the baking temperature of the tundish, the pouring superheat is controlled at 15-30°C, and the corresponding drawing speed is selected as 1.6-1.8m / min; the crystallizer water flow rate used for primary cooling is 2400-2600L / min; the plug rod curve is strictly controlled, and the secondary cooling adopts the cooling curve corresponding to the drawing speed. The end electromagnetic stirring parameter + light pressure is used for pulling and straightening. Among them, the end electromagnetic stirring parameter uses a current of 360-380A; frequency 3.0-6.0Hz; the total light pressure reduction rate is 20mm, and the first five racks are pressed down, and the reduction amounts are (3-5-5-4-3mm) respectively. The end electromagnetic stirring + light pressure method is used to improve the casting quality of the 160mm×160mm small square billet, and at the same time, the central segregation phenomenon of this type of steel with relatively high sulfur elements is reduced.

[0041] The low-temperature rolling adopts a heating process, and the rolling is carried out through rough rolling, finishing rolling and wire laying, and then cooled through a Stelmor cooling line. Specifically: the heating and soaking temperature is controlled at 900-950℃, and the heating time is ≥180min; the selection of the heating temperature is mainly based on the consideration that after the sulfide is heated at 900-1300℃ for more than two hours, the amount of oversized MnS in the steel is significantly reduced, which is beneficial to the breakage of the sulfide in the subsequent rolling process; the heating temperature within the range of 900-1300℃ is beneficial to the breakage of the sulfide. The innovation of the present invention is low-temperature heating rolling, and the so-called low temperature is to select a lower temperature that meets the sulfide breakage conditions for heating. At the same time, when the heating temperature is 900-950℃, its temperature will be reduced by 80-100℃ after dephosphorization after it is taken out of the furnace, so that its deformation process avoids the 900℃ with higher plasticity of MnS; the air-fuel ratio of the heating furnace should be controlled to 0.4-0.7, the temperature of the first heating stage is 800-850℃, the temperature of the second heating stage is 850-950℃, and the temperature of the soaking stage is 900-950℃; among them, the soaking stage time should be guaranteed to be ≥80min, in addition to ensuring the uniformity of the temperature inside and outside the steel billet. Control, rough rolling temperature 800-850℃, wire laying temperature 790-830℃, Stelmor cooling line insulation cover all open, turn on the first three fans, determine the fan air volume according to the size of the steel type, so that the wire rod is quickly cooled to below 550℃, and the cooling rate is 3-5℃ / s. Obtain a hot-rolled wire rod with a diameter of Φ5.5-20mm.

[0042] Finally, the finished product processing process is carried out: the finished wire rod is sent to the customer, and the customer's processing process is generally: mechanical shelling / shot blasting → initial straightening → one-pass drawing → fine straightening → cutting (sizing) → straightening (polishing) → chamfering → oil soaking → packaging (this processing method is a typical process for producing silver bright rods of this type of steel). Finally, it is sent to downstream customers for cutting processing.

[0043] In the present invention, after the whole process of smelting-LF furnace refining-continuous casting-rolling is controlled, the high-quality sulfur-based free-cutting steel finally obtains a sulfide spindle rate (sulfide aspect ratio ≤ 3) of ≥50% in the ingot. After rolling with a suitable rolling process, the sulfide spindle rate in the finished wire rod is ≥45%, and the finished wire rod has excellent cutting performance.

[0044] The following are several specific embodiments of the present invention:

[0045] Example 1-Example 5

[0046] A low temperature rolled high quality free cutting steel comprises the following components in mass percentage: as shown in Table 1, the remainder not shown in Table 1 is Fe and unavoidable impurities.

[0047] Comparative Example 1-Comparative Example 6

[0048] A free-cutting steel comprises the following components in mass percentage: as shown in Table 1, the remainder not shown in Table 1 is Fe and inevitable impurities.

[0049] Table 1 Alloy composition of each embodiment and comparative example (unit: O, N in ppm, others in wt%)

[0050]

[0051]

[0052] The free-cutting steel production process of the above embodiments and comparative examples includes the following process flow:

[0053] Converter smelting - LF furnace refining - continuous casting - low temperature rolling;

[0054] in:

[0055] The converter smelting is mainly carried out for deoxidation and alloying. The alloy raw materials of the steel of the present invention are mainly lime, wollastonite, aluminum iron, ferrophosphorus, low-carbon ferromanganese and high-sulfur ferrosulfur alloy. The components C, Si, Mn, P and S are basically adjusted in place during the converter steelmaking process, and LF is fine-tuned.

[0056] The LF furnace refining: after the molten steel is seated, the molten steel is stirred by bottom blowing argon, and the argon flow rate is 700-1000NL / min; the temperature is increased according to the inlet temperature, the amount of alloy added and the outlet temperature; the refining slag is low-basicity slag, and the basicity is 2.4-2.8 to ensure the sulfur recovery rate; wherein, the whole process is controlled by the final active oxygen range of 30-55ppm, which indirectly guarantees the oxygen content in the final product. When the oxygen content exceeds, aluminum iron is used to deoxidize the molten steel, and silicon carbide is used to deoxidize the slag surface to ensure the deoxidation balance of the molten steel-slag surface; the added alloy material is ferrosulfur, ferrophosphorus, low-carbon ferromanganese, high-sulfur ferrosulfur alloy, etc., to fine-tune the alloy composition. Preferably, the active oxygen range is controlled to satisfy K value = 2×(Mn / S) + LF active oxygen value, 35≤K value≤69.

[0057] The continuous casting is to carry out continuous casting of small square billets, adopt induction heating of the tundish, control the temperature of the molten steel in the tundish to be 15-30°C above the liquidus temperature, adopt the combined process of electromagnetic stirring + light pressure reduction to improve the quality of the billet, and solve the central segregation phenomenon that is very easy to occur in this type of steel, and the specification of the continuous casting billet is 160mm×160mm 2 . Specifically: the entire continuous casting process uses argon sealing to protect the casting throughout the process, the steelmaking exit temperature is adjusted according to the baking temperature of the tundish, the pouring superheat is controlled at 15-30°C, and the corresponding drawing speed is selected as 1.6-1.8m / min; the crystallizer water flow rate used for primary cooling is 2400L / min; the plug rod curve is strictly controlled, and the secondary cooling adopts the cooling curve corresponding to the drawing speed. The end electromagnetic stirring parameter + light pressure is used for pulling and straightening. Among them, the end electromagnetic stirring parameter uses a current of 360A; frequency 3.0Hz; the total light pressure reduction rate is 20mm, and the first five racks are pressed down, and the reduction amounts are (3-5-5-4-3mm) respectively. The end electromagnetic stirring + light pressure method is used to improve the casting quality of the 160mm×160mm small square billet, and at the same time, the central segregation phenomenon of this type of steel with relatively high sulfur elements is reduced.

[0058] The low-temperature rolling adopts a heating process, and the rolling is carried out through rough rolling, finishing rolling and wire laying, and then cooled through the Stelmor cooling line after rolling. Specifically: the heating and soaking temperature is controlled at 900-950℃, and the heating time is ≥180min; the selection of the heating temperature is mainly considered that after the sulfide is heated for more than two hours at 900-1300℃, the amount of oversized MnS in the steel is significantly reduced, which is conducive to the breakage of the sulfide in the subsequent rolling process; at the same time, when the heating temperature is 900-950℃, its temperature will be reduced by 80-100℃ after dephosphorization after it is taken out of the furnace, so that its deformation process avoids the 900℃ with higher plasticity of MnS; the air-fuel ratio of the heating furnace should be controlled at 0.4-0.7, the heating temperature of the first stage is 800-850℃, the heating temperature of the second stage is 850-950℃, and the soaking temperature is 900-950℃; among them, the soaking time should be guaranteed to be ≥80min, in addition to ensuring the uniformity of the temperature inside and outside the steel billet. Control, the rough rolling temperature is 800-850℃, the wire laying temperature is 790-830℃, the Stelmor cooling line insulation cover is all opened, the first three fans are turned on, and the fan air volume is determined according to the size of the steel type, so that the wire rod is quickly cooled to below 550℃. The hot-rolled wire rod with a diameter of Φ5.5-20mm is obtained.

[0059] Finally, the finished product processing process is carried out: the finished wire rod is sent to the customer, and the customer's processing process is generally: mechanical shelling / shot blasting → initial straightening → one-pass drawing → fine straightening → cutting (sizing) → straightening (polishing) → chamfering → oil soaking → packaging. Finally, it is sent to downstream customers for cutting processing.

[0060] The main process parameters of the above embodiments and comparative examples are shown in Table 2.

[0061] Table 2 Main process parameters of each embodiment and comparative example

[0062]

[0063] The length-width ratios of the internal sulfide particle sizes of the ingots produced in the above embodiments and comparative examples are shown in Table 3, and the length-width ratios of the sulfide particle sizes of the finished wire rods are shown in Table 4.

[0064] Sulfide detection sampling was taken from the 1 / 2 radius of the cross section of the ingot. 10×10 specimens were randomly selected from 3 locations for sulfide detection. The sulfide ratio was evaluated according to the microscopic inspection method of the rating chart for the determination of the content of non-metallic inclusions in steel in GB-T 10561-2005. The sulfide ratio is the ratio of the number of characteristic sulfides to the total sulfides. The results are shown in Table 3.

[0065] Table 3 Aspect ratio of sulfide particle size inside the ingot of each embodiment and comparative example (% ratio)

[0066]

[0067]

[0068] According to the microscopic inspection method of the rating chart for the determination of the content of non-metallic inclusions in steel in GB-T 10561-2005, the sulfide ratio is the ratio of the number of characteristic sulfides to the total sulfides.

[0069] Table 4 Length-width ratio of sulfide particles in finished wire rods of various embodiments and comparative examples (% share)

[0070] Serial number Less than or equal to 3 Greater than 3 and less than or equal to 6 Greater than 6 and less than or equal to 9 Greater than 9 Example 1 47.5 33.4 10.3 8.8 Example 2 47.7 36.2 9.5 6.6 Example 3 48.1 33.1 11.2 7.6 Example 4 48.4 33.4 11.6 6.6 Example 5 47.3 37.5 10.2 5 Comparative Example 1 33.7 31.6 19.3 15.4 Comparative Example 2 29.9 34.8 22.5 12.8 Comparative Example 3 27.2 34.6 23.7 14.5 Comparative Example 4 28.4 30.2 23.6 17.8 Comparative Example 5 31.1 29.2 24.1 15.6 Comparative Example 6 30.5 35.8 22.4 11.3

[0071] Among them, the Mn / S ratio of Comparative Example 1 exceeds the range of 3.5-7.0, the LF active oxygen range of Comparative Example 2 exceeds the range of 30-55ppm, the final total oxygen content exceeds 0.0140%, and the K value exceeds the range of 35≤K≤69; resulting in a significant reduction in the proportion of spindle-shaped sulfides in the ingot. Comparative Examples 3 and 4 are mainly due to the soaking temperature and soaking time not meeting the range requirements of the embodiment; Comparative Examples 5 and 6 are mainly due to the initial rolling temperature and the spinning temperature not meeting the range requirements of the embodiment; resulting in a significant reduction in the proportion of spindle-shaped sulfides in the finished wire rod.

[0072] Figure 1 and Figure 2 The morphology of the ingot sulfide and the finished wire rod sulfide of Example 1, wherein: Figure 1 This is a picture of a 160mm×160mm square billet. Figure 2 The following is a photo of the sulfide of the finished wire rod after rolling into a Φ10.0 specification. The sulfide morphology pictures of 20 different areas inside the ingot and the wire rod were randomly selected for photography, and then the sulfide morphology was statistically analyzed using processing software. The statistical results are shown in Tables 3 and 4, respectively. The default is that when the aspect ratio of the sulfide is ≤3, it is a spindle-shaped sulfide, and its finished product has better cutting performance. The shape of the sulfide with a ratio of >9 is closer to a long strip, and its anisotropy is greater, resulting in a greatly increased tendency for lateral cracking.

[0073] The underlined data above do not meet the requirements of the present invention.

[0074] The description of the above embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A low temperature rolled high quality free cutting steel, characterized in that: The low temperature rolled high quality free cutting steel comprises the following components in percentage by weight: C≤0.09%, Si≤0.006%, Mn: 0.95~1.65%, P: 0.03~0.08%, S: 0.28~0.45%, Al≤0.030%, N≤0.0060%, O≤0.0140%, and the rest are Fe and other inevitable impurities.

2. The low temperature rolled high quality free cutting steel according to claim 1, characterized in that: The composition of the low temperature rolled high quality free cutting steel also satisfies Mn / S: 3.5-7.

0.

3. The production process of low temperature rolled high quality free cutting steel according to claim 1 or 2, characterized in that: The production process includes the following process flow: Converter smelting - LF furnace refining - continuous casting - low temperature rolling.

4. The production process according to claim 3, characterized in that: The LF furnace refining controls the active oxygen range to be 30-55 ppm.

5. The production process according to claim 3 or 4, characterized in that: In the LF furnace refining, the active oxygen range is controlled to satisfy K value=2×(Mn / S)+LF active oxygen value, 35≤K value≤69.

6. The production process according to claim 3, characterized in that: The continuous casting adopts a combined method of end electromagnetic stirring parameters and light pressure reduction for tension straightening, wherein the end electromagnetic stirring parameters are selected as current 360-380A; frequency 3.0-6.0Hz; and the total reduction rate of light pressure reduction is 15-20mm.

7. The production process according to claim 3 or 4, characterized in that: The continuous casting obtains a slurry sulfide spindle rate of ≥50%.

8. The production process according to claim 3, characterized in that: In the low temperature rolling, the heating soaking temperature is controlled at 900-950° C., and the soaking period time is ≥80 minutes.

9. The production process according to claim 3 or 8, characterized in that: The low temperature rolling also includes a starting rolling temperature of 800-850°C and a spinning temperature of 790-830°C.

10. The production process according to any one of claims 3 to 9, characterized in that: After low-temperature rolling, the sulfide spindle rate in the finished wire rod is ≥45%.

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