Low-hardness tool steel wire rod and production process thereof

Abstract

The invention provides a low-hardness tool steel wire rod and a production technology thereof. The low-hardness tool steel wire rod is composed of, by mass, 0.56%-0.60% of C, 0.60%-0.90% of Mn, 0.17%-0.37% of Si, 0.70%-0.90% of Cr, 0.09%-0.13% of V, smaller than or equal to 0.025% of P, smaller than or equal to 0.025% of S, smaller than or equal to 0.25% of Ni, smaller than or equal to 0.30% of Cu, smaller than or equal to 0.030% of Al and the balance Fe and inevitable impurities. Small square billets of 160mm * 160mm are adopted for rolling, components are optimized, a reasonable controlled rolling and controlled cooling process is adopted, the phenomenon that a wire rod generates an abnormal structure is avoided, and the structure of the wire rod is pearlite and ferrite; and meanwhile, the low hardness of the wire rod is guaranteed, the hardness of the wire rod is smaller than or equal to 25 HRC, deep processing of the wire rod is facilitated, the requirements of users for hot forging and drawing machining can be met, and wide application prospects are achieved.

Description

Technical Field

[0001] This invention belongs to the field of tool steel wire rod production technology, specifically relating to a low-hardness tool steel wire rod and its production process. Background Technology

[0002] Currently, carbon, CrV, and CrMo tool steels are commonly used to manufacture various hot-forged and precision wire-drawing hand tools. Traditional tool steels often incorporate high levels of Cr, V, and Mo alloys to ensure hardenability. While increasing the alloy content guarantees hardenability, it also leads to higher wire rod hardness, greater stress, and increased susceptibility to deformation during subsequent processing, such as bending after blanking and large dimensional deviations in tools after hot forging.

[0003] The main processing steps for hot forging of tool steel are: wire rod → straightening → blanking → induction heating → hot forging → machining → heat treatment → surface treatment. The main processing steps for wire drawing are: wire rod → spheroidizing annealing → pickling and phosphating → drawing → straightening → blanking → cold heading → finishing → quenching and tempering → shot peening → surface treatment. Furthermore, wire rod has high hardness, resulting in high strength but low plasticity. When manufacturing wire drawing tools, an annealing process is necessary to reduce the hardness and facilitate cold drawing, increasing production costs and hindering market application. Summary of the Invention

[0004] To address the aforementioned issues, this invention provides a low-hardness tool steel wire rod and its manufacturing process. Through optimized composition, smelting, rolling, and other rational designs, the produced wire rod exhibits no abnormal structure and low hardness, meeting the requirements of users for hot forging and drawing processes.

[0005] To achieve the above objectives, the present invention first provides a low-hardness tool steel hot-rolled wire rod, which is composed of the following components by mass percentage:

[0006] C: 0.56-0.60%, Mn: 0.60-0.90%, Si: 0.17-0.37%, Cr: 0.70-0.90%, V: 0.09-0.13%, P: ≤0.025%, S: ≤0.025%, Ni ≤0.25%, Cu ≤0.30%, Al ≤0.030%, with the balance being Fe and unavoidable impurities.

[0007] Further optimizing the range according to the embodiments, the low-hardness tool steel wire rod is composed of the following components by mass percentage: C: 0.58-0.59%, Mn: 0.70-0.85%, Si: 0.22-0.25%, Cr: 0.80-0.85%, V: 0.10-0.12%, P: ≤0.015%, S: ≤0.015%, Ni ≤0.10%, Cu ≤0.10%, Al ≤0.010%, with the balance being Fe and unavoidable impurities.

[0008] This invention also provides a production process for hot-rolled wire rod of low-hardness tool steel, comprising the following main steps:

[0009] BOF converter smelting → LF refining → 160mm*160mm square billet continuous casting → billet heating → controlled rolling and cooling → inspection and packaging. Specific operations are as follows:

[0010] (1) Converter smelting: The C content of the steel is 0.08-0.20%, the P content of the steel is ≤0.020%, and the steel temperature is ≥1600℃; the steel is tapped using a double-plate sliding plate; the converter smelting uses low-titanium molten iron and scrap steel, and it is prohibited to smelt after Ti-containing steel, so as to effectively reduce harmful elements such as P and Ti added to the steel from the source.

[0011] (2) LF Refining: Based on the molten steel smelted in step (1) in the converter, the steel is refined using the Al deoxidation process, maintaining the white slag time at ≥20 min, and using the calcium treatment process to modify the sulfide inclusions. The soft blowing time is controlled at ≥15 min, and argon gas is used for bottom blowing and stirring throughout the process; this promotes the homogenization of temperature and composition, promotes the removal of inclusions by flotation, improves the purity of the molten steel, and obtains refined molten steel.

[0012] (3) Continuous casting: Based on the molten steel refined in step (2), continuous casting is carried out to obtain steel billets; wherein the continuous casting is carried out under full protection, the superheat of the continuous casting furnace is controlled at 20-30℃, the casting speed is 1.7~2.0m / min, and the specific water content is 0.66~0.70L / kg;

[0013] (4) Steel billet heating: Based on the continuous casting process in step (3), the steel billet is heated in a walking beam furnace. In order to promote the diffusion of elements such as C, P, and S, a high-temperature heating and rolling process is adopted. The preheating section temperature is 750-850℃, the heating section temperature is 980-1060℃, the soaking section temperature is 1020-1080℃, the total heating time is 90-150 min, the air-fuel ratio in the furnace is 0.48-0.58, and the water descaling pressure is ≥12MPa.

[0014] (5) Controlled rolling: Based on the steel billet heated in step (4), it is rolled into... For wire rod, the initial rolling temperature is maintained at 940-980℃, the sizing temperature at the infeed reduction is 865-895℃, and the wire drawing temperature is 820-850℃.

[0015] (6) Controlled cooling: The hot-rolled wire rod obtained in step (5) is coiled by the wire rod spinning machine and then air-cooled on the Steyrmo line; the finished product speed is controlled at 20-30 m / s, the initial roller speed is 0.13-0.18 m / s, all fans are turned off, the first two heat insulation covers are turned on and the last two are turned off, so as to ensure that the wire rod undergoes phase change under slow cooling conditions.

[0016] Preferably, in step (1), the final carbon content of the converter is ≥0.10%, the P content of the steel tapped from the converter is ≤0.015%, and the tapping temperature is ≥1610℃.

[0017] Preferably, the white slag time in step (2) is ≥23 min and the soft blowing time is ≥20 min.

[0018] Preferably, the size of the continuous casting billet in step (3) is 160mm*160mm; the superheat is 22-28℃, the casting speed is 1.8~2.0m / min, and the water content is 0.68~0.70L / kg.

[0019] Preferably, in step (4), the preheating section temperature is 770-830℃, the heating section temperature is 1000-1040℃, the soaking section temperature is 1030-1060℃, the total heating time is 110-130 min, the air-fuel ratio is 0.50-0.55, and the high-pressure water descaling pressure is ≥13MPa.

[0020] Preferably, the initial rolling temperature in step (5) is 950-970°C, the sizing temperature is 870-890°C, and the wire drawing temperature is 825-845°C.

[0021] Preferably, the initial roller speed in step (6) is 0.14 to 0.16 m / s, and the finished product speed is 22 to 28 m / s.

[0022] The wire rod obtained based on this invention has a hardness ≤25HRC, and its microstructure is pearlite + ferrite with no abnormal microstructure.

[0023] The advantages and technical effects of this invention are:

[0024] This invention optimizes the composition and process, employing reasonable components and controlled rolling and cooling processes to avoid abnormal microstructure in the wire rod, resulting in a pearlite + ferrite microstructure. Simultaneously, it ensures low hardness in the wire rod, with a hardness ≤25HRC, which is beneficial for deep processing and can meet the requirements of users for hot forging and drawing, thus possessing broad application prospects. Detailed Implementation

[0025] The present invention will be further described below with reference to specific embodiments. Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and implementations of the present invention.

[0026] It should be understood that the terminology used herein is merely for describing particular embodiments and is not intended to limit the invention. Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0027] Various improvements and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, which will be obvious to those skilled in the art.

[0028] Comparative Example 1:

[0029] The rolled wire rod has a specification of Φ15mm and a specific chemical composition by weight percentage of C: 0.65%, Si: 0.26%, Mn: 0.75%, P: 0.011%, S: 0.002%, Cr: 1.1%, V: 0.15%, Al: 0.020%, Ni: 0.01%, Cu: 0.01%, with the remainder being iron and unavoidable impurities.

[0030] Its production process includes BOF converter smelting → LF refining → 160mm*160mm square billet continuous casting → billet heating → controlled rolling and controlled cooling, etc., among which:

[0031] (1) BOF smelting: the final carbon content of the converter is 0.10%, the P content of the steel tapped from the converter is 0.012%, and the tapping temperature is 1615℃.

[0032] (2) LF refining: white slag time 23min, soft blowing time 25min.

[0033] (3) Continuous casting: superheat 23℃, casting speed 1.9m / min, water content 0.69L / kg.

[0034] (4) Steel billet heating and descaling: preheating section temperature 790~820℃, heating section temperature 1010~1035℃, soaking section temperature 1040~1055℃, total heating time 115min, air-fuel ratio 0.50~0.55, high-pressure water descaling pressure ≥15MPa.

[0035] (5) Rolling: Initial rolling temperature 968℃, sizing temperature 885℃, wire drawing temperature 830℃;

[0036] (6) Cooling and collection: All fans are turned off; the initial roller speed is 0.16m / s; all insulation covers except the first two are closed.

[0037] Example 1:

[0038] The specific chemical composition by weight percentage of the low-hardness tool steel wire rod is C: 0.58%, Si: 0.22%, Mn: 0.70%, P: 0.011%, S: 0.013%, Cr: 0.80%, V: 0.10%, Ni: 0.06%, Cu: 0.09%, Al: 0.009%, with the remainder being iron and unavoidable impurities.

[0039] Its production process includes BOF converter smelting → LF refining → 160mm*160mm square billet continuous casting → billet heating → controlled rolling and controlled cooling, etc., among which:

[0040] (1) BOF smelting: the final carbon content of the converter is 0.13%, the P content of the steel tapped from the converter is 0.010%, and the tapping temperature is 1620℃.

[0041] (2) LF refining: white slag time 25min, soft blowing time 23min.

[0042] (3) Continuous casting: superheat 25℃, casting speed 1.9m / min, water content 0.69L / kg.

[0043] (4) Steel billet heating and descaling: preheating section temperature 785~810℃, heating section temperature 1010~1030℃, soaking section temperature 1045~1055℃, total heating time 123min, air-fuel ratio 0.50~0.55, high-pressure water descaling pressure ≥15MPa.

[0044] (5) Rolling: Initial rolling temperature 970℃, sizing temperature 889℃, wire drawing temperature 836℃;

[0045] (6) Cooling and collection: All fans are turned off; finished product speed is 22m / s, initial roller speed is 0.14m / s; all insulation covers except the first two insulation covers are turned off.

[0046] Example 2:

[0047] The specific chemical composition by weight percentage of the low-hardness tool steel wire rod is C: 0.59%, Si: 0.25%, Mn: 0.85%, P: 0.010%, S: 0.010%, Cr: 0.85%, V: 0.12%, Ni: 0.08%, Cu: 0.05%, Al: 0.010%, with the remainder being iron and unavoidable impurities.

[0048] Its production process includes BOF converter smelting → LF refining → 160mm*160mm square billet continuous casting → billet heating → controlled rolling and controlled cooling, etc., among which:

[0049] (1) BOF smelting: the final carbon content of the converter is 0.15%, the P content of the steel tapped from the converter is 0.009%, and the tapping temperature is 1618℃.

[0050] (2) LF refining: white slag time 23min, soft blowing time 22min.

[0051] (3) Continuous casting: superheat 22℃, casting speed 1.9m / min, water content 0.69L / kg.

[0052] (4) Steel billet heating and descaling: preheating section temperature 788~820℃, heating section temperature 1005~1025℃, soaking section temperature 1035~1050℃, total heating time 120min, air-fuel ratio 0.50-0.55, high-pressure water descaling pressure ≥15MPa.

[0053] (5) Rolling: Initial rolling temperature 960℃, sizing temperature 875℃, wire drawing temperature 830℃;

[0054] (6) Cooling and collection: All fans are turned off; finished product speed is 22m / s, initial roller speed is 0.14m / s; all insulation covers except the first two insulation covers are turned off.

[0055] The performance of the wire rods in the comparative and example samples was tested, and the results are shown in the table below:

[0056]

[0057] The low-hardness tool steel wire rod prepared by this invention has a hardness of ≤25HRC, which meets the requirements for deep processing; moreover, the wire rod is pearlite + ferrite and has no abnormal structure.

[0058] Note: The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Therefore, although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention. All technical solutions and improvements that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A low-hardness tool steel wire rod, characterized in that, Composed of the following components by mass percentage composition: C: 0.56-0.60%, Mn: 0.60-0.90%, Si: 0.17-0.37%, Cr: 0.70-0.90%, V: 0.09-0.13%, P: ≤0.025%, S: ≤0.025%, Ni ≤0.25%, Cu ≤0.30%, Al ≤0.030%, with the balance being Fe and unavoidable impurities.

2. The low-hardness tool steel wire rod according to claim 1, characterized in that, Composed of the following components by mass percentage composition: C: 0.58-0.59%, Mn: 0.70-0.85%, Si: 0.22-0.25%, Cr: 0.80-0.85%, V: 0.10-0.12%, P: ≤0.015%, S: ≤0.015%, Ni ≤0.10%, Cu ≤0.10%, Al ≤0.010%, with the balance being Fe and unavoidable impurities.

3. The low-hardness tool steel wire rod according to claim 1 or 2, characterized in that, The wire rod has a hardness of ≤25HRC and a microstructure of pearlite + ferrite with no abnormal structures.

4. The production process of low-hardness tool steel wire rod according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Converter smelting: The C content of the tapped steel is 0.08-0.20%, the P content of the tapped steel is ≤0.020%, and the tapping temperature is ≥1600℃; (2) LF refining: maintain white slag time ≥ 20 min, control soft blowing time ≥ 15 min, and use bottom blowing argon gas stirring throughout the process; (3) Continuous casting: Based on the molten steel refined by LF in step (2), continuous casting is carried out. The continuous casting process is protected. The superheat of the continuous casting furnace is controlled at 20-30℃, the casting speed is 1.7~2.0m / min, and the specific water volume is 0.66~0.70L / kg. (4) Steel billet heating: preheating section temperature 750~850℃, heating section temperature 980~1060℃, soaking section temperature 1020~1080℃, total heating time 90~150min, air-fuel ratio in heating furnace 0.48~0.58, water descaling pressure ≥12MPa; (5) Controlled rolling: Based on the steel billet heated in step (4), it is rolled into φ10~20mm wire rod, with the initial rolling temperature maintained at 940-980℃, the sizing temperature at the inlet / outlet reduction temperature at 865~895℃, and the wire drawing temperature at 820-850℃. (6) Cooling control: The finished product speed is 20-30m / s, the initial roller speed is 0.13-0.18m / s, all fans are turned off, the first two heat insulation covers are turned on, and the rest are turned off.

5. The production process of low-hardness tool steel wire rod according to claim 4, characterized in that, In step (1), the final carbon content of the converter is ≥0.10%, the P content of the steel tapped from the converter is ≤0.015%, and the tapping temperature is ≥1610℃.

6. The production process of low-hardness tool steel wire rod according to claim 4, characterized in that... The white slag time in step (2) is ≥23 min, and the soft blowing time is ≥20 min.

7. The production process of low-hardness tool steel wire rod according to claim 4, characterized in that, In step (3), the dimensions of the continuously cast square billet are 160mm*160mm; the superheat is 22-28℃, the casting speed is 1.8~2.0m / min, and the water content is 0.68~0.70L / kg.

8. The production process of low-hardness tool steel wire rod according to claim 4, characterized in that, In step (4), the preheating section temperature is 770-830℃, the heating section temperature is 1000-1040℃, the soaking section temperature is 1030-1060℃, the total heating time is 110-130 min, the air-fuel ratio is 0.50-0.55, and the high-pressure water descaling pressure is ≥13MPa.

9. The production process of low-hardness tool steel wire rod according to claim 4, characterized in that, The rolling temperature in step (5) is 950-970℃, the sizing temperature is 870-890℃, and the wire drawing temperature is 825-845℃.

10. The production process of low-hardness tool steel wire rod according to claim 4, characterized in that, The initial roller speed in step (6) is 0.14 to 0.16 m / s, and the finished product speed is 22 to 28 m / s.

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