Cr-V spring hot-rolled ribbon steel and preparation method thereof

Abstract

The Cr-V spring hot-rolled narrow strip steel comprises the following components in percentage by mass: 0.50% < = omega [C] < = 0.60%, 0.15% < = omega [Si] < = 0.30%, 0.65% < = omega [Mn] < = 0.85%, omega [P] < = 0.015%, omega [S] < = 0.005%, 0.90% < = omega [Cr] < = 1.20%, 0.10% < = omega [V] < = 0.20%, and 0.01% < = omega [Al] < = 0.04%. The method has the advantages that stress relief annealing and striping operation are not needed, the cost is saved, the production difficulty is reduced, and it is ensured that the mechanical property requirement is met.

Description

Technical Field

[0001] This invention belongs to the field of special steel production technology, and particularly relates to a Cr-V series hot-rolled narrow strip steel for springs and its preparation method. Background Technology

[0002] Cr-V series spring steel is a medium-to-high carbon alloy steel that combines the advantages of alloying elements such as chromium and vanadium, giving it excellent mechanical properties, wear resistance, and corrosion resistance. These properties make Cr-V series spring steel widely used in many key fields, including the automotive industry, mechanical engineering, construction, and agricultural machinery. In the automotive industry, it is widely used in engine parts, suspension systems, clutch plates, drive shafts, and critical suspension springs, due to its excellent fatigue strength, heat resistance, and wear resistance. Furthermore, in mechanical engineering, it is also used to manufacture torsion springs, torsion bars, and other spring components, meeting the requirements of high strength and high reliability. Simultaneously, the high hardness and wear resistance of Cr-V series spring steel also make it an ideal material in the manufacture of cutting tools and bearings.

[0003] Currently, the research hotspots of Cr-V series spring steel mainly focus on the following aspects: First, optimizing the chemical composition and heat treatment process of Cr-V series spring steel to obtain better mechanical properties and wear resistance; second, developing new processing technologies, such as laser welding and cold spraying, to improve material utilization and processing efficiency; and third, studying the performance of Cr-V series spring steel in specific application environments, such as stability and reliability under high temperature, high pressure, and corrosive environments.

[0004] However, since Cr-V series spring steel is mainly supplied in bars, wires, and wide coils, wide coils require stress-relief annealing and slitting during use by downstream cold-rolling users. This significantly increases production costs, and thick-gauge slitting steel carries a greater risk of edge cracking during cold rolling. Furthermore, cold-rolling thick Cr-V series spring steel wide strips presents challenges in rolling, production processes, manufacturing costs, and thickness precision control. Summary of the Invention

[0005] The purpose of this invention is to solve the problems of high production cost, high risk of edge cracking, high rolling difficulty, and difficulty in quality control of existing Cr-V series hot-rolled narrow strip steel for springs. It provides a Cr-V series hot-rolled narrow strip steel for springs that can be produced without stress-relief annealing and slitting operations, thereby saving costs, reducing production difficulty, and ensuring that it meets mechanical performance requirements.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A Cr-V series hot-rolled narrow strip steel for springs has the following composition and mass fraction: 0.50%≤ω[C]≤0.60%, 0.15%≤ω[Si]≤0.30%, 0.65%≤ω[Mn]≤0.85%, ω[P]≤0.015%, ω[S]≤0.005%, 0.90%≤ω[Cr]≤1.20%, 0.10%≤ω[V]≤0.20%, and 0.01%≤ω[Al]≤0.04%. The control of Al is mainly to ensure the cleanliness of the molten steel, while reducing the content of harmful elements O and S, thereby improving its service life. The combination of Cr, V, and C elements is mainly to meet the mechanical performance requirements of the material, especially to promote the precipitation of nano-scale secondary carbides during processing and heat treatment, achieving precipitation strengthening.

[0007] To further achieve the objectives of this invention, a method for preparing Cr-V series hot-rolled narrow strip steel for springs is also provided, comprising: primary refining furnace → LF refining furnace → vacuum refining furnace → continuous casting → billet treatment → heating → rolling → cooling, as detailed below: (1) The conditions for tapping steel from the primary refining furnace are ω[C]≥0.08%, ω[P]≤0.010%, and temperature T≥1600℃. The order of charging during the tapping process of the primary refining furnace includes Al-containing deoxidizer, alloy, pre-melted slag, and lime. The type of primary refining furnace is determined based on the actual operating conditions of the steel plant. High carbon content is required for tapping, mainly to reduce the oxygen potential in the molten steel, thereby reducing the formation of initial inclusions. At the same time, it can stabilize the composition of the refining slag, which on the one hand promotes the absorption of inclusions and improves the cleanliness of the molten steel; on the other hand, it ensures stable product quality. The regulations on the amount of deoxidizer, pre-melted slag, and lime added are mainly to create a suitable refining slag system. The selection of the type of deoxidizer is mainly determined based on the actual operating conditions of each plant.

[0008] (2) During the LF refining process, the initial ω[Al] ≥ 0.03%, the amount of lime added ≤ 3 kg / t, and the amount of diffusion deoxidizer ≤ 2 kg / t, wherein the diffusion deoxidizer includes SiC, carbon powder, Al wire, and calcium carbide; The addition of lime in the LF refining process is mainly to promote the absorption of inclusions during the refining process; the initial Al content setting in the LF process is mainly to ensure absolute oxygen control of Al in the molten steel, prevent the formation of low-melting-point inclusions, and thus prevent contamination of the molten steel.

[0009] (3) During the vacuum refining process, the ultimate vacuum time is ≥5min, the static stirring time is ≥20min, and the Ca line is 0.05~0.1m / ton. The vacuum refining equipment includes VD furnace and RH furnace. The selection of vacuum equipment is determined based on the actual working conditions of the steel plant. The specified ultimate vacuum time is mainly to reduce the content of H and N elements in the molten steel. Feeding Ca wire after vacuum treatment is mainly to ensure smooth production and at the same time to lower the melting point of hard inclusions and improve the fatigue life of the material.

[0010] (4) During the continuous casting process, the following methods are adopted: electromagnetic stirring of the crystallizer, electromagnetic stirring at the end, special protective slag for spring steel, weak cooling in the secondary cooling stage, and full-process protective casting. The use of electromagnetic stirring in the crystallizer and at the end is mainly to reduce the segregation of alloying elements and ensure the uniformity of composition in narrow strip steel; protective slag, secondary cooling, and protective casting are mainly to ensure the smooth progress of the casting process and at the same time ensure the surface quality of the continuously cast billet.

[0011] (5) During the heating process, the heating furnace is a walking beam furnace, which is divided into a preheating section, a heating section 1, a heating section 2, a heating section 3 and a soaking section. The furnace temperature of each heating section is controlled. The total furnace time of the high temperature section, namely the heating section 3 and the soaking section, is 70~120 min. The temperature settings for different heating zones in the heating furnace serve two purposes: firstly, to ensure that stress cracks do not occur during the billet heating process; and secondly, to quickly pass through the decarburization-sensitive temperature range of high-carbon steel, thereby reducing decarburization. Severe decarburization will significantly reduce the quenching hardness of narrow strip steel. Strict control of the high-temperature period is also intended to reduce the depth of the decarburized layer.

[0012] (6) During the rolling process, the initial rolling temperature is 1080~1200℃, the final rolling temperature is 850~950℃, the coiling is fast, the coiling temperature is 450~700℃, and the coiling is air-cooled after rolling. The rolling temperature is set primarily to ensure the smoothness of the plate shape and rolling process, and to prevent cracking. The coiling temperature is set primarily to make full use of the self-tempering process after coiling, so as to relieve stress and prevent cracking during uncoiling in subsequent processes.

[0013] Furthermore, the Cr-V series spring steel is supplied in the form of hot-rolled narrow strip steel, with a thickness of 3.0~10.0mm and a width of 160~450mm.

[0014] Further, in step (1), the content includes 0.6~1.8 kg / t of Al deoxidizer, 3~6 kg / t of pre-melted slag, and 4~7 kg / t of lime. The primary smelting furnace includes an electric furnace and a converter. The alloy includes various alloys containing Si, Mn, Cr, and V elements.

[0015] Furthermore, in step (1), the tapping conditions of the primary smelting furnace are: ω[C]=0.10%, ω[P]=0.008%, and temperature T=1612℃.

[0016] Furthermore, in step (2), the initial Al content is 0.035%, the amount of lime added is ≤3kg / t, and the amount of diffusion deoxidizer is ≤1.5kg / t.

[0017] Furthermore, in step (3), during the vacuum refining process, the ultimate vacuum time is 6 minutes and the static stirring time is 28 minutes.

[0018] Furthermore, in step (5), the preheating section furnace temperature is ≤750℃, the first heating section furnace temperature is 700~1000℃, the second heating section furnace temperature is 950~1150℃, the third heating section furnace temperature is 1000~1200℃, and the soaking section furnace temperature is 1150~1250℃.

[0019] Furthermore, in step (5), during the heating process, the actual furnace entry adopts a 2-in-1-out-of-furnace method, with a preheating section temperature of 530℃, a heating section temperature of 865℃, a heating section temperature of 1030℃, a heating section temperature of 1174℃, a soaking section temperature of 1210℃, and a furnace time of 93 minutes in the high-temperature section.

[0020] Furthermore, in step (6), the initial rolling temperature is 1112℃, the final rolling temperature is 912℃, and the rapid winding temperature is 632℃.

[0021] In this invention, the mechanical properties of Cr-V series spring narrow strip steel are achieved through the design of C, Cr, and V element compositions, combined with hot rolling, cold rolling, and heat treatment processes. During the smelting process, the cleanliness of the molten steel is ensured by controlling the C content during tapping, the Al content and slag composition during LF refining, and the effective removal of harmful gas elements during the vacuum process, thereby improving the service life of the Cr-V series spring narrow strip steel. During the rolling process, strict control of heating temperature and temperature control during rolling reduces decarburization of the narrow strip steel while ensuring dimensional accuracy and shape, ultimately safeguarding the performance uniformity and machinability of the Cr-V series spring narrow strip steel. The process of this invention eliminates the need for stress-relief annealing and slitting operations throughout. By optimizing the smelting and rolling processes, the development of Cr-V series hot-rolled spring narrow strip steel can be completed without adding extra equipment and processes, saving costs while ensuring that the product surface quality and performance indicators meet the needs of end users. Detailed Implementation Example

[0022] To make the present invention clearer, the following further describes a Cr-V series hot-rolled narrow strip steel for springs and its preparation method. The specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0023] In this embodiment, a method for preparing Cr-V series hot-rolled narrow strip steel for springs includes the following steps: primary refining furnace → LF refining furnace → vacuum refining furnace → continuous casting → billet treatment → heating → rolling → cooling. By adopting Al deoxidation process for smelting, and combining the processes of steel tapping, refining, rolling and post-rolling cooling, a method for preparing Cr-V series hot-rolled narrow strip steel for springs is formed.

[0024] The constituent elements and their mass fractions of this Cr-V series hot-rolled narrow strip steel for springs are as follows: 0.50%≤ω[C]≤0.60%, 0.15%≤ω[Si]≤0.30%, 0.65%≤ω[Mn]≤0.85%, ω[P]≤0.015%, ω[S]≤0.005%, 0.90%≤ω[Cr]≤1.20%, 0.10%≤ω[V]≤0.20%, 0.01%≤ω[Al]≤0.04%.

[0025] Primary refining furnace tapping conditions: ω[C]=0.10%, ω[P]=0.008%, temperature T=1612℃. The charging sequence during primary refining furnace tapping process is: deoxidizer → alloy → pre-melted slag → lime, containing 0.6~1.8kg / t of Al deoxidizer, 3~6kg / t of pre-melted slag, and 4~7kg / t of lime. Primary refining furnaces include electric furnaces and converters, and alloys include various alloys containing Si, Mn, Cr, and V elements.

[0026] LF refining process: initial Al content = 0.035%, lime addition ≤ 3 kg / t, diffusion deoxidizer ≤ 1.5 kg / t; vacuum refining process: ultimate vacuum time 6 min, static stirring time 28 min, Ca line 80 m after vacuum breaking; vacuum refining equipment includes VD furnace and RH furnace.

[0027] Heating process: The actual furnace entry adopts a 2-in-1-out-of-furnace method. The preheating section temperature is 530℃, the first heating section temperature is 865℃, the second heating section temperature is 1030℃, the third heating section temperature is 1174℃, and the soaking section temperature is 1210℃. The high-temperature section, which is the furnace time of the third section plus the soaking section, is 93 minutes.

[0028] Rolling process: initial rolling temperature 1112℃, final rolling temperature 912℃, rapid coiling, coiling temperature 632℃, rolled product specifications 8.5*415mm.

[0029] The narrow strip steel prepared by the method of this invention meets the requirements of end users in terms of surface quality and performance indicators. By adopting the Al deoxidation process for smelting and combining the processes of tapping, refining, rolling and post-rolling cooling, the cleanliness of the molten steel is improved, the content of harmful elements is reduced, and an ideal metallographic structure is obtained. This invention optimizes the smelting process and rolling process, eliminating the need for stress-relief annealing and slitting operations, thereby reducing production difficulty and saving costs.

[0030] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A Cr-V series hot-rolled narrow strip steel for springs, characterized in that: The composition and mass fraction of the narrow strip steel are as follows: 0.50%≤ω[C]≤0.60%, 0.15%≤ω[Si]≤0.30%, 0.65%≤ω[Mn]≤0.85%, ω[P]≤0.015%, ω[S]≤0.005%, 0.90%≤ω[Cr]≤1.20%, 0.10%≤ω[V]≤0.20%, 0.01%≤ω[Al]≤0.04%.

2. A method for preparing Cr-V series hot-rolled narrow strip steel for springs as described in claim 1, comprising: primary refining furnace → LF refining furnace → vacuum refining furnace → continuous casting → billet treatment → heating → rolling → cooling, characterized in that: (1) The conditions for tapping steel from the primary refining furnace are ω[C]≥0.08%, ω[P]≤0.010%, and temperature T≥1600℃. The order of charging during the tapping process of the primary refining furnace includes Al-containing deoxidizer, alloy, pre-melted slag, and lime. (2) During the LF refining process, the initial ω[Al] ≥ 0.03%, the amount of lime added ≤ 3 kg / t, and the amount of diffusion deoxidizer ≤ 2 kg / t, wherein the diffusion deoxidizer includes SiC, carbon powder, Al wire, and calcium carbide; (3) During the vacuum refining process, the ultimate vacuum time is ≥5min, the static stirring time is ≥20min, and the Ca line is 0.05~0.1m / ton. The vacuum refining equipment includes VD furnace and RH furnace. (4) During the continuous casting process, the following methods are adopted: electromagnetic stirring of the crystallizer, electromagnetic stirring at the end, special protective slag for spring steel, weak cooling in the secondary cooling stage, and full-process protective casting. (5) During the heating process, the heating furnace is a walking beam furnace, which is divided into a preheating section, a heating section 1, a heating section 2, a heating section 3 and a soaking section. The furnace temperature of each heating section is controlled. The total furnace time of the high temperature section, namely the heating section 3 and the soaking section, is 70~120 min. (6) During the rolling process, the initial rolling temperature is 1080~1200℃, the final rolling temperature is 850~950℃, the coiling is fast, the coiling temperature is 450~700℃, and the coiling is air-cooled after rolling.

3. The method for preparing Cr-V series hot-rolled narrow strip steel for springs according to claim 2, characterized in that: The Cr-V series spring steel is supplied in the form of hot-rolled narrow strip steel, with a thickness of 3.0~10.0mm and a width of 160~450mm.

4. The method for preparing Cr-V series hot-rolled narrow strip steel for springs according to claim 2, characterized in that: In step (1), the content includes 0.6~1.8 kg / t of Al deoxidizer, 3~6 kg / t of pre-melted slag, and 4~7 kg / t of lime. The primary smelting furnace includes an electric furnace and a converter. The alloy includes various alloys containing Si, Mn, Cr and V elements.

5. The method for preparing Cr-V series hot-rolled narrow strip steel for springs according to claim 2, characterized in that: In step (1), the tapping conditions of the primary smelting furnace are: ω[C]=0.10%, ω[P]=0.008%, and temperature T=1612℃.

6. The method for preparing Cr-V series hot-rolled narrow strip steel for springs according to claim 2, characterized in that: In step (2), the initial Al content is 0.035%, the amount of lime added is ≤3kg / t, and the amount of diffusion deoxidizer is ≤1.5kg / t.

7. The method for preparing Cr-V series hot-rolled narrow strip steel for springs according to claim 2, characterized in that: In step (3), during the vacuum refining process, the ultimate vacuum time is 6 minutes and the static stirring time is 28 minutes.

8. The method for preparing Cr-V series hot-rolled narrow strip steel for springs according to claim 2, characterized in that: In step (5), the preheating section furnace temperature is ≤750℃, the first heating section furnace temperature is 700~1000℃, the second heating section furnace temperature is 950~1150℃, the third heating section furnace temperature is 1000~1200℃, and the soaking section furnace temperature is 1150~1250℃.

9. The method for preparing Cr-V series hot-rolled narrow strip steel for springs according to claim 2, characterized in that: In step (5), during the heating process, the actual furnace entry adopts the 2-in-1-out-of-furnace method, with a preheating section temperature of 530℃, a heating section temperature of 865℃, a heating section temperature of 1030℃, a heating section temperature of 1174℃, a homogenization section temperature of 1210℃, and a furnace time of 93 minutes in the high-temperature section.

10. The method for preparing Cr-V series hot-rolled narrow strip steel for springs according to claim 9, characterized in that: In step (6), the initial rolling temperature is 1112℃, the final rolling temperature is 912℃, and the rapid winding temperature is 632℃.