Heating process for reducing surface decarburization of spring steel

Abstract

The invention discloses a heating process for reducing surface decarburization of spring steel, which is characterized in that during billet heating, peak temperature intervals such as 800 DEG C and 1100 DEG C which are easy to cause intensification of a decarburized layer are avoided, the heating temperature is controlled between 950 DEG C and 1050 DEG C, the heating rate is adjusted according to production requirements, the spring steel quickly passes through a two-phase region, the retention time in the region is reduced, and the surface decarburization of the spring steel is reduced. The formation of a grain boundary ferrite fully decarburized layer is inhibited; the heat preservation time is controlled within 1.5-2 hours; after heating is completed, the steel billet is rapidly taken out and cooled to the room temperature in an air cooling mode; the spring steel is made of W55SiCrC steel for high-end automobiles. The method for optimizing the heating temperature, rapidly passing through the two-phase region and reasonably setting the heat preservation time is utilized, the thickness and structure uniformity of a decarburized layer on the surface of the spring steel are remarkably improved, and therefore the anti-fatigue performance of the spring steel is remarkably improved, and the service life of the spring steel is remarkably prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of metal thermal processing, in particular to a heating process for reducing surface decarburization of spring steel. Background Art

[0002] High-end automotive spring steel is widely used in key components such as automotive suspension and shock absorbers. Its quality and performance are directly related to the safety and service life of the car. With the rapid development of lightweight and high-performance automobiles, spring steel needs to meet the requirements of high strength, high toughness and long life at the same time. However, the problem of decarburization on the surface of spring steel has always been one of the important factors affecting its fatigue performance and service life. Studies have shown that the decarburization layer on the surface of spring steel will significantly reduce the fatigue resistance. When a full decarburization layer appears on the surface, it may cause the fatigue life to be reduced by more than 50%. Therefore, how to effectively control the thickness of the decarburization layer is a key technical issue in the production of spring steel.

[0003] Surface decarburization of spring steel mainly occurs in the heating stage, including billet heating before rolling and heat treatment heating. In the prior art, the main factors affecting decarburization include heating temperature, holding time, furnace atmosphere, and chemical composition of steel. Among them, heating temperature and holding time are key variables that determine the depth and organizational characteristics of the decarburization layer. Studies have shown that at lower heating temperatures (700-1150°C), partial decarburization is the main decarburization. With the increase of temperature and holding time, the thickness of the total decarburization layer shows a trend of first increasing and then decreasing, and reaches a peak at 1100°C. In addition, due to the low carbon content at the grain boundaries in the two-phase region (γ+α) heating stage, a full decarburization layer is easily generated at the grain boundaries, thereby exacerbating the problem of surface decarburization.

[0004] At present, in order to alleviate the decarburization problem, methods such as optimizing the furnace atmosphere (such as inert gas protection), surface coating protection or changing the chemical composition of the steel grade are usually adopted. However, these methods often increase production costs or have high requirements on the operating process, and are difficult to be widely promoted in large-scale industrial production. In contrast, optimizing the heating temperature and holding time, combined with a method of quickly passing through the two-phase zone, is an economical, efficient and easy-to-implement solution. Based on existing research results, developing a more reasonable spring steel heating process to effectively control the thickness of the decarburization layer has become an important research direction in the field of spring steel production technology. The present invention studies the decarburization behavior of spring steel under different heating conditions, and proposes a technical solution for optimizing the heating process to reduce surface decarburization, which has important industrial application value and promotion prospects.

[0005] Publication No. CN 116024416 A introduces a production method for improving the decarburization depth of hot-rolled 60Si2Mn spring round steel, including billet preparation, furnace charging step control, heating control, controlled rolling and controlled cooling, etc., using round continuous casting billets, large rolling ratio, furnace charging step control and control of residual oxygen content in the furnace, etc., which can reduce the decarburization rate and total decarburization depth and improve production efficiency. This patent targets high-end automotive spring steel W55SiCrC, and achieves better results in reducing the thickness of the decarburization layer (lower total decarburization layer thickness and ferrite decarburization layer thickness) by more accurately optimizing the heating process parameters (such as clearly avoiding a specific decarburization peak temperature range, strictly controlling the holding time, etc.), and does not mention additional equipment or complex operation requirements, further reflecting the simplicity and efficiency of the process, which can better meet the performance requirements of high-end automotive spring steel.

[0006] Publication No. CN 116590505 A discloses a production method for reducing the depth of the decarburization layer of a wire coil. Under a specific chemical composition of the coil steel, the decarburization layer of the wire coil can be controlled to within 0.6% D and there is no complete decarburization layer on the surface through full grinding of the steel billet, control of the residual oxygen content in the heating furnace, the temperature of the soaking section and the time in the furnace, specific starting rolling and coiling temperatures, and slow cooling of the coil in an insulation cover after coiling and nitrogen protection. The invention discloses a heating process for reducing surface decarburization of spring steel. High-end automobile spring steel W55SiCrC is taken as the research object. By optimizing the heating temperature (avoiding 800°C and 1100°C, rapidly heating from 950°C to 1050°C and shortening the residence time in the two-phase region), the holding time (1.5 to 2 hours) and the cooling method (air cooling), the total decarburization layer thickness of the spring steel is successfully controlled within 80μm, and the thickness of the ferrite decarburization layer can be reduced to below 15μm. The process has the advantages of simple process flow, low cost, convenient operation, etc., and is suitable for large-scale industrial production.

[0007] Publication No. CN 114855088 A discloses a production method for controlling the decarburization depth of tool steel wire rods. Through a specific process flow (including a series of steps such as converter smelting) and key process steps (finishing rolling temperature 900-980°C and rapid cooling in a water tank followed by weak cooling after finishing rolling, and self-tempering using waste heat at a wire-spinning temperature of 850-880°C), hot-rolled tool steel wire rods of specific specifications are produced using existing equipment and process conditions, with a decarburization depth of ≤1.0D% and no local full decarburization. This patent proposes more precise heating process parameter control for high-end automotive spring steel, which can control the thickness of the spring steel decarburization layer at a lower level (total decarburization layer thickness within 80μm, ferrite decarburization layer thickness below 15μm, which is better than the tool steel wire rod decarburization layer depth ≤1.0D% in publication number CN 114855088 A), and does not involve complex smelting, refining, vacuum treatment and other process flows. Efficient carbon reduction can be achieved only by optimizing the heating process, which has more advantages in cost and ease of operation, and provides a more efficient technical solution for the manufacture of high-end automotive spring steel. Summary of the invention

[0008] The purpose of the present invention is to provide a heating process for reducing decarburization on the surface of spring steel. By optimizing the heating temperature, quickly passing through the two-phase zone, and reasonably setting the holding time, the thickness of the decarburization layer on the surface of the spring steel and the uniformity of the structure are significantly improved, thereby significantly improving the fatigue resistance and service life of the spring steel.

[0009] The present invention aims at the problems of difficult control of surface decarburization, complex process and high cost in the prior art. Through in-depth research on the heating process of spring steel for high-end automobiles, the influence of heating temperature and holding time on decarburization behavior is clarified, and it is proposed to avoid the peak temperature range of decarburization (800℃ and 1100℃), select 950℃ to 1050℃ as the optimal temperature range of the heating process, and shorten the residence time in the two-phase region to reduce the formation of grain boundary ferrite decarburization layer. In addition, the present invention further reduces the total surface decarburization layer thickness by strictly controlling the holding time and balancing the decarburization and oxidation reactions, thereby ensuring the surface quality and mechanical properties of the spring steel.

[0010] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0011] The present invention discloses a heating process for reducing surface decarburization of spring steel, comprising: steel billet preparation, heating temperature optimization, holding time control, cooling process control, and decarburization detection; wherein:

[0012] When heating the steel billet, avoid the peak temperature range of 800℃ and 1100℃ which easily lead to the aggravation of the decarburization layer. Control the heating temperature between 950℃ and 1050℃. Adjust the heating rate according to production needs, quickly pass through the two-phase region, reduce the residence time in this area, and inhibit the formation of the grain boundary ferrite full decarburization layer.

[0013] The holding time is controlled within 1.5 to 2 hours, which not only ensures that the austenite structure is fully homogenized, but also avoids excessive decarburization caused by too long holding time;

[0014] After heating, the billet is quickly taken out and cooled to room temperature by air cooling to avoid prolonged high temperature which may cause surface oxidation.

[0015] The spring steel is W55SiCrC steel for high-end automobile spring steel.

[0016] Furthermore, the chemical composition of the spring steel includes by weight percentage: C 0.51% to 0.59%, Si 1.40% to 1.60%, Mn 0.60% to 0.70%, P≤0.020%, S≤0.010%, Cr 0.60% to 0.70%, and the rest is Fe and unavoidable trace impurities, with a total weight fraction of 100%.

[0017] Furthermore, the depth of the decarburized layer on the surface of the steel billet was determined using a metallographic microscope.

[0018] Furthermore, the chemical composition of the spring steel includes by weight percentage: C 0.55%, Si 1.50%, Mn 0.65%, P 0.018%, S 0.009%, Cr 0.65%, and the rest is Fe and inevitable trace impurities, with a total weight fraction of 100%.

[0019] Furthermore, when the billet is heated, the heating temperature is controlled at 960°C, the heating rate is 10°C / min, the two-phase region is passed quickly, the residence time is reduced to 10 minutes, and the formation of the grain boundary ferrite full decarburization layer is suppressed;

[0020] The holding time is controlled at 1.8 hours to ensure that the austenite structure is fully homogenized and to avoid excessive decarburization;

[0021] After heating, the billet is quickly taken out and cooled to room temperature by air cooling to ensure that surface oxidation is kept to a minimum.

[0022] Analysis using a metallographic microscope showed that the total decarburization layer thickness of the steel billet was 75 μm, of which the ferrite decarburization layer thickness was 12 μm.

[0023] Furthermore, the chemical composition of the spring steel includes by weight percentage: C 0.57%, Si 1.45%, Mn 0.68%, P 0.015%, S 0.008%, Cr 0.67%, and the rest is Fe and inevitable trace impurities, with a total weight fraction of 100%.

[0024] Furthermore, when the billet is heated, the heating temperature is controlled at 970°C, the heating rate is 12°C / min, the two-phase region is passed quickly, the residence time is reduced to 8 minutes, and the formation of the grain boundary ferrite decarburization layer is avoided;

[0025] The holding time is controlled at 1.7 hours to ensure that the austenite structure is fully homogenized and the surface decarburization reaction is effectively slowed down;

[0026] After heating, the billet is quickly taken out and cooled to room temperature by air cooling, and the surface oxide layer is thin and uniform;

[0027] Analysis using a metallographic microscope showed that the total decarburization layer thickness of the steel billet was 72 μm, of which the ferrite decarburization layer thickness was 10 μm.

[0028] Furthermore, the chemical composition of the spring steel includes by weight percentage: C 0.53%, Si 1.55%, Mn 0.63%, P 0.017%, S 0.010%, Cr 0.62%, and the rest is Fe and unavoidable trace impurities, with a total weight fraction of 100%;

[0029] Furthermore, when the billet is heated, the heating temperature is controlled at 980°C, the heating rate is 15°C / min, the two-phase region is passed quickly, the residence time is reduced to 6 minutes, and the formation of the decarburized layer is effectively reduced;

[0030] The holding time is controlled at 1.5 hours, which not only ensures the homogenization of the structure but also inhibits the surface decarburization;

[0031] After heating, the billet is quickly taken out and cooled to room temperature by air cooling. The oxide layer is well controlled and the surface is smooth.

[0032] Analysis using a metallographic microscope showed that the total decarburization layer thickness of the steel billet was 70 μm, of which the ferrite decarburization layer thickness was 8 μm.

[0033] Compared with the prior art, the beneficial technical effects of the present invention are:

[0034] (1) By optimizing the heating temperature, shortening the residence time in the two-phase region, and reasonably controlling the holding time, the present invention can control the total decarburization layer thickness of the spring steel within 80 μm, wherein the ferrite decarburization layer thickness can be reduced to less than 15 μm, thereby effectively avoiding the problem of surface strength reduction caused by decarburization.

[0035] (2) The reduction in the thickness of the decarburized layer significantly improves the surface quality of the spring steel and enhances its fatigue resistance. The present invention can effectively solve the problem of reduced fatigue life caused by surface decarburization in the traditional production process, thereby extending the service life of the product and meeting the performance requirements of high-end automotive spring steel.

[0036] (3) The present invention does not require complicated furnace atmosphere optimization or expensive coating protection. It can achieve significant carbon reduction effects simply by optimizing heating process parameters. It is simple to operate and low-cost. It can be quickly promoted and applied in existing industrial production lines, providing effective technical support for enterprises to reduce costs and increase efficiency. DETAILED DESCRIPTION

[0037] The following is a further detailed description of a heating process for reducing surface decarburization of spring steel according to the present invention.

[0038] Embodiment: This embodiment is a preferred embodiment among various implementation modes of the present invention.

[0039] A heating process for reducing surface decarburization of spring steel in this embodiment comprises: steel billet preparation, heating temperature optimization, holding time control, cooling process control, and decarburization detection.

[0040] Further: The test material is taken from the high-end automobile spring steel W55SiCrC billet, and its chemical composition mass percentage includes: C 0.51%~0.59%, Si 1.40%~1.60%, Mn 0.60%~0.70%, P≤0.020%, S≤0.010%, Cr 0.60%~0.70%, and the rest is Fe and unavoidable trace impurities, with a total mass fraction of 100%;

[0041] Further: When heating the steel billet, avoid the peak temperature range of 800℃ and 1100℃, which is likely to lead to the aggravation of the decarburization layer. It is preferred that the heating temperature be controlled between 950℃ and 1050℃, and the heating rate be adjusted according to production needs to quickly pass through the two-phase region (γ+α), reduce the residence time in this region, and inhibit the formation of the grain boundary ferrite full decarburization layer;

[0042] Further: the holding time is controlled within 1.5 to 2 hours, which not only ensures that the austenite structure is fully homogenized, but also avoids excessive decarburization caused by too long holding time;

[0043] Further: After heating is completed, the billet is quickly taken out and cooled to room temperature by air cooling to avoid prolonged high temperature stay which may cause aggravated surface oxidation.

[0044] The depth of decarburized layer on the surface of the steel billet was determined using a metallographic microscope.

[0045] Embodiment 1: A heating process for reducing surface decarburization of spring steel according to the present invention is carried out in the following steps:

[0046] The test material is taken from W55SiCrC billet, a high-end automobile spring steel. The mass percentage of its chemical composition includes: C 0.55%, Si 1.50%, Mn 0.65%, P 0.018%, S 0.009%, Cr 0.65%, and the rest is Fe and inevitable trace impurities, with a total mass fraction of 100%;

[0047] When the billet is heated, the heating temperature is controlled at 960°C, the heating rate is 10°C / min, the two-phase region (γ+α) is passed quickly, the residence time is reduced to 10 minutes, and the formation of the grain boundary ferrite full decarburization layer is suppressed;

[0048] The holding time is controlled at 1.8 hours to ensure that the austenite structure is fully homogenized and to avoid excessive decarburization;

[0049] After heating, the billet is quickly taken out and cooled to room temperature by air cooling to ensure that surface oxidation is kept to a minimum.

[0050] Analysis using a metallographic microscope showed that the total decarburization layer thickness of the steel billet was 75 μm, of which the ferrite decarburization layer thickness was 12 μm.

[0051] Embodiment 2: A heating process for reducing surface decarburization of spring steel according to the present invention is carried out in the following steps:

[0052] The test material was taken from W55SiCrC billet, a high-end automobile spring steel. The mass percentage of its chemical composition includes: C 0.57%, Si 1.45%, Mn 0.68%, P 0.015%, S 0.008%, Cr 0.67%, and the rest is Fe and inevitable trace impurities, with a total mass fraction of 100%;

[0053] When heating the billet, the heating temperature is controlled at 970°C, the heating rate is 12°C / min, the two-phase region (γ+α) is passed quickly, and the residence time is reduced to 8 minutes to avoid the formation of grain boundary ferrite decarburization layer;

[0054] The holding time is controlled at 1.7 hours to ensure that the austenite structure is fully homogenized and the surface decarburization reaction is effectively slowed down;

[0055] After heating, the billet is quickly taken out and cooled to room temperature by air cooling, and the surface oxide layer is thin and uniform;

[0056] Analysis using a metallographic microscope showed that the total decarburization layer thickness of the steel billet was 72 μm, of which the ferrite decarburization layer thickness was 10 μm.

[0057] Embodiment 3: A heating process for reducing surface decarburization of spring steel according to the present invention is carried out in the following steps:

[0058] The test material was taken from W55SiCrC billet, a high-end automobile spring steel. The mass percentage of its chemical composition includes: C 0.53%, Si 1.55%, Mn 0.63%, P 0.017%, S 0.010%, Cr 0.62%, and the rest is Fe and inevitable trace impurities, with a total mass fraction of 100%;

[0059] When heating the billet, the heating temperature is controlled at 980°C, the heating rate is 15°C / min, the two-phase region (γ+α) is passed quickly, the residence time is reduced to 6 minutes, and the formation of decarburized layer is effectively reduced;

[0060] The holding time is controlled at 1.5 hours, which not only ensures the homogenization of the structure but also inhibits the surface decarburization;

[0061] After heating, the billet is quickly taken out and cooled to room temperature by air cooling. The oxide layer is well controlled and the surface is smooth.

[0062] Analysis using a metallographic microscope showed that the total decarburization layer thickness of the steel billet was 70 μm, of which the ferrite decarburization layer thickness was 8 μm.

[0063] Comparative Example 1: A heating process for reducing surface decarburization of spring steel according to the present invention is carried out in the following steps:

[0064] The test material was taken from W55SiCrC billet, a high-end automobile spring steel, and its chemical composition by mass percentage was: C0.56%, Si 1.50%, Mn 0.65%, P 0.019%, S 0.009%, Cr 0.65%, and the rest was Fe and unavoidable trace impurities, with a total mass fraction of 100%;

[0065] When heating the steel billet, the heating temperature is controlled at 1100°C, the heating rate is 5°C / min, and the holding time is controlled at 2 hours;

[0066] After heating is completed, the billet is cooled to room temperature by air;

[0067] Analysis using a metallographic microscope showed that the total decarburization layer thickness of the steel billet was 135 μm, of which the ferrite decarburization layer thickness was 24 μm.

[0068] Comparative Example 2: A heating process for reducing surface decarburization of spring steel according to the present invention is carried out in the following steps:

[0069] The test material was taken from high-end automobile spring steel W55SiCrC billet, and its chemical composition by mass percentage was: C0.54%, Si 1.48%, Mn 0.66%, P 0.018%, S 0.010%, Cr 0.67%, and the rest was Fe and inevitable trace impurities, with a total mass fraction of 100%;

[0070] When heating the steel billet, the heating temperature is controlled at 800°C, the heating rate is 8°C / min, and the holding time is controlled at 2.5 hours;

[0071] After heating is completed, the billet is cooled to room temperature by air;

[0072] Analysis using a metallographic microscope showed that the total decarburization layer thickness of the steel billet was 98 μm, of which the ferrite decarburization layer thickness was 22 μm.

[0073] Comparative Example 3: A heating process for reducing surface decarburization of spring steel according to the present invention is carried out in the following steps:

[0074] The test material was taken from W55SiCrC billet, a high-end automobile spring steel, and its chemical composition by mass percentage was: C0.52%, Si 1.60%, Mn 0.62%, P 0.020%, S 0.010%, Cr 0.68%, and the rest was Fe and unavoidable trace impurities, with a total mass fraction of 100%;

[0075] When the billet is heated, the heating temperature is controlled at 1050°C, but the holding time is extended to 3 hours, and the heating rate is 6°C / min;

[0076] After heating is completed, the billet is cooled to room temperature by air;

[0077] Analysis using a metallographic microscope showed that the total decarburization layer thickness of the steel billet was 150 μm, of which the ferrite decarburization layer thickness was 50 μm.

[0078] Comparative Example 4: A heating process for reducing surface decarburization of spring steel according to the present invention is carried out in the following steps:

[0079] The test material was taken from W55SiCrC billet, a high-end automobile spring steel, and its chemical composition by mass percentage was: C0.55%, Si 1.42%, Mn 0.65%, P 0.018%, S 0.010%, Cr 0.65%, and the rest was Fe and unavoidable trace impurities, with a total mass fraction of 100%;

[0080] When heating the steel billet, the heating temperature is controlled at 900°C, the heating rate is 7°C / min, and the holding time is 1 hour;

[0081] After heating is completed, the billet is cooled to room temperature by air;

[0082] Analysis using a metallographic microscope showed that the total decarburization layer thickness of the steel billet was 100 μm, of which the ferrite decarburization layer thickness was 25 μm.

[0083] Comparative Example 5: A heating process for reducing decarburization on the surface of spring steel according to the present invention is carried out in the following steps:

[0084] The test material was taken from W55SiCrC billet, a high-end automobile spring steel, and its chemical composition by mass percentage was: C0.58%, Si 1.46%, Mn 0.64%, P 0.017%, S 0.010%, Cr 0.66%, and the rest was Fe and unavoidable trace impurities, with a total mass fraction of 100%;

[0085] When the billet is heated, the heating temperature is controlled at 1020°C, the heating rate is 5°C / min, and it passes through the two-phase region quickly, but the cooling method adopts slow cooling;

[0086] After cooling to room temperature, test;

[0087] Analysis using a metallographic microscope showed that the total decarburization layer thickness of the steel billet was 120 μm, of which the ferrite decarburization layer thickness was 40 μm.

[0088] It can be seen from the above embodiments and comparative examples that comparative example 1 has a too high heating temperature and a slow heating rate, comparative example 2 has a too low heating temperature and a too long insulation time, comparative example 3 has a too long insulation time, comparative example 4 has a low heating temperature and insufficient insulation time, and comparative example 5 fails to effectively suppress the oxidation reaction due to the slow cooling method. These factors all lead to the intensification of the decarburization reaction and the generation of a large amount of decarburization layer.

[0089] The present invention has the following advantages: (1) In the embodiment, by optimizing the heating temperature (950°C to 1050°C), shortening the residence time in the two-phase region and reasonably controlling the holding time (1.5 to 2 hours), the total decarburization layer thickness is significantly reduced to within 80 μm, and the ferrite decarburization layer thickness is reduced to below 15 μm. In the comparative example, since the heating temperature, holding time or cooling method are not optimized, the decarburization layer thickness is generally high, exceeding the control range of the embodiment, and reducing the surface quality of the steel. (2) The embodiment achieves effective control of the decarburization layer by adjusting the process parameters (such as heating temperature, heating rate, holding time and cooling method) without adding additional equipment or complex operations. This method is simple, efficient and suitable for large-scale industrial promotion. In the comparative example, the use of unreasonable process parameters leads to serious decarburization problems, which not only increases the rework rate, but also requires additional protection measures (such as coating or atmosphere protection), thereby increasing production costs and operational complexity. (3) The embodiment explicitly proposes to avoid the decarburization peak temperature range of 800°C and 1100°C, quickly pass through the two-phase region, and reduce the residence time, thereby solving the problem of the formation of a full decarburization layer of grain boundary ferrite in theory and practice. The embodiment achieves effective control of the thickness of the decarburization layer through process optimization and innovative design, significantly improves the surface quality of spring steel, and reduces production costs, and has outstanding technical advancement and practical application value.

[0090] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A heating process for reducing surface decarburization of spring steel, characterized in that: include: Billet preparation, heating temperature optimization, holding time control, cooling process control, decarburization detection; including: When heating the steel billet, avoid the peak temperature range of 800℃ and 1100℃ which easily lead to the aggravation of the decarburization layer. Control the heating temperature between 950℃ and 1050℃. Adjust the heating rate according to production needs, quickly pass through the two-phase region, reduce the residence time in this area, and inhibit the formation of the grain boundary ferrite full decarburization layer. The holding time is controlled within 1.5 to 2 hours, which not only ensures that the austenite structure is fully homogenized, but also avoids excessive decarburization caused by too long holding time; After heating, the billet is quickly taken out and cooled to room temperature by air cooling to avoid prolonged high temperature which may cause surface oxidation. The spring steel is W55SiCrC steel for high-end automobile spring steel.

2. The heating process for reducing surface decarburization of spring steel according to claim 1, characterized in that: The chemical components of the spring steel include by weight percentage: C 0.51% to 0.59%, Si 1.40% to 1.60%, Mn 0.60% to 0.70%, P≤0.020%, S≤0.010%, Cr 0.60% to 0.70%, and the rest are Fe and unavoidable trace impurities, with a total weight fraction of 100%.

3. The heating process for reducing surface decarburization of spring steel according to claim 1, characterized in that: The depth of decarburized layer on the surface of the steel billet was determined using a metallographic microscope.

4. The heating process for reducing surface decarburization of spring steel according to claim 1, characterized in that: The chemical components of the spring steel include by weight percentage: C 0.55%, Si 1.50%, Mn 0.65%, P0.018%, S 0.009%, Cr0.65%, and the rest are Fe and inevitable trace impurities, with a total weight fraction of 100%.

5. The heating process for reducing surface decarburization of spring steel according to claim 4, characterized in that: When the billet is heated, the heating temperature is controlled at 960°C, the heating rate is 10°C / min, the two-phase region is passed quickly, the residence time is reduced to 10 minutes, and the formation of the grain boundary ferrite full decarburization layer is suppressed; The holding time is controlled at 1.8 hours to ensure that the austenite structure is fully homogenized and to avoid excessive decarburization; After heating, the billet is quickly taken out and cooled to room temperature by air cooling to ensure that surface oxidation is kept to a minimum. Analysis using a metallographic microscope showed that the total decarburization layer thickness of the steel billet was 75 μm, of which the ferrite decarburization layer thickness was 12 μm.

6. The heating process for reducing surface decarburization of spring steel according to claim 1, characterized in that: The chemical components of the spring steel include by weight percentage: C 0.57%, Si 1.45%, Mn 0.68%, P0.015%, S 0.008%, Cr0.67%, and the rest are Fe and inevitable trace impurities, with a total weight fraction of 100%.

7. The heating process for reducing surface decarburization of spring steel according to claim 6, characterized in that: When heating the billet, the heating temperature is controlled at 970°C, the heating rate is 12°C / min, the two-phase region is passed quickly, the residence time is reduced to 8 minutes, and the formation of the grain boundary ferrite decarburization layer is avoided; The holding time is controlled at 1.7 hours to ensure that the austenite structure is fully homogenized and the surface decarburization reaction is effectively slowed down; After heating, the billet is quickly taken out and cooled to room temperature by air cooling, and the surface oxide layer is thin and uniform; Analysis using a metallographic microscope showed that the total decarburization layer thickness of the steel billet was 72 μm, of which the ferrite decarburization layer thickness was 10 μm.

8. The heating process for reducing surface decarburization of spring steel according to claim 1, characterized in that: The chemical components of the spring steel include by weight percentage: C 0.53%, Si 1.55%, Mn 0.63%, P 0.017%, S 0.010%, Cr 0.62%, and the rest are Fe and inevitable trace impurities, with a total weight fraction of 100%.

9. The heating process for reducing surface decarburization of spring steel according to claim 8, characterized in that: When heating the billet, the heating temperature is controlled at 980℃, the heating rate is 15℃ / min, the billet passes through the two-phase zone quickly, the residence time is reduced to 6 minutes, and the formation of decarburized layer is effectively reduced; The holding time is controlled at 1.5 hours, which not only ensures the homogenization of the structure but also inhibits the surface decarburization; After heating, the billet is quickly taken out and cooled to room temperature by air cooling. The oxide layer is well controlled and the surface is smooth. Analysis using a metallographic microscope showed that the total decarburization layer thickness of the steel billet was 70 μm, of which the ferrite decarburization layer thickness was 8 μm.