A rolling production method for improving internal defects of medium carbon nickel / sulfur steel

Abstract

The present application belongs to the field of special steel production and processing in the metallurgical industry, and provides a rolling production method for improving internal defects of medium-carbon nickel / sulfur-containing steel. The method uses preheating and slow heating for production, improves the internal quality of nickel / sulfur-containing steel (internal cracks, shrinkage holes and other defects) under the premise of not changing the organizational performance of the steel, greatly increases the yield of medium-carbon nickel / sulfur-containing steel, improves the core quality and saves the production cost.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of special steel production and processing in the metallurgical industry, and relates to a continuous casting and heating rolling process, in particular to a rolling production method for improving internal defects of medium-carbon nickel / sulfur-containing steel. BACKGROUND

[0002] With the rapid development of China's economy, the domestic and foreign automobile manufacturing industry is also rapidly progressing and developing. Under this background, the number and variety of automobile steels are also increasing, and the demand for the surface and internal quality of steel is also continuously improving. Although high-nickel steel or nickel-containing and sulfur-containing steel has good hardenability, easy machinability, strong toughness and other mechanical properties, and also has good welding performance, and nickel-containing steel has been the main product of automobile steel at home and abroad, mainly used in gear, shaft and other parts. However, the phase transformation region of medium-carbon nickel / sulfur-containing steel is prone to produce unbalanced structure, produce large stress or sulfide aggregation due to billet problems, and the core quality rolling is unable to completely weld.

[0003] The document "Research on Hot Ductility of High Nickel Steel Billet" (Gao Yong, Tian Yong, Zhu Yingguang, Dong Enlong, Hao Sen, Li Yiyi, Ansteel Group Anshan Iron and Steel Co., Ltd., Institute of Metal, Chinese Academy of Sciences) uses data simulation to conduct hot ductility experiments on high nickel steel billets, obtains a high nickel steel hot ductility mathematical model, and based on the experimental results, uses finite element method to simulate and optimize the continuous casting process of high nickel steel. The document obtains that the high nickel steel billet can improve the pulling speed and superheat, ensure that the corner temperature of the straightening section billet is above the critical temperature, and can prevent the generation of cracks, but does not explain the improvement of internal quality, and does not involve the control and improvement of internal quality in the rolling production process.

[0004] The document "Analysis of Influencing Factors and Countermeasures of Internal Quality of Hot Rolled Bearing Steel GCr15" (Shi Qiuying, Lu Dengyao, Xining Special Steel Group Co., Ltd., Zhongtian Iron and Steel Group Co., Ltd.) reports the shrinkage cavity, carbide liquation and micro-pore defects of continuous casting bearing steel, which are mainly determined by high-temperature diffusion during continuous casting and heating, and the initial deformation amount during rolling. The continuous casting superheat is controlled within the range of 20-30℃, the end electromagnetic stirring is used and the ideal position is ensured, the heating temperature is maintained at 1180-1220℃, the rolling pace of the 150mm×150mm section of the continuous casting billet is controlled at 1.0 branch / min, the rolling pace of the 180mm×220mm section is controlled at 2.0 branch / min, the compression ratio is controlled at ≤12, and the rolling compression ratio of the initial rolling 7 passes is controlled at 5.0 or more, which can reduce or eliminate the shrinkage cavity, carbide liquation and micro-pore.

[0005] The low-multiple test results of the microalloyed steel continuous casting billet with and without the end electromagnetic stirring (F-EMS) in the document "Influence of End Electromagnetic Stirring on Macrostructure and Microstructure of Continuous Casting Billet" (Zhang Zhiyuan, Zeng Zhaohui, Ning Mei, Lu Juguai, Sun Meihong, Yang Cuili, Lu Hong) show that the columnar crystal zone of the billet without the end EMS is relatively developed and accounts for a large proportion; the end EMS is started, the center porosity is dispersedly distributed in a large area in the core of the billet, the columnar crystal is partially broken, and there is an obvious white segregation band at about one-half radius of the billet.

[0006] Through literature retrieval and patent query, there is no mention of the improvement of the internal cracks, shrinkage holes and other defects of the medium-carbon nickel / sulfur-containing steel in rolling production. SUMMARY

[0007] To solve the problem that the internal cracks, shrinkage holes and other defects of the medium-carbon nickel / sulfur-containing steel need to be improved in rolling production in the prior art, the application provides a rolling production method for improving the internal defects of the medium-carbon nickel / sulfur-containing steel, which greatly increases the yield of the medium-carbon nickel / sulfur-containing steel without changing the microstructure and performance of the steel under the premise of improving the internal quality problems (internal cracks, shrinkage holes and other defects) of the nickel / sulfur-containing steel, improves the core quality and saves the production cost.

[0008] To achieve the above-mentioned purpose, the technical scheme of the application is as follows:

[0009] A rolling production method for improving the internal defects of a medium-carbon nickel / sulfur-containing steel, the rolling production method comprising sequentially processing the raw material through the following processing procedures: continuous casting billet, heating, dephosphorization, rough rolling, continuous rolling, bar reducing and finishing rolling, slow cooling and ultrasonic flaw detection, and finally obtaining a finished bar;

[0010] The heating is divided into four heating sections, which are a preheating section, a first heating section, a second heating section and a soaking section in sequence, and the temperature rising rate of each section is not more than 5 ℃ / min (such as 5 ℃ / min, 4.5 ℃ / min, 4 ℃ / min, 3.5 ℃ / min, 3 ℃ / min, 2.5 ℃ / min, 2 ℃ / min, 1.5 ℃ / min, 1 ℃ / min, 0.5 ℃ / min);

[0011] The preheating section temperature is ≤650℃ (e.g., 645℃, 640℃, 635℃, 630℃, 625℃, 620℃, 615℃, 610℃, 600℃), the first heating section temperature is 800~850℃ (e.g., 805℃, 810℃, 815℃, 820℃, 825℃, 830℃, 835℃, 840℃, 845℃), and the second heating section temperature is 1100℃. ~1130℃ (e.g., 1105℃, 1110℃, 1115℃, 1120℃, 1125℃, 1128℃), and the temperature of the heat spreader is 1180~1220℃ (e.g., 1181℃, 1185℃, 1189℃, 1191℃, 1195℃, 1199℃, 1201℃, 1205℃, 1209℃, 1211℃, 1215℃, 1219℃).

[0012] This invention employs a preheating and slow heating method to produce rolled medium-carbon nickel / sulfur steel, which improves the shrinkage cavity defect problem in medium-carbon nickel / sulfur steel and greatly increases the yield of medium-carbon nickel / sulfur steel, thereby improving core quality and saving production costs.

[0013] In medium-carbon nickel / sulfur steel, the primary carbides formed during continuous casting of the billet are Fe3C, resulting in dendritic segregation. During heating, the carbides cannot dissolve and diffuse, leading to liquefaction within the steel. If the heating rate is too fast or the temperature is too high, the carbides melt into a liquid or semi-liquid state, forming intergranular cracks or intergranular tearing under external force. If these cracks cannot be welded together during subsequent rolling, they are highly prone to forming defects such as micropores and shrinkage cavities.

[0014] Since segregation mainly occurs during the solidification stage of the steel billet, the movement of molten steel can be enhanced by induced electromagnetic forces in the molten core of the billet, thereby affecting the convection, heat transfer, and mass transfer processes, and thus influencing the solidification process. Furthermore, high-temperature diffusion can improve segregation. Therefore, controlling the heating temperature and holding time can inhibit the growth and aggregation of sulfides, improving core quality. In particular, controlling the heating rate to no more than 5℃ / min can improve segregation and prevent excessively rapid heating, which can easily lead to the aggregation of sulfides in the steel core and cause excessive temperature gradients within the billet, resulting in increased stress and deformation, and potentially causing core cracks or core-limiting pores.

[0015] The method of this invention is applicable to the continuous casting and hot rolling production of all steels containing Ni and S raw materials, especially when the Ni content in the raw materials is ≥0.7% and the S content is ≥0.02%. It can significantly improve internal quality problems of the steel, such as internal cracks and shrinkage cavities, while greatly increasing the yield.

[0016] Further, the Ni content in the raw material is 0.7%-5.0% (e.g., 0.8%, 0.9%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%), and the S content is 0.02%-2% (e.g., 0.03%, 0.05%, 0.07%, 0.09%, 0.11%, 0.13%, 0.15%, 0.17%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 1.9%).

[0017] Further, the raw material is 39NiCrMoS3, wherein carbon comprises 0.35%–0.44% (e.g., 0.36%, 0.37%, 0.38%, 0.39%, 0.40%, 0.41%, 0.42%, 0.43%) and silicon comprises 0.2%–0.42% (e.g., 0.21%, 0.23%, 0.25%, 0.28%, 0.31%, 0.33%, 0.35%, 0.37%). 0.39%, 0.41%); Manganese 0.50%–0.83% (e.g., 0.51%, 0.53%, 0.55%, 0.57%, 0.59%, 0.61%, 0.63%, 0.65%, 0.67%, 0.69%, 0.71%, 0.73%, 0.75%, 0.77%, 0.79%, 0.81%); Phosphorus ≤0.025% (e.g., 0.024%, 0.022%). 0.020%, 0.018%, 0.016%, 0.014%, 0.012%, 0.01%); Sulfur 0.02%–0.05% (e.g., 0.021%, 0.023%, 0.025%, 0.030%, 0.035%, 0.04%, 0.045%, 0.047%, 0.049%); Chromium 0.7%–1.10% (e.g., 0.75%, 0.8%, 0.01%). 85%, 0.9%, 0.95%, 1.0%, 1.05%); Nickel 0.7%–1.20% (e.g., 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1.0%, 1.05%, 1.10%, 1.15%); Molybdenum 0.16%–0.3% (e.g., 0.17%, 0.19%, 0.21%, 0.23%, 0.25%, 0.27%, 0.29%).

[0018] Furthermore, the heat preservation time of the preheating section is ≥120 min (e.g., 130 min, 150 min, 170 min, 180 min, 190 min, 200 min, 210 min, 220 min, 230 min, 240 min), and the heating rate is 0.6℃ / min.

[0019] Further, the heating first section has a temperature increasing rate of 3℃ / min and a holding time of 100-120min (e.g. 101min, 103min, 105min, 107min, 109min, 111min, 113min, 115min, 117min, 119min). Preferably, the temperature of the heating first section is 800-820℃.

[0020] Further, the heating second section has a temperature increasing rate of 5℃ / min and a holding time of 80-120min (e.g. 85min, 90min, 95min, 100min, 105min, 110min, 115min).

[0021] Further, the heating second section has a temperature increasing rate of 5℃ / min and a holding time of 80-120min (e.g. 85min, 90min, 95min, 100min, 105min, 110min, 115min).

[0022] In the above technical solution, the holding time of each stage is controlled, which further inhibits the growth and aggregation of sulfides and improves the core quality.

[0023] Further, in the phosphorus removal process, high-pressure water is used to remove surface iron oxide scale, and the high-pressure water has a pressure of 26-30MPa (e.g. 26.5MPa, 27MPa, 27.5MPa, 28MPa, 28.5MPa, 29MPa, 29.5MPa), preferably 28-30MPa (e.g. 28.5MPa, 29MPa, 29.5MPa).

[0024] Further, in the rough rolling process, the inlet temperature is generally 1000-1050℃ (e.g. 1005℃, 1015℃, 1020℃, 1025℃, 1030℃, 1035℃, 1040℃, 1045℃), and the rough rolling pass is 5-7 passes, preferably 6 passes.

[0025] Further, the continuous rolling process includes a medium rolling process and a pre-precision rolling process, and the continuous rolling process obtains a suitable incoming material for bar reducing sizing. The medium rolling inlet temperature is 900-950℃ (e.g. 905℃, 910℃, 915℃, 920℃, 925℃, 930℃, 935℃, 940℃, 945℃).

[0026] Further, the medium rolling pass is 5-7 passes, preferably 6 passes, and the pre-precision rolling pass is 2-4 passes, preferably 4 passes.

[0027] Further, in the process of the bar reducing sizing and finishing rolling, the bar reducing sizing and finishing rolling is KOCKS unit rolling, and / or the finish rolling temperature is 800-850 DEG C (such as 805 DEG C, 810 DEG C, 815 DEG C, 820 DEG C, 825 DEG C, 830 DEG C, 835 DEG C, 840 DEG C, 845 DEG C).

[0028] Further, in the process of the slow cooling, the bar after the bar reducing sizing and finishing rolling is preferably rapidly discharged on a cooling bed to carry out pit cooling, and the discharging temperature is greater than or equal to 400 DEG C (such as 405 DEG C, 410 DEG C, 420 DEG C, 430 DEG C, 440 DEG C, 450 DEG C, 460 DEG C, 470 DEG C, 480 DEG C, 490 DEG C, 500 DEG C, 520 DEG C, 550 DEG C), preferably greater than or equal to 450 DEG C (such as 455 DEG C, 460 DEG C, 470 DEG C, 480 DEG C, 490 DEG C, 500 DEG C, 520 DEG C, 550 DEG C).

[0029] Further, the process of the ultrasonic flaw detection is automatic ultrasonic flaw detection, and the flaw detection standard is GB / T4162 A-level standard. The automatic ultrasonic flaw detection is carried out by using a GE ultrasonic flaw detector.

[0030] Further, the diameter of the finished bar is 50-110 mm (such as 55 mm, 60 mm, 65 mm, 70 mm, 75 mm, 80 mm, 85 mm, 90 mm, 95 mm, 100 mm, 105 mm).

[0031] Compared with the prior art, the present application has the following positive effects:

[0032] The rolling production method optimizes the continuous casting and heating process, can improve the internal quality problems (such as internal cracks, shrinkage holes and other defects) of the nickel / sulfur-containing steel, meanwhile does not change the organization and performance of the steel, saves the production cost, and improves the yield of the medium-carbon nickel / sulfur-containing steel. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The macrograph of the medium-carbon nickel / sulfur-containing steel produced in Example 4 of the present application;

[0034] Figure 2 The crystal phase organization photograph (one) of the medium-carbon nickel / sulfur-containing steel produced in Example 4 of the present application;

[0035] Figure 3 The crystal phase organization photograph (two) of the medium-carbon nickel / sulfur-containing steel produced in Example 4 of the present application;

[0036] Figure 4 The macrograph of the medium-carbon nickel / sulfur-containing steel produced in Comparative Example 2 of the present application;

[0037] Figure 5 The crystal phase organization photograph (one) of the medium-carbon nickel / sulfur-containing steel produced in Comparative Example 2 of the present application;

[0038] Figure 6 Crystal phase structure photograph (two) of medium carbon nickel-sulfur containing steel produced for the present application comparative example 2. DETAILED DESCRIPTION

[0039] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described below in conjunction with examples. The examples of the present application are implemented on the premise of the technical solutions of the present application, and detailed implementation manners and processes are given. It should be understood by those skilled in the art that the examples are only used to help understand the present application, and should not be regarded as a specific limitation on the present application, and the protection scope of the present application is not limited to the following examples. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0040] Unless otherwise specified and / or described, all numerical values involving the amount of components are "molar or mass numerical values or ratios" throughout. Unless otherwise specified, the raw materials used in the present application can be obtained from commercially available products.

[0041] In the present application, the endpoints of the ranges and any values disclosed are not limited to the precise values or points stated. These ranges or values should be interpreted as including values proximate to the recited ranges or points. For ranges, the endpoints are included within the range, and the endpoints are included with the individual points within the range, and the individual points are included within the range. Any numerical values, however, should be understood to include any and all combinations of two or more values.

[0042] The present application adopts the technical principle of pre-heating and slow heating to produce medium carbon nickel-sulfur containing steel:

[0043] Primary carbide is mainly Fe3C during continuous casting of the steel billet, which produces dendritic segregation. During the heating process, the carbide cannot dissolve and diffuse, and liquid segregation is generated inside the steel. If the heating speed is too fast and the heating temperature is too high, the carbide melts into liquid or semi-liquid state, and intergranular cracks or intergranular tearing are formed under the action of external force. If the intergranular cracks or intergranular tearing cannot be welded in the subsequent rolling process, micro-pores, shrinkage holes and other defects are easily formed.

[0044] Since the main formation stage of liquid segregation is generated in the solidification stage of the smelted billet, the molten steel movement can be strengthened by means of the induced electromagnetic force in the liquid core of the casting billet, so as to affect the processes of convection, heat transfer and mass transfer of the molten steel, thereby affecting the solidification process. The segregation condition can also be improved through high-temperature diffusion, so that the heating temperature and the holding time are controlled, the growth and aggregation of sulfides are inhibited, and the core quality is improved; in particular, the temperature rising rate is controlled to be not more than 5℃ / min, the segregation condition is improved, and the aggregation of sulfides in the core of the steel material is avoided, and at the same time, the temperature difference gradient in the internal steel billet is too large, which can cause the increase of the stress and deformation of the steel billet, and can cause the generation of core cracks or core limiting pore defects.

[0045] Finally, the above-mentioned principle is used to produce the rolled medium-carbon nickel / sulfur-containing steel, the shrinkage hole defect problem of the medium-carbon nickel / sulfur-containing steel is improved, the yield of the medium-carbon nickel / sulfur-containing steel is greatly increased, the core quality is improved, and the production cost is saved.

[0046] The present application produces a medium-carbon nickel / sulfur-containing steel material for rolling, which is mainly for the medium-carbon nickel / sulfur-containing steel material with [Ni] content of 0.7%-5.0% and [S] content of ≥0.02% in the chemical composition.

[0047] The present application provides the following specific embodiments:

[0048] A rolling production method for improving internal defects of medium-carbon nickel / sulfur-containing steel, taking 39NiCrMoS3 as raw material, and sequentially passing through the following processing procedures: continuous casting billet, heating, dephosphorization, rough rolling, continuous rolling, bar reducing and sizing unit finishing rolling, slow cooling and ultrasonic flaw detection, and finally obtaining finished bar.

[0049] The rolling production method specifically comprises the following steps:

[0050] (1) Continuous casting 39NiCrMoS3 billet: the raw material of the present application is continuous casting, that is, obtained through conventional smelting, refining and continuous casting procedures, and the obtaining method is not described in detail, but the raw material composition is as follows: carbon 0.35%-0.44%; silicon 0.2%-0.42%; manganese 0.50%-0.83%; phosphorus ≤0.025%; sulfur 0.02%-0.05%; chromium 0.7%-1.10%; nickel 0.7%-1.20%; molybdenum 0.16%-0.3%.

[0051] (2) billet heating: in turn, preheating section, heating section one, heating section two, soaking section, wherein, the preheating section temperature≤650℃, the heating rate is 0.6℃ / min, the holding time≥120min; the heating section one temperature is 800~850℃, preferably 800~820℃, the heating rate is 3℃ / min, the holding time is 100~120min; the heating section two temperature is 1100~1130℃, the heating rate is 5℃ / min, the holding time is 80~120min; the soaking section temperature is 1180~1220℃, the heating rate is 5℃ / min, the holding time is 80~120min, preferably the holding time is 80min.

[0052] (3) billet dephosphorization: high pressure water is used to remove surface iron oxide skin, the high pressure water pressure is 26~30MPa, preferably 28~30MPa.

[0053] (4) billet rough rolling: after the billet dephosphorization, the billet enters the rough rolling mill, the inlet temperature is generally 1000~1050℃, the rough rolling pass is 5~7 passes, preferably 6 passes, the rough rolling billet is obtained by large reduction rough rolling mill, wherein, the large reduction is that the maximum reduction reaches 60mm.

[0054] (5) rolling billet continuous rolling: the obtained rough rolling billet is sent to the continuous rolling mill for rolling, the continuous rolling process includes the medium rolling process and the pre-precision rolling process, the obtained material after the continuous rolling is suitable for entering the bar reducing diameter, wherein, the medium rolling pass is 5~7 passes, preferably 6 passes, the pre-precision rolling pass is 2~4 passes, preferably 4 passes, the medium rolling inlet temperature is 900~950℃.

[0055] (6) material precision rolling: the precision rolling is the bar reducing diameter, the bar reducing diameter precision rolling is the KOCKS mill rolling, the finish rolling temperature is 800~850℃.

[0056] (7) slow cooling: after the bar reducing diameter precision rolling, the obtained bar is rapidly offline on the cooling bed for pit cooling, wherein, the offline temperature≥400℃, preferably≥450℃.

[0057] (8) automatic flaw detection: the automatic flaw detection process is that the GE ultrasonic flaw detector is used for automatic ultrasonic flaw detection, the flaw detection standard is GB / T4162 A level standard for internal flaw detection of the steel, and the finished bar is obtained.

[0058] The inventors find that the medium carbon nickel / sulfur steel with good structure can be obtained by the above implementation method, and the internal quality is obviously improved. The overall structure does not change, and is more uniform.

[0059] The technical solutions in the embodiments of the present application will be clearly and completely described below, so that those skilled in the art can practice and reproduce. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art belong to the scope of protection of the present application.

[0060] Embodiments 1-9

[0061] A rolling production method for improving internal defects of medium-carbon nickel / sulfur steel, and the specific steps are as follows:

[0062] (1) Control the final stirring current to be 400 A, the overheating degree to be 40 DEG C, and the drawing speed to be 0.53 mm / min, so as to obtain 39NiCrMoS3 continuous casting billets;

[0063] (2) Billet heating: sequentially including a preheating section, a first heating section, a second heating section, and a soaking section, wherein the preheating section temperature is less than or equal to 650 DEG C, the temperature rising rate is 0.6 DEG C / min, and the holding time is greater than or equal to 120 min; the first heating section temperature is 800-850 DEG C, the temperature rising rate is 3 DEG C / min, and the holding time is 120 min; the second heating section temperature is 1100-1130 DEG C, the temperature rising rate is 5 DEG C / min, and the holding time is 80 min; and the soaking section temperature is 1180-1220 DEG C, the temperature rising rate is 5 DEG C / min, and the holding time is 80 min.

[0064] (3) Billet phosphorus removal: high-pressure water is used to remove the surface iron oxide scale, and the high-pressure water pressure is 29 MPa.

[0065] (4) Billet rough rolling: after the billet is subjected to phosphorus removal, the billet enters a rough rolling mill, the inlet temperature is generally 1000 DEG C, the rough rolling is performed for 6 passes, and a rough rolling billet is obtained by passing through a large reduction rough rolling mill, wherein the large reduction is that the maximum reduction reaches 60 mm.

[0066] (5) Billet continuous rolling: the obtained rough rolling billet is sent to a continuous rolling mill for rolling, the continuous rolling process includes a medium rolling process and a pre-precision rolling process, and a suitable incoming material for bar reducing is obtained after continuous rolling, wherein the medium rolling is performed for 6 passes, the pre-precision rolling is performed for 4 passes, and the medium rolling inlet temperature is 900 DEG C.

[0067] (6) Incoming material precision rolling: the precision rolling is bar reducing, the bar reducing precision rolling is KOCKS mill rolling, and the final rolling temperature is 825 DEG C.

[0068] (7) Slow cooling: after the bar reducing precision rolling, the bar is rapidly discharged to the cooling bed for pit cooling, wherein the discharging temperature is 500 DEG C.

[0069] (8) Automatic flaw detection: the automatic flaw detection process is automatic ultrasonic flaw detection by using a GE ultrasonic flaw detector, the flaw detection standard is GB / T4162 A-level standard for internal flaw detection of the steel, and a finished product bar with a diameter of 110 mm is obtained.

[0070] Among them, the only difference between Examples 1 to 9 is the difference in the preheating section temperature, the heat preservation time and the heat soaking section temperature in (2). The specific parameters and results can be seen in Table 1.

[0071] Table 1

[0072] Item Soaking zone measured temperature / °C Preheating zone measured temperature / °C Preheating zone holding time / min Core pass rate Example 1 1190-1210 632 120 98％ Example 2 1180-1190 648 120 95％ Example 3 1190-1210 649 120 94％ Example 4 1190-1210 630 120 98％ Example 5 1210-1220 649 120 91％ Example 6 1190-1210 623 120 100％ Example 7 1190-1210 643 120 94％ Example 8 1190-1210 642 150 96％ Example 9 1190-1210 631 121 97％

[0073] Comparative Examples 1-9

[0074] A rolling production method for improving internal defects of medium carbon nickel / sulfur steel is different from the embodiment only in the difference of the preheating temperature and holding time and the soaking temperature in (2). The specific parameter variables and results can be seen in Table 2.

[0075] Table 2

[0076] Item Soaking zone measured temperature / °C Preheating zone measured temperature / °C Preheating zone holding time / min Core pass rate Comparative Example 1 1221-1240 649 120 63％ Comparative Example 2 1160-1179 648 120 54％ Comparative Example 3 1180-1190 663 120 83％ Comparative Example 4 1190-1210 687 120 46％ Comparative Example 5 1190-1210 660 120 50％ Comparative Example 6 1150-1179 741 80 26％ Comparative Example 7 1150-1179 698 70 44％ Comparative Example 8 1210-1240 671 95 75％ Comparative Example 9 1210-1240 659 90 77％

[0077] As can be seen from the test data in Tables 1 and 2, the method of this invention can yield medium-carbon nickel / sulfur steel with a better microstructure, and its internal quality is significantly improved. The overall microstructure remains unchanged and is relatively uniform. The low-magnification photographs and crystal phase microstructure photographs of the medium-carbon nickel / sulfur steel obtained in Example 4 are shown below. Figure 1-3 As shown, the low-magnification photograph and crystal phase structure photograph of the medium-carbon nickel / sulfur steel obtained in Comparative Example 2 are as follows: Figure 4-6 As shown. From Figure 3 and Figure 6 It can be seen that the microstructure under both different experimental conditions was F+P (ferrite + pearlite), with a small amount of B (bainite) microstructure. The microstructure and properties of the steel did not undergo phase transformation under temperature changes during rolling, therefore the microstructure and properties remained unchanged. Furthermore, through... Figure 2 and Figure 5 A comparison shows that, Figure 5 The tissue is uneven. Figure 2 The tissue is relatively uniform.

[0078] Specifically, as can be seen from the test data in Tables 1 and 2, the core qualification rate of the materials obtained in Examples 1, 3, 4, 6, 9 and Comparative Examples 4 and 5, and the materials obtained in Examples 2 and Comparative Example 3, decreased as the preheating temperature increased, even when the temperature of the soaking zone was the same and the holding time of the preheating zone was basically the same. This shows that the preheating temperature has a crucial impact on the core quality and should not be too high. Furthermore, the comparison with the comparative examples shows that the core quality is significantly improved when the preheating temperature is less than 650°C.

[0079] The core qualified rate of the materials obtained in Examples 2, 3, 5 and Comparative Examples 1, 2 increases first and then decreases with the increase of the soaking zone temperature under the condition that the preheating zone temperature is substantially the same and the soaking time is the same, and the core qualified rate greatly increases and the core quality is obviously improved when the soaking zone temperature is between 1180℃ and 1220℃. This is because that the insufficient diffusion, the aggregation of sulfides in the core of the steel material and / or the too large temperature difference gradient in the steel billet may cause the increase of the stress and deformation of the steel billet, and the core crack or core limited porosity defects may be generated when the soaking zone temperature is too low; and the too large temperature difference gradient, the increase of the stress and deformation may easily cause the core defects when the soaking zone temperature is too high. Therefore, the soaking zone temperature of 1180℃ to 1220℃ is very important to the core quality.

[0080] The core qualified rate of the materials obtained in Examples 7, 8 increases with the increase of the preheating zone soaking time under the condition that the soaking zone temperature is the same and the preheating zone temperature is substantially the same, and thus it can be seen that the appropriate prolongation of the preheating zone soaking time can improve the core quality.

[0081] In addition, the core qualified rate of the materials obtained in Examples and Comparative Examples 6-9 can be compared, and it can be seen that the core qualified rate of the materials obtained in Comparative Examples 6, 7 is not as good as that of Comparative Examples 8, 9, and is not as good as that of Examples in which the preheating zone temperature is ≤650℃, the soaking time is ≥120min and the soaking zone temperature is 1180-1220℃. The above only describes the preferred embodiments of the present application and is not used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application is within the protection scope of the claims of the present application.

Claims

1. A rolling production method for improving internal defects in medium-carbon nickel / sulfur steel, characterized in that, The rolling production method includes processing the raw materials sequentially through the following steps: continuous casting billet, heating, descaling, rough rolling, continuous rolling, bar sizing and finishing rolling, slow cooling and ultrasonic testing, finally obtaining the finished bar. The heating process is divided into four stages: preheating, heating stage one, heating stage two, and homogenization stage. The heating rate in each stage does not exceed 5°C / min. The temperature of the preheating section is ≤650℃, the temperature of the first heating section is 800~850℃, the temperature of the second heating section is 1100~1130℃, and the temperature of the heat spreader section is 1180~1220℃. The raw material is 39NiCrMoS3, wherein: carbon 0.35%~0.44%; silicon 0.2%~0.42%; manganese 0.50%~0.83%; phosphorus ≤0.025%; sulfur 0.02%~0.05%; chromium 0.7%~1.10%; nickel 0.7%~1.20%; molybdenum 0.16%~0.3%; The heat preservation time of the preheating section is ≥120 min; The holding time for the heating section is 100-120 minutes; The heat preservation time for the second heating stage is 80–120 min; The heat preservation time of the heat-spreading section is 80-100 minutes.

2. The rolling production method as described in claim 1, characterized in that, The heating rate of the preheating section is 0.6℃ / min.

3. The rolling production method as described in claim 1, characterized in that, The heating rate of the heating section is 3℃ / min.

4. The rolling production method according to any one of claims 1-3, characterized in that, The heating rate of the second heating stage is 5℃ / min.

5. The rolling production method as described in claim 1, characterized in that, The heating rate of the heat spreader is 5℃ / min.

6. The rolling production method as described in claim 1, characterized in that, In the dephosphorization process, high-pressure water is used to remove the surface iron oxide scale, and the pressure of the high-pressure water is 26-30 MPa. And / or, in the roughing process, the inlet temperature is 1000-1050℃, and the number of roughing passes is 5-7; And / or, the continuous rolling process includes intermediate rolling and pre-finishing rolling processes, and after continuous rolling, a material suitable for bar sizing is obtained. The intermediate rolling inlet temperature is 900-950°C, the intermediate rolling passes are 5-7, and the pre-finishing rolling passes are 2-4. And / or, in the bar reduction sizing finishing rolling process, the bar reduction sizing finishing rolling is performed by a KOCKS mill, and the final rolling temperature is 800-850℃; And / or, in the slow cooling process, after the bar is sizing and precision rolled, the bar is quickly removed from the cooling bed for pit cooling, and the removal temperature is ≥400℃; And / or, the ultrasonic testing process is automated ultrasonic testing, and the testing standard is GB / T4162 Class A standard.

7. The rolling production method as described in claim 6, characterized in that, The high-pressure water pressure is 28–30 MPa.

8. The rolling production method as described in claim 6, characterized in that, The roughing rolling process consists of 6 passes.

9. The rolling production method as described in claim 6, characterized in that, The number of intermediate rolling passes is 6.

10. The rolling production method as described in claim 6, characterized in that, The pre-finishing rolling passes are 4 passes.

11. The rolling production method as described in claim 6, characterized in that, The lower temperature is ≥450℃.

12. The rolling production method as described in claim 1, characterized in that, The diameter of the finished bar is 50-110mm.

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