Decarburization control method for producing 45 strip steel by using hot continuous rolling unit

Abstract

The invention relates to the technical field of carbon structural steel production, in particular to a decarburization control method for producing 45 strip steel through a hot continuous rolling unit. The method comprises the following steps: 1) setting the width of a furnace blank to be W, mm; the thickness is D, mm; w is not less than 700mm and not more than 1430mm, and D is not more than 200mm; (2) the heating furnace is divided into a preheating section, a first heating section, a second heating section and a soaking section; the furnace temperature of a preheating section is not more than 850 DEG C, the furnace temperature of a first heating section is not more than 1200 DEG C, the furnace temperature of a second heating section is not more than 1350 DEG C, and the furnace temperature of a soaking section is more than 1200 DEG C and less than 1250 DEG C; 3) controlling the heating in-furnace time: controlling the total in-furnace time to be more than 160 minutes; (4) controlling the time of a heating interval: controlling the second heating section time and the soaking section time to be more than 60 minutes; and (5) the charging temperature and the discharging temperature are controlled, specifically, the charging temperature is controlled to be 300-700 DEG C, and the discharging temperature is controlled to be 1200-1250 DEG C. And a decarburized layer meets the decarburization requirement of high-quality 45 steel, and the quality of the 45 strip steel is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon structural steel production, and specifically to a decarburization control method for producing 45 strip steel by a hot continuous rolling mill. Background Art

[0002] 45 is the grade of steel. 45 steel is a high-quality carbon structural steel, which can be produced by a conventional hot rolling continuous mill. Its characteristics are higher strength and anti-deformation ability compared with ordinary A3 steel. When not heat-treated: HB≤229; heat treatment: normalizing; impact energy: Aku≥39J; it has relatively high strength, good plasticity and toughness. Before tempering after quenching of 45# steel plate, the hardness greater than HRC55 (up to HRC62 at most) is qualified. After heat treatment and then tempering, it can reach HRC42 - 46, which can not only ensure its good mechanical properties but also meet the surface hardness requirements. It is used to make small-section quenched and tempered parts with large loads, large-sized normalized parts with small stresses, and surface hardened parts with low requirements for the core strength. 45 steel is widely used in downstream industries such as saw blades and vehicle parts.

[0003] However, for 45 steel produced by a conventional hot rolling continuous mill, problems such as insufficient hardness in heat treatment, incomplete quenching, and processing fracture often occur during subsequent use. Through metallographic testing, it is found that severe decarburization on the surface of the strip steel raw material is one of the main reasons for subsequent processing cracking or fatigue failure. In a high-temperature environment, the decarburization on the surface layer exceeds the oxidation rate, resulting in severe decarburization, which affects the strength of the final product and causes the above-mentioned defects. Summary of the Invention

[0004] In order to overcome the deficiencies of the prior art, the present invention provides a decarburization control method for producing 45 strip steel by a hot continuous rolling mill, so that the decarburized layer meets the decarburization requirements of high-quality 45 steel and improves the quality of 45 strip steel.

[0005] To achieve the above purpose, the present invention is realized by adopting the following technical solutions:

[0006] A decarburization control method for producing 45 strip steel by a hot continuous rolling mill, and the 45 strip steel is composed of chemical components with the following weight percentages:

[0007] C: 0.45% - 0.48%, Si: 0.18% - 0.22%, Ti: 0.015% - 0.025%, Mn: 0.6% - 0.7%, and the balance is Fe and unavoidable impurities;

[0008] Specifically, it includes the following steps:

[0009] 1) The width of the furnace charge is W, in mm; the thickness is D, in mm;

[0010] Control: 700mm ≤ W ≤ 1430mm, D ≤ 200mm;

[0011] 2) The heating furnace is divided into a preheating section, a first heating section, a second heating section, and a soaking section;

[0012] Control the furnace temperature in the heating zones:

[0013] Furnace temperature in the preheating section ≤ 850°C, furnace temperature in the first heating section ≤ 1200°C, furnace temperature in the second heating section ≤ 1350°C, 1200 < furnace temperature in the soaking section < 1250°C;

[0014] 3) Control the residence time in the heating furnace:

[0015] Control the total residence time > 160 min;

[0016] 4) Control the time in the heating zones:

[0017] Control the time in the second heating section + the time in the soaking section > 60 min;

[0018] 5) Control the charging temperature and the discharging temperature:

[0019] Control the charging temperature to be 300°C - 700°C, and control the discharging temperature to be 1200°C - 1250°C.

[0020] Furthermore, the thickness of the 45 steel strip is D1, the decarburized layer thickness of the 45 steel strip is D2, and D2 < D1 × 15%.

[0021] Furthermore, in the chemical composition of the 45 steel strip by weight percentage: Ti: 0.018%.

[0022] Furthermore, in step 2), the heating furnace is a walking beam heating furnace.

[0023] Furthermore, in step 2), 500°C ≤ furnace temperature in the preheating section ≤ 850°C, 1000°C ≤ furnace temperature in the first heating section ≤ 1200°C, 1200°C ≤ furnace temperature in the second heating section ≤ 1350°C, 1200 < furnace temperature in the soaking section < 1250°C.

[0024] Furthermore, in step 3), control the total residence time > 165 min.

[0025] Furthermore, in step 4), control the time in the second heating section + the time in the soaking section > 65 min.

[0026] Furthermore, in step 5), control the charging temperature to be 320°C - 700°C.

[0027] Furthermore, in step 5), control the discharging temperature to be 1220°C - 1250°C.

[0028] Compared with the existing methods, the beneficial effects of the present invention are as follows:

[0029] 1. The present invention improves the steel burning process of the conventional walking beam reheating furnace for hot continuous rolling, and controls the in-furnace time of each section and the total in-furnace time according to the furnace inlet temperature. First, by controlling the heating system of the reheating furnace, the decarburization sensitive temperature range of the billet for 45 steel is avoided and minimized as much as possible; then, by controlling the heating temperature and residence time of each section of walking beam preheating, the first heating stage and the second heating stage, the residence time of the billet in the decarburization sensitive temperature section is reduced, the generation of the decarburized layer is reduced, the requirements of downstream users for processing and use are met, the product quality is improved, and the decarburization requirements of high-quality 45 steel are met. It has a good demonstration effect on the process adjustment and optimization of similar medium and high carbon products.

[0030] The heating production process for 45 steel is optimized, the heating process itself is innovated, and by controlling process parameters such as the relevant heating temperature, etc., the conditions for serious decarburization defects during the production process are reduced, the serious decarburization defects on the surface of the strip steel finished product are avoided, and the processing performance of users is improved.

[0031] By adopting the method described in the present invention, the thickness of the decarburized layer of the strip steel is less than 1.5% of the strip steel thickness. Furthermore, the hardness and wear resistance of the parts are improved, the fatigue strength of the parts is enhanced, the generation of quenching cracks is reduced, and the service life of the parts is increased.

[0032] 2. The decarburization phenomenon of 45 steel is more obvious at temperatures of 950°C and above. That is, before 950°C, the thickness of the decarburized layer increases rapidly with the increase of temperature, but after exceeding 950°C, the thickness of the decarburized layer decreases significantly with the increase of temperature, because the decarburized layer can only be formed when the decarburization speed exceeds the oxidation speed. When the oxidation speed is very high, obvious decarburization may not occur, that is, after the decarburized layer is generated, the iron is oxidized into scale.

[0033] The present invention controls the temperature of the preheating section at ≤850°C. Since the preheating section belongs to a strong oxygen atmosphere, the oxidation speed can be significantly increased, the generation of the decarburized layer can be avoided, and the decarburization sensitive period can be effectively avoided; after entering the heating and soaking sections, in order to further avoid the decarburized layer, the present invention selects to control the furnace temperature of the first heating section at ≤1200°C, the furnace temperature of the second heating section at ≤1350°C, and 1200°C < the furnace temperature of the soaking section < 1250°C; at the same time, control the total in-furnace time > 160 min, and control the time of the second heating section + the time of the soaking section > 60 min; to ensure the heating uniformity, avoid the coarsening of austenite grains during austenitization, reduce the brittle fracture rate, refine the grains, and be beneficial to improving the comprehensive mechanical properties of 45 steel. Brief Description of the Drawings

[0034] Figure 1 is the metallographic structure diagram of the present invention. Detailed Embodiments

[0035] The present invention discloses a decarburization control method for producing 45 strip steel by a hot continuous rolling mill. Those skilled in the art can draw on the content of this article and appropriately improve the process parameters to achieve it. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are all considered to be included in the present invention. The method and application of the present invention have been described through preferred embodiments, and relevant personnel can obviously make changes or appropriate alterations and combinations to the methods and applications described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0036] A decarburization control method for producing 45 strip steel by a hot continuous rolling mill, and the 45 strip steel is composed of chemical components with the following weight percentages:

[0037] C: 0.45% - 0.48%, Si: 0.18% - 0.22%, Ti: 0.015% - 0.025%, Mn: 0.6% - 0.7%, and the balance is Fe and inevitable impurities;

[0038] Specifically, it includes the following steps:

[0039] 1) The width of the slab charged into the furnace is W, in mm; the thickness is D, in mm;

[0040] Control 700mm ≤ W ≤ 1430mm, D ≤ 200mm;

[0041] 2) The heating furnace is divided into a preheating section, a first heating section, a second heating section, and a soaking section;

[0042] Control the furnace temperature in the heating zone:

[0043] The furnace temperature in the preheating section ≤ 850°C, the furnace temperature in the first heating section ≤ 1200°C, the furnace temperature in the second heating section ≤ 1350°C, 1200 < the furnace temperature in the soaking section < 1250°C;

[0044] 3) Control the residence time in the furnace during heating:

[0045] Control the total residence time > 160 min;

[0046] 4) Control the time in the heating zone:

[0047] Control the time in the second heating section + the time in the soaking section > 60 min;

[0048] 5) Control the charging temperature and the discharging temperature:

[0049] Control the charging temperature to be 300°C - 700°C, and control the discharging temperature to be 1200°C - 1250°C.

[0050] Furthermore, the thickness of the 45 strip steel is D1, and the thickness of the decarburized layer of the 45 strip steel is D2, D2 < D1 × 15%.

[0051] Further, in the chemical composition of the 45 strip steel by weight percentage: Ti: 0.018%.

[0052] Further, in step 2), the heating furnace is a walking beam heating furnace.

[0053] Further, in step 2), 500°C ≤ preheating section furnace temperature ≤ 850°C, 1000°C ≤ heating section 1 furnace temperature ≤ 1200°C, 1200°C ≤ heating section 2 furnace temperature ≤ 1350°C, 1200 < soaking section furnace temperature < 1250°C.

[0054] Further, in step 3), control the total time in the furnace > 165 min.

[0055] Further, in step 4), control the heating section 2 time + soaking section time > 65 min.

[0056] Further, in step 5), control the charging temperature to be 320°C to 700°C.

[0057] Further, in step 5), control the discharging temperature to be 1220°C to 1250°C.

[0058] Example 1:

[0059] A decarburization control method for producing 45 strip steel by a hot continuous rolling mill. The 45 strip steel is composed of the following chemical components by weight percentage:

[0060] C: 0.4517%, Si: 0.1906%, Si: 0.1906%, Ti: 0.018%, Mn: 0.6643%, P: 0.01813%, S: 0.00179%, and the balance is Fe and unavoidable impurities.

[0061] Specifically, it includes the following steps:

[0062] 1) The slab size is 200×1250×10500 mm, and the finished product thickness is 4.5 mm.

[0063] 2) Control the furnace temperature in the heating section:

[0064] Upper: Control the heating section 1 furnace temperature to be displaced by 1170°C, the heating section 2 furnace temperature to be 1310°C, and the soaking section furnace temperature to be 1250°C;

[0065] Lower: Control the heating section 1 furnace temperature to be displaced by 1160°C, the heating section 2 furnace temperature to be 1280°C, and the soaking section furnace temperature to be 1230°C.

[0066] 3) Control the time in the furnace during heating:

[0067] Control the total time in the furnace to be 164 min.

[0068] 4) Control the time of the heating section:

[0069] Control the sum of the second heating time and the soaking time to be 62 min;

[0070] 5) Control the charging temperature and the discharging temperature:

[0071] Control the charging temperature to be 732 °C and the discharging temperature to be 1242 °C.

[0072] In this embodiment, the thickness of the steel plate is 4.5 mm and the decarburized layer thickness is 0.016 mm.

[0073] Embodiment 2:

[0074] A decarburization control method for producing 45 strip steel by a hot continuous rolling mill. The 45 strip steel is composed of chemical components with the following weight percentages:

[0075] C: 0.4587%, Si: 0.2125%, Si: 0.1906%, Ti: 0.018%, Mn: 0.634%, P: 0.01258%, S: 0.00823%, and the balance is Fe and unavoidable impurities.

[0076] Specifically, it includes the following steps:

[0077] 1) The slab size is 200×1250×10500 mm, and the finished product thickness is 4.5 mm.

[0078] 2) Control the furnace temperature in the heating section:

[0079] Upper: Control the furnace temperature in the first heating section to be 1170 °C, the furnace temperature in the second heating section to be 1310 °C, and the furnace temperature in the soaking section to be 1250 °C;

[0080] Lower: Control the furnace temperature in the first heating section to be 1160 °C, the furnace temperature in the second heating section to be 1280 °C, and the furnace temperature in the soaking section to be 1230 °C.

[0081] 3) Control the time in the furnace during heating:

[0082] Control the total time in the furnace to be 164 min.

[0083] 4) Control the time of the heating section:

[0084] Control the sum of the second heating time and the soaking time to be 62 min;

[0085] 5) Control the charging temperature and the discharging temperature:

[0086] Control the charging temperature to be 732 °C and the discharging temperature to be 1242 °C.

[0087] In this embodiment, the thickness of the steel plate is 4.5 mm, and the thickness of the decarburized layer is 0.016 mm.

[0088] Example 3:

[0089] A decarburization control method for producing 45 steel strips by a hot continuous rolling mill. The 45 steel strip is composed of chemical components with the following weight percentages:

[0090] C: 0.4517%, Si: 0.1906%, Si: 0.1906%, Ti: 0.018%, Mn: 0.6643%, P: 0.01813%, S: 0.00179%, and the balance is Fe and unavoidable impurities;

[0091] Specifically, it includes the following steps:

[0092] 1) The slab size is 200×1250×10500 mm, and the finished thickness is 4.0 mm.

[0093] 2) Control the furnace temperature in the heating section:

[0094] Upper: Control the furnace temperature displacement in the first heating stage to 1170 °C, the furnace temperature in the second heating stage to 1310 °C, and the soaking section furnace temperature to 1250 °C;

[0095] Lower: Control the furnace temperature displacement in the first heating stage to 1160 °C, the furnace temperature in the second heating stage to 1280 °C, and the soaking section furnace temperature to 1230 °C.

[0096] 3) Control the residence time in the furnace during heating:

[0097] Control the total residence time in the furnace to 159 min.

[0098] 4) Control the time in the heating section:

[0099] Control the sum of the time in the second heating stage and the soaking section to 63 min;

[0100] 5) Control the charging temperature and the discharging temperature:

[0101] Control the charging temperature to 670 °C and the discharging temperature to 1234 °C.

[0102] In this embodiment, the thickness of the steel plate is 4.0 mm, and the thickness of the decarburized layer is 0.01 mm.

[0103] Example 4:

[0104] A decarburization control method for producing 45 steel strips by a hot continuous rolling mill. The 45 steel strip is composed of chemical components with the following weight percentages:

[0105] C: 0.4587%, Si: 0.2125%, Si: 0.1906%, Ti: 0.018%, Mn: 0.634%, P: 0.01258%, S: 0.00823%, the balance being Fe and unavoidable impurities.

[0106] Specifically, it includes the following steps:

[0107] 1) The slab size is 200×1250×10500 mm, and the finished product thickness is 4.0 mm.

[0108] 2) Control the furnace temperature in the heating zone:

[0109] Upper: Control the furnace temperature displacement in the first heating stage to 1170 °C, the furnace temperature in the second heating stage to 1310 °C, and the soaking stage furnace temperature to 1250 °C;

[0110] Lower: Control the furnace temperature displacement in the first heating stage to 1160 °C, the furnace temperature in the second heating stage to 1280 °C, and the soaking stage furnace temperature to 1230 °C.

[0111] 3) Control the residence time in the furnace during heating:

[0112] Control the total residence time in the furnace to 159 min.

[0113] 4) Control the time in the heating zone:

[0114] Control the time in the second heating stage + the soaking stage time to 63 min;

[0115] 5) Control the charging temperature and the discharging temperature:

[0116] Control the charging temperature to 670 °C and the discharging temperature to 1234 °C.

[0117] In this embodiment, the steel plate thickness is 4.0 mm, and the decarburized layer thickness is 0.01 mm.

[0118] Example 5:

[0119] A decarburization control method for producing 45 strip steel by a hot continuous rolling mill. The 45 strip steel is composed of chemical components with the following weight percentages:

[0120] C: 0.4517%, Si: 0.1906%, Si: 0.1906%, Ti: 0.018%, Mn: 0.6643%, P: 0.01813%, S: 0.00179%, the balance being Fe and unavoidable impurities;

[0121] Specifically, it includes the following steps:

[0122] 1) The slab size is 200×1250×10500 mm, and the finished product thickness is 4.0 mm.

[0123] 2) Control the furnace temperature in the heating zone:

[0124] Upper: Control the furnace temperature displacement in the first heating stage at 1170 °C, the furnace temperature in the second heating stage at 1310 °C, and the soaking section furnace temperature at 1250 °C;

[0125] Lower: Control the furnace temperature displacement in the first heating stage at 1160 °C, the furnace temperature in the second heating stage at 1280 °C, and the soaking section furnace temperature at 1230 °C.

[0126] 3) Control the residence time in the furnace during heating:

[0127] Control the total residence time in the furnace to be 173 min.

[0128] 4) Control the time in the heating zone:

[0129] Control the time in the second heating stage + the soaking section time to be 78 min;

[0130] 5) Control the charging temperature and the discharging temperature:

[0131] Control the charging temperature to be 333 °C and the discharging temperature to be 1220 °C.

[0132] In this embodiment, the thickness of the steel plate is 4.0 mm and the decarburized layer thickness is 0.008 mm.

[0133] Example 6:

[0134] A decarburization control method for producing 45 strip steel by a hot continuous rolling mill. The 45 strip steel is composed of chemical components with the following weight percentages:

[0135] C: 0.4587%, Si: 0.2125%, Si: 0.1906%, Ti: 0.018%, Mn: 0.634%, P: 0.01258%, S: 0.00823%, and the balance is Fe and unavoidable impurities.

[0136] Specifically, it includes the following steps:

[0137] 1) The slab size is 200×1250×10500 mm, and the finished product thickness is 4.0 mm.

[0138] 2) Control the furnace temperature in the heating zone:

[0139] Upper: Control the furnace temperature displacement in the first heating stage at 1170 °C, the furnace temperature in the second heating stage at 1310 °C, and the soaking section furnace temperature at 1250 °C;

[0140] Lower: Control the furnace temperature displacement in the first heating stage at 1160 °C, the furnace temperature in the second heating stage at 1280 °C, and the soaking section furnace temperature at 1230 °C.

[0141] 3) Control the residence time in the furnace during heating:

[0142] Control the total in-furnace time to be 173 min.

[0143] 4) Control the time of the heating section:

[0144] Control the time of the second heating stage + soaking stage to be 78 min;

[0145] 5) Control the charging temperature and discharging temperature:

[0146] Control the charging temperature to be 333 °C and the discharging temperature to be 1220 °C.

[0147] In this embodiment, the thickness of the steel plate is 4.0 mm and the thickness of the decarburized layer is 0.008 mm.

[0148] By using the method described in the present invention, the thickness of the decarburized layer of the strip is less than 1.5% of the strip thickness. Thereby, the hardness and wear resistance of the part are improved, the fatigue strength of the part is enhanced, the generation of quenching cracks is reduced, and the service life of the part is increased.

[0149] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered within the protection scope of the present invention.

Claims

1. A decarburization control method for producing 45 strip steel by a hot continuous rolling mill, characterized in that the 45 strip steel consists of chemical components with the following weight percentages as follows: C: 0.45% - 0.48%, Si: 0.18% - 0.22%, Ti: 0.015% - 0.025%, Mn: 0.6% - 0.7%, and the balance is Fe and unavoidable impurities; Specifically, it includes the following steps: 1) The width of the furnace charge is W, in mm; the thickness is D, in mm; Control 700mm ≤ W ≤ 1430mm, D ≤ 200mm; 2) The heating furnace is divided into a preheating section, a first heating section, a second heating section, and a soaking section; Control the furnace temperature in the heating zone: The furnace temperature in the preheating section ≤ 850°C, the furnace temperature in the first heating section ≤ 1200°C, the furnace temperature in the second heating section ≤ 1350°C, 1200 < the furnace temperature in the soaking section < 1250°C; 3) Control the residence time in the furnace: Control the total residence time > 160 min; 4) Control the time in the heating zone: Control the time in the second heating section + the time in the soaking section > 60 min; 5) Control the charging temperature and the discharging temperature: Control the charging temperature to be 300°C - 700°C, and control the discharging temperature to be 1200°C - 1250°C.

2. The decarburization control method for producing 45 strip steel by a hot continuous rolling mill according to claim 1, characterized in that the thickness of the 45 strip steel is D1, and the decarburized layer thickness of the 45 strip steel is D2, D2 < D1 × 15%.

3. The decarburization control method for producing 45 strip steel by a hot continuous rolling mill according to claim 1, characterized in that in step 2), the heating furnace is a walking beam heating furnace.

4. The decarburization control method for producing 45 strip steel by a hot continuous rolling mill according to claim 1, characterized in that in step 2, 500°C ≤ the furnace temperature in the preheating section ≤ 850°C, 1000°C ≤ the furnace temperature in the first heating section ≤ 1200°C, 1200°C ≤ the furnace temperature in the second heating section ≤ 1350°C, 1200 < the furnace temperature in the soaking section < 1250°C.

5. The decarburization control method for producing 45 strip steel by a hot continuous rolling mill according to claim 1, characterized in that in step 3, control the total residence time > 165 min.

6. The decarburization control method for producing 45 strip steel by a hot continuous rolling mill according to claim 1, characterized in that in step 4, control the time in the second heating section + the time in the soaking section > 65 min.

7. The decarburization control method for producing 45 strip steel by a hot continuous rolling mill according to claim 1, characterized in that in step 5, control the charging temperature to be 320°C - 700°C.

8. The decarburization control method for producing 45 strip steel by a hot continuous rolling mill according to claim 1, characterized in that in step 5, control the discharging temperature to be 1220°C - 1250°C.

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