Heating method of medium-thickness-wall carbon manganese steel

Abstract

The invention discloses a heating method of medium-thickness-wall carbon manganese steel. A heating process of a carbon manganese steel annular furnace is as follows: a preheating section 1: 960 + / -20 DEG C; the preheating section 2 is 1130 + / -20 DEG C; the heating section is 1: 1240 + / -20 DEG C; the heating section 2 is 1260 + / -20 DEG C; the soaking section is 1: 1260 + / -10 DEG C; the soaking section 2 is 1250 + / -10 DEG C; according to the heating method for the medium-thickness-wall carbon manganese steel, research on the heating technology of the C-Mn steel large-section continuous casting round pipe blank is carried out, the heating temperature of the pipe blank directly influences the surface quality and the size precision of the steel pipe, the heating temperature of each section in a furnace is optimized, the fuel gas consumption economical efficiency is improved, and the energy consumption is reduced. And the risks of overheated structures and rolling defects of the hot-rolled steel pipe caused by excessive heating of the pipe blank are reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of seamless steel pipe continuous casting round billet production, and in particular relates to a heating method for medium-thick wall carbon manganese steel. Background Art

[0002] Among the hot-rolled steel varieties, the energy consumption per ton of steel for hot-rolled seamless steel pipes ranks first, among which the energy consumption cost for heating the tube billets accounts for more than 60% of the total power cost for hot rolling. Affected by the transition process such as the layout of each unit of hot rolling and the transmission mechanism, in order to ensure that the high-temperature piercing and rolling is in the plastic zone of the steel, the maximum heating temperature in the annular heating furnace is usually set to the upper limit of 1250℃~1310℃. However, the high-temperature optimal plastic zone of low and medium carbon steel is basically less than 1250℃. Secondly, the temperature control distribution of the preheating, heating, and soaking sections in the annular heating furnace has not been finely controlled, which not only fails to control the gas consumption, but also easily produces structural defects.

[0003] Excessive heating temperature of continuous casting round billet may lead to:

[0004] 1. Severe oxidation and large metal loss reduce the friction of the metal surface, which may cause slipping and jamming accidents during perforation and deformation.

[0005] 2. The grains of the steel billet are coarse and uneven, which causes the mechanical properties of the steel pipe to decrease; overburned structure is produced, and decarburization occurs in severe cases; the existence of overburned structure causes a large number of irregular inward folds in the rough pipe after perforation.

[0006] 3. The local temperature rise on the surface of the steel billet causes "softening", resulting in the difference in metal flow rate inside and outside the steel billet, resulting in metal accumulation at the roll gap, causing external folding or external scarring defects.

[0007] 4. The high temperature of the steel billet can easily cause hot tools to stick to the steel, resulting in scarring defects on the outer surface of the steel pipe.

[0008] Too low heating temperature for continuous casting round billet may lead to:

[0009] 1. Increase the deformation resistance of steel, reduce the plasticity of steel, and the cracks cannot be healed, forming external folding defects. In severe cases, rolling accidents are prone to occur and steel cannot be rolled.

[0010] 2. It is easy to cause uneven heating of the tube in the longitudinal or transverse direction, commonly known as "yin and yang surface", resulting in extremely poor uniformity of spiral black bands in the rough tube and wall thickness of the steel tube, and in severe cases, causing rolling accidents.

[0011] 3. The temperature system of the hot rolling mill depends on the deformation system to a certain extent. When the heating temperature is too low, the continuous rolling mill and the fixed-tension reducing mill will have difficulty biting the steel, and even shaft breakage and roll breakage accidents may occur.

[0012] 4. It is easy to cause uneven melting and agglomeration of borax or other lubricants, resulting in linear internal straight lines, scratches or internal scars along the axial direction on the inner surface of the steel pipe. Summary of the invention

[0013] The purpose of the present invention is to provide a heating method for medium-thick wall carbon manganese steel, to carry out research on the heating process of C-Mn steel large-section continuous casting round tube billets, the heating temperature of the tube billets directly affects the surface quality and dimensional accuracy of the steel pipe, optimizes the heating temperature of each section in the furnace, improves the economy of gas consumption, and reduces the risk of overheating structure and rolling defects in hot-rolled steel pipes caused by excessive heating of the tube billets.

[0014] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0015] The present invention discloses a heating method for medium-thick wall carbon-manganese steel, and the heating process of the carbon-manganese steel ring furnace is as follows:

[0016] Preheating section 1: 960±20℃; Preheating section 2: 1130±20℃; Heating section 1: 1240±20℃; Heating section 2: 1260±20℃; Soaking section 1: 1260±10℃; Soaking section 2: 1250±10℃.

[0017] Furthermore, the carbon manganese steel is a carbon manganese steel with a wall thickness of ≥16 mm.

[0018] Furthermore, the carbon-manganese steel has a carbon content of 0.30-0.38% by mass and a manganese content of 1.2-1.8% by mass.

[0019] Furthermore, by reducing the heat input in the preheating section, the accumulation of thermal stress in the material during the preheating process is effectively slowed down, avoiding adverse effects caused by excessive temperature.

[0020] Furthermore, the preheating temperature can ensure that the material can quickly and evenly reach the required temperature in the subsequent heating stage without affecting the subsequent rolling process.

[0021] Compared with the prior art, the beneficial technical effects of the present invention are:

[0022] Based on the research on the high-temperature plasticity characteristics of carbon-manganese steel products and the influence of the final rolling temperature on the performance of steel pipes, the heating process technology of tube blanks with different wall thickness designs is formed, so that the tube blanks can be pierced and rolled in the optimal plastic zone, and the high-temperature organization of the tube blanks can be controlled, which is conducive to improving the microstructure stability and uniformity of the products, and is the basis for ensuring the performance of hot-rolled products and the stable and uniform deformation of alloy steel. Secondly, by optimizing the burning temperature, burning time and rhythm, the fuel consumption economy can be greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described below in conjunction with the accompanying drawings.

[0024] Figure 1 is the high temperature plasticity curve of C-Mn steel;

[0025] Figure 2 To compare the impact energy stability before and after optimization;

[0026] Figure 3 To optimize the before and after tissue comparison. DETAILED DESCRIPTION

[0027] The technical solution adopted by the present invention is as follows:

[0028] Further: The ring heating furnace is the main equipment for heating steel pipe billets. The uniformity and stability of its internal temperature are directly related to the initial temperature state of the steel pipe before entering the rolling mill. When the heating temperature of the ring furnace is set too high, the steel pipe billet will absorb more heat during its stay in the furnace, resulting in a high temperature when it leaves the furnace. This high initial temperature is often difficult to quickly reduce to the ideal final rolling temperature range after entering the rolling mill, even after multiple rolling deformations and heat dissipation.

[0029] Further: On the contrary, if the heating temperature of the annular furnace is set too low and the steel pipe round billet is not fully heated to the expected temperature in the furnace, then during the rolling process, more energy needs to be absorbed to achieve sufficient plastic deformation capacity, which will lead to increased rolling force and reduced rolling efficiency. In order to compensate for the insufficient temperature, it may be necessary to increase the rolling passes or increase the roll temperature, which may indirectly affect the control accuracy of the final rolling temperature.

[0030] Further: When the final rolling temperature is too high, it will lead to coarse grains, uneven structure, increased residual stress and other problems. It may also cause defects such as thickened oxide scale, cracks, scratches and other defects on the surface of the steel pipe. These defects not only affect the appearance quality of the steel pipe, but also may become a source of stress concentration, reducing the bearing capacity and service life of the steel pipe. Therefore, in the process of steel pipe production, it is very important to strictly control the final rolling temperature within a reasonable range to ensure that the steel pipe has excellent performance and reliable quality.

[0031] Further: In order to obtain the ideal final rolling temperature, the heating temperature of the ring furnace needs to be accurately controlled and optimized. According to the steel pipe material, specifications and rolling process requirements, the heating temperature range is reasonably set to ensure that the steel pipe reaches the best initial temperature state before rolling.

[0032] Further: Carbon manganese steel (carbon content: 0.30-0.38%, manganese content: 1.2-1.8%) was selected for high temperature tensile thermoplasticity test, and the test temperatures were 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃, 1200℃, 1250℃, and 1300℃. The high temperature tensile plasticity curve of the test steel is shown in Figure 1 .

[0033] Further: From the high-temperature plasticity curve of the test steel, it can be seen that the high-temperature plasticity diagram of C-Mn steel is clearly divided into two intervals, 800℃-1220℃. Above 1220℃, the cross-sectional shrinkage first increases and then decreases steadily, among which 800℃-1220℃>60%, and above 1220℃<60%, indicating that the optimal temperature deformation area of ​​the steel is 800℃-1220℃.

[0035] Further: In the past, the heating process for carbon manganese steel strictly followed the parameters specified in Table 1. However, this heating method often resulted in the performance of the finished steel pipe failing to meet the standards, especially the high final rolling temperature, which directly affected the final quality and application performance of the product.

[0036] Table 1 Carbon manganese steel ring furnace heating process

[0037]

[0038] Based on the above in-depth analysis, a set of heating process solutions tailored for medium and thick-walled carbon manganese steel billets was designed. The specific parameters are shown in Table 2. This solution fully takes into account the characteristics that the temperature of medium and thick-walled billets drops more gently from the furnace to the rolling stage compared with thin-walled billets. Therefore, on the premise of ensuring smooth rolling process and maintaining a suitable final rolling temperature, the temperature settings of the preheating zone and the soaking zone were scientifically optimized. Specifically, the temperature of the preheating zone was significantly reduced by nearly 100°C, and the soaking zone was also reduced by nearly 20°C accordingly, thereby achieving the refined regulation and reduction of the overall heating temperature of the billet.

[0039] Table 2 Heating process of carbon manganese steel ring furnace with medium and thick wall (wall thickness ≥ 16mm)

[0040]

[0041] Furthermore: the rolling process was tracked and it was found that after the temperature was lowered, the service life of the plug, guide plate and roller tended to be stable, and there was no phenomenon of increased consumption of hot tools due to lowering the incoming material temperature.

[0042] Further: After cooling, the product performance was tracked and analyzed, and the tensile performance, impact performance and the content of main chemical elements of the finished product were statistically analyzed. It was found that the mechanical properties of the product did not change much, but the impact performance was more stable than before. The impact work stability comparison can be seen. Figure 2 .

[0043] Further: After the temperature drops, the product organization is tracked and analyzed, and the banded organization is improved. The organization comparison before and after optimization is shown in Figure 3 .

[0044] Further: Based on the above analysis and research, it can be shown that the technical solution is feasible, which can not only achieve the stability of product performance, but also save energy. Comparing the natural gas energy consumption of the annular furnace before and after optimization, when rolling the same specification steel pipe, the natural gas energy consumption of the heating furnace is saved by nearly 7%.

[0045] The carbon manganese steel heating process of each embodiment is shown in Table 3:

[0046] Table 3 Heating process of each embodiment

[0047]

[0048] In the heating process designed in Example 2, a notable feature is that the temperature of the soaking section is as high as 1280°C. When the tube billet undergoes such high-temperature uniform heating and then comes out of the furnace, its surface and internal temperatures are maintained at a relatively high level. However, the high furnace temperature directly leads to a high temperature of the tube billet when it enters the final rolling process, which will cause abnormal growth of grains, increased structural inhomogeneity, and a sharp change in internal stress. These changes further weaken the mechanical properties of the material and increase the risk of product defects such as cracks, deformation, uneven hardness, and reduced toughness, which directly affects the quality and performance of the final product, resulting in performance parameters that cannot meet established standards or customer requirements.

[0049] In Example 3, the temperature of the soaking section was precisely reduced by about 20°C, while the temperatures of other sections remained unchanged. This subtle but critical adjustment is intended to optimize the thermal stress distribution and microstructural evolution of the tube billet throughout the heating process, thereby improving the effect of the heating process at the source. By lowering the temperature of the soaking section, the tube billet achieves a predetermined homogenization state while reducing the risk of overheating due to excessive temperature. After moderately lowering the temperature, the stress distribution of the tube billet during the heating process becomes more uniform, which helps to reduce potential defects such as cracks caused by thermal stress concentration. Continuous tracking and analysis of product performance show that this process improvement has brought significant positive effects. Specifically, the product defect rate has dropped significantly, and the incidence of common problems including cracks, inward folds, uneven tissue, and banded tissue has been greatly reduced. This shows that moderate adjustment of the temperature of the soaking section effectively inhibits the formation of undesirable tissues and improves the overall quality level of the tube billet.

[0050] The heating process of Example 1 is further optimized on the basis of Example 3. This optimization is not a simple adjustment of the temperature of a single section, but a comprehensive adjustment of the entire heating process curve, so as to achieve further optimization of the overall temperature distribution. The temperature of preheating zone 1 was greatly reduced by nearly 100°C. This adjustment is based on an in-depth study of the material properties of medium and thick-walled carbon-manganese steel. As an important material widely used in industrial production, the organizational evolution and performance changes of carbon-manganese steel during the heating process are particularly sensitive to temperature. Excessively high preheating temperatures may lead to increased surface oxidation of the material, coarsening of the grains, and uneven distribution of internal stress, thereby affecting the mechanical properties and processing properties of the final product. By reducing the heat input at this stage, the accumulation of thermal stress of the material during the preheating process is effectively slowed down, avoiding the adverse effects caused by excessively high temperatures. At the same time, a moderate preheating temperature can still ensure that the material can quickly and evenly reach the required temperature in the subsequent heating stage without affecting the subsequent rolling process.

[0051] The test data of mechanical properties also fully verified the effectiveness of this process improvement. After cooling, the key indicators of the product, such as tensile strength, yield strength, elongation and impact toughness, all met the technical requirements, showing even better mechanical properties.

[0052] 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 method for heating medium-thick wall carbon manganese steel, characterized in that: The heating process of carbon manganese steel ring furnace is as follows: Preheating section 1: 960±20℃; Preheating section 2: 1130±20℃; Heating section 1: 1240±20℃; Heating section 2: 1260±20℃; Soaking section 1: 1260±10℃; Soaking section 2: 1250±10℃.

2. The method for heating medium-thick wall carbon manganese steel according to claim 1, characterized in that: The carbon manganese steel is a carbon manganese steel with a wall thickness of ≥16 mm.

3. The method for heating medium-thick wall carbon-manganese steel according to claim 1, characterized in that: The carbon-manganese steel has a carbon content of 0.30-0.38% by mass and a manganese content of 1.2-1.8% by mass.

4. The method for heating medium-thick wall carbon manganese steel according to claim 1, characterized in that: By reducing the heat input in the preheating section, the accumulation of thermal stress in the material during the preheating process is effectively slowed down, avoiding the adverse effects caused by excessive temperature.

5. The method for heating medium-thick wall carbon manganese steel according to claim 1, characterized in that: The preheating temperature can ensure that the material can quickly and evenly reach the required temperature in the subsequent heating stage without affecting the subsequent rolling process.

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