Q235G continuous casting billet and rolling method thereof

Abstract

The invention discloses a Q235G continuous casting billet and a rolling method thereof. In the rolling process, the mass ratio of Mn to S is controlled to be larger than or equal to 8.5. According to the method, the Mn alloy is added in the tapping procedure, and the content of the Mn element in the molten steel is adjusted again according to the content of the S element in the LF refining process, so that the mass ratio of Mn to S reaches that Mn / S is larger than or equal to 8.5, the hot brittleness phenomenon caused by precipitation of low-melting-point FeS at the grain boundary is avoided, the strength, high-temperature plasticity and forging plasticity of the Q235G steel are improved, and the quality of the Q235G steel is improved. And it is guaranteed that the blank has better extensibility and fluidity in the rolling process, and the quality defect that the blank is rolled through in the rolling process is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of steel rolling, and in particular to a Q235G continuous casting billet and a rolling method thereof. Background Art

[0002] As the unfavorable situation of serious overcapacity of common steel grades in my country's steel industry becomes more prominent, enterprises are also trying every means to achieve reduced production to ensure benefits. Among them, for traditional steel grades such as Q235, since their profit margins are very low, it is crucial to achieve product upgrades and expand product profit margins through optimization and improvement of rolling processes while keeping the chemical composition unchanged or slightly adjusted. In addition, the strength upgrade of steel grades also directly brings about the weight reduction effect of the prepared structural parts, which can save steel usage, improve material utilization, and reduce the production cycle cost of steel. Q235G is a low-cost steel for pipe industry, and the chemical composition of its basic elements is as follows: C = 0.05% ~ 0.20%, Mn = 0.10% ~ 0.20%, P ≤ 0.035%, S ≤ 0.035%. The composition of this steel is similar to that of ordinary carbon steel, but the content of Mn, Si and other elements is significantly reduced, and the deoxidation requirements in the steel are not high, so the production cost is relatively low, but in the early stage of development, there are often quality defects such as rolling through during the hot rolling process, which has a greater impact on production.

[0003] The investigation found that the mass ratio of Mn and S elements (Mn / S) in Q235G steel with hole defects was relatively low. The analysis shows that the Q235G hole defect is essentially a deformation defect, which is related to the strength, plasticity and other performance indicators of steel during the rolling process. It is well known that the Mn / S in steel has a great influence on the performance of steel, mainly because the S in steel is easy to combine with the Fe in steel to form FeS with low melting point distributed in the grain boundary, causing intergranular brittleness, which significantly reduces the strength and plasticity of steel; on the other hand, a part of S combines with manganese in steel to form MnS, which is dispersed in the austenite matrix in a dispersed form, thereby enhancing the high temperature strength and plasticity of steel; if the Mn / S in steel is high, the more MnS is generated and the less FeS is generated, the higher the strength and plasticity of the steel, and vice versa.

[0004] In actual work, due to the low Mn / S ratio, the strength, high temperature plasticity and forging plasticity of the steel are seriously insufficient, which cannot guarantee the effective extension and continuous flow of the metal material during the rolling process, and eventually causes the material to rupture and form hole defects.

[0005] Based on this, the existing technology still needs to be improved. Summary of the invention

[0006] In order to solve the above technical problems, an embodiment of the present invention proposes a Q235G continuous casting billet and a rolling method thereof to solve the quality defect problem of being rolled through that occurs during the above rolling process.

[0007] In order to solve the above technical problems, some embodiments of the present invention disclose a rolling method for Q235G continuous casting billet, and during the rolling process, the mass ratio of Mn element to S element is controlled to be: Mn / S≥8.5.

[0008] Furthermore, it includes: a converter process, a LF refining process, a continuous casting process, and a rolling process.

[0009] Furthermore, the converter process includes a blowing process and a steel-tapping process, wherein: The blowing process adopts a staged oxygen supply method for blowing; The oxygen supply method is: the opening gun position is 700-750mm, the process gun position is 810-1100mm, and the end gun position is 700-750mm.

[0010] Furthermore, in the steel-making process, Mn alloy is added according to 0.20% to 0.25% of the mass percentage of the finished steel.

[0011] Furthermore, during the LF refining process, electric arc heating is used and argon is blown from the bottom throughout the process. Furthermore, during the LF refining process, the amount of Mn alloy added is adjusted according to the sulfur content in the molten steel so that the mass ratio of Mn to S reaches Mn / S≥8.5.

[0012] Furthermore, the rolling process includes a rough rolling stage and a finish rolling stage.

[0013] Furthermore, the starting rolling temperature in the rough rolling stage is 1000-1100°C.

[0014] Furthermore, the starting rolling temperature in the finishing rolling stage is 810-910°C, and the final rolling temperature in the finishing rolling stage is 740-840°C.

[0015] On the other hand, an embodiment of the present invention further discloses a Q235G continuous casting billet, which is rolled according to the above-mentioned Q235G continuous casting billet rolling method.

[0016] Furthermore, in terms of mass percentage, the chemical composition of the Q235G continuous casting billet includes: C 0.13%-0.18%, Si 0.12%-0.25%, Mn 0.20%-0.40%, P≤0.035%, S≤0.035%, and the rest is iron and unavoidable impurities.

[0017] By adopting the above technical solution, the present invention has at least the following beneficial effects: The present invention provides a Q235G continuous casting billet and a rolling method thereof. Under the condition that the equipment process conditions remain unchanged, during the rolling process, the strength, high temperature plasticity and forging plasticity of Q235G steel are improved by controlling Mn / S≥8.5, so as to ensure that the billet has better ductility and continuous fluidity during the rolling process, and avoid the quality defect of being rolled through during the rolling process. BRIEF DESCRIPTION OF THE DRAWINGS In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 A rolling flow chart of a Q235G continuous casting billet disclosed in some embodiments of the present invention. DETAILED DESCRIPTION

[0019] The following is a further detailed description of the embodiments of the present disclosure in conjunction with the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to exemplarily illustrate the principles of the present disclosure, but cannot be used to limit the scope of the present disclosure. The present disclosure can be implemented in many different forms and is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

[0020] The present disclosure provides these embodiments to make the present disclosure thorough and complete, and to fully express the scope of the present disclosure to those skilled in the art. It should be noted that unless otherwise specifically stated, the relative arrangement of the parts and steps, the composition of the materials, the numerical expressions and the numerical values ​​set forth in these embodiments should be interpreted as being merely exemplary, and not as limiting.

[0021] It should be noted that, in the description of the present disclosure, unless otherwise specified, the meaning of "multiple" is greater than or equal to two; the terms "upper", "lower", "left", "right", "inner", "outer", etc., indicating the orientation or positional relationship, are only for the convenience of describing the present disclosure and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present disclosure. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0022] In addition, the words "first", "second" and similar words used in the present disclosure do not indicate any order, quantity or importance, but are only used to distinguish different parts. "Vertical" does not mean vertical in the strict sense, but is within the tolerance range. "Parallel" does not mean parallel in the strict sense, but is within the tolerance range. "Include" or "comprising" and similar words mean that the elements before the word include the elements listed after the word, and do not exclude the possibility of including other elements.

[0023] It should also be noted that in the description of the present disclosure, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present disclosure can be understood according to the specific circumstances. When a specific device is described as being located between a first device and a second device, there may or may not be an intermediate device between the specific device and the first device or the second device.

[0024] All terms used in the present disclosure have the same meanings as those understood by those of ordinary skill in the art to which the present disclosure belongs, unless otherwise specifically defined. It should also be understood that terms defined in general dictionaries, for example, should be interpreted as having meanings consistent with their meanings in the context of the relevant technology, and should not be interpreted in an idealized or extremely formal sense, unless explicitly defined as such herein.

[0025] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered part of the specification.

[0026] Some embodiments of the present invention disclose a rolling method for a Q235G continuous casting billet, wherein the mass ratio of the Mn element to the S element is controlled to be Mn / S≥8.5 during the rolling process. Specifically, the ratio of the Mn alloy element can be adjusted according to the content of the S element in the steel to ensure that the Mn / S in the final steel is not less than 8.5. Controlling Mn / S≥8.5 can improve the strength and plasticity of the steel, ensure that the metal material can effectively extend and flow continuously during the rolling process, and avoid the formation of hole defects caused by material rupture.

[0027] Some embodiments of the present invention disclose a rolling method for Q235G continuous casting billet, which, on the basis of the above embodiments, includes: a converter process, an LF refining process, a continuous casting process, and a rolling process. Among them, the converter process includes a blowing process and a steel-out process. During operation, the blowing process adopts a staged oxygen supply method for blowing, and the interaction between the oxygen stream and the molten pool is changed by adjusting the oxygen gun position to control the blowing process. The staged oxygen supply method can improve the efficiency and quality of steelmaking while reducing production costs. By accurately controlling the oxygen supply process, impurities in the molten steel can be better removed and the purity and quality of the steel can be improved. Specifically, the oxygen supply method can be: the opening blowing gun position is 700-750, the process gun position is 810-1100mm, and the terminal gun position is 700-750. Adopting a low lance position at the beginning of blowing can promote the melting of scrap steel; raising the lance position during blowing can further melt the early slag, facilitate the addition of the second batch of slag, and promote uniform temperature rise of the molten pool; lowering the lance position again at the end of blowing can suppress the FeO content in the slag, avoid splashing, and increase the decarburization rate.

[0028] Some embodiments of the present invention disclose a rolling method for Q235G continuous casting billet. On the basis of the above embodiments, in the steel-making process, Mn alloy is added according to 0.20% to 0.25% of the mass percentage of the finished steel. In the LF refining process, electric arc heating is adopted, and argon is blown at the bottom throughout the whole process. In addition, in the LF refining process, the amount of Mn alloy added is adjusted again according to the content of sulfur element in the molten steel, so that the mass ratio of Mn to S reaches Mn / S≥8.5. The electric arc heating has high heating efficiency and rapid temperature rise. At the same time, it has little pollution to the molten steel, which is beneficial to maintain the purity of the molten steel. By blowing argon at the bottom, on the one hand, the impact and stirring effect of argon can be utilized to effectively enhance the stirring effect, thereby shortening the smelting time; on the other hand, the blowing of argon can push the gas and inclusions insoluble in the molten steel to the surface of the molten steel and form slag, thereby achieving a purification effect. In the present embodiment, in the steel tapping process, Mn alloy is added according to 0.20% to 0.25% of the mass percentage of the finished steel, and in the LF refining process, the amount of Mn alloy added is adjusted according to the sulfur content in the molten steel. By adding Mn alloy twice, the content of Mn element in the molten steel is timely adjusted to make the mass ratio of Mn to S reach Mn / S≥8.5, so as to ensure the strength and plasticity of the steel.

[0029] Some embodiments of the present invention disclose a rolling method for a Q235G continuous casting billet. On the basis of the above embodiments, the rolling process includes a rough rolling stage and a finishing rolling stage. The starting rolling temperature of the rough rolling stage is 1000-1100°C, and fine and uniform austenite grains can be obtained by repeated rolling in the high-temperature recrystallization zone of austenite. The starting rolling temperature of the finishing rolling stage is 810-910°C, and the finishing rolling temperature is 740-840°C, so as to obtain the strain accumulation effect in the low-temperature non-recrystallization zone, increase the phase transformation driving force induced by intragranular defects, deformation hardening and residual strain of austenite.

[0030] Some embodiments of the present invention also disclose Q235G continuous casting billet, whose chemical composition, measured by mass percentage, includes: C 0.13%-0.18%, Si 0.12%-0.25%, Mn 0.20%-0.40%, P≤0.035%, S≤0.035%, and the rest is iron and unavoidable impurities.

[0031] The following is an explanation with reference to specific embodiments and comparative examples.

[0032] Embodiment 1 of the present invention discloses a rolling method of a Q235G continuous casting billet, which is rolled in sequence through a converter process, a LF refining process, a continuous casting process, a rolling process and the like. Specifically, the converter process includes a blowing process and a steel-out process, wherein the blowing process adopts a staged oxygen supply method for blowing, the opening gun position is 700mm, the process gun position is 810mm, and the terminal gun position is 700mm. In the steel-out process, Mn alloy is added according to 0.20% of the mass percentage of the finished steel out; during the LF refining process, arc heating is adopted, argon is blown at the bottom throughout the process, and the addition amount of Mn alloy is adjusted according to the content of sulfur element in the molten steel, so that the mass ratio of Mn to S reaches Mn / S=8.9; the starting rolling temperature of the rough rolling stage of the rolling process is 1000℃, the starting rolling temperature of the finishing rolling stage of the rolling process is 810℃, and the final rolling temperature of the finishing rolling stage is 740℃, and no hole quality defects occur.

[0033] Embodiment 2 of the present invention discloses a rolling method of a Q235G continuous casting billet, which is rolled in sequence through a converter process, a LF refining process, a continuous casting process, a rolling process and the like. Specifically, the converter process includes a blowing process and a steel-out process, wherein the blowing process adopts a staged oxygen supply method for blowing, the opening gun position is 720mm, the process gun position is 900mm, and the terminal gun position is 720mm. In the steel-out process, Mn alloy is added according to 0.22% of the mass percentage of the finished steel out; during the LF refining process, arc heating is adopted, argon is blown at the bottom throughout the process, and the amount of Mn alloy added is adjusted according to the sulfur content in the molten steel, so that the mass ratio of Mn to S reaches Mn / S=9.6; the starting rolling temperature of the rough rolling stage of the rolling process is 1050℃, the starting rolling temperature of the finishing rolling stage of the rolling process is 830℃, and the final rolling temperature of the finishing rolling stage is 760℃, and no hole quality defects occur.

[0034] Embodiment 3 of the present invention discloses a rolling method of a Q235G continuous casting billet, which is rolled in sequence through a converter process, a LF refining process, a continuous casting process, a rolling process and the like. Specifically, the converter process includes a blowing process and a steel-out process, wherein the blowing process adopts a staged oxygen supply method for blowing, the opening gun position is 750mm, the process gun position is 1100mm, and the terminal gun position is 750mm. In the steel-out process, Mn alloy is added according to 0.24% of the mass percentage of the finished steel out; during the LF refining process, arc heating is adopted, argon is blown at the bottom throughout the process, and the amount of Mn alloy added is adjusted according to the content of sulfur in the molten steel, so that the mass ratio of Mn to S reaches Mn / S=10.1; the starting rolling temperature of the rough rolling stage of the rolling process is 1100℃, the starting rolling temperature of the finishing rolling stage of the rolling process is 910℃, and the final rolling temperature of the finishing rolling stage is 840℃, and no hole quality defects occur.

[0035] Comparative Example 1 discloses a rolling method for a Q235G continuous casting billet, which is rolled in sequence through a converter process, a LF refining process, a continuous casting process, a rolling process and the like. Specifically, the converter process includes a blowing process and a steel-out process, wherein the blowing process adopts a staged oxygen supply method for blowing, with a start-blowing gun position of 720 mm, a process gun position of 900 mm, and a terminal gun position of 720 mm; during the LF refining process, arc heating is adopted, argon is blown at the bottom throughout the process, and a Mn alloy is added to make the mass ratio of Mn to S reach Mn / S=5.8; the start rolling temperature of the rough rolling stage of the rolling process is 1020°C, the start rolling temperature of the finishing rolling stage of the rolling process is 850°C, and the final rolling temperature of the finishing rolling stage is 840°C, and 3 coils have hole quality defects during the rolling process.

[0036] Comparative Example 2 discloses a rolling method for a Q235G continuous casting billet, which is rolled in sequence through a converter process, a LF refining process, a continuous casting process, a rolling process and the like. Specifically, the converter process includes a blowing process and a steel-out process, wherein the blowing process adopts a staged oxygen supply method for blowing, with a start-blowing gun position of 740 mm, a process gun position of 1000 mm, and a terminal gun position of 740 mm; during the LF refining process, arc heating is adopted, argon is blown at the bottom throughout the process, and a Mn alloy is added to make the mass ratio of Mn to S reach Mn / S=6.7; the start rolling temperature of the rough rolling stage of the rolling process is 1040°C, the start rolling temperature of the finishing rolling stage of the rolling process is 880°C, and the final rolling temperature of the finishing rolling stage is 780°C, and 2 coils have hole quality defects during the rolling process.

[0037] From the above, it can be seen that although the same rolling process is used in Examples 1-3 and Comparative Examples 1-2, due to the difference in Mn / S, Mn / S ≥ 8.5 in Examples 1-3, no hole quality defects occur during the rolling process, while Mn / S < 8.5 in Comparative Examples 1-2, and hole quality defects occur to varying degrees in the final finished steel. It can be seen that Mn / S ≥ 8.5 can effectively avoid the hole quality defects of Q235G.

[0038] According to statistics, during the period from January to March 2023, among the 147 furnaces of Q235G produced by a certain production workshop, 144 furnaces had Mn / S ≥ 8.5, and the defect rate was only 0.08%, while there were 3 furnaces with Mn / S < 8.5, and the defect rate reached 31.7%.

[0039] In summary, by adding Mn alloy in the steel-making process and adjusting the Mn content in the molten steel according to the S content in the LF refining process, the mass ratio of Mn to S reaches Mn / S ≥ 8.5, avoiding the hot brittleness caused by the precipitation of low-melting point FeS at the grain boundary, improving the strength, high-temperature plasticity and forging plasticity of Q235G steel, ensuring that the billet has better ductility and fluidity during the rolling process, and avoiding the quality defect of being rolled through during the rolling process. So far, various embodiments of the present disclosure have been described in detail. In order to avoid obscuring the concept of the present disclosure, some details known in the art are not described. Based on the above description, those skilled in the art can fully understand how to implement the technical solution disclosed here.

[0040] Although some specific embodiments of the present disclosure have been described in detail by way of examples, it should be understood by those skilled in the art that the above examples are for illustration only and are not intended to limit the scope of the present disclosure. It should be understood by those skilled in the art that the above embodiments may be modified or some technical features may be replaced by equivalents without departing from the scope and spirit of the present disclosure. In particular, the various technical features mentioned in the various embodiments may be combined in any manner as long as there is no structural conflict.

Claims

1. A rolling method for Q235G continuous casting billet, characterized in that: During the rolling process, the mass ratio of Mn element to S element is controlled to be: Mn / S≥8.

5.

2. The rolling method of Q235G continuous casting billet according to claim 1, characterized in that: include: Converter process, LF refining process, continuous casting process, rolling process.

3. The rolling method of Q235G continuous casting billet according to claim 2, characterized in that: The converter process includes a blowing process and a steel-tapping process, wherein: The blowing process adopts a staged oxygen supply method for blowing; The oxygen supply method is as follows: the opening gun position is 700-750mm, the process gun position is 810-1100mm, and the terminal gun position is 700-750mm.

4. The rolling method of Q235G continuous casting billet according to claim 3, characterized in that: In the steel tapping process, Mn alloy is added according to 0.20% to 0.25% of the mass percentage of the finished steel.

5. The rolling method of Q235G continuous casting slab according to claim 2, characterized in that: During the LF refining process, electric arc heating is used and argon is blown from the bottom throughout the process. Furthermore, during the LF refining process, the amount of Mn alloy added is adjusted according to the sulfur content in the molten steel so that the mass ratio of Mn to S reaches Mn / S≥8.

5.

6. The rolling method of Q235G continuous casting billet according to claim 2, characterized in that: The rolling process includes a rough rolling stage and a finish rolling stage.

7. The rolling method of Q235G continuous casting billet according to claim 6, characterized in that: The starting rolling temperature in the rough rolling stage is 1000-1100°C.

8. The rolling method of Q235G continuous casting billet according to claim 6, characterized in that: The starting rolling temperature of the finishing rolling stage is 810-910°C, and the final rolling temperature of the finishing rolling stage is 740-840°C.

9. A Q235G continuous casting billet, characterized in that: The Q235G continuous casting billet is rolled according to the rolling method of any one of claims 1 to 8.

10. The Q235G continuous casting billet according to claim 9, characterized in that: Calculated by mass percentage, the chemical composition of the Q235G continuous casting billet includes: C 0.13%-0.18%, Si 0.12%-0.25%, Mn 0.20%-0.40%, P≤0.035%, S≤0.035%, and the rest is iron and unavoidable impurities.

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