1180mpa grade hot dip galvanized dual phase steel and method of making the same
By controlling the chemical composition and preparation process of 1180MPa grade hot-dip galvanized duplex steel and introducing dispersed metastable carbides, the problem of hydrogen embrittlement sensitivity was solved, and the delayed cracking resistance of high-strength materials was improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHOUGANG GROUP CO LTD
- Filing Date
- 2024-03-26
- Publication Date
- 2026-06-19
AI Technical Summary
Existing 1180MPa grade hot-dip galvanized duplex steel is highly sensitive to hydrogen embrittlement during use, leading to unpredictable risks.
By controlling the chemical composition and preparation process, a large number of dispersed metastable carbides are introduced to adsorb hydrogen atoms, thereby hindering the diffusion of hydrogen atoms to the stress concentration area and improving the hydrogen-induced delayed cracking capability of the material.
It significantly improves the material's ability to delay hydrogen cracking, reduces hydrogen embrittlement sensitivity, and ensures that the material has good resistance to delayed cracking under high strength.
Smart Images
Figure CN118064801B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the technical fields of automotive steel and engineering structural steel, and in particular to a 1180MPa grade hot-dip galvanized duplex steel and its preparation method. Background Technology
[0002] As the automotive industry increasingly demands energy conservation, emission reduction, and collision safety, the need for duplex steel with higher strength and better formability is becoming more urgent. Currently, 1180MPa grade hot-dip galvanized duplex steel has been widely used in body reinforcement components, but due to its high sensitivity to hydrogen embrittlement, there are unpredictable risks during its use. Summary of the Invention
[0003] This application provides a 1180MPa grade hot-dip galvanized duplex steel and its preparation method to solve the technical problem of low hydrogen-induced delayed cracking ability of duplex steel in the prior art.
[0004] In a first aspect, this application provides a 1180MPa grade hot-dip galvanized duplex steel, the chemical composition of which includes:
[0005] C: 0.10 wt% - 0.15 wt%, Si: 0.2 wt% - 0.5 wt%, Mn: 2.0 wt% - 2.5 wt%, Cr: 0.3 wt% - 0.6 wt%, Al: 0.01 wt% - 0.05 wt%, P ≤ 0.02 wt%, S ≤ 0.01 wt%, Nb: 0 - 0.04 wt%, Ti: 0 - 0.04 wt%, Fe.
[0006] Optionally, the metallographic structure of the duplex steel includes at least one of the following: ferrite, tempered martensite, bainite, and carbides.
[0007] Optionally, the ferrite content is 10%-40% by volume, the sum of the tempered martensite and the bainite content is 70%-80% by volume, and the carbide content is greater than 0.15% by volume.
[0008] Secondly, this application provides a method for preparing 1180MPa grade hot-dip galvanized duplex steel, used to prepare the duplex steel described in any one of the first aspects, the method comprising:
[0009] Molten steel containing the chemical composition described in the first aspect is continuously cast to obtain a billet;
[0010] The billet is hot-rolled at a set billet heating temperature and a set hot rolling final rolling temperature.
[0011] The hot-rolled billet is wound up at a set winding temperature;
[0012] The coiled billet is cold-rolled under a set cold rolling deformation amount;
[0013] The cold-rolled billet is continuously annealed under the following conditions: set annealing temperature, set slow cooling temperature, set rapid cooling temperature, set aging temperature, and set belt speed.
[0014] Optionally, the set billet heating temperature is 1150℃-1250℃, and the set hot rolling final rolling temperature is 880℃-900℃.
[0015] Optionally, the set winding temperature is 540℃-560℃.
[0016] Optionally, the set cold rolling deformation amount is 40%-65%.
[0017] Optionally, the set annealing homogenization temperature is set to 780℃-820℃, and the set slow cooling temperature is set to 680℃-720℃.
[0018] Optionally, the set rapid cooling temperature is set to 250℃-300℃, and the set aging temperature is set to 350℃-400℃.
[0019] Optionally, the set belt speed is 70mpm-120mpm.
[0020] The technical solutions provided in this application have the following advantages compared with the prior art:
[0021] The method provided in this application introduces a large number of dispersed metastable carbides into the microstructure of hot-dip galvanized duplex steel. Since metastable carbides are effective hydrogen traps, they can effectively prevent hydrogen atoms from diffusing to stress concentration areas after adsorbing hydrogen atoms, thereby effectively improving the hydrogen-induced delayed cracking capability of the material. Attached Figure Description
[0022] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.
[0023] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0024] Figure 1 A typical microstructure of a 1180MPa grade hot-dip galvanized duplex steel provided in the embodiments of this application;
[0025] Figure 2 A comparison of slow strain rate tensile stress-strain curves before and after hydrogen purging, provided in the embodiments of this application. Detailed Implementation
[0026] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0027] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.
[0028] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.
[0029] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the orientation shown in the accompanying drawings. Furthermore, in the description of this application, the terms "comprising" and "including" mean "including but not limited to".
[0030] In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, without necessarily requiring or implying any actual relationship or order between these entities or operations. In this document, "and / or" describes the association between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c," or "at least one of a, b, and c," can both represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.
[0031] The technical solution provided in this application is to solve the above-mentioned technical problems, and the overall approach is as follows:
[0032] In a first aspect, this application provides a 1180MPa grade hot-dip galvanized duplex steel, the chemical composition of which includes:
[0033] C: 0.10 wt% - 0.15 wt%, Si: 0.2 wt% - 0.5 wt%, Mn: 2.0 wt% - 2.5 wt%, Cr: 0.3 wt% - 0.6 wt%, Al: 0.01 wt% - 0.05 wt%, P ≤ 0.02 wt%, S ≤ 0.01 wt%, Nb: 0 - 0.04 wt%, Ti: 0 - 0.04 wt%, Fe.
[0034] In this embodiment, the positive effect of a C mass fraction of 0.10%-0.15% is to ensure that the strength of the strip is within a reasonable range and to ensure that the strip has a certain hardenability. When the mass fraction value is greater than the maximum value of the range or less than the minimum value of the range, it will result in the strip strength being too high or too low.
[0035] In this embodiment, the positive effect of Si mass fraction of 0.2%-0.5% is to ensure that the strength of the strip is within a reasonable range and the surface quality of the strip. When the mass fraction value is greater than the maximum value of this range, it will result in the strip strength being too high and the surface quality being poor. When the mass fraction value is less than the minimum value of this range, it will result in the strip strength being too low.
[0036] In this embodiment, the positive effect of a Mn mass fraction of 2.0%-2.5% is to ensure that the hardenability of the strip is within a reasonable range. When the mass fraction is greater than the maximum value at the end of the range, the adverse effect is that the strip strength is too high. When the mass fraction is less than the minimum value at the end of the range, the adverse effect is that the hardenability of the strip is insufficient and the martensite content in the microstructure is insufficient.
[0037] In this embodiment, the positive effect of a Cr mass fraction of 0.3%-0.6% is to ensure that the hardenability of the strip is within a reasonable range. When the mass fraction is greater than the maximum value at the end of the range, the adverse effect is that the alloy cost is too high. When the mass fraction is less than the minimum value at the end of the range, the adverse effect is that the hardenability of the strip is insufficient.
[0038] In this embodiment, Al is a deoxidizer in the smelting process, with a mass fraction of 0.01%-0.05%. When the mass fraction is greater than the maximum value at the end of the range, the adverse effect is excessive inclusions. When the mass fraction is less than the minimum value at the end of the range, the adverse effect is insufficient deoxidation.
[0039] In this embodiment, P is a residual element in the steelmaking process, which is generally controlled to be ≤0.02%. When the mass fraction is greater than the maximum value at the end of this range, the adverse effect will be that the structure is more brittle.
[0040] In this embodiment, S is a residual element in the steelmaking process, which is generally controlled to be ≤0.01%. When the mass fraction is greater than the maximum value at the end of this range, the adverse effect will be excessive inclusions.
[0041] In this embodiment, the positive effect of having a Nb mass fraction of 0% to 0.04% is to refine the grains; when the mass fraction value is greater than the maximum value at the end of this range, the adverse effect is that the alloy cost is too high.
[0042] In this embodiment, the positive effect of a Ti mass fraction of 0% to 0.04% is to provide precipitation strengthening; when the mass fraction value is greater than the maximum value at the end of this range, the adverse effect is that the alloy cost is high and the performance fluctuates greatly.
[0043] In some embodiments, the metallographic structure of the duplex steel includes at least one of the following: ferrite, tempered martensite, bainite, and carbides.
[0044] In some embodiments, the ferrite content is 10 vol%-40 vol%, the sum of the tempered martensite and the bainite content is 70 vol%-80 vol%, and the carbide content is greater than 0.15 vol%.
[0045] In this embodiment, a ferrite volume fraction of 10-40% positively ensures that the strip's strength and elongation are within a reasonable range. When the volume fraction is greater than or less than the extreme values of this range, the adverse effect is that the strength is either too low or too high. Similarly, a tempered martensite and bainite volume fraction of 60-90% positively ensures that the strip's strength is within a reasonable range. When the volume fraction is greater than or less than the extreme values of this range, the adverse effect is that the strength is either too high or too low. A carbide volume fraction between 0.15-1% positively ensures the strip's resistance to delayed cracking. When the carbide volume fraction is less than the extreme values of this range, the resistance to delayed cracking is insufficient; when the carbide volume fraction is greater than the extreme values of this range, it easily leads to lower strip strength.
[0046] Secondly, this application provides a method for preparing 1180MPa grade hot-dip galvanized duplex steel, used to prepare the duplex steel described in any one of the first aspects, the method comprising:
[0047] Molten steel containing the chemical composition described in the first aspect is continuously cast to obtain a billet;
[0048] The billet is hot-rolled at a set billet heating temperature and a set hot rolling final rolling temperature.
[0049] The hot-rolled billet is wound up at a set winding temperature;
[0050] The coiled billet is cold-rolled under a set cold rolling deformation amount;
[0051] The cold-rolled billet is continuously annealed under the following conditions: set annealing temperature, set slow cooling temperature, set rapid cooling temperature, set aging temperature, and set belt speed.
[0052] In some embodiments, the set billet heating temperature is 1150℃-1250℃, and the set hot rolling final rolling temperature is 880℃-900℃.
[0053] In this embodiment, the billet heating temperature is set at 1150℃-1250℃ to ensure microstructure homogenization and solid solution of microalloying elements. Excessive temperature may lead to abnormal grain growth, while insufficient temperature may result in uneven microstructure and inadequate solid solution of microalloying elements. The hot rolling final temperature is set at 880℃-900℃ primarily to ensure a good hot-rolled microstructure. Excessive final rolling temperature may result in coarse grains, while insufficient final rolling temperature may lead to mixed grains.
[0054] In some embodiments, the set winding temperature is 540℃-560℃.
[0055] In this embodiment, the coiling temperature is set between 540℃ and 560℃, which takes into account the influence of the cold rolling mill load and the surface quality of the cold rolled coil. If the coiling temperature is too low, cold rolling will become difficult, and if the coiling temperature is too high, the surface quality of the finished coil will deteriorate.
[0056] In some embodiments, the set cold rolling deformation amount is 40%-65%.
[0057] In this embodiment, the cold rolling reduction rate is set to 40%-65% based on two considerations: if the reduction rate is too low, it will be difficult to obtain a finer microstructure and the yield strength of the material will be too low; if the reduction rate is too high, the mill load will be too large, which is not conducive to the control of the sheet shape.
[0058] In some embodiments, the set annealing temperature is 780℃-820℃, and the set slow cooling temperature is 680℃-720℃.
[0059] In this embodiment, the annealing homogenization temperature is set at 780℃-820℃, which falls within the two-phase temperature range of the metallographic composition. Since the slow cooling section has almost no heating capacity, and also in order to adjust the ferrite content, the slow cooling temperature is controlled at 680℃-720℃.
[0060] In some embodiments, the set rapid cooling temperature is set to 250℃-300℃, and the set aging temperature is set to 350℃-400℃.
[0061] In this embodiment, the rapid cooling temperature of 250℃-300℃ is used to induce the transformation of austenite formed in the two-phase region into martensite and bainite. The aging temperature of 320℃-360℃ is used to induce the precipitation of a large number of dispersed metastable carbides within the martensitic matrix, thereby fixing hydrogen elements.
[0062] In some embodiments, the set belt speed is 70mpm-120mpm.
[0063] In this embodiment, the positive effect of a belt speed between 70-120 mpm is to ensure the mechanical properties and coating quality of the strip steel. When the belt speed is lower than the end value of this range, it is easy to cause insufficient strip steel strength and surface inclusion defects. When the belt speed is higher than the end value of this range, it is easy to cause excessive strip steel strength and incomplete coating defects.
[0064] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.
[0065] Relevant experimental and effect data:
[0066] The preparation method of the embodiment includes:
[0067] (1) The molten steel is smelted in a converter and then continuously cast to obtain a continuous casting billet. In this embodiment, a total of 5 heats of steel were smelted. The actual chemical composition of the continuous casting billet of the 5 heats of steel is shown in Table 1.
[0068] Table 1 Chemical composition of steel from furnaces 1-5
[0069] Furnace number C Si Mn Cr Al P S Nb Ti 1# 0.12 0.35 2.3 0.40 0.05 0.011 0.003 0.025 0.025 2# 0.155 0.32 2.3 0.41 0.05 0.011 0.003 0.025 0.025 3# 0.12 0.1 2.3 0.42 0.05 0.011 0.003 0.025 0.025 4# 0.12 0.31 2.6 0.42 0.05 0.011 0.003 0.025 0.025 5# 0.12 0.35 2.3 0.75 0.05 0.011 0.003 0.025 0.025
[0070] (2) The above-mentioned continuously cast billets are cleaned by machine and then hot-charged into the furnace. The heating temperature of the continuously cast billets is 1150-1250℃, the hot rolling finishing temperature is 890℃, and the coiling temperature is 550℃. The hot-rolled plate is further cold-rolled to obtain cold-hardened strip steel, with a cold rolling deformation of 50%.
[0071] (3) The above-mentioned cold-hardened strip steel was subjected to continuous annealing to obtain the finished product. The annealing process and mechanical properties are shown in Table 2. The heat number of Examples 1-4 is 1#, and the heat numbers of Examples 5-8 are 2#-5# respectively, as shown in Table 2. The annealing temperature of the strip steel is between 780-820℃, the rapid cooling temperature is between 250-300℃, the aging temperature is between 320-360℃, and the strip speed is between 70-120mpm.
[0072] To test the delayed cracking resistance of materials under different annealing processes, tensile samples were immersed in a 0.5 mol / L H2SO4 solution (with 0.5 g / L thiourea added as a poisoning agent) at a concentration of 0.5 mA / cm. 2 After being charged with hydrogen for 3 minutes, the sample was stretched on a slow-speed tensile testing machine at a strain rate of 5 × 10⁻⁶. -5 / s, such as Figure 2 As shown. Using the formula HEI = (1 - TE) H The hydrogen embrittlement susceptibility of the sample is calculated as ( / TE0)*100%, where HEI (Hydrogen Embrittlement Index) is the hydrogen embrittlement susceptibility index, and TE... H TE0 represents the elongation after hydrogen charging, while TE0 represents the elongation without hydrogen charging. The performance and hydrogen embrittlement sensitivity index of different annealing processes are shown in the table below.
[0073] Table 2 Mechanical properties and hydrogen embrittlement sensitivity index under different annealing processes
[0074]
[0075]
[0076] In Example 1, the rapid cooling temperature was the same as the aging temperature, resulting in the absence of a large amount of dispersed metastable carbides in the matrix. The measured carbide volume fraction was less than 0.1%, leading to an excessively high hydrogen embrittlement sensitivity index. In Examples 2 and 3, the rapid cooling temperature was 250℃, and the aging temperatures were 320℃ and 360℃, respectively. This facilitated the precipitation of dispersed metastable carbides in the matrix. The measured metastable carbide volume fractions were 0.28% and 0.33%, respectively, resulting in lower hydrogen embrittlement sensitivity indices and excellent resistance to delayed cracking. Because Example 3 had a higher aging temperature, the carbide fraction in the microstructure was higher, resulting in better resistance to delayed cracking. In Example 4, the excessively fast strip speed led to a lower number of metastable carbides in the matrix, resulting in a higher hydrogen embrittlement sensitivity index. The annealing processes of Examples 5-8 were basically the same as in Example 3, but the C content in Example 5 was significantly higher (see Table 1), resulting in significantly higher tensile strength of the strip steel and a decreased resistance to delayed cracking. The Si content in Example 6 was significantly low, resulting in a tensile strength below the lower limit of 1180 MPa. The Mn and Cr contents in Examples 7 and 8 were high (see Table 1), which also led to higher tensile strengths and higher hydrogen embrittlement sensitivity indices. Figure 1 Typical microstructure of hot-dip galvanized duplex steel provided in the embodiments of this application.
[0077] The differences in the delayed cracking resistance of the above embodiments demonstrate that the approach of the present invention can indeed significantly improve the hydrogen embrittlement resistance of 1180MPa grade hot-dip galvanized duplex steel.
[0078] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.
[0079] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this application, terms such as "comprising" and "including" mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than one" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.
[0080] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.
Claims
1. A 1180MPa grade hot-dip galvanized duplex steel, characterized in that, The chemical composition of the duplex steel includes: C: 0.10 wt% - 0.15 wt%, Si: 0.2 wt% - 0.5 wt%, Mn: 2.0 wt% - 2.5 wt%, Cr: 0.3 wt% - 0.6 wt%, Al: 0.01 wt% - 0.05 wt%, P ≤ 0.02 wt%, S ≤ 0.01 wt%, Nb: 0 - 0.04 wt%, Ti: 0 - 0.04 wt%, balance Fe; The metallographic structure of the duplex steel includes at least one of the following: ferrite, tempered martensite, bainite, and carbides. The ferrite content is 10%-40% by volume, the sum of the tempered martensite and the bainite content is 70%-80% by volume, and the carbide content is greater than 0.15% by volume. The method for preparing the hot-dip galvanized duplex steel includes: Molten steel containing the aforementioned chemical composition is continuously cast to obtain a billet; The billet is hot-rolled at a set billet heating temperature and a set hot rolling final rolling temperature. The hot-rolled billet is wound up at a set winding temperature; The coiled billet is cold-rolled under a set cold rolling deformation amount; The cold-rolled billet is continuously annealed under the following conditions: annealing homogenization temperature, slow cooling temperature, rapid cooling temperature, aging temperature, and belt speed. The set annealing homogenization temperature is 780℃-820℃, and the set slow cooling temperature is 680℃-720℃; The set rapid cooling temperature is set to 250℃-300℃, and the set aging temperature is set to 350℃-400℃. The set belt speed is 70mpm-120mpm.
2. The hot-dip galvanized duplex steel according to claim 1, characterized in that, The set billet heating temperature is set to 1150℃-1250℃, and the set hot rolling final rolling temperature is set to 880℃-900℃.
3. The hot-dip galvanized duplex steel according to claim 1, characterized in that, The set winding temperature is 540℃-560℃.
4. The hot-dip galvanized duplex steel according to claim 1, characterized in that, The set cold rolling deformation value is 40%-65%.