Wear-resistant cold-rolled DP steel sheet and production method and application thereof

Abstract

The invention relates to a wear-resistant cold-rolled DP steel sheet and a production method and application thereof. The wear-resistant cold-rolled DP steel sheet comprises the following chemical components in percentage by mass: 0.20%-0.65% of C, 0.6%-1.2% of Si, 1.2%-2% of Mn, 0.5%-1.0% of Cr, less than or equal to 0.03% of S, less than or equal to 0.04% of P, less than or equal to 0.3% of Mo, less than or equal to 0.5% of Ni, less than or equal to 0.2% of total mass fraction of microalloying elements, and the balance of Fe and inevitable impurities. According to the invention, the wear-resistant DP steel sheet composed of ferrite, martensite and granular cementite is obtained by designing spheroidizing annealing between the cold rolling process and the continuous annealing process by adopting higher carbon content greater than or equal to 0.20% and a proper amount of Cr, and has the comprehensive properties of wear resistance, high strength, easy formation and good welding.

Description

Technical Field

[0001] The invention relates to the technical field of steel materials, and in particular to a wear-resistant cold-rolled DP steel sheet and a production method and application thereof. Background Art

[0002] Cold-rolled DP dual-phase steel is a high-strength material for car bodies. On the one hand, it has good dimensional accuracy and surface quality. It is usually supplied in the form of steel coils. After being supplied to the machinery factory, it is uncoiled and cut into steel plates. Finally, the steel plates are processed by stamping or rolling and welded into car body parts (such as door rings, inner plates, etc.). Cold-rolled DP dual-phase steel can be widely used in car bodies, mainly due to its high strength and formability. Because high strength can improve car body safety and achieve lightweight, easy formability reduces the defective rate when steel plates are stamped in batches, and good product quality can be obtained while reducing costs. On the other hand, the high strength and formability of cold-rolled DP dual-phase steel are guaranteed by its microstructure, that is, a mixed structure of soft ferrite and hard martensite. The soft ferrite makes the material easy to form, while the hard martensite ensures high strength.

[0003] At present, the production process to achieve the microstructure and mechanical properties of cold-rolled DP dual-phase steel is mainly continuous annealing, which mainly includes: dual-phase zone heating in a continuous annealing furnace → slow cooling → rapid cooling → overaging → final cooling → water cooling → flattening → post-processing → coiling and other processes. The ferrite and austenite obtained by dual-phase zone heating complete the structural transformation to obtain ferrite and martensite in the rapid cooling stage, that is, the austenite formed by heating is transformed into martensite after cooling. At present, the DP dual-phase steel commonly used in car bodies is 590DP and 780DP at the grades of 590MPa and 780MPa, but with the development of lightweight technology, the strength of steel used for car bodies is getting higher and higher. Steel companies have developed dual-phase steels of 980MPa and even above 1100MPa by increasing the carbon content and / or adjusting the process to increase the martensite content. Naturally, the elongation decreases with the increase in strength.

[0004] Although DP steel is an advanced high-strength steel with high tensile strength, its wear resistance is not excellent due to the low martensite content in the microstructure. For body parts such as automobile chassis or door sills that are often subjected to friction, wear and impact, the wear resistance needs to be further improved. In view of this, the present invention provides a wear-resistant cold-rolled DP steel sheet and its production method and application. Summary of the invention

[0005] The technical problem to be solved by the present invention is to solve the poor wear resistance of DP steel and to provide a high-strength, easily formable and wear-resistant DP steel sheet for automobile chassis parts and a production method thereof.

[0006] The technical solution of the present invention to solve the above technical problems is as follows:

[0007] In a first aspect, a wear-resistant cold-rolled DP steel sheet, the chemical composition of the wear-resistant cold-rolled DP steel sheet is as follows by mass fraction: C: 0.20% to 0.65%, Si: 0.6% to 1.2%, Mn: 1.2% to 2%, Cr: 0.5% to 1.0%, S≤0.03%, P≤0.04%, Mo≤0.3%, Ni≤0.5%, the total mass fraction of micro-alloying elements does not exceed 0.2%, and the rest is Fe and unavoidable impurities.

[0008] Based on the above technical solution, the present invention can also be improved as follows.

[0009] Furthermore, the chemical composition of the wear-resistant cold-rolled DP steel sheet is calculated by mass fraction as follows: C: 0.40% to 0.6%, Si: 0.8% to 1.2%, Mn: 1.6% to 2%, Cr: 0.6% to 1%, S≤0.03%, P≤0.04%, Mo≤0.2%, Ni≤0.4%, V≤0.1%, Nb≤0.03%, Ti≤0.1%, the total mass fraction of micro-alloying elements does not exceed 0.2%, and the rest is Fe and unavoidable impurities.

[0010] Furthermore, the microalloying elements include at least one of V, Nb and Ti, and the mass fraction of each microalloying element does not exceed 0.1%.

[0011] In a second aspect, a method for preparing a wear-resistant cold-rolled DP steel sheet comprises the following steps:

[0012] (1) obtaining a cold-rolled DP steel sheet;

[0013] (2) The cold-rolled DP steel sheet is subjected to spheroidizing annealing to obtain a DP steel sheet having a ferrite and granular pearlite or pure granular pearlite structure, and then subjected to continuous annealing to obtain a DP steel sheet having a mixed structure of ferrite, martensite and cementite, that is, a wear-resistant cold-rolled DP steel sheet.

[0014] Furthermore, the spheroidizing annealing in step (2) adopts a periodic hood annealing method, a periodic continuous annealing or a cycle annealing, and the annealing temperature is 670°C to 800°C.

[0015] Further, the continuous annealing described in step (2) is specifically as follows: heating the DP steel sheet having ferrite and granular pearlite or pure granular pearlite structure to 700°C to 840°C, and sequentially performing slow cooling, rapid cooling, overaging, final cooling, water cooling, leveling, post-treatment and coiling. Among them, the slow cooling temperature is 650°C to 720°C, the rapid cooling rate is 8°C / s to 20°C / s, the overaging temperature is 250 to 350, the final cooling temperature is 180, circulating water is used for water cooling, the leveling elongation is 0.8 to 1%, and the post-treatment depends on the customer, such as oiling, and finally coiling at room temperature. When surface hot-dip treatment is performed, hot-dip is performed after rapid cooling, and then cooling, leveling, post-treatment and coiling are performed according to the hot-dip process to obtain the hot-dip product described in this product.

[0016] Furthermore, the step (1) of obtaining the cold-rolled DP steel sheet comprises the following consecutive steps: steelmaking, refining, continuous casting, hot rolling, and cold rolling to obtain the cold-rolled DP steel sheet.

[0017] Furthermore, steelmaking can be carried out using conventional converter or electric furnace processes familiar to technicians.

[0018] Furthermore, the refining can be carried out by using conventional ladle refining, RH refining or VOD refining processes familiar to technicians.

[0019] Furthermore, the continuous casting is specifically as follows: a slab continuous casting machine is used for protected continuous casting, the thickness of the ingot is 100 to 300 mm, the width is 780 mm to 2250 mm, and a light reduction process or a heavy reduction process is used to obtain the ingot.

[0020] Further, the hot rolling specifically comprises: heating the ingot to 1100° C. to 1250° C., keeping the temperature for 1.5 to 4 hours, and then sequentially performing high pressure dephosphorization, rough rolling, finish rolling, laminar cooling and coiling to obtain a hot rolled steel coil; the strip thickness of the hot rolled steel coil is 2.8 mm to 10 mm;

[0021] The cold rolling specifically includes: the hot rolled steel coil is cold rolled with a total reduction rate of 30% to 80% to obtain a cold rolled steel coil, namely a cold rolled DP steel sheet; the strip thickness of the cold rolled steel coil is 0.6mm to 3.0mm.

[0022] In a third aspect, an application of a wear-resistant cold-rolled DP steel sheet is used to prepare automobile chassis parts.

[0023] The beneficial effects of the present invention are as follows: the present invention adopts a high carbon content of ≥0.20% to form an appropriate amount of alloy cementite, and ensures that sufficient carbon remains in the matrix to obtain a high-strength matrix, an appropriate amount of Cr is mainly used to form alloy cementite to avoid too fast dissolution of pure cementite during heating, and spheroidizing annealing is designed between cold rolling and continuous annealing processes to obtain a wear-resistant DP steel sheet composed of ferrite, martensite and granular cementite (or alloy cementite, as superhard particles), which has the comprehensive properties of wear resistance, high strength, easy forming and good welding, wherein its tensile strength is ≥490MPa and the elongation is 6% to 36%; the wear-resistant DP steel sheet is suitable for the preparation of automobile chassis parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the hot-rolled ferrite + lamellar pearlite microstructure diagram of the present invention;

[0025] Figure 2 This is a microstructure diagram of spheroidized annealed granular pearlite of the present invention;

[0026] Figure 3 It is the quenched cementite + ferrite + martensite diagram of the dual phase region of the present invention;

[0027] Figure 4 This is a physical picture of the tensile specimen of the present invention. DETAILED DESCRIPTION

[0028] The principles and features of the present invention are described below, and the examples are only used to explain the present invention and are not used to limit the scope of the present invention. If no specific technology or conditions are specified in the embodiments, the technology or conditions described in the literature in this field or the product instructions are used. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased through regular channels.

[0029] Examples 1-3

[0030] The chemical compositions of the wear-resistant DP steel sheets in Examples 1-3 are shown in Table 1 (the remainder is Fe and unavoidable impurities) by mass fraction.

[0031] Table 1 Chemical composition of hot rolled sheets in Examples 1-3 by mass fraction

[0032] Example 1 2 3 C / ％ 0.2 0.4 0.65 Si / % 1.2 0.8 0.6 Mn / % 2.0 1.6 1.2 Cr / ％ 1.0 0.6 0.5 S / ％ 0.01 0.01 0.01 P / ％ 0.03 0.02 0.02 Mo / % 0.2 0 0 Ni / % 0.4 0 0 V / ％ 0.1 0 0 Nb / % 0.02 0.03 0 Ti / % 0 0 0

[0033] The present embodiment relates to a method for preparing a wear-resistant DP steel sheet, comprising the following steps:

[0034] (1) Steelmaking: Steelmaking is carried out using the conventional converter process familiar to technicians.

[0035] (2) Refining: The conventional ladle refining and RH refining processes familiar to technicians are used for smelting.

[0036] (3) Continuous casting: A slab continuous casting machine is used for protected continuous casting. The thickness of the ingot is 100 to 300 mm. The ingot is obtained by a light reduction process.

[0037] (4) Hot rolling: The billet is heated to 1100℃~1250℃ in a heating furnace and kept warm for 3 hours. High pressure dephosphorization, rough rolling, finishing rolling, laminar cooling and coiling are completed in sequence to obtain hot rolled steel coils. The strip thickness of the hot rolled steel coils is 2.8mm~10mm and the width is 780mm~2250mm.

[0038] (5) Cold rolling: After the hot-rolled steel coil is pickled and cold-rolled, the cold-rolled product thickness is 0.6 mm to 3.0 mm, and the total reduction rate is 30% to 80%, thereby obtaining a cold-rolled steel coil.

[0039] (6) Spheroidizing annealing: The cold-rolled steel coil is subjected to spheroidizing annealing to obtain a cold-rolled steel coil with a structure of ferrite and granular pearlite or pure granular pearlite. The spheroidizing annealing can be carried out by a periodic bell-type annealing method, that is, the steel coil is placed in a bell-type furnace for heating at a temperature of 670°C to 800°C for a holding time of 1 to 15 hours. The atmosphere in the furnace is controlled to prevent decarburization.

[0040] (7) Continuous annealing: The ferrite and granular pearlite or pure granular pearlite in the spheroidizing annealed cold-rolled steel coil are transformed into a mixed structure mainly composed of ferrite, martensite and cementite (or alloy cementite). The specific process is that the strip is heated to 700°C to 840°C, and then slowly cooled, rapidly cooled, over-aged, finally cooled, water cooled, leveled, post-treated and coiled to obtain the product described in the present invention; when the surface is hot-dip treated, hot-dip is performed after rapid cooling, and then cooling, leveling, post-treatment and coiling are performed according to the hot-dip process to obtain the hot-dip product described in the present invention ( Figure 4 ).

[0041] The wear-resistant DP steel sheets prepared in Examples 1-3 and commercial DP590, commercial DP780, and commercial QP980 were tested for mechanical properties and wear resistance. P590, DP780, and QP980 were obtained from steel mills or automobile factories. The test results are shown in Table 2.

[0042] According to T / CFA 010604-3-2016: Impact abrasive wear test method for steel materials, the wear resistance test was carried out on the MLD-10 dynamic load impact abrasive wear tester. The test conditions are: the friction couple is quenched 45# steel with an outer diameter of 50mm and an inner diameter of 25mm, the speed is 200r / min; the dynamic load is 10Kg, the abrasive is 60-80 mesh quartz sand, and the quartz sand flow rate is 6Kg / h. Pre-grinding for 15min before the test makes the sample and the friction pair better match. The formal test time is 1h. After pre-grinding and testing, the sample must be taken out, placed in alcohol and ultrasonically cleaned, blown dry, and weighed on an electronic balance with an accuracy of 0.0001g. The mass change before and after is measured, which is the friction weight loss. The larger the value, the worse the wear resistance, and vice versa, the better the wear resistance.

[0043] Table 2 Comparison of wear resistance of the present invention and conventional DP steel

[0044]

[0045] The data in Table 2 show that the wear-resistant DP steel of the present invention has a wear resistance of about 15% or more higher than that of conventional DP steel of the same strength level. Since it still has good plasticity, it is a very suitable new material for automobile chassis parts.

[0046] Depend on Figures 1 to 3 It can be seen that the present invention adopts a high carbon content ≥ 0.20% to form an appropriate amount of alloy cementite and ensure that there is enough carbon remaining in the matrix to obtain a high-strength matrix. An appropriate amount of Cr is mainly used to form alloy cementite to avoid the pure cementite from dissolving too quickly when heated. Between the cold rolling and continuous annealing processes, spheroidizing annealing is designed to obtain a wear-resistant DP steel sheet composed of ferrite, martensite and granular cementite (or alloy cementite, as superhard particles).

[0047] In summary, the present invention adopts a steel sheet containing a relatively high carbon content ≥0.20%, an appropriate amount of Cr, and designs spheroidizing annealing between cold rolling and continuous annealing processes, thereby obtaining a wear-resistant DP steel sheet composed of ferrite, martensite and granular cementite (or alloy cementite, as superhard particles), which has the comprehensive properties of wear resistance, high strength, easy forming and good welding, wherein its tensile strength is ≥490MPa and the elongation is 6% to 36%; the wear-resistant DP steel sheet is suitable for the preparation of automobile chassis parts.

[0048] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A wear-resistant cold-rolled DP steel sheet, characterized in that: The chemical composition of the wear-resistant cold-rolled DP steel sheet is calculated by mass fraction as follows: C: 0.20% to 0.65%, Si: 0.6% to 1.2%, Mn: 1.2% to 2%, Cr: 0.5% to 1.0%, S≤0.03%, P≤0.04%, Mo≤0.3%, Ni≤0.5%, the total mass fraction of micro-alloying elements does not exceed 0.2%, and the rest is Fe and unavoidable impurities.

2. A wear-resistant cold-rolled DP steel sheet according to claim 1, characterized in that: The chemical composition of the wear-resistant cold-rolled DP steel sheet is calculated by mass fraction as follows: C: 0.40% to 0.6%, Si: 0.8% to 1.2%, Mn: 1.6% to 2%, Cr: 0.6% to 1%, S≤0.03%, P≤0.04%, Mo≤0.2%, Ni≤0.4%, V≤0.1%, Nb≤0.03%, Ti≤0.1%, the total mass fraction of micro-alloying elements does not exceed 0.2%, and the rest is Fe and unavoidable impurities.

3. The wear-resistant cold-rolled DP steel sheet according to claim 1, characterized in that: The microalloying elements include at least one of V, Nb and Ti, and the mass fraction of each microalloying element does not exceed 0.1%.

4. A method for preparing a wear-resistant cold-rolled DP steel sheet according to any one of claims 1 to 3, characterized in that: The steps include: (1) obtaining a cold-rolled DP steel sheet; (2) The cold-rolled DP steel sheet is subjected to spheroidizing annealing to obtain a DP steel sheet having a ferrite and granular pearlite or pure granular pearlite structure, and then subjected to continuous annealing to obtain a DP steel sheet having a mixed structure of ferrite, martensite and cementite, that is, a wear-resistant cold-rolled DP steel sheet.

5. The method for preparing a wear-resistant cold-rolled DP steel sheet according to claim 4, characterized in that: The spheroidizing annealing in step (2) adopts a periodic hood annealing method, a periodic continuous annealing or a cycle annealing, and the annealing temperature is 670°C to 800°C.

6. The method for preparing a wear-resistant cold-rolled DP steel sheet according to claim 4, characterized in that: The continuous annealing in step (2) is specifically as follows: heating the DP steel sheet having a ferrite and granular pearlite or pure granular pearlite structure to 700°C to 840°C, and sequentially performing slow cooling, rapid cooling, overaging, final cooling, water cooling, flattening, post-treatment and coiling.

7. The method for preparing a wear-resistant cold-rolled DP steel sheet according to claim 4, characterized in that: The step (1) of obtaining the cold-rolled DP steel sheet comprises the following consecutive steps: steelmaking, refining, continuous casting, hot rolling, and cold rolling to obtain the cold-rolled DP steel sheet.

8. The method for preparing a wear-resistant cold-rolled DP steel sheet according to claim 7, characterized in that: The continuous casting specifically comprises: using a slab continuous casting machine for protected continuous casting, the thickness of the cast slab is 100-300 mm, and a light reduction process or a heavy reduction process is used to obtain the cast slab.

9. The method for preparing a wear-resistant cold-rolled DP steel sheet according to claim 8, characterized in that: The hot rolling specifically comprises: heating the ingot to 1100° C. to 1250° C., keeping the temperature for 1.5 to 4 hours, and then sequentially performing high-pressure dephosphorization, rough rolling, finish rolling, laminar cooling and coiling to obtain a hot-rolled steel coil; the strip thickness of the hot-rolled steel coil is 2.8 mm to 10 mm; The cold rolling specifically includes: the hot-rolled steel coil is cold-rolled with a total reduction rate of 30% to 80% to obtain a cold-rolled steel coil, namely a cold-rolled DP steel sheet; the strip thickness of the cold-rolled steel coil is 0.6 mm to 3.0 mm.

10. An application of a wear-resistant cold-rolled DP steel sheet, characterized in that: The wear-resistant cold-rolled DP steel sheet according to any one of claims 1 to 3 is used for preparing automobile chassis parts.

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