High-strength high-specific-impulse heavy plate for automobile and preparation method thereof

Abstract

The application relates to a high-strength plastic product difference thick plate for automobiles and a preparation method thereof, and belongs to the rolling technical field.The mass percentage of chemical elements of the difference thick plate is as follows: C: 0.22-0.28%, Si: 1.55-1.65%, Mn: 1.50-1.65%, P: <=0.002%, S: <=0.002%, N: <=0.003%, Al: <=0.04%, and the rest is Fe and inevitable impurities.The preparation method of the high-strength plastic product difference thick plate for automobiles is as follows: (1) steelmaking and blank making; (2) hot rolling; (3) cold rolling; (4) variable-thickness rolling; and (5) quenching and partitioning heat treatment.The high-strength plastic product difference thick plate for automobiles prepared by the application has a thick zone thickness of 2.0 mm and a thin zone thickness of 1.0 mm.The high-strength plastic product difference thick plate for automobiles prepared by the application has different thickness zones, and the performance of the different thickness zones is different, so that the automobile parts can maximize the carrying capacity of the metal under the condition of uneven load distribution, greatly reduce the structure weight, save energy and reduce emissions, and have high production efficiency, low production cost, and easy realization of large-scale industrial production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of rolling, and particularly relates to a high-strength and high-plasticity differential thick plate for automobiles and a preparation method thereof. BACKGROUND

[0002] The cold-rolled differential thick plate is used in the automobile manufacturing, shipbuilding, bridge and other industries, and has the advantages of saving material, reducing weight, reducing welds, reducing cost, improving efficiency and the like. The differential thick plate produced by the variable thickness rolling method has thin areas, thick areas and transition areas with different thicknesses. Compared with the laser welding plate, the differential thick plate has no welds, good quality, low production cost, high efficiency, and the length and shape of the transition area can be designed according to the stress condition of the stamping part in service, and it is paid more attention due to the more obvious effect of saving material and reducing weight. The differential thick plate has been applied in the manufacturing of automobile lightweight parts at home and abroad, and there are many automobile lightweight parts made of the differential thick plate on the automobile, including the B column, the anti-collision beam and the front longitudinal beam, and at present, the low-alloy steel differential thick plate is more applied. The differential thick plate as the automobile steel should have high strength and high plasticity while ensuring the saving of material and reducing weight, so as to well meet the performance requirements of the automobile in the aspects of lightweight and collision safety. At present, the high-strength and high-plasticity differential thick plate has not been developed and applied, and the high-strength and high-plasticity differential thick plate of the low-alloy steel generally has a strength-plasticity product of less than 15000 MPa·%. Therefore, the development of the high-strength and high-plasticity differential thick plate and the preparation method thereof can promote the application process of the high-strength and high-plasticity differential thick plate in the automobile lightweight. SUMMARY

[0003] The application aims to provide a high-strength and high-plasticity differential thick plate for automobiles and a preparation method thereof, and the mechanical properties of the differential thick plate with different thicknesses are obtained by the combination of the variable thickness rolling and the quenching and partitioning heat treatment process.

[0004] The high-strength and high-plasticity differential thick plate for automobiles provided by the application has the mass percentage of the chemical elements as follows: C: 0.22-0.28%, Si: 1.55-1.65%, Mn: 1.50-1.65%, P: ≤0.002%, S: ≤0.002%, N: ≤0.003%, Al: ≤0.04%, and the rest is Fe and inevitable impurities.

[0005] The thickness of the thick area of the high-strength and high-plasticity differential thick plate for automobiles is 2.0 mm, and the thickness of the thin area is 1.0 mm, and the high-strength and high-plasticity differential thick plate for automobiles has a transition area, and the transition area curve is a straight line dominant transition.

[0006] The tensile strength of the high strength and plastic product difference thick plate for automobile is greater than 1500MPa, and the strength and plastic product is greater than 15000MPa%. The tensile strength of the thick area is 1560-1650MPa, the yield strength is 850-1020MPa, the elongation is 13-16%, and the strength and plastic product is 21500-25500MPa%; the tensile strength of the thin area is 1500-1600MPa, the yield strength is 860-1050MPa, the elongation is 10-12%, and the strength and plastic product is 15400-16800MPa%.

[0007] The microstructure of the thick area and the thin area of the high strength and plastic product difference thick plate for automobile is mainly martensite and a small amount of residual austenite.

[0008] The preparation method of the high strength and plastic product difference thick plate for automobile comprises the following steps:

[0009] Step 1: steelmaking and billet preparation

[0010] According to the chemical composition of the high strength and plastic product difference thick plate for automobile, smelting is carried out in a 150kg vacuum smelting furnace, and then the ingot is cast into a steel billet with a size of 60mm*60mm*450mm after forging;

[0011] Step 2: hot rolling

[0012] After heating the steel billet in a heating furnace, rolling is carried out on a 450mm hot rolling mill, and then air cooling is carried out after 6 passes, so as to obtain a hot rolling slab with a thickness of 4.5mm;

[0013] Step 3: cold rolling

[0014] After pickling the hot rolling slab, cold rolling is carried out to 2.2mm, and then annealing treatment is carried out and the furnace is cooled to room temperature;

[0015] Step 4: variable thickness rolling

[0016] After pickling the cold rolling plate, single-pass variable thickness rolling is carried out on a four-roll cold rolling mill, and the rolling gap is adjusted in real time to obtain a difference thick plate;

[0017] Step 5: quenching and partitioning heat treatment

[0018] After heating the difference thick plate in a heating furnace, quenching and carbon partitioning process is carried out in a salt bath furnace, and finally rapid quenching and cooling to room temperature are carried out to obtain a high strength and plastic product difference thick plate.

[0019] Further, the heating temperature in step 2 is 1200-1250℃, and the holding time is 6 hours.

[0020] Further, the annealing temperature in step 3 is 610-630℃, and the holding time is 1 hour.

[0021] Further, the difference thick plate thickness zone in step 4 is 2.0 mm, the thin zone is 1.0 mm, and a transition zone is provided with a straight line dominant transition curve.

[0022] Further, the heating temperature in step 5 is an austenitizing temperature of 900-950 DEG C and holding for 10-20 min, and then salt bath quenching to a temperature of 250-290 DEG C and holding for 20-300 s for carbon partitioning process.

[0023] The beneficial effects of the present application: the high strength and plastic product of the present application for automobile is greater than 1500 MPa, the strength and plastic product is greater than 15000 MPa, the maximum strength and plastic product reaches 25500 MPa, which can be used as raw material for manufacturing lightweight automobile parts. The product prepared by the present application has different thickness zones, and the performance of different thickness zones is different, which can maximize the carrying capacity of the metal under the condition of uneven load distribution of automobile parts, greatly reduce the structure weight, and obtain good energy saving and emission reduction effect. The method of the present application uses variable thickness rolling and heat treatment method to obtain high strength and plastic product of difference thick plate, which has the advantages of high production efficiency, low production cost and easy realization of large-scale industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 It is a schematic diagram of two kinds of longitudinal variable thickness plates, wherein (a) is a schematic diagram of laser welding plate, and (b) is a schematic diagram of the rolling difference thick plate of the present application;

[0025] Figure 2 It is a schematic diagram of the high strength and plastic product of the present application for automobile;

[0026] Figure 3 It is a scanning electron microscope tissue photo of the high strength and plastic product of the present application for automobile, wherein (a) is the structure of the thin zone (thickness 1.0 mm), and (b) is the structure of the thick zone (thickness 2.0 mm);

[0027] Figure 4 It is a scanning electron microscope tissue photo of the high strength and plastic product of the present application for automobile, wherein (a) is the structure of the thin zone (thickness 1.0 mm), and (b) is the structure of the thick zone (thickness 2.0 mm);

[0028] Figure 5 It is a scanning electron microscope tissue photo of the high strength and plastic product of the present application for automobile, wherein (a) is the structure of the thin zone (thickness 1.0 mm), and (b) is the structure of the thick zone (thickness 2.0 mm);

[0029] Figure 6Scanning electron microscope microstructure photograph of the high strength and plastic product difference thick plate for automobile prepared in the embodiment 4 of the present application, wherein (a) is the microstructure of the thin area (thickness 1.0 mm), (b) is the microstructure of the thick area (thickness 2.0 mm);

[0030] Figure 7 Scanning electron microscope microstructure photograph of the high strength and plastic product difference thick plate for automobile prepared in the embodiment 5 of the present application, wherein (a) is the microstructure of the thin area (thickness 1.0 mm), (b) is the microstructure of the thick area (thickness 2.0 mm);

[0031] Figure 8 Scanning electron microscope microstructure photograph of the high strength and plastic product difference thick plate for automobile prepared in the embodiment 6 of the present application, wherein (a) is the microstructure of the thin area (thickness 1.0 mm), (b) is the microstructure of the thick area (thickness 2.0 mm);

[0032] Figure 9 X-ray diffraction spectrum of the thin area and thick area microstructure of the high strength and plastic product difference thick plate for automobile prepared in the embodiment 6 of the present application. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all the other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0034] In order to facilitate the understanding of the present application, several embodiments of the present application are given. However, the present application can be realized in many different forms, and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0035] Figure 1 Schematic diagram of two kinds of longitudinal variable thickness plates, wherein (a) is a schematic diagram of a laser tailor-welded plate, (b) is a schematic diagram of a rolled difference thick plate of the present application; Figure 2 Schematic diagram of the high strength and plastic product difference thick plate for automobile prepared in the embodiment of the present application.

[0036] Embodiment 1

[0037] A high strength and plastic product difference thick plate for automobile, the mass percentage of chemical elements of which is: C: 0.25%, Si: 1.58%, Mn: 1.55%, P: 0.002%, S: 0.001%, N: 0.003%, Al: 0.04%, and the rest is Fe and inevitable impurities.

[0038] The preparation method of the high strength and plastic product difference thick plate for automobile described above, comprising the following steps:

[0039] Step 1: Steelmaking

[0040] According to the chemical composition of the high strength and plastic product difference thick plate for automobile, smelting was carried out in a 150 kg vacuum melting furnace, and then the ingot was cast and forged to obtain a steel billet with a size of 60 mm x 60 mm x 450 mm;

[0041] Step 2: Hot rolling

[0042] The steel billet was heated to 1200℃ in a heating furnace for 6 hours, and then rolled on a 450 mm hot rolling mill for 6 passes and then air cooled to obtain a hot rolled plate with a thickness of 4.5 mm;

[0043] Step 3: Cold rolling

[0044] The hot rolled plate was pickled and cold rolled to 2.2 mm, and then annealed at 620℃ for 1 hour and then cooled to room temperature in the furnace;

[0045] Step 4: Variable thickness rolling

[0046] The cold rolled plate was pickled and single-pass variable thickness rolling was carried out on a four-roll cold rolling mill by real-time dynamic adjustment of the roll gap to obtain a difference thick plate with a thick area of 2.0 mm, a thin area of 1.0 mm and a transition area with a straight line dominant transition curve;

[0047] Step 5: Quenching and partitioning heat treatment

[0048] The above difference thick plate was heated to an austenitizing temperature of 900℃ in a heating furnace for 10 min, and then salt bath quenched to 250℃, and then carbon partitioning process was carried out at this temperature for 300 s, and finally rapidly quenched to room temperature to obtain a high strength and plastic product difference thick plate for automobile.

[0049] The scanning electron micrograph of the high strength and plastic product difference thick plate for automobile prepared in this example is shown in Figure 3 As can be seen from the figure, most of the structure is lath martensite, and the volume fraction of residual austenite in the thin area and the thick area is 3-6% as measured by XRD.

[0050] The mechanical properties of the high strength and plastic product difference thick plate for automobile prepared in this example were detected, and the tensile strength of the thick area was 1594 MPa, the yield strength was 863 MPa, the elongation was 15.3%, and the strength and plastic product was 24309 MPa%; The tensile strength of the thin area was 1515 MPa, the yield strength was 865 MPa, the elongation was 11.0%, and the strength and plastic product was 16660 MPa%.

[0051] Example 2

[0052] A high strength and plastic product difference thick plate for automobile, the mass percentage of chemical elements of which is: C: 0.26%, Si: 1.62%, Mn: 1.60%, P: 0.002%, S: 0.001%, N: 0.003%, Al: 0.04%, and the rest is Fe and inevitable impurities.

[0053] The preparation method of the above-mentioned high strength and plastic product difference thick plate for automobile, comprising the following steps:

[0054] Step 1: steelmaking and billet making

[0055] According to the chemical composition of the high strength and plastic product difference thick plate for automobile, smelting is carried out in a 150kg vacuum smelting furnace, and then the ingot is cast and forged to obtain a steel billet with a size of 60mmx60mmx450mm;

[0056] Step 2: hot rolling

[0057] The steel billet is heated to 1200℃ in a heating furnace and kept for 6 hours, and then rolled on a 450mm hot rolling mill for 6 passes and then air-cooled to obtain a hot-rolled plate with a thickness of 4.5mm;

[0058] Step 3: cold rolling

[0059] The hot-rolled plate is pickled and cold-rolled to 2.2mm, and then annealed at 620℃ for 1 hour and cooled to room temperature in the furnace;

[0060] Step 4: variable thickness rolling The pickled cold-rolled plate is single-pass variable thickness rolled on a four-roll cold rolling mill, and the roll gap is adjusted in real time to obtain a difference thick plate with a thick area of 2.0mm, a thin area of 1.0mm and a transition area with a straight line dominant transition curve;

[0061] Step 5: quenching and partitioning heat treatment

[0062] The above-mentioned difference thick plate is heated to an austenitizing temperature of 900℃ in a heating furnace and kept for 10min, and then quenched in a salt bath to 250℃, kept at this temperature for 60s for carbon partitioning process, and finally rapidly quenched to room temperature to obtain a high strength and plastic product difference thick plate.

[0063] The scanning electron micrograph of the high strength and plastic product difference thick plate for automobile prepared in this embodiment is shown in Figure 4 As can be seen from the figure, most of the structure is lath martensite, and the volume fraction of residual austenite in the thin area and the thick area is 3-6% as measured by XRD.

[0064] The mechanical property of the high strength and plastic product difference thick plate prepared in the embodiment is detected, and the tensile strength of the thick area is 1648 MPa, the yield strength is 1005 MPa, the elongation is 14.8%, and the strength and plastic product is 24315 MPa%; the tensile strength of the thin area is 1602 MPa, the yield strength is 970 MPa, the elongation is 10.5%, and the strength and plastic product is 16826 MPa%.

[0065] Example 3

[0066] A high strength and plastic product difference thick plate for automobile, the mass percentage of chemical elements is: C: 0.25%, Si: 1.58%, Mn: 1.55%, P: 0.002%, S: 0.001%, N: 0.003%, Al: 0.04%, and the rest is Fe and inevitable impurities.

[0067] The preparation method of the high strength and plastic product difference thick plate for automobile, comprising the following steps:

[0068] Step 1: steelmaking and billet preparation

[0069] The chemical composition of the high strength and plastic product difference thick plate for automobile is smelted in a 150 kg vacuum smelting furnace, and then cast into ingots, and then forged to obtain a steel billet with a size of 60 mm*60 mm*450 mm;

[0070] Step 2: hot rolling

[0071] The steel billet is heated to 1200 DEG C in a heating furnace and kept for 6 hours, and then rolled on a 450 mm hot rolling mill for 6 passes and then air cooled to obtain a hot rolled plate with a thickness of 4.5 mm;

[0072] Step 3: cold rolling

[0073] The hot rolled plate is pickled and cold rolled to 2.2 mm, and then annealed at 620 DEG C for 1 hour and then cooled to room temperature in the furnace;

[0074] Step 4: variable thickness rolling The cold rolled plate is pickled and single-pass variable thickness rolled on a four-roll cold rolling mill, and the roll gap is adjusted in real time to obtain a difference thick plate with a thick area of 2.0 mm and a thin area of 1.0 mm and a transition area, and the transition area curve is a straight line dominant transition;

[0075] Step 5: quenching and partitioning heat treatment

[0076] The difference thick plate is heated to an austenitizing temperature of 900 DEG C in a heating furnace and kept for 10 min, and then quenched in a salt bath to 250 DEG C, and kept at this temperature for 20 s for carbon partitioning process, and finally rapidly quenched to room temperature to obtain a high strength and plastic product difference thick plate.

[0077] The automobile high strength and plastic product difference thick plate prepared in the embodiment has a scanning tissue photo as shown in FIG. 2. Figure 5 As shown in the figure, most of the tissue is lath martensite, and the volume fraction of residual austenite in the thin area and the thick area is 3-6% as measured by XRD.

[0078] The automobile high strength and plastic product difference thick plate prepared in the embodiment is subjected to mechanical property detection, and the tensile strength of the thick area is 1650 MPa, the yield strength is 990 MPa, the elongation is 13%, and the strength and plastic product is 21450 MPa·%. The tensile strength of the thin area is 1595 MPa, the yield strength is 1010 MPa, the elongation is 10.0%, and the strength and plastic product is 15546 MPa·%.

[0079] Example 4

[0080] An automobile high strength and plastic product difference thick plate, the mass percentage of chemical elements of which is: C: 0.26%, Si: 1.62%, Mn: 1.60%, P: 0.002%, S: 0.001%, N: 0.003%, Al: 0.04%, and the rest is Fe and inevitable impurities.

[0081] The preparation method of the automobile high strength and plastic product difference thick plate, comprising the following steps:

[0082] Step 1: steelmaking and billet making

[0083] The automobile high strength and plastic product difference thick plate is smelted in a 150 kg vacuum smelting furnace according to the chemical composition, and then cast into an ingot, and then forged to obtain a steel billet with a size of 60 mm×60 mm×450 mm;

[0084] Step 2: hot rolling

[0085] The steel billet is heated to 1200℃ in a heating furnace and kept for 6 hours, and then rolled on a 450 mm hot rolling mill for 6 passes and then air-cooled to obtain a hot-rolled plate with a thickness of 4.5 mm;

[0086] Step 3: cold rolling

[0087] The hot-rolled plate is pickled and then cold-rolled to 2.2 mm, and then annealed at 620℃ for 1 hour and then furnace-cooled to room temperature;

[0088] Step 4: variable thickness rolling The cold-rolled plate is pickled and then single-pass variable thickness rolled on a four-roll cold rolling mill, and the rolling gap is adjusted in real time to obtain a difference thick plate with a thick area of 2.0 mm and a thin area of 1.0 mm and a transition area, and the transition area curve is a straight line dominant transition;

[0089] Step 5: quenching and partitioning heat treatment

[0090] The differential thickness plate is heated to an austenitizing temperature of 900℃ in a heating furnace and held for 10 min, then salt bath quenched to 270℃, held for 300 s at this temperature for carbon partitioning process, and finally quenched to room temperature to obtain the high strength and plastic product differential thickness plate.

[0091] The scanning electron micrograph of the high strength and plastic product differential thickness plate prepared in this example is shown in FIG. 1. Figure 6 As can be seen from the figure, most of the structure is lath martensite, and the volume fraction of residual austenite in the thin and thick regions is 3-6% as determined by XRD.

[0092] The mechanical properties of the high strength and plastic product differential thickness plate prepared in this example were tested, and the tensile strength of the thick region was 1561 MPa, the yield strength was 858 MPa, the elongation was 14.8%, and the strength and plastic product was 23025 MPa·%; the tensile strength of the thin region was 1500 MPa, the yield strength was 868 MPa, the elongation was 10.8%, and the strength and plastic product was 15894 MPa·%.

[0093] Example 5

[0094] A high strength and plastic product differential thickness plate for automobiles, the mass percentage of chemical elements being: C: 0.25%, Si: 1.58%, Mn: 1.55%, P: 0.002%, S: 0.001%, N: 0.003%, Al: 0.04%, and the rest being Fe and unavoidable impurities.

[0095] The preparation method of the above-mentioned high strength and plastic product differential thickness plate for automobiles comprises the following steps:

[0096] Step 1: steelmaking and billet making

[0097] The steelmaking and billet making according to the chemical composition of the high strength and plastic product differential thickness plate for automobiles is carried out in a 150 kg vacuum melting furnace, and then the ingot is cast and forged to obtain a steel billet with a size of 60 mm x 60 mm x 450 mm;

[0098] Step 2: hot rolling

[0099] The steel billet is heated to 1200℃ in a heating furnace and held for 6 hours, then rolled on a 450 mm hot rolling mill for 6 passes and then air cooled to obtain a hot rolled plate with a thickness of 4.5 mm;

[0100] Step 3: cold rolling

[0101] The hot rolled plate is pickled and then cold rolled to 2.2 mm, and then annealed at 620℃ for 1 hour and then cooled to room temperature in the furnace;

[0102] Step 4: variable thickness rolling

[0103] The cold-rolled plate is subjected to single-pass variable-thickness rolling on a four-roller cold rolling mill to obtain a differential thickness plate with a thick zone of 2.0 mm and a thin zone of 1.0 mm and a transition zone, and the transition zone curve is a straight line dominant transition;

[0104] Step 5: quenching and partitioning heat treatment

[0105] The differential thickness plate is heated to an austenitizing temperature of 900℃ in a heating furnace and kept for 10 min, then quenched in a salt bath to 270℃, kept at this temperature for 60 s for carbon partitioning process, and finally rapidly quenched to room temperature to obtain a high strength and plastic product differential thickness plate.

[0106] The scanning electron micrograph of the high strength and plastic product differential thickness plate prepared in this embodiment is shown in Figure 7 As can be seen from the figure, most of the structure is lath martensite, and the volume fraction of residual austenite in the thin zone and the thick zone is 3-6% as determined by XRD.

[0107] The mechanical properties of the high strength and plastic product differential thickness plate prepared in this embodiment were tested, and the tensile strength of the thick zone was 1600 MPa, the yield strength was 915 MPa, the elongation was 14.5%, and the strength and plastic product was 23200 MPa·%; the tensile strength of the thin zone was 1564 MPa, the yield strength was 928 MPa, the elongation was 10.8%, and the strength and plastic product was 16808 MPa·%.

[0108] Example 6

[0109] A high strength and plastic product differential thickness plate for automobiles, the mass percentage of chemical elements is: C: 0.26%, Si: 1.62%, Mn: 1.60%, P: 0.002%, S: 0.001%, N: 0.003%, Al: 0.04%, the rest is Fe and unavoidable impurities.

[0110] The preparation method of the above-mentioned high strength and plastic product differential thickness plate for automobiles comprises the following steps:

[0111] Step 1: steelmaking and billet making

[0112] The steelmaking and billet making of the above-mentioned high strength and plastic product differential thickness plate for automobiles is carried out in a 150 kg vacuum melting furnace, and then cast into ingots, and then forged to obtain a steel billet with a size of 60 mm x 60 mm x 450 mm;

[0113] Step 2: hot rolling

[0114] The steel billet is heated to 1200℃ in a heating furnace and kept for 6 hours, then rolled on a 450 mm hot rolling mill, rolled 6 times and then air cooled to obtain a hot rolled plate with a thickness of 4.5 mm;

[0115] Step 3: cold rolling

[0116] The hot-rolled slab is pickled and cold-rolled to 2.2 mm, and then annealed at 620℃ for 1 hour and cooled to room temperature in the furnace;

[0117] Step 4: variable thickness rolling

[0118] The cold-rolled plate is pickled and single-pass variable thickness rolled on a four-roll cold rolling mill by real-time dynamic adjustment of the roll gap to obtain a differential thickness plate with a thick zone of 2.0 mm, a thin zone of 1.0 mm and a transition zone with a straight line dominant transition curve;

[0119] Step 5: quenching and partitioning heat treatment

[0120] The differential thickness plate is heated to an austenitizing temperature of 900℃ in a heating furnace for 10 min, then quenched in a salt bath to 270℃, and then held at this temperature for 20 s for carbon partitioning, and finally rapidly quenched to room temperature to obtain a high strength and ductility differential thickness plate.

[0121] The scanning electron micrograph of the high strength and ductility differential thickness plate for automobiles prepared in this example is shown in Figure 8 As can be seen from the figure, most of the structure is lath martensite, and the volume fraction of residual austenite in the thin zone and the thick zone is 3-6% as determined by XRD. Figure 9 The X-ray diffraction pattern of the thin zone and the thick zone structure of the high strength and ductility differential thickness plate for automobiles prepared in this example is shown in

[0122] The mechanical properties of the high strength and ductility differential thickness plate for automobiles prepared in this example were tested, and the tensile strength of the thick zone was 1620 MPa, the yield strength was 1010 MPa, the elongation was 15.8%, and the strength and ductility product was 25515 MPa·%; the tensile strength of the thin zone was 1562 MPa, the yield strength was 990 MPa, the elongation was 10.0%, and the strength and ductility product was 15620 MPa·%.

Claims

1. A high-strength, high-density, high-density sheet metal for automobiles, characterized in that: The automobile high strength and plastic product difference thick plate has the following chemical element mass percentage: C: 0.22-0.28%, Si: 1.55-1.65%, Mn: 1.50-1.65%, P: ≤0.002%, S: ≤0.002%, N: ≤0.003%, Al: ≤0.04%, and the rest is Fe and inevitable impurities. The automobile high strength and plastic product difference thick plate is prepared by the following steps. Step 1: steelmaking and billet making The automobile high strength and plastic product difference thick plate is prepared by the following steps. Step 2: hot rolling The steel billet is heated in a heating furnace and then rolled on a 450mm hot rolling mill for 6 passes and then air-cooled to obtain a hot-rolled plate blank with a thickness of 4.5mm. Step 3: cold rolling The hot-rolled plate blank is pickled and then cold-rolled to 2.2mm, and then annealed and cooled to room temperature in the furnace. Step 4: variable thickness rolling The cold-rolled plate is pickled and then single-pass variable thickness rolled on a four-roll cold rolling mill by real-time dynamic adjustment of the roll gap to obtain a difference thick plate. Step 5: quenching and partitioning heat treatment The difference thick plate is heated in a heating furnace, then subjected to a quenching and partitioning process in a salt bath furnace, and finally rapidly quenched to room temperature to obtain a high strength and plastic product difference thick plate. The heating temperature is an austenitizing temperature of 900-950℃ and the holding time is 10-20min, and then the salt bath quenching is performed to a certain temperature between 250-290℃ and the carbon partitioning process is performed for 20-300s.

2. The high-strength product difference thick plate for automobiles according to claim 1, characterized by The automobile high strength and plastic product difference thick plate has a thickness of 2.0mm in the thick zone and a thickness of 1.0mm in the thin zone, and has a transition zone with a straight line dominant transition curve.

3. The high-strength product difference thick plate for automobiles according to claim 1, characterized by The automobile high strength and plastic product difference thick plate has a tensile strength greater than 1500MPa and a strength and plastic product greater than 15000MPa•%; the thick zone has a tensile strength of 1560-1650MPa, a yield strength of 850-1020MPa, an elongation of 13-16%, and a strength and plastic product of 21500-25500MPa•%; the thin zone has a tensile strength of 1500-1600MPa, a yield strength of 860-1050MPa, an elongation of 10-12%, and a strength and plastic product of 15400-16800MPa•%.

4. The high-strength product difference thick plate for automobiles according to claim 1, characterized by The heating temperature in step 2 is 1200-1250℃ and the holding time is 6 hours.

5. The high-strength product difference thick plate for automobiles according to claim 1, characterized by The annealing temperature in step 3 is 610-630℃ and the holding time is 1 hour.

6. The high-strength, high-stiffness, high-specific-ductility, heavy plate for automobiles according to claim 2, characterized by The automobile high strength and plastic product difference thick plate has a microstructure mainly composed of martensite and a small amount of residual austenite in the thick zone and the thin zone.

Images