Method and device for preparing corrosion-resistant hot stamping part

Abstract

Disclosed is a method for manufacturing a corrosion-resistant hot-stamping part and a device thereof. The method includes the following steps: blanking a bare steel plate into a required blank shape; heating the blank to above AC3 in an oxygen-free heating furnace to austenite the blank; putting the austenitized blank into a mold to mold a part; and conducting a surface treatment of the part to form a corrosion-resistant coating layer on a surface of the part. The hot-stamping part manufactured using the described method has good surface quality and great corrosion-resistant performance

Claims

1. A method for manufacturing a corrosion-resistant hot-stamping part without shot blasting, comprising: blanking a bare steel plate into a required blank shape, heating the blank to above AC3 in an oxygen-free heating furnace to austenitize the blank; wherein the oxygen-free heating furnace is a vacuum heating furnace and a vacuum degree of the vacuum heating furnace is 50-500 Pa; putting the austenitized blank into a mold to mold a part; conducting an ultrasonic cleaning or pickling on the part, then using an electroplating process to form a corrosion-resistant coating layer on a surface of the part; and conducting a dehydrogenation treatment; wherein the dehydrogenation treatment comprises heating the part to 140° C.-190° C. and insulating the part at the temperature for 10-30 min; wherein the electroplating process comprises firstly using a current density of 5-10 A/dm.sup.2 for 0.5-2 min to strike plating the part; and using a current density of 1-3 A/dm.sup.2 for 1-15 min to electroplating the part; wherein a tensile strength of the part after treated reaches 1300-1650 Mpa wherein the step heating the blank to above AC3 in an oxygen-free heating furnace to austenize the blank, wherein the oxygen-free heating furnace is a vacuum heating furnace and a vacuum degree of the vacuum heating furnace is 50-500 Pa comprises: putting the blanking blank into an oxygen-free furnace; starting vacuum pump to vacuumize the furnace to make the vacuum degree inside of the furnace 50-500 Pa; then using nitrogen gas inflate the vacuum furnace which makes the inside of vacuum furnace to achieve one atmospheric pressure; and heating the blank to above AC3 to austenize the blank; wherein the oxygen-free heating furnace is a vacuum heating furnace and a vacuum degree of the vacuum heating furnace is 50-500 Pa.

2. The method for manufacturing the corrosion-resistant hot-stamping part according to claim 1, wherein an oxygen content in the vacuum heating furnace when heating is below 0.5%.

3. The method for manufacturing the corrosion-resistant hot-stamping part according to claim 1, wherein the vacuum degree of the vacuum heating furnace is 50-100 Pa.

4. The method for manufacturing the corrosion-resistant hot-stamping part according to claim 1, wherein a time for heating the blank and a time for insulating the part by the oxygen-free heating furnace is 60-300 s in total.

5. The method for manufacturing the corrosion-resistant hot-stamping part according to claim 1, wherein the blank in the oxygen-free heating furnace is heated to 880° C. -950° C.

6. The method for manufacturing the corrosion-resistant hot-stamping part according to claim 1, wherein a time for transferring the blank after heating from the oxygen-free heating furnace to the mold is 5-10 s.

7. The method for manufacturing the corrosion-resistant hot-stamping part according to claim 1, wherein a temperature for the blank in the mold starting to be molded is 650° C. -850° C.

8. The method for manufacturing the corrosion-resistant hot-stamping part according to claim 1, wherein the mold has a water cooling system, and the water cooling system makes the blank cooling at a speed of not less than 30° C./s during the molding.

9. The method for manufacturing the corrosion-resistant hot-stamping part according to claim 1, wherein the corrosion-resistance coating layer comprises a Zn coating, a Zn—Fe alloy coating, a Zn—Al alloy coating, or a Zn—Ni alloy coating.

10. The method for manufacturing the corrosion-resistant hot-stamping part according to claim 1, wherein a heating speed in the vacuum heating furnace is 20° C./s-50° C./s.

11. The method for manufacturing the corrosion-resistant hot-stamping part according to claim 1, wherein a time for pickling the part is 5 s-15 s.

12. The method for manufacturing the corrosion-resistant hot-stamping part according to claim 11, wherein an auxiliary anodizing or a pictographic anodizing is used when electroplating.

13. The method for manufacturing the corrosion-resistant hot-stamping part according to claim 1, wherein between the step “putting the austenitized blank into a mold to mold a part” and the step “conducting an ultrasonic cleaning or pickling on the part”, further comprising laser trimming or hole- cutting the part.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order to better explain the technical method in this invention or existing technology, the figures for embodiments or existing technology is introduced as following. The described figures below are only some embodiments in this invention, for general technical personnel of this field, on the premise of not giving creative labor, other figures can be obtained according to the existing figures.

(2) FIG. 1 is a flowchart of a method for manufacturing corrosion-resistant hot-stamping part in an embodiment of this invention;

(3) FIG. 2 is a surface oxidation effect diagram of a bare steel plate under a vacuum degree of 10 Pa after heating;

(4) FIG. 3 is a surface oxidation effect diagram of a bare steel plate under the vacuum degree of 100 Pa after heating;

(5) FIG. 4 is a surface oxidation effect diagram of a bare steel plate under one atmospheric pressure after heating;

(6) FIG. 5 is a metallograph of zinc coating layer of a part in case 1 of this invention;

(7) FIG. 6 is a coating metallograph of a Al—Si coated plate in comparison case 4 of this invention;

(8) FIG. 7 is a coating metallograph of the Al—Si coated plate after heating in comparison case 4 of this invention;

(9) FIG. 8 is a coating metallograph of the Al—Si coated plate after hot stamping in comparison case 4 of this invention;

(10) FIG. 9 is a coating metallograph of a hot-dip galvanized plate in comparison case 4 of this invention;

(11) FIG. 10 is a coating metallograph of the hot-dip galvanized plate after heating in comparison case 4 of this invention;

(12) FIG. 11 is a coating metallograph of the hot-dip galvanized plate after hot stamping in comparison case 4 of this invention;

(13) FIG. 12 is a corrosion photo of the hot-stamped bare steel plate after 720 h weight loss salt spray test in comparison case 4 of this invention;

(14) FIG. 13 is a corrosion photo of the hot-stamped Al—Si coated plate after 720 h weight loss salt spray test in comparison case 4 of this invention;

(15) FIG. 14 is a corrosion photo of the hot-stamped and hot-dip galvanized plate after 720 h weight loss salt spray test in comparison case 4 of this invention;

(16) FIG. 15 is a corrosion photo of the part after 720 h weight loss salt spray test in case 1 of this invention;

(17) FIG. 16 is a scratch corrosion photo of an electrophoretic coating layer of the hot-stamped bare steel plate after 720 h salt spray test in comparison case 4 of this invention;

(18) FIG. 17 is a scratch corrosion photo of an electrophoretic coating layer of the hot-stamped Al—Si coated plate after 720 h salt spray test in comparison case 4 of this invention;

(19) FIG. 18 is a scratch corrosion photo of an electrophoretic coating layer of the hot-stamped and hot-dip galvanized plate after 720 h salt spray test in comparison case 4 of this invention;

(20) FIG. 19 is a scratch corrosion photo of an electrophoretic coating layer of the part after 720 h salt spray test in case 1 of this invention;

(21) FIG. 20 is a scratch corrosion photo of a substrate after electrophoresis of the hot-stamped bare steel plate after 720 h salt spray test in comparison case 4 of this invention;

(22) FIG. 21 is a scratch corrosion photo of a substrate after electrophoresis of the hot-stamped Al—Si coated plate after 720 h salt spray test in comparison case 4 of this invention;

(23) FIG. 22 is a scratch corrosion photo of a substrate after electrophoresis of the hot-stamped and hot-dip galvanized plate after 720 h salt spray test in comparison case 4 of this invention;

(24) FIG. 23 is a scratch corrosion photo of a substrate after electrophoresis of the part after 720 h salt spray test in case 1 of this invention.

DETAILED DESCRIPTION OF THE INVENTION

(25) With the figures shown in this invention, a clear and complete description of this technical proposal is as below. The described embodiments are only a part of this invention, not all the embodiments. Based on the embodiments of this invention, all the other embodiments obtained by general technical personnel of this field are within the scope of this invention.

(26) Shown in FIG. 1, an embodiment of this invention provides a method for manufacturing a corrosion-resistant hot-stamping part, including the following steps:

(27) Firstly, blank a 22MnB5 bare steel plate into a required shape, a specific blanking method includes cold stamping and laser cutting. The bare steel plate can be generally understood as steel plate without coating on the surface.

(28) Then heating the blank to above AC3 heating the blank to above AC3 in an oxygen-free heating furnace) in an oxygen-free heating furnace to austenize the blank. The maximum temperature of the blank in oxygen-free furnace is from 860° C. to 1000° C., the blank in the oxygen-free heating furnace is heat to 880° C. to 950° C. Specifically, put the blanking blank into the oxygen-free furnace to be heated to an austenitic state and heat preserved to so that austenite in the blank is homogenized. The oxygen-free furnace is an inert gas protection furnace or vacuum heating furnace. The vacuum degree of vacuum furnace is between 0.1-500 Pa. To be better, the vacuum degree of vacuum furnace is between 0.1-100 Pa. Specifically, after the furnace door closed, start vacuum pump to vacuumize the furnace for 40-120 s, make the vacuum degree inside of the furnace 0.1-100 Pa, then use 99.999% nitrogen gas inflate the vacuum furnace which makes the inside of vacuum furnace to achieve one atmospheric pressure. Then electrify the heating components inside the furnace to heat the blank. During heating the blanking, in order to shorten the heating time, heat the surface of heating components to 1200° C. to 2000° C. After the temperature of the blank reaches austenitizing temperature, the temperature of the surface of the heating element is lowered, and the blank is subjected to heat preservation to homogenize the austenite. According to the thickness of different blanks, heating and thermal insulation time is 60-300 s. Using vacuum furnace to heat the blank into a high temperature state, so that the oxidation phenomenon of the blank can be reduced to a great extent. Therefore, the surface quality of the part after forming is excellent, the shot blasting process can be cancelled, and the surface of the heated part is almost free of residual oxide, the pickling time before the part electroplating is greatly reduced, and the risk of hydrogen embrittlement in the electroplating process of the part is greatly reduced.

(29) Then use an end picker to pick up the austenitized blank and place into a mold quickly to form a part. Specifically, a time for transferring the blank from heating furnace to the mold is 5-10 s, reducing time of the high temperature blank exposing to the air, avoiding the high temperature blank oxidation as well as the the temperature of the high-temperature blank is also prevented from being greatly reduced. In this embodimentation case, the forming method is hot-stamping, the temperature of blank is 880° C. to 950° C. while the blank is picked up from the furnace, the temperature of blank start to forming in the mold is 650° C. to 850° C., and excellent forming performance of the steel plate is facilitated. The mold is provided with a water cooling system to make the part cooling at a speed not lower than 30° C./s during the molding process for a better mechanical property of the part.

(30) Then, conduct a surface treatment to form a corrosion-resistant coating layer on the part surface. Specifically, the surface treatment includes electroplating, the corrosion-resistant layer includes electroplating layer. More specifically, the corrosion-resistant layer includes Zn coating, Zn—Fe alloy coating, Zn—Al alloy coating and Zn—Ni alloy coating. Pure zinc has the function of sacrificial anode protection, but corrosion rate is high. When the zinc content is between 3%-10%, Zn—Al alloy coating has higher corrosion-resistant performance, the higher the aluminum content, the better the corrosion-resistant, but when the mass percent of aluminum content is between 15%-25%, the corrosion-resistant performance Zn—Al alloy coating gets degraded. Therefore, it's preferable the mass percent of aluminum content between 3%-10% in the Zn—Al alloy coating mentioned. Compared to the pure zinc coating, the zinc-iron alloy containing a small amount of iron is improved by several times. When the mass percent of Fe content is between 10%-18%, the adhesion performance between Zn—Fe alloy coating and steel plate is the best. It's not easy to get peeling or cracking. For the part after forming, when the Fe content in Zn—Fe alloy coating is 0.3%-0.6%, the part can also get 5 times higher corrosion-resistant performance than pure zinc coating. Therefore, it's preferable the Fe content in Zn—Fe alloy coating layer less than 1% or 10-20%. In addition, the Zn—Fe alloy coated part has Fe element, so the welding performance in better during the following welding process. After passivation, alloy coating with nickel content <10%(mass percent) has 3-5 times higher corrosion-resistant performance than zinc coating. Zn—Ni alloy coating with nickel 10%-15% (mass percent) content has 6-10 times higher corrosion-resistant performance than zinc coating. The Zn—Ni alloy coating has moderate pore which is good for dehydrogen process and the coating layer also has lower hydrogen embrittlement property; and after the electrogalvanizing nickel alloy is resistant to neutral salt mist time exceeding 720 h, the electrophoretic process can be cancelled. Therefore, it's preferable the mass percent of nickel content is 5%-15% in the Zn—Ni alloy coating layer.

(31) Furthermore, ultra-high strength steel has hydrogen embrittlement susceptibility, to reduce the risk of hydrogen embrittlement during plating process, ultrasonic cleaning or weak acid cleaning process for 5-10 s is adopted before plating. In addition, adopt low hydrogen embrittlement plating process, according to the coating layer thickness requirement, first using 5-10 A/dm.sup.2 of the current density for 0.5-2 min to pulse plating for forming a dense thin coating layer which can prevent hydrogen atom gets into steel base material, and then the part is electroplated with a current density of 1-3 A/dm 2 for 5-15 min, so that the surface of the part forms the electrogalvanized layer with the required thickness. After the part is electroplated, the part is heated to between 140° C.-200° C., and the part is subjected to heat preservation for 10-30 minutes at this temperature to remove the part, thereby improving the mechanical property of the part.

(32) Furthermore, between step” putting the austenitized blank into a mold to mold a part” and step” conducting a surface treatment of the part to form a corrosion-resistant coating layer on a surface of the part, there's a step: laser trimming or hole-cutting the part. Compared to proceeding plating before trimming and hole cutting, plating after trimming and hole cutting process can save plating solution. what's more, the trimming and hole cutting area can also be plated, and the corrosion resistance is improved due to the protection of the electroplating layer at the trimming edge or cutting hole of the part.

(33) The following 4 cases specify above embodiments:

(34) Case 1:

(35) 1. Using 22MnB5 bare steel plate having a thickness of 1.4 mm to blank to get a blank with required shape.

(36) 2. Putting the blank into a vacuum furnace, starting a vacuum pump to vacuumize the furnace for 80 s after the furnace door closed, making the vacuum degree inside the furnace reaches 100 Pa, then using 99.999% nitrogen gas inflate the vacuum furnace which makes the inside of vacuum furnace to achieve one atmospheric pressure, then starting the heating components in the furnace to heat the blank. Heating the blank to 930° C. and hold for thermal insulation, the heating and thermal insulation time of the blank in vacuum furnace is total of 140 s for this process. After the thermal insulation time of the blank is finished, the furnace door is opened for fetching.

(37) 3. Quickly putting the austenitized blank into the mold with water cooling for thermoforming to form part;

(38) 4. Laser trimming the part;

(39) 5. Adopting acid zinc plating process for electroplating the part. Wherein, before electroplating, using ultrasonic waves to clean the part for 20 s, pickling for 5-10 s using 5-10% hydrochloric acid, the zinc electroplating process is acid zinc electroplating which adopt electroplating with acidic potassium chloride with high cathodic polarization efficiency. Each composition and its content of the plating solution: 200 g/L potassium chloride, Zinc ion 32 g/L, boric acid 27 g/L, bath temperature 26° C., pH value 4.5, using 8 A/dm.sup.2 high current to pulse plating for 30 s, then use a low current of 2 A/dm.sup.2conduct normal electroplating for 8 min, finally forming a 5 um coating layer.

(40) 6. Conducting the dehydrogen process to the electroplated part, specifically, heating the electroplated part to 160° C. and hold the part at this temperature for 20 min.

(41) Case 2:

(42) 1. Using a 22MnB5 bare steel plate have a thickness of 1.4 mm to blanking to get a blank with required shape.

(43) 2. Putting the blank into a vacuum furnace, starting a vacuum pump to vacuumize the furnace for 40 s after the furnace door closed, making the vacuum degree inside furnace reaches 10 Pa, then using 99.999% nitrogen gas inflate the vacuum furnace which makes the inside of vacuum furnace to achieve one atmospheric pressure. Then starting the heating components in the furnace to heat the blank. Heating the blank to 930° C. and hold for thermal insulation, the heating and thermal insulation time of the blank in vacuum furnace is total of 140 s. After the thermal insulation time of the blank is finished, the furnace door is opened for fetching.

(44) 3. putting the austenitized blank into the mold with water cooling for thermoforming to form part;

(45) 4. Laser trimming the part;

(46) 5. Adopt alkaline zinc electroplating process for electroplating the part. Before electroplating, use hydrochloric acid with 8% mass concentration to clean the part for 10 s. The zinc electroplating process is alkaline electroplating. Each composition and its content of the plating solution: Sodium hydroxide 130 g/L, zinc ion concentration 12 g/L, PH value 9, using 6 A/dm high current to pulse plating for 60 s, Then use a low current of 2 A/dm.sup.2conduct normal electroplating for 8 min, finally forming a 8 um coating layer.

(47) 6. Conducting the dehydrogen process to the electroplated part, specifically, heating the electroplated part to 190° C. and hold the part at this temperature for 15 min

(48) Case 3:

(49) 1. Using a 22MnB5 bare steel plate have a thickness of 1.4 mm to blanking to get a blank with required shape.

(50) 2. Putting the blank into a vacuum furnace, starting a vacuum pump to vacuumize the furnace for 90 s after the furnace door closed, making the vacuum degree inside the furnace reaches 50 Pa, then using 99.999% nitrogen gas inflate the vacuum furnace which makes inside of the vacuum furnace to achieve one atmospheric pressure. Then starting the heating components in the furnace to heat the blank. Heating the blank to 930° C. and hold for thermal insulation, the heating and thermal insulation of the blank in vacuum furnace is total 140 s. After the thermal insulation time of the blank is finished, the furnace door is opened for fetching.

(51) 3. Quickly putting the austenitized blank into the mold with water cooling for thermoforming to form part;

(52) 4. Laser trimming the part;

(53) 5. Adopting alkaline Zn—Fe electroplating process for electroplating the part. Before electroplating, ultrasonic clean part for 20 s. Each composition and its content of the plating solution: Zinc sulfate 80 g/L, ferric chloride 7 g/L, sodium dihydrogen phosphate 36 g/L, potassium pyrophosphate 25 g/L, PH 8.5, current density 2.1 A/dm.sup.2, coating thickness 6 um; The mass fraction of Fe in the coating layer is 0.3-0.6%.

(54) 6. Conducting the dehydrogen process to the electroplated part, specifically, heat the electroplated part to 170° C. and hold the part at this temperature for 25 min

(55) Comparison Case 4:

(56) A bare steel plate, a hot-dip galvanized plate, a Al—Si coating plate are respectively heated for 4 min in a conventional atmosphere roll bottom heating furnace at a temperature of 930° C. and make the blank austenitized, then conduct hot-stamping process.

(57) Conduct metallography test, 720 h salt spray test and scratch test on part in case 1-3 and comparison case 4, and mechanical performance test and hydrogen content test comparison are carried out.

(58) Shown in FIG. 2-4, heat blanks under different vacuum degree, the oxidation results of bare steel plate is: no oxidation under 10 Pa-100 Pa vacuum degree, severe oxidation under normal atmosphere.

(59) FIGS. 5-11 shows the metallography of coating cross section of different coating steel plates after heating and forming process. The coating layer is dense on the Al—Si coating plate and hot galvanizing plate in comparison case 4, but severe damaged after heating and hot-stamping. In cases 1-3, the coating density of bare steel plate is not damaged when plating after heating and hot-stamping.

(60) Based on FIG. 12-23 and table 1, after 720 h salt spray test, the severest corrosion is on the part that made of bare steel plate in comparison case 4. Hot galvanizing plate corrosion is less. Corrosion rate of Al—Si coating plate is 1.38×10−4 g/mm.sup.2, the corrosion rate of bare steel plate in case 1-3 is as low as 5.74×10.sup.−6 g mm which is 20 times higher corrosion-resistant than Al—Si coating part in comparison case 4.

(61) The scratch test shows that the width of scratches on each part is roughly 1 mm before hot-stamping. After 720 h salt spray, the width of base material corrosion of bare steel plate and Al—Si coating plate in comparison case 4 is 1.54 mm and 3.22 mm. The galvanized part in case1 has no corrosion on base material due to the sacrifice anode protection.

(62) TABLE-US-00001 TABLE 1 Salt spray test results on Case 1 and Comparison case 4 Scratch Corrosion Corrosion width width of width of after hot coating base 720 h forming layer material Material corrosion Weight Weight Area and after after weight weight loss loss area loss e-coating 720hsalt 720hsalt Plate (g) (g) (g) percent mm2 (g/mm2) (mm) spray(mm) spray (mm) Bare 185.26 148.78 36.48 19.69% 19006 1.9E−3 1.20 8.51 1.54 steel plate in comparison case 4 Al-Si 149.69 147.15 2.54  1.69% 18400 1.38E−4 1.479 9.42 3.22 coating plate in comparison case 4 Hot 241.73 237.57 4.16  1.72% 10504 3.96E−4 0.938 6.67 0 galvanizing plate in comparison case 4 Case 1 235.85 235.74 0.11  0.4% 19173 5.74E−6 0.957 6.08 0 se 1

(63) Table 2 is the results for mechanical test and hydrogen test of the hot-stamping part in case 1 and comparison case 4. It shows that the bare plate after hot-stamping and galvanizing and the bare plate after hot-stamping, galvanizing and dehydrogen both can meet the tensile strength, yield strength and elongation standard for hot forming production. And the hydrogen content in bare plate after hot-stamping is almost on the same level with it in Al—Si coating plate.

(64) TABLE-US-00002 TABLE 2 Mechanical test and hydrogen test results Tensile Yield strength strength Elongation Hydrogen (Rm) (Rp0.2) (A) content NO. (MPa) (MPa) (%) (ppm) Hot forming 1300-1650 950-1250 ≥5.0 — production standard Bare steel 1405.123 1050.68 5.8 2.10 plate in comparison case 4 Al- Si coating 1453.125 1145.927 6.200 3.32 plate in comparison case 4 Galvanizing 1462.183 1147.762 6.200 3.51 plate not dehydrogenate Galvanizing 1479.053 1226.599 7.460 3.36 plate in case 1

(65) This invention also provides a manufacturing device for corrosion-resistant hot-stamping part using the above mentioned method. It includes a blanking mechanism, a heating mechanism, a molding mechanism and a surface treatment mechanism:

(66) The blanking mechanism is used to blank the bare steel plate into the required blank shape.

(67) The heating mechanism is used to heat the blank after blanking.

(68) The molding mechanism is used to mold the blank after the heating into the part.

(69) The surface treatment mechanism is used to conduct surface treatment of the part to form corrosion-resistant coating layer on the part surface.

(70) A specific embodiment is applied in the invention to describe the principle and embodiment of the invention. The description of this embodiment is only used to help understand the method of the invention and its core idea; At the same time, for the general technician in the field, according to the idea of the invention, there will be some changes in the specific way of embodiment and the scope of application. To sum up, the description of content should not be construed as a limitation of this invention.