Rapid preheating for improving surface quality of uncoated press hardened steel components

Abstract

A method of manufacturing an uncoated press hardened steel (CFPHS) assembly includes heating a CFPHS blank to a first predetermined temperature within a first predetermined temperature range using a heater at a first predetermined heating rate; transferring the CFPHS blank to a furnace; soaking the CFPHS blank in the furnace for a predetermined time at a second predetermined temperature within a second predetermined temperature range; and pressing and forming the CFPHS blank in a press / press to form a CFPHS assembly.

Description

[0001] The information provided in this section is for the purpose of generally presenting the background of the present disclosure. The work of the presently named inventors, to the extent described in this section, and aspects of the description that may not constitute prior art at the time of filing are neither expressly nor impliedly admitted to be prior art to the present disclosure. Technical Field

[0002] The present disclosure relates to the manufacture of press hardened steel (PHS) components, and more particularly to methods for improving the surface quality of coated free press hardened steel (CFPHS) components. Background Art

[0003] Press hardening of steel (PHS) increases the strength of steel. PHS is often used in load-bearing components of vehicles, construction equipment and / or other industrial equipment. In the press hardening of steel process, the steel billet is heated to a temperature range for austenitization, transferred to a punch / press while hot, and formed and pressed between two or more dies of the punch / press. In some instances, the steel billet is cold formed into an intermediate shape before austenitization and forming and pressing.

[0004] When the billet is uncoated, an oxide layer is formed on the billet surface after austenitization during transfer to the punch / press. This oxide layer needs to be removed after forming and pressing. For example, the oxide layer can be descaled by shot peening, which increases costs and production cycle time. In order to avoid the formation of an oxide layer, the billet can be coated with a coating that inhibits the formation of an oxide layer. For example, the billet can be coated with an aluminum-silicon alloy (AlSi) to inhibit the oxide coating and avoid the cost and time required to remove the oxide layer. Summary of the invention

[0005] A method for manufacturing a coating-free press hardened steel (CFPHS) component includes heating a CFPHS blank to a first predetermined temperature within a first predetermined temperature range at a first predetermined heating rate using a heater; transferring the CFPHS blank to a furnace; soaking the CFPHS blank in the furnace at a second predetermined temperature within a second predetermined temperature range for a predetermined time; and pressing and forming the CFPHS blank in a stamping machine / press to form the CFPHS component.

[0006] In other features, the first predetermined temperature is 500°C to 950°C. The first predetermined heating rate is 20°C / second to 300°C / second. The heater is selected from an induction heater, a resistance heater, a laser heater, or a combination thereof. The second predetermined temperature is 900°C to 950°C. The predetermined time is 5 seconds to 500 seconds. The predetermined time is 5 seconds to 50 seconds.

[0007] In other features, after preheating in the heater, the CFPHS component includes an oxide layer having a thickness of greater than or equal to 0.1 microns to less than or equal to 1.5 microns. The oxide layer covers greater than or equal to 90% of the exposed surface of the CFPHS component. After preheating in the heater, the CFPHS component includes an oxide layer having a thickness of greater than or equal to 0.1 microns to less than or equal to 1.0 microns.

[0008] The method of manufacturing a coating-free press hardened steel (CFPHS) component includes heating a CFPHS blank to a first predetermined temperature in a range of 500° C. to 950° C. using a heater at a first predetermined heating rate in a range of 20 to 300° C. / second; transferring the CFPHS blank to a furnace; soaking the CFPHS blank in the furnace at a second predetermined temperature in a range of 900° C. to 950° C. for a predetermined time; and pressing and forming the CFPHS blank in a stamping press / press to form a CFPHS component. After preheating in the heater, the CFPHS component includes an oxide layer having a thickness of greater than or equal to 0.1 microns to less than or equal to 1.5 microns.

[0009] In other features, the heater is selected from an induction heater, a resistance heater, a laser heater, or a combination thereof. The predetermined time is 5 seconds to 500 seconds. The predetermined time is 5 seconds to 50 seconds. The oxide layer has a thickness greater than or equal to 0.1 micron to less than or equal to 1.0 micron. The oxide layer covers greater than or equal to 90% of the exposed surface of the CFPHS component.

[0010] A method for manufacturing a coating-free press hardened steel (CFPHS) component includes heating a CFPHS blank to a first predetermined temperature in a range of 500° C. to 950° C. using one or more of induction heating, resistance heating, laser heating, or a combination thereof at a first predetermined heating rate in a range of 20 to 300° C. / second; transferring the CFPHS blank to a furnace; soaking the CFPHS blank in the furnace at a second predetermined temperature in a range of 900° C. to 950° C. for a predetermined time in a range of 5 seconds to 50 seconds; transferring the CFPHS blank to a punch / press; and pressing and forming the CFPHS blank in the punch / press to form a CFPHS component. The CFPHS component includes an oxide layer having a thickness of greater than or equal to 0.1 microns to less than or equal to 1.5 microns.

[0011] In other features, the oxide layer has a thickness of greater than or equal to 0.1 micrometers to less than or equal to 1.0 micrometers. The oxide layer covers greater than or equal to 90% of the exposed surface of the CFPHS component.

[0012] The present invention discloses the following technical solutions.

[0013] Solution 1. A method of manufacturing a coating-free press hardened steel (CFPHS) component, comprising:

[0014] heating the CFPHS blank to a first predetermined temperature within a first predetermined temperature range using a heater at a first predetermined heating rate;

[0015] Transferring the CFPHS billet to a furnace;

[0016] soaking the CFPHS blank in a furnace at a second predetermined temperature within a second predetermined temperature range for a predetermined time; and

[0017] The CFPHS blank is pressed and formed in a punch / press to form a CFPHS component.

[0018] Option 2. The method according to Option 1, wherein the first predetermined temperature is 500°C to 950°C.

[0019] Option 3. The method according to Option 1, wherein the first predetermined heating rate is 20°C / sec to 300°C / sec.

[0020] Option 4. The method according to Option 1, wherein the heater is selected from an induction heater, a resistance heater, a laser heater or a combination thereof.

[0021] Embodiment 5. The method according to embodiment 1, wherein the second predetermined temperature is 900°C to 950°C.

[0022] Embodiment 6. The method according to embodiment 1, wherein the predetermined time is from 5 seconds to 500 seconds.

[0023] Embodiment 7. The method according to embodiment 1, wherein the predetermined time is from 5 seconds to 50 seconds.

[0024] Embodiment 8. The method according to embodiment 1, wherein after preheating in the heater, the CFPHS component comprises an oxide layer having a thickness greater than or equal to 0.1 microns and less than or equal to 1.5 microns.

[0025] Embodiment 9. The method according to embodiment 8, wherein the oxide layer covers greater than or equal to 90% of the exposed surface of the CFPHS component.

[0026] Embodiment 10. The method according to embodiment 1, wherein after preheating in the heater, the CFPHS component comprises an oxide layer having a thickness of greater than or equal to 0.1 micrometer to less than or equal to 1.0 micrometer.

[0027] Embodiment 11. A method of manufacturing a coating-free press hardened steel (CFPHS) component, comprising:

[0028] heating the CFPHS blank to a first predetermined temperature in a range of 500° C. to 950° C. using a heater at a first predetermined heating rate in a range of 20 to 300° C. / second;

[0029] Transferring the CFPHS billet to a furnace;

[0030] soaking the CFPHS billet in a furnace at a second predetermined temperature in the range of 900° C. to 950° C. for a predetermined time; and

[0031] Pressing and shaping the CFPHS blanks in a punch / press to form CFPHS components,

[0032] Wherein after preheating in the heater, the CFPHS component includes an oxide layer having a thickness greater than or equal to 0.1 microns and less than or equal to 1.5 microns.

[0033] Embodiment 12. The method according to Embodiment 11, wherein the heater is selected from an induction heater, a resistance heater, a laser heater or a combination thereof.

[0034] Embodiment 13. The method according to embodiment 11, wherein the predetermined time is from 5 seconds to 500 seconds.

[0035] Embodiment 14. The method according to embodiment 11, wherein the predetermined time is from 5 seconds to 50 seconds.

[0036] Embodiment 15. The method according to Embodiment 11, wherein the oxide layer has a thickness of greater than or equal to 0.1 micrometer and less than or equal to 1.0 micrometer.

[0037] Embodiment 16. The method of embodiment 11, wherein the oxide layer covers greater than or equal to 90% of the exposed surface of the CFPHS component.

[0038] Embodiment 17. A method of manufacturing a coating-free press hardened steel (CFPHS) component, comprising:

[0039] heating the CFPHS blank to a first predetermined temperature in the range of 500° C. to 950° C. at a first predetermined heating rate in the range of 20 to 300° C. / second using one or more of induction heating, resistance heating, laser heating, or a combination thereof;

[0040] Transferring the CFPHS billet to a furnace;

[0041] soaking the CFPHS blank in a furnace at a second predetermined temperature in the range of 900° C. to 950° C. for a predetermined time in the range of 5 seconds to 50 seconds;

[0042] Transferring the CFPHS blanks to the punch / press; and

[0043] Pressing and shaping the CFPHS blanks in a punch / press to form CFPHS components,

[0044] The CFPHS component includes an oxide layer having a thickness greater than or equal to 0.1 micrometers and less than or equal to 1.5 micrometers.

[0045] Option 18. The method according to Option 17, wherein the oxide layer has a thickness of greater than or equal to 0.1 micron and less than or equal to 1.0 micron.

[0046] Embodiment 19. The method of embodiment 17, wherein the oxide layer covers greater than or equal to 90% of the exposed surface of the CFPHS component.

[0047] Further areas of applicability of the present disclosure will become apparent from the detailed description, claims and drawings.The detailed description and specific examples are intended for illustrative purposes only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The present disclosure will be more fully understood from the detailed description and accompanying drawings, in which:

[0049] Figure 1 is a functional block diagram of an example of a method of manufacturing a coating-free press hardened steel (CFPHS) component according to the present disclosure;

[0050] Figure 2 is a flow chart of an example of a method of manufacturing a CFPHS assembly according to the present disclosure; and

[0051] Figure 3 is a cross-sectional view showing an example of an oxide layer of a CFPHS component according to the present disclosure.

[0052] Among the drawings, reference numerals may be repeated to identify similar and / or identical elements. DETAILED DESCRIPTION

[0053] Although the method of making coating-free press hardened steel (CFPHS) according to the present disclosure is described in the context of vehicle structural components, the method of making CFPHS may be used in other applications.

[0054] In the press hardening process of steel, the steel billet is heated to a temperature in the range of 900°C to 950°C for austenitization, transferred while hot to a punch / press, and formed and pressed between two or more dies of the punch / press. In some examples, the steel billet is cold formed into an intermediate shape prior to austenitization and forming and pressing.

[0055] In order to avoid the formation of an oxide layer, the steel billet can be coated with a coating that inhibits the formation of an oxide layer. For example, the steel billet can be coated with an aluminum-silicon alloy (AlSi) layer to inhibit the oxide coating and avoid the cost and time required to remove the oxide layer after pressing and forming. In order to reduce production time, other heating methods can be used to quickly preheat the steel billet before heating in the furnace (to reduce the amount of time required in the furnace). However, AlSi-coated PHS is incompatible with rapid preheating. Due to the high heating rate, the AlSi coating melts without alloying.

[0056] In the press hardening (PHS) process of steel according to the present disclosure, a steel billet containing uncoated PHS (CFPHS) is rapidly preheated. After rapid preheating, the steel billet is transferred to a furnace for a soaking time and transferred to a punch / press for pressing and forming of a CFPHS component. After pressing and forming the CFPHS component, no descaling is required, which reduces costs.

[0057] A method of manufacturing a coating-free press-hardened steel (CFPHS) component is described in commonly assigned U.S. Patent Publication 2021002746, published on January 7, 2021, which is hereby incorporated by reference in its entirety. As described therein, a CFPHS blank is hot stamped into a press-hardened component of a predetermined shape that is coating-free (and does not require descaling).

[0058] The steel alloy used for the CFPHS blank contains carbon (C), chromium (Cr), silicon (Si) and iron (Fe). During the hot stamping process, a portion of the Cr and Si combines with atmospheric oxygen to form a first layer containing oxides rich in the portion of Cr and Si. When there is sufficient oxygen in the atmosphere, a portion of the Fe combines with the atmospheric oxygen to form a second layer containing oxides rich in Fe. The first and second layers prevent, inhibit or minimize further oxidation, so that a descaling step such as shot peening or sand blasting is not required.

[0059] C is present in the steel alloy at a concentration of greater than or equal to about 0.01 wt % to less than or equal to about 0.35 wt %. Cr is present in the steel alloy at a concentration of greater than or equal to about 1 wt % to less than or equal to about 9 wt %. Si is present in the steel alloy at a concentration of greater than or equal to about 0.5 wt % to less than or equal to about 2 wt %. Fe makes up the balance of the steel alloy (unless additional elements (some of which are described below) are added).

[0060] In various embodiments, the CFPHS component further comprises manganese (Mn) at a concentration of greater than or equal to 0 wt % to less than or equal to 3 wt %. In various embodiments, the steel alloy further comprises nitrogen (N) at a concentration of greater than or equal to approximately 0 wt % to less than or equal to approximately 0.01 wt %. In various embodiments, the steel alloy further comprises molybdenum (Mo) at a concentration of greater than or equal to approximately 0 wt % to less than or equal to approximately 0.8 wt %. In various embodiments, the steel alloy further comprises boron (B) at a concentration of greater than or equal to approximately 0 wt % to less than or equal to approximately 0.005 wt %. In various embodiments, the steel alloy further comprises niobium (Nb) at a concentration of greater than or equal to approximately 0 wt % to less than or equal to approximately 0.3 wt %. In various embodiments, the steel alloy further comprises vanadium (V) at a concentration of greater than or equal to approximately 0 wt % to less than or equal to approximately 0.3 wt %.

[0061] The rapid preheating of the CFPHS blank improves the surface quality of the CFPHS component and does not require descaling. The method for manufacturing the CFPHS combines rapid preheating and furnace soaking, so that the surface quality of the CFPHS can be optimized. A preformed protective oxide layer is formed during the rapid preheating process. The shortened furnace heating soaking is used to reduce the oxidation time. In some examples, the CFPHS component is used for anti-collision structural components, such as automotive pillars, door beams, and bumper beams.

[0062] Now refer to Figure 1 , the CFPHS blank 110 is transferred to a heater 114 that performs rapid preheating of the CFPHS blank 110. In some examples, one or more conveyors 118 and / or robots 130 (with one or more end effectors 134) are used to transfer the CFPHS blank during the manufacturing process of the CFPHS component.

[0063] The heater 114 heats the CFPHS blank 110 to a first predetermined temperature range at a first predetermined heating rate. In some examples, the first predetermined heating rate is in a range of 20°C / sec to 300°C / sec. In some examples, the first predetermined temperature is in a range of 500°C to 950°C. The final temperature of the CFPHS blank 110 will vary depending on the specifications and dimensions of the CFPHS blank 110. In some examples, the heater 114 is selected from an induction heater, a resistance heater, a laser heater, or a combination thereof.

[0064] After rapid preheating, the CFPHS blank 110 is transferred to a furnace 120 for heating. In some examples, the furnace 120 soaks the CFPHS blank 110 at a temperature in a range of 900° C. to 950° C. In some examples, the CFPHS blank 110 is heated for a predetermined soaking time in a range of 5 seconds to 500 seconds. In some examples, the CFPHS blank 110 is heated for a predetermined time in a range of 5 seconds to 50 seconds.

[0065] After heating in the furnace 120 , the CFPHS blank 110 is transferred to a stamping machine / press 140 including two or more dies 144 for pressing and forming to produce a pressed and formed CFPHS component 150 .

[0066] The combination of the use of CFPHS, preheating, and soaking in the furnace (short soaking time) allows for the desired surface quality and base metal mechanical properties to be obtained. In some examples, the oxide layer on the CFPHS component has a thickness in the range of greater than or equal to 0.1 microns and less than or equal to 1.5 microns. In some examples, the oxide layer covers greater than or equal to 90% of the exposed surface of the CFPHS component. In some examples, the oxide layer on the CFPHS component has a thickness in the range of greater than or equal to 0.1 microns and less than or equal to 1.0 microns.

[0067] Now refer to Figure 2 , a method 200 for manufacturing a CFPHS component is shown. At 210, a coating-free press hardened steel (CFPHS) blank is transferred to a rapid heater. At 220, the rapid heater performs rapid preheating of the CFPHS blank. The rapid heater preheats the CFPHS blank to a first predetermined temperature range at a first predetermined heating rate.

[0068] At 230, after rapid preheating, the CFPHS billet is transferred to a furnace. At 232, the CFPHS billet is soaked in the furnace at a second predetermined temperature for a predetermined soaking time. In some examples, the second predetermined temperature is in the range of 900°C to 950°C. In some examples, the CFPHS billet 110 is soaked for a predetermined soaking time in the range of 5 seconds to 500 seconds. In some examples, the CFPHS billet 110 is soaked in the furnace for a predetermined time in the range of 5 seconds to 50 seconds.

[0069] After heating in the furnace, the CFPHS blank is transferred to a stamping machine / press including two or more dies at 240. At 242, the CFPHS blank is formed and press-hardened into a CFPHS component.

[0070] The method of manufacturing CFPHS components according to the present disclosure produces components with consistent desired surface quality. The method simplifies furnace atmosphere requirements (in other words, the furnace can be operated using atmospheric air rather than nitrogen or other gas environments). The method of manufacturing CFPHS components reduces energy consumption by reducing the heat treatment cycle time of the CFPHS components.

[0071] The CFPHS component has improved appearance after spot welding and corrosion resistance after painting. The method of manufacturing the CFPHS component reduces costs (avoiding descaling) by using CFPHS instead of coated PHS (such as AlSi coated PHS). The method of manufacturing the CFPHS component also improves the production efficiency of hot stamping due to the shorter furnace heating cycle (which reduces the production cycle).

[0072] The foregoing description is merely illustrative and is by no means intended to limit the present disclosure, its application or use. The broad teachings of the present disclosure can be implemented in various forms. Therefore, although the present disclosure includes specific examples, the true scope of the present disclosure should not be so limited, because after studying the drawings, the specification and the appended claims, other modifications will become apparent. It should be understood that, without changing the principles of the present disclosure, one or more steps in the method can be performed in different orders (or simultaneously). In addition, although each embodiment is described above as having certain features, any one or more of those features described in any embodiment of the present disclosure can be implemented in any of other embodiments and / or combined with the features of any of other embodiments, even if the combination is not explicitly described. In other words, the embodiments described are not mutually exclusive, and the replacement of one or more embodiments with each other remains within the scope of the present disclosure.

[0073] Various terms are used to describe the spatial and functional relationships between elements (e.g., between modules, circuit elements, semiconductor layers, etc.), including "connected," "engaged," "coupled," "adjacent," "immediately adjacent," "on top," "above," "below," and "disposed." Unless explicitly described as "direct," when the relationship between a first and a second element is described in the above disclosure, the relationship can be a direct relationship in which there are no other intervening elements between the first and second elements, but can also be an indirect relationship in which there are one or more intervening elements (spatially or functionally) between the first and second elements. As used herein, the phrase at least one of A, B, and C should be interpreted to mean a logical (A or B or C) using a non-exclusive logical "or," and should not be interpreted to mean "at least one of A, at least one of B, and at least one of C."

[0074] In the drawings, the direction of the arrows, as indicated by the arrows, generally indicates the flow of information (such as data or instructions) related to the diagram. For example, when component A and component B exchange various information, but the information transmitted from component A to component B is related to the diagram, the arrow may point from component A to component B. The unidirectional arrow does not imply that no other information is transmitted from component B to component A. In addition, for information sent from component A to component B, component B may send a request for the information or a confirmation of receipt of the information to component A.

Claims

1. A method of manufacturing a coating-free press hardened steel (CFPHS) component, comprising: heating the CFPHS blank to a first predetermined temperature within a first predetermined temperature range using a heater at a first predetermined heating rate; Transferring the CFPHS billet to a furnace; soaking the CFPHS blank in a furnace at a second predetermined temperature within a second predetermined temperature range for a predetermined time; and The CFPHS blank is pressed and formed in a punch / press to form a CFPHS component.

2. The method according to claim 1, wherein the first predetermined temperature is 500°C to 950°C.

3. The method according to claim 1, wherein the first predetermined heating rate is 20°C / sec to 300°C / sec.

4. The method according to claim 1, wherein the heater is selected from an induction heater, a resistance heater, a laser heater or a combination thereof.

5. The method according to claim 1, wherein the second predetermined temperature is 750°C to 1200°C. The method according to claim 1 , wherein the predetermined time is from 5 seconds to 500 seconds. The method according to claim 1 , wherein the predetermined time is from 5 seconds to 50 seconds.

8. The method of claim 1, wherein after preheating in the heater, the CFPHS component comprises an oxide layer having a thickness of greater than or equal to 0.1 microns to less than or equal to 1.5 microns.

9. The method of claim 8, wherein the oxide layer covers greater than or equal to 90% of the exposed surface of the CFPHS component.

10. The method of claim 1, wherein after preheating in the heater, the CFPHS component comprises an oxide layer having a thickness of greater than or equal to 0.1 micrometers to less than or equal to 1.0 micrometers.

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