CN115232930A - Hot stamping forming process and hot stamping forming components - Google Patents

Abstract

The invention provides a hot stamping forming process and a hot stamping forming component. The process includes induction heating to 700-940 DEG C, then heating and heat preservation in a heating furnace; cooling to 800-875 DEG C; Above 550°C; hot stamping and cooling to below 250°C. The invention makes full use of the advantages of high thermal efficiency of induction heating, low energy consumption, uniform heating temperature distribution, etc., realizes the controllability of rapid heating and oxidation time, controls the solid solution and coarsening degree of VC precipitated particles in the raw material, and effectively avoids austenite The coarsening of the bulk grains makes the structure more uniform, and the mechanical properties are further improved compared with the traditional hot stamping process. On the one hand, the grains are refined, and on the other hand, the precipitation of VC consumes the C content in the matrix, thereby reducing the amount of martensite in the hot stamping state. The C content can ensure the toughness of the material after hot stamping through two mechanisms: grain refinement and VC precipitation and carbon reduction to suppress high-carbon martensite.

Description

Hot stamping forming process and hot stamping forming components

technical field

The present invention relates to the technical field of hot stamping and hot stamping components, in particular, a hot stamping process and hot stamping components.

Background technique

In recent years, due to the urgent needs of global energy conservation and emission reduction, environmental protection economy and the improvement of automobile safety requirements, automobile lightweight and safety have become the focus of the current automobile manufacturing industry and urgently to be solved. Reducing vehicle body weight is an effective means to achieve energy saving and emission reduction of automobiles, but the lightening of automobiles does not come at the expense of safety. On the contrary, the requirements for automobile collision safety are getting higher and higher. The primary goal of new high-strength and toughness automotive steels is to increase material strength. However, high strength also brings new difficulties to automobile manufacturing. The cold stamping method is adopted, the forming performance is reduced, the required stamping force is large, and it is easy to crack; in addition, the parts spring back after forming, and its shape and dimensional accuracy are difficult to guarantee. Based on the problems existing in cold forming technology, hot stamping forming technology has received great attention and has developed rapidly.

The so-called hot stamping forming technology is to heat the high-strength steel plate to a temperature above the austenitization temperature, and after holding for a period of time, it is quickly transferred to the mold and stamped rapidly. The microstructure is transformed from austenite to uniform martensite, so that the formed parts have higher mechanical strength and good dimensional accuracy. At present, the hot stamping steel widely used in the automotive industry is an alloy structural steel represented by 22MnB5, which has a high austenitizing temperature (AC3 about 930 ° C), low hardenability, poor toughness after forming, and cold bending. Limited performance, delayed cracking, etc. In addition, the conventional hot stamping process relies on a roller hearth furnace or a walking furnace to heat the web by radiation and convection. The thickness of the web and the coating have a great influence on the effective heating temperature, which will cause the heating device to occupy a larger space and higher There are a series of disadvantages such as long heating time, high energy consumption, low heating efficiency, and decarburization of the steel plate surface. Based on the discussion of potential problems of traditional hot stamping steel and forming process, it is particularly important to develop hot stamping steel with high strength and toughness and its forming process.

The patent CN101583486A mainly uses a roller hearth furnace, a walking furnace, etc. to heat the pre-coating sheet. In a conventional heating furnace, the coated steel plate is heated by thermal radiation and thermal convection, and thermal radiation is the main method, accounting for about 80% to 90% of the total heat exchange. This patent formulates different austenitization times according to the thickness of the steel plate and the austenitization temperature. The austenitization time is related to the thickness of the steel plate and the austenitization temperature. The thicker the steel plate and the lower the austenitization temperature, the longer the austenitization time. Usually, after heating to the austenitizing temperature (880-940 ℃), it needs to be kept for a period of time to ensure complete austenitization and uniform austenite grain structure. However, the long-term heating process inevitably causes the coarsening of grains. In addition, the heating electric furnace usually occupies a large area and the construction cost is high; the operation process of the electric furnace needs to be equipped with a ceramic hearth roller and a protective atmosphere, coupled with the limitation of temperature control accuracy, it will inevitably lead to the continuous waste of heat energy and electric energy. The energy utilization rate is greatly reduced; the furnace rolls are easy to scale and break, and the replacement is inconvenient, and the maintenance cost of the furnace rolls is high;

Patent CN106399837A patent provides a kind of steel for hot stamping, characterized in that, the steel for hot stamping includes the following components by weight: 0.27-0.40% C; 0.2-3.0% Mn; 0.11-0.4% V; 0-0.8% Si; 0-0.5% Al; 0-2% Cr; 0-0.15% Ti; 0-0.15Nb; 0-0.004% B; Ni, Cu; and unavoidable impurity elements, the steel for hot stamping can reach a yield strength of 1300 MPa to 1700 MPa and a tensile strength of 1800 to 2200 MPa without tempering after hot stamping, and 6 to 9% elongation. In addition, the patent also provides a hot stamping forming process, that is, the invented steel is heated to 800-920°C for 1-10000s and then quickly transferred to the hot-stamping die (300s). However, in the process of hot stamping heat treatment, improper process control can easily cause grain coarsening and dissolution and coarsening of nano-precipitated phases.

SUMMARY OF THE INVENTION

According to the above technical problems, a hot stamping forming process and a hot stamping forming component are provided. The invention mainly utilizes the advantages of high induction heating speed, high thermal efficiency, high temperature control accuracy, uniform heating, good product quality, less heating oxide scale, low mold cost and operating cost, less environmental pollution, good controllability, and easy automation. A series of advantages, realize the controllability of rapid heating and oxidation time, control the solid solution and coarsening degree of VC precipitated particles in the raw material, effectively avoid the coarsening of austenite grains, make the structure more uniform, and have better mechanical properties than traditional hot stamping. The process is further improved. On the one hand, the grains are refined, and on the other hand, VC precipitation consumes the C content in the matrix, thereby reducing the C content in the martensite in the hot stamping state (inhibiting the formation of high-carbon martensite). The two mechanisms of particle and VC precipitation and carbon reduction ensure the toughness of the material after hot stamping.

The technical means adopted in the present invention are as follows:

A hot stamping forming process, comprising:

(a) Austenitization of steel:

Induction heating of steel for hot stamping or its preformed components, heating to 700-940°C, with an average heating rate of ≥20°C/s;

Then enter the heating furnace with a furnace temperature of 931 to 970 ° C for heating and heat preservation; the heating and heat preservation time is 60 to 300 s; among them, the hot stamping steel with a thickness of 0.5 to 1.5 mm or its preformed components have a furnace temperature of 60 to 300s. Heating in a heating furnace with a temperature of 931-960°C, and heating and holding time of 60-150s; steel for hot stamping with a thickness of >1.5mm-2mm or its preformed components heated in a heating furnace with a furnace temperature of 941-970°C , the heating and holding time is 120 ~ 240s; the steel for hot stamping with a thickness of >2mm ~ 2.5mm or its preformed components is heated in a heating furnace with a furnace temperature of 941 ~ 970 ℃, and the heating and holding time is 180 ~ 300s;

The steel material for hot stamping or its preformed member includes the following components by weight: 0.3-0.40% C; 0.2-3.0% Mn; 0.11-0.4% V; 0-0.8% Si; 0-0.5% Al; 0～2% Cr; 0～0.15% Ti; 0～0.15Nb; and satisfy Ti+Nb≥0.03; 0～0.004% B; Mo, Ni, Cu whose total content is less than 2%; Avoided impurity elements;

(b) cooling the steel material for hot stamping or its preformed member obtained in step (a), cooling to 800-875° C., keeping the temperature for 0-30 minutes, and cooling time ≤ 120s; wherein, the thickness of 0.5-1.5mm The cooling time of steel for hot stamping or its preformed components is ≤60s; the cooling time of steels for hot stamping or its preformed components with a thickness of >1.5mm~2mm is ≤90s; The cooling time of the steel for stamping or its pre-formed components is ≤120s;

(c) transferring the steel for hot stamping or its preformed member obtained in step (b) to a hot stamping die, and ensuring that the temperature of the steel for hot stamping or its preformed member is 550°C when transferred to the die above ℃;

(d) Select the suitable press tonnage (0-2000 tons) according to the size of the steel used for hot stamping or its pre-formed components, and determine the pressure holding time (0-3min) according to the thickness of the plate,

The steel material for hot stamping or its preformed member is cooled to 250°C or lower at an average cooling rate of not less than 10°C/s in the die by the die cooling system.

The present invention also discloses a hot stamping forming component, the hot stamping forming component is made by the hot stamping forming process according to any one of claims 1 to 3, and has a thickness of 1800 without tempering. ~2300MPa tensile strength, and 6~10% elongation.

After tempering, the properties of the hot stamping-formed component reach a yield strength of 1500 MPa to 1900 MPa, a tensile strength of 1800 to 2200 MPa, and an elongation of 7 to 12%.

After the step (a) of the forming process of the hot stamping forming component is completed, the composite carbonitride of V, Ti and Nb exists in the austenite grain boundary and in the preformed component of the steel material for hot stamping forming. The size of the precipitated particles is 0.1 to 200 nm. The austenite intercept grain size of the steel for hot stamping or its preformed parts is 1-15 microns.

In the step (b) of the forming process of the hot stamping forming component, a certain amount of VC and/or V and Ti, Nb are precipitated in the austenite grain including the grain boundary of the steel material for hot stamping forming or its preformed component. The composite carbonitride, the carbide particle size in the austenite crystal is 0.1-30 nm.

The volume fraction of the composite carbonitride of VC and/or V, Ti and Nb of the hot stamped component is greater than 0.08%, the volume fraction of martensite is greater than 90%, and the rest are ferrite and other structures.

The invention also discloses a tempering process, comprising:

(1) The hot stamping forming component is obtained by the above-mentioned hot stamping forming process;

(2) Heating the hot stamping and forming member to 140-210°C and maintaining the temperature for 5-60 minutes; or heating the hot-stamping forming member to 120-260°C at a heating rate of 0.001-100°C/s and maintaining the temperature for 0.5-60 minutes. 120min, then cool in any way.

The hot stamping forming components are used for high-strength components of automobiles, including safety structural components such as A-pillars, B-pillars, bumpers, roof frames, and door anti-collision beams of automobiles.

Compared with the prior art, the present invention has the following advantages:

1. The present invention makes full use of the advantages of induction heating, such as high thermal efficiency, low energy consumption, and uniform heating temperature distribution, to achieve rapid heating and controllability of oxidation time, and to control the degree of solid solution and coarsening of VC precipitated particles in the raw material, effectively avoiding the need for The coarsening of the austenite grains makes the structure more uniform, and the mechanical properties are further improved compared with the traditional hot stamping process. The C content in the body ensures the toughness of the material after hot stamping through two mechanisms: grain refinement and VC precipitation and carbon reduction.

2. After the tempering process, its performance reaches a yield strength of 1500MPa to 1900MPa, a tensile strength of 1800 to 2200MPa, and an elongation of 7 to 12%. The material elongation and toughness are further improved to meet the crash performance requirements.

Based on the above reasons, the present invention can be widely promoted in the fields of hot stamping and the like.

Description of drawings

In order to illustrate the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to these drawings without creative efforts.

FIG. 1 is the SEM microstructure of the sample after induction heating + mold quenching under the hot stamping process provided by the present invention in Example 1. FIG.

FIG. 2 shows the precipitates on the martensite of the sample after induction heating + die quenching under the hot stamping process provided by the present invention in Example 1. FIG.

Detailed ways

It should be noted that the embodiments of the present invention and the features of the embodiments may be combined with each other under the condition of no conflict. The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

In order to make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments It is only a part of the embodiments of the present invention, but not all of the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

A hot stamping forming process, comprising:

(a) Austenitization of steel:

Induction heating of steel for hot stamping or its preformed components, heating to 700-940°C, with an average heating rate of ≥20°C/s;

Then enter the heating furnace with a furnace temperature of 931 to 970 ° C for heating and heat preservation; the heating and heat preservation time is 60 to 300 s; among them, the hot stamping steel with a thickness of 0.5 to 1.5 mm or its preformed components have a furnace temperature of 60 to 300s. Heating in a heating furnace with a temperature of 931-960 °C, and heating and holding time for 60-150s; steel materials for hot stamping with a thickness of 1.5 mm-2 mm or their preformed components are heated in a heating furnace with a furnace temperature of 941-970 °C, The heating and holding time is 120-240s; the steel for hot stamping with a thickness of >2mm-2.5mm or its pre-formed components is heated in a heating furnace with a furnace temperature of 941-970°C, and the heating and holding time is 180-300s;

The steel material for hot stamping or its preformed member includes the following components by weight: 0.3-0.40% C; 0.2-3.0% Mn; 0.11-0.4% V; 0-0.8% Si; 0-0.5% Al; 0-2% Cr; 0-0.15% Ti; 0-0.15Nb; and satisfy Ti+Nb≥0.03; 0-0.004% B; Mo, Ni, Cu whose total content is less than 2%; Avoided impurity elements;

(b) cooling the steel material for hot stamping or its preformed member obtained in step (a), cooling to 800-875° C., keeping the temperature for 0-30 minutes, and cooling time ≤ 120s; wherein, the thickness of 0.5-1.5mm The cooling time of steel for hot stamping or its preformed components is ≤60s; the cooling time of steels for hot stamping or its preformed components with a thickness of >1.5mm~2mm is ≤90s; The cooling time of the steel for stamping or its pre-formed components is ≤120s;

(c) transferring the steel for hot stamping or its preformed member obtained in step (b) to a hot stamping die, and ensuring that the temperature of the steel for hot stamping or its preformed member is 550°C when transferred to the die above ℃;

(d) According to the size of the steel used for hot stamping or its preformed components, select the tonnage of the press that is suitable for it, and determine the holding time according to the thickness of the plate,

The steel material for hot stamping or its preformed member is cooled to 250°C or lower at an average cooling rate of not less than 10°C/s in the die by the die cooling system.

The present invention also discloses a hot stamping forming component, the hot stamping forming component is made by the hot stamping forming process according to any one of claims 1 to 3, and has a thickness of 1800 without tempering. ~2300MPa tensile strength, and 6~10% elongation.

After tempering, the properties of the hot stamping-formed component reach a yield strength of 1500 MPa to 1900 MPa, a tensile strength of 1800 to 2200 MPa, and an elongation of 7 to 12%.

After the step (a) of the forming process of the hot stamping forming component is completed, the composite carbonitride of V, Ti and Nb exists in the austenite grain boundary and in the preformed component of the steel material for hot stamping forming. The size of the precipitated particles is 0.1 to 200 nm. The austenite intercept grain size of the steel for hot stamping or its preformed parts is 4-15 microns.

In the step (b) of the forming process of the hot stamping forming component, a certain amount of VC and/or V and Ti, Nb are precipitated in the austenite grain including the grain boundary of the steel material for hot stamping forming or its preformed component. The composite carbonitride, the carbide particle size in the austenite crystal is 0.1-30 nm.

The volume fraction of the composite carbonitride of VC and/or V, Ti and Nb of the hot stamped component is greater than 0.08%, the volume fraction of martensite is greater than 90%, and the rest are ferrite and other structures.

Also disclosed is a tempering process, comprising:

(1) The hot stamping forming component is obtained by the above-mentioned hot stamping forming process;

(2) Heating the hot stamping and forming member to 140-210°C and maintaining the temperature for 5-60 minutes; or heating the hot-stamping forming member to 120-260°C at a heating rate of 0.001-100°C/s and maintaining the temperature for 0.5-60 minutes. 120min, then cool in any way.

The hot stamping forming components are used for high-strength components of automobiles, including safety structural components such as A-pillars, B-pillars, bumpers, roof frames, and door anti-collision beams of automobiles.

Example 1

The hot stamping forming steel material composition used in the present invention is as follows:

Table 1 Chemical composition of test materials (wt.%)

C Si Mn P S Als Cr Ti V Nb B N 0.35 0.25 1.4 0.010 0.002 0.039 0.3 0.03 0.19 0.015 0.0025 0.0036

The conventional hot stamping process (A) and the hot stamping process (B) involved in the present invention are shown in Table 2:

Table 2 Main process parameters of hot stamping

The microstructure of the hot stamping formed component prepared by induction heating process B is shown in Figure 1, and its precipitation morphology is shown in Figure 2.

The mechanical properties of the parts prepared by hot stamping processes A to D are shown in Table 2:

Table 2 Mechanical properties of parts after hot stamping

The results show that the microstructure of the hot-formed steel component prepared by the invention is full martensite, and a large number of fine nano-scale precipitates are distributed on the martensite matrix. Regardless of the quenched state or the quenched state + baking and tempering state (170℃/20min), the yield strength is nearly 130MPa higher than that of the conventional hot stamping process, and the corresponding three-point bending angle under the maximum load of VDA238-100 is also increased by more than 7°. Therefore, the induction rapid heating + sufficient austenitization and the precipitation control during the cooling process involved in the present invention are very significant in improving the final performance of the component.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: The technical solutions described in the foregoing embodiments can still be modified, or some or all of the technical features thereof can be equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the embodiments of the present invention. scope.

Claims (10)

1. A hot stamp-forming process, comprising:

(a) Austenitizing steel:

induction heating the steel for hot stamping forming or the preformed component thereof to 700-940 ℃, wherein the average heating rate is more than or equal to 20 ℃/s;

then the mixture enters a heating furnace with the furnace temperature of 931-970 ℃ for heating and heat preservation; heating and keeping the temperature for 60-300 s;

the steel material for hot press forming or the preformed member thereof comprises the following components by weight: 0.3 to 0.40 percent of C;0.2 to 3.0 percent of Mn; 0.11-0.4% of V;0 to 0.8 percent of Si;0 to 0.5 percent of Al;0 to 2 percent of Cr;0 to 0.15 percent of Ti;0 to 0.15Nb; and Ti + Nb is more than or equal to 0.03; 0-0.004% of B; mo, ni, cu with the total content of less than 2 percent; and unavoidable impurity elements;

(b) And (3) cooling: cooling the steel for hot stamping forming or the preformed member thereof obtained in the step (a) to 800-875 ℃, and keeping the temperature for 0-30 minutes, wherein the cooling time is less than or equal to 120s;

(c) Transferring: transferring the hot stamping steel or the preformed component thereof obtained in the step (b) to a hot stamping forming die, and ensuring that the temperature of the hot stamping steel or the preformed component thereof is above 550 ℃ when the hot stamping steel or the preformed component thereof is transferred to the hot stamping forming die;

(d) Hot stamping and forming: selecting a press tonnage matched with the steel for hot stamping forming or the preformed component thereof according to the size, and determining the pressure maintaining time according to the thickness of the plate; the hot press-forming steel material or the preformed member thereof is cooled in the press-forming die to 250 ℃ or lower at an average cooling rate of not less than 10 ℃/s by a cooling system of the press-forming die.

2. A hot press forming process according to claim 1, wherein in the step (a), the steel material for hot press forming having a thickness of 0.5 to 1.5mm or the preformed member thereof is heated in a heating furnace having a furnace temperature of 931 to 960 ℃ for 60 to 150 seconds; heating the steel for hot stamping forming with the thickness of more than 1.5 mm-2 mm or the preformed component thereof in a heating furnace with the furnace temperature of 941-970 ℃ for 120-240 s; a steel material for hot press forming having a thickness of 2mm to 2.5mm or a preformed member thereof is heated in a heating furnace at a furnace temperature of 941 to 970 ℃ for 180 to 300 seconds.

3. The hot press forming process according to claim 1, wherein in the step (b), the cooling time of the steel material for hot press forming or the preformed member thereof having a thickness of 0.5 to 1.5mm is 60s or less; the cooling time of the steel for hot stamping forming or the preformed component thereof with the thickness of more than 1.5 mm-2 mm is less than or equal to 90s; the cooling time of the steel material for hot stamping forming or the preformed component thereof with the thickness of more than 2mm to 2.5mm is less than or equal to 120s.

4. A hot press formed member, characterized in that it is produced by a hot press forming process according to any one of claims 1 to 3, having a tensile strength of 1800 to 2300MPa and an elongation of 6 to 10% without tempering, and is used for automotive high-strength members including a-pillars, B-pillars, bumpers, roof frames, door impact beams.

5. A hot-press formed member characterized in that the hot-press formed member has, after tempering, yield strength of 1500MPa to 1900MPa, tensile strength of 1800 MPa to 2200MPa, and elongation of 7% to 12%.

6. The hot-stamped component according to claim 4, wherein the steel material for hot-stamping or the preform component thereof has a carbonitride of V, ti and Nb in austenite grain boundaries and in the crystal grains, and the precipitated particle size is 0.1 to 200nm, after the step (a) of the forming process of the hot-stamped component is completed.

7. A hot-stamped component according to claim 4, wherein the hot-stamped steel or preformed component thereof has an austenite intercept grain size of 1 to 15 microns after step (a) of the hot-stamping process.

8. The hot-stamped component according to claim 4, wherein in the step (b) of the forming process of the hot-stamped component, the steel for hot-stamping or the preformed component thereof precipitates a certain amount of carbonitride of VC and/or V with Ti and Nb in austenite grains including grain boundaries, the carbide grain size in the austenite grains being 0.1 to 30nm.

9. A hot-stamped component according to claim 4, wherein the volume fraction of composite carbonitrides of VC and/or V with Ti and Nb is greater than 0.08%, the volume fraction of martensite is greater than 90%, and the balance is ferrite and other structures.

10. A tempering process, comprising:

(1) Obtaining a hot stamp-formed member by a hot stamp-forming process according to any one of claims 1 to 3;

(2) Heating the hot stamping forming component to 140-210 ℃, and preserving heat for 5-60 min, or heating the hot stamping forming component to 120-260 ℃ at a heating rate of 0.001-100 ℃/s, preserving heat for 0.5-120 min, and then cooling in any mode.

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