JP6575119B2 - Method for producing heat-treated hollow metal member excellent in chemical conversion treatment of inner surface - Google Patents

Description

  The present invention relates to a method for producing a heat-treated hollow metal member excellent in chemical conversion treatment on the inner surface, and specifically, it is produced by subjecting a hollow steel material to heat treatment or bending with heat treatment, and has high strength and excellent chemical conversion treatment. Therefore, the present invention relates to a method for manufacturing a heat-treated hollow metal member suitably used for automobiles, for example.

  In recent years, from the viewpoint of global environmental problems and collision safety performance, there has been a demand for thinner and higher strength structural parts for automobiles. In order to meet these demands, structural parts for automobiles made of high-strength steel sheets are increasing. However, when a structural component for automobiles is manufactured by press molding using a high-strength steel plate as a raw material, molding defects such as wrinkles and springback are likely to occur. For this reason, it is not easy to manufacture structural parts for automobiles by press molding using a high-strength steel plate as a raw material.

  As a technique for solving such a problem, a technique for manufacturing a high-strength molded product by processing a steel material hot and quenching it by quenching has been put into practical use. For example, a hot press (also referred to as a hot stamp) can form a complicated shape with high dimensional accuracy because a steel sheet as a forming material is soft and highly ductile at high temperatures. Further, by heating the steel plate in the austenite region and quenching in the mold, it is possible to simultaneously achieve high strength of the steel plate by martensitic transformation.

  However, since it heats to high temperature of 800-1000 degreeC, the problem that the steel plate surface oxidizes arises. If this scale remains, the adhesion between the steel sheet and the coating film will be inferior when coating in the next step, leading to a reduction in corrosion resistance. Therefore, after press molding, a scale removal process such as shot blasting is required.

  In Patent Document 1, in a method of bending a hollow steel material (for example, a steel pipe), the steel material is locally heated by the heating device while the heating device and the cooling device are moved relative to the steel material, and the deformation resistance is caused by the heating. A bending moment is applied to a greatly lowered portion to bend into a desired shape bent in two or three dimensions, and then cooled by a cooling device (in this specification, “three-dimensional hot bending quenching” 3DQ: 3 Dimensional Hot Bending and Direct Quench) ”. According to this three-dimensional hot bending quenching, it is possible to efficiently produce a high-strength molded article having a high bending accuracy, for example, 900 MPa class or higher.

  However, even in this method, the steel material is heated to the austenite region and rapidly cooled with a cooling medium to increase the strength of the steel material by martensitic transformation. Therefore, oxide scale is generated on the surface of the manufactured molded product. In the case of coating in the next step, there is a problem that the adhesion between the steel material and the coating film is inferior and the corrosion resistance is lowered.

  With respect to these problems, according to Patent Document 2, when the steel material is fed in the longitudinal direction thereof, the steel material to be fed is heated to a quenchable temperature range and then cooled to quench the steel material. An invention relating to a method and an apparatus for manufacturing a hardened steel material capable of suppressing or eliminating the generation has been disclosed.

  According to the present invention, the steel material is heated to the quenchable temperature range by the heating device arranged at the first position while being sent in the longitudinal direction while the steel material is being sent in the longitudinal direction, and the steel material is more than at the first position. When quenching a steel material by spraying a cooling medium on the steel material by a cooling device arranged at a second position downstream of the feed direction of the steel, the space around the portion of the steel material heated by the heating device is inert. By filling the gas or reducing gas, it is possible to manufacture a hardened steel material in which the generation of oxide scale is suppressed. Furthermore, by supplying an inert gas or a reducing gas to the inside of the steel material, scale formation on the inner surface of the steel material can also be suppressed or eliminated.

  On the other hand, there is an invention disclosed in Patent Document 3 as a heat treatment method focusing on cleaning the inside of a metal tube. In this invention, as a first method, a metal tube unwound from a metal tube coil placed on a payoff table is continuously heat-treated through a heating furnace, and then wound on a receiving table. The purge gas is blown into the metal tube being heat-treated from the tube end of the metal tube coil on the receiving table side to remove residual oil in the metal tube. As a second method, in a heat treatment method for a metal tube, a metal tube unwound from a metal tube coil placed on a payoff table is continuously heat-treated through a heating furnace and then wound on a receiving table. A purge gas is blown into the metal tube being heat-treated from the tube end of the side metal tube coil to remove residual oil in the metal tube. As a third method, in a heat treatment method for a metal tube in which a metal tube unwound from a metal tube coil placed on a payoff table is continuously heat-treated through a heating furnace and then wound on a receiving table, the payoff table Purge gas is blown into the metal tube being heat-treated from the tube end of the metal tube coil on the side, and then purge gas is blown into the metal tube being heat-treated from the tube end of the metal tube coil on the receiving table side to remove residual oil in the metal tube. .

JP 2007-83304 A JP 2011-89150 A JP-A-9-217120

  For example, among hollow metal members used as structural members of automobiles, those that may allow moisture to enter the interior of the automobile when used, require corrosion resistance not only on the outer surface side but also on the inner surface side of the hollow member. In addition, the inner surface side is also subjected to coating and chemical conversion treatment as a base treatment. For this reason, it is requested | required that the heat-processed hollow metal member used for them is excellent in the chemical conversion treatment property of an inner surface.

  In the manufacturing method disclosed in Patent Document 1, when the oxide scale is generated on the outer surface of the member by heat treatment, the adhesion of the coating film is inferior and the corrosion resistance is reduced as described above, but the inner surface of the hollow member is the inside of the hollow member. Since the amount of oxygen present in the space is limited and the inner surface is not exposed to cooling water or water vapor, the amount of scale produced is smaller than the outer surface. However, a certain amount of scale is generated, which adversely affects the chemical conversion treatment of the inner surface, even if it does not cause extreme deterioration of coating film adhesion.

  In order to suppress the generation of scale on the inner surface, if an inert gas or a reducing gas is supplied into the hollow member by the method disclosed in Patent Document 2, the generation of scale on the inner surface can be suppressed or eliminated.

  However, as a result of extensive studies by the present inventors in order to further improve the invention, it has been found that, depending on the production conditions, the chemical conversion processability may be slightly inferior even though scale formation is suppressed. The reason seems to be related to the following.

  The surface of the material of the hollow metal member that is subjected to heat treatment is in a state where the lubricating oil remains adhered in the manufacturing process of the material, or in some cases, rust is generated during the period until the heat treatment is performed. In order to prevent, rust preventive oil is applied.

  When the material in this state is heated, those oil components are thermally decomposed to generate gas containing fine particles of products such as soot. Although the gas is dispersed and has no influence on the outer surface side of the member, the gas stays in place on the inner surface side of the member and comes into contact with the inner surface of the member after heat treatment, and the pyrolysis product contained in the gas adheres. Conceivable.

  For this reason, as in the invention disclosed in Patent Document 2, even if the inert gas or reducing gas is retained and filled in the steel material, the generation of scale can be suppressed, but the thermal decomposition generated from the oil It has been found that it is difficult to sufficiently prevent the adhesion of objects, and it is important to prevent the generated gas from staying inside the member.

  In addition, Patent Document 2 exemplifies supplying an inert gas or a reducing gas from the rear end portion of the steel material in the steel material feed direction to the inside of the steel material, and discharging it from the front end portion in the feed direction to the outside. It has also been found that the thermal decomposition product generated from the oil component passes through the product side after the heat treatment and is considered to adhere to the inner surface of the member after the heat treatment.

  In response to the above problem, the first method disclosed in Patent Document 3, which is a heat treatment method focused on cleaning the inside of a metal tube, is applied, and a purge gas is blown from the tip in the feed direction to heat and vaporize. It is conceivable to discharge the oil from the rear end in the feed direction to the outside.

  However, the heat treatment method disclosed in Patent Document 3 is a technique assumed for copper tubes or copper alloy tubes such as heat exchangers, and since the heating temperature is about 700 ° C. at the highest, This method is based on the premise of vaporization and recondensation, but when heated rapidly to a temperature range of 900 to 1100 ° C for the purpose of induction hardening of steel, the oil is thermally decomposed and fine particles of products such as soot are generated. However, if this adheres to the inner surface of the member on the rear end side in the feed direction due to the flow of the purge gas, it turns out that even if the part is heated later, it remains as it is without being vaporized, and there is a problem that it affects the chemical conversion treatment performance. did.

  In order to eliminate the thermal decomposition products generated from the oil, it is conceivable to degrease the steel before it is subjected to heat treatment, but it increases the cost due to the addition of the process and adheres to the inner surface of the hollow member. Since it is difficult to degrease the oil, and when degreasing, rust may be generated even during the drying process, it is not realistic to perform the heat treatment after degreasing.

  The present invention has been made in view of such problems, and prevents thermal decomposition products generated from oil from adhering to the inner surface of the product after heat treatment, and unheated on the rear end side in the feed direction. It aims at providing the manufacturing method of the heat-processed hollow metal member which has the outstanding chemical conversion property by making it the deterioration of chemical conversion property by the thermal decomposition product adhering to a member inner surface. More specifically, the present invention is manufactured by subjecting a hollow metal member to heat treatment or bending with heat treatment, and has high strength and excellent chemical conversion treatment. It aims at providing the manufacturing method of a metal member.

  In the method for producing a heat-treated hollow metal member, the present inventors control the gas flow inside the hollow member so that the thermal decomposition product generated from the oil does not adhere to the inner surface of the product after the heat treatment on the front side in the feed direction, Discovered that even if pyrolysis products adhere to the inner surface of the member on the rear end side in the feed direction, combustion can be ensured by burning with a small amount of oxygen in the gas inside the member, and the present invention is completed. It came to do. The present invention is listed below.

(1) While relatively moving the heating device and the cooling device with respect to the hollow steel member, the heating device locally heats the hollow steel member to a temperature range of Ac _{3 to} 1100 ° C. , and then the cooling device. a method of manufacturing a heat-treated hollow steel member by cooling and heat treatment, toward the rear end from the relative feed direction of the distal end portion of the hollow steel member with respect to the heating device and the cooling device, the hollow A method for producing a heat-treated hollow steel member, characterized by flowing a gas containing 0.01 to 1% by volume of oxygen and an inert gas at a flow rate of 0.1 m / second or more inside a steel member.

(2) Production of a heat-treated hollow steel member as described in item (1), wherein the gas contains 0.01 to 1% by volume of oxygen, and the balance is an inert gas and an unavoidable impurity. Method.

(3) The method for producing a heat-treated hollow steel member according to item 1 or 2, wherein a flow rate of the gas is 2.0 m / second or less.

(4) Heat-treating hollow metal member by locally heating the hollow metal member by the heating device and then cooling and heat-treating by the cooling device while moving the heating device and the cooling device relative to the hollow metal member A method of manufacturing
Flowing gas at a flow rate of 0.1 m / second or more from the inside of the hollow metal member toward the rear end portion in the relative feeding direction of the hollow metal member with respect to the heating device and the cooling device,
Heat treatment the hollow metal member, wherein the at hollow metal member, to bending or shearing the desired bent shape in two or three dimensions giving bending moment or shear force to the locally pressurizing hot sites Manufacturing method.

  According to the present invention, the product generated from the oil can be prevented from adhering to the inner surface of the product, so that the adhering material can be prevented from inhibiting the formation of a chemical conversion film, and the inner surface is excellent in chemical conversion treatment, and thus after coating. It is possible to provide a heat-treated hollow metal member having excellent corrosion resistance.

  As an application site of the heat-treated hollow metal member according to the present invention, in the case of an automobile part, it is possible to reduce the vehicle weight and improve the collision safety by increasing the strength by quenching steel, and at the same time, corrosion resistance is required. It is preferably a part, and examples thereof include various pillars, door beams, reinforcements such as roofs and bumpers, frames, and arms.

The reason for limitation of the manufacturing method of the heat-treated hollow metal member according to the present invention will be described below.
In the present invention, while the heating device and the cooling device are moved relative to the hollow metal member, the hollow metal member is locally heated and cooled to perform heat treatment to produce a heat treated hollow metal member. At this time, in the present invention, the flow rate of the gas inside the hollow metal member is 0.1 m / second or more from the front end portion to the rear end portion in the relative feeding direction of the hollow metal member with respect to the heating device and the cooling device. Rinse with.

  If the gas inside the hollow metal member stays or flows from the rear end to the front end in the feed direction, the gas generated from the adhering oil in the heated part of the hollow metal member will be applied to the inner surface of the product after heat treatment. There is a possibility that the thermal decomposition product adheres upon contact, and the adhered matter inhibits the formation of the chemical conversion film.

  Moreover, even when the gas flowed from the front end portion to the rear end portion in the relative feeding direction of the hollow metal member with respect to the heating device and the cooling device, it occurred when the gas flow rate was less than 0.1 m / sec. The effect of preventing gas from flowing to the product side cannot be obtained sufficiently. For this reason, in the present invention, the gas is introduced into the hollow metal member at a flow rate of 0.1 m / second or more from the front end portion to the rear end portion in the relative feeding direction of the hollow metal member with respect to the heating device and the cooling device. Shed.

  The flow velocity of the gas flowing inside the hollow metal member in the present invention is the average value in the space section inside the hollow metal member at room temperature, and the gas at room temperature without directly measuring the flow velocity inside the hollow metal member It is obtained by dividing the flow rate by the space cross-sectional area.

  By doing so, the gas generated in the heated portion flows to the rear end side in the feed direction of the hollow metal member and comes into contact with the inner surface of the unheated hollow metal member, but the pyrolysis product is present there. Even if it adheres, the portion is a portion to be heated thereafter, so that it is considered that it is burned by a small amount of oxygen contained in the gas, and excellent chemical conversion property can be ensured.

  By the way, since the rear end portion of the hollow metal member is connected to a jig (for example, a chuck) for feeding the hollow metal member, it cannot be heated, but the strength member and structure of an automobile or the like targeted by the present invention Cutting off the non-heated portion at the rear end of the member in the member is disadvantageous in terms of cost, so it is important to make a product including these portions. Furthermore, in the member which is the object of the present invention, it is possible to provide a part not intentionally heated in the middle.

  As described above, it is assumed that the portion where the pyrolysis product adheres to the inner surface of the hollow metal member is not heated after that, but the pyrolysis product is originally deposited on the oil component adhering to the inner surface of the hollow metal member. In the process of chemical conversion treatment / painting, since this member is removed together with the oil by degreasing performed immediately before chemical conversion treatment, there is no adverse effect.

  The gas flowing inside the hollow metal member is preferably a gas mainly containing an inert gas and containing 0.01 to 1% by volume or less of oxygen. By adjusting the oxygen concentration to 1% by volume or less, it is possible to moderate the oxidation of the surface of the heated part and suppress the formation of scales, so it synergizes with the effect of preventing the adhesion of thermal decomposition products generated from oil. The chemical conversion processability can be further improved.

  Examples of the inert gas include argon and nitrogen. When the oxygen concentration exceeds 1% by volume, the formation of scale becomes remarkable, so the oxygen concentration is preferably 1% by volume or less. On the other hand, if the oxygen concentration is less than 0.01% by volume, the pyrolysis product generated from the oil adheres to the inner surface of the member on the rear end side in the feed direction. The oxygen concentration is preferably 0.01 vol% or more because it is considered that the oxygen remains in the tank without being sufficiently burned and the chemical conversion treatment property is relatively inferior.

  Furthermore, the flow rate of the gas flowing inside the hollow metal member is preferably 2.0 m / second or less. If gas is flowed at a flow rate of 0.1 m / sec or more, the effect of preventing the generated gas from contacting the inner surface of the product can be obtained sufficiently. From this viewpoint, the upper limit of the flow velocity of the gas flowing inside the hollow metal member is particularly determined. Although it is not necessary, if the flow rate is excessively increased, the amount of oxygen that contacts the heated portion of the hollow metal member per unit time increases, so that the formation of scale becomes remarkable, and the chemical conversion processability may be deteriorated. Therefore, the flow rate of the gas flowing inside the hollow metal member is preferably 2.0 m / second or less.

  As one aspect of the present invention, during the heating and cooling of the hollow metal member, a bending moment or a shearing force is applied to the portion of the hollow metal member where the deformation resistance is greatly reduced by heating, so that it is two-dimensional or three-dimensional. It is preferable to manufacture the heat-treated hollow metal member by so-called three-dimensional hot bending quenching, in which bending or shearing into a desired bent shape is performed. This is because a heat-treated hollow metal member having an arbitrary bending shape with high strength and high rigidity can be produced by three-dimensional hot bending quenching.

In addition, when manufacturing a heat-treated hollow steel material having an arbitrary bending shape by three-dimensional hot bending quenching using a hollow steel material as a hollow metal member, the temperature rise rate of the steel material is 300 ° C./second or more and 3000 ° C./second or less. After heating to a temperature range of Ac ₃ points to 1100 ° C and holding in this temperature range for 0.2 seconds to 0.8 seconds, cooling to room temperature at a cooling rate of 300 ° C / second to 2000 ° C / second This is exemplified.

  In addition to improving the chemical conversion treatment property of the inner surface of the heat-treated hollow metal member which is the object of the present invention, it is desirable to simultaneously carry out a method for improving the post-coating corrosion resistance of the outer surface. It is preferable to carry out by the method described above.

  In order to confirm the effect of the present invention, a rectangular cross-section ERW steel pipe (40 mm × 40 mm × wall thickness 1.6 mm) having the chemical composition shown in Table 1 was prepared as a raw material.

  This material steel pipe was heat-treated under the conditions shown in Table 2 using the three-dimensional hot bending quenching apparatus disclosed in Patent Document 2 to produce a heat-treated steel pipe as a product.

  Processing was performed at a feed rate of the raw steel pipe of 80 mm / second, and the atmosphere of the heated part on the outer surface was nitrogen blowing. In Table 2, which will be described later, the flow rate of the gas inside the material steel pipe is expressed by a positive value in the direction from the front end to the rear end in the feed direction of the material steel pipe, and is expressed by a negative value in the opposite direction. In Table 2, No. No. 3 was tempered by controlling the cooling process of the three-dimensional hot bending quenching apparatus.

  The cross-sectional structure of the obtained heat-treated steel pipe was observed with four fields of view at a magnification of 500 times using a scanning electron microscope after nital etching to confirm the steel structure.

  Moreover, the film thickness of the scale was measured by X-ray photoelectron spectroscopy analysis on the inner and outer surfaces of the heat-treated steel pipe.

  Furthermore, the heat-treated steel pipe is treated with a surface conditioner PL-X manufactured by Nippon Parkerizing Co., Ltd. after degreasing, and subjected to chemical conversion treatment for 120 seconds under the standard conditions of the processing liquid using PBL3080 manufactured by Nippon Parkerizing Co., Ltd. The subsequent surface was observed with a scanning electron microscope, and the coating state of the chemical conversion film was evaluated.

  Specifically, if there are many parts called scales with no chemical conversion film attached, the corrosion resistance after coating will decrease, and 10 fields of view will be observed with a scanning electron microscope at a magnification of 500 times to form a uniform chemical conversion film. If the area ratio of the scale is 5% or less, the chemical conversion processability is evaluated as “good”, and if the area ratio of the scale is 10% or less, the chemical conversion processability is evaluated as “no problem”. Those having an area ratio exceeding 10% were evaluated as x because there was a problem in chemical conversion treatment.

  In addition, after performing the same chemical conversion treatment as described above, electrodeposition coating with a film thickness of 20 μm was performed with PN-110 manufactured by Nippon Paint to obtain a coated product, and this coated product was heated at 40 ° C. as a coating film adhesion test. A cross-cut tape peeling evaluation after immersion for 240 hours was performed, and rust and swelling of the cut portion after 180 cycles of the JASO combined cycle corrosion test were evaluated.

  In the coating film adhesion test, it was determined that there was no lattice that was largely peeled off, and small peeling at the cut intersection was 5 area% or less. In the evaluation of rust and blistering in the JASO test, it was determined that the maximum width of rust or blistering on both sides of the cut was 8 mm or less.

  The results are summarized in Table 2. In Table 2, M in the “steel structure” column represents martensite, and TM represents tempered martensite. In the evaluation results of the corrosion resistance after painting, “good” was indicated as “good”, and “bad” was indicated as “poor”.

  As shown in Table 2, it can be seen that satisfying the range defined in the present invention provides a heat-treated hollow metal member that is excellent in chemical conversion treatment on the inner surface and, in turn, excellent in corrosion resistance after coating.

Claims (4)

While the heating device and the cooling device are moved relative to the hollow steel member, the hollow steel member is locally heated by the heating device to a temperature range of Ac _{3 to} 1100 ° C. , and then cooled by the cooling device. a method of manufacturing a heat-treated hollow steel member by heat treatment, the relative feed direction of the distal end portion of the hollow steel member with respect to the heating device and the cooling device toward the rear end, of the hollow steel member A method for producing a heat-treated hollow steel member, wherein a gas containing 0.01 to 1% by volume of oxygen and an inert gas is caused to flow at a flow rate of 0.1 m / second or more. 2. The method for producing a heat-treated hollow steel member according to claim 1, wherein the gas contains 0.01 to 1% by volume of oxygen, and the remainder is a gas composed of an inert gas and inevitable impurities . The method for producing a heat-treated hollow steel member according to claim 1 or 2, wherein a flow rate of the gas is 2.0 m / sec or less. While the heating device and the cooling device are moved relative to the hollow metal member, the hollow metal member is locally heated by the heating device and then cooled and heat-treated by the cooling device to produce a heat-treated hollow metal member. A method,
Flowing gas at a flow rate of 0.1 m / second or more from the inside of the hollow metal member toward the rear end portion in the relative feeding direction of the hollow metal member with respect to the heating device and the cooling device,
Heat treatment the hollow metal member, wherein the at hollow metal member, to bending or shearing the desired bent shape in two or three dimensions giving bending moment or shear force to the locally pressurizing hot sites Manufacturing method.