JP5094325B2 - High strength composite metal material and manufacturing method thereof - Google Patents

Description

  The present invention relates to a high-strength composite metal material having a structure in which steel layers and copper-based layers are alternately stacked and integrated, and excellent in toughness in the stacking direction, and a method for manufacturing the same.

In a high-strength metal material, “strength (hardness)” and “toughness” are generally in a trade-off relationship, and it is very difficult to make them compatible at a high level. Examples of general-purpose high-strength metal materials include steel materials that have been subjected to quenching / tempering treatment or high-temperature transformation treatment to produce a transformation phase (such as a martensite phase or a bainite phase). Since these have a high strength of 300 to 750 HV, they are widely used in many high-strength applications such as mechanical structural members, tools, and blades. However, the 2 mmV notch impact value at room temperature is about 100 J / cm ² at most, and it is difficult to stably provide such a toughness with this type of steel material.

On the other hand, as a typical steel material specialized in toughness, hatfield steel (high Mn austenitic steel) can be mentioned. With this type of steel material, it is possible to obtain a steel material exhibiting extremely high toughness with a ² mmV notch impact value at room temperature of about 300 J / cm ² . However, the intensity level is only about 200HV. In addition, if this kind of material is cold-rolled, the strength can be increased to a region where the hardness exceeds 400 HV, but in this case, the 2 mmV notch impact value at room temperature decreases to a level well below 200 J / cm ^2. Resulting in.

  Various non-ferrous metal materials are known that use precipitation strengthening to increase their strength, but in general, non-ferrous metal materials such as copper alloys and aluminum alloys achieve strength levels of 500 to 750 HV. It is not easy to do. In the case of realizing a strength level of 300 to 500 HV, the cost is higher than that of a steel material having the same strength level, and it is difficult to provide excellent toughness.

JP 2004-082667 A

  An object of the present invention is to provide a metal material that uses a general-purpose material to achieve both “high strength” and “high toughness” in a certain direction at a high level that has been considered difficult until now.

The above-mentioned object is a composite metal material in which a steel layer having a thickness of 0.05 to 2 mm and a copper-based layer having a thickness of 0.001 to 0.2 mm are alternately stacked and joined to each other, Steel and copper-based layers in which the transformation phase that has undergone quenching / tempering treatment or isothermal transformation treatment accounts for 50% by volume or more is composed of copper or copper alloy that has been melted and cooled, and has an equivalent hardness defined by the following formula (1) This is achieved by a high- strength composite metal material having H of 300 HV or higher.
H = (Σ [Ts × Hs] + Σ [Tc × Hc]) / (ΣTs + ΣTc) (1)
here,
Σ [Ts × Hs]; the sum of the product of thickness Ts (mm) and hardness Hs (HV) of each steel layer for all steel layers Σ [Tc × Hc]; thickness Tc of each copper-based layer ( mm) and the product of hardness Hc (HV) for all copper layers ΣTs; Total steel layer thickness (mm)
ΣTc: Total copper layer thickness (mm)

  In the present specification, in the composite metal material (laminated body), the thickness direction of each layer is referred to as “lamination direction”. The number of steel layers is preferably 5 or more, for example. Each steel layer may be composed of the same steel type or a mixture of different steel types. The thickness of each steel layer may be the same or different. Each copper-based layer may also be composed of the same material or different materials. Moreover, the thickness of each copper-type layer may be the same, and may differ.

  The thickness Ts (mm) of each steel layer and the thickness Tc (mm) of each copper-based layer can be determined by performing microscopic observation on a cross section parallel to the lamination direction of the composite metal material. The hardness Hs (HV) of each steel layer and the hardness Hc (HV) of each copper-based layer can be generally determined by performing hardness measurement using a micro Vickers hardness meter on the cross section. However, in the case where measurement is not possible because of the thinness, a measurement value using a sample that has been subjected to a process for imparting the same thermal history to a material having the same composition may be substituted. If the copper-based layer is made of copper derived from electroplating and is difficult to measure because of its thin cross-sectional hardness, a value of Hc = 85 HV may be used.

Further, in the present invention, a composite metal material in which a steel layer having a thickness of 0.05 to 2 mm and a copper-based layer having a thickness of 0.001 to 0.2 mm are alternately laminated and bonded to each other, Is steel in which the transformation phase that has undergone quenching / tempering treatment or isothermal transformation treatment occupies 50 volume% or more, the copper-based layer is made of copper or a copper alloy, and the equivalent hardness H defined by the above formula (1) is 300 HV or more The thickness (ΣTs + ΣTc) in the stacking direction is 10 mm or more, and the 2 mmV notch impact value I (J) at normal temperature (20 ° C.) evaluated by an impact test piece in which the depth direction of the V notch coincides with the stacking direction. / Cm ² ) and the equivalent hardness H (HV) is provided as a high-strength composite metal material having a product I × H of 75,000 or more.

Moreover, as a manufacturing method of said composite metal material, in this invention, the copper which used as the plating original plate the steel plate with a thickness of 0.05-2 mm which has a chemical composition which becomes 350 or more hardness by hardening / tempering process or a constant temperature transformation process. A thickness of 0.001 to 0.00 is obtained by laminating a plated steel sheet in a plurality of layers, maintaining a temperature not lower than the melting point of copper and not higher than 1200 ° C. while applying a load in the laminating direction, and cooling after the copper is melted. A step of obtaining a laminate in which a steel layer is bonded via a copper layer of 2 mm,
A step of subjecting the laminate to a heat treatment of a heat pattern corresponding to the quenching / tempering treatment or isothermal transformation treatment under a condition that the hardness of the steel layer is 350 HV or higher;
A method for producing a high-strength composite metal material having excellent toughness in the stacking direction is provided.

  According to the present invention, a composite metal material that achieves both “high strength” and “high toughness” in a certain direction at a high level using a relatively inexpensive general-purpose material has been realized. Its toughness is dramatically improved so that it cannot be considered from the original material constituting the composite metal material.

  It is considered that the composite metal material of the present invention can contribute to the thinning of the member, the simplification of the structure, the performance improvement, and the like in various uses where it is desired to apply a metal material having high strength and high toughness. Such applications include, for example, impact absorbing members for automobiles and transportation equipment, seismic isolation members, bulletproof members, and the like, and various application developments are expected. Moreover, since it can also manufacture using a commercially available copper plating steel plate, raw material cost is restrained low and manufacture is also comparatively easy.

  FIG. 1 schematically shows a cross-sectional structure of the composite metal material of the present invention. Steel layers and copper-based layers are laminated alternately. Adjacent layers are tightly joined. Its bonding strength is comparable to brazing. The copper-based layer is a copper or copper alloy layer. When the copper-based layer is copper, it is sometimes called a “copper layer”. As for the number of laminated layers, the number of steel layers is required to be at least 2 or more, but 5 or more is a suitable target, and more preferably 10 or more. In FIG. 1, for convenience, the number of steel layers is three. As the end in the stacking direction, either a steel layer or a copper-based layer is selected according to the application. One end may be a steel layer and the other end may be a copper-based layer. When the number of steel layers is i, the number of copper layers is i-1, i, i + 1 (where i is an integer of 2 or more).

  The composite metal material of the present invention is greatly characterized by extremely high toughness in the stacking direction. FIG. 2 schematically shows the sampling direction of the V-notch impact test piece. When the impact direction applied by the hammer in the impact test is the stacking direction (FIG. 2 (a)) is called flat-wise, and when it is perpendicular (FIG. 2 (b)), it is edgewise. (Edge-wise). The toughness in the stacking direction is evaluated by a flat-wise impact test.

FIG. 3 illustrates an appearance (photograph substituted for drawing) of a 2 mm V notch impact test piece cut out from the composite metal material of the present invention after being subjected to a flat-wise impact test. This corresponds to Example No. 3 of the present invention described later. In this example, each steel layer is composed of the same steel type S55C, and the copper-based layer is copper. The total thickness ratio ΣTs / ΣTc of both layers is about 25, and the majority is occupied by the steel layer. In the case of a normal S55C steel material (bulk material), the heat treatment conditions (quenching / tempering) when this composite metal material is produced have a hardness of about 450 HV and a ² mmV notch impact value of about 15 J / cm ² . However, this composite metal material maintains an equivalent hardness of about 426 HV, and the ² mmV notch impact value in the stacking direction shows an extremely high value of 229 J / cm ² . When an austempering treatment is applied to a laminate having the same structure as this, a composite metal material exhibiting an amazing toughness with an equivalent hardness of 470 HV and a ² mmV notch impact value of 337 J / cm ^{2 in} the lamination direction can be obtained. (Invention example No. 1 in Examples described later).

  Thus, in the composite metal material of the present invention, the toughness in the stacking direction is remarkably improved so as not to be considered from the toughness of each material constituting the steel layer and the copper-based layer. Although the mechanism has not been fully elucidated at the present time, the observation of the impact specimen after the test shows that cracks generated in the steel layer with low toughness are difficult to propagate to the adjacent steel layer due to the presence of the copper-based layer. It is inferred that This is also affirmed because the impact value by the edgewise test piece is the same value as that of the bulk steel material and no improvement in toughness like flatwise is observed. Even when the same steel type is used for the steel layer, if appropriate tempering is not performed after quenching (that is, it cannot be said that the steel layer has undergone quenching / tempering treatment), even if flatwise, as described above No significant improvement in toughness is observed.

  The thickness of the steel layer may be in the range of about 0.05 to 2 mm, and the thickness of the copper-based layer may be in the range of about 0.001 to 0.2 mm. However, it is preferable that the total thickness ratio ΣTs / ΣTc of both layers is 4 or more in order to sufficiently exhibit the high strength of the steel layer. On the other hand, in order to significantly improve the toughness in the stacking direction, it is effective to set ΣTs / ΣTc to 50 or less, and more preferably 30 or less. Further, in order to homogenize the characteristics, after each steel layer and each copper-based layer are made of the same material, the thickness Ts of each steel layer and each copper-based layer thickness Tc are respectively The average value of Ts and the average value of Tc are desirably in the range of ± 50%, and more preferably in the range of ± 30%. When a laminated body is formed using a copper-plated steel sheet as will be described later, the thickness of each steel layer can be adjusted to, for example, 0.1 to 1 mm, and the thickness of each copper layer can be adjusted to a range of, for example, about 5 to 50 μm. Efficient.

The composite metal material of the present invention employs high strength steel for the steel layer. As a result, a material having both high strength and high toughness in the stacking direction can be obtained. As the high-strength steel, a steel type that is strengthened by quenching / tempering treatment or isothermal transformation treatment is adopted. This type can generate a “transformation phase” by applying a predetermined quenching / tempering treatment or isothermal transformation treatment after a high-temperature heat treatment when joining with a copper-based layer, thereby increasing the Strengthened. The “transformation phase” is a phase generated at a temperature lower than the A ₁ transformation point by subjecting the steel material to quenching / tempering treatment or isothermal transformation treatment. The transformation phase obtained by quenching / tempering treatment is typically a martensite phase (including those refined by tempering). Examples of the isothermal transformation treatment include austemper, and the transformation phase obtained thereby is typically a bainite phase. Depending on the treatment, different types of transformation phases may coexist. Normally, carbides are present in the remainder of the transformation phase, but other residual austenite phase, pro-eutectoid ferrite phase and the like may also exist. It is advantageous for increasing the strength that the transformation phase is present in an amount of 50% by volume or more. In order to stably realize an equivalent hardness of 300 HV or higher (described later), it is preferable to use a material having a chemical composition that has a hardness of 350 HV or higher by quenching / tempering treatment or isothermal transformation treatment.

  As a specific steel type constituting the steel layer, S10C, S35C, S55C, SCM435, SUP6, SK85, SK100, SK120, SUJ2, SUS420J2 and the like can be cited as examples. When a plurality of steel types are mixed and used in one laminate, steel types that can adopt the same heat treatment are combined.

Specific examples of the chemical composition include the following.
[1] By mass%, C: 0.1 to 1.5%, Mn: 0.2 to 2%, P: 0.03% or less, S: 0.03% or less, balance Fe and inevitable impurities [ 2] In the above [1], further containing Si: 2.5% or less [3] In the above [1] or [2], Cr: 2% or less, Ni: 2% or less, Mo: 2% or less , Ti: 0.5% or less, Nb: 0.5% or less, V: 0.5% or less, B: 0.02% or less

  The copper-based layer is made of copper or a copper alloy. The copper alloy here has a copper content of 50% by mass or more. In the case of a copper alloy (for example, Cu—Ni series) whose melting point rises by addition of an alloy element, a composition range having a melting point of approximately 1150 ° C. or less is employed. Since the copper-based layer is subjected to quenching / tempering treatment or isothermal transformation treatment together with the steel layer after forming the laminated body, when it is composed of a copper alloy, a brittle phase is present when subjected to such a thermal history. An alloy system that does not form is desirable. Suitable examples include copper having a purity of 90% or more, and copper derived from electrolytic copper plating corresponds to this.

  The composite metal material of the present invention is a material having an equivalent hardness H defined by the above formula (1) of 300 HV or more. If the equivalent hardness is lower than this, the strength may be insufficient as compared with the above steel types. The equivalent hardness H is more preferably 350 HV or more, and the equivalent hardness H is more preferably 400 HV or more. The equivalent hardness H can be controlled mainly by the total thickness ratio ΣTs / ΣTc of the steel layer and the copper-based layer and the hardness Hs (HV) of the material constituting the steel layer. As long as the steel material having a metallographic structure defined in the present invention is used for the steel layer, the hardness Hs of the steel layer and the hardness Hc of the copper-based layer are in a relationship of Hs> Hc. By increasing the total thickness ratio ΣTs / ΣTc of the steel layer and the copper-based layer, the corresponding hardness increases.

The thickness (ΣTs + ΣTc) of the composite metal material of the present invention can enjoy high toughness in the stacking direction even if it is as thin as about 1 mm, but if (ΣTs + ΣTc) is about 10 mm or more, it is flat. Using the 2 mm V notch impact test piece of Wise, the V notch impact value in the stacking direction can be measured directly. A product having a product I × H of ² mmV notch impact value I (J / cm ² ) at normal temperature (20 ° C.) and the equivalent hardness H (HV) of 75,000 or more is particularly suitable in the present invention. It is extremely difficult to realize a material in which I × H shows such a high value in a bulk material made of a single steel type.

  The composite metal material of the present invention is characterized in that adjacent steel layers and copper-based layers are tightly joined. As a method for obtaining such a joint structure, it is extremely effective to use copper or a copper alloy constituting each copper-based layer as a brazing material. There is a method in which a thin copper or copper alloy sheet is sandwiched between steel materials as the brazing material and heated to the melting point or higher of the brazing material. However, as a more efficient technique, the present invention provides a method using a copper-plated steel sheet.

  In this case, a steel plate having a thickness of 0.05 to 2 mm made of a steel type that is strengthened by quenching / tempering treatment or isothermal transformation treatment as described above is used, and a copper-plated steel plate obtained by applying electrolytic copper plating to the steel plate. Prepare. Usually, the copper electroplating is applied to both sides of the steel sheet, but the weight per unit area of the copper plating is sufficient to form a copper layer having a thickness of 0.001 to 0.2 mm by using the copper plating layer as a brazing material. To do. The electrolytic copper-plated steel sheet is laminated in a plurality of layers, maintained at a temperature not lower than the melting point of copper and not higher than 1200 ° C. while applying a certain amount of load in the stacking direction, to melt the copper in the plated layer, and then cooled. Since the melting point of copper is 1083 ° C. in the case of pure copper, the copper (brazing material) of each layer can be melted in a short time by charging in a furnace set at a furnace temperature of about 1150 ° C. it can. Heating to a temperature exceeding 1200 ° C. is not preferable because economical efficiency is impaired and contamination in the furnace due to evaporation of copper increases. The thickness Tc of the copper layer can also be controlled by the load in the stacking direction applied during the heating. That is, as the load is increased, the amount of copper (brazing material) removed in a molten state from between the steel plates increases, and the thickness of the copper layer becomes thinner. However, if the amount of copper to be excluded is excessive, it is not preferable because the copper yield deteriorates.

  The laminated body thus obtained is subjected to a heat treatment for strengthening the steel of the steel layer, that is, a heat treatment corresponding to a quenching / tempering treatment or a constant temperature transformation treatment according to the steel type, in the laminating direction. A composite metal material of the present invention having significantly improved toughness can be obtained.

An electrolytic copper-plated steel sheet having a thickness of 0.27 mm was prepared using steel (S55C) having the following chemical composition as a plating base sheet. This steel sheet is obtained by applying matte Cu plating to a surface of a 0.25 mm-thick plating original plate with a thickness of 0.01 mm per side.
[Steel composition]
By mass%, C: 0.55%, Si: 0.20%, Mn: 0.80%, P: 0.012%, S: 0.008%, Cr: 0.13%, remaining Fe and inevitable Impurities

A cut plate of 100 × 50 mm was taken from the copper-plated steel plate, and 100 cut plates were stacked and set in a high-temperature vacuum furnace. FIG. 4 schematically shows how to set. 100 cut plates were stacked on the surface plate. At that time, non-slip steel blocks were arranged in all directions. A weight was placed on top of the stacked cut plates so that the average surface pressure between the plated steel plates (surface pressure acting between the 50th sheet and the 51st sheet from the top) was about 40 gf / cm ² . After setting in this state and evacuation, an Ar atmosphere was set, and then brazing heat treatment was performed under the following conditions.
[Brazing heat treatment]
Temperature rise from room temperature to 1000 ° C in about 3 hours → 1000 ° C × 10 minutes hold → Temperature rise to 1150 ° C → 1150 ° C × 10 minutes hold → Cool to room temperature in the furnace

From the laminate obtained by brazing heat treatment, 2 mmV notch impact test pieces of flat width and edge width were prepared. In Flatwise, the number of layers (number of steel layers) in the test piece was set to 40. About this test piece, it heat-processed on the following two types of conditions.
[Heat treatment A]
Austemper treatment (steel layer 500 HV target); 810 ° C. × 20 minutes hold → 300 ° C. × 30 minutes hold → air cooling [heat treatment B]
Quenching and tempering treatment (steel layer 450HV target); 850 ° C x 20 minutes hold → oil cooling (60 ° C) → 400 ° C x 60 minutes hold → air cooling

  About the test piece after heat processing, the cross-sectional hardness of the steel layer and the copper layer was measured with the micro Vickers hardness meter. Moreover, the average thickness of the copper layer was measured (the average thickness of the steel layer was 0.25 mm constant). The equivalent hardness was obtained by substituting these measured values into the equation (1).

  Further, a Charpy impact test at 20 ° C. was performed on the 2 mm V notch impact test piece after the heat treatment by a method based on JIS Z2242.

The results are shown in Table 1. Table 1 also shows a 2 mmV notch impact value when the S55C bulk material having the same composition as described above is subjected to a quenching and tempering treatment for 500 HV. FIG. 5 shows the relationship between the equivalent hardness and the 2 mmV notch impact value. FIG. 5 also shows data of a steel grade hatfield steel (high Mn austenitic steel) bulk material showing the toughness at the top level of the steel material.
For reference, FIG. 6 shows a cross-sectional metal structure photograph of the laminate after the brazing heat treatment and after quenching and tempering (heat treatment B). (B) in FIG. 6 corresponds to No. 3 in Table 1, which is a composite metal material of the present invention.

  The composite metal material of the present invention has extremely high toughness (impact value) in the stacking direction as compared with the bulk material of S55C constituting the steel layer. In particular, the material subjected to the heat treatment A austempering treatment exhibits toughness in the stacking direction that exceeds the steel type IRS2 water tough material while having an equivalent hardness of 470 HV. The edgewise impact test showed toughness equivalent to that of the bulk material.

The figure which showed typically the cross-section of the composite metal material of this invention. The figure which showed typically the extraction direction of the V notch impact test piece. The drawing substitute photograph which illustrated the external appearance after using for the flatwise impact test about the 2mmV notch impact test piece cut out from the composite metal material of this invention. The figure which showed typically how to set the sample in brazing heat processing. The graph which showed the relationship between equivalent hardness and a 2 mmV notch impact value. The metal structure photograph of the cross section of the laminate after brazing heat treatment and after quenching and tempering (heat treatment B).

Claims (4)

A composite metal material in which a steel layer having a thickness of 0.05 to 2 mm and a copper-based layer having a thickness of 0.001 to 0.2 mm are alternately laminated and joined to each other, and the steel layer is quenched and tempered. Alternatively, a steel or copper-based layer in which the transformation phase that has undergone the isothermal transformation treatment accounts for 50% by volume or more is composed of copper or a copper alloy that is cooled after being melted, and an equivalent hardness H defined by the following formula (1) is 300 HV or more. High strength composite metal material.
H = (Σ [Ts × Hs] + Σ [Tc × Hc]) / (ΣTs + ΣTc) (1)
here,
Σ [Ts × Hs]; the sum of the product of thickness Ts (mm) and hardness Hs (HV) of each steel layer for all steel layers Σ [Tc × Hc]; thickness Tc of each copper-based layer ( mm) and the product of hardness Hc (HV) for all copper layers ΣTs; Total steel layer thickness (mm)
ΣTc: Total copper layer thickness (mm) A composite metal material in which a steel layer having a thickness of 0.05 to 2 mm and a copper-based layer having a thickness of 0.001 to 0.2 mm are alternately laminated and joined to each other, and the steel layer is quenched and tempered. Or the steel in which the transformation phase which passed through the isothermal transformation process occupies 50 volume% or more, a copper-type layer is comprised with copper or a copper alloy, the equivalent hardness H defined by the following (1) formula is 300HV or more, and a lamination direction Thickness (ΣTs + ΣTc) is 10 mm or more, and a 2 mm V notch impact value I (J / cm ² ) at room temperature and an equivalent hardness H (HV) by an impact test piece in which the depth direction of the V notch coincides with the stacking direction. ) Product I × H is 75000 or more .
H = (Σ [Ts × Hs] + Σ [Tc × Hc]) / (ΣTs + ΣTc) (1)
here,
Σ [Ts × Hs]; the sum of the product of thickness Ts (mm) and hardness Hs (HV) of each steel layer for all steel layers Σ [Tc × Hc]; thickness Tc of each copper-based layer ( mm) and the product of hardness Hc (HV) for all copper layers ΣTs; Total steel layer thickness (mm)
ΣTc: Total copper layer thickness (mm) The high-strength composite metal material according to claim 1 or 2, wherein the number of steel layers is 5 or more. A copper-plated steel sheet having a thickness of 0.05 to 2 mm and having a chemical composition with a hardness of 350 HV or higher by quenching / tempering treatment or isothermal transformation treatment is laminated in multiple layers, and a load is applied in the lamination direction. While being applied, the temperature is maintained at a temperature not lower than the melting point of copper and not higher than 1200 ° C., and after cooling, the copper is melted to obtain a laminate in which the steel layers are joined via the copper layer having a thickness of 0.001 to 0.2 mm. Process,
A step of subjecting the laminate to a heat treatment of a heat pattern corresponding to the quenching / tempering treatment or isothermal transformation treatment under a condition that the hardness of the steel layer is 350 HV or higher;
High intensity method of producing a composite metal material that have a.