JP2020526666A - Preservation of mechanical properties in steel alloys after machining and in the presence of stress concentration sites - Google Patents

Abstract

The present invention relates to the retention of mechanical properties in high-strength steel at reduced thicknesses, and mechanical property performance is also retained at relatively high strain rates. These new steels may offer advantages for a number of applications where reduced sheet thickness is desired. In addition, the alloys herein retain useful mechanical properties after the introduction of geometric discontinuities and associated stress concentrations.

Description

Field of Invention The present disclosure relates to the retention of mechanical properties in high-strength steels at reduced thicknesses, and mechanical property performance is also retained at relatively high strain rates. These new steels may offer advantages for a number of applications where reduced sheet thickness is desired. In addition, the alloys herein retain useful mechanical properties after the introduction of geometric discontinuities and associated stress concentrations.

Steel is an engineering material of choice where cost, strength and ductility are key factors. Therefore, steel continues to be used in a number of applications in our daily lives, including building construction, appliances and automobiles. Various types of steel alloys exist to achieve this range of needs and have a range of targeted properties used for these wide range of applications. Names that fit three different classes based on measurement characteristics, especially maximum tensile strain and tensile stress before fracture, are provided for the range of steels. These three classes are: Low Strength Steel (LSS), High Strength Steel (HSS) and High Performance High Strength Steel (AHSS). High Performance High Strength Steels (AHSS) Steels are primarily of interest for advanced engineering applications and are classified by tensile strength greater than 700 MPa, Martensite Steel (MS), Two Phase (DP) Steels, Transformation Induced Plasticity (TRIP) ) Includes types such as steel and composite phase (CP) steel. As the strength level increases, the tendency for maximum tensile elongation (ductility) of steel becomes negative and the elongation at high tensile strength decreases. For example, the tensile elongation of LSS, HSS and AHSS ranges from 25% to 55%, 10% to 45%, and 4% to 30%, respectively.

The area where steel offers a particular engineering advantage is in automobiles, where many different types of steel are utilized throughout the vehicle in different locations. Current consumer demands and government regulations force automakers to design vehicles that achieve even higher fuel efficiency. Automotive designers have confirmed that weight loss, especially in white body construction, has the greatest potential for improving fuel efficiency. The process of reducing vehicle weight, known as weight reduction, is achieved through reducing the thickness of the white body structure and increasing the geometric complexity of various parts using high-strength, high formability materials. Can be done. Therefore, increasingly high-strength steels are desired throughout automobile assembly to allow for thickness reduction and weight reduction.

Safety must be maintained or improved as well during the weight reduction process. Speed limits on motorways are increasing on a regular basis, and consumers expect safety performance to be a large part of automotive design. The white body structure of an automobile is designed to provide a rigid structure that will protect passengers in the event of a collision while moving at high speed. During a vehicle collision, dynamic loads, rapid deformation and energy dissipation occur throughout the vehicle and especially the white body structure. The time frame in which this occurs can be 100 ms. High strain rates are observed throughout the white body structure during this time, and the material needs to be able to withstand complex loads over the strain rate range. For example, a low speed collision that occurs in a parking lot will result in a lower strain rate for the white body than a collision on a highway. The mechanical properties of the material with respect to the white body structure have been measured over this range of strain rates by a number of means, including uniaxial tensile testing, their response during collisions can be predicted and design considerations are considered. Will be done. High strain rates can result in changes in mechanical properties and are the maximum weight that auto designers can achieve by requiring additional thickness to maintain safety under high strain rate conditions. Limit the conversion.

As advances in engineering and technology occur, there is an increasing motivation for smaller scales. With consumers, and expansion, engineers / designers are regularly looking for size-efficient products. Consumers look for products that accomplish the required task while occupying the smallest possible volume. A good example of this phenomenon can be found in the electronics industry, where mobile phones, tablets and other devices are regularly reduced in size due to continuous design iterations. The tendency of products to smaller sizes dramatically increases the demands on the engineering materials from which the products are made. As the overall size of a part decreases, defects inherent in routine manufacturing processes can result in a significant reduction in material properties. High-strength materials are particularly affected by the reduction in part size to small or very small due to the complex and often special processing required to achieve their properties.

Martensitic steels, for example, provide excellent strength but require quenching as a final machining step to produce the required microstructure. Quenching is difficult to control on a small scale and can potentially cause unacceptable strain in small parts. The final machining may be performed on the sheet or foil rather than on the shape of the final part, but rather on some applications. For thermally sensitive materials such as martensitic steel, heat exposure during cutting to manufacture the final part can adversely change the microstructure and impair its properties. The shape effect also plays a greater role in the mechanical properties of ductile materials on a small scale, and the effects of stress concentrators, particle size and thickness adversely change the material's mechanical response to stress. Due to these facts, expensive engineering materials are often needed for use on small scales that are either thermally insensitive or have either low alloying or simple processing such as pure materials. Will be done. Engineers will prefer not to use eccentric materials for these applications; however, routine engineering materials are often not available for use in reduced thickness and are due to exorbitant costs and processing requirements. And results in slow adoption of smaller devices.

In one embodiment, the present invention supplies a metal alloy containing at least 70 atomic% iron and at least 4 or more elements selected from Si, Mn, Cr, Ni, Cu or C to provide the alloy. A method for preserving mechanical properties in metal sheet alloys at reduced thicknesses, including the steps of melting, cooling at a rate of <250 K / s, and solidifying to thicknesses from 25.0 mm to 500 mm. Be directed. This is the step of processing the alloy into a sheet having a thickness of T ₁ , where the sheet has a total elongation of X ₁ (%), a maximum tensile strength of Y ₁ (MPa), and Z ₁ (MPa). The steps are followed, with a yield strength of. This is then the step of further machining the alloy into a second sheet with a reduction in thickness T ₂ <T ₁ , where the second sheet has a total elongation of X ₂ = X ₁ ± 10%, Y ₂ The step continues, with a maximum tensile strength of = Y ₁ ± 50 MPa and a yield strength of Z ₂ = Z ₁ ± 100 MPa.

In one other embodiment, the invention supplies a metal alloy containing at least 70 atomic% iron and at least 4 or more elements selected from Si, Mn, Cr, Ni, Cu or C. To retain the mechanical properties of the metal sheet alloy at relatively high strain rates, including the steps of melting the alloy, cooling at a rate of <250 K / s, and solidifying to a thickness from 25.0 mm to 500 mm. Regarding the method. This is then the step of processing the alloy into a sheet shape with a thickness of 1.2 mm to 10.0 mm, which is the total elongation of X ₁ (%) when the sheet is tested at a strain rate S _1. , With a maximum tensile strength of Y ₁ (MPa) and a yield strength of Z ₁ (MPa), followed by a step. This is a step of deforming a sheet from an alloy at a strain rate S ₂ > S ₁ , and the sheet has a total elongation of X ₃ = X ₁ ± 7%, a maximum tensile strength Y ₃ = Y ₁ ± 200 MPa, And the yield strength Z ₃ = Z ₁ ± 50 MPa, the step continues.

In yet another embodiment, the invention supplies a metal alloy containing at least 70 atomic% iron and at least 4 or more elements selected from Si, Mn, Cr, Ni, Cu or C. , A method for preserving the mechanical properties of a metal sheet alloy, comprising the steps of melting the alloy, cooling at a rate of <250 K / s, and solidifying to a thickness from 25.0 mm to 500 mm. .. This is then a step of processing the alloy into a sheet having a thickness of 1.2 mm to 10.0 mm, wherein the sheet has a total elongation of X ₁ (%) and a maximum tensile strength of Y ₁ (MPa). , And with a yield strength of Z ₁ (MPa), the step continues. The stress concentration site can then be introduced and then the sheet from the alloy can be deformed so that the sheet has a total elongation of X ₄ ≥ 0.2 X ₁ (%) and a maximum tensile strength Y ₄ ≥ 0.5 Y ₁ (MPa). ), And the yield strength Z ₄ ≧ 0.6 Z ₁ (MPa).

The following detailed description may be better understood with reference to the accompanying drawings provided for illustrative purposes and should not be considered as limiting any aspect of the invention.

Summary of new ductility achievements in alloys herein on a reduced length scale Summary of novel ductility achievements in alloys herein at high strain rates Summary of maintained ductility in alloys herein with introduced stress concentration sites, such as edge notches. Yield strength and maximum tensile strength as a function of alloy 2 sheet thickness Alloy 2 Tensile elongation as a function of sheet thickness Comparison of stress-strain curves for two sheets of alloy with different thicknesses Effect of sheet thickness on tensile elongation of samples from various alloys Effect of sheet thickness on yield strength in samples from various alloys Effect of sheet thickness on maximum tensile strength in samples from various alloys SEM images of microstructure at the center of alloy 1 sheet samples of varying thickness: a) 0.7 mm thick cold rolled sheet, b) 0.7 mm thick cold rolled and annealed. Sheets, c) 0.5 mm thick cold-rolled sheets, and d) 0.5 mm thick cold-rolled and annealed sheets. SEM images of microstructure at the center of alloy 2-sheet samples of varying thickness: a) 1.0 mm thick cold-rolled sheet, b) 1.0 mm thick cold-rolled and annealed. Sheets, c) 0.5 mm thick cold-rolled sheets, d) 0.5 mm thick cold-rolled and annealed sheets, e) 0.2 mm thick cold-rolled sheets , And f) 0.2 mm thick cold-rolled and annealed sheet SEM images of microstructure at the center of alloy 27 sheet samples of varying thickness: a) 0.8 mm thick cold rolled sheet, b) 0.8 mm thick cold rolled and annealed. Sheets, c) 0.5 mm thick cold-rolled sheets, d) 0.5 mm thick cold-rolled and annealed sheets, e) 0.4 mm thick cold-rolled sheets , And f) 0.4 mm thick cold-rolled and annealed sheet SEM images of microstructure at the center of alloy 37 sheet samples of varying thickness: a) 1.4 mm thick cold rolled sheet, b) 1.4 mm thick cold rolled and annealed. Sheets, c) 0.5 mm thick cold-rolled sheets, d) 0.5 mm thick cold-rolled and annealed sheets, e) 0.3 mm thick cold-rolled sheets , And f) 0.3 mm thick cold-rolled and annealed sheet Schematic of ASTM D 638 Type V Tensile Sample Shape; all dimensions are in millimeters Schematic diagram of a direct tension split-Hopkinson rod (SHB) device Effect of strain rate on tensile elongation at fracture on alloy 2 sheets Bright ^- field TEM micrograph of microstructure in the gauge section of a sample from an alloy 2 sheet tested at a strain rate of 1200s ^-1 ; a) low magnification image, b) high magnification image Bright ^- field TEM micrograph of microstructure in the gauge section of a sample from an alloy 2 sheet tested at a strain rate of 500s ^-1 ; a) low magnification image, b) high magnification image Bright ^- field TEM micrograph of microstructure in the gauge section of a sample from an alloy 2 sheet tested at a strain rate of 100s ^-1 ; a) low magnification image, b) high magnification image Bright ^- field TEM micrograph of microstructure in gauge section of sample from alloy 2 sheets tested at strain rate of 10s ^-1 ; a) low magnification image, b) high magnification image Bright ^- field TEM micrograph of microstructure in the gauge section of a sample from an alloy 2 sheet tested at a strain rate of 0.7s ^-1 ; a) low magnification image, b) high magnification image Bright ^- field TEM micrograph of microstructure in the gauge section of a sample from an alloy 2 sheet tested at a strain rate of 0.0007s ^-1 ; a) low magnification image, b) high magnification image Ferrite scope measurements in the gauge section of samples from alloy 2 sheets tested at different strain rates Schematic of a notched tensile sample Notch diameter with a constant depth of 0.5 mm effect on a) tensile elongation of the sheet from alloy 2 and b) maximum tensile strength Semicircular notch diameter effect on a) tensile elongation and b) maximum tensile strength of the sheet from alloy 2 SEM image of the fracture surface in sample 1 from alloy 2 having a notch with a diameter of 1 mm, a) at the center of the fractured section, b) near the edge of the fractured section. SEM image of the fracture surface in sample 2 from alloy 2 having a notch with a diameter of 6 mm, a) at the center of the fractured section, b) near the edge of the fractured section

Preservation of mechanical properties in alloys herein at reduced thickness and relatively high strain rates is shown in FIGS. 1 and 2. FIG. 1 shows a summary of the retention of mechanical properties of alloys herein when the thickness is reduced. In step 1 of FIG. 1, the starting condition is to supply a metal alloy. The metal alloy will preferably contain at least 70 atomic% iron and at least 4 or more elements selected from Si, Mn, Cr, Ni, Cu or C. The alloy chemistry is melted, cooled at a rate of <250 K / s, and solidified to a thickness of 25.0 mm to 500 mm or less. The casting process can be performed in a variety of processes including ingot casting, bloom casting, continuous casting, thin slab casting, thick slab casting, thin strip casting, belt casting and the like. A preferred method would be continuous casting in sheet formation by thin slab casting, thick slab casting, and thin strip casting. Preferred alloys indicate a percentage of austenite (γ-Fe) from at least 10% by volume to 100% by volume and all increments in between. The alloy is then in the range of 1.2 mm to 10.0 mm, therefore 1.2 mm, 1.3 mm, 1.4 mm 1.5 mm. 1.6mm, 1.7mm, 1.8mm, 1.9mm, 2.0mm, 2.1mm, 2.2mm, 2.3mm, 2.4mm, 2.5mm, 2.6mm, 2.7mm, 2. 8mm, 2.9mm, 3.0mm, 3.1mm, 3.2mm, 3.3mm, 3.4mm, 3.5mm, 3.6mm, 3.7mm, 3.8mm, 3.9mm, 4.0mm, 4.1 mm, 4.2 mm, 4.3 mm, 4.4 mm, 4.5 mm, 4.6 mm, 4.7 mm, 4.8 mm, 4.9 mm and 5.0 mm, 5.1 mm, 5.2 mm, 5. 3 mm. 5.4 mm. 5.5 mm, 5.6 mm, 5.7 mm, 5.8 mm, 5.9 mm, 6.0 mm, 6.1 mm, 6.2 mm, 6.3 mm, 6.4 mm, 6.5 mm, 6.6 mm, 6. 7mm, 6.8mm, 6.9mm, 7.0mm, 7.1mm, 7.2mm, 7.3mm, 7.4mm, 7.5mm, 7.6mm, 7.7mm, 7.8mm, 7.9mm, 8.0 mm, 8.1 mm, 8.2 mm, 8.3 mm, 8.4 mm, 8.5 mm, 8.6 mm, 8.7 mm, 8.8 mm, 8.9 mm, 9.0 mm, 9.1 mm, 9.1 mm. Processed into a sheet with a thickness T ₁ including thicknesses of 2 mm, 9.3 mm, 9.4 mm, 9.5 mm, 9.6 mm, 9.7 mm, 9.8 mm, 9.9 mm and 10.0 mm. ..

The steps for producing this sheet from a cast product to a thickness T ₁ can vary depending on the unique manufacturing route and the unique targeted goals. As an example, consider thick slab casting as one process route to reach this target thickness sheet. The alloy will typically be cast through a water-cooled mold in the thickness range of 150-300 mm. The cast ingot after cooling will then preferably be prepared for hot rolling, which may include some surface treatment to remove surface defects including oxides. The ingot will then pass through a rough rolling mill hot roller, which may include several passes that typically result in a transfer bar slab with a thickness of 15 to 100 mm. The transfer bar will then pass through a continuous / tandem hot rolled finish stand for producing hotband coils with a thickness T ₁ in the range referenced above from 1.2 mm to 10.0 mm.

Another example would preferably be to process the cast material through a thin slab casting process. In this case, after the casting typically forms a thickness of 35 to 150 mm by passing through a water-cooled mold, the newly formed slab brings the slab directly to the target temperature. Go directly to hot rolling without cooling by auxiliary tunnel furnace or induction heating applied to. The slabs are then hot rolled directly in a multi-stand finish rolling mill, preferably 1 to 7. After hot rolling, the strips are rolled into hot band coils with a thickness of 1.2 mm to 10.0 mm and a thickness T ₁ in the range referenced above. Bloom casting would be similar to the example above, but higher thicknesses could typically be cast to a thickness of 200-500 mm and the initial breaker step would need to reduce the initial casting thickness, which Note that it will allow it to pass through hot rolling rough rolling mills. Strip casting would be similar, but may be cast directly after casting to a lower thickness of T ₁ , preferably with a thickness of 1.2 mm to 10.0 mm, by only one hot rolling stand. ..

Thus, the unique process of proceeding from the slab material in step ₁ to a preferred thickness T ₁ of 1.2 mm to 10 mm and then in step 2 to a preferred thickness in the range 0.2 mm to less than 1.2 mm. May include hot rolling, cold rolling, and / or cold rolling followed by annealing. Therefore, in step 2, the alloy thickness is preferably 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm. 0.6 mm. 0.7 mm. 0.8 mm. It can be up to 0.9 mm, 1.0 mm, 1.1 mm, 1.2 mm but may not include 1.2 mm. Hot rolling is generally used to provide preferred thicknesses from 1.2 mm to 10.0 mm and is typically performed in rough rolling mills, finish rolling mills, and / or stickel rolling mills. .. Cold rolling is preferably performed in step 1 and / or step 2, and is generally performed using a tandem rolling mill, a z-rolling mill, and / or a reverse rolling mill. The cold-rolled material according to the characteristic target can be annealed to recover ductility loss from the cold-rolling process either partially or by recovering ductility. Typically, as cold rolling progresses and a higher amount of gauge reduction occurs, ductility will decrease and cold rolling will continue until or just before cracks are observed. Restoration of tensile ductility of cold-rolled sheets is generally caused by heat treatment above 700 ° C. Once a sheet with the thickness T ₁ specified in step 2 is formed, then the sheet has a total elongation of X ₁ (%), a maximum tensile strength of Y ₁ (MPa), and a Z ₁ (MPa). Will indicate yield strength. Preferred properties for alloys herein in step 2 are tensile elongations from 12 to 80%, maximum tensile strength values from 700 to 2100 MPa, and yield strengths in the range 250 to 1500 MPa.

In step 3, the alloy is preferably cold rolled and annealed to a thickness T ₂ <T _{1 in} the same manner as in step 2. In step 3, the total elongation is X ₂ = X ₁ ± 10%, Y ₂ = Y ₁ ± 50 MPa, and Z ₂ = Z ₁ ± 100 MPa, as compared with the alloy in step 1 and after step 2. Maintained at a certain level. The thickness of the alloy in step 3 is identified as T ₂ and is less than the thickness T ₁ in step 2. Preferred properties of the alloy in step 3 are as follows: X ₂ = 2 to 90%; Y ₂ = 650 MPa to 2150 MPa and Z ₂ = 150 MPa to 1600 MPa.

FIG. 2 shows a ductility retention summary of the present disclosure in alloys herein when the strain rate is relatively high, i.e. the alloy experiences a strain rate of S ₂ from> 0.007 to 1200 s- ¹ . Steps 1 and 2 are identical to those described above in connection with FIG. Once the sheet having a thickness of 10.0mm from 1.2mm are formed, then the sheet is in the range of preferably not more 0.007S ^-1 or less and from 0.007 to 0.0001 s ^-1, distortion When tested at speed S ₁ , it will show total elongation of X ₁ (%), maximum tensile strength of Y ₁ (MPa), and yield strength of Z ₁ (MPa). Preferred properties for this alloy would be a tensile elongation of 12 to 80%, a maximum tensile strength value of 700 to 2100 MPa, and a yield strength in the range of 250 to 1500 MPa. In step 3, when the sheet having a thickness of 0.2 mm to less than 1.2 mm is deformed at an engineering strain rate S ₂ > S ₁ , the alloy is X ₃ = X ₁ ± 7%, maximum tensile strength. Y ₃ = Y ₁ ± 200 MPa and yield strength Z ₃ = Z ₁ ± 50 MPa are shown. The preferred properties of the alloy in step 3 are: X ₃ = 5 to 87%; Y ₃ = 500 MPa to 2300 MPa and Z ₃ = 200 MPa to 1550 MPa.

The alloys herein are also shown to avoid brittle fracture when stress concentration sites such as notches at the sheet edge are introduced. The stress concentration sites herein are locations on alloy sheets where stress can be concentrated, including geometric discontinuities, cracks, chips, dents, etc. on the surface, such as notches, holes, cuts, etc. Not limited to. FIG. 3 shows a summary of how the introduction of stress concentration sites such as edge notches retains changes in mechanical properties in the alloys herein. Once a sheet with a thickness of 1.2 mm to 10.0 mm was formed in step 2, the sheet then had a total elongation of X ₁ (%), a maximum tensile strength of Y ₁ (MPa), and Z ₁ ( It will show the yield strength of MPa). Preferred properties for this alloy are again a tensile elongation of 12 to 80%, a maximum tensile strength value of 700 to 2100 MPa, and a yield strength in the range of 250 to 1500 MPa. In step 3, the sheet experiencing stress concentration can show the following in response to deformation: X ₄ ≥ 0.2 X ₁ (%), maximum tensile strength Y ₄ ≥ 0.5 Y ₁ (MPa), And yield strength Z ₄ ≧ 0.6 Z ₁ (MPa). The preferred properties of the alloy in step 3 are as follows: X ₄ ≥ 2.4%; Y ₄ ≥ 350 MPa and Z ₄ ≥ 150 MPa.

Alloys The chemical compositions of alloys herein are shown in Table 1, which provides the preferred atomic ratios utilized.

As can be seen from Table 1, the alloys herein are Fe greater than 70 atomic% and at least four selected from the following six (6) elements: Si, Mn, Cr, Ni, Cu and C. Containing, or essentially consisting of, an iron-based metal alloy having the above elements. Impurity levels for other elements range from 0 to 5000 ppm. Thus, if there are 5000 ppm of elements other than the identified selected elements, the levels of such selected elements can then be present in combination at lower levels to constitute 5000 ppm of impurities. The sum of all the elements (selected elements and impurities) will be 100 atomic percent.

With respect to the above, and as can be further seen from Table 1, preferably Fe is present at levels above 70 atomic percent, when four or more elements are selected from the six (6) elements shown. Alternatively, 5 or more elements are selected, or all 6 elements are selected to provide a formulation of elements totaling 100 atomic percent. Preferred levels of the element, if selected, can fall within the following range: Si (1.14 to 6.13), Mn (3.19 to 15.17), Cr (0.78 to 8.64). Ni (0.9 to 11.44), Cu (0.37 to 1.87) and C (0.67 to 3.68). Therefore, it can be understood that when four (4) elements are selected, two of the six elements can be excluded and excluded. If five (5) elements are selected, one of the six elements may be excluded. Further, a particularly preferred level of Fe is in the range of 73.95 to 84.69 atomic%. Again, the levels of impurities in other elements are preferably controlled in the range of 0 to 5000 ppm (0 to 0.5% by weight).

Laboratory slab casting alloys were weighed to 3,000 to 3,400 grams according to the atomic ratios in Table 1 using commercially available iron additive powders and base steel raw materials with known chemical properties. As shown above, impurities can be present at various levels depending on the raw materials used. Impurity elements will generally include the following elements; Al, Co, N, P, Ti, Mo, W, Ga, Ge, Sb, Nb, Zr, O, Sn, Ca, and S are: If present, it will be in the range of 0 to 5000 ppm (1 / 1,000,000) (0 to 0.5% by weight) at the expense of the desired elements described above. Preferably, the level of impurities is controlled to be in the range of 0 to 3000 ppm (0.3 wt%).

The quantity was loaded into a zirconia-coated silica crucible placed in an Indutherm VTC 800V vacuum tilting casting machine. The instrument was then emptied of the casting and melting chambers and flushed twice with argon to atmospheric pressure prior to casting to prevent oxidation of the melt. The melt was heated by a 14 kHz RF induction coil for approximately 5 to 7 minutes, depending on alloy composition and volume mass, until fully melted. After the final solid was observed to melt, additional heating for 30-45 seconds was allowed to provide overheating and ensure melt uniformity. The foundry then emptied the chamber, tilted the crucible, and poured the melt into a water-cooled copper mold. The melt was allowed to cool under vacuum for 200 seconds before the chamber was filled with argon to atmospheric pressure.

Laboratory casting corresponds to step 1 in FIGS. 1, 2 and 3 and provides a slab with a thickness of 50 mm. The slab thickness in step 1 can vary from 25.0 to 500 mm, depending on the equipment capacity.

Thermal Analysis Samples between 50 mg and 150 mg from each alloy herein were taken under as-cast conditions. The sample was heated at a rate of 40 ° C./min to an initial lamp temperature between 900 ° C. and 1300 ° C., depending on the chemistry of the alloy. The temperature was then increased at 10 ° C./min to a maximum temperature between 1425 ° C. and 1515 ° C., depending on the chemistry of the alloy. Once this maximum temperature was achieved, the sample was cooled back to the initial lamp temperature at a rate of 10 ° C./min before being reheated to maximum temperature at 10 ° C./min. Suggested scanning calorimetry (DSC) measurements were taken using the Netzsch Pegasus 404 DSC throughout all four stages of the experiment, and this data is in the range 1102 to 1505 ° C. (Table 2) Solid phase temperature of each alloy. And used to determine the liquidus temperature. The liquidus-solidarity gap varies from 31 to 138 ° C., depending on the chemistry of the alloy. Thermal analysis provides information on maximum temperature for the following hot rolling processes, which vary depending on the chemistry of the alloy.

Laboratory hot rolling The alloys herein were preferably processed into laboratory hot bands by hot rolling of laboratory slabs at high temperatures. Laboratory alloying is developed to simulate hot band production from slabs produced by continuous casting. Industrial hot rolling is carried out by heating the slab in a tunnel furnace to a target temperature and then passing it through either a reverse rolling mill or a multi-stand rolling mill or a combination of both to reach the target gauge. To. During rolling on either rolling mill type, the temperature of the slab gradually decreases due to heat loss to the air and to the working rolls, so the final hot band is formed at the reduced temperature. To. This is simulated in the laboratory by heating in a tunnel furnace between 1100 ° C and 1250 ° C and then hot rolling. Since laboratory rolling mills are slower than industrial rolling mills, which cause a greater loss of heat between each hot rolling pass, the slabs are reheated for 4 minutes between the passes to reduce temperature drops, The final temperature on the target gauge upon exiting the laboratory rolling mill is generally in the range of 800 ° C to 1000 ° C, depending on the furnace temperature and final thickness.

Prior to hot rolling, the laboratory slabs were preheated in the Lucifer EHS3GT-B18 furnace. The set point of the furnace varies between 1100 ° C and 1250 ° C, depending on the melting point of the alloy and the points in the hot rolling process, the initial temperature is set higher to promote higher reductions and later temperatures. Is set low to minimize surface oxidation on the hot band. The slabs could be dipped for 40 minutes before hot rolling to ensure they reached the target temperature and then extruded from the tunnel furnace into the Fen Model 0612 high rolling mill. The 50 mm casting is hot rolled through a rolling mill for 5 to 10 passes before air cooling is allowed. The final thickness range after hot rolling is preferably 1.8 mm to 4.0 mm with variable rolling per pass in the range of 20% to 50%.

Tensile samples were cut from the laboratory hot band using wire EDM. Tensile properties were measured on an Instron mechanical test frame (Model 3369) using Instron's Bluehill control and analysis software. Samples have been tested under displacement control at a constant displacement rate of 0.036 mm / s and include, but are not always limited to, mechanical compatibility, sample slippage, and wedge action grip settings used. Depending on the factors of, the sample strain rate calculated from the video strain measurement, which ranges from 4.4 x 10 ^-4 s ^-1 to 6.8 x 10 ^-3 s ^-1 , was obtained.

The tensile properties of the alloy under hot rolling conditions with a thickness of 1.8 to 2.3 mm are listed in Table 3 including the magnetic phase volume percent (Fe%) measured by a ferrite scope. The maximum tensile strength value can vary from 913 to 2011 MPa with a tensile elongation of 13.0 to 69.5%. The yield strength is in the range of 250 to 1313 MPa. The mechanical properties of hot bands from steel alloys herein depend on the chemistry of the alloy, the working conditions, and the mechanical response of the material to the working conditions. Relative magnetic phase volume percent was measured by a ferrite scope with a magnetic phase volume percent of 0.1 to 64.9 Fe% in the hot band, depending on the chemistry of the alloy. It should be noted that the properties of Table 3 correspond to step 2 of FIGS. 1, 2 and 3. Further processing of the hot band can occur additionally, for example through cold rolling and annealing as shown in Case 1.

Cases Case # 1 Tensile properties of sheets at 1.2 mm thickness The hot bands from the alloys listed in Table 1 have a final target gauge thickness of 1.2 mm through multiple cold rolling passes. Cold-rolled to. Cold rolling is defined as rolling at ambient temperature. The hot band material was media blasted prior to cold rolling to remove surface oxides that could be embedded during the rolling process. The resulting washed sheet material was rolled using a Fen Model 0612 high rolling mill. The sheet is fed through rolls and the roll gap is reduced for each subsequent pass until the desired thickness is achieved or the material cures to the point where additional rolling does not achieve a significant reduction in thickness. Annealing was applied before the next rolling to restore ductility. Multiple cycles of cold rolling and annealing can be applied. Once the final gauge thickness was achieved, the sample was cut from each cold-rolled sheet by wire EDM. Tensile properties were measured on an Instron mechanical test frame (Model 3369) using Instron's Bluehill control and analysis software. All tests were performed at ambient temperature in displacement control. Samples have been tested under displacement control at a constant displacement rate of 0.036 mm / s and include, but are not always limited to, mechanical compatibility, sample slip, and wedge action grip settings used. Depending on the factors of, the sample strain rate calculated from the video strain measurement, which ranges from 4.4 x 10 ^-4 s ^-1 to 6.8 x 10 ^-3 s ^-1 , was obtained.

The tensile properties of the 1.2 mm thick sheet from the alloys herein after cold rolling are listed in Table 4. The maximum tensile strength value after cold rolling is in the range of 1360 to 2222 MPa; the yield strength varies from 1006 to 2073 MPa and the tensile elongation is recorded in the range of 4.2 to 37.2%. The magnetic phase volume percent was measured by a ferrite scope in the range of 1.6 to 84.9 Fe% on cold-rolled sheets depending on the chemistry of the alloy.

* 1.2 mm thickness was not achieved in these alloys due to high strength and equipment limitations. Alloys are tested to a thickness of 1.3 to 1.4 mm.

Samples are not baked under conditions intended to simulate expected heat exposure during the industrial continuous annealing process, which represents the final treatment of the sheet material in step 2 in FIGS. 1, 2 and 3. Annealed. Samples were loaded into a furnace preheated to 850 ° C., held at temperature for 10 minutes, wrapped in foil to minimize oxidative damage, and held under a stable argon stream. Samples were removed at temperature and allowed to air cool to ambient temperature prior to testing. Tensile properties were measured on an Instron mechanical test frame (Model 3369) using Instron's Bluehill control and analysis software. All tests are performed at a constant displacement rate of 0.036 mm / s at ambient temperature in displacement control and include, but are not always limited to, mechanical compatibility, sample slippage, and wedge action grip settings used. Depending on some factors, we provided sample strain rates calculated from video strain measurements, ranging from 4.4 x 10 ^-4 s ^-1 to 6.8 x 10 ^-3 s ^-1 .

The tensile properties of the 1.2 mm sheet from the alloys herein after annealing are listed in Table 5. Maximum tensile strength values for annealed sheets from alloys herein range from 725 to 2072 MPa; yield strengths vary from 267 to 1428 MPa and tensile elongations range from 12.8 to 76.9. Recorded in the range up to%. Relative magnetic phase volume percent was measured by a ferrite scope with a magnetic phase volume percent of 0.2 to 68.2 Fe%, depending on the chemistry of the alloy.

The properties of the cold-rolled and annealed sheet from the alloys herein correspond to step 2 in FIGS. 1, 2 and 3.

* 1.2 mm thickness was not achieved in these alloys due to high strength and equipment limitations. Samples were tested to a thickness of 1.3 to 1.4 mm.

This example is from an alloy of 1.2 to 1.4 mm thick, tested at strain rates from 4.4 x 10 ^-4 s ^-1 to 6.8 x 10 ^-3 s ^-1. Demonstrate the properties of the sheet material.

Case # 2 Sheet thickness effect on the tensile properties of alloy 2 The hot band from alloy 2 was cold rolled into sheets with different thicknesses through multiple cold rolling passes. Once the target gauge thickness was achieved, the sample was cut from each cold-rolled sheet by wire EDM. Samples were annealed under conditions intended to simulate expected heat exposure during the industrial continuous annealing process. The sample was wrapped in stainless steel foil to prevent oxidation and loaded into a preheated furnace at 850 ° C. Samples were left in the furnace for 10 minutes, while the furnace was purged with argon before being removed and allowed for air cooling. The only exception was final annealing for 4.8 mm materials. In contrast to the 10-minute annealing used for all other thicknesses, this annealing was an air-cooled annealing at 850 ° C. for 20 minutes. The purpose of this change was to allow more time for the material to warm because it was a very thick sample. Tensile properties were measured on an Instron mechanical test frame (Model 5984) using Instron's Bluehill control and analysis software. All tests were performed at ambient temperature in displacement control. All samples have been tested at displacement rates of 0.125 mm / s and include, but are not always limited to, mechanical compatibility, sample slippage, and wedge action grip settings used. Correspondingly, sample strain rates calculated from video strain measurements were obtained, ranging from 9.1 x 10 ^-4 s ^-1 to 1.9 x 10 ^-3 s ^-1 .

The results of tensile tests of sheets from alloys 2 processed to different thicknesses are listed in Table 6. In the sample having a thickness of less than 1.2 mm, which represents step 3 in FIG. 1, the tensile strength varies from 1100 to 1190 MPa and the yield strength is between 408 and 439 MPa. 4 and 5 show the tensile properties of the alloy 2 sheet as a function of thickness. The average tensile elongation is 53.7% for the 2 alloy sheets and the thickness is 0.20 to 1. (compared to the average 61.5% for the 2 sheets of alloy with a thickness of 1.2 mm). It changes up to 03 mm. Slightly higher elongation is observed up to 66.4% in thicker sheet samples above 1.2 mm. The stress-strain curves in FIG. 6 also demonstrate stress-strain behavior and consistent properties in sheet samples with different thicknesses.

This case demonstrates that high ductility was maintained in sheets with a wide range of thicknesses from 4.8 mm to as small as 0.2 mm. A reduction in sheet thickness to less than 1.2 mm results in an average total elongation greater than that in sheets having a thickness of more than minus 7.8% and 1.2 mm. The average maximum tensile strength is 25 MPa smaller than that of the corresponding sheet having a thickness of 1.2 mm or more, and the average yield strength is 67 MPa smaller.

Case # 3 Thickness effect on the tensile properties of the sheet from the selected alloy The hot bands from alloy 1, alloy 27, and alloy 37 have different thicknesses less than 1.2 mm through multiple cold rolling passes. The sheet was cold rolled. Once the target gauge thickness was achieved, the sample was cut from each cold-rolled sheet by wire EDM. Samples were annealed under conditions intended to simulate expected heat exposure during the industrial continuous annealing process, which represents the final treatment in sheet processing in step 2 in FIG. The sample was wrapped in stainless steel foil to prevent oxidation and loaded into a preheated furnace at 850 ° C. Samples were left in the furnace for 10 minutes, while the furnace was purged with argon before being removed and allowed for air cooling. Tensile properties were measured on an Instron mechanical test frame (Model 5984) using Instron's Bluehill control and analysis software. All tests were performed at ambient temperature in displacement control. All samples have been tested at displacement rates of 0.125 mm / s and include, but are not always limited to, mechanical compatibility, sample slippage, and wedge action grip settings used. Correspondingly, sample strain rates calculated from video strain measurements were obtained, ranging from 9.1 x 10 ^-4 s ^-1 to 1.9 x 10 ^-3 s ^-1 .

The results of tensile tests of sheets from alloys processed to different thicknesses are listed in Table 7 representing step 3 in FIG. Tensile elongation for alloy 1 ranges from 44.9 to 51.1%, for alloy 27 in the range 63.8 to 73.8%, and for alloy 37 from 6.0 to 7.0%. It is measured in the range of. Tension elongation as a function of sheet thickness is shown in FIG. 6 for the selected alloy. 8 and 9 show the yield strength and maximum tensile strength of sheets with different thicknesses for the selected alloy. The maximum tensile strength ranges from 1203 to 1269 MPa for one alloy sheet, 972 to 1067 MPa for 27 alloy sheets, and 1493 to 1614 MPa for 37 alloy sheets. Yield strength varies from 375 to 444 MPa for one alloy sheet, from 367 to 451 MPa for 27 alloy sheets, and from 612 to 820 MPa for 37 alloy sheets.

This case demonstrates that the tensile ductility of the alloys herein is maintained even at sheet thicknesses as small as 0.2 mm, corresponding to those having a thickness of more than minus 7.3% and 1.2 mm. Demonstrate average total elongation above that on the sheet. The average maximum tensile strength is in the range of ± 35 MPa of the corresponding sheet having a yield strength in the range of ± 98 MPa and a thickness of 1.2 mm or more.

Case # 4 Microstructure in sheets from selected alloys at different thicknesses Hot bands from alloys 1, 2, alloys 27, and 37 have different thicknesses less than 1.2 mm through multiple cold rolling passes. It was cold-rolled into a sheet having a shaving. Once the target gauge thickness was achieved, the sample was cut from each cold-rolled sheet by wire EDM. Samples were annealed under conditions intended to simulate expected heat exposure during the industrial continuous annealing process. The sample was wrapped in stainless steel foil to prevent oxidation and loaded into a preheated furnace at 850 ° C. The cold-rolled and annealed microstructure is investigated by SEM to show structural changes during processing. To prepare the SEM sample, the pieces were cut from the sheet by EDM and attached in epoxy, and the sheet cross section was gradually and finally polished with 0.02 μm silica with 9 μm, 6 μm and 1 μm diamond suspension solutions. .. The SEM survey was conducted by Carl Zeiss SMT Inc. This was done using the EVO-60 scanning electron microscope manufactured by.

FIG. 10 shows the microstructure of alloy 1 sheet samples with different thicknesses. The cold-rolled structure is shown in FIGS. 10a and 10c at the center of the sheet having thicknesses of 0.7 and 0.5 mm, respectively. Cold-rolled samples have highly deformed microstructures where grain boundaries are difficult to find. The microstructures in these sheet samples after annealing are shown in FIGS. 10b and 10d represented by equiaxed grains and recrystallized structures with clear grain boundaries.

FIG. 11 shows the microstructure of alloy 2 sheet samples with different thicknesses. The cold-rolled structure is shown in FIGS. 11a, 11c and 11e at the center of the sheet having thicknesses of 1.0, 0.5 and 0.2 mm respectively. Cold-rolled samples have highly deformed microstructures where grain boundaries are difficult to find. The microstructures of these sheet samples after annealing are shown in FIGS. 11b, 11d and 11f represented by equiaxed grains and recrystallized structures with clear grain boundaries.

The structure of the sheet sample from alloy 27 is similar to alloy 1 and alloy 2 and is shown in FIG. The recrystallized microstructure in the sheet from alloy 27 has few twins as compared to other investigated alloys, as shown in FIGS. 12b, 12d and 12f.

Alloy 37 is a different type of alloy in which annealing does not lead to typical recrystallized structure formation. FIG. 13 shows the structure at the center of the sheet from the alloy 37 having different thicknesses after cold rolling and after cold rolling and annealing. Only a small difference is observed between the cold-rolled structure and the annealed structure. Corresponding samples at different thicknesses have substantially the same structure.

This case demonstrates that the microstructure is maintained in the alloys herein after annealing the cold-rolled sheet, independent of the final sheet thickness.

Example # 5 Strain Rate Effect on Tensile Ductility of Sheets from Alloy 2 Alloy 2 slabs were cast according to the atomic composition provided in Table 1. Following casting, the slab is continuously hot rolled through smaller roll gaps to produce a hot band coil in the range of 2 to 5 mm thick, after which approximately 1 representing the sheet material in step 2 in FIG. It underwent a cold rolling and annealing cycle until the target thickness of .4 mm was achieved. Annealing was performed in this case in the temperature range from 950 to 1050 ° C.

The tensile properties of the material were characterized as a function of strain rate. Tensile samples were tested in ASTM D638 Type V tensile shape shown in FIG. 14 at 0.0007s ^-1 , 0.7s ^-1 , 10s ^-1 , 100s ^-1 , 500s ^-1 and 1200s ^-1 nominal strain rates. .. Tensile samples tested at strain rates from 0.0007s ^-1 to 500s ^-1 were tested on the MTS Servo-Hydraulic Test Frame. The sample was loaded into the grip and loaded by raising the crosshead at the speed required to generate the nominal strain rate. A slack adapter consisting of a cup and cone rod assembly was used at strain rates greater than 1s ^-1 to allow the test frame to achieve the targeted constant strain rate before applying load to the sample. Onboard rods were used at 500s- ¹ to mitigate the effects of standing waves on the test equipment that occurred during the high strain rate test. A split-Hopkinson rod (SHB) was used with a strain rate of 1200s ^-1 . The SHB device consisted of a 7075 Al incident rod and a transmission rod with a diameter of 25.4 mm, and the test sample was firmly fixed between the Al rods. Strain gauges were used on transfer rods and incident rods to measure strain on the rods. The striker tube was fired around the incident tube towards the striker plate to generate a tensile strain pulse and strain in the sample was recorded. A schematic diagram of the SHB is provided in FIG.

Strains in tensile samples were measured by mechanical extensometers at strain rates of 0.0007s ^-1 and 0.7s ^-1 . Digital Image Correlation (DIC) was used to measure strain on samples tested at 10s ^-1 , 100s ^-1 and 500s ^-1 . Five tensile samples were tested at all strain rates. In the case of one sample at a strain rate of 0.0007s ^-1 , anomalies that resulted in sample loss occurred. The two samples tested at 1200s ^-1 did not fail during the test.

The measured strains at break are provided in Table 8. The measured strain is plotted in FIG. 16 as a function of strain rate. Table 9 provides average ductility as measured by tensile elongation at break for each nominal strain rate. It should be noted that the average tensile elongation measured at all strain rates is close to 55.5% of the total average over all strain rates. At strain rates from 0.0007s ^-1 to 500s ^-1 , the average tensile elongation at break is within approximately ± 3% of the overall average for all tests. The tests at 1200s ^-1 were measured to have higher tensile elongation at break than all other tests, but due to the nature of this test tool these values are slightly lower than the actual values. Can be measured high. Maximum tensile strength is measured in the range of 944 to 1187 MPa with yield strength of 347 to 512 MPa (Table 10).

The tensile properties in Tables 8 to 10 represent the sheet material in step 3 in FIG.

This case demonstrates that the tensile ductility of the alloys herein is maintained over a relatively large range of strain rates from 0.007 to 1200s- ¹ . The measured average maximum tensile strength is 62 MPa lower at higher strain rates and the average yield strength is 59 MPa lower.

Example # 6 Microstructural strain rate effect on sheet from alloy 2 Microstructure of sample from sheet from alloy 2 tested at 5 different strain rates ranging from 0.0007s ^-1 to 1200s ^-1 (See Case # 5) was investigated by TEM. For TEM investigations, the piece is cut from the gauge section of the deformed sample by a diamond saw. Grinding and polishing are then performed to make a thin foil from the cut pieces. Polishing was carried out gradually with 9 μm, 6 μm and 1 μm diamond suspension solutions, and finally with 0.02 μm silica. Foil with a thickness of 70-80 μm was obtained after polishing. The 3 mm diameter disc was punched out of foil and the final polishing was performed by electropolishing using a twin jet grinder. The chemical solution used was 30% nitric acid mixed in a methanol base. For thin areas that are inadequate for TEM observation, the TEM sample can be ion milled using the Gatan Precision Ion Polishing System (PIPS). Ion milling is typically performed at 4.5 keV and the tilt angle is reduced from 4 ° to 2 ° to cut through thin areas. The TEM survey was performed using a JEOL 2100 high resolution microscope operating at 200 kV.

FIG. 17 shows a brightfield TEM image of the sample tested at 1200s- ¹ . Deformed twins can be found to be prominent in fast deformed samples, which are the formation of twins that do not occur through mechanical deformation but occur during heat treatment. Twins are clear and sharp, indicating that they are newly formed from the deformation. By twinning, which is a mode of deformation in the sample, the phase transformation is reduced because the deformed twins maintain the austenite structure. Twin formation as a method of deformation can be seen in samples deformed at strain rates of 500, 100, 10 and 0.7s ^-1 , as shown in FIGS. 18-21. Samples deformed at a strain rate of 0.0007s ^-1 have different structures that can be seen in FIG. 22 demonstrating the control of dislocations due to phase transformation during deformation as evidenced by ferrite scope measurements on the post-deformation sample gauge. .. As shown in FIG. 23, the magnetic phase volume percent that correlates with the converted product phase is highest for deformations at low strain rates of 0.0007s ^-1 .

This case demonstrates a change in the deformation mechanism during the deformation of the alloys herein with higher occurrence of twinning as the strain rate increases. Deformation due to twinning at high strain rates suppresses phase transformation (that is, reduces the total amount of ferrite produced) and provides a relatively high tensile ductility of the sheet material over a wide range of strain rates. Allows retention.

Example # 7 Notch effect on the tensile properties of the sheet from Alloy 2 The slab of Alloy 2 was cast according to the atomic composition provided in Table 1. Following casting, the slab is continuously hot rolled through smaller roll gaps to produce a hot band coil, after which a targeted thickness of approximately 1.4 mm representing the sheet in step 2 in FIG. 3 is achieved. It underwent a cold rolling and annealing cycle until

The tensile sample was cut from the sheet via wire EDM. The sample had two contrasting notches approximately centered in width and length, as shown in FIG. Samples were tested by pulling by moving one grip at a fixed rate with a displacement rate of 0.125 mm / s. Tensile properties were measured on an Instron mechanical test frame using Instron's Bluehill control and analysis software. All tests were performed at ambient temperature in displacement control. A gauge length of 50 mm centered on the notch was used. Stress was calculated based on the nominal width rather than the notched width (FIG. 24).

The tensile properties of the alloy two-sheet sample as a function of notch diameter and notch depth are listed in Table 11. The tensile elongation of the notched sample ranged from 12.4% to 40.7%, the yield strength ranged from 298 to 420 MPa, and the maximum tensile strength ranged from 636 to 1123 MPa. The effect of a notch diameter with a constant depth of 0.5 mm on the tensile properties of the sheet from Alloy 2 is shown in FIG. Changes in the tensile properties of sheets with semi-circular notches as a function of notch diameter are shown in FIG. This data represents the sheet in step 3 in FIG.

This case demonstrates an increase in tensile elongation of the notched sample from the alloys herein by increasing the notch diameter at a constant depth. In the case of increasing depth, the average elongation is shown to be independent of the notch depth (semicircle).

Case # 8 Ductile fracture surface SEM fracture analysis in the notched sample after the test was performed on a selected notched sample from the alloy 2 sheet after the tensile test (see Case # 7). Two samples with notch radii of 1.0 and 6.0 mm were selected for inspection (Table 12). The SEM survey was conducted by Carl Zeiss SMT Inc. This was done using the EVO-60 scanning electron microscope manufactured by.

In FIGS. 27 and 28, SEM images of the fractured surface after the tensile test are shown for Sample 1 and Sample 2, respectively. Images are taken from the center of the fractured section and near the edges. Both samples demonstrated ductile fracture. A finer structure is seen closer to the edge, but there is no difference in fracture mode between the center and edge of the fracture cross section.

This case demonstrates that the introduction of notches into the sheet material from the alloys herein does not cause catastrophic breakage of brittleness. The notched sample after the test demonstrates ductile fracture.

The alloys herein can be used in a variety of applications. For example, the alloys herein can be positioned in a vehicle frame, vehicle chassis or vehicle panel. In addition, the alloys herein can be used for storage tanks, freight cars or railroad tank cars. Rail tank cars may specifically include tanks, jacketed tanks or tanks with head shields. Other uses include body armor, metal shields, military vehicles and armored vehicles. Such applications apply alloys manufactured according to any one of FIGS. 1, 2 and / or 3.

Claims (31)

a. A metal alloy containing at least 70 atomic% iron and at least 4 or more elements selected from Si, Mn, Cr, Ni, Cu or C was supplied to melt the alloy and have a rate of <250 K / s. With the step of cooling with and solidifying to a thickness from 25.0 mm to 500 mm;
b. In the step of processing the alloy into a sheet having a thickness of T ₁ , the sheet has a total elongation of X ₁ (%), a maximum tensile strength of Y ₁ (MPa), and a yield of Z ₁ (MPa). With strength, with steps;
c. A step of further processing the alloy into a second sheet by a reduction in thickness T ₂ <T ₁ , where the second sheet has a total elongation of X ₂ = X ₁ ± 10%, Y ₂ = Y ₁ With a step having a maximum tensile strength of ± 50 MPa and a yield strength of Z ₂ = Z ₁ ± 100 MPa;
A method for preserving mechanical properties in metal sheet alloys at reduced thicknesses, including. The method of claim 1, wherein at least 70 atomic percent iron is combined with five or more elements selected from Si, Mn, Cr, Ni, Cu or C. The method of claim 1, wherein at least 70 atomic percent iron is combined with a total of six elements: Si, Mn, Cr, Ni, Cu and C. The method of claim 1, wherein the levels of the four elements selected are: Si (1.14 to 6.13 atomic percent), Mn (3.19 to 15.17 atomic percent), Cr. (0.78 to 8.64 atomic percent); Ni (0.9 to 11.44 atomic percent), Cu (0.37 to 1.87 atomic percent). The method of claim 1, wherein the alloy formed in step (b) exhibits X ₁ (12% to 80%), Y ₁ (700 MPa to 2100 MPa), and Z ₁ (250 MPa to 1500 MPa). The method of claim 1, wherein the alloy formed in step (b) exhibits a thickness of 1.2 mm to 10.0 mm. The method of claim 1, wherein the alloy formed in step (c) exhibits X ₂ (2 to 90%), Y ₂ (650 MPa to 2150 MPa), and Z ₂ (150 MPa to 1600 MPa). The method of claim 1, wherein the alloy formed in step (c) exhibits a thickness of 0.2 mm to <1.2 mm. The method of claim 1, wherein the alloy formed in step (c) is positioned in the vehicle frame, vehicle chassis or vehicle panel. The method of claim 1, wherein the alloy formed in step (c) is positioned in a storage tank, freight car or railroad tank car. a. A metal alloy containing at least 70 atomic% iron and at least 4 or more elements selected from Si, Mn, Cr, Ni, Cu or C was supplied to melt the alloy and have a rate of <250 K / s. With the step of cooling with and solidifying to a thickness from 25.0 mm to 500 mm;
b. Comprising the steps of processing the alloy from 1.2mm to a sheet shape having a thickness of 10.0 mm, the sheet is, _X 1 total elongation (%) when tested at a strain rate _{S 1, Y 1} With a step having a maximum tensile strength of (MPa) and a yield strength of Z ₁ (MPa);
c. A step of deforming a sheet from the alloy at a strain rate S ₂ > S ₁ , where the sheet has a total elongation of X ₃ = X ₁ ± 7%, a maximum tensile strength Y ₃ = Y ₁ ± 200 MPa, and yield. With a step having an intensity Z ₃ = Z ₁ ± 50 MPa;
A method for preserving mechanical properties in metal sheet alloys at relatively high strain rates, including. 11. The method of claim 11, wherein at least 70 atomic percent iron is combined with five or more elements selected from Si, Mn, Cr, Ni, Cu or C. 11. The method of claim 11, wherein at least 70 atomic percent iron is combined with a total of six elements: Si, Mn, Cr, Ni, Cu and C. The method of claim 11, wherein the levels of the four elements selected are: Si (1.14 to 6.13 atomic percent), Mn (3.19 to 15.17 atomic percent), Cr. (0.78 to 8.64 atomic percent); Ni (0.9 to 11.44 atomic percent), Cu (0.37 to 1.87 atomic percent). The method of claim 11, wherein the alloy formed in step (b) exhibits X ₁ (12% to 80%), Y ₁ (700 MPa to 2100 MPa), and Z ₁ (250 MPa to 1500 MPa). The method of claim 11, wherein the strain rate S ₁ is 0.007s ^-1 to 0.0001s ^-1 . 15. The method of claim 11, wherein the alloy formed in step (c) exhibits X ₃ (5% to 87%), Y ₃ (500 MPa to 2300 MPa), and Z ₃ (200 MPa to 1550 MPa). The method of claim 11, wherein the strain rate S ₂ is> 0.007s ^-1 to 1200s ^-1 . 11. The method of claim 11, wherein the process in step (c) includes roll molding, metal stamping or hydroforming. 11. The method of claim 11, wherein the alloy formed in step (c) is positioned in the vehicle frame, vehicle chassis or vehicle panel. 11. The method of claim 11, wherein the alloy formed in step (c) is positioned in a storage tank, freight car or railroad tank car. 11. The method of claim 11, wherein the alloy formed in step (c) is positioned in body armor, shields, military vehicles or armored vehicles. a. A metal alloy containing at least 70 atomic% iron and at least 4 or more elements selected from Si, Mn, Cr, Ni, Cu or C was supplied to melt the alloy and have a rate of <250 K / s. With the step of cooling with and solidifying to a thickness from 25.0 mm to 500 mm;
b. In the step of processing the alloy into a sheet shape having a thickness of 1.2 mm to 10.0 mm, the sheet has a total elongation of X ₁ (%), a maximum tensile strength of Y ₁ (MPa), and Z. _With a step having a yield strength of ₁ (MPa);
c. A step of introducing a stress concentration site and then deforming a sheet from the alloy, wherein the sheet has a total elongation of X ₄ ≥ 0.2 X ₁ (%) and a maximum tensile strength Y ₄ ≥ 0.5 Y ₁ ( With a step having MPa) and yield strength Z ₄ ≧ 0.6 Z ₁ (MPa);
A method for preserving mechanical properties in metal sheet alloys, including. 23. The method of claim 23, wherein at least 70 atomic percent iron is combined with five or more elements selected from Si, Mn, Cr, Ni, Cu or C. 23. The method of claim 23, wherein at least 70 atomic percent iron is combined with a total of six elements: Si, Mn, Cr, Ni, Cu and C. The method of claim 23, wherein the levels of the four elements selected are: Si (1.14 to 6.13 atomic percent), Mn (3.19 to 15.17 atomic percent), Cr. (0.78 to 8.64 atomic percent); Ni (0.9 to 11.44 atomic percent), Cu (0.37 to 1.87 atomic percent). 23. The method of claim 23, wherein the alloy formed in step (b) exhibits X ₁ (12% to 80%), Y ₁ (700 MPa to 2100 MPa), and Z ₁ (250 MPa to 1500 MPa). 23. The method of claim 23, wherein the process in step (c) includes roll molding, metal stamping or hydroforming. 23. The method of claim 23, wherein the alloy formed in step (c) is positioned in the vehicle frame, vehicle chassis or vehicle panel. 23. The method of claim 23, wherein the alloy formed in step (c) is positioned in a storage tank, freight car or railroad tank car. 23. The method of claim 23, wherein the alloy formed in step (c) is positioned in body armor, shields, military vehicles or armored vehicles.