METHOD OF HOT PRESS FORMING OF A STEEL ARTICLE AND STEEL ARTICLE

Abstract

A method of hot-press forming an article of zinc-coated steel or zinc alloy, wherein the steel is a product obtained by a steelmaking method comprising the steps of: - shaping molten steel into slabs; - reheating the slabs, preferably to a temperature of 1150°C or higher and preferably for a time of 60 minutes or more; - hot-rolling the steel into a strip, preferably with a finish exit rolling temperature (FRT) above the Ar3 temperature, where Ar3 denotes the temperature at which ferrite transformation begins in the steel during quenching; - coiling the hot-rolled steel strip; - pickling the hot-rolled steel strip; - continuously annealing the strip; - hot-dip coating the steel strip with zinc or zinc alloy at once; - using an immersion time of 3 seconds or more;- maintaining a hot immersion bath temperature of 420°C to 500°C - where the zinc bath contains essentially zinc, at least 0.1% Al and optionally up to 5% Al and optionally up to 4% Mg, the remainder of the bath comprising additional elements, all individually in less than 0.3% and unavoidable impurities; - forming the article by hot pressing.

Description

The present invention relates to a method of hot press forming a steel article from a zinc-coated steel or zinc alloy after continuous annealing and the subsequent hot press forming of a steel article from a zinc-coated steel or zinc alloy and to a hot-dip zinc-coated steel or zinc alloy article manufactured by hot press forming of a zinc-coated steel or zinc alloy. BACKGROUND OF THE INVENTION Hot press forming, also known as hot stamping, hot forming, press forming, and press hardening or tempering, is a technique for forming and hardening or tempering a piece of steel into a final formed article or part. Generally, a steel part is reheated and soaked at austenitizing temperatures, typically in the range of 870–940°C, and then formed and press-quenched in press dies. High temperatures are required to fully austenitize the steel and dissolve all carbides. Press quenching results in a strong martensitic structure in the steel substrate. Even when hot forming is performed in the intercritical range to develop a dual-phase structure, the reheating temperature is 760°C or higher. It is known that hot forming of uncoated steel parts results in oxidation. Zinc- and aluminum-based coatings have been applied to reduce this effect. Given their corrosion resistance, zinc-based coatings may be preferred since they also offer galvanic protection. However, due to the low melting points of zinc and zinc-iron compounds and the high superheating temperatures, surface cracking can occur during hot forming, and this cracking has been linked to zinc grain boundary penetration. One approach that has been explored to address this issue is modifying the zinc coating. Current hot-formed (ultra) high-strength products have very low in-service ductility (<8%) due to the martensitic or martensitic-bainitic microstructure obtained through press quenching. The martensitic microstructure in hot-formed products is primarily intended to provide the required strength level (>1000 MPa). However, this microstructure for hot-formed products can provide a maximum total elongation of only about 6%. Although a single-phase martensitic microstructure can provide good bending capacity (e.g., >100° for a 1000 MPa level and about 50° for a 1500 MPa level), the shock energy absorption capacity of these products is low due to the low total elongation. A method for producing an uncoated ultra-high-strength steel is known from US2016 / 0312323A1, among others.This method comprises a step of providing a ferrous alloy comprising carbon and more than 2.5% by weight of manganese, a step of annealing the ferrous alloy to a first temperature to form an annealed alloy, hot forming the annealed alloy to a second temperature to form an intercritical or austenite structure, and cooling the austenitic alloy thus annealed. J bQCn / 77n7 / q / YILI to form ultra-high-strength steel. In one embodiment, the annealed alloy is hot-formed within an intercritical annealing temperature range. In another embodiment, the hot-forming temperature is within an austenitizing annealing range. The soaking time is between approximately 1 minute and approximately 10 minutes. In the Examples, the hot-forming thermal cycles were simulated without inducing actual deformation, following a continuous annealing step of cold-rolled sheets. It does not describe the continuous annealing method or the method of applying any coating to the steel strips. EP18155866 describes a method of hot-forming a steel part coated with Zn or a Zn alloy containing more than 3.1 wt% Mn using a soaking time of up to only 3 minutes.The method of coating the steel strip with zinc or zinc alloy is not described, nor is a soaking time longer than 3 minutes during reheating considered. A longer soaking time is preferred for steels containing a relatively high amount of manganese to allow for effective diffusion. BRIEF DESCRIPTION OF THE INVENTION An objective of the present invention is to provide galvanic protection in relation to hot-pressed steel strip articles offered by zinc-based coatings for (ultra) high strength steels, while reducing the risk of (micro) crack generation. Another objective of the invention is to provide a hot-dip galvanizing process that makes it possible to coat steel strips containing high amounts of Mn with Zn or Zn alloy, simultaneously giving a continuous annealing process that gives the desired microstructures to achieve high ductility in the final product. Another objective of the invention is to provide a hot-dip galvanized or zinc alloy coated steel article formed in a hot press with high strength and high deformation capacity at room temperature. Accordingly, the method according to the invention is a hot press forming method of a steel article from a steel strip coated with zinc or zinc alloy, wherein the steel strip has a composition in % by weight of: C: 0.05-0.3; Mn: 3.0-12.0; Al: 0.04-3.0; optionally one or more additional alloying elements: Yes: less than 1.5; Cr: less than 2.0; V: less than 0.1; Nb: less than 0.1; Ti: less than 0.1; Mo: less than 0.5; unavoidable impurities, such as 7 bQCn / 77n7 / q / YILI S: less than 30 ppm by weight; P: less than 0.04; the remainder being Fe; Understanding the steel strip manufacturing method, the steps of: - mold the molten steel into a sheet; - reheat the iron to a temperature above 1150°C and maintain it at that temperature for 60 minutes or more; - hot roll the steel into a strip, preferably with an exit finish hot rolling temperature (FRT) higher than the Ar3 temperature, where Ar3 denotes the temperature at which the ferrite transformation begins in the steel during cooling; - roll up the hot-rolled steel strip; - pickle the hot-rolled steel strip; - optionally cold rolling the pickled hot-rolled steel strip into a cold-rolled steel strip, wherein in the case of cold rolling, the hot-rolled strip after cooling and pickling is batch-annealed at a temperature TB for a period PB, TB and PB being chosen so that the steel has a microstructure exhibiting more than 60% by volume of ferrite after cooling to room temperature, wherein in a preferred embodiment TB and PB are chosen so that TB is 650°C or less and PB is 24 hours or more; - continuously annealing the strip according to an annealing thermal cycle where the temperature of the steel strip is preferably rising at a rate of 1-15°C / s in the heating section, then remains at a relatively stable level for soaking in the soaking section where a soaking atmosphere is maintained, at a temperature between TMIN and TMAX where TMIN = TMAX-100°C, where the continuous annealing is considered to end at the point in the heating cycle where the temperature of the steel strip drops, preferably at a rate of 0.5-10°C / s: - where TMAX is equal to or less than the lower of Ac3-100°C and 700°C; - where the soaking atmosphere has a dew point of -40 to -10°C; - wherein continuous annealing comprises in the heating section pre-oxidizing the steel strip in an annealing atmosphere having an oxygen content of 500 to 3000 ppm by volume; - where the soaking atmosphere is a reducing atmosphere, preferably containing between 115% by volume of Hydrogen and Nitrogen; - where the continuous annealing time, which consists of the time in the heating section plus the time in the soaking section, is 150 seconds or more, preferably 180 seconds or more; - hot-dip coating the steel strip with zinc or zinc alloy while simultaneously: - Use an immersion time of 3 seconds or more; - Keep in the hot immersion bath at a bath temperature of 420°C to 500°C; - where the zinc bath contains essentially zinc, at least 0.1% by weight of Al and optionally 71?QCn / 77n7 / 3 / YILI up to 5% by weight of Al and optionally up to 4% by weight of Mg, the remainder of the bath comprising additional elements, all individually in less than 0.3% by weight and unavoidable impurities; - forming the article using a hot press, which includes the following steps: - provide a piece taken from a strip of steel coated with zinc or zinc alloy by hot-dip galvanizing; - reheat the part to a TRH part temperature in the range of Ac3-300°C to 750°C, - soak the piece at TRH for a period longer than 3 minutes and up to 15 minutes; - transfer the piece to the press within 30 seconds; - forming the article in the press, thereby cooling the article; - Remove the article from the press. Steel with the specified composition is processed into hot-rolled or cold-rolled strips using a specific manufacturing process. The strips are then continuously annealed using controlled temperatures, treatment durations, dew points, and atmospheres at different stages of the process. This prevents surface enrichment of the steel's alloying elements, providing a suitable surface for good adhesion of the zinc or zinc alloy coating to the steel substrate by hot-dip galvanizing. The specified continuous annealing process takes place at a low intercritical temperature at or below the lower of Ac3-100°C or 700°C. This allows for the partitioning of manganese between the ferritic and austenitic phases of the steel, enabling the formation of the desired microstructure with high amounts of retained austenite after hot-press forming.Then, the zinc-coated or zinc-alloy steel strips in the form of parts are reheated in the same intercritical temperature region (from Ac3-300°C to 750°C, preferably 700°C) for more than 3 minutes so that the effective partitioning of Mn between ferrite and austenite can occur again. The reheating temperature of the parts is chosen so that penetration of the grain boundaries by the liquid zinc or zinc alloy does not occur, minimizing microcracks on the surface during hot forming of the steel article. Preferably, in hot-formed steel coated with zinc or zinc alloy by hot-dip, comprising a steel substrate provided with the hot-dip coated layer, the length of any microcrack in the steel substrate is 5 pm or less. For a steel containing Mn in the range of 3 to 12% by weight, conventionally denoted as “a medium Mn steel”, a good adherent coating of Zn or Zn alloy can be applied to the strip surfaces by hot-dip galvanizing. Just before hot immersion in the zinc or zinc alloy bath, the steel undergoes continuous annealing at an intercritical temperature. This allows for the effective distribution of manganese between the ferrite and austenite phases of the steel. This characteristic facilitates manganese distribution during the subsequent reheating of the zinc-coated steel or zinc alloy for hot press forming, resulting in the desired final microstructure with high amounts of retained austenite. Reheating steel parts coated with Zn or Zn alloy to a temperature in the range of Ac3-300°C to 750°C, preferably 700°C, minimizes the formation of Zn or 7 bQCn / 77n7 / q / YILI liquid Zn alloy and its penetration into the grain boundaries of the steel substrate for reheating durations equal to or greater than 3 minutes. The selected preheating within the steel's intercritical temperature range also ensures the prior partitioning of Mn that occurred during the preceding continuous annealing between ferrite and austenite. A reheating time of more than 3 minutes results in more effective Mn partitioning, thus increasing the thermal stability of the austenitic phase and yielding high fractions of retained austenite after cooling the article to room temperature. In one embodiment of the method, the Mn content of the steel is 6.0% by weight or higher. This substantially suppresses the Ac3 temperature in the steel, as explained later. As a result, less Zn-rich liquid phase formation occurs during reheating and hot press forming. This suppresses zinc-induced liquid metal embrittlement, minimizing microcracking in the hot-formed items. Furthermore, the lower reheating required by this preferred embodiment also saves energy costs during hot press forming and causes less oxidation of the zinc coating on the steel surface. Therefore, the weldability of the hot-formed items is improved, and the need for sandblasting after hot forming is eliminated. In one variation of the method, the plate is reheated to a temperature above 1200°C, or preferably above 1250°C, and held at that temperature for 60 minutes or more. This achieves the effect of distributing the Mn homogeneously throughout the molten steel plates. In an additional variation of the method, the plate is reheated to a specific temperature and held at that temperature for 120 minutes or more. This achieves an even more homogeneous distribution of Mn in the cast steel plates, minimizing any microsegregation. In another variation of the method, the HRT is in the range of Ac3-300°C to 700°C. This achieves the effect of forming minimal amounts of zinc-rich liquid phase on the steel surface, reducing changes in liquid phase penetration into the steel substrate, further minimizing or eliminating zinc-induced liquid metal embrittlement and the microcracking phenomenon. In another variation of the method, the part is transferred to the press within 10 to 15 seconds. This minimizes the temperature loss of the steel part, allowing for easier forming and minimizing or eliminating shrinkage in the formed item. The invention also relates to a hot-pressed steel article coated with zinc or zinc alloy by hot-dip, obtainable by the method of any of claims 1 to 5, which has a microstructure comprising by volume % ferrite: 30% or more, preferably 40% or more; retained austenite: 20% or more, preferably 30% or more; martensite: 40% or less, preferably 30% or less, including 0%. With that microstructure of the steel article containing 20% ​​by volume or more, preferably 30% by volume or more of retained austenite in combination with the given amounts of ferrite and 71?QCn / 77n7 / 3 / YILI martensite, ductility as expressed by total elongation and bending capacity is achieved at high levels. These microstructures also ensure that high strength values ​​are achieved in the article, particularly due to the retained austenite that transforms into strong martensite during cold deformation such as in a shock and due to any initial martensite present in the microstructure of the article. In one aspect according to the invention, the hot-pressed steel article coated with zinc or a hot-dip zinc alloy has the following mechanical properties: yield strength > 800 MPa, ultimate tensile strength > 820 MPa, total elongation > 10%, and bend angle at a thickness of 1 mm > 80°. This article is particularly suitable for automotive applications, such as front or rear longitudinal bars, lower portions of B-pillars, bumper beams, etc. Due to the high mechanical properties (i.e., total elongation, bending capacity, and strength values), high impact energy absorption can be achieved in the article. The invention is based on modifying the composition of the steel substrate, which is provided with a zinc or zinc alloy coating; designing the processing route so that the steel can be manufactured in a cold-rolled and / or hot-rolled form; designing the continuous annealing and hot-dip galvanizing process that will make the steel suitable for coating with Zn or a Zn alloy and cause favorable microstructural changes in the steel substrate for subsequent hot stamping; and designing the hot stamping process. The essential elements for modifying the steel substrate are Mn, C, and Al. Increasing the Mn content in the steel allows for austenite transformation temperatures, where the transformation of austenite begins (Ac1) and is completed (Ac3) upon heating. This enables the steel to be annealed at lower temperatures within the intercritical phase range. This suppression of austenite transformation temperatures comprises the following advantages: Due to the low soaking temperature, the diffusion of alloying elements and subsequent selective external oxidation of these elements are reduced. It should be noted that, due to the high Mn content of the steel substrate, there is a greater potential for selective external oxidation of Mn, which would hinder the wetting capacity of the liquid zinc. - Reheating of steel parts coated with Zn or Zn alloy can also be done at a relatively low temperature, thus minimizing the growth of a thick oxide, i.e.: more metallic zinc remains. - The hot press forming temperature is also lower. This minimizes the formation of liquid zinc and its penetration into grain boundaries, and significantly reduces zinc microcracking. The steel substrate is annealed and reheated to its intercritical temperature range to achieve the desired microstructure components and ensure high mechanical properties. This metallurgical requirement also contributes to the invention. If the steel is annealed and / or reheated for hot forming above the Ac3 temperature, i.e., at the austenitic temperature, the desired microstructure cannot be achieved. If these heat treatments are performed above the steel's Ac3 temperature, then only austenite phases will be present at these temperatures. 7 bQCn / 77n7 / q / YILI soaking and the composition of this austenite would assume the basic composition of the steel, which has low thermal stability. On the other hand, when soaking takes place at an intercritical annealing temperature, two phases of austenite and ferrite coexist at the soaking temperature. This allows for the distribution of alloying elements between the austenite and ferrite. The steel of this invention contains Mn, C, and Al as essential alloying elements. Therefore, Mn and C will be distributed more in the austenite since they are gamma-genic elements, and Al more towards the ferrite since it is an alpha-genic element. Also, a low heat treatment temperature ensures that the grain size of the steel remains fine. Due to the low intercritical heat treatments, an ultrafine microstructure (grain size < 2 pm) is obtained, which improves the strength and ductility of the product. Herein lies another important aspect of steel modification. The high manganese content of steel, ranging from 3 to 12% by weight, causes significant manganese enrichment in the austenite through partitioning during annealing and reheating within the intercritical temperature range. This manganese enrichment, along with carbon enrichment, increases the thermal stability of the intercritical austenite. Therefore, during quenching or tempering at room temperature, the intercritical austenite does not transform into martensite or any other phase to a greater extent, allowing a high amount of austenite (>20% by volume) to be retained in the steel's microstructure at room temperature. The retained austenite transforms into martensite during loading, causing the transformation-induced plasticity (TRIP) effect.The high strength, high elongation, and high bending capacity of the product are achieved due to the TRIP effect, which increases the work-hardening rate. A manganese content greater than 12 wt% will make continuous casting of the steel difficult due to extreme segregation, and the plasticity enhancement mechanism will change from TRIP to TWIP (twin-induced plasticity). A manganese content less than 3 wt% will not provide sufficient manganese enrichment in the austenite to achieve adequate amounts of retained austenite at room temperature. Similar to the effects of Mn, as described above, C also enriches the intercritical austenite, increasing its thermal stability and causing austenite stabilization at the microstructure at room temperature. However, C is effective in smaller quantities than Mn, and therefore the C content range for modifying the steel chemistry in the present invention is 0.05 to 0.3 wt%. If the C content is less than 0.05 wt, a sufficient austenite stabilization effect is not achieved, and a C content above 0.3 wt will make subsequent processing of the fabricated article, such as spot welding, difficult. Welding is an essential step in assembling automotive components to the body and is therefore a very important aspect to consider. C is also added to the steel in the present invention to increase strength. Aluminum is not an austenite-stabilizing element in steel; rather, it is a ferrite-stabilizing element. However, it is added to steel at 0.04–3% by weight to broaden the intercritical temperature range (from Ac1 to Ac3). With the high level of manganese (Mn), the steel becomes sensitive to small variations in processing temperature, and the resulting microstructure can change, leading to variable mechanical properties. The addition of aluminum ensures the robustness of the steelmaking process. 7 bQCn / 77n7 / q / YILI that the annealing and reheating temperatures of the steel can be selected with small variations to achieve the desired mechanical properties. When Al is not present, in addition to a minimum level required for steel deoxidation (i.e. < 0.04 wt%), more precise furnaces must be used, but the invention will still function. The maximum amount of Al is limited to 3 wt to reduce oxide scale formation during hot rolling and rolling forces during hot and cold rolling. To manufacture hot-rolled and / or cold-rolled steel strips, unique processing steps must be employed in this invention because steel contains relatively high amounts of alloying elements, particularly manganese (Mn). Manganese tends to segregate after melting when its content exceeds approximately 2% by weight. This will impair product performance, resulting in non-homogeneous properties and potentially leading to cracking. Therefore, it is necessary to thoroughly homogenize the molten slabs. This is achieved by subjecting the slabs to relatively high temperatures, above 1150°C, preferably above 1200°C, for a sufficiently long time, preferably 60 minutes or more. Therefore, due to the high alloy content, rolling forces are high during hot rolling of the strips. Hot rolling of steel is made possible by using hot rolling at a relatively high temperature within the austenitic temperature range. The finish rolling temperature (FRT) is maintained well above the Ar3 temperature, which is above 900°C, to keep the required hot rolling forces relatively low. Furthermore, when optional cold rolling is applied to hot-rolled strips to reduce the gauge of the final steel product, it will not be possible to cold roll the material unless appropriate preprocessing is undertaken. In particular, the coiled steel after hot rolling is subjected to batch annealing, preferably for 24 hours or more at a low temperature within the steel's intercritical temperature range. This batch annealing temperature should preferably be lower than 650°C, because at higher temperatures, large amounts of retained austenite will form after the steel cools to room temperature. High amounts of martensite may also appear in the microstructure if a high batch annealing temperature is used. Both martensite and retained austenite make cold rolling difficult by increasing the rolling strength.When the martensitic phase is hard, the retained austenite transforms into hard martensite during cold rolling, thereby increasing the rolling strength. Therefore, batch annealing of the coiled material is desirable to keep the retained austenite and martensite content lower and increase the amount of ferrite. The ferritic phase does not provide as high austenite work hardening during cold rolling as retained austenite and therefore keeps the rolling strength low, making cold rolling possible. Next, during steel processing, the invention requires the design of the continuous annealing process such that, during continuous annealing, the steel surface remains clean and free of oxides, making it suitable for the subsequent hot-dip galvanizing step. The continuous annealing and hot-dip galvanizing steps of the present invention are shown schematically on the left side of Figure 1. The challenge lies in the fact that, in addition to creating 7 bQCn / 77n7 / q / YILI A steel surface that is sensitive to good adhesion of Zn or Zn alloys, the continuous annealing treatment must also provide a steel substrate microstructure where sufficient partitioning of Mn and C between ferrite and austenite takes place, leading to a high fraction of austenite retained in the substrate before reheating during hot press forming. To achieve both requirements, the maximum soaking temperature, TMAX, during continuous annealing is kept lower than Ac3-100°C and 700°C. This temperature is within the intercritical temperature range of the steel optimized to achieve maximum partitioning of Mn to austenite. A temperature above 700°C, regardless of the chemistry of the steels of this invention, will lead to severe external selective oxidation of the steel surface.Sufficient distribution of Mn from ferrite to austenite is ensured by a soaking time of at least 150 s, preferably greater than 180 s. A short soaking time will not lead to sufficient Mn enrichment in the austenite to provide adequate thermal stability, since Mn is a relatively large substituent alloying element in steel and diffuses slowly. Carbon, on the other hand, being a small interstitial alloying element in steel, can diffuse faster than Mn. Therefore, the requirement for a minimum soaking time is primarily driven by the diffusivity of Mn rather than C. A heating rate in the range of 1 to 15°C / s above the soaking temperature is preferred.A slower heating rate for continuous annealing production is less economically attractive, and a faster rate will make the operation of the continuous annealing line extremely risky and therefore impractical. In addition to maintaining the low soaking temperature described above during continuous annealing, the annealing atmosphere must also be controlled to ensure the steel substrate surface is receptive to good adhesion of zinc or zinc alloys during hot-dip galvanizing. Therefore, the annealing atmosphere during heating the steel strip to the soaking temperature is kept oxidizing, typically with oxygen contents between 500 and 3000 ppm by weight. Due to this pre-oxidizing atmosphere, selective internal oxidation occurs, and a thin layer of wüstite forms. Then, during the soaking of the steel substrate at the annealing temperature, a reducing atmosphere is maintained, preferably containing 1 to 15% H₂ by volume. This reducing atmosphere during soaking reduces the wüstite.At the soaking temperature for this application, the diffusion rate of the alloying elements is low, and therefore the enrichment of the alloying elements is slow. An oxygen content below 500 ppm by weight during heating would allow the Mn and Si atoms to oxidize on the steel surface, eventually leading to poor wetting of the molten zinc. Conversely, an oxygen content above 3000 ppm by weight will cause excessive oxidation of Fe, leading to the formation of a thick FeO layer on the steel surface. This surface is not susceptible to the adhesion of Zn or Zn alloys. Furthermore, these FeO particles can be picked up by the rollers during the production process, resulting in numerous surface defects. After ensuring during continuous annealing that the surface of the steel substrate is free from enrichment of alloying elements as described above, the steel strip is immersed in a bath containing liquid Zn or Zn alloy maintained between temperatures of 420°C and 500°C. Below a bath temperature of 420°C, the Zn will remain solid, and above 500°C, 7 bQCn / 77n7 / q / YILI will result in excessive evaporation of the liquid Zn or Zn alloy. The typical temperature optimized for the liquid's viscosity and evaporation is in the range of 450-465°C. Furthermore, the immersion time of the steel strip in the liquid Zn or Zn alloy bath is also important. This duration is determined by the speed at which the steel strip passes through the continuous annealing line. The line speed in the continuous annealing installation should be adjusted to ensure a minimum immersion time of 3 seconds for the steel strip in the galvanizing bath. This additional 3 seconds is necessary to achieve good adhesion between the steel strip and the Zn or Zn alloy. The above hot-dip galvanizing conditions are applicable to a Zn bath containing essentially zinc, at least 0.1 wt% of Al and optionally up to 5 wt% of Al and up to 4 wt% of Mg, the remainder of the bath comprising additional elements, all individually in less than 0.3 wt%, and unavoidable impurities. Consequently, the invention is not limited solely to a pure Zn coating but is applicable to a wide range of Zn-based coating variations. The present invention relates to the hot press forming of a steel substrate, and its processing into a coated strip operates in tandem or cascade with the hot forming process, which is also part of the invention. The hot forming cycle is shown schematically on the right side of Figure 1. According to the invention, for hot press forming of the steel strip or part coated with Zn or Zn alloy, the substrate must be reheated to a low temperature in the intercritical temperature region of the specially designed steel substrate. The typical reheating temperature range, TRH, is from Ac3-300°C to 750°C, preferably 700°C. The selection of this temperature range is based on several considerations: - There is no need for complete austenitization; - The hot-formed components of this invention do not need to be sandblasted to remove Zn oxides before welding, as is done for conventionally hot-formed steels, since the zinc oxide present after heat treatment is still very thin. This reduces the manufacturing costs of the hot-formed parts by eliminating the cost of sandblasting and improving spot-weldability. The essential characteristics of the steel substrate microstructure of this invention do not change significantly during the hot press forming process. Therefore, the press temperature can be lower than in conventional hot press forming. In this way, the embrittlement of the metal by zinc can be minimized. When the formation of microcracks during hot forming is minimized, the product achieves high fatigue strength and durability. Due to the low reheating temperature above, the oxidation of the Zn or Zn alloy coating is also minimized and the metallic coating remains relatively thick, which gives good galvanic protection to the steel substrate in performance, thus increasing the corrosion resistance of the product; The aforementioned benefits due to the selection of a low reheating temperature during hot forming are related to the coating of Zn or Zn alloy onto the substrate of 7 bQCn / 77n7 / q / YILI steel. This selection of the reheating temperature of the part also contributes to the development of the correct microstructure in the steel substrate to achieve the desired mechanical properties and ultimately the mechanical performance. As described above, the substrate during the preceding continuous annealing step already formed a substantial amount of retained austenite due to the selection of the soaking temperature within the intercritical temperature range of the steel substrate. Intercritical reheating for hot forming adds to this by further facilitating the distribution of Mn and C in the austenite so that retained austenite with greater mechanical stability can be obtained in the hot-formed steel substrate.The reheating step will also create an additional amount of retained austenite due to the added opportunity for austenite-stabilizing elements to diffuse into the intercritical austenite. The reheated part is transferred to a forming tool for deformation, typically a press, where it is deformed into a desired shape. The transfer time is preferably within 30 seconds, more preferably within 10 to 15 seconds to avoid overcooling. After forming in the press, the article is cooled. Press quenching, which is essential in traditional hot forming, is not necessary in the present invention because the intercritical austenite with a high Mn content is very stable and, when partially transformed into martensite, has a very high hardenability, making press quenching at higher speeds unnecessary. The formed article can be removed from the press and allowed to cool in the ambient atmosphere. Forced air quenching or combined press quenching followed by (forced) air quenching is also possible. The reheated workpiece is transferred from the furnace or other heating equipment to the forming tool for deformation. Ideally, the transfer time should be short, preferably within 10 to 15 seconds. In an advantageous manner, the temperature drop of the steel workpiece during transfer does not exceed 150°C. Preferably, the temperature drop is in the range of 100–150°C. If the temperature drop is greater, the workpiece could be severely deformed in the subsequent forming step. Furthermore, the present invention allows the formed article to be removed from the hot forming press immediately after forming, for example, at an exit temperature in the range of 100-450°C, such as 200-425°C, because press tempering is not strictly necessary. In one embodiment, this cooling step is carried out in the press, advantageously at a temperature in the range of 100–250°C, preferably in the range of 150–200°C. A cooling rate of at least 3°C / s is suitable given the hardenability of the modified steel substrate. Even this relatively slow cooling rate will ensure that the austenite transforms back into martensite in the formed article. Advantageously, the quenching rate is at least 5°C / s. After removal from the press, the formed article is allowed to cool further at room temperature. The key to achieving the mechanical properties of the invention is the process chain described above, from the chemistry of the modified steel substrate to the unique microstructure in the final hot-formed condition. The chemistry of the modified steel in the process of the invention leads to 7 bQCn / 77n7 / q / YILI to at least 20% by volume of retained austenite and at least 30% by volume of ferrite, while martensite is 40% by volume or less, including 0% by volume. This relatively high fraction of retained austenite is metastable and gives the TRIP effect to achieve a superior combination of strength, elongation, and bending capacity, leading to high impact strength of the hot-dip galvanized or hot-formed zinc-alloy coated steel article. Even though retained austenite is relatively stable, its ductility is inherently higher than that of ferrite and martensite because the face-centered cubic (FCC) crystal structure gives high ductility values. The steel used in the method according to the invention is an inventive steel concept comprising carbon, manganese, and aluminum as its principal constituents. Optionally, other alloying elements selected from silicon, chromium, vanadium, niobium, titanium, and molybdenum may be present. Unavoidable impurities such as N, P, S, O, Cu, Ni, Sn, Sb, etc. (originating from the starting materials used to prepare the steel composition) may be present but in very low concentrations. They are not intentionally added or are specifically controlled within predetermined limits. The remainder of the steel composition is iron. Carbon is present in an amount of 0.05–0.3% by weight, preferably 0.05–0.25% by weight, and more preferably 0.08–0.2% by weight. It is added primarily for strength, although carbon also contributes to stabilizing the austenite. In the present composition, the austenite-stabilizing effect of manganese is much more pronounced due to its higher proportion. Too little carbon will not yield the desired strength level of 820 MPa or more, and preferably 1000 MPa or more. If the carbon content exceeds 0.3%, the weldability of the formed parts may be compromised. Manganese is present in an amount of 3.0–12.0 wt%. Manganese lowers Ac1 and Ac3 temperatures, stabilizes austenite, increases strength and toughness, and causes the TRIP effect by stabilizing the austenite microstructure at room temperature. At levels below 3.0 wt, the intended effects are not achieved, while amounts above 12.0 wt will cause casting and segregation problems. Also, the deformation mechanism would change from transformation-induced plasticity (TRIP) to twinning-induced plasticity (TWIP). If the Mn content is too low, insufficient austenite will be retained at room temperature, and the stability of the retained austenite will be too low, resulting in the ductility benefit not being obtained. Preferably, the Mn content is in the range of 3.5–10.5 wt. In one form, Mn reaches 5.0-9.0% by weight. In other forms, it is 5.5-8%.5% by weight, such as 6.0-7.5% by weight. Aluminum can be added to expand the Ac1-Ac3 temperature range to increase the robustness of the process for industrial applications. The Al is present in an amount of 0.04-3.0% by weight, preferably 0.5-2.5%, and most preferably in the range of 1.0-2.2%. Silicon, if present, is added in an amount less than 1.5 wt% to increase strength through solid solution strengthening. If present, the amount is typically greater than 0.01 wt% and less than 1.5 wt%, with a preferred range of 0.1–1.0 wt%. Aluminum and silicon help suppress cementite precipitation, preventing ductility deterioration. Furthermore, both aluminum and silicon increase the peak annealing temperature, maximizing the amount of retained austenite at room temperature. Therefore, intercritical annealing is facilitated. 7 bQCn / 77n7 / q / YILI the diffusion of Mn to have an effective Mn distribution in austenite. Optionally, one or more additional microalloying elements, selected from the group of V, Nb, Ti, and Mo, are present. These microalloying elements increase strength through precipitation hardening by their carbides, nitrides, or carbonitrides. Cr, another optional element of this invention, also increases the peak annealing temperature to achieve the highest amount of retained austenite at room temperature and reduces the sensitivity of the retained austenite content at room temperature. This results in the effective distribution of Mn in the austenite and increases the robustness of the process during annealing. If present, the preferred additions of these optional alloying elements are: V: 0.01–0.1 wt.%; and / or Nb: 0.01–0.1 wt.%; and / or Ti: 0.01–0.1 wt.%; and / or Mo: 0.05–0.5 wt.%; and / or Cr: 0.1-2.0% by weight. The composition of the zinc or zinc alloy coating is not limited. Hot-dip coating may be carried out using a standard Gl coating bath, where Gl stands for “normal galvanizing, i.e., hot-dip coating using a bath containing primarily zinc.” Various Zn coating baths may be used, such as zinc baths containing essentially zinc, at least 0.1 wt% Al and optionally up to 5 wt% Al and optionally up to 4 wt% Mg, the remainder of the bath comprising additional elements, all individually in less than 0.3 wt%, and unavoidable impurities. A zinc alloy coating layer may be made comprising 0.3–4.0 wt% Mg and 0.05–6.0 wt% Al and optionally at most 0.2 wt% of one or more additional elements along with unavoidable impurities, the remainder being zinc. The additional elements that may be present in a small amount of less than 0.3% by weight, for example, to form flake and / or prevent slag formation, could be selected from the group comprising Pb, Sb, Ti, Ca, Mn, Sn, La, Ce, Cr, Ni, Zr, and B1. Small amounts of these additional elements do not alter the properties of the bath or the resulting coating to any significant degree for usual applications. Preferably, when one or more additional elements are present in the coating, each is present in an amount < 0.02% by weight, preferably each is present in an amount < 0.01% by weight. The hot-pressed steel article coated with zinc or zinc alloy by hot-dip has a triple or double microstructure comprising (in % by volume): ferrite: 30% or more, preferably 40% or more; Retained austenite: 20% or more, preferably 30% or more; martensite: 40% or less including 0%, preferably 30% or less including 0%. Advantageously, the resulting article has the following properties: yield strength: 800 MPa or more; preferably 850 MPa or more, more preferably 900 MPa or more; tensile strength: 820 MPa or more; preferably 1000 MPa or more; total elongation: 10% or more; preferably 15% or more, more preferably 25% or more; minimum bend angle at a thickness of 1.0 mm: 80° or more; preferably 90° or more. The phase fractions mentioned above were determined using X-ray diffraction (XRD). The amount of retained austenite was determined by XRD as a percentage of the sample thickness. XRD patterns were recorded in the 45–165° (2Θ) range using a standard Panalytical Xpert PRO powder diffractometer (CoKa radiation). Quantitative determination of phase proportions was performed by Rietveld analysis using the Bruker Topas software package for Rietveld refinement. Martensite content was determined from peak splitting at ferrite diffraction sites in the diffractograms. Phase grain size can be determined from scanning electron microscopy images of the microstructure. Yield strength, ultimate tensile strength, and total elongation were determined from near-static tensile tests (strain rate 3 x 10⁻⁴ s⁻¹) at room temperature according to NEN 10002. The tensile specimen geometry consisted of a gauge length of 50 mm in the rolling direction, 20 mm in width, and a nominal thickness of 1.5 mm. Bendability was determined by three-point bend tests following VDA 238-100 on nominally 1.5 mm thick, 40 mm x 30 mm specimens in both the longitudinal and transverse directions. The bend axis was along the 30 mm dimension, and the bend radius was 0.4 mm. The bend angles obtained from the nominally 1.5 mm specimens were converted to angles corresponding to a thickness of 1.0 mm using the following formula: bend angle at a thickness of 1.0 mm = measured angle x square root of the actual thickness in mm.From those converted bend angles, for a specific heat treatment condition, the lowest value of the length and cross-section specimens was taken to claim the intervals in this invention. Using a continuous intercritical annealing step in the steel strip manufacturing process, as explained previously, before reheating the strip cuts, Mn partitioning occurs from ferrite to austenite, making the intercritical austenite even more stable. During cooling after intercritical annealing through hot-dip galvanizing, the intercritical austenite does not significantly transform into martensite due to its high stability and low Ms content (i.e., high thermal stability), resulting in a triple (ferrite + retained austenite + martensite) or duplex (ferrite + retained austenite) structure. For high Mn contents, for example, greater than 10.5 wt%, a completely duplex structure can be obtained, while for Mn contents below 10.5 wt%, a triple structure forms.Furthermore, the increased Mn levels ensure a low reheating temperature (Trh) (e.g., less than 700°C) and a high amount of retained austenite (20% by volume or more). This high amount of retained austenite completely or partially transforms the martensite during deformation, causing a transformation-induced plasticity (TRIP) effect that results in a high strain hardening rate (= high elongation and high strength). When steel strip is intercritically annealed (using a continuous annealing process step) below 700°C, the strip exhibits high strength and ductility due to the presence of a high amount of retained austenite. During reheating for hot forming, also within the intercritical temperature range, below 750°C or preferably below 700°C, additional Mn redistribution can occur, further stabilizing the austenite. However, some Mn redistribution can occur when the annealing and reheating temperatures differ. This can, in some cases, lead to a slightly lower amount of retained austenite after hot forming compared to after continuous annealing and galvanizing. 7 bQCn / 77n7 / q / YILI by hot-dip quenching. However, a high amount of retained austenite (>20% by volume) is still obtained for the invention to function. Martensite, if present, can be slightly quenched, but this phenomenon will contribute to even higher elongation values. The residual elongation (or in-service ductility) of the article is preferably 25% or more due to the steel composition and the strip annealing and part reheating steps. An intercritical annealing step, as well as the intercritical reheating step of a medium-manganese approach, is preferably used to obtain a mixed microstructure of ultrafine ferrite (0.5–2.0 µm) and areas of martensite and retained high austenite. Therefore, high ductility is achieved in the final product. A hot-pressed steel article coated with zinc or hot-dip zinc alloy is a preferred automotive component, such as a front / rear longitudinal bar or bumper beams, particularly those requiring high energy absorption combined with high strength. Non-limiting examples include B-pillars and structural chassis parts. The invention will be clarified with reference to the examples described below. BRIEF DESCRIPTION OF THE FIGURES Reference is made to the Figures in which: Figure 1 shows a schematic of the continuous annealing and hot-dip galvanizing cycles and the subsequent hot forming cycle. Figures 2a and 2b show the sampling of the investigation of the microcracks after hot forming (Figure 2a) an Ω-shaped profile (Figure 2b) the schematic location. DETAILED DESCRIPTION OF THE INVENTION Ingots of the steels of the three chemistries of the invention A, B, and C, measuring 200 mm x 100 mm x 100 mm, were cast by melting the charges in a vacuum induction furnace. The chemical compositions of these steels are provided in Table 1, along with the conventional 22MnB5 steel grade, which is commonly used for hot forming. The 22MnB5 grade was received in the G1 coated condition to a thickness of 1.5 mm and was further processed for comparison purposes. The ingots of the steels of the invention A, B, and C were reheated for 2 hours at 1250°C and as-rolled to a thickness of 25 mm. The strips were then reheated to 1250°C for 30 minutes and hot rolled to a thickness of 3 mm with a finish rolling temperature (FRT) of 900°C, which is in the austenitic phase range for all three steels.The austenite-to-ferrite transformation temperature during cooling (Ar3) for steels A, B, and C, measured by dilatometry, was 798, 805, and 725°C, respectively. The hot-rolled steels underwent coil quenching simulations from 680°C in a muffle furnace and were thus cooled to room temperature. The hot-rolled strips were then annealed for 96 hours at 600°C in a muffle furnace under a protective atmosphere and cooled air. The strips were pickled in HCl to remove oxides at 90°C and cold-rolled to a thickness of 1.5 mm using multiple passes. The cold-rolled A steel strips were subjected to continuous annealing at 675°C for 5 minutes, while the B and C steels were annealed at 650°C for 5 minutes. All the steel strips were then directly immersed in a galvanizing bath (hot-dip galvanizing) comprising a Zn alloy containing mainly Zn and 0.4 wt% Al. The dimensions of the strips were 7 bQCn / 77n7 / q / YILI 200 mm x 105 mm x 1.5 mm. The bath temperature was maintained at 465°C, and an immersion time of 5 seconds was used. The strips were then cooled to room temperature at 5°C / s, which is similar to air cooling. These continuous annealing and hot-dip galvanizing simulations were performed in a hot-dip annealing simulator. The atmosphere during the soaking portion of the continuous annealing cycle was set to NH5 gas with a dew point of -30°C and 5% H2 gas by volume. During heating (i.e., the initial portion of continuous annealing), the atmosphere was varied with an air-to-fuel ratio (λ) of 0.98, 1.005, 1.01, and 1.02, with a fixed dew point of 20°C. It should be mentioned that when λ > 1, the atmosphere is considered to be oxidizing and when λ < 1, it is considered to be reducing.A schematic of the continuous annealing and hot-dip galvanizing cycle is shown in Figure 1, along with the subsequent hot press forming operation and the oxygen content in the annealing atmosphere during the heating part of the continuous annealing for different values ​​of λ are summarized in Table 2. The Zn-coated strips were then hot-formed in a hot-forming press supplied by SMG GmbH & Co. KG using the thermal cycles shown in Table 4. The thermal cycles are also shown schematically on the right side of Figure 1. Two types of forming tool were used: a flat tool for obtaining specimens for tensile, bending, contact strength, corrosion, and microstructure testing, and a top-hat tool for obtaining omega-shaped profiles for microcrack investigation (Figure 2a). Additional reheating time-temperature combinations were used for contact strength and corrosion measurements, which are provided in Table 10 and Table 11, respectively. Galvanized strips measuring 30 mm x 200 mm (roll direction x cross direction) were subjected to a Zn adhesion test used in the automotive industry. In this test, Betamate 1496V cement (at least 150 mm long, 4–5 mm thick, and at least 10 mm wide) was applied to the center of the strips on both sides. The cement was then cured in an oven at 175°C for 30 minutes. The samples were then held firmly with the cement side facing outwards and bent at a moderate speed to a 90° angle with a bend radius of 1.1 mm. The samples were then visually inspected and assigned a code describing the Zn delamination status. Tensile tests were performed according to NEN10002 at a near-static strain rate of 3 x 10⁻⁵ s⁻¹. Tensile specimens with a gauge length of 50 mm in the rolling direction and a width of 20 mm were used. Three-point bend tests were performed according to VDA 238-100 on 40 mm x 30 mm x 1.5 mm specimens in both the longitudinal and transverse directions using a bend radius of 0.4 mm (punch radius). Bend angles were converted to a sheet thickness of 1.0 mm using the formula described above. The following are the abbreviations and symbols used in the tables to present the tensile and bend test results. Rp = yield strength, Rm = ultimate tensile strength, Ag = uniform elongation, Aso = total elongation with a gauge length of 50. BA = bend angle, L = longitudinal specimen where the bend axis is parallel to the rolling direction, T = transverse specimen where the bend axis is perpendicular to the rolling direction. 71?QCn / 77n7 / 3 / YILI The amount of retained austenite was determined by X-ray diffraction (XRD) at a percentage of the sample thickness. XRD patterns were recorded in the 45–165° (2Θ) range on a standard Panalytical Xpert PRO power diffractometer (CoKa radiation). Quantitative determination of phase proportions was performed by Rietveld analysis using the Bruker Topas software package for Rietveld refining. Martensite content was determined from peak divisions at ferrite diffraction sites in the diffractograms. Hot-formed omega-shaped profiles were investigated for microcracks. The dimensions of the omega profiles, as well as the microcrack investigation scheme, are shown in Figures 2a and 2b. From the Ω profiles, 1 cm wide sections were cut along the height, and the specimens were investigated for microcracks in cross-sections of the coated steels using a light microscope at 1000X magnification. A length of approximately 1 cm from the mid-height toward the base of the profiles was examined for this purpose. The contact strength of hot-formed parts of steels B and D was measured for a wide range of time and temperature combinations (given in Table 10) according to ISO 18594 without sandblasting to obtain an indication of the weldability of the hot-formed material. Under the same reheating conditions, the corrosion resistance of the coated steels was also determined without sandblasting. Corrosion testing of hot-formed steels B and D was carried out according to VDA 621-415. Each part was phosphated and electro-coated, followed by etching. Parallel wide and narrow marks (1 mm and 0.3 mm wide and 100 mm long) were made on the specimens in the longitudinal direction. A distance of 30 mm was maintained between the two types of marks and a distance of 35 mm from the edge of the specimen.A 5% by volume solution of NaCl + 10 g of NaHCO3 in 150 liters of H2O was used as the corrosion medium. The formation of red rust (Zn oxides) on the marks was monitored for several weeks, and the percentage of mark length covered with red rust was taken as a measure of corrosion. For both corrosion resistance and contact resistance measurements, an unheated 22MnB5 steel specimen was also included for comparison. The results of the zinc alloy coating adhesion test are provided in Table 3. The result where the coating remained intact after the test is indicated by “P” (pass), and the result where the coating delamined during the test is denoted by “F” (fail). It can be observed that when λ was 0.98, i.e., no oxygen present in the heating section during continuous annealing (see Table 2), the coating delamined during the tests for all three steels A, B, and C. On the other hand, when the λ value was 1.005 and 1.01, corresponding to oxygen content in the heating section of 800 and 1700 ppm by weight, respectively, all three coated steels passed the coating adhesion tests. However, when the value of λ was 1.02 (= oxygen content of 3700 ppm by weight in the continuous annealing heating section), the coating delamined during testing on all three steels.These results show that an optimal amount of oxygen is necessary during the continuous annealing heating of the steel strips of the invention to ensure good coating adhesion to the steel surfaces. In the case of no oxygen present (λ = 0.98), selective oxidation of Mn occurs on the steel surface, preventing its reduction back to metallic Mn. Consequently, the substrate surface is not susceptible to the adhesion of Zn or Zn alloys during hot dipping. However, when excessive oxygen is present at 3700 ppm by weight (λ = 1.02), many Fe oxides form a thick FeO layer on the steel surface. This surface is not susceptible to the adhesion of Zn or Zn alloys. Furthermore, these FeO particles can be picked up on the rollers during the production process, resulting in numerous surface defects.The tensile properties of the steels in their hot-dip galvanized condition, i.e., before hot forming, are provided in Table 5, and the corresponding steel substrate microstructures are shown in Table 6, along with those of the Gl 22MnB5 grade (D steel) as received. Due to the use of intercritical annealing temperatures for soaking during continuous annealing, high fractions of retained austenite were obtained in all three steels of the invention, along with the desired amounts of ferrite and small amounts of martensite (Table 6). This was made possible by the enrichment of the intercritical austenite with Mn and C during annealing, which increased the thermal stability of the austenite by lowering its Ms temperature.Conversely, the 22MnB5 grade, which was not modified by any chemical composition of the invention and non-continuously annealed according to the goal of austenite stabilization, has a ferritic-pearlitic microstructure, containing no retained austenite. The effects of the specific microstructures obtained in the steels of the invention A, B, and C are reflected in their mechanical properties (Table 5). These steels have much higher yield strength and tensile strength values, along with good total elongation due to the improved strain hardening rate achieved from the retained austenite TRIP effect. This benefit is also reflected in the higher Rm x A50 values ​​of the steels of the invention, which are indicators of the steels' high energy absorption capacity. The mechanical properties after hot press forming and the corresponding microstructural components of all these steels are presented in Table 7 and Table 8, respectively. It is observed that in the steels of the invention, under all reheating conditions, more than 30% by volume of retained austenite was achieved in their microstructures due to the partitioning of Mn (and C) in the austenite during intercritical reheating. In steel B, with increasing reheating time, the retained austenite content increased for any particular reheating temperature due to a greater partitioning of Mn in the austenite. Generally, with the highest reheating temperature, the retained austenite content decreased slightly due to the lower partitioning of Mn in the austenite (which can also be shown by ThermoCalc calculations).In general, the retained austenite content in steels A, B, and C is similar to or slightly higher after hot forming than before (Table 6 and Table 8). Therefore, it might seem obvious that little benefit occurred due to the additional Mn partitioning during hot forming. However, this is not the case, as will be clarified by comparing the corresponding total elongation, tensile strength, and the product of total elongation and tensile strength (Table 5 and Table 7) shortly. In contrast to the >30% by volume of retained austenite in the steels of the invention, the conventional 22MnB5 grade produced a predominantly martensitic microstructure (98.3% by volume) after hot forming. The ferrite fractions in the steels of the invention... 7 bQCn / 77n7 / q / YILI invention are greater than 40% by volume and the martensite fractions are less than 20% by volume. As a result of the desired microstructures formed in the steels of the invention, attractive mechanical properties were obtained (Table 7). More than 20% total elongation, yield strength greater than 800 MPa, and ultimate tensile strength greater than 950 MPa were achieved in the steels of the invention. The steels containing more Mn (steel C) also achieved higher ultimate tensile strength and total elongation values ​​than the steels containing less Mn (steels A and B) due to the greater amount of retained austenite. The energy absorption values ​​(Rm x A50 values) in the steels of the invention after hot forming are also unusually high. The conventional 22MnB5 grade, which achieved a tensile strength above 1500 MPa due to poor total elongation, has a much lower energy absorption capacity. The energy absorption capacities of the steels of the invention under all reheating conditions are at least 2.5 times greater than those of grade 22MnB5. Also, the bend angles at a thickness of 1.0 mm of the hot-formed steels of the invention are much greater than those of 22MnB5. Steels A, B, and C achieved minimum bend angles above 100°. As mentioned, these spectacular mechanical properties of the steels of the invention are due to the high fractions of austenitic phase retained in their microstructures, which provides high work hardening due to the TRIP effect. The additional Mn enrichment in the austenite during reheating is reflected in the higher energy absorption values ​​of the hot-formed steels of the invention compared to hot-dip galvanized steels. The results of the microcrack investigation are provided in Table 9. Microcracks were present in small numbers and of short length after hot forming the steels of the invention at low temperatures. However, the Gl 22MnB5 grade, conventionally hot formed at a higher temperature, showed a greater number of longer microcracks on its surface. This minimization of microcracks in the steels of the invention is due to the low reheating and hot forming temperature, which minimizes the diffusion and penetration of zinc into the grain boundaries of the steel, preventing embrittlement of the metal during hot forming. However, for 22MnB5, due to the use of higher temperatures, the same benefits are not obtained. The results of the contact strength measurements are provided in Table 10. It can be seen that when the reheating temperature of a steel of the invention (steel B) is up to 700°C for various soaking times of up to 15 minutes, the contact strength values ​​are low, comparable to those of Gl 22MnB5 (steel D) as immersed and much lower than those of Gl 22MnB5 reheated to higher temperatures (800-900°C). It should be mentioned that Gl 22MnB5 as immersed is weldable, and therefore the low contact strength values ​​of the steels of the invention after hot forming suggest that this steel is also weldable. However, the contact strength value of steel B increases upon reheating to 800°C, indicating oxidation of the Zn or Zn alloy coating.This will affect the spot welding capability of the hot-formed components and therefore the welding capability from the point of view of the reheating temperature should be limited to 700°C or less. 71?QCn / 77n7 / 3 / YILI Similar corrosion trends were observed, as shown in Table 11. Red rust formation increased slowly with reheating temperature in steel B up to 700°C and then increased sharply at a reheating temperature of 800°C. Up to 700°C, the percentage of red rust is low, slightly higher than the percentage of red rust in Gl 22MnB5 as dipped, indicating good corrosion resistance of the hot-formed product. The corrosion resistance is much higher than that of Gl 22MnB5 (steel D) when hot-formed at 900°C. Therefore, these results suggest that the steel of the invention has greater corrosion resistance due to its Zn or Zn alloy coating when the reheating temperature is limited to 700°C.Severe oxidation of the Zn-based coating at 800°C causes a significant decrease in corrosion resistance. 7 bQCn / 77n7 / q / YILI Table 1: Steel composition in % by weight Steel C Mn Si Al PSB Cr Mo Ni Cu A 0.155 7.4 0.20 1.99 0.0012 0.0015 0.0001 0.004 0.001 0.004 0.03 B 0.13 6.9 0.20 2.02 0.0010 0.0018 0.0002 0.004 0.001 0.002 0.03 C 0.14 10.1 0.18 1.7 0.00010 0.004 0.0001 0.024 0.001 0.014 0.02 D 0.23 1.24 0.02 0.03 0.002 0.0008 0.003 0.01 0.001 0.001 0.03 Table 1 (Continued) Steel continued Nb Ti VWN Sn Co Fe Observation A 0.0009 0.001 0.0015 0.002 0.006 0.0010 0.001 Remainder Invention B 0.0008 0.001 0.0013 0.001 0.004 0.0008 0.001 Remainder Invention C 0.0005 0.002 0.0014 0.001 0.006 0.0007 0.001 Remainder Invention D 0.0007 0.001 0.0015 0.001 0.005 0.0007 0.0002 Remainder Reference Table 2: Annealing atmospheres used for steels A, B and C Heating Section Soaking Section λ Value Oxygen Content (ppm) Dew Point (°C) Hydrogen Content (% by volume) Dew Point (°C) 0.98 0 20 5 -30 1.005 800 20 5 -30 1.01 1700 20 5 -30 1.02 3700 20 5 -30 Table 3: Zn adhesion test results (F = fail, P = pass) Value of λ in the Heating Section Steel A Steel B Steel C 0.98 FFF 1.005 PPP 1.01 PPP 1.02 FFF Table 4: Reheating time and temperatures Steel Reheating Temperature (°C) Reheating Time (s) A 650 180 B 530 300 530 900 620 300 620 900 675 300 675 900 C 650 300 700 300 D 900 300 71?QCn / 77n7 / 3 / YILI Table 5: Mechanical properties of Zn-coated parts before hot forming Steel Annealing Temperature (°C) RP (MPa) Rm (MPa) Ag (%) Aso (%) Rm X A50 (% in MPa) A 650 939 959 20.1 23.4 22440.6 B 675 970 997 9.5 15.1 15054.7 C 650 1065 1166 13.5 14.3 16673.8 D 750 380 661 15.1 19.8 13087.8 Table 6: Microstructural components of the Zn-coated parts before hot forming Steel Austenite Retained (% by volume) Ferrite (% by volume) Martensite (% by volume) Pearlite (% by volume) A 38.3 44.9 16.8 0 B 35.2 51.3 14.5 0 C 52.1 43.1 4.8 0 D 0 62.9 0 37.1 Table 7: Mechanical properties of steel after hot press forming Steel Reheating Temperature (°C) Reheating Time (s) Rp (MPa) Rm (MPa) Ag (%) Aso (%) Rm X Aso (% in MPa) BA-L @ 1 mm thickness (°) BA-T @ 1 mm thickness (°) A 675 180 868 979 23.5 25.5 24964.5 105 129 B 530 300 905 1021 22.7 24.1 24606.1 117 137 900 889 1015 23.5 25.7 26085.5 129 145 620 300 873 1003 21.9 24.3 24372.9 111 125 900 867 1007 23.9 25.3 25477.1 124 151 675 300 906 1025 22.3 23.9 24497.5 107 126 900 901 1032 21.8 24.3 25077.6 123 141 C 650 300 1050 1150 42.1 45.3 52095 106 115 700 300 810 1373 25.1 27.2 37345.6 100 117 D 900 300 988 1550 3.9 6.1 9455 73 79 Table 8: Microstructural components of steels after hot forming Steel Reheating Temperature (°C) Reheating Time (s) Retained Austenite (% by volume) Ferrite (% by volume) Martensite (% by volume) A 675 180 37.1 45.3 13.6 B 530 300 34.2 53.1 12.7 900 36.9 52.9 10.2 620 300 32.5 54.1 13.4 900 35.0 53.9 11.1 675 300 30.1 52.8 17.1 900 33.3 51.5 15.2 C 650 300 53.1 45.3 1.6 700 300 49.3 44.6 6.1 D 900 300 0 1.7 98.3 7 bQCn / 77n7 / q / YILI Table 9: Results of microcrack analysis after hot forming Steel Reheating Temperature (°C) Reheating Time (s) Number of Cracks Maximum Crack Length (pm) A 675 180 0 NA B 530 300 0 NA 900 0 NA 620 300 0 NA 900 2 3.0 675 300 1 2.8 900 5 4.6 C 650 300 0 NA 700 300 0 NA D 900 300 30 27.1 Table 10: Contact resistance results Steel Reheating Temperature (°C) Reheating Time (s) Resistance (mΩ) B 400 600 0.112 500 240 0.122 360 0.095 480 0.087 530 300 0.086 900 0.087 600 180 0.094 300 0.084 420 0.121 620 300 0.091 900 0.090 675 300 0.093 900 0.093 700 180 0.161 300 0.164 420 0.179 800 180 0.475 300 1.861 420 2.987 D 900 180 3.102 20 No overheating 0.125 7 bQCn / 77n7 / q / YILI Table 11: Corrosion test results after 1 week of testing Steel Reheating Temperature (°C) Reheating Time (s) Red Rust (%) B 400 600 25 500 240 25 360 25 480 25 530 300 30 900 35 600 180 40 300 40 420 40 620 300 40 900 40 675 300 45 900 45 700 180 45 300 45 420 45 800 180 100 300 95 420 98 D 900 180 95 20 No reheating 25

Claims

1. A method of hot-pressing a steel article from a zinc-coated or zinc-alloy steel strip, wherein the steel strip has the following composition by weight percent: C: 0.05-0.3; Mn: 3.0-12.0; Al: 0.04-3.0; optionally one or more additional alloying elements: Si: less than 1.5; Cr: less than 2.0; V: less than 0.1; Nb: less than 0.1; Ti: less than 0.1; Mo: less than 0.5; unavoidable impurities, such as S: less than 30 ppm by weight; P: less than 0.04; the remainder being Fe; the method of manufacturing the steel strip is characterized in that it comprises the steps of: - molding the molten steel into a plate; - reheat the iron to a temperature above 1150°C and maintain it at that temperature for 60 minutes or more;- hot-roll the steel into a strip, preferably with a finishing exit hot-rolling temperature (FRT) higher than the Ar3 temperature, where Ar3 denotes the temperature at which ferrite transformation begins in the steel during cooling; - coil the hot-rolled steel strip; - pickle the hot-rolled steel strip;- continuously annealing the strip according to an annealing thermal cycle where the temperature of the steel strip is preferably rising at a rate of 1-15°C / s in the heating section, then remains at a relatively stable level for soaking in the soaking section where a soaking atmosphere is maintained, at a temperature between TMIN and TMAX where TMIN = TMAX-100°C, where the continuous annealing is considered to end at the point in the heating cycle where the temperature of the steel strip falls, preferably at a rate of 0.5-10°C / s: - where TMAX is equal to or less than the lower of Ac3-100°C and 700°C; - where the soaking atmosphere has a dew point of -40 to -10°C; - wherein continuous annealing comprises in the heating section pre-oxidizing the steel strip in an annealing atmosphere having an oxygen content of 500 to 3000 ppm by volume;7 71?QCn / 77n7 / 3 / YILI - wherein the soaking atmosphere is a reducing atmosphere, preferably containing between 115% by volume of Hydrogen and Nitrogen; - wherein the continuous annealing time, which consists of the time in the heating section plus the time in the soaking section, is 150 seconds or more, preferably 180 seconds or more; - hot-dip coating the steel strip with zinc or zinc alloy while: - using an immersion time of 3 seconds or more; - maintaining it in the hot-dip bath at a bath temperature of 420°C to 500°C; - wherein the zinc bath contains essentially zinc, at least 0.1% by weight of Al and optionally up to 5% by weight of Al and optionally up to 4% by weight of Mg, the remainder of the bath comprising additional elements, all individually in less than 0.3% by weight, and unavoidable impurities;- forming the article in a hot press, comprising the steps of: - providing a piece taken from the steel strip coated with zinc or zinc alloy by hot dipping; - reheating the piece to a part temperature (RTH) in the range of Ac3-300°C to 750°C; - immersing the piece at RTH for a period of more than 3 minutes and up to 15 minutes; - transferring the piece to the press within 30 seconds; - forming the article in the press, thereby cooling the article; - removing the article from the press.

2. The method according to claim 1, further characterized in that it additionally comprises, between the pickling and annealing steps, cold rolling the pickled hot-rolled steel strip into a cold-rolled steel strip, wherein in the case of cold rolling, the hot-rolled strip after cooling and pickling is subjected to batch annealing at a temperature TB for a period PB, TB and PB being chosen such that the steel has a microstructure exhibiting more than 60% by volume of ferrite after cooling to room temperature, wherein in a preferred embodiment TB and PB are chosen such that TB is 650°C or lower and PB is 24 hours or longer.

3. The method according to claim 1 or 2, further characterized in that the Mn content is 6.0% by weight or more.

4. The method according to any of claims 1 to 3, further characterized in that the iron is reheated to a temperature above 1200°C, preferably 1250°C and is maintained at that temperature for a time of 60 minutes or more.

5. The method in accordance with any of claims 1 to 4, further characterized in that the iron is reheated to a temperature and maintained at the same temperature for a period of time of 120 minutes or more.

6. The method according to any of claims 1 to 5, further characterized in that TRH is in the range of Ac3-300°C to 700°C. 7 71?QCn / 77n7 / 3 / YILI 7. The method in accordance with any of claims 1 to 6, further characterized in that the transfer of the part to the press is within 10-15 seconds.

8. A hot-pressed steel article coated with zinc or zinc alloy by hot-dip, obtainable by the method as claimed in any of claims 1 to 6, characterized in that it has a microstructure comprising by volume % ferrite: 30% or more, preferably 40% or more; retained austenite: 20% or more, preferably 30% or more; martensite: 40% or less, preferably 30% or less, including 0%.

9. The hot-pressed steel article coated with zinc or zinc alloy by hot-dip according to claim 8, further characterized in that the microstructure comprises ferrite in an amount of 40% or more.

10. The hot-pressed steel article coated with zinc or zinc alloy by hot-dip according to claim 8 or claim 9, further characterized in that the microstructure comprises retained austenite in an amount of 30% or more.

11. The hot-pressed steel article coated with zinc or zinc alloy by hot-dip in accordance with any of claims 8 to 10, further characterized in that it has the following properties: yield strength: 800 MPa or more, preferably 850 MPa or more, more preferably 900 MPa or more; tensile strength: 820 MPa or more, preferably 1000 MPa or more; total elongation: 10% or more, preferably 15% or more, more preferably 25% or more; minimum bend angle with a thickness of 1.0 mm: 80° or more, more preferably 90° or more.

12. The hot-pressed steel article coated with zinc or zinc alloy by hot-dip in accordance with any of claims 8 to 11, further characterized in that it comprises a steel substrate provided with a hot-dip coated layer, wherein the length of any microcrack in the steel substrate is 5 pm or smaller.