Hot-rolled steel sheet and its production method

Abstract

FIELD: metallurgy.SUBSTANCE: hot-rolled steel sheet used as a material for the manufacture of industrial machine parts, green and yellow goods. The sheet has a composition that includes the following elements, wt.%: 0.02 ≤ carbon ≤ 0.2, 3 ≤ manganese ≤ 9, 0.2 ≤ silicon ≤ 1.2, 0.9 ≤ aluminum ≤ 2.5, phosphorus ≤ 0.03, sulfur ≤ 0.03, nitrogen ≤ 0.025, titanium ≤ 0.1, 0.0001 ≤ boron ≤ 0.01, the rest is iron and inevitable impurities that appear as a result of processing. The microstructure of the steel sheet comprises, as a fraction of area, at least 60% tempered martensite, 15% to 40% retained austenite, and optionally contains up to 10% polygonal ferrite and up to 5% niobium, titanium, vanadium, or iron carbides.EFFECT: sheet has a yield strength of 650 MPa or more, a tensile strength of 750 MPa or more, a total elongation of 15% or more, and an impact strength of 70 J / cm2 or more measured at –40 °C.14 cl, 4 tbl

Description

[0001] The present invention relates to a hot-rolled steel sheet suitable for use as structural steel or steel for industrial machinery, yellow and green goods, and cryogenic applications.

[0002] In recent years, significant efforts have been made to reduce the weight of equipment and structures by using high-strength steel to improve fuel efficiency and reduce environmental impact. However, as steel strength increases, its toughness typically decreases. Given this, a key challenge in developing high-strength steel is to increase strength without sacrificing toughness.

[0003] Intensive research and development efforts are being made to reduce the amount of material used by increasing its strength. Increasing the strength of steel, however, reduces its toughness, necessitating the development of materials with both high strength and good toughness.

[0004] Earlier research and development in the field of high-strength steel with proper toughness have led to the development of several methods for producing high-strength steel, some of which are given herein for a reasonable evaluation of the present invention:

[0005] Document EP 2392681 discloses a thick-walled high-strength hot-rolled steel sheet having a composition that comprises, in mass %, 0.02 to 0.08% C; 1.0% or less Si; 0.50 to 1.85% Mn; 0.03% or less P; 0.005% or less S; 0.1% or less Al; 0.03 to 0.10% Nb; 0.001 to 0.05% Ti; 0.0005% or less B, optionally, one or two or more kinds of components selected from the group consisting of 0.010% or less Ca; 0.02% or less REE; 0.003% or less Mg; 0.5% or less V; 1.0% or less Mo; 1.0% or less Cr; 4.0% or less Ni; 2.0% or less Cu, other unavoidable impurities and the balance Fe.The steel sheet has a structure formed by a bainitic-ferrite phase or a bainitic phase in which the content of C as a solid solution component in the ferrite grains is 10 ppm or more and the hardness of the surface layer is 230HV or less in Vickers hardness units, but the steel of EP 2392681 is not capable of achieving a tensile strength of 700 MPa or more.

[0006] Document EP 2971211 discloses a method for producing a high-manganese steel component comprising a composition consisting of manganese in an amount in the range of from about 9 to about 20 wt. %, based on the total weight of the composition; carbon in an amount in the range of from about 0.5 to about 2.0 wt. %, based on the total weight of the composition, and the balance iron; and optionally chromium in an amount of from 0.5 to 30 wt. %, based on the total weight of the composition; nickel or cobalt in an amount of from 0.5 to 20 wt. %, based on the total weight of the composition; aluminum in an amount of from 0.2 to 15 wt. %, based on the total weight of the composition; molybdenum, niobium, copper, titanium or vanadium in an amount of from 0.01 to 10 wt. % based on the total weight of the composition; silicon in an amount of 0.1 to 10 wt. % based on the total weight of the composition; nitrogen in an amount of 0.001 to 3.0 wt. % based on the total weight of the composition; boron in an amount of 0.001 to 0.1 wt.% based on the total weight of the composition; or zirconium or hafnium in an amount of from 0.2 to 6 wt. % based on the total weight of the composition; wherein the method comprises heating the composition to at least about 1000°C; cooling the composition at a rate of from about 2°C per second to about 60°C per second, followed by hot rolling the composition at a temperature in the range of from about 700°C to about 1000°C; slowly cooling or isothermally holding the composition; and quenching, or accelerated cooling or air cooling the composition from a temperature in the range of from 700°C to about 1000°C until a temperature in the range of from 0°C to about 500°C is reached at a rate of at least about 10°C per second. However, when using the method of document EP 2971211, it is not possible to achieve an impact strength of 60 J / cm. 2 or more, measured at -40°C.

[0007] The purpose of the present invention is to solve the above problems by producing an affordable hot rolled steel which is characterized by both:

[0008] - yield strength of 650 MPa or more,

[0009] - tensile strength of 750 MPa or more, and preferably 800 MPa or more,

[0010] - total elongation equal to 15% or more, and more preferably greater than 18%,

[0011] - impact strength equal to 70 J / cm 2 or more, measured at -40°C, and more preferably 90 J / cm 2 , measured at -40°C.

[0012] In a preferred embodiment, the steel sheets according to the invention may also exhibit a yield strength to tensile strength ratio of 0.5 or greater.

[0013] Another object of the present invention is also to make available a method for manufacturing said steels that is compatible with traditional industrial processes, while at the same time being robust to changes in manufacturing parameters.

[0014] The hot rolled steel sheet of the present invention can optionally be coated with zinc or zinc alloys to enhance its corrosion resistance.

[0015] Carbon is present in steel in an amount of 0.02% to 0.2%. Carbon is an element necessary for increasing the strength of steel by helping to stabilize austenite at room temperature. However, a carbon content of less than 0.02% does not contribute to imparting tensile strength to the steel of the present invention. On the other hand, when the carbon content exceeds 0.2%, this steel exhibits poor weldability and also deteriorated impact toughness, which limits the use of steel for the manufacture of structural components of yellow or green goods. The preferred content in the case of the present invention can be maintained in the range of 0.03% to 0.18%, and more preferably from 0.04% to 0.15%.

[0016] The manganese content in the steel of the present invention is from 3% to 9%. This element is gammagenic and therefore plays an important role in controlling the proportion of retained austenite, as well as enriching the retained austenite with manganese to impart hardenability and toughness to the steel. It has been found that, to ensure the strength and toughness of steel, the amount of manganese is at least 3 mass%. However, when the manganese content is greater than 9%, it causes adverse effects, such as stabilizing the austenite too much and depriving the steel of the present invention of the ability to exhibit the TRIP effect. In addition, the manganese content of greater than 9% leads to excessive segregation along the center line, which consequently deteriorates the formability and weldability of the steel of the present invention. The preferred content for the present invention can be maintained in the range of from 3.5% to 8.5%, and more preferably from 4% to 8%.

[0017] The silicon content in the steel of the present invention is from 0.2% to 1.2%. Silicon is a solid solution strengthener for the steel of the present invention. In addition, silicon retards the precipitation of cementite and limits its formation, although it often cannot completely eliminate the formation of cementite. Si maintains the concentration of C in solid solution in the austenite composition substantially in the range from values ​​​​below the Ms temperature to values ​​​​below room temperature. Therefore, silicon promotes the formation of retained austenite at room temperature. However, a Si content of more than 1.2% leads to problems such as surface defects, which has an adverse effect on the steel of the present invention. In view of the above, the concentration is adjusted within the upper limit of 1.2%.The preferred content for the present invention can be maintained in the range of 0.3% to 1%, and more preferably 0.4% to 0.8%.

[0018] Aluminum is an essential element and is present in this steel in an amount of 0.9% to 2.5%. Aluminum is an alphagenic element, and a minimum of 0.9% aluminum is required to increase the intercritical temperature range, thereby imparting a certain strength and toughness to the steel of the present invention. Aluminum is also used to remove oxygen from the steel in a molten state to purify the steel of the present invention, and it also prevents the formation of a gas phase by oxygen. However, in any case, if the amount of aluminum is more than 2.5%, it is difficult to perform casting due to the occurrence of surface defects on slabs, such as breakthroughs. In view of the above, the preferred range of the amount of aluminum is 1% to 2.3%, and more preferably 1% to 2%.

[0019] The phosphorus content in the steel of the present invention ranges from 0% to 0.03%. Phosphorus degrades hot ductility and toughness, particularly due to its tendency to segregate at grain boundaries or co-segregate with manganese. For these reasons, its content is limited to 0.02%, and preferably below 0.015%.

[0020] Sulfur is not an essential element, but may be contained in steel as an impurity. From the perspective of the present invention, the sulfur content is preferably as low as possible, but is 0.03% or less in terms of manufacturing cost. In addition, if the steel has a higher sulfur content, it combines with the formation of sulfides, especially with manganese, which has an adverse effect on the steel of the present invention. In view of the above, a sulfur content of less than 0.01% is preferable.

[0021] The nitrogen content is limited to 0.025% to prevent material aging and to minimize the precipitation of nitrides during hardening, which are detrimental to the mechanical properties of this steel. Therefore, the preferred upper limit for nitrogen is 0.02%, and more preferably 0.005%.

[0022] Molybdenum is an optional element, the content of which in the steel of the present invention is from 0% to 0.6%. Molybdenum increases hardenability, which essentially allows the steel of the present invention to achieve the properties specified for thicker gauges. When used in combination with titanium and boron, it improves the toughness of the steel of the present invention. To effectively contribute to the improvement of hardenability, a minimum of 0.1% molybdenum is required. However, the introduction of molybdenum unnecessarily increases the cost of adding alloying elements, so for economic reasons, its content is limited to 0.6%. The preferred limit for molybdenum is in the range of 0% to 0.4%, and more preferably, from 0% to 0.3%.

[0023] Titanium is an optional element and is present in the steel of the present invention in an amount of 0% to 0.1%. Titanium imparts strength to the steel of the present invention by forming carbides and controlling the grain size during the first annealing. However, in any case, when titanium is present in an amount greater than 0.1%, it imparts excessive strength and hardness to the steel of the present invention, which reduces the toughness to a value outside the specified limits. The preferred limit of titanium content is from 0% to 0.09%, and more preferably, it is from 0% to 0.08%.

[0024] Boron is an optional element of the steel of the present invention and may be present in an amount of 0.0001% to 0.01%. Boron imparts toughness to the steel of the present invention when added together with titanium and molybdenum.

[0025] Chromium is an optional element for the present invention. The steel of the present invention may contain from 0% to 0.5% chromium. Chromium is an element that ensures the hardenability of steel, but a chromium content greater than 0.5% leads to segregation along the centerline, along with manganese.

[0026] Niobium is an optional element for the present invention. In the steel of the present invention, niobium may be contained in an amount of 0% to 0.1% and is added to the steel of the present invention to form carbides or carbonitrides to impart strength to the steel of the present invention through precipitation hardening. Niobium also regulates the grain size during the first annealing. The preferred limiting content is 0% to 0.05%.

[0027] Vanadium is an optional element that may be present in the steel of the present invention in an amount of 0% to 0.15%. Vanadium is effective in increasing the strength of steel by forming carbides, nitrides or carbonitrides, and the upper limit is 0.15% for economic reasons. Even if vanadium is present in an amount above 0.15%, it does not bring any significant benefit to the steel of the present invention.

[0028] Nickel can be added as an optional element in amounts ranging from 0% to 1% to enhance the strength and toughness of the steel of this invention. To achieve these effects, a minimum content of 0.01% is preferred. However, the nickel content is limited to 1% for economic reasons.

[0029] Copper can be added as an optional element in amounts ranging from 0% to 1% to increase the strength of the steel of this invention and improve its corrosion resistance. To achieve these effects, a minimum copper content of 0.01% is preferred. However, copper content above 1% may cause problems such as hot brittleness during hot rolling.

[0030] The calcium content in the steel of the present invention is below 0.005%. Calcium is added to the steel of the present invention in a preferable amount of 0.0001 to 0.005% as an optional element, especially in the treatment of inclusions, thereby inhibiting the harmful effects of sulfur.

[0031] Other elements, such as magnesium, may also be added in the following mass ratios: magnesium ≤ 0.0010%. These elements enable grain refinement during solidification, up to the specified maximum content levels.

[0032] The rest of the steel composition consists of iron and inevitable impurities formed as a result of processing.

[0033] The microstructure of steels includes several components, in fractions of the area of ​​the entire microstructure.

[0034] Tempered martensite is present in the steel of the present invention in a proportion of at least 60%, and the tempered martensite is a matrix phase for the steel of the present invention. The tempered martensite of the steel of the present invention is preferably characterized by an aspect ratio of 4 to 12, and more preferably from 5 to 11. The aspect ratio is the ratio between the largest and smallest dimensions within a single grain. Tempered martensite is formed from martensite that is formed during cooling after the first annealing. Then, such martensite is tempered during the annealing process. Tempered martensite of the steel of the present invention imparts ductility and strength. It is preferable that the content of tempered martensite is from 65% to 84%, and more preferably from 70% to 80% in proportions of the area of ​​​​the entire microstructure.

[0035] Fresh martensite may also optionally be present in the steel of the present invention. Fresh martensite may form from the unstable retained austenite remaining during cooling after annealing. Fresh martensite may be present in an amount of 0% to 15%, preferably 0% to 10%, or, even better, no fresh martensite.

[0036] Retained austenite is an essential constituent of the microstructure of the steel of the present invention and is present in an amount of from 15% to 40%. The retained austenite of the present invention imparts toughness to the steel of the present invention. The retained austenite of the present invention can be stabilized at room temperature by enriching it with manganese and carbon. The percentage of carbon in the retained austenite is preferably higher than 0.8 mass% and lower than 1.1 mass%. It is preferable that the percentage of manganese in the retained austenite is preferably greater than 5 mass%, and more preferably greater than 5.5 mass%. The preferred range of the austenite content is from 18% to 35%, and more preferably from 18% to 30%, while the preferred range of the carbon content in the austenite is preferably from 0.9 mass% to 1.1 mass%, and more preferably from 0.95 mass%. % to 1.05 mass%.

[0037] In the steel of the present invention, the amount of polygonal ferrite ranges from 0% to 10% of the microstructure as a percentage of its area. In the present invention, polygonal ferrite imparts high strength and elongation to the steel of the present invention. Polygonal ferrite can form in the steel of the present invention during soaking and cooling after annealing. However, in any case, if the polygonal ferrite content in the steel of the present invention exceeds 10%, strength is not achieved.

[0038] Bainite may be present in the steel of the present invention in an amount of 0% to 5%. Bainite in an amount of up to 5% does not affect the target properties of the steel of the present invention.

[0039] In addition to the description of the above-mentioned microstructure, it should be noted that the microstructure of hot-rolled steel does not contain microstructural components such as pearlite and cementite. Carbides of alloying elements such as niobium, titanium, vanadium, and iron may be present in the steel of the present invention in a total amount of 0% to 5%. These carbides can increase the strength of the steel of the present invention through precipitation hardening, but in any case, when the carbide content is 5% or more, a certain amount of carbon is partially consumed for their precipitation, which is unfavorable for the stabilization of residual austenite, and the steel of the present invention cannot have adequate toughness.

[0040] The hot-rolled steel according to the invention can be produced by any suitable method. A preferred method is to produce a semi-finished steel casting with the chemical composition according to the invention. Casting can be performed either in ingots or continuously in the form of thick slabs, thin slabs, or thin strips, i.e., with a thickness ranging from approximately 220 mm to 350 mm for slabs to several tens of millimeters for thin strip.

[0041] For example, a slab with the chemical composition described above is produced by continuous casting. The slab produced by the continuous casting process can be used directly at high temperatures after continuous casting, or it can be first cooled to room temperature and then reheated for hot rolling.

[0042] The slab is reheated to a temperature in the range of Ac3 + 50°C to 1300°C. If the slab temperature is below the lowest value of Ac3 + 50°C, an excessive load is applied to the rolling mill. Taking into account the above, the slab temperature is high enough that hot rolling can be carried out entirely in the austenitic range. Reheating at temperatures above 1300°C should be avoided, as it causes productivity loss and is also expensive on an industrial scale, and some segregated areas may melt, which may lead to fracture or cracking of the slab. Taking into account the above, the preferred reheating temperature is in the range of Ac3 + 100°C to 1280°C.

[0043] The hot rolling finishing temperature for the present invention is at least Ac3, and preferably from Ac3 to Ac3 + 100°C, more preferably from 840°C to 1000°C, and even more preferably from 850°C to 990°C.

[0044] Then, the hot-rolled steel is cooled from the final hot-rolling temperature to a temperature in the range of Ms to 20°C at a cooling rate of 1°C / s to 50°C / s to obtain a hot-rolled steel strip. In a preferred embodiment, the cooling rate for this cooling step is 1°C / s to 45°C / s, and more preferably 25°C / s to 40°C / s.

[0045] The hot rolled strip can optionally be coiled, wherein the coiling temperature is from 20°C to 800°C. The hot rolled steel is heated from a temperature in the range of Ms to 20°C up to a first annealing temperature TA1, which is from Ac3 to Ac3+150°C, and preferably from Ac3 to Ac3+120°C, and more preferably from Ac3 to Ac3+100°C, and such heating is performed at a heating rate HR1 of at least 1°C / s. The hot rolled steel strip is held at TA1 for a period of time from 5 seconds to 6000 seconds to ensure transformation into 100% austenite.

[0046] Then the hot-rolled steel is cooled, wherein the cooling is performed from the temperature TA1 to the cooling stop temperature T1, which is in the range of Ms-10°C to 15°C, at a cooling rate CR1 of from 0.1°C / s to 150°C / s. In a preferred embodiment, the cooling rate CR1 for such cooling is from 0.1°C / s to 120°C / s. The preferred temperature T1 is from Ms-50°C to 20°C. The cooling rate for cooling after soaking should be high enough to achieve the transformation of austenite into martensite. The cooling rate after the first annealing is selected such that it ensures the presence of at least 80% martensite in the hot-rolled strip at the temperature T1.

[0047] The hot rolled steel is heated from the temperature T1 to the second annealing temperature TA2, which is from 550°C to Ac3, preferably from 600°C to Ac3 -40°C, and such heating is performed at a heating rate HR2 of at least 1°C / s.

[0048] Hot rolled steel is held at TA2 temperature for a period of time ranging from 5 seconds to 6000 seconds to ensure the microstructure is transformed to form 10% to 25% austenite.

[0049] Then, the hot-rolled steel is cooled, wherein the cooling is performed from the temperature TA2 to the cooling stop temperature T2, which is in the range of Ms-10°C to 15°C, at a cooling rate CR2 of from 0.1°C / s to 150°C / s. In a preferred embodiment, the cooling rate CR2 for such cooling is from 0.1°C / s to 120°C / s. The preferred temperature T2 is from Ms-20°C to 20°C. The cooling rate after soaking should be high enough to prevent the transformation of austenite into bainite, such that a sufficient amount of carbon is available to stabilize the retained austenite during cooling after annealing. During said cooling, fresh martensite can be formed from some amount of unstable retained austenite.

[0050] Then, the hot-rolled steel is cooled to room temperature at a cooling rate CR3 of 0.1°C / s to 150°C / s to obtain a hot-rolled steel sheet. The hot-rolled steel sheet thus obtained has a thickness of preferably 2 mm to 100 mm, and more preferably 2 mm to 80 mm, and even more preferably 2 mm to 50 mm.

[0051] EXAMPLES

[0052] The following tests, examples, illustrative explanation of examples and tables, which are presented in this document, are non-limiting in nature and should be considered as given for illustrative purposes only, and they will display the advantageous features of the present invention.

[0053] The compositions of steel sheets made from steels of various compositions are presented in Table 1, with the steel sheets produced in accordance with the process parameters listed in Table 2, respectively. Table 3 further shows the microstructures of the steel sheets obtained during testing, and Table 4 presents the results of evaluating the achieved properties. The Ac3 and Ms temperatures are determined through thermodynamic calculations performed using software similar to Thermo-Calc®.

[0054]

[0055]

[0056] Table 3

[0057] Table 3 presents the results of testing conducted in accordance with standards using various microscopes, such as SEM, EPMA, EBSD, XRF, or any other microscope, to determine the microstructural composition of steels, both in accordance with the invention and in comparison. The area fractions of carbides are measured on polished samples after etching in a 2% nital etching solution for 10 seconds and examined using SEM. The fractions of polygonal ferrite and tempered martensite are measured using EBSD, while electron backscatter diffraction (EBSD) is an SEM-based method for determining crystal orientations with submicron resolution. In a scanning electron microscope (SEM), the electron beam is focused on a test sample tilted at an angle of 70°. They direct electrons that satisfy the Bragg condition for a family of planes and cause the appearance of Kikuchi bands.Electrons strike a phosphorescent screen, generating a beam of light that is detected and digitized by a camera. The resulting BSE pattern is analyzed and indexed. This process is repeated for each analyzed point. For this steel sample, BSE analysis of at least four images corresponding to a magnification of 1000x allows for the identification of microcomponents in the form of polygonal ferrite and tempered martensite, their locations, and their area percentages. The area percentage of retained austenite is measured using X-ray fluorescence (XRF), as shown in Table 3.

[0058] These results are presented in this paper in area fractions:

[0059]

[0060] Sample I4 contains 1% niobium carbides, while sample R1 contains 2% iron carbides. The samples did not contain any fresh martensite or bainite.

[0061] Table 4

[0062] Table 4 provides examples of the mechanical properties of steels, both in accordance with the invention and the reference steels. Tensile tests were conducted in accordance with NBN EN ISO6892-1 using A25 tensile specimens to determine tensile strength, yield strength, and total elongation. Toughness was determined using the Charpy test method, performed in accordance with ISO 148-1. All measurements on the invention and reference steels were performed on the steel sheet taken in the longitudinal direction (LD). The results of various mechanical tests conducted in accordance with the standards are presented below.

[0063]

[0064] I = sheet according to the invention; R = comparison sheet; underlined values ​​do not correspond to the invention.

Claims

1. Hot rolled steel sheet having a composition that includes the following elements, wt.%: 0.02 ≤ carbon ≤ 0.2, 3 ≤ manganese ≤ 9, 0.2 ≤ silicon ≤1.2, 0.9 ≤ aluminum ≤ 2.5, phosphorus ≤ 0.03, sulfur ≤ 0.03, nitrogen ≤ 0.025, titanium ≤ 0.1, 0.0001 ≤ boron ≤ 0.01, the remainder being iron and inevitable impurities resulting from processing, the microstructure of said steel sheet comprises, in proportion to area, at least 60% tempered martensite, from 15% to 40% retained austenite and, optionally, contains up to 10% polygonal ferrite and up to 5% carbides of niobium, titanium, vanadium or iron.

2. Hot rolled steel sheet according to item 1, the composition of which includes from 0.3% to 1% silicon.

3. Hot rolled steel sheet according to item 1 or 2, the composition of which includes from 0.03% to 0.18% carbon.

4. Hot rolled steel sheet according to any one of paragraphs 1-3, the composition of which includes from 3.5% to 8.5% manganese.

5. Hot rolled steel sheet according to any one of paragraphs 1-4, the composition of which includes from 1% to 2.3% aluminum.

6. Hot rolled steel sheet according to any one of paragraphs 1-5, in which the amount of martensite is from 70% to 80%.

7. Hot rolled steel sheet according to any one of paragraphs 1 to 6, in which the amount of retained austenite is from 18% to 35%.

8. A hot rolled steel sheet according to any one of paragraphs 1 to 7, which is characterized by a tensile strength of 750 MPa or more and a total elongation of 15% or more.

9. Hot rolled steel sheet according to any one of claims 1 to 8, wherein the aspect ratio of the tempered martensite is from 4 to 12.

10. A method for producing hot-rolled steel sheet, comprising the following successive stages: - a semi-finished product is obtained from steel with a composition according to any of paragraphs 1-5; - reheat the specified semi-finished product to a temperature in the range from Ac3 +50°C to 1300°C; - rolling the said semi-finished product in the austenitic range, in which the final hot rolling temperature must be at least Ac3 to obtain hot rolled steel; - then the said hot rolled steel is cooled from the final hot rolling temperature to a temperature in the range from Ms to 20°C, at a cooling rate from 1°C / s to 50°C / s; - after this, said hot-rolled steel is heated at a heating rate HR1 of at least 1°C / s, from a temperature in the range from Ms to 20°C, to a temperature TA1 of from Ac3 to Ac3 +150°C, at which it is held for a period of time from 5 to 6000 seconds; - then the said hot rolled steel is cooled, wherein the cooling is started from the temperature TA1 and cooled to the cooling stop temperature T1, which is from Ms -10°C to 15°C, at a cooling rate CR1, which is from 0.1°C / s to 150°C / s; - after this, said hot rolled steel is heated at a heating rate HR2 of at least 1°C / s from T1 to a temperature TA2 of 550°C to Ac3, at which it is held for a period of time of 5 to 6000 seconds; - then the said hot-rolled steel is cooled, wherein the cooling is started from the temperature TA2 and cooled to the cooling stop temperature T2, which is from Ms -10°C to 15°C, at a cooling rate CR2, which is from 0.1°C / s to 150°C / s to obtain a hot-rolled steel sheet.

11. The method according to claim 10, wherein the temperature TA2 is from 600°C to Ac3 -40°C.

12. The method according to claim 10 or 11, wherein the temperature T1 is from Ms -20°C to 20°C.

13. Use of steel sheet according to any of paragraphs 1-9 for the manufacture of industrial machine parts or green or yellow goods.

14. An industrial machine comprising a part obtained from hot-rolled steel sheet according to any one of paragraphs. 1-9.

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