EP4555119A1 - Hot rolled steel and a method of manufacturing thereof - Google Patents

Hot rolled steel and a method of manufacturing thereof

Info

Publication number
EP4555119A1
EP4555119A1 EP22754915.1A EP22754915A EP4555119A1 EP 4555119 A1 EP4555119 A1 EP 4555119A1 EP 22754915 A EP22754915 A EP 22754915A EP 4555119 A1 EP4555119 A1 EP 4555119A1
Authority
EP
European Patent Office
Prior art keywords
hot rolled
rolled steel
steel
temperature
anyone
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP22754915.1A
Other languages
German (de)
French (fr)
Inventor
Laura MOLI SANCHEZ
Nele Van Steenberge
Sarata CISSE
Tom Waterschoot
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
ArcelorMittal SA
Original Assignee
ArcelorMittal SA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by ArcelorMittal SA filed Critical ArcelorMittal SA
Priority to MA71432A priority Critical patent/MA71432A/en
Publication of EP4555119A1 publication Critical patent/EP4555119A1/en
Pending legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
    • C21D1/22—Martempering
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/02—Hardening by precipitation
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
    • C21D9/085—Cooling or quenching
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

Definitions

  • the present invention relates to hot rolled steel suitable for use under corrosive environment particularly under the environments containing chlorides.
  • US20100037994 claims for a method of processing a workpiece of maraging steel comprising receiving a workpiece of maraging steel having a composition comprising 17wt%-19wt% of nickel, 8wt%-12wt% of cobalt, 3wt%-5wt% of molybdenum, 0.2wt%- 1.7wt% of titanium, 0.15wt%-0.15wt% of aluminum, and a balance of iron and that has been subjected to thermomechanical processing at an austenite solutionizing temperature; and directly aging the workpiece of maraging steel at an aging temperature to form precipitates within
  • EP2840160 p provide a maraging steel excellent in fatigue characteristics, including, in terms of % by mass: C: ⁇ 0.015%, Ni: from 12.0 to 20.0%, Mo: from 3.0 to 6.0%, Co: from 5.0 to 13.0%, Al: from 0.01 to 0.3%, Ti: from 0.2 to 2.0%, O: ⁇ 0.0020%, N: ⁇ 0.0020%, and Zr: from 0.001 to 0.02%, with the balance being Fe and unavoidable impurities.
  • EP2840160 provide adequate strength required but does not provides for a steel that has corrosion resistance in Chloride environment.
  • the purpose of the present invention is to solve these problems by making available a hot rolled steel that simultaneously have: - a tensile strength greater than or equal to 1100 MPa and preferably above 1200 MPa, - a hardness of less than or equal to 545 Hv and preferably less than or equal to 535Hv. - a corrosion resistance steel wherein a steel is considered corrosion resistance when the loss of thickness due to corrosion is less than 0.07mm/year and preferably less than 0.06mm/year
  • the steel according to the invention may also present a yield strength 850 MPa or more
  • such steel can also have a good suitability for forming, in particular for rolling with good weldability and coatability.
  • the hot rolled steel sheet of the present invention may optionally be coated to further improve its corrosion resistance.
  • the above object and other advantages of the present invention will become more apparent by describing in detail the preferred embodiment of the present invention.
  • the chemical composition of the hot rolled martensitic steel comprises of the following elements wherein the each element is denoted by its presence in weight percentage: Nickel is present in the steel from 5% to 16%. Nickel is an essential element for the steel of present invention to impart strength to the steel by forming inter-metallics with Aluminum and Titanium during the heating before tempering.
  • Nickel is also effective in suppressing the ferrite phase formation to increase the martensite phase ratio and improving the corrosion resistance. Nickel also plays a pivotal role in formation of reverted austenite during the tempering which restricts the hardness of steel till 550Hv. But Nickel less than will 5% will not be able to be able to impart strength due to the decrease in formation of inter-metallics whereas when Nickel is present more than 16% it will form more than 10% reverted austenite which is also detrimental for the tensile strength of the steel. A preferable content for Nickel for the present invention may be kept from 6% to 15% and more preferably from 6.5% to 14%. Aluminum is an essential element that that constitutes 0.5% to 3% of the Steel of present invention.
  • Aluminum increases the strength of the steel of present invention by forming inter-metallics with Nickel and titanium during the tempering.
  • Aluminum is an essential element for imparting the corrosion resistance properties to the steel of present invention.
  • Further Aluminum is also added to the molten state of the steel to clean steel of present invention by removing oxygen existing in molten steel to prevent oxygen from forming a gas phase.
  • Preferable limit for Aluminum is from 0.8% to 2.5% and more preferably from 0.9% to 2%.
  • Titanium content of the steel of present invention is from 0.1% to 1%. Titanium forms inter-metallic to impart strength to the steel. If titanium is less than 0.1% the requisite effect is not achieved.
  • a preferable content for the present invention may be kept from 0.1% to 0.9% and more preferably from 0.2% to 0.8%.
  • Chromium is an essential element that constitutes 4% to 15% of the Steel of present invention. Chromium is an important element for ensuring the corrosion resistance under severe corrosive environments, the stress corrosion cracking resistance. Further, when Chromium assists in effectively transforming the steel microstructure to martensite during the cooling after annealing. To obtain these effects, Cr must be contained at least 4%. However, when the content exceeds 15%, ferrite is easily formed in the metal structure of steel, and it becomes difficult to obtain a martensite structure by quenching. Therefore, the preferred Chromium content is from 5% to 14% and a more preferred range is 6% to 12%. Carbon is present in the steel from 0.0001% to 0.03%. Carbon is a residual element and comes from processing.
  • Impurity Carbon below 0.0001% is not possible due to process limitation and presence of Carbon above 0.03 must be avoided as it decreases the corrosion resistance of the steel.
  • Phosphorus constituent of the steel of present invention is from 0.002% to 0.02%. Phosphorus reduces the spot weldability and the hot ductility, particularly due to its tendency to segregate at the grain boundaries or co-segregation. For these reasons, its content is limited to 0.02% and preferably lower than 0.015%.
  • Sulfur is not an essential element but may be contained as an impurity in steel and from point of view of the present invention the Sulfur content is preferably as low as possible but is 0.005% or less from the viewpoint of manufacturing cost.
  • Nitrogen is limited to 0.01% to avoid ageing of material, nitrogen forms the nitrides which impart strength to the steel of present invention by precipitation strengthening with Vanadium and Niobium but whenever the presence of nitrogen is more than 0.01% it can form high amount of Aluminum Nitrides which are detrimental for the present invention hence the preferable upper limit for nitrogen is 0.005%.
  • Cobalt is an optional element for the steel of present invention and is present from 0% to 7%. The purpose of adding cobalt is to assist in imparting ductility to the steel.
  • cobalt also helps in forming the inter-metallics of Nickel by decreasing the rate Nickel to form solid solution. But when Cobalt is present more than 7% it forms reverted austenite in excess which is detrimental for the strength of the steel.
  • a preferable content for Cobalt for the present invention may be kept from 0% to 6% and more preferably from 0% to 5%.
  • Molybdenum is an optional element that constitutes 0% to 6% of the Steel of present invention; Molybdenum increases the strength of the steel of present invention by forming inter-metallics with Nickel and titanium during the heating for tempering. Molybdenum assists for achieving the corrosion resistance properties to the steel of present invention.
  • Molybdenum excessively increases the cost of the addition of alloy elements, so that for economic reasons its content is limited to 6%.
  • Preferable limit for molybdenum is from 0% to 5% and more preferably from 0% to 4%.
  • Niobium is an optional element for the present invention. Niobium content may be present in the steel of present invention from 0% to 0.1% and is added in the steel of present invention for forming carbides or carbo-nitrides to impart strength to the steel of present invention by precipitation strengthening.
  • Vanadium is an optional element that constitutes from 0% to 0.3% of the steel of present invention.
  • Vanadium is effective in enhancing the strength of steel by forming carbides, nitrides or carbo-nitrides and the upper limit is 0.3% due to the economic reasons. These carbides, nitrides or carbo-nitrides are formed during the second and third step of cooling.
  • Preferable limit for Vanadium is from 0 % to 0.2%.
  • Copper may be added as an optional element in an amount of 0% to 0.5% to increase the strength of the steel and to improve its corrosion resistance. A minimum of 0.01% of Copper is required to get such effect. However, when its content is above 0.5%, it can degrade the surface aspects.
  • Manganese content of the steel of present invention is from 0 % to 2%. This element is gammagenous.
  • Manganese provides solid solution strengthening and suppresses the ferritic transformation temperature and reduces ferritic transformation rate hence assist in the formation of martensite. But when Manganese content is more than 2% it produces adverse effects such as it retards transformation of Austenite to Martensite during cooling after annealing. Manganese content of above 2% can get excessively segregated in the steel during solidification and homogeneity inside the material is impaired which can cause surface cracks during a hot working process.
  • the preferred limit for the presence of Manganese is from 0 % to 1%.
  • Silicon content of the steel of present invention is from 0% to 1%. Silicon is an element that contributes to increasing the strength by solid solution strengthening.
  • Silicon is a constituent that can retard the precipitation of carbides during cooling after annealing, therefore, Silicon promotes formation of Martensite. But Silicon is also a ferrite former and also increases the Ac3 transformation point which will push the annealing temperature to higher temperature ranges that is why the content of Silicon is kept at a maximum of 1%. Silicon content above 1% can also temper embrittlement.
  • the preferred limit for the presence of Silicon is from 0% to 0.5% and more preferably from 0% to 0.4%.
  • Other elements such as Boron, Oxygen or Magnesium can be added individually or in combination in the following proportions by weight: Boron 0.001%, Oxygen ⁇ 0.004%, Magnesium ⁇ 0.0010%.
  • the remainder of the composition of the Steel consists of iron and inevitable impurities resulting from processing.
  • the microstructure of the Steel comprises: Martensite constitutes at least 95% of the microstructure by area fraction and is the matrix microstructure of the steel of present invention.
  • the martensite of the present invention can comprise both fresh and tempered martensite.
  • fresh martensite is an optional microconstituent which is preferably limited in the steel at an amount of from 0% to 4%, preferably from 0 to 2% and even better equal to 0%.
  • Fresh martensite may form during cooling after tempering.
  • Tempered martensite is formed from the martensite which forms during the second step of cooling after annealing and particularly after below Ms temperature and more particularly from Ms-10°C to 20°C.Such martensite is then tempered during the holding at a tempering temperature Temper from 450°C to 680°C.
  • the martensite of the present invention imparts ductility and strength to such steel.
  • the content of martensite is from 96% to 99% and more preferably from 96% to 98%.
  • Reverted Austenite is present in the steel of present invention from 1% to 5% by area fraction.
  • the reverted austenite is formed from the transformation of martensite into austenite during the tempering of the steel and also get enriched and stabilized with Nickel simultaneously.
  • the reverted austenite of the steel of present invention imparts both hardness as well as corrosion resistance.
  • the content of reverted austenite is from 1% to 4% and more preferably from 1% to 3%.
  • Inter-metallic compounds of Nickel, Titanium and Aluminum are present in the steel of present invention.
  • the inter-metallic are formed during the heating to tempering temperature as well as during the tempering process.
  • Inter-metallic compounds formed are both inter -granular as well as intra-granular inter-metallic.
  • Inter granular Inter- metallic compounds of the present invention are present in both Martensite and Reverted Austenite. These inter-metallic compounds of present invention can be cylindrical or globular in shape.
  • Inter-metallic compounds of the steel of present invention are formed as Ni3Ti, Ni3Al or Ni3(Ti,Al) inter-metallic compounds.
  • Inter- metallic compound of the steel of present invention imparts the steel of present invention strength and corrosion resistance especially against the chlorides environment.
  • G-phase intermetallic such as Ti 6 Si 7 Ni 16 or Mn 6 Si 7 Ni 16 are present in the steel they increase the hardness of the steel beyond 550Hv and are also detrimental for the corrosion resistance properties of the steel of present invention.
  • G-phase also makes the steel brittle. Therefore, the steel of present invention is kept free from G-phase inter-metallics.
  • the microstructure of the hot rolled steel sheet is free from microstructural components, such as Ferrite, Bainite, Pearlite and Cementite but may be found in traces. Some traces of inter-metallic compound of Iron such as Iron-Aluminum and Iron-Nickel may be present but their presence has no significant influence over the in-use properties of the steel.
  • the steel of present invention can be formed in to seamless tubular product or steel sheet or even a structural or operational part to be used industry having a harsh environment containing chlorides or any other industry that has corrosive environment.
  • a steel sheet according to the invention can be produced by the following method.
  • a preferred method consists in providing a semi-finished casting of steel with a chemical composition according to the invention.
  • the casting can be done either into ingots, billets, bars or continuously in form of thin slabs or thin strips, i.e. with a thickness ranging from approximately 220mm for slabs up to several tens of millimeters for thin strip.
  • a slab having the above-described chemical composition is manufactured by continuous casting wherein the slab optionally underwent the direct soft reduction during the continuous casting process to avoid central segregation.
  • the slab provided by continuous casting process can be used directly at a high temperature after the continuous casting or may be first cooled to room temperature and then reheated for hot rolling.
  • the temperature of the slab, which is subjected to hot rolling is preferably at least 1150° C and must be below 1300°C. In case the temperature of the slab is lower than 1150° C, excessive load is imposed on a rolling mill. Therefore, the temperature of the slab is preferably sufficiently high so that hot rolling can be completed in the in 100% austenitic range. Reheating at temperatures above 1275°C causes productivity loss and is also industrially expensive. Therefore, the preferred reheating temperature is from 1150°C to 1275°C. Thereafter the reheated slab is subjected to hot rolling.
  • the hot rolling finishing temperature for the present invention is from 800°C to 975°C and preferably from 800°C to 950°C.
  • the preferred CS1 temperature range is 15°C to Ms-20°C.
  • the cooling rate CR1 from hot roll finishing temperature to CS1 is preferably from 1°C/s to 100°C/s.
  • the CR1 for cooling after hot roll finishing temperature is from 1°C/s to 80°C/s and more preferably from 1°C/s to 50°C/s.
  • the TA is from Ae3 +20°C to Ae3 +350°C and more preferably from Ae3 +40°C to Ae3 +300°C.
  • the heating starts from CS1 to the TA temperature at a heating rate HR1 of at least 1°C/s, In a preferred embodiment, the heating rate HR1 for such heating is at least 5°C/s and more preferably at least 10°C/s or more. Then cooling the hot rolled steel strip after holding at annealing temperature, preferably at a cooling rate CR2 of 1°C/s to 100°C/s.
  • the cooling rate CR2 for cooling after holding at annealing temperature is from 1°C/s to 80°C/s and more preferably from 1°C/s to 50°C/s.
  • the hot rolled steel strip is cooled to temperature range CS2 which is from 10°C to Ms after annealing and preferably the CS2 temperature is from 15°C to Ms-20°C.
  • the fresh Martensite is formed and the cooling rate CS2 must be above 1°C/s to ensures that the hot rolled strip is completely martensitic in nature.
  • the annealed hot rolled steel strip is heated to the tempering temperature Ttemper at a heating rate HR2 which is from 0.1°C/s to 100°C/s, preferably from 0.1°C/s to 50°C/s, an even more preferably from 0.1°C/s to 30°C/s.
  • HR2 heating rate
  • inter-metallic of Nickel, Titanium and Aluminum are formed.
  • Inter-metallic compounds formed during this heating and tempering are both intra-granular as well as intergranular which forms as Ni3Ti, Ni3Al or Ni3(Ti,Al) inter- metallic compounds.
  • the tempering temperature Ttemper is from 450°C to 700°C where the steel is tempered for a duration from 30 minutes to 72 hours.
  • the Ttemper is from 490°C to 690°C and more preferably from 500°C to 680°C.
  • the reverted austenite formed during tempering is enriched with nickel due to the reason that in tempering temperature range of present invention some of the inter-metallic formed during heating dissolves and enriches the austenite with nickel and this nickel enriched reverted austenite is stable at room temperature.
  • the hot rolled steel strip is cooled to room temperature to obtain the hot rolled steel.
  • the surface fractions of phases in the microstructure are determined through the following method: a specimen is cut from the steel sheet, polished and etched with a reagent known per se, to reveal the microstructure.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
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Abstract

A hot rolled steel having a composition comprising the following elements, 5%≤Nickel≤16 %, 0.5%≤Aluminum≤3%, 0.1%≤Titanium≤1%, 4%≤Chromium≤15%, 0.0001% ≤ Carbon ≤ 0.03%, 0.002 % ≤ Phosphorus ≤ 0.02 %,0 % ≤ Sulfur ≤ 0.005%, 0 % ≤ Nitrogen ≤ 0.01%, 0 % ≤ Cobalt ≤ 7%,0% ≤ Molybdenum ≤ 6%,0% ≤ Niobium ≤ 0.1%, 0% ≤ Vanadium ≤ 0.3%, 0% ≤ Copper ≤ 0.5%, 0% ≤ Manganese ≤ 2%,0% ≤ Silicon ≤ 1%, 0% ≤ Boron≤ 0.001%, 0% ≤ Oxygen ≤ 0.004%, 0% ≤ Magnesium ≤ 0.0010%, the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of said steel sheet comprising in area fraction, at least 95% of Martensite, 1% to 5% of Reverted Austenite and inter-metallic compounds of Aluminum, Titanium and Nickel.

Description

HOT ROLLED AND STEEL AND A METHOD OF MANUFACTURING THEREOF The present invention relates to hot rolled steel suitable for use under corrosive environment particularly under the environments containing chlorides. Earlier research and developments in the field of high strength and high formability steel with corrosion resistance have resulted in several methods for steel, some of which are enumerated herein for conclusive appreciation of the present invention: US20100037994 claims for a method of processing a workpiece of maraging steel, comprising receiving a workpiece of maraging steel having a composition comprising 17wt%-19wt% of nickel, 8wt%-12wt% of cobalt, 3wt%-5wt% of molybdenum, 0.2wt%- 1.7wt% of titanium, 0.15wt%-0.15wt% of aluminum, and a balance of iron and that has been subjected to thermomechanical processing at an austenite solutionizing temperature; and directly aging the workpiece of maraging steel at an aging temperature to form precipitates within a microstructure of the workpiece of maraging steel, without any intervening heat treatments between the thermomechanical processing and the direct aging, wherein the thermomechanical processing and the direct aging provide the workpiece of maraging steel with an average ASTM grain size of 10. But US20100037994 does not ensures corrosion resistance and only claims for a method of processing maraging steel economically. EP2840160 pprovide a maraging steel excellent in fatigue characteristics, including, in terms of % by mass: C: ≤0.015%, Ni: from 12.0 to 20.0%, Mo: from 3.0 to 6.0%, Co: from 5.0 to 13.0%, Al: from 0.01 to 0.3%, Ti: from 0.2 to 2.0%, O: ≤0.0020%, N: ≤0.0020%, and Zr: from 0.001 to 0.02%, with the balance being Fe and unavoidable impurities. EP2840160 provide adequate strength required but does not provides for a steel that has corrosion resistance in Chloride environment. The purpose of the present invention is to solve these problems by making available a hot rolled steel that simultaneously have: - a tensile strength greater than or equal to 1100 MPa and preferably above 1200 MPa, - a hardness of less than or equal to 545 Hv and preferably less than or equal to 535Hv. - a corrosion resistance steel wherein a steel is considered corrosion resistance when the loss of thickness due to corrosion is less than 0.07mm/year and preferably less than 0.06mm/year In a preferred embodiment, the steel according to the invention may also present a yield strength 850 MPa or more Preferably, such steel can also have a good suitability for forming, in particular for rolling with good weldability and coatability. Another object of the present invention is also to make available a method for the manufacturing of these sheets that is compatible with conventional industrial applications while being robust towards manufacturing parameters shifts. The hot rolled steel sheet of the present invention may optionally be coated to further improve its corrosion resistance. The above object and other advantages of the present invention will become more apparent by describing in detail the preferred embodiment of the present invention. The chemical composition of the hot rolled martensitic steel comprises of the following elements wherein the each element is denoted by its presence in weight percentage: Nickel is present in the steel from 5% to 16%. Nickel is an essential element for the steel of present invention to impart strength to the steel by forming inter-metallics with Aluminum and Titanium during the heating before tempering. Nickel is also effective in suppressing the ferrite phase formation to increase the martensite phase ratio and improving the corrosion resistance. Nickel also plays a pivotal role in formation of reverted austenite during the tempering which restricts the hardness of steel till 550Hv. But Nickel less than will 5% will not be able to be able to impart strength due to the decrease in formation of inter-metallics whereas when Nickel is present more than 16% it will form more than 10% reverted austenite which is also detrimental for the tensile strength of the steel. A preferable content for Nickel for the present invention may be kept from 6% to 15% and more preferably from 6.5% to 14%. Aluminum is an essential element that that constitutes 0.5% to 3% of the Steel of present invention. Aluminum increases the strength of the steel of present invention by forming inter-metallics with Nickel and titanium during the tempering. Aluminum is an essential element for imparting the corrosion resistance properties to the steel of present invention. Further Aluminum is also added to the molten state of the steel to clean steel of present invention by removing oxygen existing in molten steel to prevent oxygen from forming a gas phase. Preferable limit for Aluminum is from 0.8% to 2.5% and more preferably from 0.9% to 2%. Titanium content of the steel of present invention is from 0.1% to 1%. Titanium forms inter-metallic to impart strength to the steel. If titanium is less than 0.1% the requisite effect is not achieved. A preferable content for the present invention may be kept from 0.1% to 0.9% and more preferably from 0.2% to 0.8%. Chromium is an essential element that constitutes 4% to 15% of the Steel of present invention. Chromium is an important element for ensuring the corrosion resistance under severe corrosive environments, the stress corrosion cracking resistance. Further, when Chromium assists in effectively transforming the steel microstructure to martensite during the cooling after annealing. To obtain these effects, Cr must be contained at least 4%. However, when the content exceeds 15%, ferrite is easily formed in the metal structure of steel, and it becomes difficult to obtain a martensite structure by quenching. Therefore, the preferred Chromium content is from 5% to 14% and a more preferred range is 6% to 12%. Carbon is present in the steel from 0.0001% to 0.03%. Carbon is a residual element and comes from processing. Impurity Carbon below 0.0001% is not possible due to process limitation and presence of Carbon above 0.03 must be avoided as it decreases the corrosion resistance of the steel. Phosphorus constituent of the steel of present invention is from 0.002% to 0.02%. Phosphorus reduces the spot weldability and the hot ductility, particularly due to its tendency to segregate at the grain boundaries or co-segregation. For these reasons, its content is limited to 0.02% and preferably lower than 0.015%. Sulfur is not an essential element but may be contained as an impurity in steel and from point of view of the present invention the Sulfur content is preferably as low as possible but is 0.005% or less from the viewpoint of manufacturing cost. Further if higher Sulfur is present in steel it combines to form Sulfides and reduces its beneficial impact on the steel of present invention, therefore preferred below 0.003% Nitrogen is limited to 0.01% to avoid ageing of material, nitrogen forms the nitrides which impart strength to the steel of present invention by precipitation strengthening with Vanadium and Niobium but whenever the presence of nitrogen is more than 0.01% it can form high amount of Aluminum Nitrides which are detrimental for the present invention hence the preferable upper limit for nitrogen is 0.005%. Cobalt is an optional element for the steel of present invention and is present from 0% to 7%. The purpose of adding cobalt is to assist in imparting ductility to the steel. Additionally, cobalt also helps in forming the inter-metallics of Nickel by decreasing the rate Nickel to form solid solution. But when Cobalt is present more than 7% it forms reverted austenite in excess which is detrimental for the strength of the steel. A preferable content for Cobalt for the present invention may be kept from 0% to 6% and more preferably from 0% to 5%. Molybdenum is an optional element that constitutes 0% to 6% of the Steel of present invention; Molybdenum increases the strength of the steel of present invention by forming inter-metallics with Nickel and titanium during the heating for tempering. Molybdenum assists for achieving the corrosion resistance properties to the steel of present invention. However, the addition of Molybdenum excessively increases the cost of the addition of alloy elements, so that for economic reasons its content is limited to 6%. Preferable limit for molybdenum is from 0% to 5% and more preferably from 0% to 4%. Niobium is an optional element for the present invention. Niobium content may be present in the steel of present invention from 0% to 0.1% and is added in the steel of present invention for forming carbides or carbo-nitrides to impart strength to the steel of present invention by precipitation strengthening. Vanadium is an optional element that constitutes from 0% to 0.3% of the steel of present invention. Vanadium is effective in enhancing the strength of steel by forming carbides, nitrides or carbo-nitrides and the upper limit is 0.3% due to the economic reasons. These carbides, nitrides or carbo-nitrides are formed during the second and third step of cooling. Preferable limit for Vanadium is from 0 % to 0.2%. Copper may be added as an optional element in an amount of 0% to 0.5% to increase the strength of the steel and to improve its corrosion resistance. A minimum of 0.01% of Copper is required to get such effect. However, when its content is above 0.5%, it can degrade the surface aspects. Manganese content of the steel of present invention is from 0 % to 2%. This element is gammagenous. Manganese provides solid solution strengthening and suppresses the ferritic transformation temperature and reduces ferritic transformation rate hence assist in the formation of martensite. But when Manganese content is more than 2% it produces adverse effects such as it retards transformation of Austenite to Martensite during cooling after annealing. Manganese content of above 2% can get excessively segregated in the steel during solidification and homogeneity inside the material is impaired which can cause surface cracks during a hot working process. The preferred limit for the presence of Manganese is from 0 % to 1%. Silicon content of the steel of present invention is from 0% to 1%. Silicon is an element that contributes to increasing the strength by solid solution strengthening. Silicon is a constituent that can retard the precipitation of carbides during cooling after annealing, therefore, Silicon promotes formation of Martensite. But Silicon is also a ferrite former and also increases the Ac3 transformation point which will push the annealing temperature to higher temperature ranges that is why the content of Silicon is kept at a maximum of 1%. Silicon content above 1% can also temper embrittlement. The preferred limit for the presence of Silicon is from 0% to 0.5% and more preferably from 0% to 0.4%. Other elements such as Boron, Oxygen or Magnesium can be added individually or in combination in the following proportions by weight: Boron 0.001%, Oxygen ≦ 0.004%, Magnesium ≦ 0.0010%. Up to the maximum content levels indicated, these elements make it possible to refine the grain during solidification. The remainder of the composition of the Steel consists of iron and inevitable impurities resulting from processing. The microstructure of the Steel comprises: Martensite constitutes at least 95% of the microstructure by area fraction and is the matrix microstructure of the steel of present invention. The martensite of the present invention can comprise both fresh and tempered martensite. However, fresh martensite is an optional microconstituent which is preferably limited in the steel at an amount of from 0% to 4%, preferably from 0 to 2% and even better equal to 0%. Fresh martensite may form during cooling after tempering. Tempered martensite is formed from the martensite which forms during the second step of cooling after annealing and particularly after below Ms temperature and more particularly from Ms-10°C to 20°C.Such martensite is then tempered during the holding at a tempering temperature Temper from 450°C to 680°C. The martensite of the present invention imparts ductility and strength to such steel. Preferably, the content of martensite is from 96% to 99% and more preferably from 96% to 98%. Reverted Austenite is present in the steel of present invention from 1% to 5% by area fraction. The reverted austenite is formed from the transformation of martensite into austenite during the tempering of the steel and also get enriched and stabilized with Nickel simultaneously. The reverted austenite of the steel of present invention imparts both hardness as well as corrosion resistance. Preferably, the content of reverted austenite is from 1% to 4% and more preferably from 1% to 3%. Inter-metallic compounds of Nickel, Titanium and Aluminum are present in the steel of present invention. The inter-metallic are formed during the heating to tempering temperature as well as during the tempering process. Inter-metallic compounds formed are both inter -granular as well as intra-granular inter-metallic. Inter granular Inter- metallic compounds of the present invention are present in both Martensite and Reverted Austenite. These inter-metallic compounds of present invention can be cylindrical or globular in shape. Inter-metallic compounds of the steel of present invention are formed as Ni3Ti, Ni3Al or Ni3(Ti,Al) inter-metallic compounds. Inter- metallic compound of the steel of present invention imparts the steel of present invention strength and corrosion resistance especially against the chlorides environment. However, when G-phase intermetallic such as Ti6Si7Ni16 or Mn6Si7Ni16 are present in the steel they increase the hardness of the steel beyond 550Hv and are also detrimental for the corrosion resistance properties of the steel of present invention. G-phase also makes the steel brittle. Therefore, the steel of present invention is kept free from G-phase inter-metallics. In addition to the above-mentioned microstructure, the microstructure of the hot rolled steel sheet is free from microstructural components, such as Ferrite, Bainite, Pearlite and Cementite but may be found in traces. Some traces of inter-metallic compound of Iron such as Iron-Aluminum and Iron-Nickel may be present but their presence has no significant influence over the in-use properties of the steel. The steel of present invention can be formed in to seamless tubular product or steel sheet or even a structural or operational part to be used industry having a harsh environment containing chlorides or any other industry that has corrosive environment. In a preferred embodiment for the illustration of the invention a steel sheet according to the invention can be produced by the following method. A preferred method consists in providing a semi-finished casting of steel with a chemical composition according to the invention. The casting can be done either into ingots, billets, bars or continuously in form of thin slabs or thin strips, i.e. with a thickness ranging from approximately 220mm for slabs up to several tens of millimeters for thin strip. For example, a slab having the above-described chemical composition is manufactured by continuous casting wherein the slab optionally underwent the direct soft reduction during the continuous casting process to avoid central segregation. The slab provided by continuous casting process can be used directly at a high temperature after the continuous casting or may be first cooled to room temperature and then reheated for hot rolling. The temperature of the slab, which is subjected to hot rolling, is preferably at least 1150° C and must be below 1300°C. In case the temperature of the slab is lower than 1150° C, excessive load is imposed on a rolling mill. Therefore, the temperature of the slab is preferably sufficiently high so that hot rolling can be completed in the in 100% austenitic range. Reheating at temperatures above 1275°C causes productivity loss and is also industrially expensive. Therefore, the preferred reheating temperature is from 1150°C to 1275°C. Thereafter the reheated slab is subjected to hot rolling. The hot rolling finishing temperature for the present invention is from 800°C to 975°C and preferably from 800°C to 950°C. Then cooling the hot rolled steel strip obtained in this manner from hot roll finishing temperature to a cooling stop temperature CS1 which is from 10°C to Ms. The preferred CS1 temperature range is 15°C to Ms-20°C. The cooling rate CR1 from hot roll finishing temperature to CS1 is preferably from 1°C/s to 100°C/s. In a preferred embodiment, the CR1 for cooling after hot roll finishing temperature is from 1°C/s to 80°C/s and more preferably from 1°C/s to 50°C/s. Thereafter heating the hot rolled steel strip to an annealing temperature TA which is from Ae3 to Ae3 +350°C. Hot rolled steel strip is held at the annealing temperature for a duration greater than or equal to 30 minutes. In a preferred embodiment, the TA is from Ae3 +20°C to Ae3 +350°C and more preferably from Ae3 +40°C to Ae3 +300°C. The heating starts from CS1 to the TA temperature at a heating rate HR1 of at least 1°C/s, In a preferred embodiment, the heating rate HR1 for such heating is at least 5°C/s and more preferably at least 10°C/s or more. Then cooling the hot rolled steel strip after holding at annealing temperature, preferably at a cooling rate CR2 of 1°C/s to 100°C/s. In a preferred embodiment, the cooling rate CR2 for cooling after holding at annealing temperature is from 1°C/s to 80°C/s and more preferably from 1°C/s to 50°C/s. The hot rolled steel strip is cooled to temperature range CS2 which is from 10°C to Ms after annealing and preferably the CS2 temperature is from 15°C to Ms-20°C. During this cooling step the fresh Martensite is formed and the cooling rate CS2 must be above 1°C/s to ensures that the hot rolled strip is completely martensitic in nature. Then the annealed hot rolled steel strip is heated to the tempering temperature Ttemper at a heating rate HR2 which is from 0.1°C/s to 100°C/s, preferably from 0.1°C/s to 50°C/s, an even more preferably from 0.1°C/s to 30°C/s. During this heating as well as during tempering inter-metallic of Nickel, Titanium and Aluminum are formed. Inter-metallic compounds formed during this heating and tempering are both intra-granular as well as intergranular which forms as Ni3Ti, Ni3Al or Ni3(Ti,Al) inter- metallic compounds. The tempering temperature Ttemper is from 450°C to 700°C where the steel is tempered for a duration from 30 minutes to 72 hours. In a preferred embodiment the Ttemper is from 490°C to 690°C and more preferably from 500°C to 680°C. During the tempering holding the fresh martensite transformed to tempered martensite as well as due to the presence of Nickel some amount of Fresh martensite reverted to form reverted austenite. The reverted austenite formed during tempering is enriched with nickel due to the reason that in tempering temperature range of present invention some of the inter-metallic formed during heating dissolves and enriches the austenite with nickel and this nickel enriched reverted austenite is stable at room temperature. There after the hot rolled steel strip is cooled to room temperature to obtain the hot rolled steel. EXAMPLES The following tests, examples, figurative exemplification and tables which are presented herein are non-restricting in nature and must be considered for purposes of illustration only and will display the advantageous features of the present invention. Steels sheets made of steels with different compositions are gathered in Table 1 wherein the each element is denoted by its presence in weight percentage and the remaining is Iron and other process impurities, where the steel are produced according to process parameters as stipulated in Table 2, respectively. Thereafter Table 3 gathers the microstructures of the steel obtained during the trials and table 4 gathers the result of evaluations of obtained properties. s ) d C0 e 5 0 s M° ( 4 0 2 s e r 3e ) p AC° 9 1 x ( 0 8 6 7 e e r u 1 C 0 . 0 0 s t n e 3 m V 7 7 e 0 6 l . 0 e 0 . 0 e h , t b 1 i n i N 0 . 0 0 S 5 e . r 4 e h o 1 5 1 – w, M 0 . 4 0 2 . o 5 : W M al 4 . 7 u 7 6 8 m + : + o 0 8 9 r o a l u C . 8 o f C g 8 u C 6 n 5 i . m r 1 0 8 1 5 1 w o f – i N 0 0 0 o . 0 . l + l u g n i N 3 0 0 o f C3 t w 3 e . 5 5 h t 1 n o l 1 e l – o f r C S 0 0 4 f 0 0 . 0 o – c r 1 0 . 0 e c o e p e h 1 n M4 t t f - . h o l 4 a P 1 4 0 1 d r . 0 . o 2 g i e A + e c 8 6 0 . 0 n o c it c r w n n i a +i n a C d r n 9 . d e o T c 0 7 2 e v i 8 s c 0 0 5 C 0 0 0 n d – s a 1 + . 0 0 . i e t 0 e h a i N e r n i b t l u c 6 . p 6 x e ) C N 6 r 9 C 9 o l . 7 0 t g a n c 1 – e ° r ( 0 1 id s i n a n s i + t d i S i 7 7 r o s e M T 1 0 0 l 6 . n e e t a 1 5 . 5 1 . c 0 c p 0 t l a 3 n t m o u + o a s – c c l s a n t c M l 3 A 7 0 1 . 0 n : s l C e 6 . n s i 5 2 1 . 0 s e e u t 2 e - 0 m 3 t n i 1 3 l s a e 3 e l e C N 8 4 e A 0 5 e c r 0. 0 v . h t – 2 e e h 7 8 d t 3- e p 1 e l n l . i 4 h t s 5 5 t l a r r 6 7 n i e a e 9 h g i 1 I 1 R e d o f = r n s s e r e = e h 3 w u M M h w W e A n i 5 0 1 5 1 g ni r ) e s ( 0 0 p e 0 6 0 me m 3 6 i 3 T t r e p ) m C 0 0 e t ° ( 5 5 5 5 T C 2 ) R s . / 0 0 n o C C° ( 3 3 i t n e v g ) n i ni l s e . 1 a ( e 0 0 0 0 h t e e l n m 8 1 8 1 o t b n i t g a A n i T d f ) r o C o 0 0 c s ° l ( e 0 9 0 c 8 at e A t T o s n ) : n o s / s e d C° u l e ( a t 5 5 1 1 1 v n e R d e m H n il e r l ) C e p ° m ( d n i 1 0 sr S 2 0 2 u; e e C c t n e e r ma 1 ) r R s / C 0 0 e f e a C ° ( 3 3 r p = s R s T e ; c h n o o s r i p n ) i 0 0 i t F C° ( 5 n 8 5 8 e e v n h R i t H e s r e T h t g o h t ta ni g : t ) 0 0 g a C° 0 2 0 2 n i d 2 2 2 e h ( 1 1 r o e l e b l e l e c R c a b b a T a T a T s l a i r 1 I 1 = I T R 5 Table 3 Table 3 exemplifies the results of the tests conducted in accordance with the standards on different microscopes such as Scanning Electron Microscope for determining the microstructures of both the inventive and reference steels. The surface fractions of phases in the microstructure are determined through the following method: a specimen is cut from the steel sheet, polished and etched with a reagent known per se, to reveal the microstructure. The determination of Reverted Austenite is done by XRD and for the martensite the dilatometry studies were conducted according the publication of S.M.C. Van Bohemen and J. Sietsma in Metallurgical and materials transactions, volume 40A, May 2009-1059. The results are stipulated herein: I = according to the invention; R = reference; underlined values: not according to the invention. Table 4 exemplifies the mechanical properties of both the inventive steel and reference steels. In order to determine the tensile strength and hardness the tests are conducted in accordance of NBN EN ISO 6892-1 standards on a A25 type sample. The corrosion resistance test is conducted according to the accelerated Chloride corrosion resistance test wherein the thickness of the steel samples is measured in millimeters (mm) before immersing such steel samples in a chlorides solution having chlorides concentration of 1000ppm for one week duration at 20°C temperature. Then bring out the steel samples after one week. Thereafter, the thickness of the steel samples is measured again. The difference in thickness of the steel samples denotes the loss of steel due to corrosion and it is denoted by mm/year. Hence, more the reduction in thickness more is a steel prone to corrosion and less reduction in thickness denotes corrosion resistance. The results of the various mechanical tests conducted in accordance to the standards are gathered Table 4 I = according to the invention; R = reference; underlined values: not according to the invention.

Claims

CLAIMS 1. A hot rolled steel having a composition comprising the following elements, expressed in percentage by weight: 5 % ≤ Nickel ≤ 16 % 0.5% ≤ Aluminum ≤ 3 % 0.1 % ≤ Titanium ≤ 1% 4% ≤ Chromium ≤ 15% 0.0001% ≤ Carbon ≤ 0.03% 0.002 % ≤ Phosphorus ≤ 0.02% 0 % ≤ Sulfur ≤ 0.005% 0 % ≤ Nitrogen ≤ 0.01% and can contain one or more of the following optional elements 0 % ≤ Cobalt ≤ 7% 0% ≤ Molybdenum ≤ 6% 0% ≤ Niobium ≤ 0.1% 0% ≤ Vanadium ≤ 0.3% 0% ≤ Copper ≤ 0.5% 0% ≤ Manganese ≤ 2% 0% ≤ Silicon ≤ 1% 0% ≤ Boron≤ 0.001% 0% ≤ Oxygen ≤ 0.004% 0% ≤ Magnesium ≤ 0.0010% the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of said steel sheet comprising in area fraction, at least 95% of Martensite, 1% to 5% of Reverted Austenite and inter- metallic compounds of Aluminum, Titanium and Nickel.
2. Hot rolled steel according to claim 1, wherein the composition includes 6% to 15% of Nickel.
3. Hot rolled steel according to claim 1 or 2, wherein the composition includes 0.8% to 2.5% of Aluminum.
4. Hot rolled steel according to anyone of claims 1 to 3, wherein the composition includes 5% to 14% of Chromium.
5. Hot rolled steel according to anyone of claim 1 to 4, wherein the composition includes 0.1% to 0.9% Titanium.
6. Hot rolled steel according to anyone of claims 1 to 5, wherein the inter-metallic compounds of Aluminium, Titanium and Nickel are at least one or more from Ni3Ti, Ni3Al or Ni3(Ti,Al).
7. Hot rolled steel according to anyone of claims 1 to 6, wherein the reverted austenite is from 1% to 4%.
8. Hot rolled steel according to anyone of claims 1 to 7, wherein said steel has a tensile strength of 1100 MPa or more and a hardness equal to or less than 545 Hv.
9. A method of production of a hot rolled steel comprising the following successive steps: - providing a steel composition according to anyone of claims 1 to 5; - reheating said semi-finished product to a temperature from 1150°C to 1300°C; - rolling the said semi-finished product in the austenitic range wherein the hot rolling finishing temperature shall be from 800°C to 975°C to obtain a hot rolled steel strip; - then cooling the said hot rolled steel strip to a temperature CS1 which is from 10°C to Ms - thereafter heat the hot rolled steel strip to an annealing temperature TA which is from Ae3 to Ae3 + 350°C at a heating rate HR1 which is at least 1°C/s, holding the hot rolled strip at TA temperature during at least 30 minutes - then cooling it at a rate from 1°C/s to 100°C/s to temperature CS2 which is in temperature range from 10°C to Ms - thereafter reheat the hot rolled steel strip to the tempering temperature Ttemper which is from 450°C to 700°C with a heating rate HR2 which is in a range from 0.1°C/s to 100°C/s and holding the hot rolled steel strip in the tempering temperature range during 30 minutes to 72 hours - then cool the hot rolled steel strip to room temperature to obtain a hot rolled steel.
10. A method according to claim 9, wherein the annealing temperature TA is from Ae3 +20°C to Ae3 + 350°C.
11. A method according to anyone of claims 9 or 10, wherein the tempering temperature Ttemper is from 490°C to 690°C.
12. A method according to anyone of claims 9 to 11, wherein the heating rate HR2 for tempering is from 0.1°C/s to 50°C/s.
13. A method according to anyone of claims 9 to 12, wherein the hot rolling finishing temperature is from 800°C to 950°C.
14. Use of a steel according to anyone of claims 1 to 8 or of a steel produced according to the method of claims 9 to 13, for the manufacture of structural or operational parts for industry having harsh environment.
15. A seamless tube, pipe or a part obtained according to claim 14.
EP22754915.1A 2022-07-12 2022-07-12 Hot rolled steel and a method of manufacturing thereof Pending EP4555119A1 (en)

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Family Cites Families (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH02310339A (en) * 1989-05-24 1990-12-26 Kawasaki Steel Corp Martensitic stainless steel having excellent strength, spring characteristics and formability
JP2780582B2 (en) * 1992-11-20 1998-07-30 日本鋼管株式会社 Maraging steel excellent in delayed fracture resistance and method of manufacturing the same
JP5362995B2 (en) * 2005-01-25 2013-12-11 ケステック イノベーションズ エルエルシー Martensitic stainless steel strengthened by Ni3Tiη phase precipitation
US20100037994A1 (en) 2008-08-14 2010-02-18 Gopal Das Method of processing maraging steel
JP5528986B2 (en) * 2010-11-09 2014-06-25 株式会社日立製作所 Precipitation hardening type martensitic stainless steel and steam turbine member using the same
JP5764503B2 (en) * 2012-01-19 2015-08-19 三菱日立パワーシステムズ株式会社 Precipitation hardening type martensitic stainless steel, steam turbine long blade, turbine rotor and steam turbine using the same
JP6317542B2 (en) * 2012-02-27 2018-04-25 三菱日立パワーシステムズ株式会社 Steam turbine rotor
JP6653113B2 (en) 2013-08-23 2020-02-26 大同特殊鋼株式会社 Maraging steel with excellent fatigue properties
US20170167265A1 (en) * 2015-12-10 2017-06-15 General Electric Company Steam turbine, bucket, and method of making bucket
CN108251759B (en) * 2018-02-01 2019-09-27 南京理工大学 Inverted austenitic toughened martensitic stainless steel and method of manufacturing the same
WO2020054540A1 (en) * 2018-09-13 2020-03-19 大同特殊鋼株式会社 Precipitation hardening-type martensite-based stainless steel and underground excavation drill component
WO2020128568A1 (en) * 2018-12-17 2020-06-25 Arcelormittal Hot rolled and steel and a method of manufacturing thereof

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