Martensitic stainless steel

Abstract

A martensitic stainless TMCP steel containing 0,15 w-% or less carbon and 10,5 w-% to 15,0 w-% chromium, wherein Charpy V impact energy is ≥ 34 J / cm2 at a temperature ≤ 0 °C and the Kaltenhauser Ferrite Factor (KFF) is ≤ 9,2 and the yield strength (Rp0.2) is ≥ 800 MPa.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a martensitic stainless TMCP (thermo mechanical control process) steel.BACKGROUND OF THE INVENTION

[0002] In addition to good corrosion resistance, very high strength and hardness are the main advantages of conventional martensitic stainless steels. On the other hand, poor impact toughness especially at low temperatures and challenging weldability are their main disadvantages.SUMMARY

[0003] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features of the present disclosure, nor is it intended to be used to limit the scope of the present disclosure.

[0004] It is an objective of the present disclosure to provide a technical solution of a martensitic stainless TMCP steel.

[0005] The objective above is achieved by the features of the independent claims in the appended claims. Further embodiments and examples are apparent from the dependent claims, the detailed description, and the accompanying tables.

[0006] According to first aspect of the present invention, there can be provided a martensitic stainless TMCP steel comprising 0,15 w-% or less carbon and 10,5 w-% to 15,0 w-% chromium, wherein Charpy V impact energy is ≥ 34 J / cm 2< at a temperature ≤ 0 °C and the Kaltenhauser Ferrite Factor (KFF) is ≤ 9,2 and the yield strength (Rp0.2) is ≥ 800 MPa.

[0007] In an embodiment, the martensitic stainless TMCP steel is in form of a strip, a sheet, a plate, a bar, or a wire.

[0008] In an embodiment, the martensitic stainless TMCP steel contains in weight-% (w-%): C: 0,004 w-% to 0,15 w-%, Si: 0,005 w-% to 1,0 w-%, Mn: 0,01 w-% to 3,0 w-%, P: 0,060 w-% or less, S: 0,030 w-% or less, Cr: 10,5 w-% to 15,0 w-%, Ni: 0,01 w-% to 4,0 w-%, Cu: 0,005 w-% to 2,0 w-%, N: 0,20 w-% or less, Al: 0,001 w-% to 0,30 w-%, the balance being Fe and remainder elements which do not affect notably on steel properties.

[0009] In an embodiment, the martensitic stainless TMCP steel contains in weight-%: C: 0,030 w-% or less, Si: 1,0 w-% or less, Mn: 1,5 w-% or less, P: 0,040 w-% or less, S: 0,015 w-% or less, Cr: 10,5 w-% to 12,5 w-%, Ni: 1,0 w-% or less, N: 0,030 w-% or less, the balance being Fe and remainder elements which do not affect notably on steel properties.

[0010] In an embodiment, the martensitic stainless TMCP steel contains in weight-%: C: 0,08 w-% to 0,15 w-%, Si: 1,0 w-% or less, Mn: 1,5 w-% or less, P: 0,040 w-% or less, S: 0,015 w-% or less, Cr: 11,5 w-% to 13,5 w-%, Ni: 0,75 w-% or less, the balance being Fe and remainder elements which do not affect notably on steel properties.

[0011] The Kaltenhauser Ferrite Factor KFF of the martensitic stainless TMCP steel satisfies the following equation: where symbol of each element means its chemical composition as w-%.

[0012] In an embodiment, the martensitic stainless TMCP steel contains in w-%: Mo: 0,05 w-% to 4,0 w-%,

[0013] In an embodiment, the martensitic stainless TMCP steel contains in weight-%: C: 0,06 w-% to 0,15 w-%, Si: 1,0 w-% or less, Mn: 1,5 w-% or less, P: 0,040 w-% or less, S: 0,015 w-% or less, Cr: 12,0 w-% to 14,0 w-%, Mo: 0,3 w-% to 0,8 w-%, the balance being Fe and remainder elements which do not affect notably on steel properties.

[0014] In an embodiment, the martensitic stainless TMCP steel contains in w-%: Nb: 0,001 w-% to 0,50 w-%.

[0015] In an embodiment, the martensitic stainless TMCP steel contains in w-%: Ti: 0,001 w-% to 0,50 w-%.

[0016] In an embodiment, the martensitic stainless TMCP steel contains in w-%: V: 0,001 w-% to 0,80 w-%.

[0017] In an embodiment, the martensitic stainless TMCP steel contains in w-%: B: 0,0001 w-% to 0,0090 w-%.

[0018] In an embodiment, the martensitic stainless TMCP steel comprises 0,004 w-% to 0,15 w-% carbon.

[0019] In an embodiment, the yield strength of the martensitic stainless TMCP steel is ≥ 850 MPa.

[0020] In an embodiment, the yield strength of the martensitic stainless TMCP steel is ≥ 900 MPa.

[0021] In an embodiment, the yield strength of the martensitic stainless TMCP steel is ≥ 960 MPa.

[0022] In an embodiment, the martensitic stainless TMCP steel has tensile strength Rm of 900 MPa or more.

[0023] In an embodiment, the Kaltenhauser Ferrite Factor (KFF) of said steel is ≤ 9,0.

[0024] In an embodiment, the Kaltenhauser Ferrite Factor (KFF) of said steel is ≤ 8,0.

[0025] In an embodiment, the Kaltenhauser Ferrite Factor (KFF) of said steel is ≤ 7,2.

[0026] In an embodiment, Charpy V impact energy of said steel is ≥ 34 J / cm 2< at a temperature ≤ -20 °C.

[0027] In an embodiment, Charpy V impact energy of said steel is ≥ 34 J / cm 2< at a temperature ≤ -40 °C.

[0028] In an embodiment, Charpy V impact energy of said steel is ≥ 34 J / cm 2< at a temperature ≤ -60 °C.

[0029] In an embodiment, ductile to brittle transition temperature T34J / cm 2< of the martensitic stainless TMCP steel is 0°C or less.

[0030] In an embodiment, ductile to brittle transition temperature T34J / cm 2< of the martensitic stainless TMCP steel is -20°C or less.

[0031] In an embodiment, ductile to brittle transition temperature T34J / cm 2< of the martensitic stainless TMCP steel is -40°C or less.

[0032] In an embodiment, ductile to brittle transition temperature T34J / cm 2< of the martensitic stainless TMCP steel is -60°C or less.

[0033] In an embodiment, total elongation (At) of said steel is 5,0 w-% to 15,0 w-%, measured as A50.

[0034] In an embodiment, the carbon content in said steel is 0,004 w-% to 0,050 w-%.

[0035] In an embodiment, the carbon content in said steel is 0,004 w-% to 0,030 w-%.

[0036] In an embodiment, the carbon content in said steel is 0,005 w-% to 0,050 w-%.

[0037] In an embodiment, the carbon content in said steel is 0,007 w-% to 0,050 w-%.

[0038] In an embodiment, the carbon content in said steel is 0,05 w-% to 0,15 w-%.

[0039] In an embodiment, the carbon content in said steel is 0,05 w-% to 0,10 w-%.

[0040] In an embodiment, the carbon content in said steel is 0,10 w-% to 0,15 w-%.

[0041] In an embodiment, the amount of ferrite in said steel is ≤ 12 volume-% (≤ 12 vol-%).

[0042] In an embodiment, the amount of ferrite in said steel is ≤ 7 volume-% (≤ 7 vol-%).

[0043] In an embodiment, the amount of ferrite in said steel is ≤ 3 volume-% (≤ 3 vol-%).

[0044] In an embodiment, the amount of ferrite in said steel is ≤ 1 volume-% (≤ 1 vol-%).

[0045] In this invention, it has been found that novel martensitic stainless TMCP steels with excellent low-temperature toughness and good weldability can be produced by using appropriate steel compositions and filler metal compositions for welding.

[0046] Martensitic stainless TMCP steel means a steel produced by controlled hot working and subsequent cooling. There are many methods of TMCP (thermo mechanical control process). The process, in which the various stages of rolling are temperature-controlled and the finishing temperature is precisely defined, is called controlled rolling. In case of martensitic stainless TMCP steel, the controlled rolling process usually includes hot rolling pass or passes above Tnr (non-recrystallization temperature) and then a rolling pass or passes below Tnr, and finally cooling as accelerated cooling or air cooling.

[0047] In practice, Tnr is the temperature below which recrystallisation of austenite grain structure does not occur between consecutive rolling passes. Above Tnr, austenite grain structure is renewed by recrystallisation.

[0048] Martensitic stainless TMCP steel means a steel where martensite is the major metallic phase of the microstructure. In addition to martensite, the microstructure of the present steel may contain some ferrite. In an embodiment, the amount of ferrite in martensitic stainless TMCP steel is 12 volume-% or less.

[0049] Volume fraction as volume-% (vol-%) of ferrite in a martensitic microstructure may be obtained from images of the etched surface microstructure with the aid of optical microscope, for example. Manual assessing of ferrite percentage, e.g. according to ASTM E562 standard, or some software may be used.

[0050] In martensitic stainless TMCP steel prior austenite grains (PAGs) are thinned and also elongated after finished controlled rolling. This is because one or more rolling passes will be carried out in the non-recrystallization temperature range, i.e. below Tnr, before cooling to ambient temperature.

[0051] In an embodiment, a total reduction means a total reduction ratio, i.e., the amount of cross-sectional reduction as percentage taking place during controlled rolling below non-recrystallization temperature (Tnr).

[0052] In an embodiment, the last rolling pass or passes during controlled rolling is carried out with 20% or more total reduction ratio at such temperatures, where no remarkable recrystallization occurs. In an embodiment this may mean temperatures below the non-recrystallization temperature (Tnr) where the controlled rolled austenite grain structure does not transform to new equiaxed grain structure, but austenite grains stay elongated and thinned or also flattened after the passes.

[0053] Suitable chemical composition together with this metallurgical phenomenon results in an ultra-high strength martensitic stainless TMCP steel after cooling. This kind of steel may be very suitable for use in several applications including, but not limited to: pipes and tubes, for use in construction and oil & gas applications, different structural applications for use for example in construction industry such as beams and bars, including rebars, containers for use in, e.g. marine, waste and railways, multiple-element gas container (MEGC) structures, railway wagons and wear plates, frames and beams for use in cranes, transportation industry and trailers.

[0054] Thus, good weldability in an embodiment of the novel strong and tough steel is essential.

[0055] Other features and advantages of the present disclosure will be apparent upon reading the following detailed description and reviewing the accompanying tables.BRIEF DESCRIPTION OF THE TABLES

[0056] The accompanying tables, which are included to provide a further understanding of the invention and constitute a part of this specification, illustrate embodiments of the invention and together with the description help to explain the principles of the invention. In the tables: Table 1 lists compositions (w-%) and Kaltenhauser Ferrite Factors (KFF) of the test steels, Table 2 lists results of yield strength Rp0.2, tensile strength Rm, uniform elongation Ag, total elongation At, and hardness (HV20), in longitudinal test directions, Table 3 lists Charpy V Notch (CVN) impact energies (J / cm 2< ) at different temperatures and ductile to brittle transition temperatures DBTT (T34J / cm 2< ), in transverse test directions, Table 4 lists results of tensile tests and Charpy V Notch CVN tests (T34J / cm 2< ) of a MAG and a laser weld, in transverse test directions, and Table 5 lists non-recrystallization temperatures (Tnr) of the test steels. DETAILED DESCRIPTION

[0057] Various embodiments of the present disclosure are further described in more detail with reference to the accompanying tables. However, the present disclosure may be embodied in many other forms and should not be construed as limited to any certain structure or function discussed in the following description. In contrast, these embodiments are provided to make the description of the present disclosure detailed and complete.

[0058] According to the detailed description, it will be apparent to the ones skilled in the art that the scope of the present disclosure encompasses any embodiment thereof, which is disclosed herein, irrespective of whether this embodiment is implemented independently or in concert with any other embodiment of the present disclosure. For example, the products and / or methods disclosed herein may be implemented in practice using any numbers of the embodiments provided herein. Furthermore, it should be understood that any embodiment of the present disclosure may be implemented using one or more of the elements presented in the appended claims.Chemical composition

[0059] In an embodiment of the martensitic stainless TMCP steel according to the disclosure, it may be produced from a slab or a billet by a controlled rolling.

[0060] In an embodiment, the martensitic stainless TMCP steel may be produced from a martensitic plate, strip, sheet, bar, or wire by the controlled rolling.

[0061] In an embodiment, the martensitic stainless TMCP steel may be produced from a ferritic plate, strip, sheet, bar, or wire by the controlled rolling.

[0062] The ranges of alloying elements contents and their meanings in an embodiment of the martensitic stainless TMCP steel according to the disclosure will be presented more detailed below. "w-%" markings mean weight-%, i.e. weight percentages.

[0063] Contents of phosphorus, sulphur and nitrogen do not have any lower limits, because they are usually remainder but not real alloying elements in martensitic stainless TMCP steels. In addition, the alloying element contents below the lower limit belong to remainders.

[0064] In an embodiment of a martensitic stainless TMCP steel according to the present disclosure may comprise from 0,004 w-% to 0,15 w-% carbon (C: 0,004 w-% to 0,15 w-%).

[0065] Carbon (C) is known to be a strong austenite former that decreases Kaltenhauser Ferrite Factor (KFF). It increases significantly the mechanical strength and hardness. It may reduce the resistance to intergranular corrosion caused by chromium carbide formation and subsequent chromium depleted areas in grain boundaries. In martensitic stainless steels, higher carbon contents may also reduce toughness. The carbon content in the martensitic stainless TMCP steel may be from 0,004% to at most 0,15 w-%. If the carbon content is less than 0,004 w-%, the manufacturing costs may be too high due to a more tedious decarburization process. Higher carbon contents than 0,15 w-% C may result in too low toughness and impaired corrosion resistance. In an embodiment, the martensitic stainless TMCP steel according to the present disclosure may comprise carbon content of 0,004 w-% C to 0,15 w-% C. By lower than maximum carbon contents, i.e. 0,10 w-% or lower, susceptibility to sensitization and intergranular corrosion decreases further. Therefore, in an embodiment of the martensitic stainless TMCP steel according to the present disclosure may comprise carbon from 0,004 w-% to 0,10 w-%, preferably from 0,004 w-% to 0,050 w-%. The martensitic stainless TMCP steels with carbon contents of 0,030 w-% or less are least susceptible to intergranular corrosion, and their weldability is optimal. The carbon content 0,004 w-% to 0,030 w-% of an embodiment of the martensitic stainless TMCP steel according to the present disclosure may be optionally most preferable. In the case of good wear resistance or abrasion resistance of martensitic stainless TMCP steels, more carbon for harder steel may be needed. In an embodiment of a martensitic stainless TMCP steel according to the present disclosure may comprise from at least 0,05% to 0,15 w-% carbon, preferably 0,10 w-% to 0,15 w-% carbon.

[0066] In an embodiment of a martensitic stainless TMCP steel according to the present disclosure may comprise from at least 0,005% to 1,0 w-% silicon (Si: 0,005 w-% to 1,0 w-%)

[0067] Silicon (Si) is present in virtually all stainless steels as an alloying element or as a reminder element. It is added primarily for deoxidation during melting. Silicon promotes ferrite in martensitic stainless microstructure and increases Kaltenhauser Ferrite Factor (KFF). Silicon as a deoxidizing element may be at least partially replaced by other deoxidizers, e.g., aluminium, manganese and calcium. The silicon content in an embodiment of the present disclosure may be 0,005 w-% to 1,0% w-% Si, preferably 0,1 w-% to 1,0 w-% Si, more preferably 0,1 w-% to 0,8 w-% Si and most preferably 0,1 w-% to 0,5 w-% Si. Higher Si content than 1,0% may cause lower toughness and harmful ferrite in a martensitic stainless steel. The content may be very low and practically near zero, too, because silicon as a deoxidizing element can be even replaced by other deoxidizers, e.g., aluminium, manganese and calcium.

[0068] In an embodiment of a martensitic stainless TMCP steel according to the present disclosure may comprise 0,01 w-% to 3,0 w-% manganese (Mn: 0,01 w-% to 3,0 w-%).

[0069] Manganese (Mn) is present in virtually every steel, as an alloying element or at least as a remainder metal. It is generally alloyed to steels to improve hot ductility. Manganese and the formation of stable manganese sulphide (MnS) may eliminate the hot shortness problem and manganese is also known to improve toughness. It can be also used as a deoxidizing agent. Manganese, as an austenite former, may replace some of the nickel in stainless steels. In martensitic stainless TMCP steels, manganese reduces Kaltenhauser ferrite factor (KFF). Manganese content in an embodiment of the present disclosure may be 0,01 w-% to 3,0 w-%. With lower content than 0,01 w-% manganese atoms are ineffective to bind harmful S atoms to harmless manganese sulphide MnS. It is also possible to use other elements, e.g., calcium, replacing manganese in desulphurization. For optimizing the effect of manganese content in the martensitic stainless TMCP steel, its content is preferably from 0,1 w-% to 3,0 w-% Mn, more preferably 0,2 w-% to 2,0 w-% Mn and most preferable 0,5 w-% to 2,0 w-% Mn.

[0070] In an embodiment of a martensitic stainless TMCP steel according to the present disclosure may comprise at most 0,060 w-% phosphorus (P) (P ≤ 0,060 w-%)

[0071] Phosphorus (P) is a harmful impurity element deteriorating toughness. The optimum phosphorus content is therefore as low as possible. Phosphorus content in the martensitic stainless TMCP steel may be 0,060 w-% or less (P ≤ 0,060 w-%) or preferably 0,040 w-% or less (P ≤ 0,040 w-%), more preferably 0,030 w-% or less (P ≤ 0,030 w-%), and most preferably 0,020 w-% or less (P ≤ 0,020 w-%). In commercial stainless steel making processes minimum phosphorus content obtained is often 0,010 w-% to 0,030 w-% P.

[0072] In an embodiment of a martensitic stainless TMCP steel according to the present disclosure may comprise at most 0,030 w-% sulphur (S ≤ 0,030 w-%).

[0073] Sulphur (S) in a martensitic stainless steel is a harmful impurity element. Addition of sulphur to martensitic alloy gives it the best machining properties of any stainless steels, but this comes at a cost in terms of reduced corrosion resistance, formability and weldability. Due to these disadvantages, sulphur content may be made as low as possible, in any case ≤ 0,030 w-%. Sulphur content in a martensitic stainless TMCP steel may be ≤0,030 w-%, preferably ≤0,020 w-% and more preferably ≤0,010 w-%.

[0074] In an embodiment of a martensitic stainless TMCP steel according to the present disclosure may comprise 10,5 w-% to 15,0 w-% chromium (Cr: 10,5 w-% to 15,0 w-%).

[0075] Chromium (Cr) is a very important alloying element in stainless steels, and it gives them chiefly their good corrosion resistance. It is a strong ferrite promoting element in martensitic stainless steel and increases Kaltenhauser ferrite Factor (KFF). Increase in chromium content e.g., from 10,5 w-% to 15,0 w-%, improves corrosion resistance of a martensitic TMCP steel but does not affect remarkably mechanical properties. Chromium content in a martensitic stainless TMCP steel may be 10,5 w-% to 15,0 w-%, preferably 10,5 w-% to 14,0 w-%, more preferably 10,5 w-% to 13,0 w-%, and most preferably 11,0 w-% to 13,0 w-%. The minimum content of chromium may be 10,5 w-% to assure good enough corrosion resistance. The maximum content may be restricted to 15,0 w-%, because too much additional high-priced nickel is needed to assure martensitic phase structure with more than 15,0 w-% Cr.

[0076] In an embodiment of a martensitic stainless TMCP steel according to the present disclosure may comprise 0,01 w-% to 4,0 w-% nickel (Ni: 0,01 w-% to 4,0 w-%) .

[0077] Nickel (Ni) may improve ductility and toughness. It also strongly stabilizes austenite phase at high temperature and reduces Kaltenhauser ferrite factor (KFF). Especially with chromium contents of 11,5% or more, nickel may be usually needed as an alloying element to assure austenitic microstructure at hot-rolling temperatures. Austenite transforms to martensite during cooling of the steel. In martensitic stainless steels, nickel addition combined with lower carbon content may also improve the weldability. Nickel content may be 0,01 w-% to 4,0 w-% Ni. In an embodiment of a martensitic stainless TMCP steel according to the present disclosure may comprise 0,01 w-% to 4,0 w-% nickel. The maximum nickel content may be 4,0 w-% due to high alloying costs. Steels, especially with the lowest chromium contents, may be also manufactured without any nickel addition. Nickel content of the martensitic stainless TMCP steel is preferably 0,1 w-% to 3,0 w-%, more preferably 0,1 w-% to 2,5 w-% and most preferably from 0,1 w-% to 1,9 w-%.

[0078] In an embodiment of a martensitic stainless TMCP steel according to the present disclosure may comprise optionally 0,05 w-% to 3,0 w-% molybdenum (Mo: 0,05 w-% to 3,0 w-%) .

[0079] Molybdenum (Mo) may significantly improve the resistance to both uniform and localized corrosion. It sometimes may increase the mechanical strength and strongly promote a ferritic microstructure and increases Kaltenhauser ferrite factor (KFF). In martensitic stainless steels molybdenum may increase the hardness at higher temperatures due to its effect on the carbide precipitation. Molybdenum content in a martensitic stainless TMCP steel may be 0,05 w-% to 3,0 w-%, preferably 0,05 w-% to 2,5 w-%, and more preferably 0,1 w-% to 2,5 w-%. At higher contents than 3,0 w-% Mo, alloying costs are too high. Mo isn't obligatory alloying element in the invented steel: use of molybdenum is optional, because a martensitic stainless TMCP steel can be also produced without molybdenum addition.

[0080] In an embodiment of a martensitic stainless TMCP steel according to the present disclosure may comprise at 0,005 w-% to 2,0 w-% copper (Cu: 0,005 w-% to 2,0 w-%).

[0081] Copper (Cu) is an austenite promoting alloying element. Copper additions are known to promote corrosion resistance, especially in sulfuric acid and hydrochloric acid. In addition, ductility can be improved by copper additions. Cu isn't obligatory alloying element in the invented steel, because it can be produced without copper addition. Some copper, often ≤ 0,2 w-%, may occur without alloying as a remainder element in many stainless steels. The copper content of a martensitic stainless TMCP steel may be 0,005 w-% to 2,0 w-% Cu, preferably 0,1 w-% to 2 w-% Cu, more preferably 0,1 w-% to 1,5 w-% Cu and most preferably 0,1 w-% to 1,2 w-% Cu. Higher copper contents than 2,0 w-% will increase the material costs too much.

[0082] In an embodiment of a martensitic stainless TMCP steel according to the present disclosure may comprise at most 0,20 w-% nitrogen (N: ≤ 0,20 w-%).

[0083] Nitrogen (N) is a strong austenite former, and it reduces Kaltenhauser ferrite factor (KFF). In martensitic stainless steels nitrogen may increase both hardness and strength but it reduces the toughness. Due to reduction of toughness, it is considered as an impurity element in martensitic stainless TMCP steels. Nitrogen content may be ≤0,20 w-%, preferably ≤ 0,10 w-%, more preferably ≤0,05 w-% and most preferably ≤0,03 w-%. Higher contents than 0,20 w-% may result in poor toughness.

[0084] In an embodiment of a martensitic stainless TMCP steel according to the present disclosure may comprise 0,001 w-% to 0,30 w-% aluminium (Al: 0,001 w-% to 0,30 w-%).

[0085] Aluminium (Al) is a beneficial deoxidizing element in stainless steels. Additionally, the occurrence of aluminium nitride precipitates in a steel may reduce grain size. Aluminium is known to increase Kaltenhauser ferrite factor (KFF). In a martensitic stainless TMCP steel aluminium content is 0,001 w-% to 0,30 w-%, preferably 0,002 w-% to 0,30 w-%, more preferably 0,005 w-% to 0,30 w-%, and most preferably 0,010 w-% to 0,20 w-%. In a martensitic stainless TMCP steel maximum aluminium content may be 0,30 w-%. Higher contents do not remarkably improve the deoxidizing ability.

[0086] In an embodiment of a martensitic stainless TMCP steel according to the present disclosure may comprise optionally 0,001 w-% to 0,50 w-% niobium (Nb: 0,001 w-% to 0,50 w-%).

[0087] Niobium (Nb) promotes ferrite and increases Kaltenhauser Ferrite Factor (KFF). It may provide stabilization of the carbon as MC-type carbide to avoid chromium carbide precipitation, sensitization, and intergranular corrosion. During hot-rolling, niobium may retard recrystallization after roll passes. Non-recrystallization temperature (Tnr) may be increased remarkably with niobium alloying. Niobium content in the present steel may be 0,001 w-% to 0,50 w-% Nb (Nb: 0,001 w-% to 0,50 w-%), preferably 0,005 w-% to 0,50 w-%, more preferably 0,010 w-% to 0,50 w-%, and most preferably 0,010 w-% to 0,30 w-%. Higher than 0,50 w-% Nb may not cause any more improvements but may increase costs of alloying. By lower content than 0,001 w-% Nb only minor advantages can be obtained. Niobium isn't any obligatory element in the invented steel.

[0088] In an embodiment of a martensitic stainless TMCP steel according to the present disclosure may comprise optionally 0,001 w-% to 0,50 w-% titanium (Ti: 0,001 w-% to 0,50 w-%)

[0089] Titanium (Ti) is a strong carbide and nitride former and a ferrite promoting element. It increases Kaltenhauser ferrite factor (KFF) in martensitic stainless steels. Titanium may lower the martensite hardness by combining with carbon and increase the tempering resistance. At the same time, risk of intergranular corrosion may decrease as fewer chromium carbide precipitates occur in grain boundary areas. Titanium may also be able to increase non-recrystallization temperature Tnr. Higher titanium contents than 0,50 w-% may show a harmful distribution of precipitates of larger size. Titanium content in martensitic stainless TMCP steel may be 0,001 w-% to 0,50 w-% Ti, preferably 0,005 w-% to 0,50 w-%, more preferably 0,008 w-% to 0,30 w-%, and most preferably 0,008 w-% to 0,30 w-%. Titanium is no obligatory element in these steels.

[0090] In an embodiment of a martensitic stainless TMCP steel according to the present disclosure may comprise optionally 0,001 w-% to 0,80 w-% vanadium (V: 0,001 w-% to 0, 80 w-%) .

[0091] Vanadium forms carbides and nitrides at lower temperatures than niobium and titanium. It may be used in hardenable stainless steels to increase hardness and toughness due to fine vanadium carbide, nitride and carbonitride precipitates. Vanadium promotes ferrite. Vanadium content in a martensitic stainless TMCP steel may be 0,001 w-% to 0,80 w-% or less, preferably 0,005 w-% to 0,80 w-%, more preferably 0,005 w-% to 0,40 w-%, and most preferably 0,005 w-% to 0,30 w-%. Vanadium is no obligatory element in these steels.

[0092] In an embodiment of a martensitic stainless TMCP steel according to the present disclosure may comprise optionally 0,0001 w-% to 0,0090 w-% boron (B: 0,0001 w-% to 0,0090 w-%).

[0093] Boron may play an important role as a hardenability agent especially in low-alloyed non-stainless steels. Hardenability of high-chromium martensitic stainless steels is very good as such, however, and boron alloying does not improve it remarkably. Strength and wear resistance of martensitic stainless steel may be improved by boron addition. Higher boron contents than 0,0090 w-% may impair corrosion resistance. In a martensitic stainless TMCP steel boron content may be 0,0001 w-% to 0,0090 w-%, preferably 0,0001 w-% to 0,0020%, more preferably 0,0001 w-% to 0,0012 w-% and most preferably 0,0001 w-% to 0,0008 w-%.

[0094] In an embodiment of the martensitic stainless TMCP steel according to the present disclosure may mainly comprise iron and some or all mentioned elements. Other so called remainder elements may occur as impurity and do not clearly improve steel properties.

[0095] The mentioned limits of alloying element contents may form the composition ranges to be used in embodiments of the martensitic TMCP steel according to the present disclosure. The causes of lower and higher limits may be metallurgical, technical, environmental, and / or economical. Regarding all the mentioned alloying elements and their use, environmental tasks may be taken into consideration.

[0096] In general, stainless steels, and particularly the present martensitic stainless TMCP steel is a green material due to its 100% recyclability and because major part of its weight is scrap and other recycled materials. In fact, more than half of all the stainless steels materials that are in use today have been manufactured from scrap materials.

[0097] In addition to high recyclability and use of recycled materials, excellent strength and impact toughness properties of martensitic stainless TMCP steels produced by controlled rolling and rapid cooling may be obtained with minimized use of alloying elements, non-renewable energy and other production resources. This in turn results in lower carbon dioxide emissions.

[0098] In an embodiment of a martensitic stainless TMCP steel according to the present disclosure, it is obtained as perfect martensitic microstructure as possible, especially with minimum amounts of ferrite and chromium carbide precipitates. Otherwise, problems in toughness and corrosion properties may occur. In practice this means as fully as possible austenitic microstructure at controlled rolling temperatures and thereafter during cooling to the martensite start temperature (M S ). Austenite to martensite transformation of embodiments of martensitic stainless TMCP steels according to the present disclosure will happen between M s temperature being typically in the range 300 °C to 500 °C and M f (martensite finish temperature) being usually about 100 °C below M s . In an embodiment, finish controlled rolling temperature of martensitic stainless TMCP steel may be above M s temperature. In an embodiment, finish controlled rolling temperature of martensitic stainless TMCP steel may be above the temperature range of cold rolling, i.e. above 180°C. In an embodiment, finish controlled rolling temperature of martensitic stainless TMCP steel may be 500 °C or more and preferably 600°C or more. The steel at or above 500°C is more ductile and the rolling forces are lower than below 500°C.

[0099] The Kaltenhauser Ferrite Factor (KFF) can be used to predict the amount of martensite and ferrite in a martensitic stainless steel by taking into the account the chemical composition (w-%) of the material. KFF is a very important composition parameter. It has been reported that a fully martensitic microstructure may be immune to sensitization, the preliminary stage of intergranular corrosion. In addition, a fully martensitic structure without ferrite may result in more homogeneous microstructure and better mechanical properties such as better impact toughness.

[0100] Calculation of the KFF is presented in Equation 1. KFF = Cr + 6 Si + 8 Ti + 4 Mo + 4 Nb + 2 Al − 40 C + N − 2 Mn − 4 Ni

[0101] In an embodiment of a martensitic stainless TMCP steel according to the present disclosure Kaltenhauser ferrite factor is ≤9,2 (KFF ≤ 9,2), preferably ≤ 9,0 (KFF ≤9,0), more preferably ≤8, 0 (KFF ≤ 8,0) and most preferably ≤ 7,2 (KFF ≤ 7,2).

[0102] Ferrite and chromium carbide formation plus sensitization may occur in heat affected zones (HAZ) of weld joints during welding. Ferrite may especially easily occur with low heat inputs and fast cooling. To avoid sensitization and subsequent intergranular corrosion also in these cases, low enough KFF values may be needed. Coarse ferrite microstructures which may occur in martensitic stainless steels with high KFF values will impair their impact toughness. The same is true for coarse grained HAZ of a weld joint.

[0103] In an embodiment of a martensitic stainless TMCP steel according to the present disclosure yield strength Rp0.2 and tensile strength Rm in the test steel with lowest carbon content (Steel 1) are about 890 MPa (891 MPA in Table 2) and 1020 MPa (1022 MPa in Table 2), respectively. In an embodiment of a martensitic stainless TMCP steel according to the present disclosure lower strengths, about Rp0.2=800 MPa and Rm=900 MPa, can be obtained by still reducing carbon content. Lower carbon is known to reduce strength properties.

[0104] Minimum acceptable total elongation (At) for ultra-high strength steel is often 5% to 6%, but this percentage may vary between different steel strengths and applications, down to 3% to 4%. For some commercial martensitic-bainitic low-alloyed non-stainless steels at approximately similar strength levels as here in the experiments, total elongations of 8% to 13% have been reported. In an embodiment of a martensitic stainless TMCP steel according to the present disclosure, the total elongation (At) as A50 may be 5,0 % to 15,0% (A50: 5,0% to 15,0%), preferably 6,0% to 15,0% (A50: 6,0% to 15,0%), more preferably 7,0% to 15,0% (A50: 7,0% to 15,0%) and most preferably 8,0% to 15,0% (A50: 8,0% to 15,00) .

[0105] In an embodiment of a martensitic stainless TMCP steel according to the present disclosure, Charpy V impact energy may be 34 J / cm 2< or more at ≤ 0°C, preferably 34 J / cm 2< or more at ≤ -20°C, more preferably 34 J / cm 2< or more at ≤ -40°C, and most preferably 34 J / cm 2< or more at ≤ -60°C. This impact energy 34 J / cm 2< is acceptable in most applications. In some embodiments, for example in more demanding applications, the Charpy V impact energy at ≤ 0°C, ≤ -20°C, ≤ -40°C, or ≤ -60°C may be 38 J / cm 2< or more, or optionally 50 J / cm 2< or more, or optionally 62 J / cm 2< or more, for example.

[0106] In an embodiment of a martensitic stainless TMCP steel according to the present disclosure ductile to brittle transition temperature T34J / cm 2< , measured by Charpy V notch (CVN) impact tests, may be 0°C or less, preferably -20°C or less, more preferably -40°C or less, and most preferably -60°C or less. T34J / cm 2< is the temperature on the transition curve that corresponds to an energy level of 34J / cm 2< .

[0107] In an embodiment of martensitic stainless TMCP steel according to the present disclosure, the thickness of the plate or sheet or strip may be 3,3 mm or more, or 4,2 mm or more, or 6,2 mm or more.

[0108] The manufacturing process of stainless steel comprises a series of transformations made from the melting of the raw material until the required thickness is obtained. According to an aspect, the manufacturing process can be divided into three main stages: a steel melting shop, a hot rolling mill and a cold rolling mill. In the melting shop, from scrap, ferroalloys and other elements, the chemical composition of a steel is obtained. In the hot rolling mill, the thickness of steel slab or billet after casting is reduced. At high rolling temperatures, ductility of steel is good and rolling forces relatively low.

[0109] Conventionally, stainless steel strip, sheet or plate is rolled above the non-recrystallization temperature Tnr so that austenite grains which are flattened and elongated during or right after each rolling pass will recrystallize to new equiaxed grains. Often the temperature of hot rolling is around 1100 °C. Hot rolling passes above non-recrystallization temperature Tnr refines the originally coarse-grained austenitic microstructure of a steel and improve the mechanical properties of the final steel product.

[0110] In an embodiment of the controlled rolling process, controlled rolling of a martensitic stainless TMCP steel slab or billet may be first made above the non-recrystallization temperature Tnr, and last rolling pass or passes will be performed at lower temperatures than conventionally, i.e., below the non-recrystallization temperature Tnr. Then the steel is cooled to ambient temperature. This controlled rolling process is one variant of those used in the TMCP. The TMCP is frequently applied in the production of low-alloyed plate, strip and bar, i.e., non-stainless steels. It is to be noted here, that the controlled rolling process may be carried out in several ways or routes.

[0111] In an embodiment, the controlled rolling of martensitic stainless TMCP steel is composed of one or more rolling passes above non-recrystallization temperature Tnr and one or more rolling passes with total reduction ratio of 20% or more below Tnr.

[0112] In an embodiment, controlled rolling of martensitic stainless TMCP steel is composed of one or more rolling passes with total reduction ratio of 20% or more below non-recrystallization temperature Tnr, but not above the Tnr.

[0113] Selection from the above embodiments to be used is made depending on chemical composition, steel thickness and required properties of the martensitic stainless TMCP steel to be produced.

[0114] In an embodiment, the steel is cooled after controlled rolling to ambient temperature by an accelerated cooling by, e.g., water cooling, air cooling or using other quenching coolants. In an embodiment, the steel is simply allowed to cool to ambient temperature without using the accelerated cooling. This is an especially suitable process for thin plates, sheets, bars and wires, where the cooling is fast enough to inhibit formation of e.g. ferrite and chromium carbides in martensitic stainless TMCP steels. In an embodiment, there is not a separate cooling step, but the steel is cooled without a direct quenching step to ambient temperature.

[0115] A good estimation of the combined effect of alloying element contents, especially of microalloying elements Nb, V, Ti, and Al, on non-recrystallization temperature Tnr can be obtained. Tnr is the temperature below which recrystallization of austenite does not occur. Tnr is presented by the following Equation 2 where the symbol of each alloying element means its weight-% (w-%) in the steel: Tnr ∘ C = 887 + 464 × C + 6445 × Nb − 644 × Nb + 732 × − 230 × V + 890 × Ti + 363 × Al − 357 × Si

[0116] In an embodiment Tnr is around 800°C according to this equation, as the microalloying element contents and carbon content are low. This is the case in our test steels used in experiments. In an embodiment according to practical experiences and to this equation, small additions of niobium may increase Tnr most effectively.

[0117] Seven cast ingots manufactured in two laboratories were controlled rolled by a laboratory roller (2-high reversing rolling mill. Carl Wezel, Mühlacker, Germany). The test results show that the lowest acceptable rolling reduction may be about 20% as rolling occurs below Tnr. In an embodiment a minimum total reduction ratio below Tnr may be 20% or more, optionally 27% or more, or optionally 31% or more, or optionally 40% or more. On the other hand, in an embodiment the maximum total reduction ratio below Tnr may be 90% or less, because rolling forces will become too high at higher reduction ratios. In an embodiment the highest total reduction ratio below Tnr may be optionally 85% or less, or optionally 80% or less.

[0118] Steel plates produced by controlled rolling and direct quenching were tested by tensile tests, Charpy V-notch (CVN) impact tests, hardness measurements (HV), and welding tests. Tensile and CVN impact tests were carried out for MAG and laser weld metals, too. The results together with explanations have been presented in Tables 2 to 4.

[0119] In martensitic stainless TMCP steels, cooling rate of the steel after controlled rolling can be fast or also rather slow to result in austenite to martensite phase transformation. High chromium contents of 10,5% to 15% improve hardenability much enough to obtain martensitic microstructure also during slow air cooling. However, slow cooling may result in higher amount of ferrite and / or chromium carbide in the final microstructure, possibly impairing toughness and / or corrosion resistance. The test steels here were direct quenched after hot rolling by immersing test pieces into water to avoid possible carbides and ferrite in the steel product.Test steels

[0120] Compositions and Kaltenhauser Ferrite Factors KFFs of seven test steels according to the disclosure are presented in Table 1. Test steels are marked in the Table 1 with numbers 1, 2, 3, 4, 5, 6, 7. Carbon and nickel contents were intentionally varied, because they are known to have remarkable effect on mechanical properties, i.e., strength and toughness, of martensitic stainless steels. In addition, test steels 1, 5 and 7 were high-boron (0,0090 w-%) steels and test steels 2, 3, 4 and 6 low-boron (0,0008 w-% to 0,0012 w-%) steels. Content of chromium, the main element of martensitic stainless steel, as well as most of other alloying and impurity elements remained intentionally virtually unchanged in the test steels.

[0121] In addition to good corrosion resistance, very high strength and hardness are the main advantages of conventional quenched martensitic stainless steels. On the other hand, poor toughness especially at low temperatures and challenging weldability are their main disadvantages. In this invention, it has been surprisingly found that novel martensitic stainless TMCP steels with excellent low-temperature impact toughness and good weldability can be produced by using appropriate steel compositions and TMCP routes.

[0122] In an embodiment, the last rolling pass or passes during hot rolling are carried out with 20% to 90% total reduction ratio at such temperatures, where no remarkable recrystallization occurs. In an embodiment this means temperatures below the non-recrystallization temperature (Tnr) where, practically the controlled rolled austenite grains do not more transform by recrystallization to equiaxed austenite grains but stay elongated and flattened or pancaked grains, e.g., in plates, sheets and strips and rod like grains, e.g., in many wires and bars after the rolling pass or passes. Suitable chemical composition together with this metallurgical phenomenon results in a tough, ultra-high strength martensitic stainless TMCP steel after cooling. This kind of steel may be very suitable to different structural applications. Thus, good weldability in an embodiment of the novel strong and tough steel is essential.Tensile and hardness tests

[0123] Tensile tests for test steels were carried out by a Zwick Roell Z100 100 kN tensile testing machine (ZwickRoell GmbH & Co., Ulm, Germany). Vickers hardness values (HV20) were measured by a standard hardness tester Dia Tester 2Rc (Otto-Wolpert Werke GmbH, Ludwigshafen a.Rh., Germany).

[0124] Results of tensile tests for test steels 1, 3, 4, 5, and 7 and hardness measurements for test steels 1 to 7 produced according to the invention with total reduction ratio of 50% of controlled rolling below Tnr are presented in Table 2. Yield strength Rp0.2 varies between 891 MPa to 961 MPa, tensile strength Rm between 1022 MPa to 1184 MPa and hardness between 303 HV20 to 389 HV20. The measured hardness values of more than 300HV give the tough martensitic stainless TMCP steels with a good wear resistance. Increase in carbon content of a martensitic stainless steel, e.g. up to 0,15% of carbon, is known to improve hardness as well as wear resistance further.

[0125] According to Table 2, total elongation (At) values of the test steels are from 8,5% to 11,1%. In structural applications, minimum acceptable elongation for ultra-high strength steel is often 5%, but this percentage may vary between different steel strengths and applications, down to 3% to 4%. For some commercial martensitic-bainitic low-alloyed steels at approximately similar strength levels as here, total elongations (At) of 9% to 13% (A5 or A50) have been reported.

[0126] Somewhat different gauge lengths of 45 mm (A5) and 60mm (A60) have been used for different test steel batches. A5 is determined from a gauge length 5.56×√S0, here 45 mm, i.e where S0 is cross sectional area of the tensile test specimen before testing. Both gauge lengths of 45 mm and 60 mm give comparable yield strength, tensile strength, and uniform elongation values. The longer gauge length (60mm) is known to give somewhat smaller total elongation values than the shorter gauge length (45mm). The maximum difference caused by different gauge lengths of 45mm and 60mm in total elongation is about 2,0 percent unit. The values of total elongation A5 and A50 are very near each other, and both are used in practice. Gauge length of 50 mm (A50) is nowadays used most frequently due to renewed standardization and will be the base for the present invention.Impact toughness

[0127] Impact toughness of a conventional martensitic stainless steel after quenching is usually poor, especially at sub-zero temperatures.

[0128] Charpy V impact toughness tests were carried out by a standard Charpy impact testing machine (300 J) . Due to 5,5 mm thickness of the test plates, sub-sized Charpy V notched (CVN) samples of 10 × 5,5 × 55 mm were used. Impact energy is presented as J / cm 2< . A standard full-sized notched sample is 10 × 10 × 55 mm. Sub-sized samples are used as plate thickness is below 10 mm.

[0129] Charpy V Notch (CVN) impact energy values and ductile to brittle transition temperatures DBTT or T34J / cm 2< of the test steels, which have been finally controlled rolled below Tnr with total 50% reduction ratio, are presented in Table 3. Surprisingly, the measured transition temperatures T34J / cm 2< of all the test steels are below -20 °C. Impact tests were not carried out at 0 °C because the test steels were tough also at still lower temperatures of -20 °C to -60 °C. Steels 3 and 4 were not tested at -20 °C, too, because they were tough at much lower temperatures. For Steels 1, 5 and 7, additional tests were carried out at -25 °C.

[0130] In most demanding applications, as low as T34J / cm 2< of -40°C or even of -60°C may be needed. Especially Steels 2, 3 and 4 show good impact toughness at very low temperatures, too, even below -60°C. At -60 °C, their impact energy is still as high as 45 J / cm 2< or more. Surprisingly, the test steels 1, 5 and 7 with a high boron content have clearly higher ductile to brittle transition temperature T34J / cm 2< (-27 °C, -23 °C, and -21 °C, respectively) than other test steels with much lower boron contents. Also, their impact energies at -20 °C are clearly lower than in low-boron steels.

[0131] CVN impact tests for Steels 2 and 6 were performed also after controlled rolling with total reduction ratio of 27% below Tnr. Impact energy values were good, more than 34J / cm 2< , at the test temperatures -20°C and -40°C. According to these results, the lowest possible reduction of hot rolling below Tnr is about 20%.

[0132] Steel 1 was also rolled at temperatures above the non-recrystallization temperature. The starting temperature of final rolling stage was about 950°C and the last pass was carried out at above 850°C, i.e. above its Tnr of 813 °C. Yield strength, tensile strength, and total elongation are according to this invention, but ductile to brittle transition temperature T34J / cm 2< is as high as +8°C, showing unacceptable impact properties.MAG and laser welding

[0133] Steel 1 has been welded by MAG (Metal Active Gas) and laser methods to clarify its basic weldability. Results of transverse tensile tests and CVN tests of their weld metals are presented in Table 4. Avesta 2101 filler wire (ferritic-austenitic or duplex)) was used in MAG welding. In autogenous laser welding, no filler metal was used.

[0134] Table 4 shows that mechanical properties of the MAG weld are on a good level. Ductile to brittle transition temperature T34J / cm 2< of weld metal is -37°C. This is somewhat better than that of base metal Steel 1, probably due to existing tough austenite in the solidified weld metal. Uniform elongation and total elongation are characteristic of transverse tensile tests of weld joints. Undermatching in strength values occurred, and this is usual, too, in non-stainless ultra-high strength steels welded with duplex filler wire. More optimal strength / toughness combinations of weld joints in martensitic stainless TMCP steel may be obtained by more complete filler wire selection process.

[0135] Laser weld metal was produced by autogenous laser beam welding. Transverse yield strength and tensile strength are practically the same as those of unwelded martensitic base metal. Ductile to brittle transition temperature of weld metal (T34J / cm 2< = +27°C) is not acceptable. The ductile to brittle transition temperature T34J / cm 2< of base metal produced according to the invention is in this case 54°C lower than that of laser weld metal with the same chemical composition. It is possible, however, to improve impact toughness also of autogenous welds by modifying base metal composition.

[0136] According to the mechanical properties of the test steels presented in Tables 2 and 3, all of them are suitable for welded steel structures to be used at low temperatures, as suitable welding processes with optimized filler metals and welding parameters are used.

[0137] In Table 5, non-recrystallization temperatures Tnr of the test steels are presented. They have been calculated from the well-known Equation 2 shown earlier in this description.

[0138] It is obvious to a person skilled in the art that with the advancement of technology, the basic idea of the invention may be implemented in various ways. The invention and its embodiments are thus not limited to the examples described above, instead they may vary within the scope of the claims.

[0139] The embodiments described hereinbefore may be used in any combination with each other. Several of the embodiments may be combined together to form a further embodiment. A product, a process, or a use, disclosed herein, may comprise at least one of the embodiments described hereinbefore. It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages. It will further be understood that reference to 'an' item refers to one or more of those items. The term "comprising" is used in this specification to mean including the feature(s) or act(s) followed thereafter, without excluding the presence of one or more additional features or acts.

Claims

1. A martensitic stainless TMCP steel comprising 0,15 w-% or less carbon and 10,5 w-% to 15,0 w-% chromium, wherein Charpy V impact energy is ≥ 34 J / cm2 at a temperature ≤0 °C and the Kaltenhauser Ferrite Factor (KFF) is ≤9,2 and the yield strength (Rp0.2) is ≥ 800 MPa.

2. The martensitic stainless TMCP steel according to claim 1, comprising 0,004 w-% to 0,15 w-% carbon.

3. The martensitic stainless TMCP steel according to claim 1 or 2, wherein the yield strength of said steel is ≥ 850 MPa, preferably ≥ 900 MPa, more preferably ≥ 960 MPa.

4. The martensitic stainless TMCP steel according to any of the preceding claims, having tensile strength Rm of 900 MPa or more.

5. The martensitic stainless TMCP steel according to any of the preceding claims, wherein the Kaltenhauser Ferrite Factor (KFF) of said steel is ≤ 9,0, preferably ≤ 8,0, more preferably ≤ 7,2.

6. The martensitic stainless TMCP steel according to any of the preceding claims, wherein Charpy V impact energy of said steel is ≥ 34 J / cm2 at a temperature ≤ -20 °C, preferably at a temperature ≤ -40 °C, more preferably at a temperature ≤ -60 °C.

7. The martensitic stainless TMCP steel according to any of the preceding claims, wherein ductile to brittle transition temperature T34J / cm2 is 0°C or less, preferably -20°C or less, more preferably - 40°C or less, and most preferably -60°C or less.

8. The martensitic stainless TMCP steel according to any of the preceding claims, wherein total elongation of said steel is 5,0 % to 15,0 % measured as A50 at room temperature.

9. The martensitic stainless TMCP steel according to any of the preceding claims, wherein the carbon content in said steel is 0,004 w-% to 0,050 w-%, preferably 0,004 w-% to 0,030 w-%, more preferably 0,005 w-% to 0,030 w-%.

10. The martensitic stainless TMCP steel according to any of the preceding claims, wherein the carbon content in said steel is 0,005 w-% to 0,050 w-%, preferably 0,007% to 0,050%.

11. The martensitic stainless TMCP steel according to any of claims 1 to 8, wherein the carbon content in said steel is 0,05 w-% to 0,15 w-%, preferably 0,05% to 0,10%.

12. The martensitic stainless TMCP steel according to any of claims 1 to 8, wherein the carbon content in said steel is 0,10 w-% to 0,15 w-%.

13. The martensitic stainless TMCP steel according to any of the preceding claims, wherein the amount of ferrite is ≤ 12 vol-%, preferably ≤ 7 vol-%, more preferably ≤ 3 vol-%, most preferably ≤ 1 vol-%. SteelCSiMnPSCrNiNMoCuAlNbTiVBKFF10,0090,221,40,0230,003110,630,01900,210,00800,0170,040,0096,0320,0090,251,340,020,00311,30,590,0100,190,03200,0150,0430,00087,1930,0150,271,340,0080,00311,20,860,0100,280,04100,0150,0420,00115,940,0150,261,360,0080,00311,21,840,01300,290,03800,0150,0430,00121,8150,0190,221,40,0190,003110,610,01900,210,00900,0170,040,0095,7160,0280,271,350,0190,00311,30,590,01300,190,02600,0180,0410,00086,3870,0290,221,40,0210,004110,610,01800,210,01200,0180,040,0095,36 SteelRp0.2RmAgAtHardnessMPaMPa%%HV20189110222,410,8 13392303391710452,28,5 2341491410482,89,1 2343589811112,611,1 13716341796111842,211,0 13891 At = A5 2 At = A60 Charpy V impact energy (J / cm2)DBTT (T34J / cm2)T (°C)220-20-25-40-60Steel16560393621-272939545<-6036366< -6049856< -6056453393123-236815011-4874934392114-21 Steel 1Filler metalRp0.2RmAgA5T34J / cm2MPaMPa%%°CMAG weldAvesta 21015338212,96,3-37Laser weldno87610321,85,427Base metal89110222,410,8-27 Steel1234567Tnr °C813810809812818812825

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