A method for the heat treatment of a part made of maraging steel, which part is obtained by selective laser melting, it comprises the steps of: heating the said part made of maraging steel from ambient temperature T0 to a maximum temperature Tmax of between 600° C. and 640° C., maintaining the said maximum temperature Tmax for a duration of between 5 hours and 7 hours, and rapidly cooling the said part.

A martensitic stainless steel sheet has a composition containing, (mass %), from 0.10 to 0.15% of C, from 0.05 to 0.80% of Si, from 0.05 to 2.00% of Mn, 0.040% or less of P, 0.003% or less of S, from 0.05 to 0.50% of Ni, from 11.0 to 15.0% of Cr, from 0.02 to 0.50% of Cu, from 0.005 to 0.06% of N, from 0.001 to 0.20% of Al, from 0 to 1.00% of Mo, from 0 to 0.50% of V, from 0 to 0.01% of B, balance Fe and unavoidable impurities. An M value=420C−11.5Si+7Mn+23Ni−11.5Cr−12Mo−10V+9Cu−52Al+470N+189 is 100 or more. A carbonitride number density having a circle equivalent diameter of 1.0 μm or more is 15.0 or less per 0.01 mm.sup.2. 0.2% yield strength is 1,100 N/mm.sup.2 or more.

A steel composition is provided. The steel composition includes 0.02-0.45 wt. % carbon (C), 0-8 wt. % manganese (Mn), 0-8 wt. % nickel (Ni), 11-17 wt. % chromium (Cr), 1-3 wt. % silicon (Si), and a balance of iron (Fe). The combined concentration of the Mn and Ni is 2-8 wt. %. The steel composition is configured to form a surface oxide layer including oxides of at least one of the Cr or the Si after being subjected to press hardening. Press-hardened steel (PHS) fabricated from the steel composition and a method of fabricating a (PHS) component from the steel composition are also provided.

A method is for producing a high strength coated steel sheet having a yield stress YS>800 MPa, a tensile strength TS>1180 MPa, and improved formability and ductility. The steel contains: 15%≤C≤0.25%, 1.2%≤Si≤1.8%, 2%≤Mn≤2.4%, 0.1%≤Cr≤0.25%, Al≤0.5%, the remainder being Fe and unavoidable impurities. The sheet is annealed at a temperature higher than Ac3 and lower than 1000° C. for a time of more than 30 s, then quenched by cooling it to a quenching temperature QT between 250° C. and 350° C., to obtain a structure consisting of at least 60% of martensite and a sufficient austenite content such that the final structure contains 3% to 15% of residual austenite and 85% to 97% of martensite and bainite without ferrite, then heated to a partitioning temperature PT between 430° C. and 480° C. and maintained at this temperature for a partitioning time Pt between 10 s and 90 s, then hot dip coated and cooled to the room temperature.

An alloy which includes at least the following (in % by weight): carbon (C): 0.15%-0.25%; silicon (Si): 0.0%-0.08%; manganese (Mn): 0.03%-0.20%; chromium (Cr): 9.5%-10.5%; molybdenum (Mo): 0.4%-1.0%; tungsten (W): 1.6%-2.4%; cobalt (Co): 2.5%-3.5%; nickel (Ni): 0.0%-0.40%; boron (B): 0.003%-0.02%; nitrogen (N): 0.0%-0.40%; titanium (Ti): 0.02%-0.10%; vanadium (V): 0.10%-0.30%; niobium (Nb): 0.02%-0.08%; copper (Cu): 1.20%-2.10%; and aluminum (Al): 0.003%-0.06%, in particular 0.005%-0.04%; the remainder being iron (Fe).

A steel sheet has a predetermined chemical composition and a metal structure represented by, in area fraction, polygonal ferrite: 40% or less, martensite: 20% or less, bainitic ferrite: 50% to 95%, and retained austenite: 5% to 50%. In area fraction, 80% or more of the bainitic ferrite is composed of bainitic ferrite grains that have an aspect ratio of 0.1 to 1.0 and have a dislocation density of 8×10.sup.2 (cm/cm.sup.3) or less in a region surrounded by a grain boundary with a misorientation angle of 15° or more. In area fraction, 80% or more of the retained austenite is composed of retained austenite grains that have an aspect ratio of 0.1 to 1.0, have a major axis length of 1.0 μm to 28.0 μm, and have a minor axis length of 0.1 μm to 2.8 μm.

A high-strength steel sheet has a specific composition and a microstructure. In the microstructure, the area fraction of elongated ferrite phase grains having an aspect ratio of 3 or more is 1% or less, the average crystal grain size of martensite included in a region extending 50 μm from a surface of the steel sheet is 20 μm or less, the content of oxide particles having a minor axis length of 0.8 μm or less in the region extending 50 μm from the surface of the steel sheet is 1.0×10.sup.10 particles/m.sup.2 or more, and the content of coarse oxide particles having a minor axis length of more than 1 μm in the region extending 50 μm from the surface of the steel sheet is 1.0×10.sup.8 particles/m.sup.2 or less. The content of hydrogen trapped in the steel sheet is 0.05 ppm by mass or more.

The steel material according to the present disclosure has a chemical composition consisting of, in mass %, C: 0.20 to 0.35%, Si: 0.05 to 1.00%, Mn: 0.01 to 1.00%, P: 0.025% or less, S: 0.0100% or less, Al: 0.005 to 0.100%, Cr 0.25 to 0.80%, Mo: 0.20 to 2.00%, Ti: 0.002 to 0.050%, B: 0.0001 to 0.0050%, N: 0.0020 to 0.0100% and O: 0.0100% or less, with the balance being Fe and impurities, and satisfying Formula (1). A number density of precipitates having an equivalent circular diameter of 400 nm or more is 0.150 particles/μm.sup.2 or less. The yield strength is within a range of 655 to 965 MPa. A dislocation density ρ is 7.0×10.sup.14 m.sup.−2 or less.
5×Cr—Mo-2×(V+Ti)≤3.00  (1)

This hot-rolled steel sheet has a predetermined chemical composition, in which in a case where the thickness is denoted by t, a metallographic structure at a t/4 position from the surface includes, by area fraction, 77.0% to 97.0% of bainite or tempered martensite, 0% to 5.0% of ferrite, 0% to 5.0% of pearlite, 3.0% or more of residual austenite, and 0% to 10.0% of martensite, in the metallographic structure, the average grain size excluding the residual austenite is 7.0 μm or less, the average number density of iron-based carbides having a diameter of 20 nm or more is 1.0×10.sup.6 carbides/mm.sup.2 or more, a tensile strength is 980 MPa or more, and an average Ni concentration on the surface is 7.0% or more.

The present invention relates to the application of at least partially bainitic or interstitial martensitic heat treatments on steels, often tool steels or steels that can be used for tools. The first tranche of the heat treatment implying austenitization is applied so that the steel presents a low enough hardness to allow for advantageous shape modification, often trough machining. Thus a steel product is obtained which can be shaped with ease and whose hardness can be raised to a higher working hardness with a simple heat treatment at low temperature (below austenitization temperature).