The invention relates to the field of said steels "maraging", used in particular for applications requiring one or more of the following properties: excellent mechanical properties (very good fatigue resistance, high tensile strength and high fracture), processing simplicity thermal and dimensional stability at the end of these treatments, welding ease and good formability. These maraging steels are characterized by a martensite structure, which can be aged in order to obtain, after an aging of steel, a phase precipitation hardening intermetallic favorable for obtaining high mechanical properties. Conventionally known maraging steel type M 250, typical composition (in weight percent, as will all the compositions given in the following) Ni = 18% = 9% Co, Ti = 0.45% (grade said X2NiCoMo18-9-5), containing Ti as an element curing the remainder generally being iron and impurities resulting from the smelting. They are used to perform, especially parts with high properties, suitable for use as well as massive parts (trees engines centrifuge blades ...) and as high performance precision parts: springs for watches, blades for foils, automatic transmission belts elements type CVT (Continuous variable transmission), in particular to cars or vehicles in general, Also known, from EP-B1 -1339880, maraging steels free from Ti having the composition: Ni = 12 to 24.5%; Mo = 2.5%; Co = 4.17%; Al≤ 0.15%; Ti≤ 0.1%; N≤ 30 ppm; Si≤ 0.1%; Mn≤ 0.1%; C≤ 50 ppm; S≤ 10 ppm; P ≤ 50 ppm; H≤ 3 ppm; O≤ 10 ppm; the balance being Fe and impurities resulting from the smelting, with Ni + Mo between 20 and 27%; Co% x% Mo between 50 and 200; Ti x% N% ≤ 2.10 "4Which are produced by methods including treatments reflow vacuo type VIM (Vacuum Induction Melting) and / or VAR (Vacuum Arc Remelting), optionally coupled to a reflow treatment by electro slag ESR (Electroslag Remelting). These steels are then processed hot and cold for to obtain strips of small thickness (1 mm or less for example). After shaping of the part, is carried out a hardening treatment by precipitation which gives the part its mechanical properties heart; a subsequent surface treatment can impart to the piece increased surface properties regarding solicitation fatigue, static friction, dynamic friction ... Compared to previously known maraging steel containing about 18% Ni, 9% Co, 5% Mo, 0.5% Ti, and a bit of AI, these steels EP-B1 1,339,880 to distinguished by holding in greater fatigue (in the aged nitrided state), associated with inclusions controlled cleanliness and fatigue endurance. In more detail: the mechanical properties of cold rolling are referred Ar> 2.5% Rpo.2 <1140 MPa, Rm <1480 MPa; on aged condition, Rp 0 . 2 > 1770 MPa, Rm> 1800 MPa; finally nitrided state properties are referred Ar> 1%; Rm> 1930 MPa. It is also known from EP-B1 2180073 maraging steels with high fatigue strength and tensile strength for use in CVT belts, composition: C≤ 100 ppm; Si≤ 0.1%; Mn≤ 0.1%; P ≤ 0.01%; S≤ 50 ppm; Ni = 17 -22%; Cr = 0.1 -4.0%; MB = 3.0-7.0%; Co = 10.0 to 20.0%; Ti≤ 0.1%; Al≤ O, 05%; N≤ 300 ppm; O≤ 50 ppm; 0