Disclosed are austenitic stainless steel that can exhibit high strength while having non-magnetic properties, and a manufacturing method thereof.

The high strength non-magnetic austenitic stainless steel according to an embodiment of present disclosure includes, in percent (%) by weight of the entire composition, C: 0.02 to 0.12%, Si: 1.2% or less, Mn: 0.5 to 2.0%, Cr: 17.0 to 22.0%, Ni: 11.0 to 15.0%, Mo: 3.0% or less, N: 0.25% or less, the remainder of iron (Fe) and other inevitable impurities, satisfies C+N: 0.25% or more, and satisfies following Formulas (1) and (2).

[{Cr+Mo+1.5*Si+18}/{Ni+30*(C+N)+0.5*Mn+36}+0.262]*161−161−log(cooling rate)<0  (1)

551−462*(C+N)−9.2*Si−8.1*Mn−13.7*Cr−29*Ni−18.5*Mo≤−200  (2)

The present application provides a hot-work die steel and a preparation method thereof wherein the chemical constituents of the hot-work die steel in mass percentage are as follows: C: 0.20-0.32 wt %, Si: ≤0.5 wt %, Mn: ≤0.5 wt %, Cr: 1.5-2.8 wt %, Mo: 1.5-2.5 wt %, W: 0.5-1.2 wt %, Ni: 0.5-1.6 wt %, V: 0.15-0.7 wt %, Nb: 0.01-0.1 wt %, and a balance of iron, wherein an alloying degree is 5-7%; a tensile strength of the hot-work die steel at 700° C. is 560-700 MPa; a value of hardness of the hot-work die steel at room temperature is 32-38 HRC after holding at 700° C. for 3-5 h; and the hot-work die steel has an elongation of 14% to 16% at room temperature, a percentage reduction of area of 48% to 65%, and an impact toughness of 52-63 J at room temperature. The hot-work die steel of the present application has an excellent thermal stability as well as a good plasticity and a toughness at room temperature.

This hot-rolled steel sheet has a predetermined chemical composition, and in a case where the thickness is denoted by t, the metallographic structure at a t/4 position from the surface contains one or both of tempered martensite and lower bainite at a volume percentage of 90% or more, the tensile strength is 980 MPa or more, and the average Ni concentration on the surface is 7.0% or more.

Disclosed is a high-yield-ratio cold-rolled dual-phase steel, having the following chemical elements in percentage by mass: 0.05%-0.08% of C, 0.9%-1.2% of Mn, 0.1%-0.6% of Si, 0.030%4060% of Nb, 0.030%-0.060% of Ti, 0.015%-0.045% of Al, and the balance being Fe and other inevitable impurities. A manufacturing method for the high-yield-ratio cold-rolled dual-phase steel, comprising: (1) smelting and casting; (2) hot rolling, wherein a casting blank is controlled and soaked at a temperature of 1200° C.-1250° C.; rolled with the finish rolling temperature being 840° C.-930° C.; cooled at a speed of 20° C./s-70° C./s, and then wound at the winding temperature being 570° C.-630° C.; (3) cold rolling; (4) annealing at the soaking temperature being 750° C.-790° C. for 40 s-200 s, cooling at a speed of 30° C./s-80° C./s, the start temperature of cooling is 650° C. to 730° C., the aging temperature is 200° C. to 260° C., and the overaging time is 100 s to 400 s; and (5) leveling.

The austenitic stainless steel containing niobium according to an exemplary embodiment of the present invention includes: 16 to 26 wt. % of chromium (Cr), 8 to 22 wt. % of nickel (Ni), 0.02 to 0.1 wt. % of carbon (C), 0.2 to 1 wt. % of niobium (Nb), 0.015 to 0.025 wt. % of titanium (Ti), 0.004 to 0.01 wt. % of nitrogen (N), and 0.5 to 2 wt. % of manganese (Mn), wherein the austenitic stainless steel containing niobium has an austenitic matrix structure, a fine niobium carbide and a fine titanium nitride are precipitated in the austenitic matrix structure, and the fine niobium carbide is uniformly dispersed in the austenitic matrix structure.

The austenitic stainless steel containing niobium according to an exemplary embodiment of the present invention includes: 16 to 26 wt. % of chromium (Cr), 8 to 22 wt. % of nickel (Ni), 0.02 to 0.1 wt. % of carbon (C), 0.2 to 1 wt. % of niobium (Nb), 0.015 to 0.025 wt. % of titanium (Ti), 0.004 to 0.01 wt. % of nitrogen (N), and 0.5 to 2 wt. % of manganese (Mn), wherein the austenitic stainless steel containing niobium has an austenitic matrix structure, a fine niobium carbide and a fine titanium nitride are precipitated in the austenitic matrix structure, and the fine niobium carbide is uniformly dispersed in the austenitic matrix structure.

The steel material for a carburized bearing part according to the present invention contains, by mass %, C: 0.25 to 0.45%, Si: 0.15 to 0.45%, Mn: 0.40 to 1.50%, P: 0.015% or less, S: 0.005% or less, Cr: 0.60 to 2.00%, Mo: 0.10 to 0.35%, V: 0.20 to 0.40%, Al: 0.005 to 0.100%, Ca: 0.0002 to 0.0010%, N: 0.0300% or less and O: 0.0015% or less, with the balance being Fe and impurities, and satisfies Formulae (1) to (3).
1.20<0.4Cr+0.4Mo+4.5V<2.75  (1)
A1/A2>0.50  (2)
2.7C+0.4Si+Mn+0.45Ni+0.8Cr+Mo+V>2.55  (3)
Formula (2) shows an area fraction of sulfides containing Ca in an amount of 1 mol % or more among sulfides having an equivalent circular diameter of 1 μm or more.

An iron-based alloy includes, in weight percent, carbon from about 1 to about 2 percent; manganese from about 0.1 to about 1 percent; silicon from about 0.1 to about 2.5 percent; chromium from about 11 to about 19 percent; nickel up to about 8 percent; vanadium from about 0.8 to about 5 percent; molybdenum from about 11 to about 19 percent; tungsten up to about 0.5 percent; niobium from about 1 to about 4 percent; cobalt up to about 5.5 percent; boron up to about 0.5 percent; nitrogen up to about 0.5 percent, copper up to about 1.5 percent, sulfur up to about 0.3 percent, phosphorus up to about 0.3 percent, up to about 5 percent total of tantalum, titanium, hafnium and zirconium; iron from about 50 to about 70 percent; and incidental impurities. The alloy is suitable for use in elevated temperature applications such as in valve seat inserts for combustion engines.

An iron-based alloy includes, in weight percent, carbon from about 1 to about 2 percent; manganese from about 0.1 to about 1 percent; silicon from about 0.1 to about 2.5 percent; chromium from about 11 to about 19 percent; nickel up to about 8 percent; vanadium from about 0.8 to about 5 percent; molybdenum from about 11 to about 19 percent; tungsten up to about 0.5 percent; niobium from about 1 to about 4 percent; cobalt up to about 5.5 percent; boron up to about 0.5 percent; nitrogen up to about 0.5 percent, copper up to about 1.5 percent, sulfur up to about 0.3 percent, phosphorus up to about 0.3 percent, up to about 5 percent total of tantalum, titanium, hafnium and zirconium; iron from about 50 to about 70 percent; and incidental impurities. The alloy is suitable for use in elevated temperature applications such as in valve seat inserts for combustion engines.

Disclosed is a steel composition including specified ranges of Ni; Mo; Co; Mo+Co+Si+Mn+Cu+W+V+Nb+Zr+Ta+Cr+C; Co+Mo; Ni+Co+Mo; and traces of Al; Ti; N; Si; Mn; C; S; P; B; H; O; Cr; Cu; W; Zr; Ca; Mg; Nb; V; and Ta in specified ranges; the remainder being iron and impurities. The inclusion population, as observed by image analysis over a polished surface measuring 650 mm.sup.2 if hot-formed or hot-rolled; and measuring 800 mm.sup.2 if cold-rolled, does not contain non-metallic inclusions of diameter>10 μm, and, in the case of a hot-rolled sheet, does not contain more than four non-metallic inclusions of diameter 5-10 μm over 100 mm.sup.2, the observation being performed by image analysis over a polished surface measuring 650 mm.sup.2.