A spot welded joint of at least two steel sheets is provided. At least one of the steel sheets presents yield strength above or equal to 600 MPa, an ultimate tensile strength above or equal to 1000 MPa, uniform elongation above or equal to 15%. The base metal chemical composition includes 0.05≤C≤0.21%, 4.0≤Mn≤7.0%, 0.5≤Al≤3.5%, Si≤2.0%, Ti≤0.2%, V≤0.2%, Nb≤0.2%, P≤0.025%, B≤0.0035%, and the spot welded joint contains a molten zone microstructure containing more than 0.5% of Al and containing a surface fraction of segregated areas lower than 1%, said segregated areas being zones larger than 20 μm.sup.2 and containing more than the steel nominal phosphorus content.

A spot welded joint of at least two steel sheets is provided. At least one of the steel sheets presents yield strength above or equal to 600 MPa, an ultimate tensile strength above or equal to 1000 MPa, uniform elongation above or equal to 15%. The base metal chemical composition includes 0.05≤C≤0.21%, 4.0≤Mn≤7.0%, 0.5≤Al≤3.5%, Si≤2.0%, Ti≤0.2%, V≤0.2%, Nb≤0.2%, P≤0.025%, B≤0.0035%, and the spot welded joint contains a molten zone microstructure containing more than 0.5% of Al and containing a surface fraction of segregated areas lower than 1%, said segregated areas being zones larger than 20 μm.sup.2 and containing more than the steel nominal phosphorus content.

The invention relates to a high strength steel with a careful selection of the normal alloying elements C, Mn, Si and Al, together with micro-element addition. This a steel with a high strength and high hole expansion ratio can be produced. The invention also relates to the method to manufacture this high strength steel.

Provided is a steel sheet and a method for manufacturing same, the steel sheet, which is optimized a composition and microstructure, and which can be used for automobile parts and the like, having superb bendability, and superior balance of strength and ductility and of strength and hole expansion ratio.

Disclosed are an R-T-B-based permanent magnet material, a preparation method therefor and the use thereof. The R-T-B-based permanent magnet material comprises R, B, M, Fe, Co, X and inevitable impurities, wherein: (1) R is a rare earth element, and the R includes at least Nd and RH, M being one or more of Ti, Zr and Nb, and X including Cu, “Al and/or Ga”; and (2) in percentage by weight, R: 30.5-32.0 wt%, B: 0.95-0.99 wt%, M: 0.3-0.6 wt%, X: 0.8-1.8 wt%, and Cu: 0.35-0.50 wt%, and the balance is Fe, Co and inevitable impurities. According to the present invention, under the condition of 0.3-0.6 wt% of a high melting point metal, a permanent magnet material with an excellent magnet performance and a good squareness is obtained.

Disclosed are an R-T-B-based permanent magnet material, a preparation method therefor and the use thereof. The R-T-B-based permanent magnet material comprises R, B, M, Fe, Co, X and inevitable impurities, wherein: (1) R is a rare earth element, and the R includes at least Nd and RH, M being one or more of Ti, Zr and Nb, and X including Cu, “Al and/or Ga”; and (2) in percentage by weight, R: 30.5-32.0 wt%, B: 0.95-0.99 wt%, M: 0.3-0.6 wt%, X: 0.8-1.8 wt%, and Cu: 0.35-0.50 wt%, and the balance is Fe, Co and inevitable impurities. According to the present invention, under the condition of 0.3-0.6 wt% of a high melting point metal, a permanent magnet material with an excellent magnet performance and a good squareness is obtained.

Provided is a steel sheet which can be used for automobile parts and the like, and relates to a steel sheet having a superior balance of strength and ductility and strength and hole expansion ratio and superior bending formability, and a method for manufacturing same.

A non-oriented electrical steel sheet according to an exemplary embodiment of the present invention includes, in wt%, Si: 1.5 to 4.0%, Al: 0.5 to 1.5%, Mn: 0.05 to 0.55%, C: 0.005% or less, Ti: 0.004% or less (excluding 0%), N: 0.005% or less (excluding 0%), S: 0.005% or less (excluding 0%), and Cu: 0.01% or less (excluding 0%), and the balance of Fe and inevitable impurities, and satisfies Formula 1 and Formula 2 below.

[N]≤0.005×([Al]×[Ti])  [Formula 1]

[S]≤0.01×([Mn]+[Cu])  [Formula 2]

(In Formula 1 and Formula 2, [N], [Al], [Ti], [S], [Mn], and [Cu] represent a content (wt %) of N, Al, Ti, S, Mn, and Cu, respectively).

Provided is a steel sheet which can be used for automobile parts and the like, and relates to a steel sheet having a superior balance of strength and ductility and strength and a hole expansion ratio and superior bending formability, and a method for manufacturing same.

A steel sheet includes a predetermined composition satisfying Expression (1), in which the microstructure at the ¼ thickness position from the surface in the sheet thickness direction includes, by vol %, ferrite: 95% or more and a remainder of the microstructure: 5% or less, has a proportion of unrecrystallized ferrite in the ferrite of 5% or less, and a half width w and an X-ray wavelength λ at a peak of (200) plane of the ferrite satisfy Expression (2).

0.80≤{(Ti/48−N/14)+Nb/93}/(C/12)≤5.00  (1)

w×λ≥0.20  (2)