Nippon Steel Corporation

Nippon Steel Sumitomo Metal Corporation

Yoshihiro Daito

Masashi Sakamoto

Junichi Kodama

Masato Yuya

Takahide Umehara

Toshiyuki Manabe

Toshihiko Teshima

This hot-rolled wire rod includes, as a chemical composition, by mass %: C: 0.90% to 1.10%; Si: 0.50% to 0.80%; Mn: 0.10% to 0.70%; Cr: 0.10% to 0.40%; P: 0.020% or less; S: 0.015% or less; N: 0.0060% or less; O: 0.0040% or less; and a remainder consisting of Fe and impurities, in which Formulas (1) and (2) are satisfied by mass %, the structure of the hot-rolled wire rod consists of pearlite in an area ratio of 95.0% or more and a remainder, and TS, which is a tensile strength in unit of MPa, and TS*, which is determined from the C content, the Si content, and the Cr content, satisfy Formula (3),0.50≤[Si]+[Cr]≤0.90  (1)0.40≤[Cr]+[Mn]≤0.80  (2)−50<TS−TS*<50  (3)

Hot-rolled wire rod

A nitrided steel part excellent in bending straightening ability and bending fatigue characteristic enabling reduction of size and decrease of weight of parts or enabling demand for high load capacities to be met, using as a material a steel material containing, by mass %, C: 0.2 to 0.6%, Si: 0.05 to 1.5%, Mn: 0.2 to 2.5%, P: 0.025% or less, S: 0.003 to 0.05%, Cr: 0.05 to 0.5%, Al: 0.01 to 0.05%, and N: 0.003 to 0.025%, and having a balance of Fe and impurities, having formed on the steel surface a compound layer of a thickness 3 &#x3bc;m or less comprising iron, nitrogen, and carbon and a hardened layer formed below the compound layer, and having an effective hardened layer depth of 160 to 410 &#x3bc;m.

Nitrided steel part and method of production of same

A nitrided steel part excellent in pitting resistance and bending fatigue characteristic enabling reduction of size and decrease of weight of parts or enabling demand for high load capacities to be met, using as a material a steel material containing, by mass %, C: 0.05 to 0.25%, Si: 0.05 to 1.5%, Mn: 0.2 to 2.5%, P: 0.025% or less, S: 0.003 to 0.05%, Cr: over 0.5 to 2.0%, Al: 0.01 to 0.05%, and N: 0.003 to 0.025%, having a balance of Fe and impurities, having formed on the steel surface a compound larger of a thickness 3 &#x3bc;m or less containing iron, nitrogen, and carbon and a hardened layer formed below the compound layer, and having an effective hardened layer depth of 160 to 410 &#x3bc;m.

Provided is a steel wire rod for wire drawing containing, in terms of % by mass, C: from 0.90 to 1.20%, Si: from 0.10 to 1.30%, Mn: from 0.20 to 1.00%, Cr: from 0.20 to 1.30%, Al: from 0.005 to 0.050%, and the balance being composed of Fe and impurities, wherein a content of each N, P, and S, which are contained as the impurities, is N: from 0.0070% or less, P: from 0.030% or less, S: from 0.010% or less, and the steel wire rod having a metallographic structure of which 95% or more by volume ratio is a lamellar pearlite structure, wherein the lamellar pearlite structure has an average lamellar spacing of from 50 to 75 nm, an average length of cementites in the lamellar pearlite structure is 1.0 to 4.0 &#x3bc;m, and a percentage of a number of cementites having a length of 0.5 &#x3bc;m or less among the cementites in the lamellar pearlite structure is 20% or less.

Steel wire rod for wire drawing

A steel wire for drawing includes, as a chemical composition, by mass %: C: 0.9% to 1.2%, Si: 0.1% to 1.0%, Mn: 0.2% to 1.0%, and Cr: 0.2% to 0.6%, limits Al, N, P, and S to be predetermined ranges, and includes one or more selected from the group consisting of Mo: 0% to 0.20%, and B: 0% to 0.0030%, a remainder of Fe and impurities; in which a metallographic structure includes pearlite, a volume fraction of the pearlite is 95% or higher, an average lamellar spacing of the pearlite is 50 nm to 75 nm, an average length of cementite in the pearlite is 2.0 &#x3bc;m to 5.0 &#x3bc;m, and a ratio of the number of grains of cementite with a length of 0.5 &#x3bc;m or smaller to the cementite in the pearlite is 20% or lower.

Steel wire for drawing

A low alloy steel is heated to a temperature ranging from 550 to 620&#xb0; C., and high Kand low Kvalue processes are performed for a total process time of A: 1.5 to 10 hours. In the high Kvalue process, a nitriding potential Kgiven by Formula (1): 0.15 to 1.50, the average Kvalue K: 0.30 to 0.80, and the process time is X in hours. In the low Kvalue process, which is performed after the high Kvalue process, a nitriding potential Kgiven by Formula (1): 0.02 to 0.25, the average Kvalue K: 0.03 to 0.20, and the process time is Y in hours. Average nitriding potential value Kdetermined by Formula (2) ranges from 0.07 to 0.30.=(NHpartial pressure)/(Hpartial pressure)]&#x2003;&#x2003;(1)=()/&#x2003;&#x2003;(2)

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Tokyo, Japan

Yoshihiro Daito