Steel for cold forging/nitriding, steel material for cold forging/nitriding, and cold-forged/nitrided component

Patent metadata

Field	Value
Publication number	US-9574256-B2
Application number	US-201314389776-A
Country	US
Kind code	B2
Filing date	Feb 28, 2013
Priority date	Apr 2, 2012
Publication date	Feb 21, 2017
Grant date	Feb 21, 2017

Abstract

A steel comprises, by mass percent, C: 0.10 to 0.15%, Si: not less than 0.02% and less than 0.10%, Mn: more than 0.90% and not more than 2.50%, P≦0.030%, S≦0.050%, Cr: 0.80 to 2.0%, V: 0.05 to 0.50%, Al: 0.01 to 0.07%, N≦0.0080%, O≦0.0030%, and one or more selected from Mo, Cu, Ni, Ti, Nb, Zr, Pb, Ca, Bi, Te, Se and Sb, the balance being Fe and impurities. The composition satisfies [35≦Mn/S≦200], [20≦(669.3×log e C−1959.6×log e N−6983.3)×(0.067×Mo+0.147×V)≦80], [140×Cr+125×Al+235×V≧160] and [150≦511×C+33×Mn+56×Cu+15×Ni+36×Cr+5×Mo+134×V≦200].

First claim

The invention claimed is:

1. A steel for cold forging and nitriding, having a chemical composition comprising, by mass percent, C: 0.10 to 0.15%, Si: not less than 0.02% and less than 0.10%, Mn: more than 0.90% and not more than 2.50%, Cr: 0.80 to 2.0%, V: 0.05 to 0.50%, and Al: 0.01 to 0.07%, with the balance being Fe and impurities, wherein
P, S, N and O among the impurities are P: 0.030% or less, S: 0.050% or less, N: 0.0080% or less, and O: 0.0030% or less,
the Fn1 expressed by the formula (1) described below is 35 to 200,
the Fn2 expressed by the formula (2) described below is 20 to 80,
the Fn3 expressed by the formula (3) described below is 160 or more, and
the Fn4 expressed by the formula (4) described below is 150 to 200:
Fn1=Mn/S  (1);

Fn2=(669.3×log e C−1959.6×log e N−6983.3)×(0.067×Mo+0.147×V)   (2);

Fn3=140×Cr+125×Al+235×V  (3); and

Fn4=511×C+33×Mn+56×Cu+15×Ni+36×Cr+5×Mo+134×V   (4);

where, each symbol C, Mn, S, Cr, Mo, V, N, Al, Cu and Ni in the above formulas (1) to (4) represents the content by mass percent of the element concerned.

2. A steel for cold forging and nitriding, having a chemical composition comprising, by mass percent, C: 0.10 to 0.15%, Si: not less than 0.02% and less than 0.10%, Mn: more than 0.90% and not more than 2.50%, Cr: 0.80 to 2.0%, V: 0.05 to 0.50%, Al: 0.01 to 0.07%, and one or more elements selected from the groups (a) to (d) listed below, with the balance being Fe and impurities, wherein
P, S, N and O among the impurities are P: 0.030% or less, S: 0.050% or less, N: 0.0080% or less, and O: 0.0030% or less,
the Fn1 expressed by the formula (1) described below is 35 to 200,
the Fn2 expressed by the formula (2) described below is 20 to 80,
the Fn3 expressed by the formula (3) described below is 160 or more, and
the Fn4 expressed by the formula (4) described below is 150 to 200:
Fn1=Mn/S  (1);

Fn2=(669.3×log e C−1959.6×log e N−6983.3)×(0.067×Mo+0.147×V)   (2),

Fn3=140×Cr+125×Al+235×V  (3); and

Fn4=511×C+33×Mn+56×Cu+15×Ni+36×Cr+5×Mo+134×V   (4);

where, each symbol C, Mn, S, Cr, Mo, V, N, Al, Cu and Ni in the above formulas (1) to (4) represents the content by mass percent of the element concerned;
(a) Mo: 0.50% or less;
(b) One or more selected from Cu: 0.50% or less and Ni: 0.50% or less;
(c) One or more selected from Ti: 0.20% or less, Nb: 0.10% or less, and Zr: 0.10% or less;
(d) One or more selected from Pb: 0.50% or less, Ca: 0.010% or less, Bi: 0.30% or less, Te: 0.30% or less, Se: 0.30% or less, and Sb: 0.30% or less.

3. A steel material for cold forging and nitriding having a chemical composition according to claim 1 , wherein the content of V in precipitates determined by an extraction residue analysis is 0.10% or less.

4. A steel material for cold forging and nitriding having a chemical composition according to claim 2 , wherein the content of V in precipitates determined by an extraction residue analysis is 0.10% or less.

5. A cold forged and nitrided component having a chemical composition according to claim 1 , wherein the core hardness thereof is 200 or more in Vickers hardness, the surface hardness thereof is 700 or more in Vickers hardness, and the effective case depth thereof is 0.20 mm or more.

6. A cold forged and nitrided component having a chemical composition according to claim 2 , wherein the core hardness thereof is 200 or more in Vickers hardness, the surface hardness thereof is 700 or more in Vickers hardness, and the effective case depth thereof is 0.20 mm or more.

Assignees

• Nippon Steel & Sumitomo Metal Corp

Inventors

• Imataka Hideki
• Horimoto Masayuki
• Gyotoku Yuya
• Tanaka Kosuke

Classifications

• C23C8/50

  of ferrous surfaces · CPC title

• C22C38/42

  with copper · CPC title

• C21D9/0075

  for rods of limited length (of unlimited length C21D9/52) · CPC title

• C22C38/20

  with copper · CPC title

• C22C38/58

  with more than 1.5% by weight of manganese · CPC title