Eco-friendly pb-free free cutting steel with excellent machinability and hot workability
Abstract
There is provided a Pb-free free cutting steel is formed of 0.03 to 0.30 wt % of carbon (C), 0.01 to 0.30 wt % of silicon (Si), 0.2 to 2.0 wt % of manganese (Mn), 0.02 to 0.10 wt % of phosphorus, 0.06 to 0.45 wt % of sulfur (S), 0.04 to 0.20 wt % of bismuth (Bi), 0.04 to 0.20 wt % of tin (Sn), 0.001 to 0.015 wt % of boron (B), 0.001 to 0.010 wt % of nitrogen (N), 0.002 to 0.025 wt % of total oxygen (T[O]), and residual Fe, and unavoidable impurities, wherein S, Bi, S, B, and N satisfy a certain relationship. The steel has excellent machinability no less than conventional free cutting steel including Pb, while being eco-friendly. Also, the steel has excellent hot ductility capable of reducing occurrence of defects on a surface, thereby improving hot rolling workability.
Claims
exact text as granted — not AI-modified1 . A Pb-free free cutting steel comprising 0.03 to 0.30 wt % of carbon (C), 0.01 to 0.30 wt % of silicon (Si), 0.2 to 2.0 wt % of manganese (Mn), 0.02 to 0.10 wt % of phosphorus (P), 0.06 to 0.45 wt % of sulfur (S), 0.04 to 0.20 wt % of bismuth (Bi), 0.04 to 0.20 wt % of tin (Sn), 0.001 to 0.015 wt % of boron (B), 0.001 to 0.010 wt % of nitrogen (N), 0.002 to 0.025 wt % of total oxygen (T[0]), and residual Fe, and unavoidable impurities,
wherein S, Bi, S, B, and N satisfy one or more relationships selected from a group consisting of following Relational Expressions 1 to 3,
(
Bi
+
Sn
+
S
)
Mn
≥
0.4
,
Relational
Expression
1
Mn
3
S
≥
4.6
,
Relational
Expression
2
and
B
N
≥
2.0
.
Relational
Expression
3
2 . A Pb-free free cutting steel comprising 0.03 to 0.30 wt % of C, 0.01 to 0.30 wt % of Si, 0.2 to 2.0 wt % of Mn, 0.02 to 0.10 wt % of P, 0.06 to 0.45 wt % of S, 0.04 to 0.20 wt % of Bi, 0.04 to 0.20 wt % of Sn, 0.001 to 0.015 wt % of B, 0.001 to 0.010 wt % of N, 0.002 to 0.025 wt % of T[0], and residual Fe, and unavoidable impurities,
wherein the steel comprises one of MnO—SiO 2 —Al 2 O 3 -based oxide, CaO—SiO 2 —Al 2 O 3 -based oxide, and composite oxides with a low melting point, which is a mixture of the MnO—SiO 2 —Al 2 O 3 -based oxide and the CaO—SiO 2 —Al 2 O 3 -based oxide.
3 . The steel of claim 2 , wherein the MnO—SiO 2 —Al 2 O 3 -based oxide is formed of 20 to 65 wt % of MnO, 25 to 60 wt % of Si02, and 0 to 30 wt % of Al 2 O 3 .
4 . The steel of claim 2 , wherein the CaO—SiO 2 —Al 2 O 3 -based oxide is formed of 10 to 55 wt % of CaO, 35 to 65 wt % of SiO 2 , and 0 to 25 wt % of Al 2 O 3 .
5 . The steel of claim 2 , wherein there are five or more of the composite oxides with a low melting point in 5 g of a steel wire rod.
6 . The steel of claim 2 , wherein the S, Bi, S, B, and N satisfy one or more relationships selected from a group consisting of following Relational Expressions 1 to 3,
(
Bi
+
Sn
+
S
)
Mn
≥
0.4
,
Relational
Expression
1
Mn
3
S
≥
4.6
,
Relational
Expression
2
and
B
N
≥
2.0
.
Relational
Expression
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