STRAND FOR SAW WIRE AND MANUFACTURING METHOD THEREOF

1 . A strand for saw wire, containing:

in mass %,

C: 0.87% to 1.2%;

Si: 0.02% to 2.0%;

Mn: 0.1% to 1.0%; and

Cr: 0.5% or less,

wherein

regarding contents of C, Si, Mn and Cr, a value of parameter P represented by a following (equation 1) is 1000 or more,

a P content is 0.015% or less,

an S content is 0.015% or less,

an N content is 0.01% or less,

a balance is composed of Fe and inevitable impurities,

a metallic structure contains wire-drawn pearlite in an area ratio of 98% or more,

a diameter is 0.05 mm to 0.18 mm,

a tensile strength is 4000 MPa or more, and

a twist number in a twist test in which a grip-to-grip distance is 100 mm, and a tension equal to a tensile strength×a cross-sectional area of wire×0.5 is applied, is 5 or more.

P= 1098×[C]+98×[Si]−20×[Mn]+167×[Cr]  (equation 1)

(in the (equation 1), [C], [Si], [Mn] and [Cr] indicate contents (mass %) of C, Si, Mn and Cr, respectively.)

2 . The strand for saw wire according to claim 1 , wherein

a C content is 0.92 mass % or more,

the value of parameter P is 1050 or more, and

the metallic structure contains the wire-drawn pearlite in an area ratio of 99% or more.

3 . The strand for saw wire according to claim 1 , wherein a tensile strength under twisting is 85% or more of a tensile strength.

4 . The strand for saw wire according to claim 1 , wherein a tensile elongation under twisting is 2% or more.

5 . The strand for saw wire according to claim 1 , wherein a difference in Vickers hardness between a surface portion in which a depth from a surface of the strand for saw wire is within a range of the diameter×0.2 or less and a center portion in which a distance from a center of the strand for saw wire is within a range of the diameter×0.2 or less, is 100 or less.

6 . The strand for saw wire according to claim 1 , wherein a residual stress of a surface portion of the strand for saw wire is −100 MPa or less.

7 . The strand for saw wire according to claim 1 , further containing, in mass %, at least one kind selected from a group consisting of:

Ni: 1.0% or less;

Cu: 0.5% or less;

Mo: 0.5% or less;

V: 0.5% or less; and

B: 0.0050% or less.

8 . A manufacturing method of a strand for saw wire, comprising:

performing hot rolling on a steel billet and cooling the resultant at a rate of 10° C./second or more so as to obtain a hot-rolled wire rod whose diameter is 6 mm or less and having a structure containing 97% or more of pearlite in which a thickness of cementite is 0.03 μm or less;

performing primary wire drawing on the hot-rolled wire rod so as to obtain a primary wire-drawn material;

performing final patenting treatment on the primary wire-drawn material so as to obtain a patenting material having a structure containing 98% or more of pearlite in which a thickness of cementite is 0.02 μm or less; and

performing finish wire drawing of the patenting material by setting a wire drawing strain ε to less than 4.5,

wherein

the steel billet contains:

in mass %,

C: 0.87% to 1.2%;

Si: 0.02% to 2.0%;

Mn: 0.1% to 1.0%; and

Cr: 0.5% or less,

regarding contents of C, Si, Mn and Cr, a value of parameter P represented by a following (equation 1) is 1000 or more,

a P content is 0.015% or less,

an S content is 0.015% or less,

an N content is 0.01% or less, and

a balance is composed of Fe and inevitable impurities, and

regarding the wire drawing strain ε, a value of parameter Q represented by a following (equation 2) is 380 or more.

P= 1098×[C]+98×[Si]−20×[Mn]+167×[Cr]  (equation 1)

Q= 99×[C]+2.7×exp(ε/2)/(0.075−0.0112×[C])  (equation 2)

(in the (equation 1) and the (equation 2), [C], [Si], [Mn] and [Cr] indicate contents (mass %) of C, Si, Mn and Cr, respectively.)

9 . The manufacturing method of a strand for saw wire according to claim 8 , wherein

a C content of the steel billet is 0.92 mass % or more,

the value of parameter P is 1050 or more,

the value of parameter Q is more than 440,

a structure of the hot-rolled wire rod contains 98% or more of pearlite in which a thickness of cementite is 0.03 μm or less, and

a structure of the patenting material contains 99% or more of pearlite in which a thickness of cementite is 0.02 μm or less.

10 . The manufacturing method of a strand for saw wire according to claim 8 , wherein the steel billet further contains, in mass %, at least one kind selected from a group consisting of:

Ni: 1.0% or less;

Cu: 0.5% or less;

Mo: 0.5% or less;

V: 0.5% or less; and

B: 0.0050% or less.

11 . The manufacturing method of a strand for saw wire according to claim 8 , wherein a finishing temperature of the hot rolling is 850° C. or more.

12 . The manufacturing method of a strand for saw wire according to claim 8 , wherein the performing final patenting treatment on the primary wire-drawn material so as to obtain a patenting material comprises:

keeping a temperature of the primary wire-drawn material within a range of 950° C. to 1100° C.; and

subsequently, keeping a temperature of the primary wire-drawn material within a range of 520° C. to 600° C.