Free-cutting steel drawn material and method for manufacturing the same

Abstract

Free-cutting steel draw material having a composition that satisfies formula (1) below, containing C: 0.03% to 0.09% by mass, Mn: 0.50% to 2.00%, P: 0.020% to 0.100%, S: 0.250% to 0.500%, Cr: 0.05% to 1.50%, Cu: 0.05% to 0.27%, N: 0.0050% to 0.0150%, Pb: 0.0300% to 0.1000%, and O: greater than 0.0100% and less than or equal to 0.0400%, with the remainder being Fe and unavoidable impurities, having a composition that satisfies formula (1) below, having a steel structure in which granular Pb particles with an equivalent circle diameter of 0.05 μm to 0.5 μm are distributed at a density of 5000 particles / mm2 or more, and satisfying formulas (2), (3), and (4) below. 1.50≦[Pb] / [Cu]+[Mn] / 2[S]≦3.00 (1) 210 ≤ H0.1 ≤ 340 ··· (2) 185 ≤ H0.5 ≤ 280 ··· (3) 150 ≤ Hc ≤ 240 ··· (4)

Claims

1. In mass percent, C: 0.03% or more and 0.09% or less, Mn: 0.50% or more and 2.00% or less, P: 0.020% or more and 0.100% or less, S: 0.250% or more and 0.500% or less, Cr: 0.05% or more and 1.50% or less, Cu: 0.05% or more and 0.27% or less, N: 0.0050% or more and 0.0150% or less, Pb: 0.0300% or more and 0.1000% or less and O: More than 0.0100% and less than 0.0400% It contains, with the remainder being Fe and unavoidable impurities, and has a component composition that satisfies the following formula (1), 5000 Pb granules / mm² with an equivalent circular diameter of 0.05 μm to 0.5 μm ２ It has a steel structure distributed above, The following equations (2), (3), and (4) are satisfied: Free-cutting steel extruded material. 1.50≦[Pb] / [Cu]+[Mn] / 2[S]≦3.00... (1) 210≦H ０．１ ≦340 ・・・ (2) 185≦H ０．５ ≦280 ・・・ (3) 150 ≤ Hc ≤ 240 ... (4) Here, The brackets [] indicate the content (per unit mass %) of the element within the brackets. H ０．１ This is the Vickers hardness (in HV) at a position 0.1 mm from the surface of the drawn material, H ０．５ This is the Vickers hardness (in HV) at a position 0.5 mm from the surface of the drawn material, Hc is the Vickers hardness (in units of HV) at a position half the diameter of the drawn material from the surface of the drawn material.

2. The free-cutting steel draw material according to claim 1, wherein the aforementioned component composition further contains at least one component selected from groups A to D below. Group A: in mass%, Si: 0.20% or less, Al: 0.20% or less and Ti: 0.15% or less One or more types selected from among them. Group B: in mass%, Bi: 0.50% or less, Ca: 0.02% or less, Se: 0.15% or less and Te: 0.1% or less One or more types selected from among them. Group C: in mass%, Sb: 0.020% or less, Sn: 0.020% or less, Ni: 1.0% or less and Mo: 1.0% or less One or more types selected from among them. Group D: in mass%, Nb: 0.050% or less, V: 0.050% or less, Zr: 0.050% or less, W: 0.050% or less, Ta: 0.050% or less, Y: 0.050% or less, Hf: 0.050% or less and B: 0.050% or less One or more types selected from among them.

3. In mass percent, C: 0.03% or more and 0.09% or less, Mn: 0.50% or more and 2.00% or less, P: 0.020% or more and 0.100% or less, S: 0.250% or more and 0.500% or less, Cr: 0.05% or more and 1.50% or less, Cu: 0.05% or more and 0.27% or less, N: 0.0050% or more and 0.0150% or less, Pb: 0.0300% or more and 0.1000% or less and O: More than 0.0100% and less than 0.0400% The process involves producing a cast slab by continuous casting containing Pb, with the remainder being Fe and unavoidable impurities, having a composition satisfying the following formula (1); rolling the slab at a heating temperature of 900°C to 1050°C with a surface reduction ratio of 50% or more to form a billet; rolling the billet at a heating temperature of 1100°C or more to form a steel bar or wire rod; and then drawing the steel bar or wire rod with a surface reduction ratio of 1.0% or more, resulting in 5000 Pb granules / mm² with an equivalent circular diameter of 0.05 μm to 0.5 μm. ２ A method for producing a free-cutting steel draw having a steel structure distributed as described above, and satisfying the following formulas (2), (3), and (4). 1.50≦[Pb] / [Cu]+[Mn] / 2[S]≦3.00... (1) 210≦H ０．１ ≦340 ・・・ (2) 185≦H ０．５ ≦280 ・・・ (3) 150 ≤ Hc ≤ 240 ... (4) Here, The brackets [] indicate the content (per unit mass %) of the element within the brackets. H ０．１ is the Vickers hardness (unit: HV) at the position 0.1 mm from the surface of the drawn material to the diameter of the drawn material, H ０．５ This is the Vickers hardness (in HV) at a position 0.5 mm from the surface of the drawn material, Hc is the Vickers hardness (in units of HV) at a position half the diameter of the drawn material from the surface of the drawn material.

4. The method for producing free-cutting steel extruded material according to claim 3, wherein the component composition further contains at least one component selected from groups A to D below. Group A: in mass%, Si: 0.20% or less, Al: 0.20% or less and Ti: 0.15% or less One or more types selected from among them. Group B: in mass%, Bi: 0.50% or less, Ca: 0.02% or less, Se: 0.15% or less and Te: 0.1% or less One or more types selected from among them. Group C: in mass%, Sb: 0.020% or less, Sn: 0.020% or less, Ni: 1.0% or less and Mo: 1.0% or less One or more types selected from among them. Group D: in mass%, Nb: 0.050% or less, V: 0.050% or less, Zr: 0.050% or less, W: 0.050% or less, Ta: 0.050% or less, Y: 0.050% or less, Hf: 0.050% or less and B: 0.050% or less One or more types selected from among them.

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