Low-carbon sulphur free-cutting steel

Abstract

A low carbon sulphur free-cutting steel, in terms of mass%, is comprised of between 0.04-0.15% C, between 0.10-0.70% Si, between 0.85-1.50% Mn, between 0.040-0.120% P, between 0.250-0.400% S, less than 0.005% Al, between 0.0020-0.0120% O, between 0.0070-0.0150% N, with the remainder being Fe and unavoidable impurities; and which fulfills formula (1) and formula (2). 0.15% <= Si% + 2*P% - (5*Al% + 10*O% + 3*N%) <= 0.75% (1), ([Mn%]5) / 15 < S% < ([Mn%]5) / 2 (2).

Description

technical field [0001] The present invention relates to a low-carbon sulfur free-cutting steel containing elemental sulfur for improving machinability. Background technique [0002] In sulfur free cutting steel, a large amount of oxygen is contained in order to control the form of sulfide effective for machinability, that is, to perform spindle formation. However, since all the oxygen cannot be solid-dissolved in the sulfide, the formation of huge oxides cannot be avoided, so hairlines are formed and surface hairlines during hot rolling are caused by this. [0003] As a technique for solving this phenomenon, techniques for reducing the amount of oxygen or reducing the amount of Si as a deoxidizer to reduce the amount of oxides have been proposed (Patent Documents 1, 2, and 3). In addition, a technique of increasing solid-dissolved oxygen by increasing the amount of sulfide has also been proposed (Patent Document 4). [0004] Patent Document 1 relates to a free-cutting stee...

AI Technical Summary

Problems solved by technology

[0008] However, in the free-cutting steel described in Patent Document 1, the amount of oxygen is limited to 0.008 mass% or less, but only by reducing the amount of oxygen, the control of the form of sulfide is insufficient, and there are also extended sulfides.

In the free-cutting steels described in Patent Documents 2 and 3, the amount of Si is limited to 0.1 mass% or less, but it is used as a deoxidizer, and it is a component composition that has not been particularly considered for the improvement of machinability.

In addition, in the free-cutting steel of Patent Document 4, although a large amount of S is added, the form of sulfide cannot be controlled.

[0009] Therefore, it cannot be said that the free-cutting steels described in Patent Documents 1 to 4 have sufficient machinability.

Images