Low carbon composite free-cutting steel product excellent in roughness of finished surface and method for production thereof

A technology for surface roughness and free-cutting steel, which is applied in the field of low-carbon resulfurized free-cutting steel products and its preparation, and can solve problems affecting machinability and other issues

Inactive Publication Date: 2006-12-27
KOBE STEEL LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

[0006] In addition to these inclusions, the structure and properties (matrix propertie...

Method used

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  • Low carbon composite free-cutting steel product excellent in roughness of finished surface and method for production thereof
  • Low carbon composite free-cutting steel product excellent in roughness of finished surface and method for production thereof
  • Low carbon composite free-cutting steel product excellent in roughness of finished surface and method for production thereof

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0114] Embodiments of the present invention are explained below. The effect of improving the machinability of steel wires by controlling the hardness of proeutectoid ferrite is first demonstrated in Examples 1 and 2.

[0115] A series of steel wires with various compositions were prepared under various hot rolling conditions with actual equipment. The machinability and other properties of the steel bars were evaluated separately. Specifically, low carbon steel slabs having compositions 1 to 14 shown in Tables 1 and 2 below were prepared by melting and casting at a cooling rate of 20° C. / sec for casting solidification. Table 2 is a continuation of Table 1, and also shows the free oxygen content and Of / S in the molten steel before casting.

[0116] These billets were heated and hot-rolled under the conditions shown in Table 3 below, thereby producing steel wire rods having wire diameters shown in Table 3. The cooling rate after rolling shown in Table 3 refers to the average c...

Embodiment 2

[0136]Next, in the same manner as in Example 1, a series of low-carbon billets having compositions 15-26 shown in Tables 4 and 5 were prepared by melting. Table 5 is a continuation of Table 4 and shows the free oxygen content and the Of / S ratio in the molten steel before casting. Hot rolling was performed according to the system B in Table 3 of Example 1. The machinability and other properties of steel wires produced using actual equipment were evaluated in the same manner as in Example 1.

[0137] Table 6 shows the wire diameter of the prepared steel wire rod and the average width of MnS, the relationship between the average width of MnS and the diameter (d) of the steel product [2.8 × (log d)] and the hardness of proeutectoid ferrite ( HV). Table 6 also shows the finished surface roughness of the prepared steel wire rods as determined in the machinability test. Observing the structure of the obtained steel wire rods, it is found that they are all ferrite-pearlite structur...

Embodiment 3

[0151] The effect of improving the machinability of steel wire by controlling the difference in deformation resistance between high temperature and room temperature in a compression test of steel products was demonstrated.

[0152] A series of low carbon billets having compositions 27-41 shown in Tables 7 and 8 were produced by melting in the same manner as in Example 1. Table 8 is a continuation of Table 7 and shows the free oxygen content and the Of / S ratio in the molten steel before casting. The low-carbon billets were hot-rolled using actual equipment at the heating temperature, finish rolling temperature, and cooling rate shown in Table 9, thereby obtaining steel wires each having a diameter of 8.0 mm. The machinability and other properties of the steel wires were evaluated separately.

[0153] The cooling rate after rolling shown in Table 9 refers to the average cooling rate in the case of placing the sample steel wire rod after finish rolling on the Stelmor conveyor, a...

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Abstract

The present invention provides a low-carbon resulfurized free machining steel product excellent in machinability typified by finished surface roughness even though toxic Pb or special elements such as Bi or Te are not added, and a suitable production method thereof. A steel product has a specific composition, has contents of Mn and S satisfying the following conditions: 0.40 Mn*S 1.2 and Mn/S 3.0, and contains a ferrite-pearlite structure as the metallographic structure, in which the average width ( m) of sulfide inclusions in the steel product is 2.8* (log d) or more, wherein d (mm) is the diameter of the steel product, and pro-eutectoid ferrite in the metallographic structure has a hardness HV of 133 to 150 or a difference in deformation resistance at a strain of 0.3 between 200 DEG C and 25 DEG C is 110 MPa or more and 200 MPa or less, the deformation resistances being determined in a compression test at a deformation rate of 0.3 mm/min.

Description

technical field [0001] The present invention relates to a low-carbon resulfurized free-cutting steel product that does not contain lead (Pb) and has satisfactory machinability, and a preparation method thereof. "Steel products" here typically refer to hot-rolled bars and rods. Background technique [0002] Low-carbon resulfurized free-cutting steel products are used in small parts such as screws and threaded joints that do not require high mechanical properties but require good machinability and can be mass-produced by cutting. Free cutting steel products containing Pb in addition to S are widely used as free cutting steel products having more satisfactory machinability. Lead is a hazardous substance that damages health, and there has been a need to reduce the lead content in such free-cutting steel products. Tellurium (Te) is also used in some free-cutting steel products, but it is toxic and deteriorates hot workability, and its content must be reduced. [0003] Many stu...

Claims

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Application Information

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IPC IPC(8): C22C38/00
Inventor 家口浩坂本浩一杉村朋子阿南吾郎尾崎胜彦
Owner KOBE STEEL LTD
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