Steel and steel wire for high strength spring

A technology for heat treatment of steel and quality, applied in the field of spring steel, can solve problems such as insufficient sulfide control, and achieve high strength, high coilability, and high performance

Active Publication Date: 2007-05-09
NIPPON STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

However, this amount of addition is insufficient for the control of sulfide, which is also easily inferred from the above-mentioned Patent Document 8.

Method used

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  • Steel and steel wire for high strength spring
  • Steel and steel wire for high strength spring
  • Steel and steel wire for high strength spring

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0170] Tables 1 to 3 show the composition of the steel materials prepared for evaluation of various properties, and Tables 4 to 6 show the melting method and properties of the steel materials. A small amount of steel is smelted in a vacuum melting furnace (any one of 10kg, 150kg, 2t) or a 270t converter. The melting furnaces used for melting in each example are shown in the table. In the case of melting in a vacuum melting furnace, sufficient attention should be paid to mixing oxide generating elements from refractory materials or raw materials using magnesia crucibles, etc., and adjustments should be made so that the composition is the same as that of practical converter melting materials.

[0171] Of these slightly dissolved samples, 150 kg of material were rolled by welding with a dummy billet. In addition, after forging 10kg of charge into φ13, it is processed in the order of heat treatment (normalizing) and machining (φ10mm×400mm) to make thin straight rods. At this sta...

Embodiment 2

[0203] For the case treated with φ4mm, the chemical compositions of the present and comparative steels are shown in Tables 7 to 9, the area ratio of the rarefied region of the carburized carbides, the occupied area ratio of the alloy-based / carburized spherical carbides, and the equivalent weight Density of spherical carbides in carburized system with a circle diameter of 0.2 to 3 μm, density of spherical carbides in carburized system with an equivalent circle diameter of more than 3 μm, prior austenite grain size number, retained austenite content (mass %), tensile strength The strength, winding properties (tensile elongation), and average fatigue strength are shown in Tables 10 to 12.

[0204] Manufacturing method of sample (Wire-rod: wire rod)

[0205] In Invention Example 1 of the present invention, a material refined in a 250 t converter was produced into a billet by continuous casting. In addition, in other examples, after melting in a 2t-vacuum melting furnace, the bill...

Embodiment 70

[0230] In the case of Example 70, the tempering temperature was set to 600° C. to set a lower strength, so that the fatigue strength thereof was insufficient.

[0231] In Examples 71 to 73, the retained austenite reached a predetermined amount or more due to the fact that the cooling rate could not be ensured, even though the carbide thin region was small. Although the austenite grain size is small, the amount of retained austenite is intentionally increased by setting the cooling oil during quenching to 80°C or higher. As a result, the strength is insufficient, and fatigue properties cannot be ensured.

[0232] In the case of Examples 74 to 77, the heating temperature during quenching was set to 1000°C to suppress unsolution carbides, but the austenite grain size was increased, so sufficient ductility could not be ensured, and thus winding could not be ensured. sex.

[0233] Furthermore, in Examples 78 and 79, since the Si content was reduced, sufficient temper softening re...

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Abstract

Disclosed is a spring steel for spring steel wires which exhibits both high strength and good workability in cold coiling. This spring steel comprises, in mass %, 0.45 % to 0.70 % of C, 1.0 % to 3.0 % of Si, 0.05 % to 2.0 % of Mn, 0.015 % or less of P, 0.015 % or less of S, 0.0015 % to 0.0200 % of N, and 0.000 2% to 0.01 % of t-O, and limits Al <= 0.01 % and Ti <= 0.003 %. Also disclosed is a spring steel wire using such a spring steel. The spring steel is further characterized in that, with respect to cementite spherical carbides on a microscopic observation plane, the percentage of the area occupied by carbides having a circle-equivalent diameter of 0.2 mu m or more is 7 % or less, the density of carbides having a circle-equivalent diameter of 0.2 mu m to 3 mu m is 1 piece / m<2> or less, the density of carbides having a circle-equivalent diameter of more than 3 mu m is 0.001 piece / m<2> or less, the grain size number of prior austenite is 10 or higher, the amount of residual austenite is 15 mass % or less, and the area percentage of a thin region, where the density of cementite carbides having a circle-equivalent diameter of 2 mu m or more is low, is 3 % or less.

Description

technical field [0001] The present invention relates to a spring steel used in an engine valve spring and a suspension spring, and in particular to a spring steel and a steel wire which can be cold rolled and have high strength and high toughness. Background technique [0002] With the reduction in weight and performance of automobiles, springs are also required to be increased in strength, and the tensile strength of high-strength steel supplied for springs after heat treatment exceeds 1500 MPa. In recent years, steel wires with a tensile strength exceeding 1900 MPa are also required. This is because even if the spring is slightly softened by heating, such as stress relief annealing or nitriding treatment at the time of manufacture, it is possible to ensure that the spring does not cause troublesome material hardness. [0003] In addition, it is known that nitriding treatment and shot peening increase the surface hardness and significantly improve the durability of the spr...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C22C38/00C22C38/04C21D8/06C22C38/60C21D9/52F16F1/06
Inventor 桥村雅之萩原博宫木隆成金须贵之山崎浩一
Owner NIPPON STEEL CORP
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