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US 10,294,540 B2Granted
Steel wire for spring and method for manufacturing same
AssigneeHonda Motor Co., Ltd.
InventorHirokuni Fuchigami
Life of this patent
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Abstract
A steel wire for a spring, in which the sag resistance and the fatigue characteristics are improved by production processes without addition of alloy elements, is provided. The spring has a structure obtained by quenching and tempering and includes a first layer at a surface thereof, a second layer interior to the first layer, and a third layer, which is interior to the second layer and reaches a center of the spring, and the second layer has lower hardness than the first and the third layers.
Claims5
A production method for a steel wire for a spring, the steel wire including 0.05 to 0.8 mass % of C, the method comprising:
- a first heat cycle step including heating the entirety of the steel wire to a temperature higher than a temperature of austenite transformation point TAC3 and then quenching the steel wire;
- a second heat cycle step including heating the steel wire, wherein only a first layer at a surface of the steel wire is heated to a temperature T1, a second layer interior to the first layer is heated to a temperature T2, a third layer interior to the second layer and reaching center of the steel wire is heated to a temperature T3, and then quenching the steel wire, wherein T1>T2>T3, T1 is a temperature higher than the temperature of austenite transformation point TAC3 and T2 is a temperature lower than the temperature of austenite transformation point TAC3;
- and
- a third heat cycle step including tempering heating the entirety of the steel wire to a temperature Ttemp, wherein T3<Ttemp<T2;
- thereby yielding a steel wire having a structure with the second layer having lower hardness than the first layer and the third layer after the third heat cycle step.
2 more elements
Dependencies are inferred from the claim text.