Steel sheet

A steel sheet with controlled composition and microstructure characteristics addresses the challenge of high carbon content by enhancing hardenability and cold workability, ensuring high strength and elastic limit in mechanical parts like springs and washers.

WO2026155140A1PCT designated stage Publication Date: 2026-07-23NIPPON STEEL CORPORATION
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Patent Information

Authority / Receiving Office
WO · WO
Patent Type
Applications
Current Assignee / Owner
NIPPON STEEL CORPORATION
Filing Date
2026-01-14
Publication Date
2026-07-23

AI Technical Summary

Technical Problem

Existing steel sheets used for manufacturing high-strength mechanical parts, such as springs and washers, require improved hardenability and cold workability, especially when carbon content is high, as they often suffer from decreased hardenability due to graphite formation and reduced cold workability from excessive silicon content.

Method used

A steel sheet composition with specific ranges of C: 0.50 to 0.80%, Si: 0.50 to 2.10%, Mn: 0.20 to 1.20%, P: 0.100% or less, S: 0.100% or less, Al: 0.100% or less, Cr: 0.01 to 0.60%, N: 0.0150% or less, and controlled microstructure characteristics, including a total area ratio of ferrite and cementite particles of 95% or more, average particle sizes, and spheroidization rates, to enhance hardenability and cold workability.

Benefits of technology

The solution provides steel sheets with excellent hardenability and cold workability, ensuring high strength and elastic limit, while preventing graphite formation and maintaining sufficient hardenability even with high silicon content.

✦ Generated by Eureka AI based on patent content.

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Abstract

A steel sheet according to the present disclosure contains, in mass%, C: 0.50-0.80%, Si: > 0.50-2.10%, Mn: 0.20-1.20%, Al: 0.100% or less, Cr: 0.01-0.60%, N: 0.0150% or less, with the balance being Fe and impurities. The total area ratio of ferrite and cementite particles is 95% or more; the average particle size of the ferrite is 20.0 μm or less; the average particle size of the cementite particles is 1.50 μm or less; and the spheroidization rate of the cementite particles is from 75% to less than 85%. The Cr concentration in the residue [Cr]θ (mass%), the Mo concentration in the residue [Mo]θ (mass%), and the C content in mass% in the chemical composition of the steel sheet satisfy formula (3); and the graphitization rate GR defined by formula (4) using [C] and the C concentration of carbides in the residue [C]CB (mass%) is 5.0% or less.　[Cr]θ+[Mo]θ-2.5 / (√[C])≤0 (3) GR=(1-[C]CB / [C])×100 (4)
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