Steel plate and its manufacturing method

By controlling the composition and microstructure of high-carbon steel sheets through cold rolling and annealing, the steel sheet achieves improved workability and toughness after heat treatment, addressing the balance of properties in existing technologies.

JP7883194B1Active Publication Date: 2026-07-01NIPPON STEEL CORPORATION
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Patent Information

Authority / Receiving Office
JP · JP
Patent Type
Patents
Current Assignee / Owner
NIPPON STEEL CORPORATION
Filing Date
2025-10-03
Publication Date
2026-07-01

AI Technical Summary

Technical Problem

Existing high-carbon steel sheets struggle to balance workability, hardenability, and toughness after heat treatment (quenching and tempering), despite controlling the average particle size of cementite particles.

Method used

Control the composition and microstructure of the steel sheet by adjusting the average grain size of ferrite and cementite, with specific element ratios, and perform cold rolling and annealing under defined conditions to improve workability and toughness.

Benefits of technology

The steel sheet achieves excellent workability, hardenability, and high toughness after heat treatment, with controlled ferrite grain size, cementite particle size, and precipitation state.

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Abstract

This steel sheet has a composition, by mass, containing C: 0.70-1.30%, Si: 0.01-0.50%, Mn: 0.05-1.30%, P: 0.100% or less, S: 0.100% or less, Al: 0.100% or less, N: 0.0150% or less, Cr: 0-1.20%, Ni: 0-2.800%, Mo: 0-0.500%, V: 0-0.500%, Nb: 0-0.500%, Ti: 0-0.150%, and B: 0-0.0100%, with the remainder being Fe and impurities, and has a metallic structure containing ferrite with an average grain size of 15.0 μm or more, and cementite with an average particle size of 0.70-1.20 μm. The cementite in question has an area ratio of spheroidized cementite with an aspect ratio of 3.0 or less to all cementite, which accounts for 85% or more of the total area of ​​spheroidized cementite, and a ratio of the number of intragranular cementites to the total number of cementites of 0.70 or more.
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