| 摘要 |
PROBLEM TO BE SOLVED: To provide martensitic steel having sufficient strength and also excellent toughness even when used as automotive springs and bolts, and to provide its production method. SOLUTION: This high strength and high toughness martensitic steel contains >=0.1 mass % C, and >=80% or its metallic structure is composed of martensite. The average value of the old austenite crystal grain size numbers is >=7, and also, the area ratio occupied by the old austenite grains with the grain size numbers different by >=3.0 from the grain size number having the maximum frequency is <=10%.
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