Medium carbon steel sheet, quenched member, and method for manufacturing medium carbon steel sheet and quenched member

Abstract

This medium carbon steel sheet contains 0.10-0.80% of C, 0.01-0.3% of Si, 0.3-2.0% of Mn, 0.001-0.03% of P, 0.0001-0.01% of S, 0.001-0.10% of Al, and 0.001-0.01% of N (percentages given with respect to weight); the average carbide diameter is 0.4 mum or less; the ratio of the number of carbides that are 1.5 times or greater than the size of the average carbide diameter is 30% or less of the total number of carbides; the carbide spheroidizing rate is 90% or greater; the average ferrite grain size is 10 mum or greater; and the tensile strength (TS) is 550 MPa or less.

Description

technical field [0001] The present invention relates to a medium-carbon steel sheet excellent in cold workability, especially cold forgeability, and a method for producing the same. In addition, the present invention relates to a member (quenched member) obtained by forming the medium carbon steel sheet and then quenching it, and its manufacturing method. [0002] This application claims priority based on Patent Application No. 2011-197044 for which it applied to Japan on September 9, 2011, The content is used for this application. Background technique [0003] Members such as chains, gears, clutches, saws, and knives require wear resistance and fatigue resistance, so quenching is required to increase the strength of the members (especially the strength of the surface). [0004] Conventionally, the above-mentioned member is manufactured by hot forging steel (steel plate, steel ingot) containing 0.2% by mass or less of C, and carburizing and induction hardening to increase t...

AI Technical Summary

Problems solved by technology

[0015] However, in the steel sheet manufacturing methods of the aforementioned Patent Documents 1 and 2, the temperature range of Ac1 to Ac1+100°C is included during annealing, so not only carbides are coarsened, but also in this temperature range, the austenite part There is a difference in the size of carbides between the part that is ferrite

Due to the difference in the size of the carbides, austenite changes into a mixed crystal structure during heating during quenching in component manufacturing, and the hardenability of the steel plate and the shape accuracy of the quenched component decrease.

[0016] In this way, the prior art also has the problem that the shape accuracy of the quenched member is low.

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