US 4,021,272 AGranted

Method of isothermal annealing of band steels for tools and razor blades

AssigneeHitachi Metals, Ltd.

InventorsYoshiteru Asai, Sumio Yoshizoe

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Abstract

A method consisting in converting a coil of hot-rolled band steel for tools and razor blades into an open coil in which its convolutions are spaced apart from one another, and immersing the open coil in a series of salt baths. First of all, the open coil is immersed for 5 to 30 minutes in a salt bath held at a temperature in a range from 550.degree. to 750.degree. C. to preheat the open coil and cause preliminary precipitation of carbides. The preheated open coil is immersed for 5 to 30 minutes in a salt bath held at a temperature in a range from the temperature immediately above Acl point to the temperature of Acl point plus 50.degree. C. to make the band steel austenitic in structure. The open coil is then immersed for over 10 minutes in a salt bath held at a temperature in a range from the temperature immediately below Arl point to the temperature of Arl point minus 80.degree. C. so that the isothermal transformation may be completed. Finally, the open coil is immersed for 3 to 10 minutes in a salt bath held at a temperature in a range from 600.degree. to 650.degree. C. and air cooled thereafter. The method enables to produce band steels for tools and razor blades which contain carbides occurring in a small spheroidal structure of uniform size, have good cold-workability, have freedom from decarburizing and carburizing, and have high amenability to hardening.

Claims5

Dependent claims

A method of isothermal annealing of a hot-rolled band steel selected from the group consisting of a tool steel and a stainless steel comprising the successive steps of:

converting a coil of said hot-rolled band steel into an open coil with its convolutions spaced apart a distance great enough to allow a molten salt to pass therethrough;
immersing said open coil in a molten salt bath held at a temperature in a range of from 550.degree. to 750.degree. C. for a period of 5 to 30 minutes to preheat the open coil and cause preliminary precipitation of carbides;
immersing the preheated open coil in a molten salt bath held at a temperature in a range of from a temperature immediately above Ac.sub.1 point to the temperature of Ac.sub.1 point plus 50.degree. C. for a period of 5 to 30 minutes to make the steel austenitic in structure;
immersing the open coil in a molten salt bath held at a temperature in a range from a temperature immediately below Ar.sub.1 point to the temperature of Ar.sub.1 point minus 80.degree. C. for a period of at least 10 minutes to complete the isothermal transformation and to provide a steel product containing carbides having a small spheroidal structure of uniform size and exhibiting good cold workability and hardenability;
further heating the open coil after said isothermal transformation at a temperature of 600.degree. to 650.degree. C. for a period of three to ten minutes;
and
thereafter air-cooling the open coil.

4 more elements

Dependencies are inferred from the claim text.