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° to 750° 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° 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° 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° to 650° 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.
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° to 750° 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 1 point to the temperature of Ac 1 point plus 50° 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 1 point to the temperature of Ar 1 point minus 80° 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° to 650° C. for a period of three to ten minutes; and thereafter air-cooling the open coil.
Claim 2
Independent Claim
250 words
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° to 750° 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 1 point to the temperature of Ac 1 point plus 50° 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 1 point to the temperature of Ar 1 point minus 80° 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° to 650° C. for a period of three to ten minutes; and thereafter air-cooling the open coil.
Claim 3
Dependent Claim
25 words
A method according to claim 1, wherein said coil is opened to provide a space between each convolution that is a minimum of 2 mm.
Claim 4
Dependent Claim
29 words
A method according to claim 1, wherein said tool steel is a steel consisting of 1.15% carbon, 1.20% silicon, 0.4% manganese, 0.50% chromium, 1.5% tungsten and the balance iron.
Claim 5
Dependent Claim
26 words
A method according to claim 1, wherein said tool steel is a steel consisting of 1.25% carbon, 0.20% silicon, 0.20% manganese, 0.20chromium and the balance iron.
Claim 6
Dependent Claim
27 words
A method according to claim 1, wherein said stainless steel is a steel consisting of 0.65% carbon, 0.25% silicon, 0.66% manganese, 13.0% chromium and the balance iron.