Abstract Process for heat treatment in line with a wire rod rolling mill, of a steel wire rod containing less than 0.15 per cent of carbon and which has been previously subjected after leaving a rolling mill to the cooling treatment of a known controlled cooling process and device. The wire rod is subjected to an isothermal holding at a temperature between 200*C and 400*C so that the intersticial atoms place in a supersaturated solution during the known controlled cooling gather together on sites other than dislocations which allows the phenomenon of anchoring of the dislocations to be avoided, this anchoring being partially responsible for the deterioration of the drawability for the fine drawing of such steel wire rods. This thus allows the direct drawing of the wire rod without subsequent heat treatment to a final very small diameter. The process thereby avoids decomposition of a thin layer of non-adhering wustite formed on the surface of the wire rod during the controlled cooling treatment into an adhering layer of a superior oxide difficult to remove before the drawing off the wire rod.
A process for heat treating steel wire rod exiting from a rolling mill comprising: exiting a steel wire rod containing less than 0.15 percent carbon from a rolling mill; successively cooling said rod in two stages first to a temperature of about 800* C and then to a temperature of about 400* C thereby positioning interstitial atoms within said rod in a supersaturated solution and effecting the formation of wustite on the rod surface; and then isothermally holding said rod for at least 30 seconds at a temperature between 200* C and 400* C to effect gathering of the interstitial atoms at sites other than dislocation sites and preventing substantial decomposition of the wustite into an oxide which strongly adheres to the rod surface and thus is difficult to remove; whereby the resulting steel wire rod may be directly drawn into a fine wire without undergoing any further heat treatment.
Claim 2
Dependent Claim
150 words
A process for heat treating steel wire rod exiting from a rolling mill comprising: exiting a steel wire rod containing less than 0.15 percent carbon from a rolling mill; successively cooling said rod in two stages first to a temperature of about 800* C and then to a temperature of about 400* C thereby positioning interstitial atoms within said rod in a supersaturated solution and effecting the formation of wustite on the rod surface; and then isothermally holding said rod for at least 30 seconds at a temperature between 200* C and 400* C to effect gathering of the interstitial atoms at sites other than dislocation sites and preventing substantial decomposition of the wustite into an oxide which strongly adheres to the rod surface and thus is difficult to remove; whereby the resulting steel wire rod may be directly drawn into a fine wire without undergoing any further heat treatment.
Claim 3
Dependent Claim
33 words
A process according to claim 1; wherein said isothermal holding step comprises isothermally holding said rod at a temperature between 280* C and 350* C for a period of at least 1 minute.
Claim 4
Dependent Claim
35 words
A process according to claim 1; wherein said successive cooling step comprises first water-cooling said rod to a temperature of about 800* C and then air-cooling the rod to a temperature of about 400* C.
Claim 5
Dependent Claim
30 words
A process according to claim 1; including directly drawing said rod immediately after said isothermal holding step into a fine wire without subjecting the rod to any further heat treatment.