# US 4,394,194 A · Method for heat treating structural members > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,394,194 A - Document ID: US4394194A - Status: Granted - Kind: A - Application number: 06/192,430 - Filed: 1980-09-29 - Granted: 1983-07-19 - Earliest claimed: 1980-09-29 - Assignees: Midland Steel Products Co. - Inventors: George L. Satava; Carroll L. Deemer - Web page: https://patentgrep.com/patent/US4394194A ## CPC - C21D 1/18: Hardening (C21D1/02 takes precedence); Quenching with or without subsequent tempering (quenching devices C21D1/62) - C21D 1/42: Induction heating - C21D 9/0068: {for particular articles not mentioned below} - C21D 1/673: for die quenching - Y02P 10/25: Process efficiency - C21D: MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B) - Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS ## Abstract The present invention relates generally to an improved method and apparatus for induction heat treating and restraint quenching structural members of carbon steel, to a uniform martensitic structure, such that distortion of the member due to rapid quenching is controlled to a minimum. More specifically, the member is generally heated by induction in two stages generally to austenitizing temperature in the range of 1450.degree. to 1750.degree. F. Then the member is liquid quenched under restraint to below 1000.degree. F. to minimize distortion and finally tempered under restraint at a temperature in the range of 750.degree. to 1250.degree. F. Such structural members attain minimum physical properties after heat treating in the range of 110,000 psi yield strength and 125,000 psi tensile strength. ## Claims ### Claim 1 A method for induction heat treating and quenching of a structural member of carbon steel to a uniform martensitic structure, said structural member having a web and at least one flange substantially perpendicular thereto consisting of induction preheating the structural member to a temperature in the range of 900.degree. to 1400.degree. F. by means of at least one coil utilizing the frequency in the range of 180 to 3000 cycles; continuting in a separate induction heating stage to heat the structural member to the austenitizing temperature in the range of 1450.degree. to 1800.degree. F. by the use of at least one coil having a higher frequency than that of the prior step; liquid quenching the structural member with a multiplicity of nozzles immediately, said nozzles being disposed at an angle in the direction of the advance of the structural member and the pressure regulated from the bottom of the quench zone liquid quench within the range of 10 to 20 pounds per square inch, from the top of the quench zone liquid quench in the range of 1.5 to 6 pounds per square inch and from the sides of the quench zone liquid quench in the range of 5 to 25 pounds per square inch of the structural member to minimize distortion thereof; concurrently restraining the member by its web in a series of segmented restraining rolls placed on the bottom and the top thereof so as to present slots through which the liquid may be sprayed to quench the structural member until the structural member has reached a temperature below 1000.degree. F. to minimize localized bow distortion; induction heating the structural member to a temperatering temperature in the range of 750.degree. to 1250.degree. F. by the use of a coil having a frequency in the range of 180 to 3000 cycles; and subsequently restraining the structural member while cooling to avoid camber distortion by passing the structural member through web restraining and tapered roll flange forming rolls, followed by tapered vertical restraint rolls, and finally flange surface engaging rolls to minimize cambering distortion. ### Claim 2 (depends on 1) The method of claim 1, in which the structural member is a channel. ### Claim 3 (depends on 1) The method of claim 1, in which the structural member is a truck side rail. ### Claim 4 (depends on 1) The method of claim 1, in which the carbon steel has the following composition: carbon 0.21-30%, manganese 1.00 to 1.35%, sulfur 0.05 max., phosphorous 0.04 max., with minimum physical properties after heat treating of yield strength 110,000 psi and tensile strength 125,000 psi. ### Claim 5 (depends on 1) The method of claim 1, in which the carbon steel is an approximate SAE 1025-modified or 1027 with greater amount of manganese approximately 1.00 to 1.50%. ### Claim 6 (depends on 1) The method of claim 1, in which the hardness after tempering reaches 269 to 331 Brinell. ### Claim 7 (depends on 1) The method of claim 1, in which preheating is done with induction heating at a frequency of 3,000 cycles or less. ### Claim 8 (depends on 7) The method of claim 7, in which the preheating is done with induction preheating at a frequency of 180 cycles or more. ### Claim 9 (depends on 1) The method of claim 1, in which the heating to austenitizing temperature is done at a frequency of 10,000 cycles. ### Claim 10 (depends on 1) The method of claim 1, in which the induction tempering is done at 3,000 cycles or less. ### Claim 11 (depends on 1) The method of claim 1, in which all of the induction heating and induction tempering is done by induction heating in a shaped coil that approximates the structure of the part in question. ### Claim 12 (depends on 1) The method of claim 1, in which the preheat induction coil is an oval coil. ### Claim 13 (depends on 1) The method of claim 1, in which the structural member is a truck side rail having portions of the flange removed at points of lower stress and the heating steps are by induction heating with the amount of current passing through any section being in proportion to the cross section of metal in said section in order to avoid localized overheating in the thinner sections of metal where the flanges have been removed. ### Claim 14 (depends on 13) The method of claim 13, in which the speed of the structural member with respect to the induction preheating limits the overheating of the member. ### Claim 15 (depends on 1) The method of claim 1, wherein the concurrent restraining elements in the liquid quench restrain the web of the structural member to minimize the bow distortion of the structural member. ### Claim 16 (depends on 1) The method of claim 1, wherein the tempering temperature is in the preferred range of 1000.degree. to 1100.degree. F. ### Claim 17 (depends on 1) The method of claim 1 wherein the angle of impingement of the liquid quench is in the range of 15.degree. to 60.degree. measured on the side of impingement from which the structural member advances. ### Claim 18 (depends on 17) The method of claim 17, wherein the angle is 30.degree.. ### Claim 19 (depends on 1) The method of claim 1, wherein the rate of liquid flow in the liquid quench is in the range of 500 to 1000 gallons per minute. ### Claim 20 (depends on 1) The method of claim 1, wherein the liquid quench uses water as the quench medium. ### Claim 21 (depends on 1) The method of claim 1 wherein the point of impingement of the liquid quench is carefully controlled to impact upon the structural member at properly related points longitudinally of the structural member to control distortion. ### Claim 22 (depends on 1) The method of claim 1 wherein the drawing force and downward pressure of the upper pinch rolls after heating the structural member is controlled to affect and control growth of the structural member width.