Microtreatment of iron-based alloy, apparatus and method therefor, and articles resulting therefrom
Iron-based alloys and articles in strips, sheets, workpieces and the like are converted into high strength steel with a minimum of cost, time and effort, including producing dual phase materials. This is achievable by extremely rapid micro-treating of low, medium, and high carbon iron-based alloys and articles by rapid heating and rapid cooling at least a portion of the alloy/article. This heating step involves nearly immediately heating the iron-based alloy to a selected temperature above its austenite conversion temperature. Then, the alloy is immediately quenched, also at an extremely fast rate, on at least a portion of the iron-based alloy in a quenching unit adjacent the heating unit. This procedure forms high strength alloy in a desired area, depending upon where the treatment was performed.
1. A method for rapidly micro-treating an iron-based alloy to controllably form at least one phase of a high strength alloy, said method comprising the steps of:
providing an iron-based alloy having a first micro-structure with an austenite conversion temperature, said first microstructure being capable of being transformed to an iron-based alloy having a second micro-structure upon being rapidly heated to a selected temperature and then being immediately quenched;
rapidly heating the iron-based alloy, to a selected peak temperature above its austenite conversion temperature, wherein said selected peak temperature is a temperature of about 1000° C. to about 1425° C. in order to establish optimum grain size for most desirable mechanical properties; and
immediately quenching, within 0.01 to 10 seconds after reaching the selected peak temperature, at a rate of from 315° C/sec. to 6,000° C/sec., at least a portion of the rapidly heated iron-based alloy in a quenching unit immediately adjacent the heating unit to controllably form at least one phase of a high strength bainitic-containing alloy selected from the group consisting of coalesced bainite, Colascite, lower bainite, upper bainite and combinations thereof and at least one more phase of martensite, whereby said controllably formed bainitic-containing alloy is produced to the left of the bainitic nose, and wherein this bainitic-containing second microstructure exhibits bainitic sub-plate morphology with martensitic tri-directional precipitates, such that the length of time from ambient temperature up to the highest temperature and back down to ambient temperature is from about 0.05 seconds to about 30 seconds.
2. The method of claim 1 , wherein the resulting high strength iron-based alloy includes at least one portion of a material including at least 5% of the second microstructure selected from the group consisting of bainite, coalesced bainite, upper bainite, lower bainite, ferrite, acicular ferrite, martensite, coalesced martensite, pearlite, retained austenite, and Colascite.
3. The method of claim 1 , wherein the iron-based alloy is a low carbon steel which contains carbon in a range of between 0.001 percent carbon by weight (wt %) to 4 percent carbon by weight (wt %).
4. The method of claim 1 , wherein the iron-based alloy is in a form selected from the group consisting of wire, strips, sheets, any 2-dimensional continuous cross-section, 3-dimensionally variable workpieces, articles, hollow tubes and combinations thereof.
5. The method of claim 1 , further comprising an additional step of pre-heating the iron-based alloy to a temperature below the austenitic conversion temperature in a range of about 300° C. to about 720° C., whereby the selected peak temperature is more attainable in the rapid heating step.
6. The method of claim 1 , wherein the heating is accomplished by a heating unit selected from the group consisting of gas torches, electric resistance heaters, fluidized beds, electric furnaces, plasma furnaces, microwave ovens, open environment propane forges, gas fired units, solid fuels, high temperature salt baths, torches and any combination thereof.
7. The method of claim 6 , wherein the heating unit transfers heat by a way selected from the group consisting of radiation, conduction, convection, induction and any combination thereof.
8. The method of claim 6 , wherein the heating unit includes propane gas torch heads.
9. The method of claim 1 , wherein the selected temperature is at least between about 985° C. to about 1300° C.
10. The method of claim 1 , wherein the step of quenching the heated alloy is accomplished by a quenching means selected from the group consisting of water, water-containing aqueous solutions, oil, molten salt, brine solutions, gases including air, powders and any combination thereof.