Study Of Precipitation Of Fe-Cu Alloy

In the past, Cu’s concentration in steel was very low because of hotshortness caused by this element. Besides, it was not the only element toincrease hardness and intension properties of steel. Some other elementsshould usually be added, with Cu together, into the alloy in order to meet theneed of capability of the material. Also other strengthening methods wereused. Thanks to the development and innovation of science and technology inrecent years, people have found better methods to control the composition ofelements in materials, thus the content of incidental elements in alloys aredecreased. The new alloys called high-strength low alloy steel (HSLA steel)and clean steel have been invented. Since the problems of bad affect of Cuhave been solved, the content of Cu in steel can be raised. For instance, twokinds of steel containing high content of Cu which called high-strengthinterstitial-free steel (IF steel) and weathering resistant steel have beeninvented and developed. Both of these steels have high contents of Cu whichare higher than1wt%. As a result, the element gives full play to the effect ofimproving hardness and strength. In current days, more and more researchersare paying attentions to Cu’s effect to hardness and strength properties. Afterexperiencing heat treatment, a lot of small ε-Cu particles will precipitate inthe steel which sets the element as the only alloyed-element, and, therefore,promote a big increase of material’s strength property. Moreover, highductility is retained because of pure matrix and high-ductility precipitates. Inaddition, some special mechanical processes can refine structure by furtherlevel, also improving material’s property.Cu-contained steel has attracted much attention by exhibiting highstrength, excellent formability as well as weldability. Studying Cuprecipitates in Fe-Cu alloy will no doubt offer insight to the design of newCu-contained steels with desired properties. In this article, both mathematicalsimulation and transmission electron microscope (TEM) are used to analyze precipitation process of Cu and the rules of how composition, heatingtemperature as well as treating time affect the precipitates.Addition of Ni and Mn elements can cause promotion of precipitation.Thus, when compared to Fe-Cu alloy experiencing the same heat treatmentprocess, the alloys having Ni and Mn will result in more precipitates. What ismore, interphase precipitation is able to occur in both FeCu1.5Ni3andFeCu1.5Mn3alloys. This kind of precipitation process is influenced byheating temperature. Only the heat treatment under the temperature betweendiscontinuity point on TTT curve and transformation point may lead tointerphase precipitation. For FeCu1.5Ni3alloy and FeCu1.5Mn3alloy, thetemperature ranges are600~715℃and550~640℃, respectively. In Ni or Mnadded alloy, the precipitate’s concentration of Cu increases a little, whencompared to FeCu1.5alloy. Moreover, during the precipitating process, Niand Mn will be excluded out of the precipitate, and enrich at the interphase ofmatrix/precipitate, resulting in decrease of nucleating energy and boosting ofprecipitation. The analyzing results of experiment agree with the anticipationsbased on Cahn-Hilliard non-classical nucleation theory and Modified LangerSchwartz simulation (MLS simulation), indicating that the mathematicalmodel is reasonable.