Effects Of Zr And Mo Elements On The Microstructure Evolution Of Ti Microalloyed Low Carbon Steel During Controlled Rolling

In recent years,with the increasing level of industrialization of the country,the demand for steel with excellent comprehensive performance has become wider.Because of its excellent properties,Ti microalloy steel is abundant in production and low in price.However,Ti microalloyed steel also has many shortcomings,Ti microalloyed steel also has many disadvantages which make the Ti element play insufficient role in steel.The Ti element is easy to combine with other elements to form inclusions.At the same time,the precipitation of Ti C has a high temperature sensitivity,which may cause the performance of the steel plate to decline.Aiming at the problems of coarse austenite grains and many inclusions in the heat treatment process of Ti microalloyed steel,Zr and Mo elements are used to change the precipitated phase of the compound of Ti microalloyed steel,so as to achieve the refinement of the microalloyed steel austenite Grain effect.In this paper,Gleeble3500 thermal simulation test machine is used to conduct multi-pass high-temperature thermal simulation compression test,stress relaxation experiment and double-pass compression experiment.The evolution of controlled rolling process of Ti、Ti-Zr、Ti-Mo and Ti-Zr-Mo low carbon microalloyed steels is studied systematically.Mo element increases the high-temperature solid solubility of Ti element,and delays the precipitation of Ti element,so that the micro-alloy elements of Ti-Mo micro-alloy steel are mostly dissolved into the austenite matrix.In the hot deformation process below 975 ℃,the addition of Mo element will increase the static recrystallization activation energy,reduce the fastest precipitation temperature of Ti microalloyed steel,and the precipitation of Ti-Mo microalloyed steel in the test temperature range the period is shorter than that of Ti microalloy steel,the precipitation start time is advanced,and it can be precipitated at the initial stage of recrystallization.However,in the heat treatment process above 1000 ° C,the austenite grains do not have many undissolved phases and precipitated phases during the solution treatment to prevent the growth of austenite,so Ti-Mo microalloy under the same high temperature rolling steel austenite grains are larger than Ti microalloy steel.In order to solve the shortcomings the problem of insufficient precipitation ti microalloyed steel over 1000℃ after adding mo elements,Mo and Zr elements are added together;The Zr element completely changes the precipitation phase of Ti microalloyed steel,and the Ti C particles become(Ti,Zr)C-Ti C composite chain precipitation phase.In the thermal deformation process above 1000 ℃,the effect of Zr elements on Ti microalloyed steel is to Zr elements instead of Ti elements first precipitate and impurity elements combine,so that the Ti steel containing Zr elements has more Ti elements and C elements combined precipitate,so that the austenite grain of Ti-Zr microalloyed steel becomes smaller than that of microalloyed steel after rolling process.In the hot deformation process below 975 ℃,the addition of Zr element can reduce the static recrystallization activation energy of Ti microalloy steel.Ti-Zr-Mo microalloy steel can precipitate a large amount of Zr element during high temperature solid solution to prevent the growth of austenite grains,while the precipitation of Ti and Mo elements during rolling increases the number of precipitated phases and further strengthens the austenite the hindrance of the growth of recrystallized grains in bulk rolling,make fine grain strengthening effect better.Therefore,the addition of Ti-Zr-Mo compound can enable Ti steel to be fully refined from the beginning of high temperature solution to the end of rolling.