Effect Of Mg-RE Treatment On Inclusions And Mechanical-properties Of Ti-containing Rebar

Currently,Rebar is mainly micro-alloyed with V,but V alloys are expensive,Ti micro-alloyed rebar offers good economics compared to V micro-alloyed rebar.However,Ti microalloyed steels are predisposed to the formation of TiN with a large particle size.The main problem is control the size of TiN,while enabling Ti precipitates to act as grain refinement and precipitation strengthening.Based on the Ti micro-alloyed rebar smelting in the laboratory,this paper did a research on the smelting process adding Mg/RE in this kind of steel.In this paper,the effect of Mg-RE treatment on inclusions is clarified:using Mg-RE treatment can refining large size Ti-containing oxygen and nitrogen inclusions in steel,safeguarding the mechanical-properties of Ti-containing rebar products and exploring the feasibility of replacing V with Ti for microalloying.The experiments focus on the effect of using Mg-RE treatment on inclusions in steel and the mechanical properties of Ti-containing rebar,by analysed the mechanism by which Ti microalloyed the mechanical-properties of steel.The main conclusions are as follows:The treatment of steel with magnesium alloy could reform the alumina inclusions to magnesium aluminium spinel.Using Mg treatment caneffectively refine the inclusions,and made the inclusions in steel more dispersive.The fine spinel can provide nucleation core for the precipitation of titanium nitride subsequently.Using RE treatment is effective in reforming alumina inclusions to aluminate,rare earth compound inclusion,which can provide a core for TiN precipitation.The mechanical properties of the Mg-RE treated Ti-containing rebar meet the requirements of a 400 Mpa grade rebar,with smaller inclusions and better toughness than V microalloyed rebar.V microalloyed steels provide the best strengthening of the mechanical properties of steel,mainly due to the precipitates of V can be completely precipitated in the steel,providing excellent precipitation enhancement and a higher increase in steel strength.Ti microalloyed steels have a weaker strengthening effect on steel than V microalloyed,mainly because Ti is mainly in the form of TiN at high temperatures,which has the effect of pinning austenite grain boundaries and promoting fine grain strengthening,weakening of the later precipitation enhancement.In summary,the strengthening effect of fine grain reinforcement on the mechanical properties of the rebar does not compensate for the loss of precipitation enhancement.The strength of Ti microalloyed steels is weak than that of V microalloyed steels.V-Ti composite treatment of microalloyed steel in the presence of carbon nitride with V,Ti,reducing the amount of effective V,Ti precipitation,the weakest precipitation strengthening effect on the steel.