Study On Rolling Process,Microstructure And Properties Of Titanium Clad Steel For Ship And Ocean Engineering

The corrosion and protection of ships and marine equipments in seawater is a major problem to perplex its service performance for a long time.Integrating the corrison resistance of titanium and the strength&toughness of steel,titanium clad steel plates have a great potential in appling to the corrosion protection of marine steel structures.The manufacture process of titanium clad steel plates by hot roll bonding has become a main developing direction in China,which can fabricate the thin-in-clad and large-in-width bimetal plates.With the objective of developing the titanium clad steel plates with high strength and toughness by hot roll bonding,investigation on the rolling process numerical simulation,heat bonding temperature,Fe interlayer,heat treatment process and other aspects have been carried out in this dissertation,hoping to provide some instruction for the subsequent large industrial production and application.The hot deformation behavior of base metal steel and cladding metal titanium were investigated using a Gleeble thermal simulator and a constitutive equation for the materials were constructed.By taking the constitutive equation as the input information of Deform software,the numerical simulation of rolling process for composite slabs was conducted.And the favorable conditions of low-speed,large-reduction roll bonding process were determined.The roll bonding commercially pure titanium to high strength low alloy steel were carried out at temperature of 850℃,900℃,950℃and 1000℃.The microstructure and properties of titanium clad steel plates were studied by SEM,EPMA,HRTEM and mechanical tests.The results showed that at temperature of 850℃and 900℃,carbon can easily enrich at the bonding interface and the reaction diffusion of Fe in titanium was weak.Consequently,thin reaction layers of TiC andβ-Ti were formed and good bonding properties were achieved.While roll bonded at 950℃and 1000℃,carbon enrichment at bonding interface stayed at low degree and the diffusion reaction of Fe in titanium was strong.As a result,thick reaction layers ofα-βTi,β-Ti,Fe₂Ti or FeTi were generated and the bonding perperties were degraded.The roll bonding of titanium to steel using Fe interlayer were carried out at temperature of 850℃,900℃,950℃and 1000℃.The results showed that inserting Fe interlayer between titanium and steel had a good effect on preventing the enrichment of C at bonding interface.At temperature of 850℃and 900℃,inserting Fe interlayer can inhibit the reaction diffusion of C in titanium.Consequently,a thinner TiC layer were formed and the bonding properties were improved.At temperature of 950℃and 1000℃,inserting Fe interlayer made the reaction diffusion of Fe in Ti aggravate.Therefore,thicker Fe₂Ti and FeTi brittle reaction layers were produced and deteriorated the bonding properties.The effect of heat treatment process on the microstructure and properties of the titanium clad steel plates with no interlayer and Fe interlayer roll bonding at 850℃was studied.Moreover,the growth behaviour of FeTi and Fe₂Ti reaction layers was also studied subsequently.The results showed that the TiC reaction layer grew up at tempering temperature of 500-670℃and normalizing temperature of 850℃.With the increase of TiC layer thickness,the shear strength were reduced.Normalizing at 900℃and 950℃,the TiC layer were dissoved into Ti and steel.Thereby,the Fe reaction diffusion into Ti was so violent that very thick brittle reaction layer of Fe₂Ti and FeTi were formed,which caused the shear strength decreasing sharply.The function between the thickness growth of Fe₂Ti and FeTi and time conformed to the parabolic rule.The function of layer growth rate constant and temperature conformed to Arrhenius relationship.Compared with that of titanium clad steel without interlayer,the activation energy of FeTi and Fe₂Ti layers of titanium clad steel with Fe interlayer was smaller,and the rate constant of the reaction layer growth was larger.