**1. Introduction**

As an important metal-based material, bimetallic composite sheets have been widely used in petroleum, chemical, metallurgy, light industry, electric power, seawater desalination, shipbuilding, marine engineering, and other industries due to their unique physical chemical and mechanical properties [1–7].

As an efficient welding method, explosive welding has been widely used in preparing heterogeneous metal composite plates [8–10]. During explosive welding, the high pressure forces the different metals to achieve close contact at atomic level, promoting an excellent metallurgical combination. At the bonding interface of the two metal plates, the high pressure caused by the explosion provides energy for the joint process, and causes the flyer plate to impact with the base plate at a high speed. At high pressure, the thin flyer plate presents a dual solid–liquid state at the joint, and forms a jet to remove the contaminants and improves the quality of joint. Besides, high pressure can reduce the residual stress of the structure, thus reducing the deformation during explosive welding [11–13]. In addition, explosive welding is not limited by the shape and area of materials. This method can combine the excellent properties of different materials to obtain high bonding strength and good machining performance.

Titanium and titanium alloys are characterized by high specific strength, high temperature resistance, low density and good corrosion resistance, but their production costs are relatively high [14,15]. Carbon steel not only has weldability, formability, and thermal conductivity, it is also very cheap [16,17]. When titanium/steel bimetallic composite material is used as corrosion-resistant structural material in chemical equipment and marine engineering, it makes full use of the advantages of the two metal materials, especially the high specific strength and corrosion resistance of titanium, and also significantly reduces the material cost compared with pure titanium material.

Titanium and steel are difficult to combine by traditional welding methods due to their different lattice types, large difference in atomic radius and weak mutual solubility. In addition, a large number of intermetallic compounds (such as FeTi and Fe2Ti) forming in the weld after welding will worsen the performance of the welded joint. As a strong carbide forming element, titanium will combine with carbon to form brittle TiC, which further increases the brittleness of the welding joint [18,19]. In addition, due to the different linear expansion coefficients of the two metals and a large internal stress, the welding joint is prone to crack. In order to overcome the above shortcomings, explosive welding has become a common method to prepare titanium/steel bimetallic composite.

In previous literature, many studies reported on the titanium/steel bimetallic composite. Jiang et al. [18] found that the heat treatment process results in a significant enhancement of diffusion and microstructural transformation in explosive-rolled Ti-Steel clad plate. Besides, TiC has formed near the carbon steel side and the bonding surface was fractured at the TiC first through tensile tests. Chu et al. [20] combined experimental and numerical approaches to quantitatively investigate microstructure evolution and mechanical properties of Ti/Fe explosive-bonded interfaces, finding that the Ti/Fe interface features a wavy structure with melted zones embedded in the crests. The relationship between microstructure and mechanical properties was established. Li et al. [21] found that the σ phase was continuously distributed at the bonding interface, when the rolling temperature was 1223K, reducing the yield strength and ultimate tensile strength of the titanium/steel composite plate. Arisova et al. [22] investigated the influence of explosion welding and hot rolling on the explosive welding-rolled five-layer titanium-steel composite micromechanical properties, structure, and phase composition, founding that local melted zones formed by solid solutions based on titanium and iron because of explosive welding and the diffusion zones on all boundaries as a result of rolling.

In this paper, in order to obtain thin titanium/steel composite sheets, the explosive welded TA1/Q235B thick composite plate was hot-rolled at different temperatures. After nine passes of rolling, the 20-mm-thick explosive composite plate became a 2-mm-thick explosive-rolling composite sheet. The explosive welding and hot rolling can combine the advantages of the two separate methods. Explosive welding realizes the metallurgical bonding of TA1/Q235B, and hot rolling eliminates the defects of explosive welding and optimizes the structure. The study on the effect of rolling temperature on the interface microstructure and properties of the TA1/Q235B composite sheets can provide reference for the preparation of the titanium/steel composite sheets.
