## 1 Introduction  
Carbon steel and low alloy steel, which have a high strength, good processing performance, and low price, are widely used in marine environments [1; 2]. Due to the complex environment of the ocean, some damage will inevitably occur on the surfaces of steels. The main failure ways of steel surfaces include wear, corrosion, and oxidation [3; 4; 5]. Hence, surface modification technologies are necessary to improve the performance of steel parts. The coatings cladded on the surface of steels can greatly improve the service life of steel facilities in the ocean, which have a significant influence on the reliability of offshore steel components and can enhance the economic efficiency of the ocean [6]. Laser cladding technology is a new kind of surface modification technology. Coatings with specific properties can be obtained by melting alloy powder on the surface of a substrate through a laser beam [7]. Compared to the traditional surface modification technologies such as surfacing welding,thermal spraying, etc., the laser cladding process can control the heat input more precisely, has basically no limits on the alloy powders that can be used, and is suitable for flexible processing. The coatings by laser cladding have a dense microstructure, lower dilution rate, and less thermal deformation [8; 9; 10; 11]. In addition, laser cladding has high material utilization and low energy consumption, and it is considered as an environmentally friendly materials processing technology. Therefore, the laser cladding has been widely studied and used for surface modification in recent years [12]. [PERSON] et al. [13] researched the effect of different Al/Fe\({}_{2}\)O\({}_{3}\) thermite reactants on the Fe-based coating in laser cladding. The results showed that Al\({}_{2}\)O\({}_{3}\) ceramic and M\({}_{7}\)C\({}_{3}\) type carbide were in situ synthesized by laser cladding. With the increase of thermite reactants, the amount of Al\({}_{2}\)O\({}_{3}\) ceramic and M\({}_{7}\)C\({}_{3}\) carbide in the coatings increased gradually. The microhardness and the wear resistance of the coatings could be improved when increasing the amount of thermite reactant. [PERSON] et al. [14] used three different Ni-based alloy powders to strengthen the surface of a continuous casting roller by laser cladding. The on-line results showed that the continuous casting roller exhibited a better performance after being reinforced by the laser cladding. Powders used in laser cladding mainly include Fe-based, Ni-based, and Co-based alloy powders [15; 16; 17]. The Fe-based alloy is widely available and inexpensive, and it is the most widely used material in industrial production [18]. A good wetting performance and high bonding strength can be achieved between the coating and substrate by using Fe-based alloy powders on the surface of steel substrates in laser cladding [19; 20; 21]. [PERSON] et al. [22] prepared an FeCrBSi coating on the surface of 45 steel by laser cladding. The toughness of the coating was improved and the crack tendency was reduced by increasing the Cr content. The average microhardnesses varied from 760 to 950 HV. Adding a specific alloy component in the alloy powder could further improve the properties of the laser cladding layer [23]. Incorporating hard particles like WC [24], VC [25], TIC [26], and TiB [27] in the coating could improve the wear resistance of the coating. Rare earth elements like CeO\({}_{2}\)[28] and Y\({}_{2}\)O\({}_{3}\)[29] could refine the grain and improve the properties of the coating. Mo could refine the grain, increase the toughness, enhance the plasticity, and reduce the crack sensitivity of the coating, and was beneficial for improving the performance of the coating [30; 31]. [PERSON] et al. [32] studied the effect of Mo on the microstructure and wear resistance of laser cladded Ni-based alloys on Q235 steel. The results indicated that Mo could refine grains and synthesize polygonal equiaxed grains.