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Abstract Corrosion-resistant steel plays a vital role in marine steel structures. This study developed an SS304/HRB400 stainless-steel-clad rebar for application in a cross-sea bridge in Zhejiang Province. CO2 gas shielded welding was employed in the prefabricated steel structure, with SS304 steel as the welding wire. This study investigated the welding on the corrosion resistance of clad rebars and explored corrosion protection measures for welded joints.The results indicated that refined grains appeared in both stainless steel and carbon steel due to distinct dynamic recrystallization (DRX) during welding. The corrosion resistance, as determined by potentiodynamic polarization curve analysis of the material’s interaction with the solution ranked as follows: clad rebar (polished) > clad rebar welding (CRW) > painting the clad rebar after welding (PCRW) > clad rebar (unpolished) > carbon-steel welding (CSW) > carbon-steel bar > cold spraying zinc after clad rebar welding (ZCRW). However, an accelerated corrosion test with four samples for 600 s with a corrosion current of 0.8 A revealed minimal corrosion damage on zinc-coated surfaces. Hence, welding joints for clad steel structures are considered feasible and must be subject to cold zinc spraying after polishing to enhance their corrosion resistance.

The existing process for the preparation of cladded rebars is too complicated for large-scale industrial production. Therefore, this paper proposes a 55#/316L rebar preparation method based on vacuum hot rolling. The microstructure and mechanical properties of the composite interface of the rebar, along with the connecting technique, were studied using transmission electron microscopy, X-ray diffraction, and Vickers hardness testing. The obtained results showed that the minimum thickness of the 55#/316L rebar cladding was 0.25 mm, which was twice that of the M 329M/M 329-11 design standard used in the United States of America. Due to the diffusion of carbon, large numbers of second-phase particles were precipitated on the stainless-steel side, which resulted in intergranular chromium depletion. After multi-pass hot rolling, the minimum bonding strength of the composite interface reached 316.58 MPa, which was considerably higher than the specified value of 210 MPa. In addition, we designed three different types of rebar connection joints: sleeve, groove-welded, and bar-welded. According to the tensile test, the bar-welded joint had higher yield strength (385 MPa) and tensile strength (665 MPa) than the base rebar (376.6 MPa and 655 MPa), as well as a very high corrosion resistance.

Clad rebar is one of the key structures of marine and construction services. Therefore, it is of great importance to acknowledge the mechanical property parameters of the composite region in the structural integrity evaluation of clad rebar. The different base materials of clad rebar (20MnSiV/316L steel, 35#/316L steel, 45#/316L steel, and 55#/316L steel) are researched in this study. The composite area is further refined, and simultaneously, a refinement model of the composite region of clad rebar is established. In view of the fact that a surface hardness experiment is quite easy to conduct, a proposed method consists of obtaining the mechanical property parameters of materials using the surface hardness test. The mechanical property parameters are acquired; moreover, the relationship between yield stress and surface hardness of the stainless steel clad rebar is set up. We used this method to acquire the mechanical parameters of a composite surface uneven area of clad rebar, and we established a mechanical parameters mathematics model of clad rebar, it is a significant basis for a structural integrity evaluation of cladding materials.

Rough- and intermediate-rolled composite billets and finished clad rebars were cut using flying shears. The law of metal rheology and the mechanism of composite interface generation during clad rebar formation were then investigated using metallographic microscopy, electron backscatter diffraction, and scanning electron microscopy. The radial deformation trend of the clad rebars was greater than that of HRB400 rebars and “ears” were more likely to appear during the rolling process. The widths of the decarburization and composite zones and diffusion distances of each element decreased as the cumulative reduction rate increased. Furthermore, as deformation increased, the number of oxides on the composite interface significantly decreased, the proportion of recrystallized grains increased, and the grains became more refined. These changes led to increases in the bond and tensile strengths of the composite interface. According to the research above, the pass filling degree should be within 0.85–0.9 and the cumulative reduction rate should be over 80% when rolling clad rebars.

Clad rebars of four different base materials (20MnSiV, 35# steel, 45# steel, and 55# steel) were successfully produced by a vacuum hot rolling process. A metallographic optical microscope (OM), electron backscatter diffractometer (EBSD), electron probe micro-analyzer (EPMA), and salt spray corrosion chamber were used to investigate the clad contour, properties, and composite interface microstructure of all four rebars. The results demonstrated that the thickness of the clad layer in the 20MnSiV/316L rebar had a more uniform distribution than those in the 35#/316L rebar, 45#/316L rebar, and 55#/316L rebar because 20MnSiV was more similar to 316L stainless steel in terms of deformation tendency. As the carbon content in the base layer increased, the amount of chromium-rich carbides increased noticeably. These large amounts led to a deficiency of chromium in the rebar composite interface and reduced corrosion resistance. Furthermore, bonding performance tests revealed that the bonding strength of the rebar composite interface not only depended on the amount of chromium-rich carbides, but also on the grain size of the composite interface. The larger the grain size of the composite interface, the lower the bonding strength was.

Stainless steel cladded rebars were successfully prepared by clean-interface assembly and vacuum hot-rolling process. The interfacial microstructure and properties of the clad rebars were investigated by scanning electron microscope (SVM), transmission electron microscope (TEM), and electron probe X-ray microanalyser (EPMA). The results demonstrated that owing to the diffusion of carbon, decarburised (roughly 50 μm) and composite zones (roughly 60 μm) formed on each side of the composite interface. The decarburized zone features a single ferrite texture, hence, a relatively low micro-hardness of 138HV while, due to the large amount of martensite formed within it, the composite zone has a relatively high micro-hardness of 218HV. The salt spray test showed that the corrosion rate of the clad rebars is close to that of the round stainless bars, and is approximately one-tenth that of the carbon rebars. In addition, a layered multipass welding process was used to produce a cladding joint, which was determined to have a tensile strength greater than the standard value of the parent material and excellent corrosion resistance.