Investigation on the corrosion resistance of laser cladding Fe-based alloy coating against molten zinc

In this paper, laser cladding technology was used to prepare a Fe-based coating on H13 steel substrate and its corrosion behavior in molten zinc was studied. The results show that laser-cladding Fe-based coating can effectively protect the substrate from the corrosion of molten zinc, which is mainly related to its microstructure. The typical microstructure of the coating is composed of α-(Fe, Cr) solid solution matrix and CrFeB eutectic phases continuously distribute around the matrix. When molten zinc contacts with the surface of the coating, it corrodes the α phase matrix preferentially and CrFeB eutectic phases with better corrosion resistance interweave with each other to form a three-dimensional skeletal structure, which can play the role of diffusion barrier and slow down the diffusion rate of liquid zinc. The corrosion by molten zinc leads to the formation of a transition layer and an outer corrosion layer above the coatings. With the prolongation of the corrosion time, a large number of micro cracks are generated inside the transition layer and fracture gradually occurs under the action of thermal stress. The partial spalling of the transition layer and the corrosion of α phase matrix occur at the same time, making the corrosion depth of the coating increase continuously. However, the dense corrosion layer above the coating and the dispersed boride fragments can still function as a barrier to the inward diffusion of molten zinc.

Study on Coating Mechanism and Properties of Die CrN+DLC Layer

This paper introduces the principle of PACVD coating technology, technical characteristics, equipment composition and material characteristics of CrN+DLC. Taking H13 steel as the research object, its surface was treated with CrN+DLC. The microstructure, bonding state and hardness of the interface were studied by means of metallography, SEM, hardness and component distribution of the surface layer. The anti-crack ability and grade of DLC layer were analyzed by studying the shape of crack distribution with Rockwell hardness indentation, and the high quality layer with crack grade of HF1 was obtained. With the dual properties of diamond and graphite of DLC, it can make the die surface have lower friction coefficient, higher hardness, higher impact toughness, better solid lubrication performance and higher corrosion resistance. Surface DLC coating technology provides a new solution to improve the performance of the die.

The Study on Feasibility and Welding Characteristics of GMAW Surfacing Remanufacturing of H13 Steel Cutter Ring of TBM Hob

As H13 steel is a common material for cutters of Tunnel Boring Machine (TBM), the research on surfacing remanufacturing performance is of great value. In this paper, the phase composition of the surfacing layer of H13 steel after gas metal arc welding (GMAW) was analyzed by exploring the precipitation of hard phase in the molten pool, and the microstructure evolution of the surfacing layer was revealed. Then, we carried out simulation modeling analysis on H13 steel surfacing remanufacturing. Results show that: (1) the surfacing layer is combined with the base metal by physical metallurgy without obvious defects such as pores, inclusions and cracks in the surfacing layer; (2) the hardness of the surfacing layer is 60 HRC, which is about 1.5 times of that of the base metal; (3) the stress is mainly concentrated in the arc starting and ending points, followed by the external constraints on both sides of the surfacing layer; (4) the deformation of surfacing layer is slight, which does not affect the forming quality of base metal, while the deformation of base metal is relatively severe. This paper verifies the feasibility of H13 steel remanufacturing from experimental and simulation, providing theoretical basis for future engineering practice.

Experimental evaluation and modelling of the boronizing kinetics of AISI H13 hot work tool steel

In the study for this contribution, the AISI H13 hot work steel was pack-boronized between 2 and 6 h of exposure time within the temperature range of 800 – 1000 °C. The boriding agent was composed of a powder mixture containing (in weight percent): 90 % of boron carbide (B4C) and 10 % of sodium tetrafluoroborate (NaBF4). The SEM observations showed a less pronounced jagged interface between the boronized layer and the transient zone. A double phase boride layer (FeB and Fe2B) was identified over the surface of AISI H13 steel with the presence of metallic borides inside this compound layer. The mean diffusion coefficient (MDC) method was applied to analyze the growth of iron borides (FeB and Fe2B) as compact layers over the surfaces of AISI H13 steel. The boron activation energies in the two iron borides were also assessed from the present kinetic approach by assuming the Arrhenius relationships. Afterwards, the kinetic model was checked experimentally by considering two extra boriding conditions (925 °C for 1 and 3 h). Finally, the predicted layer thicknesses are in accordance with experimental measurements.