Microstructure Evolution During Continuous Cooling in AISI 5140 Steel Processed by Induction Heating Chromizing

Evolution of the Microstructure and Properties of Pre-Boronized Coatings During Pack-Cementation Chromizing

“…It indicates that some Cr atoms have diffused into the substrate. It is because that the formation of FP-zone is resulted from the refinement of the pearlite structure by the Cr element in solid solution of the steel matrix [11]. It can be summarized that as the chromizing time increases, the net-like and rod-like borides distributed on the HC-pearlite grains disappear, and completely change into the block-like structures of Cr2B and CrxCy which mainly distribute at the grains or phase boundaries.…”

“…Figure 7 displays the two kinds of growth modes: interface controlled growth at early stage, and diffusion controlled growth at late stage. It is well-known that Cr is a strong carbide forming element, which is able to easily react with C element at the high-temperature [11]. Moreover, the enthalpy of boride formation for Fe (Fe2B = -28 kJ mol −1 ·atom −1 ) is lower than Cr (Cr2B = -35 kJ mol −1 ·atom −1 ), indicating that Cr has a stronger propensity to react with B to form boride than Fe [52].…”

“…are the main means used to improve the surface properties of materials [1][2][3][4][5][6][7]. Thermo-diffusion coating treatments, such as carbonizing, nitriding, boronizing, and chromizing, are effective techniques for the protection of metal materials from wear and/or corrosion [8][9][10][11][12]. However, single thermo-diffusion coatings usually only improve a certain property of the parts, and can't meet the demands of some mechanical parts (gears, shafts, etc.)…”

“…However, single thermo-diffusion coatings usually only improve a certain property of the parts, and can't meet the demands of some mechanical parts (gears, shafts, etc.) working in severe environments, which are characterized by high-speed, cyclic heavy-load, and/or corrosiveness [11,13]. For example, the wear resistance of boronized sample (hardness higher than 1600 HV) can be strengthened greatly [14,15], but the corrosion resistance is still poor and is also accompanied by brittleness [14].…”

“…For chromized samples, studies have pointed out that there is a carbon-poor layer (hardness lower than the substrate) existing between the Cr coating and steel substrate [11,13,16,17]. Fortunately, it has been reported that these shortcomings can be avoided by duplex coating or composite coating treatments [18][19][20][21][22].…”