The molybdenum–iron–boron–chromium claddings with different Mo/B atomic ratios were produced on Q235 steel using argon arc welding. The microstructure and crystalline phases were studied by optical microscopy, scanning electron microscopy and XRD. In addition, the formation mechanism of hard phase was investigated by thermodynamic calculations and phase diagrams. The results showed that the claddings were composed of the Mo2FeB2, M3B2 (M: Mo, Fe and Cr) hard phases and σ-FeMoCr solid solution. In addition, calculated results revealed that the M3B2, MB and σ-FeMoCr were successively precipitated from the melting pool. Moreover, the maximum microhardness value of the cladding was about 1600 HV0.5. Wearing test indicated that claddings of lower Mo/B ratios have better wear resistance.

The objective of the study described here is to elucidate the effect of carbon and niobium on the microstructure, precipitation behaviour, and mechanical properties of 0?09C-0?11Ti (%) steel and 0?05C-0?025Nb-0?11Ti (%) steel under ultra fast cooling condition. The strengthening mechanisms are also discussed. The ferrite grains size and the size of precipitates in Ti and Nb-Ti steels were measured respectively. The mechanical properties obtained in Ti steel were similar to Nb-Ti steel with yield stress .700 MPa, elongation .20%, and good low temperature impact toughness. The study underscores that addition of higher carbon content by 0?04% under controlled rolling and ultra fast cooling conditions, we can achieve similar strength in the absence of micro-alloying element, niobium.