Tungsten alloying in microalloyed steels is of growing academic and industrial interests due to its positive role in the aspects of microstructural modification and properties improvement. This book has systematically described the functions of tungsten alloying in microalloyed steels. Topics covered include the effects of tungsten on the phase transformation behaviour of microalloyed steels by establishing the continuous cooling transformation diagrams in order to control the expected microstructure and the required mechanical properties; the effects of tungsten on the characteristics of precipitated particles in microalloyed steels; the microstructural evolution of microalloyed steels including grain size, phase component, pearlite interlamellar spacing, allotriomorphic ferrite and acicular ferrite after tungsten addition; the effects of tungsten on mechanical properties of microalloyed steels by means of hardness, impact toughness and room/low-temperature tensile properties tests; strategies for heat treatment of microalloyed steels with the purpose of determining the optimal heat treatment conditions for microalloyed steels with different tungsten additions; improvement of the corrosion resistance of microalloyed steels after tungsten addition; and the effects of tungsten on the hydrogen embrittlement behaviour of microalloyed steels. The text of this book is up-to-date, informative, readable and self-contained. It is not only a technical document that can be used in the research and development of tungsten alloying in microalloyed steels, but also a scientific and valuable literature for the metallurgists, engineers, materials scientists, academics and higher degree research students who make, use, study and design with steels and tungsten worldwide by introducing the latest research findings and achievements of tungsten alloying in microalloyed steels, and considering the metallurgical basis for steel research.