Defects in Thermo Mechanical Processing of Metals...

Defects in Thermo Mechanical Processing of Metals  Thermo mechanical processing of materials is a technique designed to improve the mechanical properties by controlling the hot-deformation process. This was originally designed to produce the required external shape of the product. Controlled rolling, controlled-cooling and direct-quenching are typical examples of thermo mechanical processing. Such processing saves energy in the manufacture of steel by minimizing or even eliminating the heat treatment after hot-deformation, thus increasing the productivity for high grade steels. It normally requires a change in alloy design and often reduces the productivity of the hot deformation process itself, but at the same time makes it possible to reduce the total amount of alloying additions and to improve weldability, while sometimes producing new and beneficial characteristics in the steel. Thermo mechanical processing is the sophisticated combination of well-defined deformation operations and well-defined heat treatment in a single production stage to control the microstructure of the material being formed. It produces materials with the desired external qualities (dimensions, shape and surface quality) and acceptable mechanical properties. The process is normally considered as the final stage in the production of steels. Thermo mechanical process defects are usually focused on individual forming technique. The defects generally range from mostly macroscopic ‘form and fracture’ related defects to defects related to strain localizations, as well as imperfections related to microstructure.  The defects in case of thermo mechanical processing have two possible origins namely (i) process related, and/or (ii) metallurgical. The first one is usually related fully to the practices of the thermo mechanical processes including the forming techniques and the heat treatment, while the metallurgical origin defects can range from the starting solidification structure to structural developments during thermo mechanical process. It is difficult to establish a clear demarcation between the...

Oxygen and Steels

Oxygen and Steels  Oxygen (O) (atomic number 8 and atomic weight 15.999) has density of 1.429 gm/litre at standard temperature and pressure. Melting point of oxygen is -218.79 deg C and boiling point is – 182.96 deg C. It is a colourless gas but the colour of liquid oxygen is pale blue. The phase diagram of the Fe-O binary system is at Fig 1. Fig 1 Fe- O binary phase diagram  There is a very strong relationship between oxygen  and steel. Oxygen is first used in the steel making process which is a controlled oxidation process. Excess oxygen going to steel during steel  making process,  if not properly taken care of, is source of many steel defects like porosity, inclusions etc. Oxygen is used in the processes of cutting, lancing, scarfing and welding of steels. Oxygen is also the cause of steel destruction by the processes of rusting, scaling and corrosion. Further transport of oxygen takes place in cylinders, tanks and pipelines made of steel. Oxygen is also used (oxy-fuel process) for heating of the steel. During steel making process, the main sources of oxygen in steel are as follows. Oxygen used for blowing in the steel making process Use of oxidizing slags and oxidizing materials ( ores, sinter etc.) during steel making processes Atmospheric oxygen dissolves in the liquid steel during steel tapping and casting operations Oxidizing refractories used in various vessels for holding liquid steel in the process of steel making Rusted and wet scrap Solubility of oxygen in liquid steel is 0.23 % at the steel making temperatures ( 1600 – 1700 deg C). However it decreases during cooling down and then drops sharply during solidification of steel reaching a level of 0.003 % in solid steel. Solubility of oxygen in steel...