Analysis on Phase Transformation (ATP) Using Computational Thermal Principles (CTP)

Computer analysis based on computational thermal principles to predict the transformation kinetics in steels at varying temperatures is of great practical importance in different areas of heat treatment. As a result, using the theory of transient state heat conduction with convective boundary conditions, an efficient program named "ATP" (Analysis on Phase Transformation) has been developed to determine the temperature distribution under different quenching conditions for different geometries such as plate, cylinder and sphere. In addition to these the microstructures and the corresponding hardness developed during quenching are predicted using Time Temperature Transformation (TTT) diagram incorporated in the analysis. To approve our work, dilation curves, Heisler charts and time-temperature history curve have been generated. This paper deals with basic objective of the program (ATP) determination of temperature, microstructure and hardness distribution and also includes an online prediction of austenite-pearlite and austenite-martensite transformation in steels along with the corresponding retained fractions. The quenching of a cylinder in gases, liquids and liquid metals is analyzed to show the non-liner effect of cylinder diameter on the temperature and microstructures. Further in the program we have considered a typical 1080 steel cylinders quenched in water for predicting and comparing the program results with experimental values and can be extended even to other grades of steels. The numerical results of program are found to be in good agreement with the experimental data obtained. Finally the quenching process analysis described in the study appears to be a promising tool for the design of heat-treatment process parameters for steels.

Study on Surface Engineering of Normalized Steels Subjected To Machine Hardening

Engineering the surfaces of components to improve the life and performance of parts used in automotive and aerospace engineering is the active area of research. Suitable Thermal/ Mechanical/Thermo mechanical surface engineering treatments will produce extensive rearrangement of atoms in metals and alloys and corresponding marked variations in Physical, Chemical and Mechanical properties. Among the more important of these treatments are heat treatment processes such as hardening by Quenching, Induction hardening and Case Carburizing which rely on phase transformations to produce desired changes in mechanical properties. Other processes where phase transformation occur are casting, welding and machining etc. [1] Phase transformation may be homogeneous or heterogeneous. Homogeneous involves rearrangements in the structure of the material taking place simultaneously in all parts of the solid, while the heterogeneous transformation involves structural changes which are more localized. Alternatively they could be called as Isothermal and Nonisothermal transformation. But irrespective of the classification, these transformations alter the structure of the material giving rise to changes in the mechanical and physical properties of the processed material. It is of interest to review some consequences of surface modification in isothermal (Normalizing) and nonisothermal transformations (Machining) of low carbon steels.

On The Enhancement of Wear Resistance of Hardened Carbon Tool Steel (AISI 1095) With Cryogenic Quenching

Many experimental investigations reveal that it is very difficult to have a completely martensitic structure by any hardening process. Some amount of austenite is generally present in the hardened steel. This austenite existing along with martensite is normally referred as the retained austenite. The presence of retained austenite greatly reduces the mechanical properties and such steels do not develop maximum hardness even after cooling at rates higher than the critical cooling rates. Strength can be improved in hardened steels containing retained austenite by a process known as cryogenic quenching. Untransformed austenite is converted into martensite by this treatment. This conversion of retained austenite into martensite results in increased hardness, wear resistance and dimensional stability of steel. Wear can be defined as the progressive loss of materials from the operating surface of a body occurring as a result of relative motion at the surface. Hardness, load, speed, surface roughness, temperature are the major factors which influences wear. Many studies on wear indicate that increasing hardness decreases the wear of a material. With this in mind, to study the surface wear on a surface modified (Cryogenic treated) steel material an attempt has been made in this paper. In this study as a Part -I Hardening was carried out on carbon tool steel (AISI 1095) of different L/D ratio with conventional quenchants like purified water, aqueous solution and Hot mineral oil. As a Part -II hardening was followed by quenching was carried out as said in Part-1 and the hardened specimen were quenched in liquid Nitrogen which is at sub zero condition. The specimens were tested for its microstructure, hardness and wear loss. The results were compared and analyzed. The alloying elements increases the content of retained austenite hence the material used was AISI1095 (Carbon 0.9%, Si 0.2%, MnO.4% and the rest Iron)