Prediction of Geometric Distortion and Residual Stresses In Hot Rolled and Heat Treated Large Rings Through Finite Element Modeling
During quenching, hot rolled steel rings, especially those with a large outer diameter to wall thickness ratio, distort and develop undesired residual stresses. These phenomena are the result of three major mechanisms: metallurgical, mechanical and thermal. This paper presents the result of a comprehensive study on the heat treatment of rings by modeling via Finite Element Analysis. The simulation is carried out with coupled analysis of heat transfer, deformation mechanics and phase transformations. The material data required for the simulation of distortion during heat treatments, including TTT/CCT phase transformation diagrams, temperature dependent physical and thermophysical properties, as well as temperature and strain rate dependent mechanical properties are calculated by computer models.
Distortion in quenching an AISI 4140 C-ring – Predictions and experiments
Abstract Heat treatment processes are used to enhance the material properties of a wide range of mechanical steel components, according to their final application. Quenching is a common step in these heat treatments, involving the fast cooling of previously austenitized parts and leading to a phase transformation from austenite to hard martensite in the material. Quenching commonly causes a geometric distortion in the parts, associated with the thermal contraction and with the change in the mechanical and geometrical properties of austenite and martensite. It is of importance to predict these distortions, so that one can design corrective post-heat treatment shape corrections or include them in the pre-heat treatment part dimensions, thus leading to a final part with adequate shape and dimensions. This study presents the results of a finite element (FE) simulation of the quenching of an AISI 4140 steel C-ring in oil, covering the analysis of the distortion caused by both thermal contraction and phase transformation. Furthermore, the distortion behavior during the cooling stage is analyzed, as well as the hardness and martensite volume fractions. Experiments were also conducted in order to obtain the geometric distortion, the microstructures and hardness of the C-rings. The FE modeling results are in good agreement with the experimental values and, to the knowledge of the authors, this is the first time that such an agreement has been obtained for the distortion caused by quenching of C-rings. The design of new products and quenching processes should consider the studied aspects, and may also be assisted by the methodology applied to this work.
Mechanical behaviour and durability of high volume fly ash cementitious composites
The purpose of this research is to separate different morphological particles of ASTM class F fly ash, and study their effect on mechanical behaviour and durability of high volume cementitious mixtures. In this research wet separation of raw fly ash is carried out, which resulted in three layers of different morphological particles. The first layer of particles float, comprise of about 1-5% of fly ash, is identified as cenospheres or hollow spheres. The second layer of particles is measured to be 55-60% of raw fly ash and consisting of porous spherical and rounded particles rich in Si and Al. The third layer particles is measured to be about 35-40% of raw fly ash. High volume fly ash cementitious composites containing second or third layer particles are tested under compression and bending, highlighting a higher strength and ductility in comparison to cementitious ones containing raw fly ash particles. KEYWORDS. Cementitious matrix; Raw fly ash; Second layer particles; Third layer particles.