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.
The influence of quenchant agitation on the heat transfer coefficient and residual stress development in the quenching of steels
Abstract This paper is concerned with the effect of variation in part orientation and quenchant circulation and agitation on the heat transfer coefficient during the quenching of steel parts, and subsequently on the development of residual stresses in the quenched part. Residual stresses arise from complex coupled interactions between phase transformation, thermal and stress effects during the rapid thermal transient of quenching. The nature of these interactions is described briefly, and their incorporation into an analytical programme using finite element analysis is outlined. In an experimental programme the effect of quenchant flow velocity was investigated for flow parallel and perpendicular to the axis of cylindrical bar specimens. Heat transfer coefficients were obtained from thermocouples embedded in the specimens, using the inverse method to process the results. Results are presented for varying positions on the bars, as well as for variation in orientation and flow velocity. Axial residual stresses are presented for two flow conditions at each orientation and are compared with experimental measurements made using the X-ray diffraction technique.
INVESTIGATING THE MICROSTRUCTURE-ULTRASONIC PROPERTY RELATIONSHIPS IN
Microstructural characterization by ultrasonic measurements and effect of microstructural phases on the ultrasonic properties were studied on AISI/SAE 1040 and 4140 steels. By rapid cooling and isothermal heat treatments, the specimens having martensite, tempered martensite, bainite, fine pearlite and coarse pearlite were obtained. Microstructures were characterized by optical and scanning electron microscopy, and hardness tests. Sound velocity and attenuation measurements were performed using the pulse-echo technique. The relationships among sound velocity, sound attenuation, microstructure and hardness were investigated. Introduction: Controlling the mechanical properties of steel components is important because the they may change considerably even in the same batch, or after application of deformation/heat treatment processes not all parts have to be the same mechanical properties, or faulty heat treatment may change these properties drastically. In order to prove that the properties are the same as the design stage, mainly destructive testing techniques like tensile testing and metallographic inspection are carried out. These traditional methods are performed by cutting a representative sample from the material and performing tests on that sample. However, in some cases precise knowledge of the actual material properties used in the structure should be known, and quality control by sampling may not support the safety requirements. Therefore, determination of the mechanical properties of materials by nondestructive techniques becomes a challenging task. Papadakis reported a comprehensive set of data on the attenuation and velocity of both longitudinal and transverse waves in hardened and tempered steels as functions of austenitizing temperature and ultrasonic frequency [1]. Klinman, et. al proposed to use the ultrasonic attenuation due to grain boundary scattering as proxy for grain size in the well-known Hall-Petch relations [2,3]. Smith et. al investigated the effect of varying the carbon content on the microstructure, ultrasonic attenuation, and ductile to brittle transition temperature in a set of high purity, iron-carbon alloys of approximately constant grain size [4]. Kopec and Hanak measured the ultrasonic attenuation in the fine pearlitic steel used for railway wheels. The measurements showed that the contribution of the scattering component can be attributed to grain, grain boundaries, grain distribution, influence of manufacture, content of the ferritic component [5]. Murav’ev investigated the influence of hardening, tempering, and annealing on the velocity of ultrasonic vibrations [6]. Prasad and Kumar have correlated sound velocity and ultrasonic attenuation with the heat-treatment conditions of steel castings [7]. Bouda et.al measured sound velocity and attenuation by both longitudinal and transverse wave at the half cylindrical shape Jominy specimens of steel [8]. The aim of this study is to determine the effect of microstructure of steel on sound velocity and ultrasonic attenuation, and to find out a correlation between ultrasonic parameters and hardness of the material, which is directly related to microstructure. Experimental: AISI/SAE 1040 and 4140 steels in the form of hot rolled bars of 30 mm diameter were cut perpendicular to the rolling direction to 5 mm thick specimens, and then, the specimens were ground to obtain appropriate roughness and surface parallelity. Since some differences in grain size and banding have been observed in the initial microstructures, all specimens were water-quenched after austenitizing at 900°C for 0,5 h. As a result, initial microstructures of all specimens became identically martensitic. After austenitization at 850°C for 0,5 h the specimens have been heat treated as shown in Table 1. In sound velocity measurements a 20 MHz normal beam longitudinal wave probe, Philips-PM3365A pulse generator and Gould Data SYS 740 Digital oscilloscope have been used. Sound velocity was determined by measuring the time taken for the ultrasonic waves to travel through thickness of the material between parallel faces. A constant force is applied to the probe so as to provide a constant thickness of couplant machine oil layer at the probe-specimen interface. For attenuation measurements, 810 backwall echo patterns have been obtained using USD 15 equipment and a 15 MHz normal beam probe. For optical and scanning electron examinations, the specimens were cut into two to observe the microstructure through the thickness. On each specimen, five Vickers hardness values were taken, and then a mean hardness value for each group was determined Table 1. Heat treatment procedures following austenitization at 850°C for 0,5 h No. AISI / SAE 1040 AISI / SAE 4140