Analysis of Crack Formation in the Casting: A Review (original) (raw)
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Fracture Mechanisms in Steel Castings
Archives of Foundry Engineering, 2013
The investigations were inspired with the problem of cracking of steel castings during the production process. A single mechanism of decohesion - the intergranular one - occurs in the case of hot cracking, while a variety of structural factors is decisive for hot cracking initiation, depending on chemical composition of the cast steel. The low-carbon and low-alloyed steel castings crack due to the presence of the type II sulphides, the cause of cracking of the high-carbon tool cast steels is the net of secondary cementite and/or ledeburite precipitated along the boundaries of solidified grains. Also the brittle phosphor and carbide eutectics precipitated in the final stage solidification are responsible for cracking of castings made of Hadfield steel. The examination of mechanical properties at 1050°C revealed low or very low strength of high-carbon cast steels.
A new criterion for internal crack formation in continuously cast steels
Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science, 2000
To estimate the cracking condition in continuously cast steels, a new model for critical fracture stress given from the measured critical strain has been proposed, which can take into account the brittle temperature range and strain rate. The effects of brittle temperature range and strain rate on critical strain for internal crack formation were analyzed. When the brittle temperature range and strain rate were increased, the possibility of internal crack formation increased due to the decreasing critical strain. To describe the thermomechanical property model of the mushy zone between zero strength temperature (ZST) and zero ductility temperature (ZDT), the yield criterion for porous metals, which can take into account δ/γ transformation, was used. Using the fitting equation for the measured critical strain and the microsegregation analysis, the thermomechanical behavior of the mushy zone could be successfully described by the proposed model, which incorporates the effects of microsegregation of solute elements and δ/γ transformation on hot tear during solidification at the given range of steel compositions and strain rates. A cracking criterion based on the difference of deformation energy in the brittle temperature range is proposed to explain the cracking phenomenon of whole carbon range.
CAUSES OF OCCURRENCE OF INTERNAL AND SURFACE DEFECTS AT CONTINUOUS CASTING OF STEEL SLABS AND
The paper was focused on search of causes of occurrence of internal and surface defects of continuously cast steel slabs. The relationships between types of defects given in literature and their occurrence in industrial practice were investigated, ensuing from preparation of the melt according to the specification of secondary metallurgy unit and equipment of the continuous casting machine. Methods leading to the analysis of causes of formation of defects at non-observation of standard of metallurgical and technological procedures are always complicated and time consuming. The paper defines occurrence of individual types of defects and possibilities, which were developed for their removal in the BOF shop with single strand slab continuous casting machine.
The paper was focused on search of causes of occurrence of internal and surface defects of continuously cast steel slabs. The relationships between types of defects given in literature and their occurrence in industrial practice were investigated, ensuing from preparation of the melt according to the specification of secondary metallurgy unit and equipment of the continuous casting machine. Methods leading to the analysis of causes of formation of defects at non-observation of standard of metallurgical and technological procedures are always complicated and time consuming. The paper defines occurrence of individual types of defects and possibilities, which were developed for their removal in the BOF shop with single strand slab continuous casting machine.
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2020
The ductility drop and decrease in strength that lead to crack formation during continuous casting of steel is typically investigated by means of the hot ductility test. In this study, hot ductility tests are performed by using a thermo-mechanical Gleeble system to simulate the deformation of steels at high temperatures and low deformation rates similar to those during continuous casting. Thus, temperature was varied between 600 and 1000 � C while strain rates covered a range from 0.001 to 0.1 s 1. Tests are carried out to identify the temperature range at which the steel is susceptible to crack formation as well as the effect of strain rate. Characterization of fractured surfaces and phase transformation after thermo-mechanical tests are conducted in the SEM and Optical Microscope. The combination of these techniques makes possible to formulate cracking mechanisms during hot processing which show critical strain for failure at temperatures between 700 and 900 � C based on the convergence of three different criteria: I) Reduction of area, II) True fracture strength-ductility and III) True total energy. This approach provides a better understanding of crack formation in steels at the high temperatures experienced during continuous casting. This information is key to productivity losses and avoid defect formation in the final cast products.
A Novel Approach for the Simulation of Surface Crack Formation in Continuous Casting
BHM Berg- und Hüttenmännische Monatshefte, 2014
The present study describes the possibilities of new experimental and numerical methods to predict the crack susceptibility under continuous casting (CC) conditions. The first method-the In-Situ Material Characterization by Bending (IMC-B) Experiment allows measuring of the critical strain values for surface defects upon all the most important process and material parameters. The IMC-B experiment uses solidified samples obtained directly from the melt and it is based on the 3-point bending test. Hence the material and process parameters are similar to CC. Strains are calculated directly after the experiment uses a simulation in Abaqus. The risk of surface cracks is provided using the new numerical tool, so-called defect indices implemented in IDS. In the framework of practical series a crack susceptibility of the commercial Nb-microalloyed steel is investigated after the subsequent cooling to the test temperature. The test temperature corresponds to the temperature at the beginning of straightening zone in cc. Samples cast at two different cooling conditions show another distribution of surface defects and critical strain value.
Impact Of Casting Process Conditions On The Structure And Ductility Of An AHSS Steel Slab
2019
The current challenge in the steel industry is to increase the quality of steel products. In this sense it is necessary to avoid defects in steel semi-finished products (slabs) as well as to develop good control on primary production technology, especially in the continuous casting conditions. For automotive steel sheet grades, the main requirements are good formability, combining high strength and ductility. Hot stamping process is used to manufacture light weight steel car body parts. Advanced High Strength Steels (AHSS) such as boron steels, are the most used for hot stamping. Low boron additions to the steel composition improve mechanical properties, provide hardenability and weight savings compared with conventional steels. Boron in these steels should remain free (in solid solution), avoiding precipitates generation in the structure. During solidification in the continuous casting, alterations of the process conditions can promote product defects and produce ductility loss. Th...
A study of breakout of a continuously cast steel slab due to surface cracks
Surface Effects and Contact Mechanics X, 2011
The solidification and cooling of a continuously cast slab and the simultaneous heating of the mold is a very complicated problem of three-dimensional transient heat and mass transfer. The solving of such a problem is impossible without numerical models of the temperature field. Experimental research and measurements must be carried out simultaneously with numerical computation. An important area of the caster is the so-called secondary cooling zone, which is subdivided into thirteen sections. In the secondary cooling zone, where the slab begins to straighten, a breakout of the steel can occur at the points of increased local chemical and temperature heterogeneity of the steel, due to increased tension resulting from the bending of the slab, and also due to high local concentration of non-metallic, slag inclusions. The changes in the chemical composition of the steel, during the actual continuous casting, are especially dangerous. In the case of two immediate consequent melts this could lead to immediate interruption of the continuous casting and to a breakout. The temperature field of a slab was calculated by means of original numerical model before, as well as after the breakout and the calculated parameters were collected. If the dimensionless analysis is applied for assessing and reducing the number of these parameters, then it is possible to express the level of a risk of breakout as the function of five dimensionless criteria.
Analysis of Internal Defects Appeared in the Continuous Casting
Scientific Bulletin of Valahia University - Materials and Mechanics, 2018
The paper presents the study of internal defects resulting from the continuous casting of steels. The 50 samples were taken from a total of 20 continuously cast bits of different steel grades. The investigation of the causes of internal defects, shown on the analyzed samples, started from the assumption that the secondary metallurgy was performed correctly. The following internal defects have been evident: internal cracks (axial cracks, section cracks), central porosity and marginal punctuation impurities.