Freckle Sample

ABOUT IRON CHARACTERISTICS OF THE CHILLE SAMPLE STRUCTURE will give information about the accuracy of the conditions in the Chill test (Melting in Metallurgy). Assuming that the chill tests are carried out in ASTM 367-60 sample preparation standards, it is very important that all samples are poured at certain temperatures. Because the chill amount is formed depending on the casting temperature. Also an important value is to avoid overcooling. It is also important to take test samples for this. In order to prevent cooling in sample casting, it should be used with at least 2.5 kg crucible lined with graphite refractories. Chill Measurement Chill test patterns can range from 1.25x2x6 inch to 13 / 16x2.5x5 inch. Higher iron-carbon equivalent may require smaller or chill sample. If the crack is long along the longitudinal axis and straight, the test sample must be broken. On the refraction surface, a region from white to black can be observed. It is called “Clean Chill” from the edge to the end of its white area. The region up to the last white peak spot visible at the end of the clean chill region is called the spotted region. Total chill is first measured from the area of formation at the intersection area at the point where gray crushing occurs. Figure 1 can be shown as an example where a chill test can be interpreted. The shapes can be observed by examining the polished edge and chill samples under a microscope. Graphite flakes of type A were formed at the top of both samples. Such scales normally occur under equilibrium conditions provided by low rate of solidification conditions. This type of graphite structure is an ideal structure for casting during grafting time. In ideal working conditions, while the solidification rate is low, there is no need for theoretical vaccination. Therefore, in the casting of a 4.3% carbon equivalent gray cast iron, if a fast solidification is required to achieve the desired mechanical properties, grafting is mandatory to ensure sufficient nucleation. In extreme cooling conditions and out of equilibrium solidification conditions, B-type graphites are formed as a result of dimensional shrinkage of the test samples. In these conditions, a decrease in material tensile strength occurs. If the solidification rate is increased, a high degree of overcooling occurs. Pre-inoculation will reduce the formation of A and D graphites, allowing for machinable casting material. In the lower parts or test samples where white iron (figure 1) was observed, the solidification rate was very high, so the carbon could not find the time required for graphite formation. This resulted in the formation of iron-carbides known as cementite. This material has a tensile strength of approximately 40000 psi but because it has a fragile structure, it is not workable. This is not desirable. A successful foundry can measure from the chill sample cross-section how much cementite it can allow in the final cast iron material. Figure 2 schematically shows structural changes in supercooling conditions. The test sample is 4.5% carbon equivalent pre-vaccination ductile iron. The chill test is a very important step for microstructural control of cast iron. It helps in calculating the amount of vaccination required. It is an important auxiliary element for both spherical cast iron and gray cast iron.