Quality Control by Means of Ultrasonic in the Production of Ductile Iron

Abstract

The paper presents several concepts of physical substantiation for the rationale of building the relationships between mechanical properties and ultrasonic inspection indicators. Special emphasis is put on assessing the influence of graphite shape number S S and the number of graphite precipitations N A on the tensile strength and longitudinal ultrasound wave velocity of ductile iron manufactured under production conditions. Tests were conducted on wedge casts which were used as samples for tensile tests and a map of the structure and longitudinal ultrasound wave velocity was determined for the cast wedges. The tensile tests were conducted and values of graphite shape number, average number of graphite precipitations and longitudinal wave velocity were determined in the place where the sample was broken. Relations between the mechanical properties, graphite shape number, number of graphite precipitations and the velocity of longitudinal ultrasonic wave were determined.KEY WORDS: ductile iron; ultrasonic method; shape and number of graphite precipitations; mechanical properties.tween tensile strength and the velocity of ultrasonic wave was also undertaken in the paper. 9) On the basis of the elongation curve of a brittle material, the author assumed that: where: UTS min , minimum tensile strength corresponding to the elastic strain range; n, fraction of tensile strength corresponding to the plastic strain range (Fig. 1).Rearranging this assumed solution, we get: It was assumed that n may be determined from the quotient of the actual Young modulus (E) and hypothetical Young modulus (E max ). As there is a relation between the velocity of ultrasonic wave and Young modulus (if there is no change in density) the values of n were determined from the expression:........................ (6) where: c L is longitudinal ultrasonic wave velocity, c L max is maximum ultrasonic wave velocity.On substitution of formula (6) into (5), we get a relationship:The values A and B are characteristic for cast iron. Despite rather controversial assumptions in the paper 6) the obtained relationship was proven to be useful for the assessment of the tensile strength of grey cast iron. Concept of Utilizing the Law of MixturesFor their description of the relationship between material structure and its property, authors of many papers employed the co-called "law of mixtures", defined as:where: W, property of material; W a , W b , properties of aand b-phases, respectively; V Va , V Vb , volume fractions of a-and b-phases, respectively.The law is derived from basic relations in stereology. Those relationships can be formulated as follows: a fraction of the length of unitary section corresponding to flat crosssections of grains of a tested phase (l a /l), fraction of surface occupied by this phase on the plane occupied by this phase on a unitary area of polished microsection (a a /a), and a fraction of volume occupied by a specific phase in the unit of alloy volume (V a /V) are expressed by the same quantity.The law of mixtures is most often use...

Influence of Cooling Rate on Microstructure Formation of Si–Mo Ductile Iron Castings

“…Tested longitudinal ultrasonic wave velocity cL decreased according to the power function with respect to the wall thickness (Figure 10a) and is linear-dependent on the number of graphite nodules NA (Figure 10b) of the ductile iron; this has already been found in the literature for standard EN-GJS 500-7 unalloyed ductile iron with casting wall thicknesses that vary from 10 to 50 mm [24]. Tested longitudinal ultrasonic wave velocity c L decreased according to the power function with respect to the wall thickness (Figure 10a) and is linear-dependent on the number of graphite nodules NA (Figure 10b) of the ductile iron; this has already been found in the literature for standard EN-GJS 500-7 unalloyed ductile iron with casting wall thicknesses that vary from 10 to 50 mm [24].…”

“…The ultrasonic wave velocity and attenuation measurements also depend on the morphological features of the graphite (shape, size, and distribution) and the metallic matrix [24,25]. Increasing the ferrite content causes a decrease in the acoustic velocity to an order of 200 m/s for a complete transformation from pearlite to ferrite (as reported by Willcox [26]).…”

“…This means that despite the great differences in the cooling rates, the tested cast iron from the Si-Mo group is characterized by a much lower sensitivity to the cooling rate that is expressed by the ultrasonic wave velocity as well as the microstructure features that are related to the graphite, matrix metal, and carbides that are present. The ultrasonic wave velocity and attenuation measurements also depend on the morphological features of the graphite (shape, size, and distribution) and the metallic matrix [24,25]. Increasing the ferrite content causes a decrease in the acoustic velocity to an order of 200 m/s for a complete transformation from pearlite to ferrite (as reported by Willcox [26]).…”

Detection of Periodic Defects Using Dual-Light Switching Lighting Method on the Surface of Thick Plates

“…In steel manufacturing conditions, many methods have been developed to improve the quality of steel and achieve automatic inspection. In this introduction, we briefly mention the various inspection techniques that have been developed for steel manufacturing environments, which include ultrasonic detection methods for stainless steel spot welds 2) and ductile iron, 3) quality monitoring using voltage signals for small-scale resistance spot welding, 4) 3D X-ray tomography inspection for fatigue in aluminum die castings, 5) and optical inspection techniques for slabs, 6,7) steel bar, 8,9) billets, 10) and silicon steel. 11) Although the several studies mentioned above have achieved good performance and can effectively detect their respective defects, it is difficult to apply them directly to defect detection in thick plate surfaces because each of these methods is optimized for a…”