Determination of the fracture toughness of inhomogeneous three-layer fusion claddings on compact specimens
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DETERMINATION OF THE FRACTURE TOUGHNESS OF INHOMOGENEOUS THREE-LAYER FUSION CLADDINGS ON COMPACT SPECIMENS M. S. Kohut and Ya. S. Hromko
UDC 375.03
We propose a method for the evaluation of the fracture toughness ( K1C ) of multilayer fusion claddings on compact specimens at elevated temperatures (20, 70, and 300°C) with cladding (in the slot) of three layers of materials with gradually increasing crack resistance. As the testing temperature increases, the value of K1C decreases for harder and stronger fusion claddings and, vise versa, increases for less strong and softer materials.
The service life of shrouds on the rolls of MVS-140A mills used to grind coal depends on the quality of the layers fused on their surfaces, the pressure upon the external layer, and the influence of elevated temperature [1]. As temperature increases to 300°C, the surface of the shroud (35L steel) produced according to the industrial technology with fusion cladding of PP-AN170 powder wire of elevated hardness (HRC 62) suffers cracking and, hence, spalling of fragments of the analyzed layer. To determine the fracture toughness ( K1C ) of one-layer fusion claddings, we use beam specimens with cracks in the weld metal, cylindrical specimens with circular cracks in the fused layer [2, 3], or compact specimens with cracks in the fusion cladding. To study multilayer fusion claddings, it is necessary to prepare several batches of these specimens and study each specimen. In what follows, we propose an engineering procedure aimed at the evaluation of the fracture toughness K1C of some fusion claddings on a single compact specimen weakened by a crack in the fused metal. Preparation of the Specimen The specimen (Fig. 1) consists of two identical parts 4 and 5 made of a material with elevated hardness (HRC 60) and a three-step slot made to apply three layers of materials with different hardnesses. The first layer has the maximum hardness and corresponds to the external fusion cladding of the shroud, the second layer has a medium hardness, and the hardness of the third layer is close to the hardness of the matrix of the shroud. After joining the ground halves of the shroud and compressing the lateral sides with ceramic plates, the three-step slot was automatically filled by fusion performed with the help of an A-1416 apparatus and PPAN170, PP-AN170M2, and PP-AN19 powder wires 1 mm in diameter for the first, second, and third layers, respectively. The procedure of fusion was realized at a current strength of 650–700 A under a voltage of 30– 32 V. The thickness of the investigated specimen was chosen from the following formula [5]: 2
K t = 2.5 1C . σ 0.2
(1)
Lviv State Agricultural University, Lviv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 3, pp. 121–122, May–June, 2007. Original article submitted May 25, 2005. 1068–820X/07/4303–0439
© 2007
Springer Science+Business Media, Inc.
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M. S. KOHUT
AND
YA. S. HROMKO
Fig. 1. Modified compact specimen for the evaluation of the fracture toughness K1C of
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