The production process of wear-resistant alloy steel plate is made by metallurgical surfacing. The welding current is generally 300-500A, and the temperature of the welding arc reaches 6000-7000 ℃. The instant high temperature makes the welding wire and the mother plate reach the melting point to form a molten pool (ie weld bead). ), and melt the alloy powder added to the molten pool to form a surfacing layer. During the surfacing welding process, the temperature of the mother plate adjacent to the molten pool will reach 600-800℃, or even higher. Because the mother plate is made of A3 low carbon steel with better toughness and the wear layer is high carbon and high chromium, during the hardfacing welding process , The temperature difference of each part of the motherboard is very large, resulting in extremely uneven expansion, contraction and deformation. In the welding process, in order to ensure the overall process performance of the wear-resistant plate, it is necessary to fasten the motherboard firmly so that it cannot be deformed freely.
In addition, the wear-resistant layer is metallurgical surfacing on the welding wire formed by a large amount of alloy powder. On the motherboard, a typical high-hardness material is formed. Due to the large difference in thermal expansion coefficient between the surfacing layer and the motherboard, the A3 low-carbon steel motherboard can withstand greater thermal deformation, while the high-hardness surfacing layer can withstand thermal deformation. Its capacity is almost zero, so it generates a great thermal stress inside. If this stress is not released immediately, problems such as breaking, cracking, and shedding of the wear-resistant layer are prone to occur. In the cooling process after thermal deformation, in order to release the welding stress existing in the surfacing composite steel plate, many cracks of different sizes and a small number of longitudinal cracks will be generated on the surface of the hardfacing layer perpendicular to the weld bead. This crack is the result of stress release, therefore, if there are no cracks or very few cracks on the surface of the wear-resistant composite board, it is definitely an unqualified product!
Our company's crack inspection standards for the wear-resistant alloy steel plates are: all wear-resistant alloy steel products are allowed to have uniformly distributed transverse cracks and a small number of longitudinal cracks. The length of the crack is less than 3 -6 welds (determined by the thickness of the wear layer), the width is less than 0.4-0.8mm (by the thickness of the wear layer), the depth is less than the thickness of the alloy layer, and no through cracks are allowed.