Analysis On Cause And Control Of Edge Defect Of Hot Rolled Strip

Edge crack is a kind of common defect in the production of hot strip, often in batch appears. The existence of the edge crack not only affect the quality of the product, but also jointly cause manufacturing equipment damage, cause product production falls, the serious influence production run smoothly, and cause major economic loss to the enterprise.For the causes of the edge crack is always the more concern to hot strip enterprise and technical workers. Previous research is generally the analysis of the specific conditions in the enterprise according to the specific production technology and production equipment and production technology, so different enterprise to the cause of formation of the edge crack has different opinions.These analysis results from the previous view, the generation of edge crack seemingly have different reasons, the deep fundamental causes to edge crack without a real reasonable scientific explanation.In this paper, according to the JiLin-jianlong of Jianlong group hot strip steel Co., LTD. With the actual production and several years of work practice and edge crack different period production process tracking, field investigation. Through the macro analysis to the edge crack defect, gas content analysis, chemical composition analysis, low acid corrosion test. Through the anatomy of the analysis to roll on edge crack from outside to inside and 3D direction of metallographic analysis research and scanning electron microscopy (sem) analysis method, the comprehensive analysis of the cause of the edge crack appeared with a comprehensive analysis of the research, through the induce deduction, clear the produce the root cause of the edge crack that edge crack formation essence.The results of the study show that, the root cause of the edge crack mean essence is the billets non-uniform deformation when rolling. All the non-uniform deformation factors can affect the edge crack formation on different degree, the easy cause the non-uniform deformation, the easy cause edge crack production. The billet defects on internal and external, composition segregation, impurity and heating equipment adjust undeserved, rolling equipment adjust inappropriately etc.The organizational structure of the density of the slab billet decides to the severity by oxidation after reheating furnace. When billet side of edge porosity, subcutaneous air bubbles, existing subcutaneous cracks, slag inclusion defect ect, the organizational structure of the billet are more loose, with the extension of time of the billet go into reheating furnace, the thin density of different materials, and its quality is increased, , the more loose of the structure of the material to oxidation. Loose material generated oxidation layer also is loose, beneficial to the spread of oxygen and aggravate the oxidation reaction.The closer of the billet structure of the organization,the more easy to be oxidation. The more vulnerable oxidation of the billet defects of internal and external metal, the more easy cause the non-uniform deformation of edges material, the harm are more serious, especially such as the same bubbles in inside and outside or crack defects. The billet defects in internal and external are more oxidation in the high temperature heating furnace, cause oxidative tissue, which can cause decarburization, rolling section of the serious the non-uniform deformation. The billet defect of internal and external is major factor that produce batch of edge craks during hot rolled strip production.Defects uneven distribution in the internal metal, the greater the volume, the more uneven distribution, the stronger of the non-uniform deformation, the defect easy cause stress concentration, causing crack source. Uneven chemical composition, the inclusion will make the organization uneven deformation.The macro deformation is part of the metal provide, the local plastic deformation is too large, so that more than the area of plastic deformation and at the time can produce micro cracks and expanded to edge crack when rolling.Heating furnace temperature improper control is generally from an accidental mistake operation or instrument failure, easy to find and control; forced to wider and uneven rolling, gib scrape cause the stress of edge metal increasing, prompting crack propagation and constantly forming new crack, continue to oxidation or even broken, fall off. These are the external cause by uneven deformation.The edge crack effectively improve is the pursuit goal of hot rolling technical workers. This research for hot rolling technology workers provide the scientific guidance about edge crack improvement, helpful in improving management of the production quality and technology, through the practice and improvement of nearly a year, edge crack defects have been significantly control, satisfactory results have been obtained.In this paper, the research work of edge crack rich the basis theoretical about the formation of edge crack and has a guiding role for practical production. In practical production, according it to go related improvement, and thereby reducing the edge crack generation, reduce the production cost.