Research On The Relationship Of The Mechanical Property And The Metallurgical Structure In Hot-rolled Strip

Recently requirement of steel quality has grown ever more harsh , which asks not only for a very good surface quality of steel, but also a higher demand of Mechanical properties. In order to find the low rate reasons of broadband Q235B steel hot-rolled and cold-formed extension of the performance, and to improve the smelting, rolling process ,and the quality of steel., this article, starting from the mechanical properties of steel strip and Organizational relationships, taking advantage of macro-fracture analysis, spectral analysis , microhardness measurement and analysis, metallographic analysis, etc. experimentizes a comprehensive analysis of the physical and chemical inspection,. At the same time, in order to identify the cause why the J55 and H40 steel casing pipe weld crack and squash and make it clear to solve this problem from the steel quality or the welding process, this thesis makes a comprehensive physical and chemical inspection through the macro-analysis, analysis of the low times, spectral composition analysis, metallographic analysis, scanning electron microscopy analysis of spectra by means of detection. Based on the results of the analysis , production process of broadband Q235B steel hot-rolled, J55 and H40 steel casing is improved and trial production is carried out in Shandong Taishan Iron and Steel Group hot-rolled plant.Study shows that there are two main reasons of failure of hot-rolled steel Q235B performance: First, high inclusions; Second, Widmanstatten Organization or Organization of granular bainite is a typical fast-cooling organizations, who reduces the plastic, advances the strength and leads to failure of its mechanical properties. By reducing the content of inclusions in steel-making process, improving the finishing temperature to 880℃~ 890℃in rolling process, increasing the cooling intensity, advancing the rolling speed , maintaining the temperature uniformity and using other measures to obtain organizations whose top and bottom surface is the fast-cooling Organization (Widmanstatten organizations or granular bainite) and the Center is the normal organization of the annealing, to solve the Q235B steel mechanical properties of the problem of failure. Direct cause of J55 and H40 steel casing pipe welding cracks and crack squash is seriously banded structure. The indirect cause is high level of non-metallic inclusions who is in a large number. Through the rolling process due to lower rolling finishing temperature and after cooling to take the previous measures such as laminar flow, it can be appropriate to reduce the level of banded structure.