Analysis And Research On Cold Bending Fracture Of Rolled Steel In Yigang

With the rapid development of economic construction in our country, thebooming of national infrastructure construction and construction industry brings onmore and more increasing demand for20MnSi hot rolled ribbed bar, so that the threadsteel output account for more than85%of the total output of the construction steel.Reinforced Concrete is main material widely used in building construction at presentand in the long run in China. Therefore, we can predict that the demand and output ofthe thread steel will continue to maintain a high level. The thread steel must have goodtoughness, good plasticity, high tensile strength, high yield strength and certainweldability during operation. The thread steel in the factory has to pass strict test ofcold-bending property, and the thread steel with unqualified cold-bending property willbear very heavily on its using.In this paper, we calculated the number of thread steel samples which occurredcold bending fracture upon the cold bending test and the months in which theyfractured in Yicheng Steel Company of Jiuquan Iron and Steel Group, thus we couldsample pointedly, protect the samples, cold bending fracture and manufacture theminto fracture surface, spectroscopic and metallographic samples. The chemicalcomposition of the samples was detected by the spectrum analyzer at physicalinspection stations of Yicheng Steel Company. The metallographic test was completedat Xi’an University of Architecture and Technology, the cold bending fracture sampleswere analyzed macroscopically, the cold bending fracture and the metallographicsurface were microscopically analyzed and their micro area composition was studied with SEM and EDS, then inclusion and structure were observed by usingmetallographic microscope.This paper synthetically analyzes the performance of thread steel produced by thebar mill of Yicheng Steel Company with the above methods to look for the causes ofcold bending fracture of the thread steel samples upon the cold bending test. In order toanalyze the causes of cold bending fracture of the thread steel of Yicheng SteelCompany and put forward the measures for improvement, this paper studies theprocess parameters of thread steel such as cold bending fracture, chemical composition,non-metallic inclusion, metallographic structure and rolling process, throughconsulting documents and considering the practical productive experiences. Then thispaper obtains the causes of cold bending fracture of steel are that contents of C and Mnare richer in steel, the excessive content and centralized distribution of the inclusion, inaddition, the bainite structure and banded structure exist in the microstructure.Combined with field technical parameters analysis and laboratory analysis, this paperpresents improving measurements suitable for cold bending fracture of the thread steelof Yicheng Steel Company in order to provide important reference for improving thesmelting, continuous casting and rolling technology of the company and define thestriving direction of solving quality problems of the Company’s thread steel.