Study On The Production Technology Of Low Cost And High Performance HRB400 Hot-rolled Ribbed Bars

The 400MPa grade hot ribbed bars, produced by Nanchang steel factory, using 20MnSiV as row material for a long period. It's costs still remain at a high level, and its mechanical properties can't meet the needs of market and development of Nanchang steel factory. In recent years, architectural material's market is complicated and confused, the price of the production changed frequently, the main production in Nanchang steel factory is screw thread reinforced bar, with the simple breed, it can't adapt to the development of market. So, it's imperative to explore the low cost and better mechanical properties hot ribbed bars.In GB 1999.2-2007, there are upper limit in chemical composition of HRB400 hot ribbed bars, but it don't have lower limit, in the condition of good properties, the manufacturer can design the chemical composition independently. So, Nanchang steel factory prepared to develop low cost hot ribbed bars by controlling the rolling and cooling parameters. In this paper, the strength of hot ribbed bars using 20MnSiV as material are improved by high pressure controlled cooling process, at the same time, converter furnace smelt can decreased the content of Mn and Nb, also, lower the cost. The chemical composition of the steel was designed,and some developments was made.Finally,best chemical composition of the steel was cleared as followed C:0.2～0.25%, Mn:1.09～1.25%, Si:0.45～0.6%, Nb:0.006～0.009%.The effects of the heating temperature to the property of the steel was investigated, associate with the properties of the products and the capability of the equipments, the most suitable heating temperature should be 1050℃The water cooling equipments are the crucial part, the cooing rates should be 500～600℃s.The effects of the steel temperature and the change of this temperature to the properties of this steel after water cooling was investigated. The temperature of the steel after water cooling was fixed at 500～550℃,the high temperature should be 680～700℃.The works are as follows, design of project, selection and installation of equipment, debugging in locale of production, analysis and sum-up of result. There are a series of problems emerged in the experiment, such as, the yield point are not evident, plastic property is bad, the hot ribbed bars split in the cold bending test. In order to settle these problems, we collected a lot of date and samples, analyzed the effect of different process parameters on the mechanical property, and find the corrective measures.The result is, if the key process parameters can be controlled properly, the mechanical property of low cost and high strength produced by Nanchang steel factory can meet the national standards, Rm≥540MPa, ReL≥400MPa, and the products have stable quality and prominent economic benefits.