Optimization And Reasearch Preparation Of Steel Bar For Prestressed Concrete

Steel Bar for Prestressed Concrete, it is also called PC steel bar. Because its significant advantages, such as remarkable strength, weldability, upsetting performance and cement bond strength, etc., it is more applicated in prestressed applications. Compared with other countries, some of our’s production of PC steel bar have a greater gap in overall performance, the strength of some products, yield ratio, toughness and other indicators are non-compliance, while mechanical properties are not concentrated, volatile quite serious.This subject studies carefully the principle laws of the heat treatment process and microalloying elements effect on mechanical properties and the ability of resistance to delayed fracture, in order to obtain optimal heat treatment process. Conclusions are as the following.(1) Experiments show that the optimum heat treatment system as follows: Quenching about 900℃, heat 14 minutes, about room temperature water cooling and tempering at 430℃, heat 6 minutes, air cooling.(2) The heading fracture of bars is caused by the non-metallic inclusions and abnormal microstructure; the presence of hydrogen and non-metallic inclusions(especially Mn S) together action caused the delayed fracture. To solve the bars fracture problem in addition to the use of clean raw materials, strengthen the desulfurization operation, control of inclusions, but also the need for mading stringent requirements for storage and transportation conditions for steel bars.(3) The tensile strength of 30 Mn Si V is higher than 30 Mn Sis, about 40 MPa, but elongation is low than 30 Mn Sis,, and still meet the requirements of GB. Discoveried after the heat treatment of base metal found: The tensile strength of 30 Mn Si V increased faster than 30 Mn Sis,——an average of 42 MPa, however, the value of yield strength is higher about 78 MPa. This leads to bars, yield ratio increased.(4) Vanadium acts as the grain refinement role during the steel bar Preparation, and this enhance the role as the quenching temperature and more obvious, while the presence of vanadium can also improve resistance to delayed fracture properties.(5) The two aging treatment can reduce the yield strength of steel rods and the yield ratio, but the impact is not great on tensile strength. The affluence of Artificial aging on the mechanical properties of steel bars is greater than the natural aging,s, this is due to the artificially aging can provide larger atomic driving force.