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HSLA steel is by adding a small amount of alloying elements on the basis of carbon steel, increase strength, and improve the use of the performance and development of a class of engineering structural steel. As we all know, alloy steel and carbon steel, the difference is quite clear. Carbon steel, iron, carbon, silicon, manganese and unavoidable sulfur, phosphorus and other impurity elements, the steel to satisfy the production technology requirements. Alloy steel is to add a particular element or combination of elements, and to obtain certain good overall performance combination of steel. The vast majority of the carbon steel smelting more or less contain alloying elements. However, these alloying elements are not intentionally added, but the amount is not very high, generally below 0.5%. These alloying elements, there are two sources: one is to bring in scrap; two kinds Ore smelting pig iron brought. In this study, a low alloy high strength steels as experimental materials to study the different content ZrC particles and rare earth element yttrium, lanthanum microalloying carbonitride size and precipitation equal of HSLA steels organization performance by scanning electron microscopy ( SEM), XRD analysis of the experimental techniques of X-ray small-angle scattering (SAXS); system strengthening effect of HSLA steel, grain refinement and nano-scale precipitates strengthening. In addition, the solid solution strengthening and dislocation strengthening also play an indirect role. In-depth study was carried out to test the good mechanical properties of steel reasons from the point of view of the microstructure. The experimental results show that the excellent mechanical properties of the experimental steel reasonably be attributed to the chemical composition and processes, its reasonable to add micro-alloying elements. By studying the different components of the experimental steel austenite in microalloyed carbonitride precipitation behavior and found: ZrC particles and rare earth elements, yttrium, lanthanum, not only reduces the growth rate of the ferrite grain and depressed proeutectoid ferrite formation to extend the the ferrite nucleation incubation period. Steel ZrC particles and rare earth elements yttrium, lanthanum and elements of the total content of 1.5%, the grain size of the ferrite ratio excluding ZrC particles and rare earth elements yttrium, lanthanum element steel small. When ZrC particles and rare earth elements yttrium, lanthanum increased to 1.0% of the total content of acicular ferrite number increased significantly. When steel ZrC particles and rare earth elements, yttrium, lanthanum, 1.5% of the total content of microstructure of bainite beam and martensite - austenite. Reduces the Ms point when the ZrC particles and the rare earth elements yttrium, lanthanum and a total content of 2.5%, there is a significant increase in the amount of residual austenite in the steel, therefore, the martensitic - austenitic increased number. Also increases the strength of the steel, but because of the emergence in austenite martensite -, so that the toughness of steel decreases.
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