Microstructures and microhardnes formation of hot-rolled if-steels after cold upsetting and annealing

V. Z. Kutsova, V. G. Ivanchenko, T. V. Koтова, G. P. Ploshenko

Abstract


Raising of problem. The low carbon steels which have relatively high plasticity and can undergo significant deformation without the danger of the fracture and with minimum energy costs are used for the manufacture of cold formed conventionally. The disadvantage of the carbon steels is a tendency to strain aging. The increasing quality requirements products has led to the new class of steels with low carbon and nitrogen contents (IF-steel). The level of their production in the world is constantly increasing. IF-steels have good formability and the combination of high strength and ductility allows to maintain high structural strength of products in emergency situations. The ferritic matrix grain refinement, solid solution alloying, regulation dislocation density and substructures in cold rolling, optional - selection of the particulate solid solution strengthening and texture strengthening phases are the main IF-steels hardening factors. The low ratio values sт/sв and high degree of strain hardening IF-steel are guaranteed high strength properties and thickness uniformity of stamping parts. The using low-carbon steels instead of the usual steels will provide strength while maintaining weight reduction is proportional to the depth of the hood. The study microstructure and microhardness results of the IF-steels after cold rainfall may be useful in cold bulk stamping sheet or cold heading fasteners. The technology of furnace treatment of liquid steel processing is applied ligatures containing calcium. Influence of calcium on the steel’s structure and properties is manifested in the consistent implementation of the multi-stage process, due to its high chemical activity: refining liquid metal globularization nonmetallic inclusions, modify the macro - and microstructure, etc. Thus, investigations of the temperature and deformation modes of treatment influences on the structure and properties of the IF-steels are relevant. Purpose – to study the influence of cold shrink with followed annealing to the structure and mechanical properties evolutions of hot rolled
IF-steels. Conclusion. The structure, grains size, dislocation density, microhardness of steels 01ЮТА and 01ЮТА* after rolling, cold upsetting and annealing were investigated. The analyzed steels are characterized by different ability to deformation and it was concluded that steel 01ЮТА* has better formability.


Keywords


hot-rolled steel; rolling; cold upsetting; annealing; structure; microhardness

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