Abstract
Problem statement. In recent decades, there has been a tendency to increase the mechanical properties of low-carbon, low-alloyed steel plate iron by using controlled rolling or hardening heat treatment of finished steel parts. At the same time, for welded parts, the most suitable is a metal having a ferrite-bainite (or bainite) structure. The work investigated the features of the ferrite-bainite structure of low-carbon and low-alloyed steel 15ХСНД for the production of connecting pipeline parts. Purpose of the article. To establish the laws of formation of a ferritic-bainitic structure in low-carbon low-alloy steels depending on the parameters of heat treatment. Determine the effect of heat treatment parameters on the properties of the connecting parts of pipelines made of these steels. Conclusion. The regularities of the influence of heat treatment parameters on the structure, mechanical properties and topography of fractures of impact samples of 15ХСНД steel with a ferrite-bainitic structure are established. Keywords: stamped-welded connecting parts of man pipelines; heat treatment; microstructure; bainite;mechanical properties; fractography
Highlights
In the production of plate steel from low-carbon lowalloy steels in the production of pipes and connecting parts of main pipelines (CPP), there has been a tendency to increase the complex of mechanical properties due to the use of either the technology of controlled rolling of rolled metal, or hardening heat treatment of finished products
Using the terminology of the authors of [9], after heat hardening of steel of the 15ХСНД type, a ferrite-bainitic structure was obtained, the ferrite component of which was quasipolygonal ferrite (QPF), which differs from polyhedral ferrite (PF) by curved boundaries, high density of dislocations that form substructural constructions
This article examines the microstructures of 15ХСНД steel after heat hardening in water with a temperature above 90 оC by the mode of complete cooling to the ambient temperature
Summary
In the production of plate steel from low-carbon lowalloy steels in the production of pipes and connecting parts of main pipelines (CPP), there has been a tendency to increase the complex of mechanical properties due to the use of either the technology of controlled rolling of rolled metal, or hardening heat treatment of finished products. For the industrial production of competitive connecting parts for main oil and gas pipelines with a diameter of up to 1 420 mm at strength levels X60−X80 and higher, parameters of hardening heat treatment of stamped-welded connecting parts were developed This developed heat treatment is ensuring the obtaining of a ferrite-bainitic or bainite structure in low-carbon low-alloy steels with a thickness of 14...50 mm. When developing technology and equipment for bulk heat hardening (HH) of stamped-welded connecting parts of piplines (CPP), the parameters of heating modes for finishing heat treatment (austenitization temperature, cooling intensity, tempering temperature, etc.) were selected, Design and technological parameters of the heating device and cooling environment providing the required level of normalized properties due to the production of parts of ferrite-bainitic or bainitic structure in the metal [1,2,3]
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