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Influence of a precedent deformation - heat treatment on structure and properties of steel 70 whith consideration of parameters of heat treatment.
In my work I will probe influence of a precedent deformation - heat treatment on structure and properties of steel 70. Thus the relation to parameters of a consequent heat treatment will be taken into account. A feed stock for manufacturing a wire is the rolled wire. On metallurgical plants a rolled wire a dia of 6-14 mm is produced. It takes place on mills of linear semi continuous and continuous type. A material for a rolled wire can be miscellaneous marks of steels. But it is known, that steel 70 is the widespread material for manufacturing a cable wire. Chain cables have the broad spectrum of the application, therefore produced production should have a high level of quality. It means, that the wire should have high tensile strength limit, should maintain large loads and well carry bending stress. All these qualities depend on a condition of received semi product and on parameters of technology of process of obtaining of a wire. Desirable structure for manufacture is structure of sorbite, because after process of wire drawing received good combination of properties, such as strength and plasticity. 1996 year the article with the new technology sorbit of rolled wires has been published. On this technology a driving rolled wire intensively chill water up to 750-800 0Ñ in the beginning short ways. Then a compressed air chill with such speed which ensures transformation of austenite to sorbit: or on the conveyor where rolled wire put separate twists and after cooling up to fixed temperature a compressed air. After that it collects in clamps, or in wells where twists of a rolled wire slowly alight downwards, chill a compressed air and stack in clamp. Indicate, that such technology guarantee stability of mechanical properties longwise rolled wires. However described way of cooling has appeared not efficient in hanks with mass more than 500 kg. Diverse ways of accelerated cooling – sorbitization a steel rolled wire from a rolling heat - target decreasing quantity of scale and maintenance of formation of fine structure (perlite) which easily distorts at a drawing.
Selecting parameters of treatment of steel, it is necessary to remember about its initial state because it often influences a structure condition of metal. On this cause of property of metal can vary not always predictedly.
The heat treatment of specially preformed samples has been conducted: samples a dia of 6,5 mm, 4,5 mm and 4,5 mm after patenting were used. The heat treatment consist of their heating to temperatures 730, 760, 800, 850 both 9000 With and their cooling on air and in water. After the mentioned treatment microhardness of steel is testing on device PMT-3 with a load 1Í.
As follows from obtained data, patenting wire has hardness on 8-10 % above, than an initial rolled wire. Under data of microstructural probes it is provided, first of all, with increase of dispersion degree of perlite. And cold plastic deformation produces substantial increase of hardness of steel (on 25 %).
Ferrite and macrolaminar perlite is the cause of the lowest hardness among original samples. In structure dragged and patenting wire perlite more finely divided, and ferrite is located more uniformly. Hereditary influence precedent straining and a heat treatment legiblly shows in an event of realization of normalization become after heating to 900 and 850 C.
It is possible to suppose, that one of principal causes of hardening of an air-hardened steel under influence of precedent cool plastic deformation is refining structure of perlite and reduction of the dimensions of perlitic colonys. It can be stipulated by hereditary influence of initial structure and substructure of perlite on structure of austenite that determines a kinetics of process austenitisetion and austenite recrystallizations at reheating and, therefore, a grain size and a degree of presence of defects of austenite to the moment of the beginning of its disintegration.
After realization of quenching character of distribution of hardness is analogous.