RESEARCH STRUCTURE FORMING AND FORMATION OF PHYSICAL-MECHANICAL PROPERTIES AT THERMOPLASTIC PROCESSING OF SPHEROIDAL GRAPHITE CAST IRON

摘要

The spheroidal graphite cast iron (SGCI) in a cast condition represents a composite consisting of a metal matrix with spherical inclusions of graphite by a diameter 10-40 microns. Depending on thermal processing SGCI has the following properties: tensile strength 350-500 MPa, specific elongation 10-20 %, hardness 140-240 HB, rate of pitting corrosion in sea water of 0,1 mm/years. Investigated influence of hot plastic deformation by lengthwise, screw rolling, extrusion and drawing on structure and properties of products from SGCI. Is established, that at all kinds of deformation graphite inclusions is irreversible lose the spherical form, being extended along a direction of current of metal in the deformation zone. It results to anisotropy of physical-mechanical properties (strength, plasticity, impact strength, coercivity, and corrosion resistance). The following properties of hot-rolled sheets from SGCI are received: Direction of measurement TS, [MPa] YS, [MPa] SE, [%] Hc, [A/M] On a direction rolling 390-500 280-380 12-17 250 Across a direction rolling 320-360 305-320 3-4 155 The subsequent heat treatment influences only a metal matrix, not changing the form of graphite inclusions. Thus, there is an additional factor of influence on structure and properties of pig iron by change of morphology graphite inclusions, that expands areas of application SGCI.