Microstructures and mechanical properties of cold rolled pipes with increased small deformation

Abstract

Purpose. Experimental study on microstructure, mechanical properties of pipe diversity on a new type of cold rolling pipe, which has the ability to perform different modes of supply and rotation. Methodology. Research method is an experimental one on modern industrial equipment using modern devices. The study was conducted when rolling pipes made of steel 08Cr18Mn10Ti on the CRP 6-20 mills. Rolling route is often 25 × 2.5 mm ® 16 × 1.5 mm, which is often used in production. Rolling was carried out on the CRP 6-20 mills in four modes of feed and rotation: mode 1 – feed is performed before the forward stroke, and rotation before the return stroke of the stand; mode 2 – the feed is performed before the forward stroke, and the rotation before the forward and reverse stroke of the stand; mode 3 – feeding is performed in the front and rear position of the stand and rotation in the rear position of the stand; mode 4 – feed and turn are performed before the forward and reverse of the stand. Findings. Metallographic studies on microstructures showed that for mode 1, the grain size on the outer surface of the pipes is less than on the inner surface. The difference reaches the value of 1–2 points. For mode 4, the opposite is true. The size of the grains on the outer surface of the pipes is larger than on the inner surface. The difference reaches the value of 1–2 points. This can be explained by the fact that in mode 1 most of the compression is performed in the forward stroke rather than in reverse stroke. And in mode 4, these crimps are close in value and smaller than in a forward stroke in mode 2. Originality. New experimental industrial data have been obtained for the first time on the state-of-the-art cold rolling mill for small-diameter pipes made of microstructures of riveted steel 08Cr18Mn10Ti in cross-sectional and longitudinal sections of the pipes on the outer and inner surfaces of the pipes and between them for four possible feeding and turning modes. For the first time, experimental industrial data on the values of strength limit, yield strength and ultimate elongation at four feeding and turning modes have been obtained as well. Practical value. The obtained experimental industrial data from a set of quality parameters of pipes – metal microstructure, mechanical properties, transverse differences in pipe packages allow one to choose modes of supply and rotation in the production of cold-formed pipes to ensure compliance with regulated quality parameters of supply and rotation pipes.