Effect of crystal orientation on inner surface roughness of micro metal tubes in hollow sinking

The crystal deformation behavior of the micro tube was investigated to clarify the crystal orientation, which suppresses the development of the inner surface roughness during the hollow sinking. Stainless steel tubes with an outer diameter of 1.50 mm and a wall thickness of 0.045 mm were drawn without an inner tool. The inner surface roughness and crystal orientation were examined using the same measurement area. The results indicated that the crystal grains with the {102} crystal planes vertical to the normal direction to the inner surface (ND) suppressed the increase in the height of the unevenness of the surrounding crystal grains, including themselves. The height deviation of the unevenness of the wall-thickened tube was larger than that of the wall-thinned one. Meanwhile, the number of crystal grains with the {102} crystal plane vertical to ND of the wall-thinned tube was larger than that of the wall-thickened one. Therefore, it was considered that this crystal orientation suppressed the development of the inner surface roughness during the hollow sinking. The development of the inner surface roughness was suppressed with decreasing wall thickness because the crystal grains rotated so that the normal direction of {102} crystal plane was parallel to the ND: meanwhile the tensile and compressive stresses were applied to the inner surface of the micro tube in the drawing and transversal directions, respectively.