17%Cr超纯铁素体不锈钢不同方向拉伸起皱的研究

RESEARCH ON RIDGING OF 17%Cr ULTRA PURE FERRITIC STAINLESS STEEL AFTER ENLONGATED ALONG VARIOUS DIRECTIONS

采用激光共焦显微镜、XRD和EBSD技术,研究了17%Cr超纯铁素体不锈钢退火板材沿3个不同方向拉伸变形后表面起皱与晶粒取向变化之间的关系,并探索了17%Cr超纯铁素体不锈钢的拉伸起皱机制.结果表明,17%Cr超纯铁素体不锈钢退火板材沿着与轧向呈0°(轧制方向,RD),45°和90°(横向,TD)3个不同方向拉伸后,表面条纹状起皱方向均与原始轧向平行,并且随拉伸角度增大,表面起皱逐步减轻.在拉伸过程,均发生<110>取向向拉伸方向(TA,拉伸变形方向)转动.但沿TD拉伸时未造成晶面转动,而沿RD拉伸则转动形成{112}和{221}面取向.17%Cr超纯铁素体不锈钢起皱与<110>//TA取向无关,而是由沿原RD分布的晶粒簇内的晶面转动造成的,并且晶粒簇内的晶向转动对起皱的影响极小.

Improved mechanical and chemistry properties of ferritic stainless steel（FSS）, such as stamping formability and corrosion resistance, have been attained by decreasing the contents of C and N. Therefore, the ultra pure ferritic stainless steel with low content of C and N is a good candidate to replace the conventional Cr-Ni austenitic stainless steel for specific applications to save the higher price of Ni. As compared to conventional austenitic stainless steel, however, the ferritic stainless steel is susceptible to develop narrow ridges on the sheet surface during forming operations. The ridges, which can extend over the whole sheet length and have a depth of 20~50 μm,destroy the smooth appearance and surface shine of the product and thereby reduce the quality of the formed work pieces. This is one of the most serious problems of ferritic stainless steel sheets. Hence, the improvement for resistance of ridging is desired for further wide applications of ferritic stainless steel. In this work, laser scanning confocal microscopy, XRD and EBSD were used to observe the corelation between surface ridging and the evolution of grain orientation of 17%Cr ultra pure ferritic stainless steel after elongated along three different directions. Furthermore, the mechanism of tensile ridging of ferritic stainless steel was discussed. The results show that the ridging direction always parallels to the original rolling direction when the 17%Cr ultra pure ferritic stainless steel is enlongated along 0°（rolling direction, RD）, 45° and 90°（transverse direction, TD） with the rolling directions, respectively. However, the height of ridging gradually decreases with the increase of the angle betweeen the rolling direction.Meanwhile, tensile texture of 110//TA（tensile axis） gradually forms after enlongated along three different directions. The most important phenomenon is that the crystal plane almost does not rotate when enlongated along TD,while {112} and {221} orientations form when enlongated along RD. Thus it can be deduced that there is no relationship between ridging and 110//TA orientation in 17%Cr ultra pure ferritic stainless steel. Moreover, the rotation of crystal direction in rolling plane has little effect on the ridging. However, the formation of ridging can be attributed to the rotation of crystal plane in rolling plane with cluster distribution.