Mechanisms of Sticking Phenomenon Occurring during Hot Rolling of Two Ferritic Stainless Steels

Abstract

Mechanisms of sticking phenomenon occurring during hot rolling of two ferritic stainless steels, STS 430J1L and STS 436L, were investigated in the present study. A hot-rolling simulation test was carried out using a high-temperature wear tester capable of controlling rolling speed, load, and temperature. The test results at 900°C and 1000°C revealed that the sticking process proceeded with three stages, i.e., nucleation, growth, and saturation, for the both stainless steels, and that STS 430J1L had a smaller number of sticking nucleation sites and slower growth rate than the STS 436L because of higher high-temperature hardness, thereby leading to less serious sticking. When the test was conducted at 1070°C, the sticking hardly occurred in both stainless steels as Fe-Cr oxide layers were formed on the surface of the rolled materials. Thus, in order to prevent or minimize the sticking, it was suggested to improve high-temperature properties of stainless steels in the case of hot rolling at 900°C to 1000°C, and to establish appropriate rolling conditions and alloy compositions for ready formation of oxide layers in the case of hot rolling at higher temperatures than 1000°C.

Effects of Alloying Elements on High-Temperature Oxidation and Sticking Occurring During Hot Rolling of Modified Ferritic STS430J1L Stainless Steels

“…[6][7][8][9][10][11][12] In the present study, hot-rolling tests were conducted by a pilot-plant-scale rolling machine, and the formation and fragmentation processes of Cr oxides were studied by steps, from which the amount of sticking was evaluated. According to the hot-rolling test results of Figures 3 through 7 and Table V, the oxide layer formed in the heating furnace is not extinguished during hot rolling, but is broken off into pieces or fragments and then remains on the surface with an increasing number of rolling passes.…”

“…Because high-temperature oxidation hardens the surface of the rolled steel as oxide layers or oxide particles are formed on the surface, it can favorably affect sticking. [10,11] This finding indicates that sticking is determined by the mutual interaction of the roll and rolled steel, and that the high-temperature oxidation behavior during hot rolling plays an important role. The sticking amount is also varied with the kind of ferritic stainless steels because their alloying elements affect the high-temperature hardness and oxidation.…”

Effects of Alloying Elements on Sticking Behavior Occurring during Hot Rolling of Modified Ferritic STS430J1L Stainless Steels

“…When the surface region of the rolled steel contains a considerable amount of hard oxides, the surface hardness increases, and the sticking onto the roll specimen surface significantly decreases, thereby leading to the reduced sticking. [10,13,[18][19][20] The sticking occurring during hot rolling of ferritic stainless steels is affected by both high-temperature hardness and oxidation of the rolled steels. Effects of hardness and oxidation on the sticking are schematically plotted as a function of test temperature, as shown in Figure 7.…”

“…[1][2][3][4][5] The hot rolling is affected mainly by wear, oxidation, thermal fatigue, heat impact, and sticking of rolled steels. [6][7][8][9][10] Here, the sticking refers to a phenomenon in which fragments of a rolled steel are detached and stuck to a roll surface; it is considered a dynamic process occurring at interfaces between the roll and rolled steel. Particularly, in the hot rolling of stainless steels, the sticking often occurs at rear parts of roughening roll stands or at front parts of finishing roll stands and leaves defects, such as scratches or dents, on rolled steel surfaces.…”

“…High-temperature oxidation can favorably affect the sticking, because it hardens the rolled steel surface as oxide layers or oxide particles are formed in the surface. [10,13] These indicate that the sticking is determined by mutual interaction of the roll and rolled steel, in which the rolling temperature and the subsequent oxidation play an important role. In addition, the sticking amount is varied with these kinds of ferritic stainless steels, because their alloying elements affect the high-temperature hardness and oxidation.…”