When the alloy steel tube billet is heated in the low temperature section, these factors cannot be i
Date:2019-07-04 View:21 Tag:When the alloy steel tube billet is heated in the low temperature section, these factors cannot be i
Steel pipe of these factors must not be ignored when the preform is heated in the low temperature section, it will affect production quality. The heating period of the low temperature section is often a critical period for heating some special alloy steels, because the steel has low heat conduction performance and low plasticity, and if the heating rate is too fast, heating cracks or even fractures may occur. because:
(1) The excessively fast heating rate will increase the temperature difference between the inside and the outside of the alloy steel tube billet , resulting in inconsistent metal volume expansion and large stress. Obviously, the larger the diameter of the tube blank, the worse the thermal conductivity; the faster the heating rate, the greater the temperature difference stress generated.
(2) Steel pipe blank tube before failure return processing procedures, the inner tube with a large residual stresses exist, especially in the presence of a large cast ingot when heat stress inside the cold ingot, so that the increased sensitivity to cracks.
(3) When the alloy steel is heated to the range of 300~500 °C, the phenomenon of “blue brittleness” will appear, which significantly reduces the plasticity and strength of the steel.
(4) When heated to Ac1, the steel will undergo a phase change, and the metal volume changes inconsistently to produce a tissue stress. The superposition of these stresses during the low temperature phase will likely destroy the continuity of the metal and cause heating cracks. Therefore, a lower heating rate should be used in the low temperature stage, which, although increasing the heating time, does not excessively increase metal oxidation and other heating defects due to low temperature.