High-temperature titanium alloy, developed in the 1950s a near a-type titanium bar alloy, its thermal stability temperature up to 450 degrees, the alloy is not only at high temperatures with good thermal stability, high creep properties and excellent damping properties, but also has a high high-temperature tensile strength. Extrusion in the a or a + P phase zone temperature and in the p phase zone temperature extrusion compared to the metal flow more uniform. The difficulty of obtaining high surface quality for extruded products is great. The effect of heat treatment on the organization and high-temperature creep properties of titanium rods and titanium alloy bars, a comparative analysis of the room temperature mechanical properties and high temperature (425T) creep properties and organizational characteristics of different heat treatment systems, to provide a certain theoretical basis for the mass production of this alloy and heat treatment system reference.
The heat treatment process of titanium rods and titanium alloy rods has the following three kinds: 1. solid solution treatment and aging: the purpose is to improve its strength, α titanium alloy and stable β titanium alloy can not be strengthened by heat treatment, in the production of only annealing. α + β titanium alloy and contains a small amount of α phase of the substable β titanium alloy can be further strengthened by solid solution treatment and aging of alloys. 2. stress relieving annealing: the purpose is to eliminate or reduce the Residual stresses generated during processing. Prevent chemical attack and reduce deformation in some corrosive environments.3. Complete annealing: the purpose is to obtain good toughness, improve machinability, facilitate reworking and improve the stability of size and organization.
Experimentally selected by three vacuum self-consumption furnace melting TA11 titanium alloy ingots, the main chemical composition in line with the requirements of the special standard, the phase transition temperature of the ingot by forging billet to 35mm, and ultimately in the 250 mill rolled into a 21.5mm titanium rods, rods microstructure of the inhomogeneous P matrix distribution of incipient a-phase. φ250 mill is the Baoji City, Lihang titanium industry limited liability company 26mm titanium and titanium alloy bar production is important. and titanium alloy bar production of important equipment. The mill is a five-stand transverse rolling mill, the first, second and third stands for the three-roll profile mill, the use of traditional oblique wedge side fixing method of fixing the breast rolls, gum wood tile for the sliding bearings. This type of mill roll gap adjustment is realized by fixing the middle roll and adjusting the position of the upper and lower rolls. The center roll is fixed by the control of the center roll journal and the gap between the wood tile sloping wedge control. The smaller the gap, the better the center roll is fixed, the lower rolling line by the influence of rolling force generated by the runout is also smaller. However, this bearing system in the titanium and titanium alloy bar rolling process has the following structural defects:
(1) in the rolling process, in order to prevent the heat wear of the glulam tile structure, the need to pour cooling water on the glulam tile cooling and lubrication, cold water is often splashed to the roll surface, making the billet surface temperature drop is very fast, especially when emulsifying titanium and titanium alloys, due to the titanium and titanium alloys with poor thermal conductivity, the billet inside and outside the temperature difference will be even greater, is not conducive to uniform deformation of the billet, the rolling accuracy can not be guaranteed;
(2) The frictional resistance of the slanting wedge side fixing method is large, and the power consumption during rolling is also large, even if a 630kW motor is used, the phenomenon of bogging down will often occur, which affects the production.
(3)When the middle and lower rolls are overfeeding, the emulsion force keeps impacting on the middle rolls, which makes the anti-loosening device of the slanting wedge fail quickly, and the stable state of the middle rolls fixing is destroyed;
(4) The adjusted hole pattern changes with the destruction of the fixed stable state of the center roll, which affects the stability of the size of titanium rods, and ultimately affects the quality of the finished product. In order to meet the conditions of stable production of titanium rods, the bearing structure of the less φ250 mill was modified, titanium and titanium alloy rods with stable dimensions, improved external surface quality and increased yield. Titanium alloy bar after double heat treatment, its microstructure is a typical bimodal organization, with the increase of the same solution temperature, the cooling rate of the accelerated growth of its grain, the organization of the grain size has been improved. With the increase of solid solution temperature, the faster the cooling speed, the better its high temperature creep performance, the higher the room temperature strength, but the plasticity is reduced.
