High temperature resistant titanium alloy, a near-a type titanium rod alloy developed in the 1950s, whose thermal stability temperature can reach 450 degrees, the alloy not only has good thermal stability at high temperature, high creep performance and Excellent damping performance, and high tensile strength at high temperature. Compared with the temperature extrusion in the a or a + P phase region, the metal flow is more uniform than the temperature extrusion in the p phase region.
Extruded products have great difficulty in obtaining high surface quality. The effect of heat treatment on the microstructure and high temperature creep properties of titanium rods and titanium alloy rods. The mechanical properties at room temperature and the creep performance and microstructure characteristics of high temperature (425T) under different heat treatment systems were compared and analyzed, which provided a certain amount for the mass production of the alloy. Theoretical basis and heat treatment system reference.
There are the following three heat treatment processes for titanium rods and titanium alloy rods:
- 1. Solution treatment and aging: The purpose is to improve its strength, α titanium alloy and stable β titanium alloy can not be strengthened heat treatment, only annealing in production. The α + β titanium alloy and the metastable β titanium alloy containing a small amount of α phase can be further strengthened by solution treatment and aging.
- 2. Stress relief annealing: the purpose is to eliminate or reduce the residual stress generated during processing. Prevent chemical attack and reduce deformation in some corrosive environments.
- 3. Fully annealed: The purpose is to obtain good toughness, improve processing performance, facilitate reprocessing and improve the stability of size and structure.
The experiment selected TA11 titanium alloy ingots smelted in three vacuum consumable furnaces. The main chemical composition meets the requirements of special standards. The phase transition temperature is forging the ingot to 35mm after forging, and finally rolled into 21.5mm titanium in a 250 mill The microstructure of the rod and rod is an uneven P matrix with primary a phase distributed. φ250 rolling mill is an important equipment for the production of titanium and titanium alloy rods under 26mm in Baoji Lihang Titanium Industry Co., Ltd. The rolling mill is a five-stand horizontal rolling mill. The first, second, and third stands are three-roller profile rolling mills, which use a traditional oblique wedge side fixing method to fix the milk roll. The bakelite tile is a sliding bearing. This kind of mill roll gap adjustment is achieved by fixing the middle roll and adjusting the position of the upper and lower rolls. The fixing of the middle roller is controlled by the inclined wedge that controls the gap between the middle roller journal and the bakelite tile. The smaller the gap is, the better the middle roll is fixed, and the smaller the jitter caused by the rolling force of the lower rolling line is. However, this bearing system has the following structural defects during the rolling of titanium and titanium alloy rods:
- (1) In the rolling process, in order to prevent the bakelite tile structure from heating and wearing, it is necessary to pour cooling water to cool and lubricate the bakelite tile. The cold water often splashes on the surface of the roll, causing the surface temperature of the blank to drop quickly, especially milk When making titanium and titanium alloys, due to the poor thermal conductivity of titanium and titanium alloys, the temperature difference between the inside and outside of the billet will be greater, which is not conducive to the uniform deformation of the billet, and the rolling accuracy cannot be guaranteed;
- (2) The frictional resistance of the side fixing method of the inclined wedge is large, and the power consumption during rolling is also large. Even if the motor is 630kW, the phenomenon of boring will often occur, which affects the production.
- (3) When the middle and lower rolls are feeding, the milking force continuously impacts on the middle roll, so that the anti-loosening device of the inclined wedge quickly fails, and the fixed state of the middle roll is destroyed;
- (4) The adjusted hole pattern changes as the fixed and stable state of the middle roller is destroyed, which affects the stability of the size of the titanium rod and ultimately affects the quality of the finished product. In order to meet the conditions for stable production of titanium rods, the bearing structure of the less φ250 rolling mill was modified. The dimensions of titanium and titanium alloy rods are stable, the quality of the outer surface is improved, and the yield is improved. After double heat treatment, the microstructure of the titanium alloy rod is a typical dual-state structure. With the increase of the solution temperature and the cooling rate, the grains grow up and the grain size of the structure is improved. With the increase of solution temperature, the faster the cooling rate, the better the high temperature creep performance, the higher the room temperature strength, but the plasticity is reduced.