At present, my country mainly adopts two-roll cold rolling and three-roll cold rolling to produce TA18 titanium alloy pipes. The main problems encountered in the production of TA18 titanium alloy thick-walled pipes used in the petroleum industry are as follows: ①The thick-walled pipes with a diameter-to-thickness ratio of less than 10 are rolled by a multi-roll mill. Defects such as joints; ②The cold straightening method cannot ensure that the straightness of the finished pipe reaches the requirement of 0.3~1mm/m. In response to the above problems, the feasibility of producing TA18 titanium alloy thick-walled pipes with two different cold rolling processes was compared, and the effect of annealing temperature on the structure and performance of the pipes, as well as the subsequent processing technology of the pipes, were studied, aiming to provide industrial production for the petroleum industry. Use high-quality TA18 titanium alloy thick-walled pipe to provide guidance.

 

 The TA18 titanium alloy used in the experiment is a Φ600mm×2400mm ingot obtained by using a 3t vacuum consumable electric arc furnace through two smelting. The ingot is forged into a billet by a 16MN fast forging machine, and then drilled and bored by a deep hole drilling and boring machine, and then covered with a copper sheet, and then extruded on a 3500t extruder into a Φ70mm×8mm tube billet. The tube billet adopts the following two kinds of cold rolling processes to roll Φ48mm×5mm finished tube.

 

Process 1: Φ70mm×8mm tube billet, two-roll cold rolling billet→Φ54mm×6mm, annealing, finishing→Φ54mm×6mm, three-roll cold rolling→Φ51mm×5.5mm, three-roll cold rolling→Φ48mm×5 ㎜Finished tube.

 

Process 2: Φ70mm×8mm tube billet, two-roll cold-rolled billet→Φ54mm×6mm, annealing, finishing→Φ54mm×6mm, two-roll cold rolling→Φ48mm×5mm finished tube.

 

The Φ48mm×5mm pipes produced by process 1 and 2 are subjected to vacuum annealing treatment at 600℃×1h, 650℃×1h, 700℃×1h and 750℃×1h respectively. After heat treatment, they are treated in RX-600 box-type resistance furnace. Heat to 500～600℃ for 30min, perform straightening, and use 150A14 feeler gauge to detect its straightness. Then, boring and mechanical polishing are used to eliminate the oxidation pollution layer on the inner and outer surfaces of the pipe, and finally the finished pipe is obtained. The results showed that:

 

(1) Compared with process 1, using process 2 can more easily obtain TA18 thick-walled pipes that meet the standard requirements, and the rolling process is relatively stable, which not only shortens the production cycle, improves production efficiency, and its comprehensive performance is also better than Process 1 pipe produced.　　

 

(2) Vacuum annealing at 700℃×1h, the room temperature mechanical properties of the pipe can be optimally matched, and the equiaxed grains are more fine and uniform.

 

(3) After hot straightening, the straightness of TA18 thick-walled pipe can reach about 0.75mm/m, and the inner surface roughness after boring is 0.864μm on average.

 

                                                                       

 

(Source: China United Steel Network)