Production Process of Titanium Plate/Sheet

The production process of titanium plate strip involves hot rolling followed by cold rolling. There are two methods for producing plates: strip method and block method.

Strip Method:

In this method, the plate billets are hot-rolled into coils, which are then processed further in subsequent cold rolling and heat treatment processes while remaining in coil form. When the desired thickness and condition are achieved, the coils are cut into plates using a cross-cutting machine.

Block Method:

This method involves cutting the hot-rolled billets into blocks, which are then processed further in subsequent cold rolling and heat treatment processes while remaining in block form.

The strip method offers higher production efficiency and yield compared to the block method. However, it requires large equipment, high investment, and complex production technology. This method is typically adopted only in collaboration with steel rolling plants equipped with strip hot rolling machines.

When the above conditions are not available, to meet the requirements for strip production, thin hot-rolled plates are typically produced on single-stand hot rolling mills. These plates are welded into coils, and then the production follows the strip method in cold rolling and subsequent processes.

Heating and Hot Rolling:

The plate billets are heated and rolled on hot rolling mills to produce hot-rolled thick plates or cold-rolled billets. Due to the tendency of titanium and its alloys to absorb hydrogen and oxidize in the hot state, the heating temperature of titanium plate billets is generally controlled between 850 to 1150°C. The heating time depends on the heating method and the size of the billets. When using flame furnaces for heating, it is essential to strictly control the furnace atmosphere to be a slightly oxidizing atmosphere. Titanium exhibits good plasticity and low deformation resistance in the hot state, making cold working relatively difficult. Therefore, it is preferable to increase the total processing rate of hot rolling to minimize the amount of cold working. In the strip method, the thick plate billets are initially rolled on a roughing mill, then rolled into coils on a continuous hot rolling mill or on a rolling mill equipped with a coil take-up unit when the thickness reaches 2 to 3mm. Alternatively, the billets are continuously rolled on a single hot rolling mill until reaching a thickness of 6 to 8mm, and then either taken up as coils or welded into coils at the end of the mill.

In the block method, hot rolling is typically performed on a single-stand hot rolling mill, sometimes requiring multiple heating, hot rolling, surface treatment, reheating, and hot rolling cycles to achieve the required thickness.

Surface Treatment:

To remove the oxide layer formed on the surface of titanium plate (strip) billets during heating, hot rolling, and annealing processes, surface treatment is required. The main treatment processes include alkali washing followed by acid washing or shot blasting followed by acid washing. The alkali washing and acid washing method involves soaking the products in a molten alkaline solution (NaOH) containing an oxidizer (NaNO3), followed by immediate water quenching after alkali washing. Subsequently, the products are acid washed in a nitric acid solution containing fluoride ions, followed by water rinsing and drying. The shot blasting and acid washing method involves high-speed impact of sand (or iron shots) on the working surface using compressed air to remove the oxide layer, followed by acid washing and drying. Alkali washing generates complex waste alkali solution and alkaline waste gas, leading to higher production costs. Therefore, shot blasting and acid washing are more commonly used in design.

Cold Rolling:

Pure titanium is usually rolled at room temperature or slightly above, while some titanium alloys require heating to 100 to 200°C before rolling. Titanium and titanium alloys exhibit rapid work hardening during cold rolling. The total processing rate between two annealing treatments for pure titanium does not exceed 50%, while for titanium alloys, it does not exceed 30% to 40%. Multiple intermediate annealing and cold rolling processes are required to produce thin products.

Annealing:

This includes intermediate annealing and final annealing. Intermediate annealing is performed in a non-vacuum annealing furnace, followed by acid washing to remove the surface oxide layer. Final annealing is typically conducted in a vacuum furnace, resulting in a clean surface without the need for acid washing. Before annealing, the cold-rolled plate strip billets need to be degreased to remove surface oil stains, thereby improving the surface quality of the plate strip after annealing.

Finishing and Inspection:

Based on the delivery conditions of various products, finishing processes include rolling, straightening, and final cutting. Inspection items include sampling inspection, visual quality, and dimensional tolerance inspection.