The titanium plate and strip are produced by hot rolling and then cold rolling. There are two production methods for the sheet, the belt type and the block type.
(1) Belt method
The slab is hot-rolled into coils, and then rolled into coils in subsequent cold-rolling, heat treatment and other processes.
(2) block method
It is cut into pieces after hot rolling, and is produced in pieces in the subsequent cold rolling, heat treatment and other processes.
The belt method has higher productivity and yield than the block method, but the equipment is huge, the investment is high, and the production technology is complex. This process is only used when there is a condition for collaborative production with a rolling mill with a hot strip mill.
When the above conditions are not met, in order to meet the needs of producing strips, thin hot-rolled strips are usually rolled on a single-stand hot-rolling mill. Welded into coils and then produced by the strip method in cold rolling and subsequent operations.
Heating and hot rolling Slabs are heated and rolled on hot rolling mills to produce hot rolled medium and heavy plate finished products or cold rolled billets. Since metal titanium is easy to absorb hydrogen and oxidize in hot state, and it aggravates with the increase of temperature and time,
Therefore, the heating temperature of titanium and its alloy slabs is generally controlled between 850 and 1150 ° C, and the heating time depends on the heating method and the size of the blank. When a flame furnace is used for heating, the atmosphere in the furnace must be strictly controlled to be a slightly oxidizing atmosphere. Titanium has good plasticity and low deformation resistance in hot state, while cold working is more difficult.
Therefore, the total working rate of hot rolling should be increased as much as possible to reduce the amount of cold working. When the belt method is used for production, it is first rolled into a thick slab on a billet mill for several passes, and then rolled to a thickness of 2 to 3 mm in a hot tandem mill or a rolling mill with an in-furnace coiler. Coils are also rolled from the billet to a thickness of 6-8mm on a hot rolling mill, and then coiled or welded into coils at the tail.
When the block method is used, it is generally rolled on a single-stand hot rolling mill, and sometimes two or three heating, hot rolling, surface treatment, reheating, and hot rolling cycles are required to roll to the required thickness.
surface treatment
In order to remove the oxide gettering layer formed on the surface of the titanium plate (strip) blank during the heating, hot rolling and annealing process, surface treatment is required. The main treatment processes are pickling after alkaline washing or pickling after sandblasting (pellet). The alkaline pickling method is to first soak the product in a molten lye (NaOH) tank containing an oxidant (NaNO3), quench it with water immediately after alkaline washing, and then pickle it in a nitric acid solution containing fluoride ions. Wash and dry.
The sand blasting (pellet) pickling method is to use compressed air to impact the sand (iron shot) on the working surface at high speed to remove the oxide layer, and then pickle and dry. During alkaline cleaning, the treatment of waste lye and alkali-containing waste gas is more complicated, and the production cost is also relatively high. Sandblasting (pellet) pickling method is mostly used in the design.
cold rolled
Pure titanium is usually rolled at room temperature or slightly higher than room temperature, and some titanium alloys need to be heated to 100-200 °C before rolling. Titanium and titanium alloys have a faster cold work hardening rate. The total processing rate between two annealing times is not more than 50% for pure titanium and 30% to 40% for titanium alloys. Multiple intermediate annealing and multiple cold rolling are required before production. Thin product.
annealing
Including intermediate annealing and finish annealing. The intermediate annealing is carried out in a non-vacuum annealing furnace, and pickling is required after annealing to remove the surface oxide layer; the finished annealing is generally carried out in a vacuum furnace, and the surface after annealing is smooth and can not be pickled. Before annealing, the cold-rolled strip should be degreased to remove oil stains on the surface, so as to improve the surface quality of the strip after annealing.
Finishing and Inspection Depending on the delivery conditions of the various products, finishing operations include rolling, straightening and cutting of the finished product. Inspection items include sampling inspection, appearance quality and dimensional tolerance inspection.
