Blog

Do you know the production process of hot and cold rolled titanium plate?

There are two production methods of titanium plate, and titanium strip is adopted.

1.Band method.

Band method is the slab through hot rolling into a roll, in the subsequent cold rolling, heat treatment and other processes are rolled into a roll, rolling to the finished product thickness and state, with the cross shear machine cut into the plate.

2.Block method.

After hot rolling, the slabs is cut into pieces, then in the subsequent cold rolling, heat treatment and other processes are in the way of block production.

The strip 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, in the conditions and the rolling mill with strip hot mill cooperative production, the use of this process.

In the absence of the above conditions, in order to meet the needs of strip production, usually, we deal it in a single hot mill rolling into thin hot strip. Welded into tape coil, and then in the cold rolling and subsequent processes according to the tape production method.

Heating and hot rolling the slab is heated and rolled on a hot rolling mill to produce hot rolling medium and thick plate products or cold rolling billets.

Due to the metal titanium is easy to absorb hydrogen and oxidization in the hot state, which is aggravated with the increase of temperature and the extension of time, the heating temperature of titanium and its alloy slab is generally controlled between 850 ℃ and 1150℃, and the heating time depends on the heating mode and blank size.

When the flame furnace is used for heating, the atmosphere in the furnace must be strictly controlled to be micro-oxidation atmosphere.Titanium has good plasticity and small deformation resistance under hot condition, while cold processing is more difficult.

Therefore, the total processing rate of hot rolling should be increased as much as possible to reduce the amount of cold processing.When the strip method is adopted for production, thick slab is first rolled through a number of passes on the rolling machine, and then rolled in a hot continuous rolling machine or a rolling mill with an in-furnace coiler to a thickness of 2 ~ 3mm, or rolled from the blank to a thickness of 6 ~ 8mm on a hot rolling machine, and then rolled into a coil or welded into a coil in its tail.When the block method is used, the mill is usually rolled on a single hot mill. sometimes two or three times of heating is required.

Hot rolled, Surface treatment, Heating again, Hot rolling cycle to roll to the required thickness.

The surface treatment is to remove the oxidizing inspiratory layer formed on the surface of titanium plate billet in the process of heating, hot rolling and annealing.

The main treatment process is alkaline pickling or sandblasting (shot) pickling after two.Alkaline pickling is a process in which the products are first soaked in a molten alkali solution (NaOH) tank containing the oxidant (NaNO3), and then immediately quenched by water after alkaline pickling, and then pickling in a nitric acid solution containing fluoride ions, and then washing and drying.Sand blasting (shot) pickling method is the use of compressed air to sand (iron shot) high speed impact on the working surface to remove the oxide layer, and then pickling, drying.

The treatment of waste lye and alkaline waste gas in alkaline washing is complicated and the production cost is high.

Cold rolled pure titanium is usually rolled at room temperature or slightly above room temperature. Some titanium alloys are heated to 100 ~ 200℃ and rolled.Titanium and titanium alloy cold work hardening speed is fast, the total processing rate between two annealing pure titanium is not more than 50%, titanium alloy is not more than 30% ~ 40%, the need for many times of intermediate annealing, many times of cold rolling, to produce thin products.

Annealing includes intermediate annealing and finished annealing.Intermediate annealing is carried out in a non-vacuum annealing furnace. After annealing, pickling is required to remove the surface oxide layer.The annealing of finished products is usually carried out in the vacuum furnace. After annealing, the surface is bright and clean.

In order to improve the surface quality of strip after annealing, the strip should be degreased before annealing.

Finishing and inspection according to the delivery conditions of various products, the finishing process includes rolling, straightening and finished product cutting.

Inspection items include sampling inspection, appearance quality inspection and dimensional tolerance inspection.

Usually, when we use titanium, we can find that crack occurs sometimes.

The welding characteristics of titanium products and titanium equipment are easily oxidized, nitrided and embrittled.

We can fine 4 reasons for the crack of titanium.

1. At 400 ° C, a large amount of hydrogen is absorbed. Hydrogen is one of the most harmful elements of titanium, which can reduce the plasticity and toughness of titanium, leading to brittle fracture. When cooling down, hydrogen does not come out to produce pores, therefore, titanium is generally required the content of the material is less than 0.01% to 0.15%. If the base material contains a large amount of hydrogen, it should be dehydrogenated in advance.
2. Titanium will be abruptly combined with oxygen and nitrogen at 600 °C to form TiO2 and TiN (very hard), which will reduce the plasticity and toughness of the welded joint and cause porosity and crack defects. 
3. When heated to above 800 ° C, TiO 2 is dissolved in titanium and diffused deep into the internal structure of the metal titanium to form an intermediate brittle layer of 0.01 to 0.08 mm thick. The higher the temperature, the longer the time, the more severe the oxidation and nitridation, and the plasticity of the welded joint drops sharply. It is required that the oxygen content in titanium is less than 0.1% to 0.15%, and titanium is also extremely easy to form brittle carbides with carbon, which reduces plasticity and weldability.
4. High melting point, 1608 ~ 1725 ° C, large heat capacity, poor thermal conductivity, welded joints are easy to overheat, coarse grains, especially β titanium alloy, the plastic joint of the welded joint is the most obvious decline, if the workpiece is structurally rigid, the role of welding stress It can also cause cracks.
5. Titanium may have cold cracks under the action of hydrogen and residual stress, and the hydrogen content in the welded joint must be strictly controlled. Once titanium is contaminated with iron ions, it becomes brittle, which is one of the important reasons for causing cracks in the titanium material of titanium equipment such as titanium reactors.