Content Introduction
Titanium, widely used in the manufacturing of rockets, missiles, and space hulls, is known as the "versatile metal" and "space metal". The production cost of titanium material is high, and the control of plate shape is difficult. In combination with the cooperation between Benxi Steel Stainless Steel and a domestic company, Benxi Steel's 20 roll Sengimir rolling mill was used for the trial production of industrial pure titanium TA1. Through the study of the characteristics of this variety, key rolling process control parameters were determined, and a production trial plan was formulated. Finally, the trial production of raw material specification 1.3 mm x 1230 mm and finished product specification 0.5 mm x 1230 mm was successfully completed, and the technical indicators of thickness accuracy, plate shape, and surface quality of the product fully meet the technical requirements, which was recognized by the user.
Titanium, with its light weight, good high and low temperature strength, corrosion resistance, excellent properties such as superconductivity, hydrogen storage, and memory, is widely used in aerospace, military industry, marine development, petrochemicals, power generation, superconductivity, and other fields. It is known as an "all-around metal", "ocean metal", "third metal", and "modern metal". Although China is a major producer of titanium materials, currently its cold rolling is generally carried out using a four or six roll mill. Due to its limited rolling capacity, multiple intermediate annealing processes are usually required to achieve the target thickness under high total reduction rates. When producing thin products with a thickness of 0.5 mm or less, the production cost is higher and the difficulty of controlling the shape is greater.
In order to further expand the variety structure and enhance market competitiveness, Bensteel Stainless Steel Cold Rolling Dandong Co., Ltd. utilized its equipment advantages of the 20 roll Senzimir rolling mill to conduct trial rolling on industrial pure titanium TA1, in order to significantly reduce the production cost of TA1 cold rolling, improve the quality and accuracy of plate shape and thickness. The raw material thickness for this trial rolling is 1.3 mm, and the target thickness is 0.5 mm. Based on previous production experience and research on the characteristics of TA1, a trial rolling plan was developed. The thickness accuracy, plate shape, and surface quality of the finished product after rolling are good, meeting the requirements of users.
1. Production process flow and equipment parameters
1.1 Raw material specifications and rolling target thickness
The raw material specifications and rolling target thickness are shown in Table 1.
Table 1 Raw Material Specifications and Rolling Target Thickness

　　1.2 Roller system ratio
To ensure normal rolling and avoid abnormal phenomena such as slipping during the rolling process, the roller system ratio and roller requirements are shown in Table 2.
Table 2 Roller System Proportions and Requirements

　　Before putting the work roll on the machine, inspect the surface of the work roll to ensure its quality; During the rolling process, if surface quality defects are caused by the working roll, the working roll should be replaced in a timely manner.
1.3 Development of Rolling Regulations
The 20 high Senzimir rolling mill of Benxi Iron and Steel adopts functions such as middle roll shifting, ADEH side roll eccentricity adjustment, and BC roll flatness adjustment. This rolling mill has more advantages in flatness control and thickness control* The adjustment of the intermediate roll and the "AS-U" roll is connected to the shape roll to form a closed-loop control. There are two thickness gauges on the inlet and outlet sides of the rolling mill for thickness measurement, which are interlocked with the pressure control and tension control to implement automatic thickness control; ADEH side roller eccentricity adjustment; BC roller flatness adjustment; Thus, thin strips with high thickness accuracy and flatness can be rolled.
Industrial pure titanium TA1 has the following cold working properties: (1) low thermal conductivity; (2) During the cold deformation process, there is no obvious yield point, and the yield strength and tensile strength are close, with a relatively high yield strength, which leads to a tendency to produce cracks during the cold deformation process; (3) It has a very high cold work hardening effect (Figure 1). When the deformation exceeds 30%, the rate of strength increase slows down and plasticity hardly decreases; (4) Due to its small elastic modulus, which is about 54% of iron, it has a large rebound during forming and processing, making cold forming difficult.

Figure 1 Work hardening curve of pure titanium
In order to achieve good flatness and thickness accuracy, strict control of process parameters such as tension, rolling force, pass reduction, and rolling speed of the strip steel is carried out during the rolling process. Given the characteristics of TA1 and ensuring rolling stability, the specified reduction rate for each pass is generally around 20%. Subsequently, the reduction amount for each pass gradually decreases, and the reduction amount for each pass is generally around 10%. It is beneficial to maintain consistent pressure of the strip steel on the rolling rolls within each pass, thereby ensuring the shape of the final product.
Based on the experience of rolling stainless steel in the early stage and the study of TA1 characteristics, a rolling schedule has been developed, as shown in Table 3.
Table 3 TA1 Rolling Regulations

　　Due to the poor thermal conductivity of pure titanium, it is required to have good lubrication and cooling effects during the rolling process. At the same time, the rolling speed should not be too fast to prevent roller sticking caused by high temperature of pure titanium, resulting in rough surface and poor surface quality of the titanium material.
1.4 Other precautions
(1) Calibrate the thickness gauge before rolling.
(2) Clean the roller conveyor before rolling and inspect the equipment to ensure stable operation.
(3) After each pass, inspect the quality of the strip steel table and replace the working rollers in a timely manner if defects are found.
(4) During the rolling process, the thickness is measured after passes 1, 2, 5, and 6. If there is a significant deviation between the measured thickness and the thickness displayed on the thickness gauge, the rolling target setting value should be adjusted in a timely manner.
(5) When rolling to the last pass, pad the paper.
2. Product defects and quality inspection
2.1 Calibration of thickness gauge
To ensure thickness accuracy and the accuracy of pressure reduction and automatic thickness control during the rolling process, TA1 samples were used to calibrate the thickness gauge before rolling. The calibration results are shown in Table 4.
Table 4 Calibration Results of Entrance and Exit Thickness Gauge mm

　　After being measured by a thickness gauge, the thickness of the sample is basically consistent with the actual sample thickness, with an error of within 0.01 mm, meeting the rolling requirements.
2.2 Rolling situation
Before rolling, inspect the surface quality of the rough rolling work rolls that are ready to be put on the machine. After the 5th pass, replace the finishing rolls and check the surface quality of the rolls. During the rolling process, the forward slip value is between 0.8% and 3.7%, and the deviation value is between? 3-7 mm, the standard deviation (STD) value does not exceed 4.5I (I=10-5, which is the relative length difference). Based on the actual data feedback of the main parameters mentioned above, the rolling effect is good and the plate shape is good. The variation of rolling force for each pass is shown in Figure 2. From Figure 2, it can be seen that the variation of rolling force in each pass gradually decreases uniformly, and the setting of rolling schedule is relatively reasonable.

Figure 2 Rolling force variation curves for each pass
2.3 Thickness inspection situation
Measure the thickness of passes 1, 2, 5, and 6 during the rolling process and compare the thickness displayed on the thickness gauge, as shown in Table 5.
Table 5 Comparison of Thickness

　　From the above table, it can be seen that the actual thickness after rolling is consistent with the specified specifications and the thickness displayed on the thickness gauge, and the final actual target thickness is within ± 0.01 mm of the set value, meeting the tolerance requirements.
2.4 Surface quality
*After the completion of the first pass rolling, the surface was inspected and no defects were found in the rolling mill roll marks. The surface of the strip was inspected during thickness measurement or before speed increase in the middle pass, and no defects were found on the final surface during the first pass rolling, meeting customer requirements.
3. Conclusion
(1) The TA1 industrial pure titanium rolled by Benxi Steel's 20 roll Senzimir mill has good thickness accuracy, plate shape, and surface quality after rolling, and all indicators have reached the expected goals, meeting customer needs.
(2) The use of a twenty high Sengimir rolling mill to roll industrial pure titanium TA1 can avoid intermediate annealing and greatly reduce rolling production costs, while also significantly improving production efficiency and product quality.
(3) The successful trial rolling of industrial pure titanium TA1 has laid a solid foundation for expanding the variety structure of this steel, enhancing market competitiveness, and achieving the combination of steel and titanium.