Titanium Sheet Plate

What steps does the titanium plate rolling process include (such as initial rolling, hot rolling, cold rolling, etc.)? What type of rolling mill is used? How to control the rolling temperature and reduction to ensure uniform microstructure and performance of the plate?

The rolling of titanium and titanium alloy plates is a complex process that integrates material science, mechanical control and process optimization. Its process flow can be divided into three core stages: initial rolling, hot rolling and cold rolling. Each stage corresponds to specific rolling mill equipment and process parameters.
(1) Initial rolling stage
The initial rolling usually uses a two-roll reversible rolling mill. Its main task is to break the columnar crystal structure of the titanium alloy ingot and achieve initial plastic deformation. In this stage, the ingot heating temperature must be strictly controlled (usually 30-50℃ above the β phase region), and casting defects must be eliminated through multiple passes of small deformation rolling (reduction per pass ≤15%). Changzhou Bokang Special Material Technology Co., Ltd. has significantly improved the microstructure uniformity of the initial rolling stage by optimizing the ingot homogenization process and combining numerical simulation to predict deformation resistance.
(2) Hot rolling stage
Hot rolling uses a four-roll irreversible rolling mill or a universal rolling mill to perform large deformation processing in the α+β two-phase region. In this stage, the grains are refined by dynamic recrystallization, and the final rolling temperature (usually not less than 850℃) must be controlled to ensure the plasticity of the material. A box-type heating furnace is used in conjunction with an induction heating compensation system to achieve a temperature accuracy of ±10℃. The distribution of hot rolling pass reduction follows the ""pyramid"" principle, that is, the first few passes use 20-25% reduction, and the subsequent passes gradually increase to 35-40%, combined with a rapid water cooling process between passes to effectively avoid excessive grain growth.
(3) Cold rolling stage
Cold rolling is carried out on a four-roll or six-roll cold rolling mill, mainly to improve the surface quality and dimensional accuracy of the plate. It is necessary to use multiple passes of small deformation rolling (single pass reduction ≤10%) combined with an intermediate annealing process, and the cumulative deformation can reach more than 80%. Changzhou Bokang has increased the plate shape control accuracy to ±5μm by introducing roller cross technology. The surface roughness of the medical-grade titanium plates it produces is Ra≤0.2μm, reaching the international leading level.
The selection of titanium rolling equipment directly affects the quality of the final plate and needs to be designed according to the material characteristics:
(1) Selection of rolling mill type
Primary rolling mill: A closed-end two-roll reversible rolling mill is used, equipped with a hydraulic AGC (automatic thickness control) system, and the roll diameter ratio is controlled between 1.8-2.2 to optimize the bite condition
Hot rolling mill: A four-roll irreversible rolling mill is used, with a working roll diameter of 350-400mm and a support roll diameter of 1400-1600mm, equipped with a bending roll system and a roll shifting device, and the plate shape control accuracy reaches ±15I
Cold rolling mill: A UC/VC combined roll system six-roll rolling mill is used, the axial shifting stroke of the intermediate roll is ±150mm, and a laser speed meter and thickness gauge are used to achieve closed-loop control
(2) Roll system material optimization
The working roll is made of high-chromium iron-based alloy (Cr12MoV), and the surface is sprayed with a CrN/Al2O3 composite coating with a hardness of more than HV1200, which effectively resists titanium adhesion. The support roller adopts infinite chilled cast iron centrifugal casting technology, and the roller surface hardness gradient difference is controlled within HS15 to ensure the stability of the roller shape.
Accurate control of temperature and deformation is the key to ensure the uniformity of the titanium plate structure and performance, and a multi-parameter coupling control model needs to be established.
(1) Temperature control system
Heating process: A three-stage heating system is adopted (preheating section 600-700℃/insulation section 850-950℃/heating section 900-980℃), and an infrared thermometer is used to achieve real-time temperature monitoring
Rolling process temperature control: In the finishing rolling stage, a roller spray system (water volume control accuracy ±0.5L/min) is used, and a resistance heating compensation system is used to control the temperature fluctuation of the rolled piece within ±20℃
Final rolling temperature management: The temperature field distribution is predicted through finite element simulation, and a temperature waiting time model between passes is established to ensure the temperature of the rolled piece. Ensure that the final rolling temperature is not less than 50℃ below the phase transformation point
(2) Algorithm for optimizing the reduction
Multi-pass reduction distribution: Based on the material work hardening model, a genetic algorithm is used to optimize the distribution of the reduction in each pass to ensure that the deformation of each pass is "parabolic"
Dynamic reduction adjustment: The rolling force is monitored in real time by a pressure gauge, and the fuzzy PID control algorithm is used to automatically adjust the reduction to compensate for the roll gap bounce (compensation accuracy ±0.02mm)
Limit deformation control: Establish a critical reduction criterion (ε_c=0.6σ_s/K), where K is the material processing Hardening coefficient, ensure that the single-pass reduction does not exceed 85% of the critical value
(3) Measures to ensure uniformity of structure
Grain size control: Control the dynamic recrystallization volume fraction through the Z parameter (Z=ε·exp(Q/RT)), and keep the Z value between 10-15 to obtain uniform equiaxed grains
Texture optimization: Use cross-rolling process (rotate the plate 45° per pass), combined with asynchronous rolling technology (the difference in line speed between the upper and lower rollers is 10-15%), to effectively weaken the base surface texture
Residual stress control: Through the tensile stress-compressive stress alternating rolling process, combined with Stress relaxation treatment during annealing controls residual stress within ±20MPa
The titanium plate rolling process requires the establishment of a full-process quality control network. Changzhou Bokang has passed ISO9001/ISO13485 system certification and built a three-level quality control system of "raw material inspection-process monitoring-finished product testing":
Online detection: equipped with plate shape meter, thickness gauge, surface detector, to achieve online control of thickness tolerance ±0.02mm and plate shape tolerance ±8I
Organization detection: EBSD technology is used to analyze grain orientation to ensure grain size ASTM Grade 8 has a fine ratio of ≥90%
Performance verification: The mechanical properties are verified by tensile test, impact test and corrosion test. The tensile strength of medical-grade titanium plate is ≥850MPa and the elongation is ≥18%, which meets the ASTM F136 standard
Non-destructive testing: Ultrasonic phased array technology is used to detect internal defects to ensure 100% flaw detection pass rate
Currently, titanium plate rolling technology is showing three major development trends:
Intelligent rolling: A virtual rolling model is established through digital twin technology to achieve online optimization of process parameters;
Near-net forming technology: Develop ultra-thin titanium plate continuous rolling technology to achieve continuous production of 0.016-inch ultra-thin plates;
Green manufacturing technology: Electroplastic rolling (EPR) technology is used to reduce the rolling temperature by 30-50°C and reduce energy consumption.