Production Of Gr12 Titanium Alloy Strip By Hot Continuous Rolling Mill

Gr12 titanium alloy  is a near-α corrosion-resistant alloy with excellent comprehensive properties and wide application scenarios. Hot continuous rolling is the key process for large-scale mass production of its strip. This Titanium alloy has a narrow rolling temperature range, poor thermal conductivity, high deformation resistance and high tendency to stick to rolls. It easily leads to problems such as inhomogeneous microstructure, surface defects and dimensional deviation during processing.

 

 

1. Composition and Microstructure

Gr12 titanium alloy takes titanium as the base, with molybdenum and nickel added and impurities strictly controlled; the matrix is mainly α-phase with a small amount of β-phase. Molybdenum refines grains and improves high-temperature strength, while nickel enhances corrosion resistance and hot workability, making it suitable for hot continuous rolling.

 

2. Main Difficulties in Hot Continuous Rolling

The narrow phase transition temperature range makes it difficult to control rolling temperature. Coupled with poor thermal conductivity, it is prone to abnormal grains, cracking and inhomogeneous microstructure and properties.

• It easily sticks to rolls at high temperatures, causing surface defects, and requires strict matching of rolling parameters.
• Large elastic springback leads to uneven thickness and edge waves in thin strips, and multi-pass rolling aggravates anisotropy.
• Easy oxidation at high temperatures; incomplete descaling impairs subsequent processing and corrosion resistance.

 

 

1. Experimental Raw Materials

Gr12 titanium alloy slabs prepared by VAR melting + forging were selected, and milled to remove oxide scale and surface defects to meet surface quality requirements.

 

2. Experimental Equipment

Tests were carried out on a 1450 mm hot continuous rolling production line, equipped with heating, descaling, rough and finish rolling, cooling, coiling and automatic gauge and shape control systems; high-chromium cast iron rolls meet the requirements of hardness and surface precision for rolling.

 

3. Experimental Scheme

• Optimize heating system: limit rolling start temperature and holding time to select optimal heating parameters.
• Formulate multi-pass rolling parameters: control reduction rate, rolling speed, finishing and coiling temperature of each pass, and explore the influence of process on microstructure and properties through orthogonal tests.
• Post-rolling annealing: set reasonable annealing temperature and holding time to eliminate internal stress, homogenize microstructure and improve plasticity.

 

4. Testing Methods

Metallographic observation, tensile testing, surface roughness measurement and ultrasonic testing were adopted to analyze microstructure, mechanical properties, surface quality and internal defects respectively.

 

 

1. Heating System

Unreasonable heating temperature and holding time cause cracking, oxidation, abnormal grains and performance degradation. The optimal system: heating at 900±20℃, holding for 2.0 min/mm, with uniform temperature, low oxidation and good microstructure, suitable for rolling.

 

2. Influence of Rolling Parameters

• Finishing temperature at 800–850℃ yields fine grains and balanced strength and plasticity; deviation deteriorates microstructure and properties and increases anisotropy.
• Rough rolling reduction rate of 18%–22% and finish rolling reduction rate of 12%–18% ensure sufficient recrystallization and reduce edge cracking and surface defects.
• Properly matched rolling speed: rough rolling at 2.5–3.5 m/s, finish rolling at 6–7 m/s, to avoid temperature drop scratches, coarse grains from heat accumulation and dimensional deviation.

 

3. Strip Shape and Surface Control

Optimize rolling control system and tension to improve thickness deviation and strip shape; combined with high-pressure water secondary descaling to completely remove oxide scale and enhance surface quality.

 

4. Annealing Process

The optimal annealing system is 700℃ holding for 45 min, which eliminates internal stress, homogenizes microstructure and improves plasticity; inappropriate temperature tends to cause residual stress, coarse grains and reduced toughness.

 

 

The complete hot continuous rolling process for Gr12 titanium strip is determined: slab finishing, standardized heating and holding, reasonable distribution of reduction rate and rolling speed, strict temperature control at each stage, and low-temperature annealing after rolling.

Industrial mass production achieves stable quality, qualified strip shape, dimensions, surface and mechanical properties, low anisotropy, no internal defects, and a comprehensive qualification rate over 98%. It meets chemical and marine working conditions, can replace imports, and reduce costs and improve efficiency.

 

 

Ruihang, as a direct factory of titanium products production, is specilized in R&D,production. The company is located in " China's Titanium Valley" , boosting the titanium industry in the world. If you have purchasing needs, feel free to contact us:Sam.Rui@bjrh-titanium.com.

 

References

[1] Zhang Xiyan, Zhao Yongqing, Bai Chenguang. Titanium Alloy Materials and Applications [M]. Beijing: Chemical Industry Press, 2005.
[2] Northwest Institute for Nonferrous Metal Research. Titanium Alloy Processing Technology Manual [M]. Xi'an: Northwestern Polytechnical University Press, 2012.
[3] Panzhihua Iron & Steel Co., Ltd. Method for Shape Control of Hot Rolled Titanium and Titanium Alloy Strip Coil [P]. China Patent: CN113976624B, 2023-11-21.
[4] GB/T 3621-2022, Titanium and Titanium Alloy Plates and Sheets [S]. Beijing: Standards Press of China, 2022.