1. Low Elastic Modulus and Springback
The elastic modulus of titanium is relatively low compared with its tensile properties. Therefore, a large rebound margin must be considered during pressing and roller operations. Precisely because of the lower elastic modulus, to achieve the same stability, the cross-section of titanium parts is slightly larger than that of the same steel parts.
2. Machining Practice
Titanium is easy to machine, but considering its tendency to stick (larger than stainless steel) and low thermal conductivity, the commonly used machining technology and the design of threads and supporting surfaces must be appropriately improved. At least it must have a rigid machine tool, sharp tools, slow speeds, large cutting volumes, and room for chip removal. It is also recommended to use a large amount of cooling lubricant.
3. Thermal Expansion
The thermal expansion coefficient of titanium is 75 percent of carbon steel. Special attention should be paid to this when combining these two materials in equipment design and manufacturing.
4. High-Temperature Atmosphere Sensitivity
Since titanium is an active metal, it is easy to combine with oxygen in the air when heated to above 600 deg C. Therefore, it is generally not recommended to use titanium for a long time at temperatures higher than this. The mechanical strength of industrial pure titanium decreases rapidly when the temperature exceeds 150-200 deg C.
The diffusion rate of hydrogen in titanium is faster than that of oxygen. Therefore, before thermal processing, the heating furnace used should have a micro-oxidizing atmosphere. This produces a relatively thin oxide film, but avoids the depth of hydrogen contamination that could otherwise occur.
Frequently Asked Questions
Why must springback be considered when forming titanium? Titanium's low elastic modulus compared with its tensile properties creates large springback after pressing and rolling.
Why is titanium machining different from steel? Titanium tends to stick to tools and has low thermal conductivity, requiring rigid machines, sharp tools, slow speeds, and generous coolant.
Why avoid long-term titanium service above 600 deg C? Titanium combines readily with oxygen above about 600 deg C, degrading the material.
Why is the thermal expansion coefficient important when joining titanium to steel? Titanium's thermal expansion coefficient is about 75 percent of carbon steel, so combined designs must allow for differential expansion to avoid distortion, stress, and premature failure.
Why is a micro-oxidizing atmosphere recommended before thermal processing? Hydrogen diffuses in titanium faster than oxygen; a micro-oxidizing atmosphere forms a relatively thin oxide film while limiting the depth of hydrogen contamination.
