Unveiling the Anti-Corrosion Logic Behind the GR7 Alloy with 0.2% Additive

Unveiling the Anti-Corrosion Logic Behind the GR7 Alloy with 0.2% Additive

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Those who deal with corrosion-resistant materials for chemical equipment, please pause for a moment. Today, let's talk about GR7. We will thoroughly explain the American standard GR7 UNSR52400 from the perspective of metallographic conditions. We will only discuss the core parameters in the standard. Let's first look at the composition logic. It is based on GR2 and adds 0.12% to 0.25% of the target, which not only enhances the ability to resist substance reduction, but the core purpose is to reduce the hydrogen overpotential and inhibit crevice corrosion and pitting corrosion. Here is a detail. Due to the addition of the target, the upper limit of iron impurity content in GR7 is relaxed to 0.3%, which is more conducive to the regulation of thermal processing plasticity than GR2's 0.2%. Now let's look at the mechanical properties. In the annealed state, the tensile strength is greater than or equal to 345 MPa, the yield strength is greater than or equal to 275 MPa, and the elongation is greater than or equal to 20%, but those who are knowledgeable know that the significance of the room temperature data is not significant. The key point is that at 300°C, its ultimate application force can still remain above 119 MPa, and at this temperature, it still retains about 85% of the room temperature strength, which is the core capital for it to be included in pressure vessel drawings and used as heat exchanger tube bundles. Let's talk about the cutting performance. The thermal conductivity of GR7 is only 16 W/(M.K), and the heat diffusion is extremely slow. Cutting cannot be completely dissipated, the linear speed must be suppressed to 30-50 meters per second per minute, and it must be combined with the special cooling liquid for high-pressure titanium alloy. Otherwise, there will be instantaneous slag flow and tool failure. Secondly, welding must strictly follow NB/T47015. The interlayer temperature must not exceed 150°C, and the purity of the backside protection argon gas must reach 99.99%, even 99.9% is not acceptable. A brief understanding of light weight embrittlement. After welding, it is recommended to heat to 400°C for 1 hour, maintain at 1 hour for stress relief annealing to restore plasticity. Finally, correct a selection misunderstanding. GR7 belongs to the near-pure titanium α-type alloy. It cannot be strengthened through solid solution aging, cold work hardening is its only strengthening path. Don't expect to replace it with TC4 for load-bearing. Its main battlefield is very clear, reducing medium environments such as acetic acid and formic acid environments for heat exchanger tubes and heads.