Q1: What is "decarburization" on the surface of a seamless pipe, and why is it detrimental for components like gears?
A: It is the loss of carbon from the steel surface layer during high-temperature processing (like heat treatment). This creates a soft surface layer, severely reducing wear resistance and fatigue strength, which are critical for gear performance.
Q2: During bending, a 20# steel pipe cracked. What material-related factors could contribute to this?
A: Possible causes include: excessively low temperature during cold bending, pre-existing micro-cracks or inclusions in the material, or a lower-than-specified elongation (ductility) of the batch of steel.
Q3: What does "over-pickling" or "over-etching" mean in pipe processing, and what are its consequences?
A: It occurs when the pipe is exposed to acid (for scale removal) for too long, at too high a temperature or concentration. It results in a rough, pitted surface and can cause hydrogen embrittlement. This damage is irreparable and harms mechanical properties-2-6.
Q4: Why might a seamless pipe made of grade 35CrMo require pre-heating before welding?
A: Pre-heating slows down the cooling rate of the weld and heat-affected zone (HAZ). This helps prevent the formation of hard, brittle martensite, which can lead to cold cracking, especially in alloy steels with higher hardenability.
Q5: In a corrosion failure analysis of a carbon steel pipe, what does "galvanic corrosion" imply?
A: It indicates that the steel pipe was electrically connected to a more "noble" metal (like copper or stainless steel) in a conductive environment. The carbon steel, being more "active," corrodes preferentially and at an accelerated rate.
