Hardness Matching and Joint Smoothness Control of Rail Welded Joints
Why must weld joint hardness match the base metal?
Wheels roll uniformly when hardness is similar. Excessively hard joints form "hard spots" and protrude; soft joints wear quickly and dent. Both cause impact, vibration, noise, and accelerated damage.
What defects result from mismatched weld joint hardness?
The main defect is a step at the joint, causing strong impact. Long-term impact induces fatigue cracks, nucleus flaw,and spalling. Impact also loosens fasteners, damages sleepers, and increases maintenance costs.
Which processes determine weld joint hardness?
Normalization after welding is critical. Temperature, time, and cooling rate control microstructure and hardness. Welding current, time, and upset also affect structure. Poor control causes uneven pearlite, coarse grains, or over-hardening.
How to quickly judge joint hardness on-site?
Use a portable Leeb hardness tester at multiple points. Hardness deviation should be within ±20HB of base metal. Obvious steps, patterns, or crushing indicate poor hardness matching.
How to optimize hardness uniformity?
Optimize welding for uniform heating. Use precise normalization and uniform cooling. Smooth hardness gradient ensures consistent wear and long-term joint smoothness.