Hydraulic cylinder rods fail for two reasons: surface wear destroying the seal interface, or fatigue cracking in the core under repeated extension and retraction cycles. The solution to both is EN40B in the Q+T condition, gas nitrided after final grinding.
The nitriding process produces a surface hardness of 700–850 HV (approximately 65–70 HRC equivalent) with compressive residual stresses that improve fatigue life — while the chromium-rich compound layer resists corrosion and mild chemical attack better than hard chrome. And critically, because nitriding is carried out at low temperature (480–530°C) with no quench, the finished rod does not distort — essential for long cylinder bores with tight tolerances.
