How can optimisation of steel for piston rods improve the economics of hydraulic cylinders?

11 June, 2019

Fusion and friction welding

The weldability of steel used for piston rods is an important characteristic. In fusion welding, the primary metallurgical consideration is that the formation of hard, brittle constituents in the weld heat affected zone (HAZ) should as far as possible be avoided. Cromax 180X rods up to 60mm in diameter can be fusion welded without preheating; for larger diameters, preheating is recommended in order to counteract fast cooling after welding and so lessen the risk that brittle constituents are formed in the HAZ.

Welded piston rods subjected to heavy loads, especially reversed compression-tension loads, are best manufactured via friction welding. Correctly executed, such a weld has equivalent strength and fatigue resistance to the base steel in the rod. Cromax 180X is designed to mitigate the risk for HAZ-embrittlement in connection with friction welding.

Suitability for induction-hardening and cold-drawing

Cromax 180X in an induction-hardened execution is available for applications where there is risk for damage to the piston rod as a result of external impact. For piston-rod applications requiring extremely high strength, Cromax 180X can also be offered in a cold-drawn execution having a minimum yield strength of 690 Mpa which is on-a-par with quenched-and-tempered low-alloy steel with considerably higher alloy content, grade 42CrMo4 for example.

Summary – a new steel grade for piston rods

A new steel grade, 180X, is now available for piston-rod applications in hydraulic cylinders. In hard-chrome-plated execution, Cromax 180X is characterised by higher strength than traditional grades used for hydraulic-cylinder piston rods. The improved yield strength means that rods can be downsized without compromise to the margin of safety against buckling under axial compressive loads and against fatigue if the loads are alternating. This offers positive benefits for both weight and cost.

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