Improvement of the transition temperature in DWT test using modified material variant P460mod (green) in comparison with conventional P460 material (red). Click on image for larger view.
The use of hydraulic cylinders made of cold drawn, seamless steel tubing is critical at temperatures below 10°C, because multiple component failure cannot be ruled out completely at this temperature or lower. Systematic investigation of ready-to-install cylinder tubes, including impact tests and drop weight tear-tests (DWTT) verified these findings.
Because impact testing does not accurately reflect true component behavior, both tests were supplemented by component burst tests to simulate realistic operating conditions. The results of the DWTT and component tests match sufficiently with regard to the lowest tolerable operating temperature and correlate with impact tests. Therefore, a minimum impact energy value can be defined for the suitability of a material for use at low temperatures.
To prevent component brittle fracture, the corresponding standard required for materials currently used to manufacture cylinders — namely, E355 and P460 — has accelerated the development of modified material variants with the lowest impact energy value. Components made of the modified steel grades exhibit a sufficiently high proportion of ductile fracture behavior at temperatures as low as -20°C. Therefore, they possess enough plastic deformation reserves to reduce the danger of multiple component failure.
The graph above demonstrates this situation using the example of the P460 and P460 modified steel grades. (These are similar to ASTM A333 Grade 10, but with 0.20% maximum V, 0.40 to 0.70 % Ni, and 1.15 to 1.70 % Mn instead of the values stated for ASTM 333 Grade 10.) The modified material allows safe operation of hydraulic cylinders at temperatures as low as –20°C.
