RESIDUAL-STRESSES IN SPRING STEEL ROUND RODS SUBJECTED TO 2 SEPARATE MANUFACTURING PROCESSES

The residual stresses remaining after each individual production phase in two separate manufacturing processes involving production of round rods from Cr-V spring steel JUS C.4830 (BS 735 A 50, AISI 6150) are discussed. The first manufacturing process comprises annealing, straightening, grinding stage 1, and grinding stage 2, and the second consists of annealing, straightening, grinding stage 1, and roll milling. The aim of the investigation was the assessment of both manufacturing processes with regard to the residual stress distribution produced. The measurements were carried out via electrochemical removal and on line measurement of strain using strain gauges. The specimens for the measurements were randomly selected from the normal production process. This caused considerable spread, and an improved representation of the results obtained was achieved via a statistical treatment. A characteristic feature of both production processes is the occurrence of compressive residual stresses in the surface and in the subsurface layers to a depth of 0.5 mm. Roll milling, in the second manufacturing process, is carried out between two roll mills with displaced axes and the residual stress standard deviation is increased because of the spiral movement of the spring steel rod between the two roll mills, and the random specimen location along the round rod. The first production process proved to be more desirable because it provides smaller scatter of residual stress values along the rods.