Surface Integrity of AISI 4150 (50CrMo4) Steel Turned with Different Types of Cooling-lubrication

Nowadays the use of new high strength alloys is growing, but these alloys are difficult to machine due to the high temperatures generated during cutting. 

A solution is the use of cutting fluids, but those have adverse environmental effects, health risks and high costs of purchase, storage and maintenance. An emerging alternative is the use of cryogenic fluids such as liquid nitrogen (LN2). Nevertheless, in order to accept a new machining process industrially, it must be assured that final structural integrity of the machined part is at least as good as that generated by conventional machining processes. Therefore, in this work it has been compared the surface integrity (roughness, hardness, residual stresses and microstructure) generated in AISI 4150 (50CrMo4) steel by dry turning, turning with lubricant (oil based emulsion) and cryogenic turning with LN2. The results prove that cryogenic machining is the best solution since it reduces machining problems of heating, leading to tool life improvement and better surface integrity of turned components.