Cutting Processes influence in hot formed DIN 22MnB5 NbMo modified alloy

Authors:
Preprint
Publisher website
Google Scholar
Abstract
This study aims to evaluate the microstructural changes of DIN 22MnB5 Niobium and Molybdenum modified alloy (22MnB5+NbMo) related to cutting processes after the press hardening step. Seven-millimeter press hardened thick sheets were Laser and Abrasive Water Jet (AWJ) cut to be adapted to their final application. The sheets were hot formed obtaining predominantly martensitic structures. The Laser cutting process was employed with 2,5 and 3,0 kW available power. In the AWJ cutting process, the employed cutting pressure was 60 kPsi. The microstructural changes related to the three cutting conditions post press hardening were investigated by optical microscopy analyzes (macro and micrograph). Scanning Electron Microscopy (SEM) and Electron Backscattered Diffraction (EBSD) were also employed. In this investigation, the relationship between the cutting processes and the microscopic aspects was also confirmed by microhardness tests. The results showed that the addition of Nb and Mo to the former alloy was important in the martensitic transformation and grain refinement. Water jet cutting did not show microstructural modifications related to the uncut material. On the other hand, Laser cutting showed some microstructural modifications for both employed conditions (2,5 and 3,0 Kw). These modifications are related much more to microhardness than to grains size and roughness. These differences can become even smaller when the cutting speed differences between the processes are taken in account (0,1 mm/min for Water Jet and 0,6 mm/min for Laser Cut). The presence of a double white zone suggests that the Laser cutting process is much time dependent than power dependent itself. These double white regions were observed only in the right exit region of the samples in the 2,5 KW condition.