Influence of batch-to-batch material variations on grindability of a medium‑carbon steel

Philipp Hoier,Bahman Azarhoushang,Per Lundin,Amir Malakizadi,Jeffrey Badger,Albin Stormvinter,Thomas Björk,Uta Klement,Fukuo Hashimoto,Peter Krajnik

doi:10.1016/j.jmapro.2021.11.012

Abstract

This study addresses the influence of material variations on the grindability of crankshaft steel. Most previous studies on the effect of material microstructure on grindability involve comparisons of significantly different steel grades. This study, in contrast, is focused on batch-to-batch grindability variations for one steel grade, a scenario frequently occurring in industry where batches from different steel makers are fed into a production line. For this purpose, a batch made of recycled steel and a batch made of ore-based steel were compared with regards to microstructure and grindability under identical grinding and dressing conditions. Although both batches met the same material specifications, microstructural variations were identified in terms of grain size and micro-constituents (inclusions, carbonitrides). While specific grinding energy, residual stress and full-width at half-maximum profiles of ground surfaces were the same for both batches, the recycled batch showed different and unfavorable variation in wheel wear and Barkhausen noise (BN) response. Larger fractions of oxide inclusions and larger grain sizes (affected by carbonitrides) were present in the recycled batch, which were the likely reasons for the differences in wheel wear and BN response, respectively. These findings may aid grindability improvement by steel-grade adjustments, e.g. modification of the distribution and type of inclusions and/or amount of elements forming carbonitrides. Furthermore, the results highlight the importance of understanding and controlling material microstructure, as existing in-line quality by BN control may not always be able to correctly indicate surface integrity, which could lead to misinterpretations (e.g. false part-rejection on the assumption of grinding burn).

Highlights

IntroductionThe manufacture of automotive crankshafts includes a number of material-conversion processes (e.g. forging, soft machining, heat treat ment) followed by grinding and superfinishing
The manufacture of automotive crankshafts includes a number of material-conversion processes followed by grinding and superfinishing
Both batches exhibited an initial decrease in specific energy with increasing material removed, likely due to typical grit self-sharpening seen with cBN wheels after dressing

Summary

Introduction

The manufacture of automotive crankshafts includes a number of material-conversion processes (e.g. forging, soft machining, heat treat ment) followed by grinding and superfinishing. The end-users noted differences with respect to permis sible material removal rates and quality-inspection results as indicated by Barkhausen noise non-destructive testing Such variations pose se vere problems in the industry, which wants to avoid adjusting grinding and dressing parameters every time a particular steel batch – obtained from different suppliers – is fed into the production line. These steel grades were chosen to test materials at opposite extremes with respect to metallurgical characteristics such as work hardening and phase transformations In this way it was possible to identify material effects on grindability assessed via grinding forces, specific grinding energy, chip formation and surface integrity. Sridharan et al [7] applied varying heat treatments to a bearing steel grade for the purpose of creating different microstructures (bainitic vs bainitic-martensitic) and assessed the resulting grindability in terms of specific grinding energy, wheel wear (G-ratio), and part distortion. The mate rial differences are correlated with the respective aspects of grindability

Experimental

Results and discussion

Conclusions