Some metallurgical aspects of chips formed in high speed machining of high strength low alloy steel

doi:10.1016/j.scriptamat.2005.01.031

Scripta Materialia

Volume 52, Issue 10, May 2005, Pages 1001-1004

https://doi.org/10.1016/j.scriptamat.2005.01.031 Get rights and content

Abstract

Adiabatic shear bands and white layers induced during high speed cutting of 30CrNi₃MoV steel were investigated by scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The results show that some non-diffusional martensitic phase transformation and dynamic recrystallization might take place in the adiabatic shear bands and white layers within the chips.

Introduction

Adiabatic shear bands (ASBs) are frequently observed in various materials subjected to a high-strain-rate loading such as ballistic impact, explosive fragmentation, high-velocity forming operations and high speed machining etc. A lot of investigations have focused on phase transformations and other thermally induced processes including carbide dissolution and dynamic recrystallization [1], [2], [3], [4], [5], [6], [7], [8], [9]. In the high speed cutting processes of metals and alloys, serrated chips can form due to the occurrence of thermoplastic shear instability, which lead to the ASBs in the primary deformation zone and white layers in the secondary deformation zone [10], [11]. At present, however, there has been little work reported on phase transformation and microstructure of the ASBs and white layers in the serrated chips of high strength steels because of the difficulties of specimen preparation for metallurgical examination, especially for transmission electron microscopy (TEM) specimens. In this paper, non-diffusional martensitic phase transformation and dynamic recrystallization in the ASBs and white layers produced in high speed cutting of 30CrNi₃MoV high strength steel are investigated by scanning electron microscopy (SEM), X-ray diffraction and TEM. The formation of the serrated chip was analyzed.

Section snippets

Experimental

30CrNi₃MoV high strength low alloy steel with composition (in wt.%) of 0.30% C, 0.90% Cr, 3.15% Ni, 0.30% Mo, 0.20% V, 0.27% Si, 0.45% Mn, and balance Fe, was selected for the present study. Specimens were quenched from 890 °C and then tempered at 200 °C for 2 h. The following are the mechanical properties at room temperature: hardness 48 HRC, yield strength 1350 MPa, elongation 12%, reduction 53%, Charpy impact toughness 55 J. The experimental materials were machined into disc specimens of 95 mm in

Mechanism analysis of serrated chip formation

Usually, the plastic deformations in the metal cutting process are classified as primary and secondary deformation zones (PDZ and SDZ, respectively) (see Fig. 1). The majority of total deformation of the workpiece material in metal machining takes place in the PDZ. Most of the energy generated in the plastic deformation converts into heat, which can then cause the temperature rise in the PDZ. However, only a very small amount of heat transfer occurs between the workpieces and tools due to the

Conclusions

(1)
The shear deformation localization during the high speed cutting of 30CrNi₃MoV high strength steel leads to a serrated chip, in which the ASBs in the primary deformation zones and the white layers in the secondary deformation zones were formed.
(2)
SEM chemical composition and X-ray diffraction analyses indicate that a non-diffusional martensite phase transformation took place in the white layers.
(3)
TEM observations show that the dynamic recrystallization in the ASB and the white layers occurred by

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Some metallurgical aspects of chips formed in high speed machining of high strength low alloy steel

Abstract

Introduction

Section snippets

Experimental

Mechanism analysis of serrated chip formation

Conclusions

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