Phase Transformation in Fe Alloys Induced by Surface Treatment

Abstract

Difference of the phase transformation behavior at deformation-induced layer depending on surface treatment methods was investigated using Fe-33mass%Ni alloy. As specimens, two kinds of specimens were prepared. One specimen has austenite (γ) single structure, and the other specimen consists of both martensite (α’) and γ phases. Using these specimens, shot-peening tests were performed, and then phase transformation behavior induced by the shot-peening was compared with that by sliding wear reported in previous literature. The deformation-induced layer induced by shot-peening has very fine microstructure consisted of both α’ and γ phases. The microstructure in the deformation-induced layer formed by shot-peening becomes similar with increasing duration of shot-peening regardless of initial microstucture. On the other hand, the deformation-induced layer induced by sliding wear is reported to have γ single structure regardless of initial microstructure. This microstructural difference between shot-peening and sliding wear comes from the difference of heat generation during the surface treatment. Therefore, it is concluded that phase transformation behavior in deformation-induced layer depends on surface treatment method.

Crystallographic Texture and Applications of Pure Cu Formed by Shot Peening

“…[1][2][3][4][5][6][7][8] Because SP can cause large strain around the peened surface, microstructures around the peened surface are highly refined and the surface hardness is therefore considerably increased. [9][10][11][12][13][14] SP is therefore a surface severe plastic deformation (SPD) process, which can induce residual compressive stress.…”

“…This subsurface layer is generally referred to as a deformation‐induced layer (DIL) and has a fine structure. [ 10–14 ] Umemoto et al found that the DIL in the Fe–3.29 mass% Si after SP consists of nanocrystallized ferrite grains of size less than 20 nm [ 10 ] Sato et al reported that a DIL that consisted of fine grains was formed by SP of an Fe–33 mass% Ni alloy [ 11 ] and SUS304 austenitic stainless steel. [ 12 ] These Fe alloys contain both the austenite phase with face‐centered cubic (fcc) crystal structure and the martensite phase with body‐centered cubic (bcc) crystal structure.…”

Effects of Strain‐Induced Cyclic Transformation on the Microstructure of the Peened Surface of SUS 304 Austenitic Stainless Steel

“…Similar results are also reported for Fe-Ni [12] alloys with high Ni content and for low-alloy steels. [13,14] Moreover, the strain-induced martensitic transformation can refine α', [15][16][17][18][19][20] whereas the straininduced reverse transformation [18,21,22] can reduce the size of γ grains.…”

“…Shot-peening (SP) is conventionally applied to improve the fatigue strength of metallic materials by inducing compressive residual stress in their surfaces. [23][24][25][26] On the other hand, SP can also induce a phase transformation such as martensitic transformation [16][17][18] and reverse transformation. [18,21,22] Sato et al have investigated temperature dependence of the reverse transformation induced by SP for SUS 304 austenitic stainless steel containing large amount of α' induced by cold rolling.…”

“…[23][24][25][26] On the other hand, SP can also induce a phase transformation such as martensitic transformation [16][17][18] and reverse transformation. [18,21,22] Sato et al have investigated temperature dependence of the reverse transformation induced by SP for SUS 304 austenitic stainless steel containing large amount of α' induced by cold rolling. [21] When the SUS 304 specimen is SPed under higher temperature than 100 °C, the volume fraction of γ on the peened surface is increased.…”