Effect of Salt Bath Nitrocarburizing and Post-Oxidation on Static and Fatigue Behaviours of a Construction Steel

Abstract

Several surface modification technologies are typically applied to improve the mechanical properties of the material surface of structural components subjected to severe conditions of load, wear and chemical erosion of the surface. The nitrocarburizing and post-oxidation heat treatment, also known as quench-polish-quench (QPQ), improves the fatigue, wear and corrosion resistance properties of the material, since it increases the surface hardness and generates surface compressive residual stresses. In the present contribution, the effects of the salt bath nitrocarburizing and post-oxidation heat treatment on the static and fatigue behaviours of 39NiCrMo3 construction steel have been investigated by experimentally testing plain as well as notched specimens. For comparison purposes, 39NiCrMo3 construction steel, both untreated and treated, and X5CrNiCuNb 16-4 stainless steel have been tested. First, the microstructure of the untreated and treated steel has been identified by metallographic analysis; micro-hardness measurements have been collected and residual stresses profiles have been obtained by using the X-ray diffraction technique. Then, experimental static and fatigue tests have been performed. Finally, the fracture surfaces have been analysed to locate fatigue crack nucleation sites.

Wires for spring construction: full scale fatigue experimental tests

“…Two identical prototypes of the test bench have been manufactured, assembled and validated. In order to test the effectiveness of the realised test benches, dynamic tests were carried out to derive the fatigue properties of a set of commercial precise ground bars made of 39NiCrMo3 tempered steel, a material extensively analysed in the scientific literature (see for instance [10,22,23]). The chemical composition of the tested material, experimentally derived using a Bruker Q4 Tasman spectrometer model 130, is reported in Table 3 and results to be compliant to the nominal values specified in relevant standards [24].…”

Fatigue Design and Defects in Metals and Alloys

“…Twelve research articles have been published in this Special Issue of Metals. The subjects are multidisciplinary, including (i) the effect of microstructural defects on the high and very high cycle fatigue strength of metallic materials [1][2][3][4][5], (ii) probabilistic fatigue prognosis incorporating the size of defects and control volume [2,4,6], (iii) the effects of plasticity, high temperature, and aggressive environment on the fatigue response [7][8][9], (iv) thermo-chemo-mechanical treatments to mitigate the detrimental effect of defects on the fatigue strength [10,11], and (v) non-destructive techniques to detect fatigue critical defects [12].…”

“…The defect is in this case the process-induced surface roughening, whose detrimental effect is overweighed by compressive residual stresses and work hardening. Campagnolo et al [11] researched the effect of nitrocarburizing and post-oxidation of the plain and fatigue strength of a low carbon steel. They found that the surface compressive residual stress field pushes crack initiation below the treated in plain samples.…”

Microstructure Characteristics of the Compound Layer Cracked during Grinding on QPQ‐Treated Cr‐Containing Steel Shafts

“…[ 9 ] It is widely recognized that higher hardness and residual compressive stress are beneficial to steel parts after QPQ treatment for improving fatigue properties. [ 10,11 ] However, the early spalling of the compound layer would accelerate the initiation and propagation of cracks, then significantly reduce fatigue life under rolling contact load. [ 12 ] The microstructure and properties of the compound layer have a decisive and complex influence mechanism on wear, corrosion, and fatigue behavior [ 13 ] of the surface.…”

“…The hardness profile of the diffusion layer would be obviously increased due to the appearance of alloy nitrides, [ 13,16 ] and thinner compound layers have been observed when the content of the nitride‐forming elements reaches some certain values. [ 11,16,17 ] It is inevitable that Cr‐nitride (CrN) appears in the compound layer on nitride‐high chromium steels. [ 18,19 ] The effect of the chromium nitride on the mechanical properties of the compound layer seems to be negative.…”