The structure, phase composition, and residual stresses of diffusion boride layers formed by thermal-chemical treatment on the die steel surface

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 23 No. 2 2021 Metrological frames with the samples were installed and fixed in a fume hood on brackets above a bath with electrolyte solution, set up on the stage of the lifting device (Fig. 2). The strain gauges were connected to the LTR-EU-2-5 “L Card” Data Acquisition System (DAS). The Mastech HY3010 current source was connected to the terminals. DAS of the UDION-2 installation controlled by the ACTest software provides obtaining, processing, visualization, and storing information from the strain gauges during the experiment. The processed information obtained from the strain gauges and the measured parameters of the samples, essential for the subsequent RS calculation, were stored in the database “Parameters of the UDION samples”. After preparatory operations, the experiment was launched: the supply and exhaust ventilation system were switched on, the test scenario was activated, the stage of the lifting mechanism with the baths was raised so that the samples were completely immersed in the solution. The current source was switched on and the DAS was started, layer-by-layer electrochemical etching (anodic dissolution) was performed. The composition of the electrolyte used and the modes of anodic dissolution are shown in Table 2. Ta b l e 2 Electrolyte composition and parameters for electrochemical etching (anodic dissolution) of samples after chemical heat treatment Electrolyte composition (g/l) t , °С Current density j, A / dm 2 Voltage U, V Etching rate V er , mm / min NaNO 3 – 60; NaNO 2 – 5; Na 2 CO 3 – 5; C 3 H 8 O 3 – 15; H 2 O – rest 30 125 11,5 0,0042 The control point movement of the strain gauges were recorded and the deformation curve was plotted in real time during the layer-by-layer electrochemical etching of the studied surface. The subsequent information processing (an array of the deformation curves, initial deformations, geometric parameters of the samples) was performed by the XUdion software (a computer program for RS calculation) [15]. The final step of the RS testing was the RS measuring protocol, containing parameters of the sample and the RS epura (RS distribution over the thickness of the removed layer). The RS calculation in the XUdion software was carried out by a mathematical model for the RS components calculation in the plates using the strip method [16] (Fig. 5): 0 2 2 2 0 8 4 ( ) 4( ) 2 ; 2 1 3 (1 ) a Z Z Z z Z dV E h E a V h a h a V V d da     σ = − − − − − + ξ         − µ ⋅ − µ   ∫ (1) 0 2 2 2 0 8 4 ( ) 4( ) 2 ; 2 1 3(1 ) a X X X X X dV E h E a V h a h a V V d da     σ = − − − − − + ξ         − µ − µ   ∫ (2) 0 2 0 2 ( ) 4( ) 2 . 2 3 a ZX du h G G a u h a h a u u d da τ τ τ τ     τ = − − − − − + ξ           ∫ (3) where σ z and σ x are RS normal components, MPa; τ zx – RS tangent component, MPa; E – the elastic modu- lus, MPa; G – the shear modulus, MPa; μ – Poisson’s ratio; 0 0 2 0 2 / / z z z x x V f l f l = + µ ⋅ ; 0 0 2 0 2 / / x x x z z V f l f l = + µ ⋅ ; ( ) 0 0 0 / 2 z x u τ = χ − χ – reduced displacements after cutting;