Enhanced Hydrogen Embrittlement Resistance in a Vanadium-Alloyed 42CrNiMoV Steel for High-Strength Wind Turbine Bolts

doi:10.1007/s40195-025-01916-z

Abstract

Abstract:

Hydrogen embrittlement (HE) remains a critical challenge for high-strength steels. This study comparatively investigates the HE behavior and hydrogen diffusion characteristics of a vanadium-micro-alloyed 42CrNiMoV steel against conventional 40CrNiMo steel through slow strain rate testing (SSRT), hydrogen thermal desorption, and hydrogen permeation measurements. The 42CrNiMoV steel demonstrated better mechanical properties and improved HE resistance under SSRT with both hydrogen pre-charged and in situ charging conditions. Microstructural analysis revealed that vanadium micro-alloying leads to grain refinement and reduces hydrogen diffusivity through vanadium carbides. Fractographic investigations revealed the environment-dependent fracture mechanisms, transitioning from ductile- to brittle-dominated failure modes under different hydrogen-charging conditions. These findings validate that vanadium micro-alloying represents a promising, cost-effective strategy for developing hydrogen-resistant high-strength steels, while emphasizing the crucial need for rigorous hydrogen ingress control in practical applications.

Key words: High-strength bolt steel, Hydrogen embrittlement, Vanadium micro-alloying, Hydrogen diffusion, Fracture mechanisms

Jiang Liu, Fengping Zhao, Wen Shi, Han Dong, Xiaofei Guo. Enhanced Hydrogen Embrittlement Resistance in a Vanadium-Alloyed 42CrNiMoV Steel for High-Strength Wind Turbine Bolts[J]. Acta Metallurgica Sinica (English Letters), 2025, 38(12): 2300-2315.

Figures/Tables 17

Table 1 Chemical compositions (wt%) of the developed 42CrNiMoV and reference 40CrNiMo steels

Material	C	Si	Mn	P	S	Cr	Mo	Ni	V	Fe
42CrNiMoV	0.45	0.25	0.75	0.012	0.007	1.20	0.32	0.35	0.08	Bal.
40CrNiMo	0.40	0.25	0.75	0.012	0.008	0.75	0.19	1.35	-	Bal.

Fig. 1 Schematic illustration of quenching and tempering (Q&T) heat treatment procedures for 42CrNiMoV and 40CrNiMo steels

Fig. 2 Microstructures of the investigated materials: a-c OM, SEM images, and prior austenite grain boundaries (PAGBs) distribution plot of 42CrNiMoV, d-f OM, SEM images, and PAGBs distribution plot of 40CrNiMo

Fig. 3 EBSD characterization of crystallographic features from a1-a3 42CrNiMoV and b1-b3 40CrNiMo steels: a1, b1 inverse-pole-figure (IPF) map, a2, b2 grain boundary distribution, a3, b3 kernel average misorientation (KAM) map, c number fraction of grain boundaries angle, d proportion of LAGBs and HAGBs and e frequency of KAM distribution

Fig. 4 TEM micrographs of test steels: a 42CrNiMoV, b 40CrNiMo, and c statistic plot of the lath width distribution, d, g high-resolution TEM (HR-TEM) images with the fast Fourier transform (FFT) diffractograms e, h and f, i the corresponding STEM-EDS maps from the 42CrNiMoV steel

Fig. 5 X-ray diffraction analysis of the phase structure and dislocation density of 42CrNiMoV and 40CrNiMo steel. a X-ray diffraction pattern, b fitting of the mean effective micro-strain according to the Williamson-Hall equation

Table 2 Mechanical properties of the investigated 42CrNiMoV and 40CrNiMo steels

Materials	R_P0.2 (MPa)	R_m (MPa)	A (%)	Z (%)	Hardness (HRC)	KV₂ at − 40 °C (J)
42CrNiMoV	1209 ± 12	1288 ± 1	14.7 ± 0.1	57.0 ± 1.4	40.0 ± 0.2	45.3 ± 1.6
40CrNiMo	1182 ± 1	1259 ± 1	14.7 ± 0.1	57.4 ± 0.5	40.5 ± 0.2	50.8 ± 1.5
Requirement*	≥ 1100	≥ 1220	≥ 8	≥ 4	≥ 39-44	≥ 27

Fig. 6 Notched tensile stress-displacement curves from SSRT test: a 42CrNiMoV, b 40CrNiMo, c HEI of the investigated steels under different hydrogen-charging conditions

Table 3 Notch tensile strength, hydrogen embrittlement index, and hydrogen content from the SSRT under different hydrogen-charging conditions

Material	Hydrogen-charging conditions	Notch tensile strength, $\sigma_{bN}$ (MPa)	HEI (%)	Hydrogen content, C_H (ppm)
42CrNiMoV	Uncharged	1854 ± 2	-	-
	Pre-charged	1822 ± 7	1.7 ± 0.4	1.74
	In Walpole	1705 ± 4	8.0 ± 0.3	0.89
40CrNiMo	Uncharged	1857 ± 5	-	-
	Pre-charged	1804 ± 3	2.9 ± 0.2	1.46
	In Walpole	1701 ± 1	8.4 ± 0.1	0.49

Fig. 7 Fracture surfaces of notch tensile specimens from 42CrNiMoV under different hydrogen-charging conditions: a, d, g uncharged, b, e, h pre-charged, c, f, i in Walpole

Fig. 8 Fracture surfaces of notch tensile specimens from 40CrNiMo under different hydrogen-charging conditions: a, d, g uncharged, b, e, h pre-charged, c, f, i in Walpole

Fig. 9 Hydrogen permeation transient from a cycled measurement

Table 4 Parameter fitting according to the hydrogen diffusion measurements

Fitting parameters	42CrNiMoV		40CrNiMo
Fitting parameters	First cycle	Second cycle	First cycle	Second cycle
t_0.63 (s)	6469	5647	2182	1883
L (cm)	0.0994		0.0835
D_app (10⁻⁷ cm² s⁻¹)	2.55	2.92	5.33	6.17
C_0app (10⁻⁵ mol cm⁻³)	2.28	1.97	1.23	0.77
N_T (10²⁵ cm⁻³)	5.27	4.59	2.47	2.12
N_ir (10²⁵ cm⁻³)	0.68		0.35

Table 5 Summaries of hydrogen content and traps provided by PAGBs and dislocations

Steels	C_H (ppm)	N_gr (× 10²¹ cm⁻³)	N_dis (× 10²¹ cm⁻³)	N_{(gr + dis)} (× 10²¹ cm⁻³)
42CrNiMoV	2.09	3.10	0.14	3.24
40CrNiMo	1.59	2.24	0.18	2.42

Fig. 10 Split of the TDS curves of the hydrogen-charged specimens of a 42CrNiMoV and b 40CrNiMo

Fig. 11 EBSD-KAM mapping near the notched root region of the failed SSRT specimen: a 42CrNiMoV-pre-charged, b 40CrNiMo-pre-charged, c 42CrNiMoV-In-Walpole and d 40CrNiMo-In-Walpole and e, f KAM distribution profiles

Fig. 12 Cross section of the notch root region in the in situ SSRT specimen from 40CrNiMo steel: a ECC image of IG crack, b EBSD-PAGBs reconfiguration map corresponding to the same region in a and the grain misorientation of PAGBs on crack propagation path

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