Influence of hydrogen pressure and internal hydrogen contents on short-term strength, plasticity, and plane-stress fracture toughness of 05Cr19Ni55 alloys at pressure up to 30 MPa was investigated. It was established that the crack resistance parameters
Heat-resistant nickel alloys are widely used in energy and aerospace engineering in contact with high-pressure hydrogen-containing gas mixtures [
In order to ensure the safety and reliability of materials for a steam and gas turbine, structural integrity and lifetime prediction are of great importance. Working structures and their elements (blades and discs) are subjected to the influence of various loads and hydrogen-containing gas. In order to ensure an adequate level of safety and optimal durability of such structural elements, experimental tests in gaseous hydrogen are required to determine the effect of various factors. By the fracture mechanics approaches, evaluation of static load durability of structures and critical crack (defect) size in technological or operational circumstances have been calculated as the values of critical stress intensity factor
In what follows, we study the influence of high-pressure gaseous hydrogen on short-term strength, plasticity, and static crack resistance of a nickel-based alloy 05Cr19Ni55 with different modes of heat treatment and chemical composition variations.
The alloy 05Cr19Ni55 from which parts used in energy, petrochemical engineering, and aerospace engineering products [
Chemical composition of 05Cr19Ni55 alloy (mass %).
CC | C | Fe | Cr | Mo | Nb | Al | N | ∑Cr, Mo, Nb, Fe | ∑ N + |
(Cr, Ni, Fe)23(C, N)6 |
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I | 0.05 | 12.0 | 19.0 | 8.87 | 1.73 | 1.49 | 0.07 | 41.60 | 0.12 | 3.1 |
II | 0.04 | 11.0 | 17.5 | 8.97 | 1.84 | 1.54 | 0.03 | 39.38 | 0.07 | 2.0 |
Characteristics of the 05Cr19Ni55 alloy modifications at 293 K and displacement rate 0.1 mm/min.
No. of order | Orientation | Heat treatment |
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MPa | % | |||||||||||
1 | TV | OM. Quenching (Q): 1323 K, 1 h |
85 | 20 | 86 | 25 | 920/930 | 570/570 | 10/2.5 | 12/4.5 | 69/28 | 0.38/0.32 |
2 | LT | OM, HT I | 85 | 20 | 107 | 25 | 1020/970 | 590/600 | 14/4.5 | 18/8 | 88/38.5 | 0.44/0.36 |
3 | LT | VAR, HT I | 85 | 20 | 128 | 22 | 1050/1010 | 620/610 | 20/6 | 32/15 | 98/51 | 0.47/0.40 |
4 | LT | OM. Q: 1253 K, 1 h. A: 1023 K, 15H, +923, 10 h (HT II) | 21 | 20 | 119 | 27 | 1040/990 | 610/610 | 17/5 | 20/9 | 94/45 | 0.45/0.38 |
5 | LT | VAR, HT II | 21 | 20 | 162 | 24 | 1080/970 | 650/660 | 35/6 | 38/19 | 116/68 | 0.50/0.42 |
6 | LT | VAR, HT II | 21 | 25 | 162 | 24 | 1080/970 | 650/660 | 35/6 | 38/19 | 126/64 | 0.50/0.40 |
7 | LT | VAR, after HT II simulation of soldering 1283 K, 15 min, A: |
36 | 10 | 138 | 21 | 1180/960 | 710/690 | 30/5 | 34/16 | 103/62 | 0.47/0.45 |
8 | LT | VAR, HT III | 36 | 20 | 138 | 21 | 1180/960 | 710/690 | 30/5 | 34/15 | 108/52 | 0.44/0.38 |
9 | LT | VAR, after HT II simulation of soldering 1473 K, 15 min + 1273 K, 1 h (HT IV) | 130 | 20 | — | 23 | 750/700 | 380/390 | 41/16 | 31/18 | — | 0.58/— |
TV: transverse orientation; LT: longitudinal orientation; OM: open melting; VAR: vacuum arc remelting;
The effect of rising
Dependences of fracture toughness
The orientation of specimens, method of melting, heat treatment regimes, grain sizes, thickness of the specimens for fracture toughness testing, the mechanical properties of alloy in the air and in hydrogen under the pressure of 30 MPa after preliminary hydrogenation (623 K, 30 MPa H2, 10 h), and coefficients of influence of hydrogen on reduction of area and
Static tensile tests were carried out on standard fivefold cylindrical specimens with a diameter of working part 5 mm using the strain-rate range
Specimens were hydrogenated in a working chamber at 623 K and hydrogen pressure 30 MPa during 1–10 h. The maximum hydrogen content in the specimens varied from 21 wppm to 27 wppm depending on the structural state of the alloy (see Table
The behavior of the rate dependences of hydrogen degradation is determined by the kinetics of penetration of hydrogen into the material and changes in the mechanisms of deformation. As the rate of short-term tension decreases, the influence of hydrogen first increases, and then the properties become stable (see Figure
Dependences of plasticity characteristics
The maximum embrittlement of hydrogenated material in hydrogen under a pressure of 30 MPa is realized at a rate less than 0.1 mm/min (0.67·10−4·s−1), which is three orders of magnitude smaller than the regulated rate of determination of the hydrogen resistance of steels with a body-centered cubic structure equal to 10 mm/min [
Similarly, the level of
The dependences of the fracture toughness of prehydrogenated specimens on the hydrogen pressure consist of two regions. In the first region (low pressures), the pressure abruptly drops, and in the second, the negative action of hydrogen becomes stable (see Figure
In hydrogen under the pressure 30 MPa,
Dependences of fracture toughness
Strength, plasticity, and fracture toughness of the alloy 05Cr19Ni55, melted in vacuum and open electric furnaces, were compared. For the same heat treatment, the alloy after vacuum arc remelting has much higher plasticity than after open melting (position 2, 3 and 4, and 5 in Table
Fracture toughness of specimens of the 05Cr19Ni55 alloy of 20 mm thickness after open and vacuum arc melting in air (light bars) and in hydrogen under pressure 30 MPa after hydrogenation (shaded bars). The numbers near curves correspond to ordinal numbers in Table
Chemical composition and quantity of intermetallics and carbide phases did not differ. Grain sizes after HT were practically the same (see Table
The relationship between mechanical properties of the alloy and texture that appeared as a result of rolling was investigated. In air, the value of the characteristics of plasticity (
Resistance to fracture of the alloy also depends on the orientation of the specimens.
The value of static fracture toughness of compact specimens of 20 mm thickness with cracks oriented in the transverse orientation in air was
In hydrogen, characteristics of crack resistance transversely and longitudinal oriented specimens are 28 and 38.5 MPa·m1/2. Similar results were obtained in the study of hydrogen embrittlement of steels 4130 and 4310 and other materials [
The most likely reason for anisotropy of mechanical properties can be anisotropic structural boundaries in the alloy, i.e., the dependence of fate crack length, falling on the structural boundary, and on the orientation of the applied load. The accumulation of hydrogen at the grain boundaries makes it easy to crack, while at transverse-loading large areas such boundaries are under the influence of normal stresses [
The difference in the degree of hydrogen embrittlement of the TV and LT samples is also due, probably, to the formed rolling process by the dislocation texture, which is decisive in hydrogen cracking [
Effect of dispersion structure of the alloy on strength, plasticity, and fracture toughness in air and hydrogen was studied. Quenching temperatures were 1253 K, 1283 K, 1323 K, and 1473 K, grain sizes is equal to 21, 36, 85, and 130 microns, respectively, and the average thickness of grain boundaries is 1, 2, 3, and 4 microns (see Figure
Microstructure of the alloy: after VAR and HT II (a), HT I (b), and HT IV (c).
After quench from 1473 K alloy has a large grain (Figure
The method of J-integral does not recommend to evaluate the materials static crack resistance in plane-strain conditions. In the absence of large local stresses during the short-term strength tests, arise the minimal embrittlement effect of hydrogen.
For the same aging regimes with decreasing grain size, parameters of plasticity and static crack resistance increased in air and hydrogen (see Table
Mechanical properties of alloys with different chemical composition at 293 K and displacement rate 0.1 mm/min.
CC |
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(Cr, Ni, Fe)23(C, N)6, mass % |
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% | MPa·m1/2 | ||||||||
I | 1080/970 | 650/660 | 35/6 | 38/19 | 0.50 | 126/64 | 162 | 0.40 | 3.1 |
ІІ | 1075/1010 | 630/650 | 42/12 | 44/29 | 0.66 | 139/89 | 171 | 0.52 | 2.0 |
Probably, this effect is due to a reduction from 3.1 to 2.0 mass % quantity of carbides and carbonitrides (see Table
X-ray patterns of the alloys with different content of carbides (I, II, see Table
Fracture surface investigation of Ni alloy specimen with cumulation of failure due to static loading at 293 K in hydrogen under the pressure of 30 MPa: (a) intergranular fracture in the area of surface cracks and (b) destruction along the boundary of the carbide matrix with carbide cracking.
With the decrease of strain rate from 100 to 0.1 mm/min, plasticity characteristics of the Ni alloy specimens in hydrogen are reduced in the interval rates 0.1–0.01 mm/min. Similarly, the level of The values of hydrogen pressure and hydrogen content by which has achieved the maximizing effect on investigated alloys fracture toughness has been established. Compact specimens thickness increasing leads to the hydrogen embrittlement increases. With compact specimen thickness increasing, the hydrogen embrittlement increases. After cumulation of failure, hydrogen has initiated the fracture by the mechanism of normal separation across the whole crack front, causing formation of the plane-strain state in the specimens. The alloy properties depend on the orientation of the samples. Strength, plasticity, and fracture toughness in air and hydrogen in transversely oriented specimens are much lower than those in longitudinally oriented specimens. Vacuum arc remelting, formation of fine structures of the thin grain boundaries, and a minimum number of carbides and carbonitrides have increased fracture toughness and hydrogen resistance of the alloy.
The data used to support the findings of this study are available from the corresponding author upon request.
The authors declare that they have no conflicts of interest.