The effect of Nb addition (0.022, 0.053, 0.078 wt%) on the hydrogen-induced delayed fracture resistance of 22MnB5 was studied by constant load test and electrochemical hydrogen permeation method. It is shown that the appropriate addition of Nb is beneficial to the improvement of the delayed fracture resistance of tested steel, especially when the steel contains high concentration of hydrogen, and the maximum delayed fracture resistance is obtained at a Nb content of 0.053%.The result of hydrogen permeation test shows that the diffusion coefficient of hydrogen in the steel containing niobium is lower than that in steel without niobium, which indicates that it is harder for hydrogen in the steels containing niobium to diffuse and aggregate. In addition, the reason for Nb improving the delayed fracture resistance of steels is discussed from two aspects: hydrogen trap effect and grain refinement effect. The analysis shows that the main reason leading to the improvement of the delayed fracture resistance is the hydrogen trapping effect of NbC while the grain refinement effect of Nb(C,N) secondary.

Effect of Nb on hydrogen-induced delayed fracture in high strength hot stamping steels

Microstructure and wear properties of Al 2 O 3 -CeO 2 /Ni-base alloy composite coatings on aluminum alloys by plasma spray

The impact of V 4 C 3 precipitates on the sensitivity to hydrogen embrittlement is evaluated in this work. Two main conditions are compared with each other, i.e. an as-quenched and a quenched and tempered condition in which carbides have precipitated. Tensile tests are performed on both uncharged and hydrogen charged specimen and a correlation with the amount of charged hydrogen is made by hot/melt extraction. The tempered induced carbides trap a significant amount of hydrogen which explains why the degree of hydrogen embrittlement increases for the quenched and tempered condition. To verify at which trapping sites hydrogen is located, thermal desorption spectroscopy is performed. A considerable amount of hydrogen is trapped in a rather irreversibly way, which still has an effect on the degree of hydrogen embrittlement. Additionally, a slightly modified temper treatment is applied to vary the carbide size and hence evaluate the impact of the hydrogen induced ductility loss.

Evaluation of the effect of V4C3 precipitates on the hydrogen induced mechanical degradation in Fe-C-V alloys

High-temperature tensile deformation behavior of hot rolled CrMnFeCoNi high-entropy alloy

Investigation on the effect of rotational speed on rolling wear and damage behaviors of wheel/rail materials

A quenched and tempered steel for a large bearing ring was investigated. The heat treatment experiments were designed by using the L 9 (3 4 ) type orthogonal form. Based on these conditions, a better combination of mechanical properties was obtained. The results showed that the quenching and the tempering temperatures were the most influential factors on the strength and toughness. The dislocation strengthening and the solid solution strengthening of the dissolved alloying carbides are the main mechanisms of increasing the strength by decreasing the tempering temperature and increasing the quenching temperature, respectively. The stripped carbides and long chain carbides strongly influence the differences in the tensile strength of the steels under different processes. The toughness AKv at −20 °C was increased by 42.2 J when the quenching temperature increased from 800 to 900 °C. The stripped undissolved carbides at lower quenching temperature promoted crack propagation and cleavage fracture and thus decreased the toughness of the steel. The AKv was increased by 47.4 J when the tempering temperature increased from 550 to 650 °C. The long chain carbides distributed along the grain boundary and the martensitic laths with a high density of dislocations at the lower tempering temperature decreased the toughness. Oil quenching can improve both the strength and toughness by refining the martensitic microstructure.

Microstructural characterization, strengthening and toughening mechanisms of a quenched and tempered steel: Effect of heat treatment parameters

Effect of large-size M23C6-type carbides on the low-temperature toughness of martensitic heat-resistant steels

Influence of vanadium and/or niobium additions on delayed fracture behavior in high strength spring steel was studied by hydrogen permeation method and slow strain rate technique (SSRT), and its mechanism was analyzed. The results show that apparent diffusion coefficient of hydrogen in microalloyed spring steels Nb-V-steel and Nb-steel is lower than that in non-microalloyed steel 60Si2MnA. Percentage of strength reduction in SSRT in air after precharged hydrogen of the microalloyed steels is smaller than that of 60Si2MnA. Addition of the microalloys changes the fracture characteristics. Thence, vanadium and/or niobium additions are a very effective and economy means to improve the hydrogen-induced delayed fracture resistance of high strength spring steel.

Effects of Niobium and Vanadium on Hydrogen-Induced Delayed Fracture in High Strength Spring Steel

The mechanical anisotropy and effects of MnS inclusions configuration on the local ductility in hot rolled bars with 0.03% sulphur were experimentally investigated and statistically regression analyzed. Results show that the elongation and reduction of area decline significantly as the angle between the gauge length and the transverse direction decreases, while the tensile strength and yield strength vary little. The reduction of area in transverse tensile tests of various rolled bars ranges widely from 6.5% to 38.1% and the differences in engineering stress–strain curve profile are mainly reflected in the local deformation stage. MnS inclusions configuration in the surface adjacent to fracture were classified into three types according to the morphology and three-dimensional distribution. When the type of MnS transitions from C to A to B, the reduction of area decreases obviously and area of ribbon-like fractures where most local deformation performs declines as well. Multiple linear regression of the parameters of MnS inclusions shows that the reduction of area is more sensitive to the length of single MnS inclusion or aggregation of tiny MnS inclusions and the local density of MnS inclusions. Voids in matrix tends to nucleate between the parallel MnS inclusions and along the line connecting two MnS inclusions with rounded or blunt tips and then grow and link up to form cracks. Besides, cracks can also be directly induced by the sharp tips of tiny MnS inclusions. In conclusion, the aggregated tiny MnS inclusions of type B should be avoided and the evenly distributed spindle-shaped MnS inclusions of type C are expected in steels requiring favorable transverse mechanical properties.

Mechanical anisotropy and local ductility in transverse tensile deformation in hot rolled steels: The role of MnS inclusions

The characteristics of complete and partial decarburizations in spring steel 60Si2MnA were systematically investigated, including the microstructure, the hardness gradient, and the formation mechanism. The relation between decarburized types and heating temperature of the steel was comprehensively discussed. It is found that heating temperature has an important influence on the decarburized types. With the rise of heating temperature, the decarburized types change from no decarburization to complete decarburization, complete and partial decarburizations, partial decarburization, and no decarburization.

Yazheng Liu

Papers

Microstructural characterization, strengthening and toughening mechanisms of a quenched and tempered steel: Effect of heat treatment parameters

Effect of large-size M23C6-type carbides on the low-temperature toughness of martensitic heat-resistant steels

Effects of Niobium and Vanadium on Hydrogen-Induced Delayed Fracture in High Strength Spring Steel

Mechanical anisotropy and local ductility in transverse tensile deformation in hot rolled steels: The role of MnS inclusions

Surface decarburization characteristics and relation between decarburized types and heating temperature of spring steel 60Si2MnA