Fatigue anisotropy in cross-rolled, hardened medium carbon steel resulting from MnS inclusions

Abstract

Anisotropy of forged steel components is especially adverse when it concerns rotationally symmetric components. Manganese sulfides (MnS) in steels may be desired for their improvement of machining properties; however, they also deteriorate fatigue behavior. A quantification of the effect of MnS on anisotropy is necessary to find an optimum for component dimensioning. To isolate the influence of MnS on anisotropy only, high cleanness of the test material is required. The test material in the current investigation was molten in a vacuum furnace to high-cleanness composition. Materials with two different S levels were produced to detect variations in anisotropy according to amount, shape, and distribution of the MnS inclusions. The two batches were cross-rolled to plates with a deformation ratio of 4.5. The MnS phase constitutes, upon forging or rolling, pancake-shaped inclusions. In the case of cross-rolling, an in-plane rotational symmetry of the inclusions could be created. The shape and size of these inclusions are essential for the mechanical behavior of the material. Push-pull fatigue testing was performed in longitudinal (in plane) and short transversal directions relative to the rolling plane. The results showed strong anisotropy of the fatigue behavior with inferior performance in short transverse directions where the principal stress is perpendicular to the flattened inclusions. The anisotropy was somewhat more pronounced for the high-S material, resulting from a different fatigue crack growth mechanism.

Morphology of Solidification Structure and MnS Inclusion in High Carbon Steel Continuously Cast Bloom

“…By comparison with deformability of Type I and III sulfides, Type II sulfides can deform to a larger extent during the hot working process of steel, resulting in high stress concentrations on sharp edges of the deformed MnS and strong material anisotropy. 4,11) Therefore, to achieve an excellent material properties of steels, MnS inclusions must be strictly controlled to be small, uniformly distributed and to have a spherical shape.…”

“…4) But the tiny dispersed MnS inclusions are beneficial for acting as nucleation of intergranular ferrite, resulting in grain refinement and mechanical properties improvement.…”

Effects of cooling rate and Al on MnS formation in medium-carbon non-quenched and tempered steels

“…In non-quenched and tempered steel, MnS may cause the deterioration of transverse impact properties because the MnS inclusions become relatively large and elongated in the hot rolling or forging direction. According to the differences in morphology and distribution among various types of MnS, Type I and Type III MnS are more beneficial compared with Type II MnS due to their appropriate sizes and uniform distributions [15][16][17][18]. As a consequence, studies on classifying and controlling MnS in non-quenched and tempered steel are necessary.…”

Multiaxial fatigue criterion accounting for anisotropy in forged components

“…Indeed, most of fatigue cracks appear in the vicinity of an inclusion, especially for hard materials. In fact, the resistance to a high cycle fatigue uniaxial loading is very different for two materials composed with approximately the same constituents but with a different number of inclusions [7]. Generally, the resistance is lower for the material containing more inclusions.…”

“…To bring out this results, we have been working on a bainitic steel METASCO MC. Several analysis show that the probability of crack initiation is high near MnSs inclusions (manganese sulphide), very common in modern steels due to their benefic role during machining (figure 6) [7]. For that reason, a new pre-processor, DIGIMICRO, is used to create realistic digital microstructures.…”