Fatigue Crack Growth Behavior of Austempered AISI 4140 Steel with Dissolved Hydrogen

Abstract

Abstract:The focus of this investigation was to examine the influence of dissolved hydrogen on the fatigue crack growth behavior of an austempered low-alloy AISI 4140 steel. The investigation also examined the influence of dissolved hydrogen on the fatigue threshold in this material. The material was tested in two conditions, as-received (cold rolled and annealed) and austempered (austenitized at 882 • C for 1 h and austempered at 332 • C for 1 h). The microstructure of the annealed specimens consisted of a mix of ferrite and fine pearlite; the microstructure of the austempered specimens was lower bainite. Tensile and Compact Tension specimens were prepared. To examine the influence of dissolved hydrogen, two subsets of the CT specimens were charged with hydrogen for three different time periods between 150 and 250 h. All of the CT samples were then subjected to fatigue crack growth tests in the threshold and linear regions at room temperature. The test results indicate that austempering resulted in significant improvement in the yield and tensile strength as well as the fracture toughness of the material. The test results also show that, in the absence of dissolved hydrogen, the crack growth rate in the threshold and linear regions was lower in austempered samples compared to the as-received (annealed) samples. The fatigue threshold was also slightly greater in the austempered samples. In presence of dissolved hydrogen, the crack growth rate was dependent upon the ∆K value. In the low ∆K region (<30 MPa √ m), the presence of dissolved hydrogen caused the crack growth rate to be higher in the austempered samples as compared to annealed samples. Above this value, the crack growth rate was increasingly greater in the annealed specimens when compared to the austempered specimens in presence of dissolved hydrogen. It is concluded that austempering of 4140 steel appears to provide a processing route by which the strength, hardness, and fracture toughness of the material can be increased with little or no degradation in the ductility and fatigue crack growth behavior.

Thermal Stability and Lubrication Properties of Biodegradable Castor Oil on AISI 4140 Steel

“…AISI 4140 steel is one of the main substrate materials for abrasive and adhesive wear applications, and it is used extensively in industrial mechanical elements thanks to its high hardness and toughness properties [9,11]. In this work, the influence of Castor oil on AISI 4140 steel was evaluated.…”

Improving the Reliability of Mechanical Components That Have Failed in the Field Due to Repetitive Stress

“…Cracks in the helix dispenser require the manufacturer to redesign the product to keep it functioning for its expected lifetime. By utilizing the above failure analysis (and tests), fractures that started in voids inside mechanical parts such as gear have been shown to propagate to their ends [23][24][25][26][27][28][29][30]. In particular, intergranular fractures of austenitic stainless steels have been identified and discussed in a similar way to the failure of the helix dispenser [31].…”

Effect of Annealing Time and Temperature Parameters on the Microstructure, Hardness and Strain-Hardening Coefficients of 42CrMo4 Steel

“…Low-alloy structural steels are widely used in mechanical, automotive, mining and machine building industries and they undergo shaping by metal forming, machining, welding, surfacing and many other techniques [1][2][3][4][5]. Particularly, the structural steel grade 42CrMo4 (AISI 4140) offers the most versatile applications and is one of the most universal grades dedicated to heat treatment and plastic deformation [1,2,[6][7][8]. However, to facilitate its deformability in cold metal forming processes, this steel requires a special heat treatment -annealing.…”

“…Nevertheless, in industrial conditions, the particularly time-effective measurement of hardness is employed to examine the softening of steel before subjecting the treated steel to metal forming processes. Although in many cases light optical microscopy (LOM) and scanning electron microscopy (SEM) give accurate results of metallographic examination [7,[13][14][15], electron back-scattered diffraction (EBSD) [16,17], transmission electron microscopy (TEM) [1,18] and X-ray diffraction (XRD) [19][20][21] seem to be much more powerful tools for evaluating microstructure development due to plastic deformation or heat-treatment. In [20] the authors employ XRD to study the hardening and tempering behaviour of the En24 steel (ISO equivalent 34CrNiMo6) via X-ray peak profile analysis.…”