Precipitation-hardening Steel Research Articles

Understanding the Relationship between Surface Quality and Chip Morphology under Sustainable Cutting Environments.

Although chip morphology changes according to the machining method and related cutting parameters, chip formation affects the quality of the machined surface. In this context, it is very important to understand the relationship between chip morphology and surface quality, especially in materials that are difficult to machine. In the presented study, the changes in chip morphology, surface morphology, and surface quality criteria (Ra and Rz) that occurred during the milling of precipitation-hardened steel in different cutting environments were analyzed. Milling experiments were carried out in dry, MQL (minimum quantity lubrication), nano-MQL (graphene), nano-MQL (hBN), Cryo, and Cryo-MQL environments using TiAlN-coated inserts and three different cutting speeds and feed rates. While the highest values in terms of Ra and Rz were measured in dry machining, the minimum values were obtained in a nano-MQL (hBN) cutting environment. Due to the lubrication and low friction provided by the MQL cutting environment, chips were formed in thinner segmented forms. This formation reduced the chip curve radius and thus provided a more stable surface morphology. On the other hand, Cryo-ambient gas could not effectively leak into the cutting zone due to the intermittent cutting process, but it increased the brittleness of the chips with the cooling effect and provided a similar surface morphology. The values of minimum Ra and Rz were obtained as 0.304 mm and 1.825 mm, respectively, at a 60 m/min cutting speed and 0.04 mm/rev feed. Consequently, the use of nano-MQL cutting medium is seriously recommended in terms of surface quality in milling operations of difficult-to-machine materials.

Microstructure and Some Mechanical Properties of AISI 630 Stainless Steel Hardened by Precipitation Hardening

AISI 630 stainless steel hardened by precipitation hardening (PH) is increasingly being used as a maraging steel. In this study, the microstructure and some tensile properties of these steels were examined at room temperature. Additionally, the impact absorption energies of the materials were calculated by conducting the Charpy impact tests on PH steels. This value, calculated as 138.9, is very close to the value obtained by other researchers

Optimization of Sandblasting to Improve the Surface Finish of 17-4PH Parts Manufactured by SLM Using Different Laser Scanning Strategies

Great advances have emerged in recent years around additive manufacturing techniques, with an increasing number of different materials (polymers, ceramics, metals). However, metal part manufacturing has always been one of the most demanded in engineering. That is due to its ability to create final functional parts with good mechanical properties. One of the most widely used technique is Selective Laser Melting (SLM). The SLM process uses a laser power source to selectively melt metal powder layer by layer. Typically, this manufacturing technique requires mechanical post-processing operations, not only to split the parts from the build-plate, but also to improve the mechanical properties and surface finish of parts or the dimensional accuracy of specific regions to ensure assembly and interchangeability. In particular, sandblasting is a method of mechanical abrasion cleaning commonly used and very useful for improving the surface topology of SLM printed parts. Besides, the laser scanning strategy used in this additive manufacturing process influences the surface quality of parts. Therefore, in this work, the sandblasting post-process has been optimized for surface roughness improving in parts printed using the most common laser scanning strategies (normal, hexagonal, concentric). The role that sandblasting pressure and time plays in the surface quality of parts, indispensable to optimize this SLM post-process, has been evaluated. Thus, surface roughness of different specimens subjected to different sandblasting parameters has been measured to optimize both values related to the laser scanning strategy used in SLM manufacturing. The material used is 17-4PH stainless steel, an alloy that presents an excellent combination of high strength and good corrosion resistance, high hardness, good thermal properties, as well as excellent mechanical properties at high temperatures. This precipitation-hardened steel has important applications in the aerospace sector, chemical and petrochemical industry, energy sector, surgical instruments, high wear components, and general metallurgy, among others.

Dynamic Constitutive Model for a Martensitic Precipitation-Hardening Steel Considering Adiabatic Shear Damage and Non-uniform Gradient Stress Change: Modeling and Applications

Dynamic Constitutive Model for a Martensitic Precipitation-Hardening Steel Considering Adiabatic Shear Damage and Non-uniform Gradient Stress Change: Modeling and Applications

Significant reduction of fatigue crack non-propagation limit caused by damage accumulation mode fatigue crack propagation in a precipitation-hardened punched steel plate

Precipitation-hardened steel exhibits specific characteristics due to the punching process that deteriorates its strength. To investigate these characteristics, fatigue tests were conducted with artificial micro defects on the punching processed surface that imitate the flaws caused by the process. The authors found that changes in material properties and the flaws change the fatigue strength properties. Specifically, the fatigue crack extends in the damage accumulation mode, which does not have the non-propagation mechanism and reduces the crack non-propagation limit. Furthermore, the damage accumulation mode fatigue crack propagation changes the fatigue limit's physical meaning from the fatigue crack non-propagation limit to the initiation limit. Finally, processing conditions that improve the fatigue strength characteristics were proposed.

Structure and Properties of Weldable Precipitation-Hardening Steel Alloyed with Copper for High-Strength Pipeline Fittings

Structure and Properties of Weldable Precipitation-Hardening Steel Alloyed with Copper for High-Strength Pipeline Fittings

Current research and developments in welding of 18% nickel maraging steel

Maraging steels are low-carbon, high nickel-containing precipitation-hardened steels with an excellent combination of strength and toughness. Their outstanding performance gained the increasing attention of scientists, industrialists, and end-users over the past six decades. The present global rapid growth in the consumption of maraging steel, particularly in aerospace, defense and other engineering applications, involves the fabrication of high-performance welded joints. Maraging steels offer relatively high flexibility from the welding point of view. Gas tungsten arc welding is the most preferred welding process for maraging steels. As the need for increased productivity is growing worldwide in many fields, such as aerospace, mechanical engineering, etc., where thick sections are used, issues like heat input, inter-pass temperature, cooling rate, and the selection of weld consumables become important for achieving defect-free joints. Many advanced techniques like plasma, laser, and hybrid welding processes are being developed to fulfil the requirements for joining higher thickness products without distortion. The major problem associated with welding maraging steel is the formation of reverted austenite in the fusion zone and the heat-affected zone. This problem can be mitigated by choosing optimized filler wires and the proper selection of post-weld heat treatment for the weldments. This paper extensively reviews the influence of welding processes and conditions on the microstructure and mechanical properties of maraging steels with due emphasis to structure–property relationships.

Influence of hexagonal scanning strategy island size on microstructure, residual stress, and corrosion behavior of 17-4 PH SS made by L-PBF

17-4 Precipitation-hardened steel has attracted worldwide attention due to its applications. In the manufacture of 17-4 PH SS using SLM, several parameters play an important role. In the present study, the hexagonal island sizes were varied as 1.25-2.5-3.75-5-6.75-7.5-8.75-10 mm to understand the microstructure, microhardness, residual stresses, and corrosion behavior of 17-4 precipitation hardened stainless steel fabricated by laser-powder bed fusion with a scan rotation angle of 90°. The results indicate that the average time per layer decreases as the island size increases. The quality of the surface increased with a decrease in hexagonal island size as scan length reduced. The hardness varied with island size and higher hardness was exhibited due to fine grain size. The medium island size microstructure consists of regular molten pools and lower heat accumulation. Large and small molten pools were observed on the front and side surface respectively for samples with different hexagonal island sizes. Austenite phase was detected in all samples with the highest intensity at hexagonal inside out sample with an island size of 2.5 mm at 43.500°. Both hexagonal samples with 2.5 mm island size and 10 mm samples almost exhibit ɣ-austenite phase in the finer grain size area, as per EBSD orientation maps. The residual stresses increased as the hexagonal island size increased because when a large island size is used, it produces a long scanning track with a weak pre-heating effect, resulting in a high-temperature gradient and high residual stress. Higher corrosion resistance was obtained for 2.5 mm hexagonal scan strategy island size because of finer grain size and lower defects.

Optimization of process parameters for direct energy deposition of 15Cr5Ni precipitation hardened stainless steel for aircraft parts repair and maintenance

In the aerospace industry, regular maintenance and repair consume maximum cost and time. Direct energy deposition is an effective cutting edge repairing technology used in aircraft parts. This paper projected direct energy deposition as an important cladding technology. And as a cladding material, the acceptability of 15Cr5Ni precipitation-hardened steel is evaluated through single-layer deposition over 304 L stainless steel via direct energy deposition. 15Cr5Ni steel is a high-strength alloy mainly used for jigs, fasteners, and landing gears in the aerospace industry. Optimization of process parameters, that is, laser power, scan speed, and powder feed rate, is performed using response surface methodology through a prediction model along with a validation test. The microstructural investigation of clad cross-section and surface morphology followed by four-dimensional X-ray microscopy reveals an improved clad quality with minimized porosity and defects. A relative error of less than 5% has been found between the prediction model and experimental values, which validate the significance of optimized process parameters toward improving the clad quality for aircraft part repairing purposes.

Early crack initiation mode during tensile fracture process in a punch-processed precipitation-hardened steel plates and evaluation method to treat the crack as an equivalent pre-crack

For partially worked metals such as punching-processed steel plates, a process-affected zone designated “shear-affected zone” (SAZ) is formed. In this study, tensile tests of punched specimens were conducted to determine the strength of partially worked metals. In the fracture surface of the specimen, a semi-elliptical crack originating in the SAZ, or “shear crack,” was observed, inclined at 45° to the remote tensile stress direction. This shear crack changed the behavior of the metal during tensile loading, e.g., ductile-brittle transition. In specimens exhibiting macroscopic brittle fracture, microscopic brittle fractures cause shear cracks before the specimen reaches its macroscopic yield point. The shear cracks in ductile fractured specimens include a similar brittle-fractured region that can be considered a pre-crack; the punched material can be considered a pre-cracked material. This study highlights the requirement for a novel mechanical model based on linear fracture mechanics to evaluate and predict the fracture mode of punched materials.

Effect of Copper Content and Heat Treatment Schedules on Mechanical Properties, Cold Resistance, and Microstructural Constituent Morphology in Precipitation-Hardened Steel

Effect of Copper Content and Heat Treatment Schedules on Mechanical Properties, Cold Resistance, and Microstructural Constituent Morphology in Precipitation-Hardened Steel

Improved mechanical properties of laser-repaired 15-5PH stainless steel by in-situ heat treatment and grain refinement

Mechanical properties of repaired part by laser melting deposition (LMD) mainly depend on microstructure of clad layer and heat affected zone (HAZ). For precipitation-hardened steel, the properties of as-deposited materials are usually not satisfactory. Post heat treatment is an effective way to improve mechanical properties but sometimes become infeasible or restricted due to various reasons. In this paper, by deliberately reducing the scanning speed to provide more energy than needed to melt the powder, heat accumulation in the deposited area is enhanced and an in-situ heat treatment is provoked. The strength of as-deposited clad layer is greatly enhanced (1290Mpa for ultimate tensile strength) by precipitation strengthening while maintaining good ductility. The possible influences of excessive heat on the HAZ are also evaluated. Experimental results show all the HAZ samples have a slightly lower strength compared to heat treated substrate. Excessive heat input does not deteriorate the strength of HAZ. On the contrary, the ductility of the material in HAZ is enhanced due to the effect of grain refinement and overage. In this way, the as-repaired parts can achieve a higher strength without heat treatment, which provides a new method for the repair of parts that cannot be subjected to post heat treatment.

Initiation and Role of Shear Crack on the Tensile Fracture Process in a Punch-Processed Precipitation-Hardened Steel Plate

Initiation and Role of Shear Crack on the Tensile Fracture Process in a Punch-Processed Precipitation-Hardened Steel Plate

Effect of manganese on the grain boundary network of lath martensite in precipitation hardenable stainless steels

The fully martensitic microstructures of a manganese bearing precipitation hardenable (PH) stainless steel and a commercial 17-4 PH steel were compared to investigate the influence of chemical composition on the grain boundary network of the lath martensitic microstructure. The martensitic transformation in both steels led to the bimodal misorientation angle distribution having multiple maxima at misorientations in the range of 10–15° and 50–60°. This closely matched with the misorientations between variants associated with the Kurdjumov-Sachs orientation relationship (K-S OR). However, the Mn addition appeared to relatively reduce the area of boundaries with misorientations near 60°. This was a result of the reduction in the area of 60°/[011] intervariant boundaries in the Mn bearing steel. The phenomenological theory of martensite revealed that the Mn addition altered the 3-variant clustering (i.e., V1V3V5) in 17-4PH steel to the 4-varaint clustering (i.e., V1V2V3V5) arrangement to minimize the strain associated with the displacive martensitic transformation, promoting the population of 60°/[111] intervariant boundaries at the expense of 60°/[011] intervariant boundary. The changes in local variant selection affected the connectivity of the grain boundary network, suggesting that grain boundary network characteristics (i.e., population and connectivity) of the lath martensite microstructure can be manipulated by altering the chemical composition of the steel. The five-parameter grain boundary analysis for both martensitic steels, however, revealed similar grain boundary plane distributions for all boundaries associated with the K-S OR, being terminated on {011} planes due to the constraint that results from the displacive phase transformation.

Effects of geometry, location, and direction on microstructure and mechanical properties of 15–5PH stainless steel fabricated by directed energy deposition

Laser-based directed energy deposition (DED) additive manufacturing (AM) was used to fabricate 15–5 precipitation-hardening (PH) stainless steel, and the geometry-dependent, location-dependent and direction-dependent microstructure as well as the mechanical properties of the resulting materials were investigated. Two different geometric components, deposition cuboid (DC) and deposition wall (DW) were fabricated, and the microstructure and mechanical properties of the samples were measured at different locations and in different directions. Finite element simulation was employed to interpret the thermal history of DED processing. The experimental and simulation results indicated that DED components presented different microstructure and mechanical properties in different geometries, directions, and locations, due to complex thermal history during DED processing. The use of post-heat treatment significantly decreased the amount of retained austenite, eliminated texture and resulted in homogeneous grain structure, leading to uniform mechanical properties. This study increases understanding of the microstructure characteristics and properties of AM PH steel.

Aluminum-alloyed lightweight stainless steels strengthened by B2-(Ni,Fe)Al precipitates

The age hardenability of Al-alloyed lightweight stainless steels with the base chemical composition Fe–10.5Cr–3Al (wt.%) and Ni concentrations in the range 3–15 wt.% was studied. Alloys containing 3% and 6%Ni exhibited almost fully ferritic matrix microstructures and a weak age hardening response. Alloys containing 9%, 12%, and 15%Ni, on the other hand, developed primarily martensitic microstructures. Differential scanning calorimetry measurements indicated the occurrence of an exothermic reaction in the approximate temperature range 375–625 °C. Dilatometry measurements indicated that the exothermic reaction was accompanied by a net contraction. Hardness measurements after aging for 5 min indicated significant hardening of alloys already at 350 °C due to the formation of B2-(Ni,Fe)Al intermetallic precipitates. The age hardening response was significantly superior to that of conventional precipitation-hardenable martensitic stainless steels. Tensile elongation in the aged condition was negatively influenced by the presence of soft ferrite regions. Processing conditions associated with a fully martensitic microstructure prior to aging are required to render a uniform age hardening response. Guidelines for the development of a new family of lightweight precipitation-hardenable steels with lower raw material costs and a higher corrosion resistance compared to the standard 18Ni maraging steels are provided.

Precipitation hardenable TiC-Steel cermets

Titanium carbide-stainless steel cermets exhibit a good combination of wear and corrosion resistance at ambient temperature. Stainless steel alloys have been applied in many industrial applications, with a variety of heat treatment procedures that can further improve performance. The current work studies the effects of heat treatments on a precipitation hardenable steel (grade 17–4 PH), in comparison with a non-heat treatable steel (316L), when used as the ductile binder phase in a cermet structure combined with TiC. Initial comparison was made for the two systems with 30 vol% of the steel phase in both cases. A significant increase in Vickers hardness was observed as a result of a 1150 °C/4 h heat treatment for this system. Moreover, the scratch resistance was significantly improved, with a scratch depth reduced from 1.74 to 0.8 μm under an applied load of 30 N. Based on this work, the feasibility of using a heat treatable binder phase is demonstrated for TiC-based cermets.

Influence of slide burnishing process on the surface characteristics of precipitation hardenable steel

The surface integrity of the material is the predominant necessity of a component to perform efficiently in varying working conditions. To improve the surface integrity of the workpiece secondary finishing processes are being performed. This work attempts to propose a realistic cryogenic slide burnishing condition for improvement of the surface integrity. The slide burnishing was performed by a novel slide burnishing tool on 17–4 precipitation hardenable stainless steel. The experiment was designed based on a central composite design. Initially, the effect of control parameters on the output response was examined by experimental analysis based on the design of experiment. Analysis of variance was used to analyze the influence of the variables on the performance indices. The regression technique was used to develop an empirical model. Optimization of process parameters for finding minimum surface roughness and maximum surface hardness was achieved by a multi-objective genetic algorithm. The optimized solutions were validated by performing confirmation experiments.

Evolution of the structure of precipitation-hardening steel during heat treatment

In order to identify the mechanism of the processes responsible for the formation of the properties of deposited steels of type 15N4M2D2G2AYuF and 20N4M2D2G2YuF, we studied the patterns of formation of their structure and phase composition as a result of heat treatment. The analysis of the results made it possible to recommend tempering at the temperature of 550 °C for two hours as the main mode of heat treatment of these steels. The development of the properties and structure of the deposited steel of the presented type is the result of multi-step interaction of several hardening mechanisms. The main role in the formation of the structure and properties is played by martensitic transformations, as well as solid-solution hardening by interstitial and substitutive atoms. At the first stage, the hardening is caused by the deposition of dispersed intermetallic compounds and carbides. In addition, dispersed particles of intermetallic phases are released at the early stages of aging and slow down the annihilation of dislocations in the matrix. With longer aging, carbides deposited at fixed dislocations contribute to hardening.

Effect of strain localization on fatigue properties of precipitation-hardened steel with an arbitrarily length crack

The present study deals with fatigue crack propagation and fatigue limit properties of two precipitation-hardened steels. One steel is more susceptible to strain localization than other. Both steels have similar tensile and micro-hardness properties. The fatigue properties are compared for a plain specimen, a specimen with a short crack and with a long crack. Effect of strain localization on fatigue properties of precipitation-hardened steel with an arbitrarily length crack is discussed with the help of plasticity-induced crack closure. The superiority of fatigue limit for precipitation-hardened steel depends on the initial crack size, and the strain localization influences notch sensitivity.