Compressive Residual Stress Field Research Articles

Crack failure behaviors of Ti–6Al–4V dovetail joints subjected to fretting fatigue and effect of laser shock dimple-textured surface coated with diamond-like carbon film

Fretting damage can lead to a reduction in fatigue strength by more than half, due to the increased stress on the fretting surface, which accelerates crack initiation and propagation. Laser shock peening (LSP) technology is an advanced method for protecting against fretting fatigue, which reduces the effective stress on the fretting surface of components by introducing a deeper compressive residual stress field. In this work, LSP was utilized to create regularly arranged dimples on the surface of titanium alloy dovetail joints, and followed by diamond-like carbon (DLC) coating to alter fretting friction. Five surface treatment samples including as-machined, conv-LSP, LSP dimple-textured, DLC, LSP dimple-textured + DLC, were prepared for fretting fatigue tests on dovetail joints. The experimental results showed that the fatigue performance of specimens treated with LSP dimple-textured + DLC is better. Furthermore, it is found that wear debris from fretting surface was discharged into crack source area during fretting fatigue, leading to the formation of a fracture debris area forms in the crack initiation zone. The crack initiation zone displays the protrusion morphology characteristics due to the friction effect induced by contact loads. There is an internal correlation between the size of fracture debris area and surface wear resistance. Fracture debris area and the protrusion morphology vary with surface treatments and applied load. This research further reveals that the variation characteristics of the crack initiation area including the fracture debris area, have a positive influence on observing and analyzing failure behavior of fretting fatigue damage.

Influence of double-side symmetric oblique laser shock peening on shape deviation, surface integrity, and fatigue properties of the blades in small-sized blisk

Double-sided symmetric oblique laser shock peening (DSOLSP) was adopted to experiment on a small-sized blisk with restricted space. The influences of different laser energies on the shape deviation, surface roughness, microhardness, and residual stress of the blades were studied. The optimum process parameters were selected based on the shape deviation results of the blades and the microstructural evolution of the surface layers was investigated. The strengthening effect of DSOLSP treatment on notched blades was evaluated by vibration fatigue tests. It was found that DSOLSP can effectively cover the fatigue vulnerable regions without interference. Two-way bending deformation was formed after DSOLSP, and the shape deviation of the blades could be controlled within ±0.02 mm. With the increase of laser energy, the surface roughness and the depth of work-hardened layer increased. The full-thickness compressive residual stress (CRS) field was induced. A gradient microstructure was generated on the surface of the blade, and the size of average nanograins on the topmost surface is approximately 36.5 nm. The fatigue strength of the DSOLSP treated blades with notches was increased by 25.9 %. The enhancement can be attributed to the synergistic strengthening of CRS and gradient microstructure.

Improvement of fatigue life of Ti-6Al-4V alloy treated by double-sided symmetric oblique laser shock peening

To improve the anti-foreign object damage (FOD) ability of Ti-6Al-4V alloy blisk blades, a blade simulation specimen was designed and subjected to double-sided symmetrical oblique laser shock peening (DSOLSP) treatment. Surface roughness, residual stress distribution, and microstructural evolution of simulated specimens of Ti-6Al-4V alloy without and with DSOLSP were investigated, and the strengthening effect was evaluated by flexural fatigue test. The results showed that after DSOLSP treatment, surface roughness of simulated specimens was reduced from Ra0.97 µm to Ra0.6 µm. DSOLSP treatment generated a compressive residual stress (CRS) field along the entire thickness direction of the simulated specimen. Nanostructures with a depth of ∼500 nm was observed at topmost surface layer, and the average size of the nanograins was about 35.2 nm. Compared with the base material, the flexural average fatigue life of the simulated specimen was increased by 8.45 times. Moreover, mathematical statistical analysis confirms that DSOLSP has a significant effect on the fatigue life of simulated samples. The development of CRS fields throughout the entire thickness direction, the grain refinement on the surface, and the reduction of surface roughness are primarily responsible for the enhancement of the flexural fatigue life of the DSOLSP simulated specimen.

Investigation on the damage mechanism of micro-cutting surface layer of aluminum alloy 7075 with different heat treatment processes

This paper investigates the machinability and microscopic surface damage mechanisms of aluminum alloy 7075 subjected to different heat treatment processes during micro-cutting. Focusing on T6 and T73 heat-treated aluminum alloy 7075, the study employs a combination of experiments and simulations to analyze micro-cutting surface morphology, cutting forces, microstructure evolution, residual stress, and damage characteristics. The findings reveal that micro-cutting of aluminum alloy 7075 after T6 heat treatment exhibits no apparent speed sensitivity in the primary cutting force, while T73 heat treatment demonstrates noticeable speed sensitivity. The surface microscopic damage during micro-cutting is influenced by both cutting speed and depth, resulting in distinct forms and degrees of damage under varying conditions. An analysis of the residual compressive stress field indicates that the magnitude of residual compressive stress on the micro-cutting surface determines crack initiation, and the maximum depth of residual compressive stress dictates crack propagation. Microscopic damage in T6 heat-treated aluminum alloy 7075 predominantly occurs in the second and third deformation zones, while T73 heat treatment leads to most damage in the third deformation zone. Notably, crack propagation is evident in T6 heat treatment at any cutting speed with a cutting depth of 150 μm, whereas it is inconspicuous in T73 heat treatment at cutting speeds below 540 m/min. Furthermore, at cutting speeds below 540 m/min and a cutting depth of 150 μm, T6 heat-treated micro-cutting is prone to oxidative wear. In contrast, at a cutting speed of 72 m/min and a cutting depth of 150 μm, the predominant wear form in T73 heat-treated micro-cutting is oxidation wear. This study underscores the intricate interplay between heat treatment processes, cutting conditions, and microscopic damage in aluminum alloy 7075 micro-cutting. The nuanced insights provided contribute to a deeper understanding of the machining characteristics of this alloy, paving the way for improved processing methodologies.

Strategy and mechanism to improve the fatigue properties of Ti6Al4V ELI alloy by microstructure modulation combined with surface strengthening process

The hot isostatic pressing (HIP) technique allows obtaining powder metallurgy Ti6Al4V parts with high densities, but its microstructure is not ideal, resulting in a lower fatigue life than expected. In this work, the ideal microstructure was obtained by heat treatment, but this process produces thermally induced porosity (TIP). After heat treatment, the fatigue strength of the bimodal Ti6Al4V alloy reached 680 MPa at 107 cycles, whereas the HIP Ti6Al4V alloy with a fully equiaxed microstructure was lower than 590 MPa. This is because the bimodal Ti6Al4V alloy has better resistance to fatigue crack initiation. This result confirmed that TIPs do not have a significant negative impact on fatigue properties. To further improve the fatigue performance, this study induced gradient nanostructured (GNS) in Ti6Al4V alloy by ultrasonic surface rolling process (USRP), and the fatigue strength of the USRP-treated specimen reached 750 MPa at 107 cycles. Combining microstructure observations and theoretical analysis, the surface hardening mechanism of the USRP-treated Ti6Al4V alloy was quantitatively described. The results showed that the plastic deformation layer is approximately 130 μm, but grain boundary strengthening maintained its effect to a depth of about 200 μm whilst dislocation strengthening maintained its effect to a depth of approximately 350 μm. Under the comprehensive effect of surface hardening and compressive residual stress field, the fatigue crack initiation period of the USRP specimen was significantly extended. This may be the primary reason behind the enhanced fatigue performance obtained through USRP treatment.

Effect of shot peening forming and shot peening strengthening post-treatment on the fatigue behavior of bolt-connected 2024HDT alloy

To improve surface integrity and suppress fretting fatigue of bolt-connected 2024HDT alloy plate-hole structure, the effect of shot peening forming (SPF) and shot peening strengthening (SPS) post-treatment on the surface integrity and fatigue behavior of 2024HDT alloy was investigated. The results showed that the SPF treatment increased the fretting fatigue resistance of the 2024HDT alloy plate-hole structure, and the failure mode changed from fretting fatigue to plain fatigue. The SPS post-treatment with three different intensities investigated here all improved the plain fatigue resistance of the SPF sample, whose failure mode also manifested as plain fatigue. This was due to the SPS treatment that flattened the surface of the SPF sample and introduced a compressive residual stress (CRS) field with a larger value and deeper distribution, while increasing the dislocation density and hardness of the SPF sample, which suppressed the initiation and propagation of fatigue cracks. SPS with a medium intensity produced an excellent surface CRS field with the lowest roughness and slightest surface damage, resulting in an improved plain fatigue resistance of 7.92%.

Evolution of cold-expanded microstructure with aging temperature and its influence on fatigue performance of hole structure at elevated temperature

A surface-strengthened layer formed by cold expansion (CX) evolves at high temperatures. The evolution of surface integrity and microstructure after a CX-treated superalloy GH4169 center hole plate was investigated in the present study. Aging at 400 ℃ and 600 ℃ took place with a duration of 500 h (CX400 and CX600). In addition, the fatigue properties at 820 MPa/600 ℃/R= 0.1 were investigated. The results show that CX has a smooth surface, a compressive residual stress field with a depth of more than 1.4 mm and a non-improved surface hardness. The statistical fatigue life of the as-received specimens was 7015 cycles, and the fatigue lives after CX and CX400 treatment were 5.27 and 2.86 times higher, respectively, indicating an increase by CX and a decrease by 400 ℃ aging. In contrast, the fatigue life of the original sample decreased to 5576 cycles with 600 ℃ aging, while the corresponding fatigue life of the CX600-treated sample was 7979 cycles, representing a significant decrease in both cases. The transformation of the main strengthening γ″ phase to the δ-phase upon aging at 600 ℃/500 h are the main reasons for the weakening of the fatigue properties, which did not occur upon aging at 400 ℃ (see TEM).

Effect of Repeated Processing Passes during Ultrasonic Rolling on Fatigue Performance and Corrosion Resistance of Ti6Al4V Alloy

Ultrasonic surface rolling processing (USRP) is a new method to improve the fatigue performance of titanium alloy, and repeated processing pass is an important factor that affects its strengthening effect. The effect of USRP passes on the surface microstructure, residual stress, fatigue performance and corrosion resistance of titanium alloy is researched via SEM, X-ray diffractometer, rotating–bending fatigue test and electrochemical impedance spectroscopy. The results show that Ti6Al4V alloy undergoes cumulative plastic deformation during USRP process, the surface grains are refined and a residual compressive stress field with a thickness of 500 μm is introduced, which together improve the fatigue performance of the Ti6Al4V alloy. Increasing the repeated processing passes will deepen the grain refinement layer and increase the surface hardening effect, but the fatigue life of the Ti6Al4V alloy does not increase with an increase in processing passes. A five-passes processing under a static force of 550 N can result in a greater gain for the fatigue resistance of the Ti6Al4V alloy; the fatigue life of a five-passes-processed sample under 600 MPa is 8 times higher than that of an untreated sample, and its fatigue crack source initiates at the subsurface away from the surface of 180 μm. Furthermore, Ti6Al4V alloys treated by USRP show a better corrosion resistance in both neutral and acidic solutions, especially for the five-passes-processed sample.

Fatigue crack growth prediction for shot-peened steel considering residual stress relaxation

The compressive residual stress field (CRSF) relaxes during the fatigue crack growth (FCG) process, and the pattern of this relaxation remains unclear. Residual stress (RS) relaxation leads to a change in residual stress intensity factor (RSIF), which significantly affects the fatigue crack growth rate (FCGR) and thus affects the assessment of fatigue crack growth rate. To this end, this work designed a series of experiments to explore the FCG behaviour in compressive residual stress fields (CRSFs) by considering RS relaxation. Firstly, shot peening(SP) treatments were conducted on the specimens. Then, residual stress fields (RSFs) at different crack propagation stages were measured to analyse the relationship between surface RS and inner RSF distribution. The derived weight function and the real-time RSF are combined to calculate the RSIF with/without considering RS relaxation. Finally, the effect of RS relaxation on the accuracy of FCGR assessment was investigated. The results show that the positive effect of CRS on the fatigue performance of the peened specimens is primarily embodied in the early stage of the FCG process. With the continuous relaxation of the CRSF, the difference in FCGR between the peened and unpeened specimens gradually decreases and tends to disappear. When the applied SIFs are large enough, the CRS would completely relax, and the inhibiting effect of CRSF on FCGR would fail. The proposed method in this work can effectively predict the FCGR of the peened specimen when considering the RS relaxation. This work could provide some meaningful insights for the assessment method of FCGR prediction in CRSF induced by surface strengthening treatment.

The effect of laser shock peening on very high cycle fatigue properties of laser welded 2A60 aluminum alloy joints

Laser shock peening (LSP) technology has the advantages of deep residual compressive stress field, low degree of cold hardening and controllable hardening area. The surface modification of welded structures has broad prospects. To predict the very high cycle fatigue (VHCF) life of an aero engine impeller, it is of great engineering significance to study the VHCF performance of 2A60 aluminum alloy. The effects of LSP on VHCF properties of laser welded joints were investigated from the S-N curve, fracture morphology, residual stress, hardness, and roughness. The results show that the S-N curves of the 2A60 aluminum alloy matrix under the condition of ethanol cooling belong to the infinite life type. The S-N curves of welded and LSP samples belong to the continuous decline type. In the process of LSP, the fatigue crack source is transferred from the surface of the sample to the second surface of the sample, which not only counteracts the residual tensile stress introduced on the surface of the sample during welding but also introduces considerable residual compressive stress on the surface of the sample. The roughness is reduced, thus improving the fatigue stsample's fatigue strength and life. The strengthening mechanism of LSP is discussed from two aspects of dislocation strengthening and residual stress. The LSP results in many dislocation proliferation within the grain, and the dislocation entanglement and dislocation wall are formed among the dislocations. The original coarse crystal is divided into multiple subgrains to achieve the effect of grain refinement. Grain refinement and high-density dislocation increase the hardness of the material.

Analytical model for predicting coverage in suspension waterjet shot peening and its influence on fatigue

Suspension waterjet peening is an emerging technology for surface modification. Coverage is a key factor affecting the integrity of a modified material surface, however such an experimental method that can be utilized for precise control has not yet been established. To determine the numerical value of coverage after surface peening treatment, In this paper, a coverage analytical method was proposed and then verified by the results through experiments. Furthermore, to explore the impact of high coverage on surface integrity, a large-scale coverage peening modification was performed on 18CrNiMo7-6 carburized steel specimens using a specialized suspension waterjet equipment. The results indicate that coverage has a significant impact on roughness and compressive residual stress field, with the highest improvement on surface and their maximum values reaching 51.6% and 24.7%, respectively. It is shown that the fatigue performance of the specimens can be significantly enhanced.

Fatigue life investigation of notched TC4 specimens subjected to different patterns of laser shock peening

The exhaustion of constructive ways for increasing the service life of parts has led to the development of new methods which can improve their material properties during operation under various loading conditions. Laser shock peening (LSP) induces compressive residual stress field which prevents fatigue crack initiation and propagation in components. Characteristics of laser impact and treatment patterns play an important role in efficiency of LSP application for improvement of fatigue properties. This work is devoted to the experimental examination of two LSP patterns to reveal the most optimal scheme from fatigue live improvement point of view. Proposed LSP pattern allowed one to increase the fatigue life of specimens with semi-circular notch by an order of magnitude. The numerical simulation of the LSP was performed to visualize the residual stress field of treated specimen after loading and to give the interpretation of the experimentally observed improvement of fatigue life.

Stress Field Simulation and its Experimental Verification of Carburizing-Quenching Process Performed on 18CrNiMo7-6 Steel

The carburizing and quenching process of 18CrNiMo7-6 steel was performed through simulation methods and experiments. The study was carried out to accurately predict the residual stress distribution of carburized samples after the quenching process. The stress and retained-austenite amount were measured via X-ray diffraction. Similarly, the carbon content was determined using a carbon sulfur analyzer, respectively. A detailed model with the coupling of thermal, metallic, and mechanical fields was built to predict the evolution of the stress field during the quenching process. The carburized “thoroughly” specimens at different carbon potentials were used to obtain the required mechanical property parameters and dilatometric parameters for FEM simulation. According to the results, the martensite transformation kinetic parameters α value of 18CrNiMo7-6 alloy steel should be 0.0202. With the increase of carbon content, the changing trend of the transformation plasticity coefficient K appeared as a 'tick' shape. A compressive residual stress field was generated at the carburized layer surface after the quenching process, and the maximum value of 340 MPa occurred at ~ 0.9 mm below the surface. The carbon profile and residual stress fields predicted from the FEM simulation corresponded closely to the experimentally determined results.

Surface layer characterization of 2205 duplex stainless steel subjected to abrasive water jet descaling

Abrasive water jet (AWJ) is an environmentally friendly and acid-free descaling technology, that has the added benefit of strengthening the material surface. However, the effects of AWJ descaling on the surface layer of heterostructured (HS) materials and the application of deformable abrasives involving high cycle times for AWJ descaling have not been extensively reported. In this study, martensitic stainless steel particles with high cycle times were subjected to AWJ descaling to investigate the effect of AWJ on the surface layer characterization of 2205 duplex stainless steel (DSS). The properties of the 2205 DSS surface layer were characterized by the surface morphology, surface roughness, microstructure, and microhardness. When exposed to an AWJ intensity of 0.245 mmA, the surface of 2205 DSS exhibited the formation of extrusion craters and flat debris. Additionally, the surface roughness Ra was measured at 3.778 µm. The gradient hardening layer was formed on the surface of the AWJ specimen, and the depth of the hardening layer was 550 µm. The maximum microhardness was 395 HV, which is approximately 30% higher than that of the original specimen. Within the AWJ specimens, dislocation networks were observed in the ferrite, while the austenite exhibited dislocation cells, deformation twins, and strain-induced martensite. Furthermore, the experimental results indicate that plastic deformation was unevenly distributed between the two phases, with the majority of deformation occurring within the austenite phase. Owing to the requirement of deformation compatibility, several of geometrically necessary dislocations (GNDs) accumulated near the austenitic phase boundary to regulate the plastic strain gradient, and the hetero-deformation induced (HDI) stress generated by these dislocations strengthens the austenite. The AWJ refines the surface material structure; increases the density of dislocations, phase boundaries, and stacking faults; forms strain-induced martensite; and introduces a residual compressive stress field, which improves the material surface hardness.

Influence of laser shock peening on microstructure and property of Ni60 cladding layer and the combined area of 20CrNiMo alloy

The effects of laser shock peening (LSP) on the microhardness, residual stress, and microstructure of the Ni60 cladding layer and the combined area of the 20CrNiMo alloy for high-speed rail brake disks are investigated to address the problem of coarse columnar crystals and residual tensile stress, which affect the coating–substrate bonding performance and the application development of the laser cladding repair process. The results indicate that LSP can improve the microhardness, prefabricate residual compressive stress field, and refine the microstructure of the cladding layer and the combined area. The surface hardness of the cladding layer increased by 14.55%, 34.92%, and 40.21% after the energy impact of 6, 9, and 12 J, with an impact depth of about 1.2, 2.2, and 2.5 mm, respectively. The roughness result showed that the effect is more satisfactory under the 9 J energy impact. The grain refinement is significant compared to the Clad specimen, with the average grain area at the molten layer's top, middle, and bottom reduced by 35.5%, 79.6%, and 85.8%, respectively. A residual compressive stress of −538 MPa is introduced on the surface of the clad layer, with a compressive stress value of −30 MPa at a depth of 2 mm. After the LSP, the microstructure and properties of the clad layer and the combined area are significantly improved. Still, no new phases appear and do not significantly affect the diffusion of elements between the dendrites and the dendrites.

Nanostructure evolution of reticular nano-TiB whiskers reinforced titanium matrix composite subjected to ultrasonic shot peening

Titanium matrix composites (TMCs) have drawn widespread attention because of their superior mechanical properties. In this study, nano-TiB whiskers reinforced TMC was fabricated using a direct laser deposition technique and then subjected to ultrasonic shot peening (USP) for different durations. The microstructure characterization results indicated that the surface grain refinement of αTi was dominated by complicated dislocation motion. The primary grain refinement mode during the microstructure evolution was the transverse splitting of the elongated lamellae. By interacting with dislocations, the TiB whiskers facilitated the evolution of nanostructures. After USP treatment, TiBw exhibited obvious fractures, but the TiB-Ti interface remained sharp and clear, showing excellent interfacial properties. The use of USP resulted in a significant compressive residual stress field, which increased with peening time. Surface hardness also increased as a result of fine grain and strain strengthening. When compared to the initial sample, the maximum microhardness of the sample after USP treatment increased by 48%.

Fluid End Blocks: Numerical Analysis of Autofrettage and Reautofrettage Based Upon a True Material Model

AbstractFluid end blocks (FEBs) are the most important components of hydraulic fracturing pumps. A potential important application of the hydraulic autofrettage process (HAP) is to strengthen the fatigue-prone FEBs. This creates a favorable compressive residual stress field near to the critical surface locations within the component and serves to increase its pressure-bearing capacity and/or improve lifetime. This requires a fundamental understanding and modeling of the complex mechanics of the HAP in order to accurately predict such residual stresses. The key outstanding modeling issue is the complex material behavior, dominated by the Bauschinger effect and associated with reversed yielding. This effect differs throughout the FEB. It has been modeled for plane axisymmetric cylinders but has not previously been incorporated into FEB analyses. In this paper, a newly developed finite element analysis (FEA)-based user programable function (UPF), featuring true material constitutive behavior, i.e., replicating an existing Bauschinger-effect characterization (BEC), is adopted to accurately simulate the HAP and quantitatively investigate the stress–strain evolution and residual stress fields throughout the FEB. This simulation is then compared with FEA modeling by a traditional bilinear kinematic hardening material model to indicate the importance of the accuracy of the material constitutive model in determining appropriate residual stresses and strains. An autofrettage pressure of 500 MPa generally achieves net compressive hoop stresses at each of four critical crossbore location. Finally, a prospective re-autofrettage sequence is described; approximate modeling suggests an improvement that might permit operation at higher working pressure.

Ironing effect on surface integrity and fatigue behavior during ultrasonic peening drilling of Ti-6Al-4V

Imposing compressive residual stress field around a fastening hole serves as a universal method to enhance the hole fatigue strength in the aircraft assembly filed. Ultrasonic Peening Drilling (UPD) is a recently proposed hybrid hole making process, which can achieve an integration of strengthening and precision-machining with a one-shot-drilling operation. Due to the ironing effect of tool flank surface, UPD introduces large compressive residual stress filed in hole subsurface. In order to reveal the strengthening mechanism of UPD, the influence of ultrasonic vibration and tool dynamic relief angle on ironing coverage rate and its corresponding effect on surface integrity in UPD were analyzed. The experiments were conducted to verify the influence of ironing effect on surface integrity and fatigue behavior of Ti-6Al-4V hole in UPD. The results indicate that the specimen features smaller surface roughness, higher micro-hardness, plastic deformation degree and circumferential compress residual stress under higher ironing coverage rate. The fatigue life increases with the raise of ironing coverage rate, and the fatigue source site in UPD shifts from surface to subsurface comparing with that without vibration assistance. The results demonstrates that a better strengthening effect can be obtained by reasonably controlling the ironing coverage rate in UPD.

Surface Mechanical Properties and Micro-Structure Evolution of 7075 Aluminum Alloy Sheet for 2-Dimension Ellipse Ultrasonic Vibration Incremental Forming: A Pretreatment for Laser Shock Peening

In this paper, a composite technique of ultrasonic incremental forming and laser shock peeing is proposed. The former process is mainly used for the manufacturing of complex-shaped sheet and strengthening coating that is prepared for subsequent laser treatment. The latter is applied for secondary surface reinforcement with ultra-high energy. This work focused on the novel ultrasonic incremental forming method and its effects on surface mechanical properties and micro-structure of a 7075 aluminum alloy. First, a kind of 2-dimension ellipse ultrasonic vibration incremental forming process and the unique double-mechanism method of sectionalized cooperative control of plastic deformation and mechanical performance were designed. Second, the single-point incremental forming, the longitudinal ultrasonic vibration incremental forming, and the 2 dimension ellipse ultrasonic vibration incremental forming were performed for the manufacture of conical components of 7075 aluminum alloy. Third, the Vickers micro-hardness testing results and images of the fracture morphology of the machined part for the novel technique confirm that softening mechanisms become dominant inside the metal sheet. Furthermore, a strengthening coating with excellent mechanical properties and a residual compressive stress field were created on its surface simultaneously. In a word, the research shows potential values of the proposed technique for the manufacture of aircraft panels of complex shape and excellent surface properties.

Numerical modeling considering initial gradient mechanical properties and experiment verification of residual stress distribution evolution of 12Cr2Ni4A steel generated by ultrasonic surface rolling

Ultrasonic surface rolling process is a promising surface strengthening technique which can improve the fatigue performance of metallic components by introducing reasonably compressive residual stress field. It is of great significance to accurately predict the residual stress distribution of parts in the simulation of ultrasonic surface rolling process. In this paper, a numerical model considering initial gradient mechanical properties (residual stress and micro-hardness) is proposed to predict the residual stress distribution of 12Cr2Ni4A carburized and quenched steel. Moreover, a method is proposed to calculate the ultrasonic surface rolling coverage based on Hertz contact theory, which can guide the optimization of process parameters. The effects of static load, rolling tool radius, amplitude and feed rate on residual stress distribution are investigated. The simulated results and measured results are compared and proved to be in good agreement, which validates the accuracy of the model proposed in this paper.