Zhichao Li

Modeling the Effect of Carburization and Quenching on the Development of Residual Stresses and Bending Fatigue Resistance of Steel Gears

Zhichao Li, and Andrew M. Freborg, Deformation Control Technology, Inc, 7261 Engle Road, Suite 105, Cleveland, OH 44130; Bruce D. Hansen, Sikorsky Aircraft Corporation, 6900 Main Street, Stratford, CT 06615; and T.S. Srivatsan, Division of Materials Science and Engineering, Department of Mechanical Engineering, The University of Akron, Akron, OH 44325. Contact e-mails: zli@ DeformationControl.com, Andy.freborg@deformationcontrol.com, bruce.hansen@sikorsky.com, and tsrivatsan@uakron.edu. JMEPEG (2013) 22:1208 ASM International DOI: 10.1007/s11665-012-0350-9 1059-9495/

Local Film Boiling and Its Impact on Distortion of Spur Gears During Batch Quenching

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Optimization of an Induction Hardening Process for a Steel Gear Component

The paper discusses results of computer simulation connected with the double distortion during batch quenching of spur gears caused by a local film boiling between teeth. A carburized gear, outside diameter 2.5 in., was intensively quenched in conditions that provided heat transfer coefficient (HTC) equal to 25 000 Wm−2K−1. In some places between teeth local film boiling took place where HTC was 800 Wm−2K−1. Computer simulation showed that maximum displacement is observed between teeth where local film boiling took place. The authors came to the conclusion that increasing critical heat flux densities and elimination of local film boiling can result in decreasing distortion of spur gear. That is true for different sizes of gear during their quenching when using the second type of intensive quenching process (IQ-2) technique (a two or three-step quenching process). It is underlined that critical heat flux densities have a great effect on distortion during batch quenching. The authors also came to the conclusion that a small amount of special additives can decrease significantly distortion during quenching of gears. That is why a global database on cooling capacity of quenchants should be available which must contain critical heat flux densities of different kinds of quenchants.

Induction Hardening Process With Preheat to Eliminate Cracking and Improve Quality of a Large Part With Various Wall Thickness

Computer simulation of heat treatment processes has improved significantly over the past two decades, relating to both the material models and the database accuracy. Simulations are being used more aggressively in part and process design rather than just as a trouble shooting agent, meaning heat treat simulation is maturing as an accepted technology. In this paper, an induction heating and spray quenching process of a steel gear is optimized using the commercial heat treatment software DANTE. As a hardening process, induction hardening of steel parts is gaining popularity due to: (1) the process is consistent on a part-to-part basis, making it easier for quality control; (2) the process is more environmentally friendly than oil or polymer immersion quenching because a water spray is the typical cooling agent; and (3) fatigue life can be improved due to higher and deeper residual compression in the hardened surface. Two steel grades, AISI 5120 and AISI 5130, may be used in a thin-walled spur gear. The simplified heat treatment process includes vacuum carburization, controlled cooling to ambient, induction heating, and spray quenching. During induction heating, the internal heat generated by eddy currents is used as direct input to drive the thermal model. A sensitivity based optimization method is combined with heat treatment simulation to optimize the delay and spray quenching practice after induction heating. The objective function is defined to minimize the distortion of the gear tooth while satisfying the residual stress, gear surface temperature, and final microstructure requirements. The results of a two-dimensional (2D) plane strain single tooth model are evaluated during the optimization process, the quenching practice variables are adjusted, and the quenching model is re-run until the optimization function is satisfied. The residual stresses predicted after induction hardening are then mapped to a three-dimensional (3D) whole gear model as the initial stress state of a tooth loading model for predicting gear stresses. The significant effect on fatigue behavior due to residual stresses from heat treatment is addressed.

Investigating a Die Quench Cracking Problem in 52100 Steel Bearing Rings With Computer Simulation

During an induction hardening process, the electromagnetic field generated by the inductor creates eddy currents that heat a surface layer of the part, followed by spray quenching to convert the austenitized layer to martensite. The critical process parameters include the power and frequency of the inductor, the heating time, the quench delay time, the quench rate, and the quench time, etc. These parameters may significantly affect case depth, hardness, distortion, residual stresses, and cracking possibility. Compared to a traditional hardening process, induction hardening has the advantages of low energy consumption, better process consistency, clean environment, low distortion and formation of beneficial residual stresses. However, the temperature gradient in the part during induction hardening is steep due to the faster heating rate of the surface and the aggressive spray quench rate, which leads to a high phase transformation gradient and high magnitude of internal stresses. Quench cracks and high magnitude of residual stresses are more common in induction hardened parts than those of conventional quench hardening processes. In this study, a scanning induction hardening process of a large part made of AISI 4340 with varying wall thickness is modeled using DANTE. The modeling results have successfully shown the cause of cracking. Based on the modeling results, a preheat method is proposed prior to induction heating to reduce the in-process stresses and eliminate the cracking possibility. This process modification not only reduces the magnitude of the in-process tensile stress, but also converts the surface residual stresses from tension to compression at the critical inner corner of the part, which improves the service life of the part. The modified process has been successfully validated by modeling and implemented in the heat treating plant. INTRODUCTION During an induction hardening process, the part surface is heated using a medium or high frequency inductor. Once the desired depth of surface layer is austenitized, the part is spray quenched to convert the austenite layer to martensite. Compared to traditional furnace heating and liquid quenching processes, the induction hardening is more energy efficient because the heating time is short, and only the part surface is heated and austenitized. With the nonuniform temperature distribution in the part after heating, induction hardening also gives more options for part optimization such as improved case depth and beneficial residual stress distribution [1-3]. When austenite transforms to martensite, the material volume expands. During induction hardening, the core of the part doesn’t transform to austenite, and the martensite transformation of the austenitized layer leads to compressive residual stresses in the surface. The compressive stresses have proven to be beneficial for both fatigue performance and wear resistance [4-6]. Stress evolution during steel heat treatment is a highly nonlinear process due to the phase transformations that occur. With phase transformations, the thermal and mechanical properties change, the material volume changes, the internal stresses within individual phases change, and the stresses between different phases also change. Simulation of heat treatment stresses and deformation is an emerging technology. Besides the variety and complexity of simulation algorithms, stress simulation requires large, accurate databases of thermal, metallurgical and mechanical properties of material phases over the entire range of temperatures experienced during processing. Induction hardening is a transient thermal process. During induction hardening of steel components, the temperature gradient and phase transformations both contribute to the evolution of the internal stresses and part dimensional change. With induction hardening, the temperature difference between Proceedings of the ASME 2017 12th International Manufacturing Science and Engineering Conference MSEC2017 June 4-8, 2017, Los Angeles, CA, USA

Effect of Preheat on Improving Beneficial Surface Residual Stresses During Induction Hardening Process

Quenching using a press with controlled die loads, commonly referred to as press quenching, is a specialized technique used to minimize distortion of critical components such as gears and high quality bearing races. Improper press load magnitudes or timing of the load application may restrict part movement during quenching to the point of imposing stresses that cause cracking, especially in a common bearing steel such as AISI 52100, high carbon, high strength steel. This paper applies a finite element based heat treat simulation tool, DANTE, to investigate the sensitivity of cracking to press quenching process parameters. The typical method for designing a press quench process to control flatness, out-of-round, and taper is by experience coupled with trial-and-error. This is accomplished by adjusting oil flow rates, flow directions, die loads, and the timing of die loads. Metallurgical phase transformations occur during the quenching process as austenite transforms to martensite and possibly to diffusive phases. Thermal contraction due to cooling and volumetric expansion due to the phase changes therefore occur simultaneously during the heat treating process. A constantly changing stress state is present in the part, and improperly applied die loads, oil flow or oil flow rate can add additional stress to result in cracking. An inconsistent cracking problem in an AISI 52100 bearing ring was evaluated using production trials, but the process statistics were not conclusive in identifying the source of the problem. Heat treatment process modeling using DANTE was used to investigate the effects of quench rate, die load pulsing, and several other process variables to determine how these parameters impact the resulting stresses generated during the press quenching operation.

Characterizing Water Quenching Systems with a Quench Probe

Applications of the induction hardening process have been gradually increasing in the heat treatment industry due to its energy efficiency, process consistency, and clean environment. Compared to traditional furnace heating and liquid quenching processes, induction hardening is more flexible in terms of process control, and it can offer improved part quality. The commonly modified parameters for the process include the inductor power and frequency, heating time, spray quench delay and quench severity, etc. In this study, a single shot induction hardening process of a cylindrical component made of AISI 4340 is modeled using DANTE. It is known that the residual stresses in a hardened steel component have a significant effect on high cycle fatigue performance, with higher magnitudes of surface residual compression leading to improved high cycle fatigue life. Induction hardening of steel components produces surface residual compression due to the martensitic transformation of the hardened surface layer, with a high magnitude of compression preferred for improved performance in general. In this paper, a preheat concept is proposed with the induction hardening process for enhanced surface residual compression in the hardened case. Preheating can be implemented using either furnace or low power induction heating, and both processes are modeled using DANTE to demonstrate its effectiveness. With the help of computer modeling, the reasons for the development of residual stresses in an induction hardened part are described, and how the preheat can be used to improve the magnitude of surface residual compression is explained. INTRODUCTION The induction hardening process is more energy efficient because only the component surface is heated and austenitized, as compared with furnace heating and liquid quenching processes where the process is applied to the entire part crosssection. Induction hardening also gives more options for process optimization for improved case depth and residual stress distribution relative to traditional furnace heating and liquid quenching processes [1-3]. Induction hardening processes generate compressive stresses in the hardened case, especially in outer part surfaces, and the compressive stresses have proven to be beneficial for both fatigue performance and wear resistance [4-5]. Stress evolution during steel heat treatment is a highly nonlinear process due to the phase transformations that occur. With phase transformations, the thermal and mechanical properties change, the material volume changes, the internal stresses within individual phases change, and the stresses between different phases also change. Simulation of stresses and deformation is an emerging technology. Besides the variety and complexity of simulation algorithms, stress simulation requires large databases of thermal, metallurgical and mechanical properties of material phases over the entire range of temperatures used during processing. Both the power and frequency of the inductor have a significant effect on the heat penetration into the part. Lower frequency tends to heat the the part deeper over a longer time duration because the eddy current gradient in the part surface is relatively low. Conversely, a higher frequency heats the shallower surface layer of the part in a shorter time. The temperature distribution in the part is a combined result of both the thermal conduction and induction heating. In some induction hardening processes, both low/medium frequency and high frequency are used together to reach the desired temperature field. Simultaneous dual fequency (SDF) induction Proceedings of the ASME 2016 International Manufacturing Science and Engineering Conference MSEC2016 June 27-July 1, 2016, Blacksburg, Virginia, USA

Enhanced Surface Residual Compression of Carburized Steel Parts Using Laser Peening Process With Preload

Quench probes have been used effectively to characterize the quality of quenchants for many years. For this purpose, a variety of commercial probes, as well as the necessary data acquisition system for determining the time-temperature data for a set of standardized test conditions, are available for purchase. The type of information obtained from such probes provides a good basis for comparing media, characterizing general cooling capabilities, and checking media condition over time. However, these data do not adequately characterize the actual production quenching process in terms of heat transfer behavior in many cases, especially when high temperature gradients are present. Faced with the need to characterize water quenching practices, including conventional and intensive practices, a quench probe was developed. This paper describes that probe, the data collection system, the data gathered for both intensive quenching and conventional water quenching, and the heat transfer coefficients determined for these processes. Process sensitivities are investigated and highlight some intricacies of quenching.

Phase Transformation Affected Quench Crack Study Using Finite Element Analysis

Residual stresses are critical to the fatigue performance of parts. In general, compressive residual stress in the surface is beneficial, and residual tension is detrimental because of the effect of stress on crack initiation and propagation. Carburization and quench hardening create compressive residual stresses in the surface of steel parts. The laser peening process has been successfully used to introduce residual compression to the surface of nonferrous alloy parts. However, the application on carburized steel parts has not been successful so far. The application of laser peening on carburized steel parts is limited due to two main reasons: 1) the high strength and low ductility of carburized case, and 2) the compressive residual stresses in the surface of the part prior to laser peening. In this paper, the carburization, quench hardening, and laser peening processes are integrated using finite element modeling. The predicted residual stresses from quench hardening and laser peening are validated against residual stresses determined from X-ray diffraction measurements. An innovative concept of laser peening with preload has been invented to enhance the residual compression in a specific region of laser peened parts. This concept is proved by FEA models using DANTE-LP.Copyright

Effect of Quenching Rate on Distortion and Residual Stresses During Induction Hardening of a Full-Float Truck Axle Shaft

Steel components are commonly heat treated to obtain favorable mechanical properties for enhanced performance. Quench hardening is one of the most important heat treatment processes to increase hardness and strength. During quenching, both thermal gradients and phase transformations contribute to the evolution of internal stresses. Higher tensile stresses in a part during quenching tend to increase the cracking possibility, which is more problematic for components with various section sizes due to stress concentration. Heat treaters believe that cracking possibility increases with larger difference of section size in a part. This is only true in some cases. If the section size difference exceeds a threshold, the cracking possibility will decrease. Due to the complex part’s responses to thermal gradient, phase transformation and unbalanced geometry, there is no robust and simple rule to characterize the cracking possibility. With the development of more advanced heat treatment computer modeling capability, the material’s response during heat treatment can be more intuitively understood. The part geometry and heat treatment process can be designed with much less potential heat treatment defects. In this paper, finite element based heat treatment software, DANTE, is used to investigate the relationship between section size difference and cracking possibility by using parts with a series of section size ratios. In this specific study, the selected part is a plain strain component made of AISI 9310. The results during oil quench process have shown that a section size ratio of 1:2 creates the highest stress concentration and cracking possibility.Copyright