An extensive experimental study has been conducted to validate the intensive ... layer, improved strength properties of the steel parts, and the use of a less ...
Proceedings of 18th ASM Heat Treating Society Conference, Chicago, 1998 EXPERIMENTAL VALIDATION OF THE INTENSIVE QUENCHING TECHNOLOGY FOR STEEL PARTS Michael A. Aronov AGAResearch, a Division of Energy International, Inc., Cleveland, Ohio Nikolay I. Kobasko Institute of Thermal Science and Engineering, Kiev, Ukraine Joseph A. Powell Akron Steel Treating Co., Akron, Ohio David Schwam and John F. Wallace Case Western Reserve University, Cleveland, Ohio
Abstract An extensive experimental study has been conducted to validate the intensive quenching process for steel parts developed by Dr. Kobasko. Experiments were performed with three different steel parts supplied by Akron Steel Treating Co. of Akron, Ohio and Queen City Steel Treating Co. of Cincinnati, Ohio. These parts are: sprockets, sockets, and socket adapters. An experimental intensive quenching system was developed and constructed. The system was installed at Akron Steel Treating Co.’s laboratory facility. Thirty-one experiments were conducted. The results of these experiments clearly demonstrated the benefits of the intensive quenching methods of steel: increased surface hardness and hardened layer, improved strength properties of the steel parts, and the use of a less expensive, less hazardous, environmentally friendly quenchant (water or polymer/water solution instead of oil).
widely introducing the intensive quenching methods to American market. Two heat treating plants (Akron Steel Treating Co. of Akron, Ohio and Queen City Steel Treating Co. of Cincinnati, Ohio) have provided the following steel parts for intensive quenching: sockets, socket adapters, and five-tooth sprockets. To validate the benefits of the intensive quenching technology, we performed an intensive experimental study at the Akron Steel Treating Co. laboratory facility. This facility has several quench and tempering furnaces. We added to this facility a unique quenching system developed by AGAResearch. The quenching system allows steel parts of different shapes to cool rapidly with a controlled cooling rate in various types of quenchants. After quenching, the parts were subjected to a detailed metallurgical analysis. To optimize the experimental program, we used experimental and computational data obtained by Dr. Kobasko in his previous studies for the similar steel parts.
Introduction
Experimental Intensive Quenching System
The objective of this study was to validate experimentally the intensive quenching technology for steel parts developed by Dr. Nikolay Kobasko. This technology significantly improves the current methods of steel hardening relative to the quality of the finished product and the overall cost of heat treatment. The intensive quenching process provides the following benefits: increased part hardness and hardened layers, improved steel mechanical properties, the use of the less alloyed steel and the use of the less costly, environmental friendly quenchants (water or polymer/water solutions instead of oil). A detailed description of the intensive quenching technology can be found in many of Dr. Kobasko’s papers (for example, References 1 and 2) and in the Heat Treating Handbook (Reference 3). The intensive quenching process is currently used in several plants in Russia, Ukraine, Bulgaria, and China. The Edison Material Technology Center of Ohio has funded this demonstration study with the purpose of
To implement the intensive quenching process, it is necessary to provide extremely high heat transfer on the parts’ surface. A preliminary analysis showed that the proper heat transfer can be achieved by the use of water or a polymer/water solution instead of oil and by providing a high velocity of the quenchant around the steel part (about 2 m/sec). We considered two design options of the experimental quenching system. In the first design, a centrifugal pump moves the quenchant, whereas in the second design an impeller moves the quenchant. We decided to use the second design approach for the quenching system since it is less costly and is widely used in the industry to agitate the quenchant in the existing quench tanks. Figure 1 presents a sketch of the experimental intensive quenching system developed. The quenching system consists of a tank filled with a quenchant and an immersed “U”-type steel tube. A Lightning Co. marine impeller equipped with a variable speed motor moves the quenchant through the “U”
tube. The motor is able to provide up to 500 rpm. Quenching of the steel part takes place in a vertical (loading) section of the “U” tube. After being heated in the quenching furnace, the steel part is manually placed on a tray. The tray then slides down quickly along the guide bars into the loading section of the “U” tube. The tray is kept in this position until the quenching process is completed.
Guide Bars
Steel Part
56
Tray
13
Baffles
Figure 2.
Results of the Measurements Conducted by the Vane-type Anemometer in ft/sec
Experimental Results 59
Figure 1.
Experimental Intensive Quenching System
We tested the experimental quenching system at AGAR facilities prior to its shipment to Akron Steel Treating Co. We filled the quenching system with water. We measured the water flow velocity for different impeller speeds: 200, 300, 400 and 500 rpm. We used two types of devices for the flow velocity measurements: a standard Pito tube manufactured by United Sensor Co. and a vane-type anemometer manufactured by ERDCO Engineering Corp. Figure 2 presents the results of the measurements conducted by the vane-type anemometer. As seen from the figure, the velocity distribution across the tube is quite uniform (10-15% from the average value) except for the relatively small region at the inner part of the tube cross section. The average flow velocity at 500 rpm was about 1 m/sec instead of the expected velocity of 2 m/sec. Nevertheless, we decided to use the quenching system for the further experimental study realizing that we would not be able to obtain the optimum quenching conditions for steel parts.
Five-tooth Sprockets Five-tooth sprockets were supplied by Queen City Steel Treating Co. Figure 3 shows a sketch of this steel part. Sprockets are a part of mining machinery. They are made of steel 86B30 and require high surface hardness. The current sprocket quenching process consists of the following steps: Heating of sprockets up to 885°C (1625°F) in the furnace with the protective atmosphere (endothermic with carbon control) Soaking for 30 min. after parts are heated up to 885°C (1625°F) Quenching in oil Tempering at 232°C (450°F) for 2 hr. According to the current practice, the sprocket surface hardness after quenching in oil is in the range from 46–50 Rockwell C units (HRC). The hardened depth is about 2–3 mm. In all tests, we maintained the above heating conditions for quenching and tempering. We cooled the steel parts in the flowing water and 5% polymer/water solution (UCON “E”). The quenchant flow velocity was about 1 m/sec. The quenchant temperature was in the range of 27°C–30°C (81°F–86°F). We have conducted a total of 20 experiments with sprockets. Twelve sprockets were intensively quenched in water and four sprockets were quenched in 5% polymer/water solution. The customer anticipated the following benefits from the intensive
quenching: no surface cracks, increased surface hardness and hardened depth. 1/8 x 45 (TYP.) 1" R. (TYP.)
B
1 - 9/32
5/16 @ 45 BOTH SIDES D
SECTION D - D
D 9 - 9/16 O.D.
1/8 R.
3/64
C 3/16
C
the maximum hardness variation of 4 HRC. Thus, the sprocket hardness increased due to the intensive quenching process by 4 HRC (52 HRC vs. 48 HRC) when parts were quenched in water and by 2 HRC when parts were quenched in the polymer/water solution. Micro-hardness measurements taken on two sprockets that were sectioned showed that the sprocket teeth were quenched uniformly throughout the cross section after intensive quenching: 53 HRC0.5 HRC and 52 HRC1.0 HRC. This is in contrast to the current practice that yields a declining hardness distribution from the surface to the part core. Socket and Socket Adapter Test Results Sockets and socket adapters were supplied by Akron Steel Treating Co. Figure 4 shows sketches of these steel parts.
SECTION C - C
A
Figure 3.
Five-tooth Sprockets
11/16
Table 1 shows the experimental results. The sprockets were examined for cracking with a die penetrant. No visible cracks were detected inside the two parts that were sectioned for depth hardness measurements. A stress analysis showed that there were practically no residual stresses on the sprocket surface after tempering. It is important to note that it’s possible to reach the compressive stresses on the sprocket surface by providing more intensive heat transfer during quenching. These compressive stresses will increase the part lifetime. Table 1. Test No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
3/8 sq.
5/16 1
A
Five-tooth Sprocket Test Results Quenchant Type Temp., °C (°F) 28 (82) 28 (82) 28 (82) 28 (82) 28 (82) 28 (82) Water 29 (84) 29 (84) 30 (86) 30 (86) 31 (88) 31 (88) 28 (82) 28 (82) 28 (82) 5% Polymer 28 (82) 28 (82) 28 (82) 28 (82) 28 (82)
A
Hardness HRC 50.9; 50.2; 50.3 53.2; 53.2; 53.2 51.6; 52.1; 53.7 51.6; 52.8; 52.6 50.3; 51.3; 50.9 49.2; 48.6; 48.4 48.8; 49.3; 49.3 51.7; 52.3; 52
The average surface hardness for parts quenched in water was 52 HRC with the maximum hardness variation throughout the part surface of 2.1 HRC (see Test No. 10). The average surface hardness for parts quenched in the polymer/water solution was 50 HRC with the maximum hardness variation throughout the part surface at 0.8 HRC. According to the current practice, the average sprocket hardness is about 48 HRC with
A
A
.687 .378 sq. 7/8
.446
15/32
B Figure 4.
Socket Adapter (A) and Socket (B)
The sockets are made of steel 4140, and the socket adapters are made of steel 4042. The current quenching process for these parts consists of the following steps: Heating parts up to 832°C (1530°F) in the furnace with an endothermic protective atmosphere Soaking for 15 min. Quenching in oil Tempering at 471°C (880°F) for 3 hr. In all tests, we maintained the above heating conditions for quenching and tempering. We cooled the steel parts in the flowing
water. The quenchant flow velocity was about 1 m/sec. The water temperature was about 23°C (73°F) in all experiments. We have conducted a total of 11 experiments with sockets and socket adapters. Six sockets and five socket adapters were intensively quenched in water. The customer’s major anticipation was an absence of surface cracks and an increased value of the torque-to-failure. No cracks were visible on the steel part surface in the experiments. After quenching, we subjected the steel parts to the torque-to-failure test. This test was conducted by Cornwell Quality Tools Co. of Cleveland, Ohio. Table 2 presents the test results. As seen from the table, the socket average value of the torque-to-failure obtained after intensive quenching was 32% greater than after quenching in oil (the current practice) whereas the part surface hardness practically did not change. The significant improvement in the part mechanical properties is mainly due to the increase of the hardened depth in the steel parts that were intensively quenched. For socket adapters, there was only a slight increase in the torque-to-failure value after intensive quenching. We obtained similar results for quenching the sockets in flowing polymer/water solution UCON “E”. However, in this case the value of the torque-to-failure increased by 28% compared with quenching in oil. Table 2. Part Type
Socket
Socket Adapter
Socket
Socket Adapter
Socket and Socket Adapter Test Results Test No.
1 2 3 4 5 6 Parts were quenched in the basket 7 8 9 10 11 Parts were quenched in the basket 12 13 14 15 16 17 18 19 20
Quenchant Type
Water
Oil
Water
Oil
5% Polymer
5% Polymer
Torque to Failure (ft/lb.) 160 171 167 152 162 173 127 127 120 122 56 58 57 57 59 56 54 58 56 127 159 161 150 156 56 57 57 57
In contrast to the sockets, there were practically no improvements in socket adapter mechanical properties (see Table 2). This is because the wall thickness of the socket adapters is less than the wall thickness of the sockets. Therefore, the realization of the intensive quenching process for the socket adapters requires greater heat transfer coefficients on the part surface or higher quenchant flow velocities. Due to the limitations of the experimental intensive quenching system, it was impossible to provide a proper cooling rate for these parts.
Summary and Conclusion
Hardness (HRC)
Compared to the current practice, the intensive quenching process provides a much greater hardness on the sprocket surface and a better uniformity of the hardness distribution throughout both the part surface and cross section with no surface cracks. Compared to the current practice, the intensive quenching process provides sockets with a much greater value of the torque-to-failure with no surface cracks (32% of improvement). There was practically no difference in the torque-to-failure value for socket adapters that were intensively quenched and for parts that were quenched in oil. To successfully realize the intensive quenching process for the socket adapters, it is necessary to provide a greater cooling rate than the rate provided by the experimental quenching system.
Acknowledgments 45
46
The authors wish to acknowledge the staff of the Edison Material Technology Center of Ohio, Akron Steel Heating Co. (Akron, Ohio), Queen City Steel Treating Co. (Cincinnati, Ohio) and Probala Associates, Inc. (Cleveland, Ohio) for providing financial and technical support for this research project.
References 43–46
1.
46
2.
46
3. 43
Tensi, H.M., N.I. Kobasko and V.S. Morganyuk, Specific Features of Using Intensive Methods of Quenching for the Strengthening Parts of Complex Configuration, pp. 239–241, Proceedings of International Heat Treating Conference: Equipment and Processes, Schaumburg, Illinois (1994) Kobasko, N.I., Peculiarity of the Process of Quenching Carburized Steel Parts, pp. 173–180, Proceedings of the Second International Conference on Carburizing and Nitriding with Atmospheres, Cleveland, Ohio (1995) N.I. Kobasko, Theory and Technology of Quenching, pp. 367–389, Springer-Verlag, New York, New York (1992)
