Papers in JOURNAL OF THE JAPAN SOCIETY FOR TECHNOLOGY OF PLASTICITY
(vol.42 no.485 June 2001)
Basic Properties of Ferrite-Pearlitic Microalloyed Steel
- Development of Microalloyed Steel for Controlled Forging ‡T-
Hiroaki YOSHIDA, Sachihiro ISOGAWA and Takashi ISHIKAWA
(Received on May 17, 2000)
It is quite important to reduce the weight of automobile components because of the need to save fuel. One of the most important methods of weight reduction is that of power train and suspension components. Conventionally these components are produced by forging using mainly microalloyed steels. Microalloyed steels have a high cost-reduction effect but the mechanical properties are inferior to those of heat-treated steels. Therefore, the improvement of the mechanical properties of microalloyed steels is strongly desired. In this study, the application of controlled forging to a newly designed ferrite and pearlite-type microalloyed steel, which contains vanadium, has been discussed in order to solve the problem. Controlled forging makes the microstructure fine;in particular, the pearlite grain size becomes one third that obtained by conventional hot forging. It was confirmed that the mechanical properties, namely, yield strength, fatigue strength and ductility of the controlled forged microalloyed steel, are enhanced up to the same level as that of the quenched and tempered steels. In this paper, the behavior of the microstructure and changes in the mechanical properties by control forging are reported.
Key words : forging, material property, thermomechanical heat treatment, microalloyed steel
The Effect of Subscale on the Hot Workability of Stainless Steels
Takahiro AITOU, Tatsuo YOKOTE and Ryuta ONODERA
(Received on May 18, 2000)
The effect of scale on surface cracking during hot working has been investigated in three types of stainless steels. The scale consists of surface scale and subscale. As the surface scale was peeled during hot working, it did not affect the workability of steels. The subscale layer including both the matrix and oxides was not peeled by compression, resulting in the occurrence of deep surface cracks during hot working. These deep surface cracks appeared in the ferritic steel, but not in the austenitic steel. It is considered that the occurrence of deep surface cracks are caused by the differences in strength between ferrite, austenite and subscale.
Key words : compression test, hot working, stainless steel, oxidation, scale
Flange and Web Profile in Stretch Flanging
- Accuracy of Formed Product in Axisymmetric
Stretch Flanging of Steel Sheet ‡U -
Shigeo ICHIKAWA, Yasuhisa TOZAWA and Naoyuki KANETAKE
(Received on May 31, 2000)
The effects of tool dimensions and blank dimensions on the accuracy of a formed product are investigated for the axisymmetric stretch flanging of a cold-rolled steel sheet. A residual bent region remains near the edge of the flange after forming. The outside of the flange except the residual bent region is cylindrical in shape and the outer diameter of the flange is only slightly smaller than that of a die, which is not related to tool dimensions or blank dimensions. The other side, the inner diameter of the flange is not uniform in the axial direction because of the nonuniformity of the thickness reduction. The flange height after forming can be predicted by a simple calculation, taking into consideration the thickness reduction of the flange and drawing of the web. Under the conditions of the present experiment, the warp of the web is generated by the springback of the die shoulder bending, thus it exhibits a concave cone.
Key words : stretch flanging, axisymmetric flanging, accuracy, flange profile, web profile, steel sheet
Development of an Upset Pipe-Bending Method by High-Frequency
Induction Heating and Its Product Size
Katsutoshi MIYASAKA and Tohru SATOH
(Received on June 21, 2000)
The successful development of a new pipe-bending system was made by means of high-frequency induction heating. The procedure of the construction concerning the upset pipe bending is as follows. A pipe is secured into a position between a front retainer and a rear retainer. One end of the chain used in this experiment is attached to the spot eccentrically positioned from the pipe center. The other end of the chain is linked with a hydraulic jack through the inside of the rear retainer. When an exclusive narrow segment of the pipe is heated owing to the generation of high-frequency induction, the said end is pulled by the hydraulic jack. Therefore, the narrow segment heated in such a manner is subjected to the eccentric axial compression load caused by pulling the chain. This might be tantamount to the formation of an upset pipe-bending system. When the eccentric ratio is changed, the axial compression load is also changed. Consequently, the change of the said load makes it possible to control the wall thickness of the pipe. For the experiments, a carbon steel pipe for the normal ping (SGP, JIS G 3452) of nominal number 100A (outer diameter Do114.3mm, thickness t4.5mm) is used. The bending radius R/Do (R:bending radius, Do:nominal outer diameter) is varied to 2.5, 3.0, 3.5, 4.0. In the meantime, the bending rate is varied to 15, 30 and 40mm/min. The thinning ratio at the bend outside wall is 2 percent or less, and this value is significantly lower than that of the conventional pipe bend. The bent pipe ovality obtained is 2 percent or less. Moreover, the reduction ratio of the length is sufficiently large in comparison with that in the case of conventional pipe bending. From the reasons mentioned above, it is revealed that the upset pipe-bending method offers specific merits such as small size, light weight and mobility in transportation compared with the conventional pipe-bending method, which is dependent on high-frequency induction heating. Thus, the new pipe-bending method can be adopted for not only floor type bending work but also on-the-site bending work.
Key words : tube forming, new pipe bending, upset bending, mobility, wall thickness, ovality, radius control, induction heating
Development of a Grain Size Prediction Method
for Forged Metals Using Numerical and Experimental Analysis
Motoi YAMAGUCHI, Satoshi KUBOTA, Tsuyoshi FUKUI and Takehiro OHNO
(Received on July 7, 2000)
Hot forging, one of the most important metal forming processes, is used not only for shaping but also for controlling the microstructure. This study was carried out to predict the grain size of forged products using numerical and experimental analysis. First, temperature and strain during hot forging were calculated using 3-dimensional FEM (finite element method) software. Second, a multistage plane strain compression test was carried out by means of the Gleeble system and the grain size was measured. The results showed that the austenitic grain size number of the forged material was 7.0 and the austenitic grain size number obtained through the simulation was 7.5, thus the grain size obtained through the simulation coincided with that of the forged material.
Key words : forging, swaging, numerical analysis, FEM, experimental analysis, plane strain, multistage compression, grain size
Twisting Process in Flexible Extrusion with Divided Dies
Mitsunobu SHIRAISHI and Makoto NIKAWA
(Received on November 29, 2000)
For manufacturing products twisted along their length, we propose a method that extrudes billets through the orifice that is stepwise assembled from several flat dies, in which the twisting angle of the extruded product is controlled by adjusting the height of the die step. The fundamental characteristics of this extrusion process are investigated by carrying out extrusion tests on products with rectangular cross sections under various heights of die steps and extrusion ratios. The specific twisting angle of the product tends to increase and then to converge as the height of the die step increases. A linear correlation exists between the specific twisting angle of the product and the bending angle. It is clarified that the specific twisting angle of the product depends on the inclination angle of the die exit.
Key words : extrusion, production system, plasticine, metal flow control, twisting, divided die