Metal treatment – Stock – Ferrous
Patent
1995-12-12
1997-04-08
Yee, Deborah
Metal treatment
Stock
Ferrous
148333, 148336, 148603, 148651, C21D 804, C22C 3802, C22C 3806
Patent
active
056183550
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a high-strength cold-rolled steel sheet comprising multiple phases, having for example, a tensile strength of not less than 440 MPa, and a process for producing the same. Since this steel sheet is suitable for deep drawing and bulging among the fundamental forming modes consisting of various types of press forming, parts having a complicated shape can be easily formed by press forming.
BACKGROUND ART
In recent years, there is an ever-increasing demand for a reduction in the weight of automobile bodies, in addition to the comfort and safety of the automobiles, which requires an increase in the strength of thin steel sheets utilized in automobile structures. Further, in the production of components of the automobile body, simplification, and continuous operation, of the production process by a reduction in the number of forming steps, and by one-body pressing, are considered technical requirements. When the thin steel sheet, among steel products used in such forming, is particularly taken into consideration, the selection criterion of the steel product is that the steel product has good formability. Stretchability, deep drawability, stretch-flange ability, and bendability are also required of the thin steel sheet. In this connection, good deep drawability, in addition to stretchability, is required in order to make it possible to prepare components having a complicated shape, such as interiors of automobiles, requiring only a small number of steps or one-body pressing.
The material properties governing the stretchability are elongation and work hardening coefficient (n value). In recent years, a high-strength multiple phase steel sheet comprising a mixed microstructure of ferrite, bainite, and austenite has been proposed as a steel sheet excellent in the above properties. This steel sheet utilizes "transformation induced plasticity" which is a phenomenon such that austenite remaining at room temperature is transformed to martensite at the time of forming, resulting in high ductility. Japanese Unexamined Patent Publication (Kokai) No. 61-157625 discloses, as a process for producing a high-strength steel sheet, a process for producing a thin steel sheet, such as a steel sheet for automobiles which should be inexpensive and mass-produced. In this prior art, Si is added to inhibit the precipitation of carbides, and ferrite transformation (bainite transformation) at low temperature is allowed to proceed to effectively enrich C in untransformed austenite, thereby stabilizing the austenite. Further, there is a report that the volume fraction and stability of retained austenite are important for providing high ductility in this steel (TETU TO HAGANE, 78 (1992) p.1480). However, no mention is made of deep drawability.
On the other hand, the Lankford value (r value) determined by a uniaxial tensile test, rather than elongation and the n value, is generally used as a material property governing the deep drawability. In general, the deep drawability of a material is tested in terms of deep drawing to a cylindrical cup. It is valuated using a formable range of blank holder force between the minimum force which can restrain wrinkles in the flange portion and the maximum force which can prevent rapture at the shoulder portion of the punch. A material having excellent deep drawability has high breaking proof stress in the shoulder portion of the punch and low shrink flanging deformation resistance in the flange portion. According to the theory of plasticity, a material having a high r value is characterized by having high fracture strength in a deformed state around plain strain in the shoulder portion of the punch and low deformation resistance under shrink flanging deformation in the flange portion. The r value is governed by a texture of the sheet, and, hence, in the development of the conventional deep drawable steel sheet, attention has been drawn mainly to the regulation of the texture. In recent years, however, that a steel utilizing deformation induced transformat
REFERENCES:
patent: 5123971 (1992-06-01), Hook
patent: 5328528 (1994-07-01), Chen
Teno To Hagne, Effects of Volume Fraction and Stability of Retained Austenite on Ductillity in Trip-Aided Dual Phase Steel Sheets, May 15, 1992.
Sosei To Hako, Journal of the JSTP, vol. 35, No. 404, p. 1109, "Effect of Deformation-Induced Transformation on Deep Drawability" --Forming Mechanism of Trip Type High-Strength Steel Sheet--, Nov. 1, 1993.
Hiwatashi Shunji
Kawasaki Kaoru
Koyama Kazuo
Sakuma Yasuharu
Takahashi Manabu
Nippon Steel Corporation
Yee Deborah
LandOfFree
High-strength steel sheet suitable for deep drawing and process does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with High-strength steel sheet suitable for deep drawing and process , we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High-strength steel sheet suitable for deep drawing and process will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2395494