Method of manufacturing multi physical properties part
A multi physical properties part used in automotive components required to be lightweight and provide collision safety, and a method of manufacturing a multi physical properties part, in which the multi physical properties part may be more economically and simply manufactured by using two or more separated die sets without using an additional heating device or treating a die surface. A method of manufacturing a multi physical properties part, which includes positioning a single heated formed article in two or more die sets, and then manufacturing a multi physical properties part including two or more regions having different physical properties by differing cooling conditions in the respective die set.
1. A method of manufacturing a multi physical properties part, the method comprising:
forming a single heated steel by using two or more separated die sets; and
then manufacturing the single heated steel into a multi physical properties part including two or more regions having different physical properties by differing cooling conditions in the respective die set.
2. The method of claim 1 , wherein the physical properties is one selected from the group consisting of yield strength, tensile strength, elongation, toughness, a plastic anisotropy index (r), and in-plane anisotropy (Δr).
3. The method of claim 2 , wherein the physical properties is tensile strength and a critical cooling rate (CCR), a minimum cooling rate able to form a martensite phase in a continuous cooling transformation (CCT) curve, of the steel is greater than about 50° C./s and less than about 600° C./s.
4. The method of claim 3 , wherein the method further comprising:
forming and pre-quenching the steel by using two or more separated die sets, after heating the steel above an Ac 3 transformation point;
air cooling a region to obtain a relatively low-strength region, in which the die set and a formed article are not allowed to be in contact with each other, and then post-quenching while the die set and the formed article are in contact with each other again; and
die quenching a region to obtain a relatively high-strength region, in which the die set and the formed article are continuously in contact with each other after the forming and pre-quenching.
5. The method of claim 4 , wherein martensite is formed to about 80 vol % or more in the high-strength region, and one or more of ferrite, bainite, and pearlite or one or more of ferrite, bainite, and pearlite and about 50 vol % or less of martensite are formed in the low-strength region.
6. The method of claim 4 , wherein the forming and pre-quenching time is within a range of about 1 second to about 6 seconds.
7. The method of claim 4 , wherein the air cooling time is within a range of about 5 seconds to about 30 seconds.
8. The method of claim 4 , wherein the post-quenching time is within a range of about 5 seconds to about 30 seconds.
9. A method of manufacturing a multi physical properties part, the method comprising:
positioning a single heated formed article in two or more separated die sets; and
then manufacturing the single heated formed article into a multi physical properties part including two or more regions having different physical properties by differing cooling conditions in the respective die set.
10. A method of manufacturing a multi physical properties part, the method comprising:
forming and pre-quenching a non-formed portion by using two or more separated die sets, after heating a partially formed article formed of a steel above an Ac 3 transformation point;
air cooling a region to obtain a relatively low-strength region, in which the die set and the formed article are not allowed to be in contact with each other, and then post-quenching while the die set and the formed article are in contact with each other again; and
die quenching a region to obtain a relatively high-strength region, in which the die set and the formed article are continuously in contact with each other after the forming and pre-quenching.