US 12,215,404 B1
Carbide-free tempered martensitic steels and preparation methods thereof
Zhiping Xiong, Beijing (CN); Dezhen Yang, Beijing (CN); Chao Zhang, Beijing (CN); Hao Zhang, Beijing (CN); and Xingwang Cheng, Beijing (CN)
Assigned to BEIJING INSTITUTE OF TECHNOLOGY, Beijing (CN)
Filed by BEIJING INSTITUTE OF TECHNOLOGY, Beijing (CN)
Filed on Dec. 29, 2023, as Appl. No. 18/401,294.
Claims priority of application No. 202310957934.3 (CN), filed on Aug. 1, 2023.
Int. Cl. C21D 9/46 (2006.01); C21D 1/18 (2006.01); C21D 6/00 (2006.01); C21D 8/02 (2006.01); C22C 38/00 (2006.01); C22C 38/02 (2006.01); C22C 38/04 (2006.01); C22C 38/06 (2006.01); C22C 38/08 (2006.01); C22C 38/12 (2006.01); C22C 38/38 (2006.01)
CPC C21D 9/46 (2013.01) [C21D 1/18 (2013.01); C21D 6/001 (2013.01); C21D 6/002 (2013.01); C21D 6/005 (2013.01); C21D 6/008 (2013.01); C21D 8/0205 (2013.01); C21D 8/0226 (2013.01); C21D 8/0263 (2013.01); C22C 38/002 (2013.01); C22C 38/02 (2013.01); C22C 38/04 (2013.01); C22C 38/06 (2013.01); C22C 38/08 (2013.01); C22C 38/12 (2013.01); C22C 38/38 (2013.01); C21D 2211/001 (2013.01); C21D 2211/008 (2013.01); C21D 2211/009 (2013.01)] 7 Claims
OG exemplary drawing
 
1. A method for preparing a carbide-free tempered martensitic steel, comprising:
(1) obtaining a first steel with heterogeneous distribution of Mn as a prefabricated product;
(2) obtaining a steel with heterogeneous distribution of Mn in a first-temperature austenite by heating the prefabricated product to the first temperature at a rate of 1-200° C./s and holding for 0-200 s, wherein the first temperature is in a range of 20° C.-200° C. above Ac3, and the Ac3 is a critical temperature for complete transformation of austenite; and
(3) obtaining the carbide-free tempered martensitic steel by performing partitioning on the steel with heterogeneous distribution of Mn in the first-temperature austenite after cooling to a temperature between a martensite transformation start temperature and a martensite transformation finish temperature;
wherein a microstructure of the carbide-free tempered martensitic steel includes Mn-rich austenite and Mn-poor martensite, and an atomic percentage of Mn in the Mn-rich austenite is not less than 4 at. %, a difference of Mn concentration between the Mn-rich austenite and the Mn-poor martensite is greater than 3 at. %, and a distribution spacing between the Mn-rich austenite is less than 2 μm,
wherein the partitioning in step (3) includes: obtaining the carbide-free tempered martensitic steel by cooling the steel with heterogeneous distribution of Mn in the first-temperature austenite to 130° C. at a rate of 20° C./s and holding for 60 s, heating to 220° C. and holding for 90 min, and cooling to room temperature.