Strengthening and toughening of a 2800-MPa grade maraging steel
Yi He *,Ke Yang,Wenshen Qu,Fanya Kong,Guoyue Su
Institute of Metal Research,Chinese Academy of Sciences,Shenyang 110016,People’s Republic of China
Received 9October 2001;accepted 23January 2002
Abstract
A new high Ni,Ti and low Mo maraging steel based on 13Ni(400)maraging steel has been developed.The optimum heat treatment was found to be cryogenic treatment (CT)at 200K followed by aging treatment at 773K for 4h in as-forged or solution condition.Optical and transmission electron microscopy (TEM)revealed that the precipitates,such as Ni 3(Mo,Ti),were well developed in lath martensite.It achieved strength of 2700MPa and fracture toughness of above 30MPa m 1/2.The balance among alloy elements and the removal of undissolved coarse particles ensured the good combination of strength and toughness by a normal thermomechanical treatment condition.D 2002Elsevier Science B.V .All rights reserved.
Keywords:Maraging steel;Strengthen;Fracture toughness;Precipitation hardening
1.Introduction
Maraging steels represent one class of ultra-high strength steels that attain their strength by precip-itation hardening.During the past four decades,many kinds of maraging steels have been developed.18%Ni maraging steels containing cobalt are typical category,which result in practical applications of various grade steels with strength up to 2400MPa,designated as 18Ni(350).In order to meet the demands of special project,2800MPa grade marag-ing steel,a higher strength maraging steel than 18Ni type,such as 13%Ni –15Co –10Mo –0.2Ti alloy (designated as 13Ni(400)),which was first invented
by Mihalisin and Bieber [1],has been a subject of many investigations [2–10].In 13Ni(400)maraging steel,as a main alloying element,nickel is obviously lower in content,whereas both cobalt and molybde-num contents are markedly increased in order to get a higher strength,and the titanium is abandoned for maintaining the toughness.However,in most cases,the strength of 13Ni(400)has difficulty reaching the designed strength,i.e.,2800MPa,because of undis-solved Fe 2Mo laves phase in the matrix,and its ductility and fracture toughness (K IC )are lower than what was expected in the forged state [2–10].In order to further strengthen and toughen the 2800MPa grade maraging steel,some other types of maraging steels,such as 15Ni–25Co –7Mo [8],16Ni –15Co –(5f 7)Mo –2.5Ti [9],17Ni –15Co –6Mo–1Ti [11],etc.,have been developed,but they still had bad toughness and ductility with designed
0167-577X/02/$-see front matter D 2002Elsevier Science B.V .All rights reserved.PII:S 0167-577X (02)00610-9
*
Corresponding author.Fax:+86-24-23891320.E-mail address:yihe@ (Y .He).
/locate/matlet
November 2002
Materials Letters 56(2002)763–
769
