淬火-碳分配-回火(Q-P-T)工艺浅介

A brief introduction to quenching-partitioning-tempering (Q-P-T) process

传统淬火-回火工艺不能满足高强度钢兼具一定韧性和廉价的要求,Speer等为在淬火钢内稳定一定量的残留奥氏体,提出淬火-碳分配(Q-P)工艺,即淬火后在一定温度保温一定时间,碳自马氏体分配至残留奥氏体、因富碳而稳定化,以保证淬火高强度钢的塑性和韧性。在Q-P工艺基础上,本文作者于2007年建议一个热处理的新工艺:淬火-碳分配-回火(Q-P-T)工艺,即淬火至Ms～Mf后,除作碳分配外,还在一定温度回火一定时间,使析出复杂碳化物,以增加强化作用。Q-P-T钢含<0.5wt%C以防止脆性,含1.5wt%Si阻碍渗碳体的析出,促进碳分配,(1.0～1.5)wt%合金元素Mn(Ni)以降低Ms温度,以及少量复杂碳化物形成元素Nb和Mo。含0.48wt%C的Q-P-T钢经Q-P-T处理后显示抗拉强度为2 160 MPa,总伸长率11%;含0.2wt%C的Q-P-T钢具抗拉强度1 150 MPa,总伸长率17%;含0.1wt%C的Q-P-T钢具有抗拉强度900 MPa和较高韧性。初步设想了Q-P-T工艺的热力学和动力学,有必要作进一步研究使Q-P-T钢的成分和性能进一步优化。

The traditional quenching-tempering process is unable to satisfy the requirement of combination mechanical property of high strength steel along with low cost. Speer et. al. suggested a quenching-partitioning （Q-P） process, i. e. , holding certain duration at certain temperature after quenching, causing carbon partitioning from martensite to retained austenite. Carbon partitioning makes carbon enrichment and austenite stabilization in order to ensure the plasticity and toughness of high strength steel. In 2007, the present author proposed a novel heat treatment process, quenching-partitioning-tempering（Q-P-T） process, based upon the Q-P process, i. e. after quenching to Ms-Mr, beside the carbon partitioning,there is also a tempering procedure, that is, holding at certain temperature for certain duration in order to enhance the complex carbide precipitation and the strengthening reaction. The Q-P-T steel contains 〈 0. 5wt% C to prevent embrittlement, 1.5wt% Si to suppress the cementite precipitation and to promote the carbon partitioning, （ 1.0-1.5 ） wt% alloying element Mn （ Ni ） to lowering Ms temperature as well as small amount of complex carbide forming elements Nb and Mo. Q-P-T steel with 0. 48wt% C has shown the ultimate tensile strength of 2 160 MPa and total elongation of 11% treated by Q-P-T. Q-P-T steel with 0.2wt% C developed ultimate tensile strength of 1 150 MPa and total elongation of 17% and 0. lwt% C Q-P-T steel shows 900 MPa and good toughness respectively. Thermodynamics and kinetics of Q-P-T process are preliminarily considered. Further work is required to optimize the composition and heat treatment parameter for the Q-P-T steel.