Heat Treatment Of A New Type Of Modified Ultrahigh Carbon Wear-resistant Steel

Abstract:Ultrahigh carbon steels (UHCSs), which are hyper-eutectoid steels containing1.0-2.1wt.%C, have been of great interest because of its high hardness, strength and wear resistance. However, the high volume fraction of carbides with high connectivity in the matrix makes ultrahigh carbon steels quite brittle after conventional solidification processe. In this paper, the applicability of quenching-partitioning-tempering (Q-P-T) process to an ultrahigh carbon steel (UHCS) has been investigated for the first time. The steel melt was modified with a multi-component modifier consisting of rare earth and low melting point alloy (Al-Bi-Sb) before casting into iron molds. The mechanism of the multi-component modifier has been investigated, and the effect of Q-P-T process on microstructure and properties was also discussed. The main conclutions are as follows:1. Mechanism of the multi-component modifier modification in UHCS behaves mainly in the following two aspects:(1) The high melting point oxide and sulfide of RE prompt heterogeneous nucleation of primary austenite.(2) The low-melting point elements such as Bi and Al may segregate at the front of liquid thus suppress growth of austenite. In addition, the LMs may also suppress the carbide growth in some directions, resulting in discontinuous or some extent spheric carbides.2. After the Q-P-T treatment (partition-tempered at400℃for30min), carbon was partitioned into austenite from martensite, creating a mixture of carbon-depleted martensite, carbon-enriched retained austenite and fine carbides. This kind of microstructure leads to a much higher impact toughness, more than28J/cm2, in comparison with the value, i.e., no more than16J/cm2, of the conventional quenching-and-tempering (Q-T) treatment (tempered400℃for2h) at the same hardness level. The optimum Q-P-T process is partition-tempered at400℃for30min, and excellent mechanical properties (Hardness52.5-56.0HRC, Impact toughness28～34J/cm2) have been achieved.3. The Q-P-T-treated steel has better abrasion resistance, about 18.1%increased, compared with the Q-T-treated alloy under high load abrasive wear conditions (170N). Whereas, under condition of dry sliding friction and wear (70N,300r/min), the Q-T-treated steel has better abrasion resistance, about7.7%increased, compared with the Q-P-T-treated steel.30figures,17tables,100references.