**Tao Jia \*, Run Ni, Hanle Wang, Jicheng Shen and Zhaodong Wang**

The State Key Lab of Rolling and Automation, Northeastern University, Shenyang 110819, China; RunNi3017@163.com (R.N.); stuwanghanle@aliyun.com (H.W.); shenjicheng@163.com (J.S.); zhdwang@mail.neu.edu.cn (Z.W.)

**\*** Correspondence: jiatao@ral.neu.edu.cn or tao.jia.81@gmail.com; Tel.: +86-24-8368-1190

Received: 30 August 2019; Accepted: 19 September 2019; Published: 26 September 2019

**Abstract:** The Cr-rich precipitates at the interphase boundary in stainless steels not only lead to the sensitization, which further induces the intergranular corrosion and intergranular stress corrosion cracking, but also significantly deteriorate the ductility and toughness. In this work, the formation of Cr-rich precipitates at the interphase boundary in type 430 stainless steel was investigated from the perspective of austenite–ferrite transformation kinetics. Cyclic heat treatment was firstly conducted to reveal the kinetic mode of transformation behavior, i.e., local equilibrium or para equilibrium. Subsequently, interrupted quenching during continuous cooling was carried out, which illustrated clearly the relevance of the formation of interphase Cr-rich precipitates to the Cr enrichment adjacent to the interphase boundary as revealed by line scanning of energy dispersive spectroscopy (EDS). Finally, this enrichment of Cr was interpreted by DICTRA simulation, which is based on the determined kinetic mode for austenite–ferrite transformation. This work has, for the first time, established the correlation between the formation of interphase Cr-rich precipitates and the austenite–ferrite transformation kinetics.

**Keywords:** transformation kinetics; local equilibrium; para equilibrium; Cr-rich precipitate; interphase boundary; type 430 stainless steel
