利用热成形钢初始组织中碳化物在奥氏体化过程溶解产生的浓度梯度能够提高残余奥氏体含量，并利用残余奥氏体的相变诱导塑性(TRIP)效应改善塑性，但不同形貌初始组织对于热成形后组织和力学性能的影响缺乏研究。因此，本工作研究了不同形貌的珠光体初始组织对新型热成形钢Fe-0.29C-1.75Si-1.2Mn-2.1Cr-0.027Nb在915 ℃下短时热成形并烘烤后力学性能和微观组织的影响。结果表明，片状珠光体(LP)初始组织在915 ℃保温20~30 s的短时热成形后，其强度和塑性均优于球状珠光体(SP)初始组织。保温25 s时，LP初始组织样品的UTS、YS和TE比SP初始组织样品分别提高约75 MPa、35 MPa和1%，比22MnB5钢分别提高490 MPa、440 MPa和3%。针对奥氏体逆转变动力学的模拟计算结果表明，由于片状渗碳体的固溶速率高于球状渗碳体，在片状渗碳体上形核、长大的奥氏体的C含量也高于球状渗碳体形核的奥氏体，因此片状渗碳体区域的马氏体相变开始温度(M_s)更低。这一方面导致LP初始组织在热成形后的马氏体相变中产生更多位错，从而提高样品屈服强度，另一方面也增加了LP初始组织热成形后的残余奥氏体分数，进而可通过增强TRIP效应而改善加工硬化，所以其抗拉强度和延伸率也更优。

New press-hardening steels (PHSs) have been developed recently to further improve strength and ductility, meeting the demand of the automobile industries. PHSs are usually formed by retaining austenite grains with sufficient fraction and stability for enhancing the transformation-induced-plasticity (TRIP) effect by deliberately introducing spherical carbide particles, where austenite grains can be nucleated and grow in company with their gradual dissolution. However, lamellar pearlite (LP) microstructure, rather than spherical pearlite (SP), is commonly formed in automotive steels during industrial hot rolling. This study investigated the influence of the initial microstructure (LP or SP) on the resultant microstructures and tensile properties of a new PHS (Fe-0.29C-1.75Si-1.2Mn-2.1Cr-0.027Nb) after press-hardening with a short solution period at 915°C and baking at 170°C. The results show that compared to an initial SP structure, an initial LP structure resulted in higher yield strength (YS), ultimate tensile strength (UTS), and total elongation (TE) after the press-hardening at 915°C for 20-30 s. On increasing the solution period to 25 s, the YS, UTS, and TE of the LP specimen were higher than those of the SP specimen (by approximately 35 MPa, 75 MPa, and 1%, respectively) and the 22MnB5 specimen (by 440 MPa, 490 MPa, and 3%, respectively). The austenitic reversion kinetics in the solution were simulated using DICTRA. The simulation results indicate that lamellar cementite dissolves more rapidly than the spherical one under identical solution treatments. Moreover, the austenite that nucleated and grew on the lamellar cementite had a higher C content than the austenite on the spherical cementite. Thus, compared to an initial SP structure, an initial LP structure resulted in a lower start temperature of martensite transformation (M_s) under identical press-hardening processes. This resulted in a higher dislocation density in martensite in the LP specimen, improving its YS and retaining more austenite, thereby enhancing the TRIP effect after press-hardening and improving work hardening. Thus, compared to an initial SP structure, the LP one resulted in higher resultant YS, UTS, and TE after press-hardening with a solution period of 20-30 s.