影响连续镀锌模拟线生产高强双相钢微观组织和性能的因素

Processing Factors That Influence the Microstructure and Properties of High Strength Dual-phase Steels Produced Using CGL Simulations

探讨如何改善镀锌或镀锌合金化钢板基层,比如在实现高强度的同时,保持高的整体成形性能(拉伸塑性)、局部成形性能(冲裁边部塑性)和良好的点焊性能。众所周知,双相钢的强度受几个因素控制,包括最终组织中的初生(未回火)马氏体量。然而,仍不完全清楚控制最终组织中马氏体量的因素,而确定这些因素是本研究项目的主要内容。最终组织中测定的新生马氏体量认为等于临界退火时形成的奥氏体量减去当钢在经历从临界退火温度(IAT)冷却至460℃、在460℃等温过程中、最终冷却至室温是转变成其他各种相变产物的奥氏体量以及在室温下保留的残余奥氏体量。最新研究发现,特定钢在临界退火过程中形成的奥氏体量受到退火温度、热轧带钢(卷取温度)和冷轧(冷压下量)等退火前条件的强烈影响。研究了退火前条件和4种退火工艺的组合,确定实现这些更高强度DP钢最佳的强度-成形性能匹配所需的最佳热处理路线。研究用钢包括(i)具有良好点焊性能的低碳钢,(ii)加入Mo提高淬透性和Cr提高强度,(iii)加入V实现细晶、析出强化和抗回火软化。当所采用的工艺适当,这些钢具有良好的综合性能,抗拉强度高达1 000 MPa、总伸长率达到25%,面缩率45%,扩孔率达到50%。给出并讨论了这些研究成果。

The purpose of this paper is to present research whose goal was to improve the substrate in galvanized or galvannealed sheet steel , such that high strength can be obtained while maintaining good global formability（ tensile ductility）, local formability（sheared-edge ductility）, and good spot weldability. It is well-known that the strength of DP steels is controlled by several factors, including the amount of fresh（untempered） martensite found in the final microstructure. However, the factors that control the amount of martensite in the final mierostrueture are not all together clear, and their identification represents a large portion of the research conducted in this program. The amount of fresh martensite found in the final mierostructure can be considered equal to the amount of austenite formed in the intereritical anneal less the amount of austenite lost to various transformation products as the steel undergoes cooling from the intercritical annealing temperature（IAT） to 460 ~C, isothermal holding at 460 ~C, final cooling to RT and any remaining austenite retained at RT. Reeent research has revealed that the amount of austenite formed during in- tercritical annealing of a given steel can be strongly influenced by the annealing temperature and the pre-annealing conditions of the hot band（coiling temperature） and cold band（% cold reduction）. Current experiments have ex- plored the combination of pre-annealing conditions and four annealing practices to help define the best thermal path needed to optimize the strength-formability balance in these higher strength DP steels. The steels used in these exper- iments contained （i） low carbon content for good spot weldability, （ii） the Mrdenability additions Mo and Cr for strength, and（iii） V for grain refinement, precipitation hardening and temper resistance. When processed correctly, these steels exhibited UTS levels up to 1 000 MPa, total elongation to 25%, reduction in area to 45%, and Hole Expansion ratios to 50%. The results of this program will be presented and discussed.