中文摘要：

通过工艺设计，对工业20钢进行了分级淬火（SQ）和临界区退火（IA）热处理，获得了马氏体体积分数相近、但马氏体分别呈离散分布和连续分布的2种双相钢．对它们的拉伸／冲击力学性能进行了表征；应用数字图像相关（DIC）方法获得双相钢的微观应变分布，并结合表面微裂纹分析，揭示了2种双相钢的不同变形断裂机制．SQ双相钢展现出较低的强度，但具有更好的塑性与冲击韧性，这源于铁素体较大变形松弛了马氏体在变形中产生的应力集中；而IA双相钢中铁素体变形受到周围马氏体的阻碍，铁素体相对小的变形不能有效松弛变形马氏体的应力，使裂纹优先在马氏体中产生，因而IA双相钢具有高强度和低塑性．

英文摘要：

Investigation of the relationship between microstructure and microscopic deformation behavior of dual phase steel is very important for high property dual phase steel development. In this work, step quenching （SQ） and intercritical annealing （IA） heat treatments were optimized to produce dual phase steels of similar martensite volume fraction, but with respectively isolated and continuous martensite distribution. The tensile and dynamic fracture properties of dual phase steels were investigated. Strain distribution of steels was measured by digi tal image correlation （DIC） method. Combined with observations of microcracks/microvoids, different deformation and fracture mechanisms were revealed. Compared to IA steel, SQ steel has lower strength, but longer elongation and higher fracture toughness, and the latter were attributed to larger deformation in ferrites that results in more stress relaxation of martensite during deformation. While in IA steel, the deformation in ferrites is blocked by adja- cent martensites, so that a relatively small strain of ferrite cannot effectively relax the stress in martensites, which resulted in higher plastic deformation in martensite than in SQ steel; therefore, cracks preferentially initiate in martensite, and IA steel exhibits higher strength and lower plasticity.