中文摘要：

对激光立体成形17-4 PH（0Cr17Ni4Cu4Nb）沉淀硬化不锈钢沉积区热处理前后的组织和常规力学性能进行了研究。光学显微镜（OM）、扫描电子显微镜（SEM）和X射线衍射（XRD）结果表明,沉积态组织主要由板条状马氏体和分布于其上和板条间少量的第二相强化质点组成。根据合金特性,推测马氏体基体上弥散析出的第二相强化质点应该为M7C3及NbC型碳化物等。靠近基材处的沉积态组织以细长的板条状淬火马氏体为主;远离基材的沉积态组织则变成粗大的板条状马氏体。沉积态试样经过固溶时效处理后,组织变为细小均匀的板条状回火马氏体,并且基体上析出了更多的第二相强化质点,这类强化质点推测应为NbC型以及M7C3,M23C6型碳化物。成形件经过热处理后,强度、硬度略微提高,而塑性则显著增加。并且其抗拉强度和塑性均高于锻棒标准,屈服强度则略低于锻棒标准。热处理前后成形件拉伸断裂均属于韧性断裂,其中M7C3型碳化物等形成的第二相质点是微观空穴和韧窝形成之源。

英文摘要：

The microstructure and mechanical properties of as-deposited and heat-treated laser solid forming（LSF） 17-4 PH（0Cr17Ni4Cu4Nb） percipitation-hardening stainless steel are investigated.The results of optic microscope（OM）,scanning electron microscope（SEM） and X-ray diffraction（XRD） show that the microstructure of as-deposited LSF 17-4 PH steel consists of lath martensite and a small quatity of the second phase strengthening particles which distribute in and between the laths.According to the characteristics of alloy,the precipitating second phase strengthening particles should be M7C3 and NbC carbides,etc.The microstructure at the bottom of the deposited LSF 17-4 PH is mainly thin lath hardened martensite,however,there are thick lath martensite at the top of the deposited one.The microstructure of heat-treated LSF 17-4 PH is thin homogeneous lath martensite and there are more second phase strengthening particles percipitated in the subtrate as well.These second phase strengthening particles should be NbC and M7C3,M23C6 carbides.After heat-treatment,the strength and hardness of samples are slightly improved,while the plasticity is highly improved.In addition,the tensile strength and plastcity of the heat-treated samples are higher than forging bar standard,meanwhile,the yield strength is slightly lower than forging bar standard.The analysis on fractography shows that both the as-deposited and heat-treated LSF 17-4 PH steel exhibit toughness fracture and the second phase particles which consist of M7C3 carbides are the resource of microcavities and dimples.