PDF《N 对汽车发动机用新型奥氏体耐热铸钢 1000 ℃ 蠕变性能的影...》

第52 卷2016 年6月Vol.

52 No.6 ACTA METALLURGICA SINICA 第6期Jun.

2016 第661-671页pp.661-671 N对汽车发动机用新型奥氏体耐热铸钢1000 ℃ 蠕变性能的影响* 张银辉1) LI Mei2) GODLEWSKI Larry A2) ZINDEL Jacob W2) 冯强1,3) 1) 北京科技大学新金属材料国家重点实验室, 北京

100083 2) Ford Research and Advanced Engineering Laboratory, Ford Motor Company, Dearborn, 48124-4356, USA 3) 北京科技大学高端金属材料特种熔炼与制备北京市重点实验室, 北京

100083 摘要为了应对汽车发动机排气温度将大幅升高至1050 ℃的要求, 本工作以新设计的3种不同N含量(0~0.55%, 质量分 数)的Nb稳定化奥氏体耐热铸钢为研究对象, 通过在1000 ℃,

50 MPa条件下的蠕变性能测试和蠕变前后的组织分析, 研究 了N对奥氏体耐热铸钢1000 ℃蠕变性能的影响规律. 结果表明: 根据N添加量的不同, 合金之间的最小蠕变速率相差接近 一个数量级. 合金的主要析出相为NbC, Nb(C, N)和富Cr相. 随着N含量的增加, 合金中NbC转变为Nb(C, N), 其形貌逐渐 从草书体状转变为不规则的混合片块状, 并最终转变为多面体块状. 其中, 草书体状NbC能有效强化铸钢的晶界和枝晶间 区域, 因而有利于提高高温蠕变性能. 富Cr相在晶界的粗化连接是合金蠕变断裂的主要裂纹源, 不利于蠕变性能. 富Cr相 的二次析出还会降低奥氏体基体固溶的C含量, 从而降低其固溶强化能力. 草书体状NbC的析出及富Cr相含量的降低是新 型奥氏体耐热铸钢蠕变性能提高的主要原因. 关键词 汽车发动机, 奥氏体耐热铸钢, 蠕变, Nb(C, N), 凝固 中图法分类号 TG142.1, TG113.2 文献标识码 A 文章编号 0412-1961(2016)06-0661-11 EFFECTS OF N ON CREEP PROPERTIES OFAUSTENI- TIC HEAT-RESISTANT CAST STEELS DEVELOPED FOR EXHAUST COMPONENT APPLICATIONS AT

1000 ℃ ZHANG Yinhui 1) , LI Mei 2) , GODLEWSKI Larry A 2) , ZINDEL Jacob W 2) , FENG Qiang 1,3) 1) State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China 2) Ford Research and Advanced Engineering Laboratory, Ford Motor Company, Dearborn 48124-4356, USA 3) Beijing Key Laboratory of Special Melting and Reparation of High-End Metal Materials, University of Science and Technology Beijing, Beijing 100083, China Correspondent: FENG Qiang, professor, Tel: (010)82375850, Fax: (010)62333447, E-mail: [email protected] Supported by Ford China University Research Program Manuscript received 2015-12-03, in revised form 2016-03-03 ABSTRACT To comply with more stringent environmental and fuel consumption regulations in recent years, automotive gasoline engines equipped with turbochargers are increasingly used to improve fuel efficiency. As a re- sult, exhaust gas temperatures are now reaching

1050 ℃, about

200 ℃ higher than the conventional temperature. Hence, there is an urgent demand in automobile industries to develop novel and economic austenitic heat-resistant * 福特与中国大学合作研究资助项目 收到初稿日期: 2015-12-03, 收到修改稿日期: 2016-03-03 作者简介: 张银辉, 男, 1985年生, 博士生 DOI: 10.11900/0412.1961.2015.00618 金属学报第52 卷steels that are durable against these increased temperatures. In this study, the effects of N addition on creep behav- ior at

1000 ℃ and

50 MPa are investigated in a series of Nb-bearing austenitic heat-resistant cast steels, which are developed for exhaust component applications. Microstructures before and after creep rupture tests are carefully characterized to illustrate the microstructural evolution during creep deformation. The results of creep tests show approximately an order of magnitude increase in the minimum creep rate among the experimental alloys with varia- tions of N addition. Microstructural analyses indicate that the morphology of NbC and Nb(C, N) is changed from Chinese-script to mixed flake-blocks, and then to faceted blocks as N additions increase. The best creep property occurs in an alloy with Chinese-script NbC, which could effectively strengthen the grain boundaries and inter- dendritic regions. The Cr-rich phases are adverse to creep properties, in particular those coarsened and coalesced phases along grain boundaries. They act as crack sources and accelerate the propagation of creep cracks. Moreover, the secondary precipitation of Cr-rich phase results in a significant decrease of C concentration in the matrix and thus reduces the solution strengthening ability during creep deformation. This study suggests that the strengthening of these austenitic cast steels can be achieved through the exploit of primary NbC and Nb(C, N) and the elimina- tion of Cr-rich phases, and therefore, N additions should be strictly controlled. KEY WORDS gasoline engine, austenitic heat-resistant cast steel, creep, Nb(C, N) carbonitride, solidification 汽车排放的尾气是城市大气污染的重要污染 源之一. 针对以汽车为主的城市交通, 中国政府相 继出台并开始实施更加严格的汽车燃油法规和尾 气排放标准. 涡轮增压技术是实现汽车小排量、 轻 量化的核心技术, 具有燃油效率更高、 动力性能更 优、 更清洁环保的优势[1,2] . 与传统自然吸气式发动 机相比, 涡轮增压汽油发动机的排气温度从