【作者】 李占杰；

【导师】 余圣甫；

【作者基本信息】 华中科技大学 ， 材料加工工程， 2007， 硕士

【摘要】 管线钢大线能量焊接时焊接热影响区显微组织的粗化,大大降低了管线钢焊接接头的韧性,这严重制约了管线钢的应用。本文针对X70、X80管线钢在大线能量焊接条件下的焊接热影响区粗晶区的显微组织变化过程,详细地研究了X70、X80管线钢焊接热影响区利用其有益夹杂物诱导针状铁素体形核、细化粗晶区显微组织的行为。针对管线钢主要采用多丝大线能量焊接的特点,研究了焊接线能量为29.8 KJ/cm、40.0 KJ/cm和50.3KJ/cm时,X80管线钢焊接热影响区的组织变化行为。结果表明,X80钢采用大线能量埋弧焊时,热影响区的粗晶区晶粒会发生长大,使得焊接热影响区的韧性降低。若能利用钢中的有益夹杂物,诱导针状铁素体形核,就可细化热影响区粗晶区的显微组织,提高韧性。采用物理模拟的方法,研究了氧化物冶金钢及其焊接热影响粗晶区的显微组织和有益夹杂物性质在大线能焊接过程中的变化。研究表明,氧化物冶金钢中直径为0.2~0.6μm的有益夹杂物在大线能量焊接热过程中不会失去其诱导针状铁素体形核和感生形核的作用,具有抑制粗晶区晶粒长大的能力。采用焊接热模拟的方法,研究了针状铁素体管线钢焊接热影响区的晶粒自细化行为,详细分析了诱导针状铁素体形核夹杂物的大小、分布在焊接热循环过程中的变化规律,揭示了有益夹杂物的性质与显微组织之间的关系,为针状铁素体管线钢焊接工艺参数的优化提供了依据。更多还原

【Abstract】 Microstructure in welding Heat Affected Zone (HAZ) of pipeline steel, when applied to large heat input welding process, will become much coarse. This leads to greatly decrease in toughness of pipeline steel, which severely restricts its applications. This thesis focused on the transformation of microstructure in HAZ of X70/80 pipeline steel. The behavior that beneficial inclusions inducing acicular ferrite nucleation thus refining microstructure in Coarse Grain Heat Affected Zone (CGHAZ) of X70/80 pipeline steel under large heat input welding conditions was investigated detailedly.Due to the fact that welding of pipeline steel is always adopted by multipilewire large heat input welding methods, transformation behavior of microstructure in HAZ of X80 pipeline steel was investigated with the selected heat input parameters 29.8 KJ/cm, 40.0 KJ/cm, and 50.3KJ/cm. It was found that when large heat input automatic submerged-arc welding was applied to X80 pipeline steel, grains in CGHAZ of the steel would grown up which lead to decrease in toughness. If beneficial inclusions in the steel can be utilized to induce acicular ferrite nucleation, microstructure in CGHAZ will be refined and toughness be improved correspondingly.Using physical simulation technology, microstructure in oxides metallurgy steel and its CGHAZ as well as the character of beneficial inclusions in the process of large heat input welding process was investigated. Results indicated that the role of beneficial inclusions with a diameter of 0.2~0.6μm that inducing acicular ferrite nucleation and sympathetic nucleation woud not lose. They have the ability of restraining growth of grains in CGHAZ.Self refining grain behavior in HAZ of acicular ferrite microstructure pipeline steel was studied systematically by welding themal simulation method. Changes on size and distribution of inclusions which induced acicular ferrite nucleation during the welding thermal circle were analyzed completely. Relations between character of beneficial inclusions and microstructure in HAZ were disclosed. Those results provided a basis for optimizing welding parameters of acicular ferrite microstructure pipeline steel.更多还原