SAF2507 SDSS热冲压成形χ相和σ相对力学性能的影响

Influence ofχphase andσphase on mechanical properties of SAF2507 SDSS during hot stamping forming

采用JMatPro软件模拟计算了SAF2507 SDSS的热力学平衡相图,并制定了热冲压成形工艺,对SAF2507 SDSS板材进行了650~1150℃的热冲压成形;通过OM、SEM和EDS研究了χ相和σ相的析出规律,运用万能试验机、硬度计和冲击机研究了材料的力学性能。结果表明,在650℃进行热冲压成形时,微观组织中无析出相;750~1050℃时,α/α晶界和α/γ相界处析出χ相和σ相,χ相和σ相的析出机理为α→χ/σ+γ_(2);在1050~1150℃时,γ相向α相转变;随着热冲压成形温度升高,材料抗拉强度和硬度先增加后减小再增加,伸长率、截面收缩率和冲击功先减小后增加再减小。拉伸试样断口断裂形式由韧窝断裂转变为解理断裂再转变为准解理断裂;热冲压成形温度为1050℃时,SAF2507 SDSS获得最佳微观组织和综合力学性能。

JMatPro software was used to simulated and calculate the thermodynamic equilibrium phase diagram of SAF2507 SDSS,and the hot stamping forming process was determined.The SAF2507 SDSS sheets were subjected to hot stamping forming at 650-1150℃.The precipitation regularity ofχphase andσphase was studied by means of OM,SEM and EDS,and the mechanical properties of material were studied by universal testing machine,hardness tester and impact machine.The results show that there is no precipitated phase in microstructure during hot stamping forming process at 650℃.χphase andσphase precipitate atα/αgrain boundaries andα/γphase boundaries at 750-1050℃,the precipitation mechanism ofχphase andσphase isα→χ/σ+γ_(2).At 1050-1150℃,γphase changes toαphase.With the increase of hot stamping forming temperature,the tensile strength and hardness of material firstly increase,then decrease and then increase,and the elongation,section reduction and impact energy firstly decrease,then increase and then decrease.The fracture form of tensile specimens changes from dimple fracture to cleavage fracture and then to quasi cleavage fracture.When the hot stamping forming temperature is 1050℃,the best microstructure and comprehensive mechanical properties of SAF2507 SDSS are obtained.