不同蠕变条件下耐热钢焊接件的空洞损伤演化

The cavity damage evolution of heat-resistant steel weldment under different creep conditions

摘要:

针对两种马氏体耐热钢焊接接头(F92/Co3W2和Co3W2/Co3W2)在105~250 MPa和873~948 K条件下开展蠕变拉伸测试，利用Larson-Miller参数法外推不同温度下焊接接头服役100 000 h寿命对应的蠕变断裂许用应力，研究其在不同蠕变条件下的空洞损伤规律. 随着外加应力的降低，两种焊件的断裂位置、断裂模式及断裂机制均发生了转变，从位于母材的穿晶塑性断裂变为细晶热影响区的沿晶脆性断裂(即Ⅳ型断裂). 针对断口区域的空洞损伤变化规律的研究表明：(1) 当断裂模式由塑性断裂转变为脆性断裂时，断口附近空洞会出现突变，塑形断口空洞“个头大数量少”而脆性断口空洞“个头小数量多”；(2) 在相同断裂模式下，随蠕变应力的减小，空洞按照“尺寸变大、数量密度增大及面积分数增大”的规律变化；(3) Ⅳ型断口处空洞存在合并链接现象，其方向与应力方向垂直.

Abstract:

Creep testing was conducted on two types of welded joints made of martensitic heat-resistant steel (F92/Co3W2 and Co3W2/Co3W2) at temperatures ranging from 873 K to 948 K and stress levels ranging from 105 MPa to 250 MPa. The Larson-Miller parameter method was employed to extrapolate the allowable creep fracture stresses for a service life of 100,000 hours at various temperatures. Additionally, the cavity damage mechanisms under different creep conditions were investigated. As the applied stress decreases, the location, mode, and mechanism of fracture in both types of welds transition from transgranular plastic fracture in the base metal to intergranular brittle fracture in the fine grain heat-affected zone (termed type IV fracture). It was observed that cavities undergo a sudden change when the fracture mode shifts from plastic to brittle fracture. Specifically, cavities associated with plastic rupture exhibit larger size but smaller number density, while cavities associated with brittle rupture show smaller size but greater number density. When the fracture mode remains the same, the cavities exhibit an increase in size, quantity, and area fraction as the stress decreases. Notably, a coalescence phenomenon was observed for cavities near the type IV fracture site, with the coalescence direction being perpendicular to the tensile direction.