The results show that the brittle fracture cause of the tubing is that the brittleness of the nitrided structure is great and the normalized structure (pearlite and network ferrite) itself is brittle.

• 结果发现,渗氮层脆性较大,而且正火组织(珠光体+网状铁素体)本身韧性较低,这是油管发生脆性断裂的原因,建议选用调质处理油管进行渗氮。