SAE 4140无缝钢管环状淬火裂纹成因分析

Cause Analysis of Ring-shape Quenching Crack in 4140 Seamless Steel Pipe

通过化学成分检测、硬度检验、金相观察、电镜扫描和能谱分析等试验手段对SAE 4140无缝钢管的管端环状裂纹进行了原因分析,结果表明,SAE 4140无缝钢管管端环状裂纹属于淬火裂纹,一般只发生在管端,其产生的原因是内外壁冷却不均,外壁冷却速度远高于内壁,导致在靠近壁厚内表位置产生应力集中而引起开裂失效。加强淬火时钢管内壁冷却,改善厚壁钢管内外壁冷却速度均匀性,控制钢管淬火后出水温度为150~200℃,利用钢管余温自回火,降低钢管淬火应力可消除这种环状裂纹。

The reason of ring-shape crack at pipe end of SAE 4140 seamless steel pipe was studied by chemical composition exam,hardness test,metallographic observation,scanning electron microscope and energy spectrum analysis.The results show that the ring-shape crack of SAE 4140 seamless steel pipe is the quenching crack,which generally occurs at the end of the pipe.The reason of the quenching crack is the different cooling rate between inside and outside wall and the outside wall cooling rate is much higher than that of the inside wall,which results in cracking failure caused by stress concentration near inside wall position.The ring-shape crack can be eliminated by increasing the cooling rate of the inside wall of the steel pipe during quenching,improving the uniformity of the cooling rate between the inside and outside wall and controlling the temperature after quenching to be within 150~200℃to reduce the quenching stress by self-tempering.