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本文用插销法研究了预热和后热对30CrMn SiNi2A 超高强钢HAZ 冷裂倾向和强韧性的影响规律。试验结果表明,250℃预热.260℃后热1h,插销临界启裂应力σ_(cr)>σ_s。用焊接热模拟试件测试了不同焊接热循环下的断裂韧性K_(IC),发现最优焊接热循环和插销试验时的最佳工艺相吻合。用透射电镜观察了HAZ 组织的精细结构,观察了残余奥氏体的分布形态,并测定了残余奥氏体的含量。发现250℃预热,260℃后热1h。可得到含9.8%残余奥氏体的、以位错板条马氏体为主带有少量下贝氏体的显微组织。残余奥氏体以薄膜状的形态分布于马氏体板条间,它既韧化了组织又阻碍了氢的扩散,对防止冷裂纹的产生是有益的。试验结果为后热工艺的制定和解释后热韧化抗裂的本质提供了理论依据。
In this paper, the influence law of preheating and post-heating on cold cracking tendency and toughness of HAZ in 30CrMn SiNi2A ultra-high strength steel was studied by means of plug-in method. The test results show that the critical crack initiation stress σ_ (cr)> σ_s of the bolt is preheated at 250 ℃ and heated at 260 ℃ for 1 h. The fracture toughness K_ (IC) under different welding thermal cycles was tested by using the welding thermal simulation specimen. The best welding thermal cycle was found to be in accordance with the best technology in the bolt test. The microstructure of HAZ was observed by transmission electron microscope. The distribution of retained austenite was observed. The content of retained austenite was also measured. Found 250 ℃ preheating, hot 1h after 260 ℃. Can get 9.8% retained austenite, with martensite mainly with a small amount of lower bainite microstructure. Residual austenite in thin film-like distribution between the martensite lath, which not only toughens the organization also hindered the proliferation of hydrogen, to prevent cold cracking is beneficial. The experimental results provide the theoretical basis for the formulation of post-thermal process and the nature of heat-toughening and cracking after the explanation.