深冷处理对YG8合金/42CrMo钢钎焊接头冲击性能的影响

Effect of cryogenic treatment on impact toughness of YG8/42CrMo brazed joints

为了提高YG8合金/42CrMo钢钎焊接头的性能,研究了深冷处理对接头冲击吸收能量和硬度的变化。选用Cu-Zn钎料对YG8合金/42CrMo钢进行钎焊热处理一体化处理,随后对接头进行-80℃×24 h三次深冷处理,最后进行回火处理。采用冲击试验和硬度测试对接头进行强度分析,通过对接头的断口形貌分析,并对比研究了焊缝的显微硬度、元素扩散情况以及XRD物相分析,进一步分析了深冷处理对焊接接头强度的影响机理。结果表明,与未深冷相比,经过深冷处理后的焊接接头冲击性能提高了31. 4%,焊缝的显微硬度降低6. 05 HV0. 05,接头强度得到提高。原因是深冷处理使硬质合金中Co相对WC硬质相的粘接更加牢固,减少了Co向焊缝扩散,避免硬质合金脆性的增加,同时Cu-Zn钎料中γ相减少,使其转变为以电子化合物Cu Zn为基的体心立方晶格固溶体β相,其高温塑性良好。

In order to improve the performance of YG8/42 CrMo brazed joints,the change of the impact toughness and hardness of the joints during cryogenic treatment process was studied. The brazing and heating treatment of YG8/42 CrMo was integrated using Cu-Zn brazing filler metal. The joints were then subjected to cryogenic treatments three times at-80 ℃ for 24 hours and finally tempered. The strength of the joint was investigated with the impact absorbed energy and the Vickers-hardness. The fracture morphology of the joints was analyzed.Moreover,the microhardness,element diffusion and XRD phase analysis of the weld were analyzed comparitively. Based on these analysis,the mechanism of cryogenic treatment effect on the brazed joint strength was investigated. The results demonstrate that the impact toughness of the brazed joints after cryogenic treatment increases by 31. 4%,the microhardness of the weld joints reduces by 6. 05 HV0. 05,and the joint strength improves compared with the samples that without cryogenic treatment. It is reasoned that the cryogenic treatment makes the adhesion of Co in the cemented carbide to the WC phase much firmer,and reduces the diffusion of Co to the weld. At the same time,the cryogenic treatment prevents the increase of brittleness of the cemented carbide,and makes the γ phase in the Cu-Zn solder transform into an electronic compound Cu Zn based bcc solid solution phase β with good high-temperature plasticity,reduces the amount of the γ phase.