深冷处理对304L奥氏体不锈钢低温冲击性能的影响

Influence of cryogenic treatment on low-temperature impact performance for 304L austenitic stainless steel

对工业生产的厚度为40 mm的304L奥氏体不锈钢中厚板进行1、3、5、7、9次深冷循环处理,分析比较多次循环深冷处理对304L奥氏体不锈钢组织、性能的影响。结果表明:在深冷过程中,材料急剧降温产生的温度应力和体积变化会导致一定量的形变诱导马氏体相变,同时材料局部存在马氏体转变起始温度较高的区域,在降温过程中也会发生马氏体相变。因此,室温冲击吸收的能量随深冷次数的增加呈现先略微下降、然后稳定上升的趋势;在-196℃低温冲击时,吸收的能量基本呈稳定上升趋势。经过3~5次的循环深冷处理,这种微量的马氏体相变组织会趋于稳定和细化,孪晶亚结构明显细化。多次深冷处理时,形变孪晶的形核需要很大动力,但长大过程却不需要大的动力,因此,局部区域混晶严重。

The cryogenic treatment with one,three,five,seven and nine cycles of 304 L austenitic stainless steel plate with the thickness of 40 mm in industry production were conducted respectively,and the influences of cryogenic treatment with many cycles on the microstructure and properties of 304 L austenitic stainless steel were analyzed and compared.The results show that the temperature stress and volume change caused by the rapid cooling of material during the cryogenic process lead to a certain amount of deformation to induce martensite transformation,meanwhile,there exists a region where the initial temperature of martensitic transformation is high locally in the material,and the martensite transformation also occurs during the cooling process.As a result,the energy absorbed by the impact at room temperature decreases slightly with the increasing of the number of cryogenic cycles,and then increases steadily,and the energy absorbed by the low-temperature impact at-196℃shows a stable upward trend.However,after three to five cycles of cryogenic treatment,the trace of martensite transformation structure tends to stabilize and refine,and the twin crystal substructure is obviously refined.Thus,during the cryogenic treatment with many cycles,the nucleation of deformation twin crystal requires a lot of power,but it does not require a lot of power during the growth process,so the mixed crystal is serious in local areas.