激光选区软化对304不锈钢加工硬化区域的影响

Effects of Selective Laser Softening Process on Work Hardening Area of 304 Stainless Steel

拉深工艺是工业制造中使用极为广泛的一种成型工艺,拉深过程中特别是在多次变形或变形量较大的冷拉深环节,容易发生加工硬化现象,一方面使得后续加工变得困难;另一方面,由于塑性和韧性的降低,工件在变形过程中或变形一段时间后容易发生开裂。采用光纤耦合半导体激光器,对发生加工硬化的304不锈钢容器器壁进行了激光软化处理,研究了加工硬化区域材料在激光辐照这种非平衡条件下的组织相变与再结晶现象,同时,利用COMSOL软件对该工艺的温度场等进行了模拟。研究发现,当所使用的激光参数使得扫描区域的最高温度在724℃至1 040℃之间时,加工硬化区域的板条状马氏体均转变成奥氏体,其中,最高温度在724~850℃之间时,材料硬度大幅降低并出现再结晶晶粒;最高温度在950~1 040℃之间时,组织发生完全再结晶,硬度降低到未拉深之前的水平。

Drawing process is widely applied in manufacturing industry. The phenomenon of work hardening is common during the process, especially in multi-stage drawing or large deformation, which makes the work piece diffieult to machine and crack in or after deforming as the decrease of the ductility and toughness. In this article, fiber-coupled diode laser was used to soften the 304 stainless steel container＇s wall that had been hardened after multi-stage drawing. The phase transformation and recrys- tallization of the work hardening district under the condition of non-equilibrium environment was investigated. Meanwhile, the temperature field of laser softening process was also studied by means of COMSOL software. Results show that the martensite phase of the work hardening area transformed into austenite phase when the maximum temperature is between 724℃ and 1 040℃ in the laser scanning district under proper processing parameters. Among the temperature interval （724-1 040℃C）, the hardness of the samples decreased seriously and the recrystallized grains appeared when the maximum temperature is between 724 ℃ and 850 ℃ ,while it fully recrystallized and the hardness down to the level of undrawed when the maximum temperature is within the region of 950 ℃ to 1 040 ℃.