预热与焊后回火对铸钢基体双金属梯度堆焊锻模堆焊层组织与性能的影响

Effect of preheat and post weld heat treatment on microstructure and mechanical properties of dies manufactured by bimetal-gradient-layer surfacing

为解决大型锻模的高成本、低寿命等问题,提出铸钢基体表面堆焊制备大型液压机用锻模新方法,针对其中的焊前预热与焊后回火工艺,将有限元分析与试验分析相结合,研究预热温度与焊后回火对堆焊层组织与力学性能的影响机理。研究结果表明:常温堆焊时,堆焊熔合区组织为马氏体+碳化物+残留奥氏体;随着预热温度的升高,冷却时间不断延长,组织呈现马氏体→贝氏体→珠光体转变趋势,显微硬度逐渐降低;当预热温度为400℃时,熔合区组织为铁素体+珠光体;焊后550℃/2 h回火后,堆焊层及热影响区硬度下降,基体中析出大量碳化物,堆焊层冲击韧性显著提高,断裂方式以韧窝断裂为主,母材性能在回火后无明显变化,说明预热与焊后热处理使堆焊层获得了较好的综合力学性能。

In order to solve the problems of high-cost and short life in large hydraulic press forging die, a new method, i.e. bimetal-gradient-layer surfacing（BGLS） based on cast-steel matrix cavity module, was adopted to manufacture hot forging die. The finite element method and experiment analysis were combined to investigate the effects of preheating and tempering on the microstructure and mechanical properties of the welds. The results show that when the specimen is preheated at room temperature, the microstructure is acircula martensite＋carbides＋retained austenite. As the preheating temperature increases, cooling time expands gradually, the microstructure has a trend of changing from martensite to bainite to pearlite and microhardness decreases. At 400 ℃, microstructure is mainly made up with ferrite＋pearlite. After 550 ℃/2 h of tempering, the microhardness of surfacing layer and heat effect zone decreases, and large amounts of carbides precipitate in the matrix. The impact energy increases and the fracture mode is mainly dimple. Based material has no change in impact energy. In conclusion, pre and post weld heat treatments improve the mechanical properties of the welds.