Causes and solutions of arc crack in die steel

弧状裂纹产生的原因是淬火时的应力又因为时棱角处产生的应力比平滑表面大10倍，所以弧状裂纹常发生在模具棱角、凸台、刀纹、尖角、直角、缺口、孔穴、凹模接线飞边等形状突变处。下面天成模具小编就来为大家分享一下模具钢弧状裂纹产生的原因及方法。

The reason of arc crack is the stress during quenching, and because the stress at the corner is 10 times larger than that on the smooth surface, the arc crack often occurs at the sharp corner, boss, knife line, sharp corner, right angle, notch, hole, die connection flash and other shape mutation. Next, Tiancheng mould editor will share the causes and solutions of arc crack in mould steel.

(1)钢中含碳(C)量和合金元素含量愈高，钢Ms点愈低，Ms点降低2℃，则淬裂纹倾向增加1.2倍，Ms点降低8℃，淬裂倾向则增加8倍；

(1) The higher the carbon (c) content and alloying element content in the steel, the lower the MS point of the steel. If the MS point decreases by 2 ℃, the tendency of quenching crack increases by 1.2 times, the MS point decreases by 8 ℃, and the tendency of quenching crack increases by 8 times;

(2)钢中不同组织转变和相同组织转变不同时性，由于不同组织比容差，造成巨大组织应力，导致组织交界处形成弧状裂纹；

(2) Because of the difference of different microstructure transformation and the same microstructure transformation in the steel, the huge microstructure stress is caused by the difference of microstructure ratio tolerance, which leads to the formation of arc crack at the junction of microstructure;

(3)淬火后未及时回火，或回火不充分，钢中残余奥氏体未充分转变，保留在使用状态中，促使应力重新分布，或模具服役时残余奥氏体发生马氏体相变产生新的内应力，当综合应力大于该钢强度极限时便形成弧状裂纹；

(3) After quenching, the residual austenite in the steel is not fully transformed and retained in the service state, resulting in stress redistribution, or martensitic transformation of the residual austenite occurs during the service of the die, resulting in new internal stress. When the comprehensive stress is greater than the limit of the strength of the steel, arc cracks are formed;

(4)具有第二类回火脆性钢，淬火后高温回火缓冷，导致钢中P、S等有害杂质化合物沿晶界析出，大大降低晶界结合力和强韧性，增加脆性，服役时在外力作用下形成弧状裂纹。欢迎关注热处理生态圈！

(4) The second kind of tempered brittle steel is tempered at high temperature and cooled slowly after quenching, which leads to the precipitation of harmful impurity compounds such as P and s along the grain boundary, greatly reducing the binding force and strength toughness of grain boundary, increasing brittleness, and forming arc cracks under the action of external force during service. Welcome to pay attention to the heat treatment ecosystem! 

预防措施：

Preventive measures:

(1)改进设计，尽量使形状对称，减少形状突变，增加工艺孔与加强筋，或采用组合装配；

(1) Improve the design, make the shape symmetrical as far as possible, reduce the shape mutation, increase the process hole and stiffener, or adopt the combination assembly;

(2)圆角代直角及尖角锐边，贯穿孔代盲孔，提高加工精度和表面光洁度，减少应力集中源，对于无法避免直角、尖角锐边、盲孔等处一般硬度要求不高，可用铁丝、石棉绳、耐火泥等进行包扎或填塞，人为造成冷却屏障，使之缓慢冷却淬火，避免应力集中，防止淬火时弧状裂纹形成；

(2) Fillet instead of right angle and sharp edge, through hole instead of blind hole, improve processing accuracy and surface finish, reduce stress concentration source, for can't avoid right angle, sharp edge, blind hole, etc. general hardness requirements are not high, can use iron wire, asbestos rope, refractory mud, etc. for wrapping or filling, artificial create cooling barrier, make it slow cooling quenching, avoid stress concentration, Prevent arc crack from forming during quenching;

(3)淬火钢应及时回火，部分淬火内应力，防止淬火应力扩展；

(3) The quenched steel should be tempered in time to eliminate part of the internal stress and prevent the expansion of quenching stress;

(4)较长时间回火，提高模具抗断裂韧性值：

(4) After tempering for a long time, the fracture toughness of the die is improved

(5)充分回火，得到稳定组织性能；

(5) Fully tempered, stable structure and properties are obtained;

(6)多次回火使残余奥氏体转变充分和新的应力；

(6) After repeated tempering, retained austenite transforms fully and new stress is eliminated;

(7)合理回火，提高钢件疲劳抗力和综合机械力学性能；

(7) Reasonable tempering can improve the fatigue resistance and comprehensive mechanical properties of steel parts;

(8)对于有第二类回火脆性模具钢高温回火后应快冷(水冷或油冷)，可二类回火脆性，防止和避免淬火时弧状裂纹形状。

(8) For the die steel with the second kind of temper brittleness, it should be cooled quickly after high temperature tempering (water cooling or oil cooling), which can eliminate the second kind of temper brittleness and prevent and avoid the arc crack shape during quenching.

以上就是小编为大家分享的模具钢弧状裂纹产生的原因及方法，希望对大家有所帮助，如果需要了解更多模具钢相关的知识欢迎各位继续关注https://www.jnqhmj.com

The above is the reason and solution of arc crack of die steel that Xiaobian shared with you. I hope it can help you. If you need more knowledge about die steel, you are welcome to continue to pay attention https://www.jnqhmj.com