什么叫热应力裂纹?焊补灰铸铁时应取哪些措施预防产热力裂纹?
推荐回答（4个）
指热塑性塑件过度暴露在较高温度下发生的裂纹及破裂。
在不影响铸件使用性能的前提下，可适当调整合金的化学成分，缩小凝固温度范围，减少凝固期的收缩量，选择抗裂性较好的共晶成分或接近共晶成分；对碳钢及合金钢进行微合金和变质处理，可大大提高铸钢件的抗裂强度。
加入稀土元素或其它元素可以达到此目的，加入量一般均在0.3%以下；改进铸钢的脱氧工艺及对钢液进行真空处理，可使钢中气体含量显著下降，减少非金属夹杂物，提高铸钢的抗裂性能；采用悬浮浇注法，即在钢水浇注的同时通过浇口或其它通道加入细颗粒金属粉末使初晶组织化。
扩展资料
避免淬裂的可有原则是设法尽量减小截面内外马氏体转变的不等时性。仅仅实行马氏体转变区内的缓冷却不足以预防纵裂的形成。一般情况下只能产生在非淬透性件中的弧裂，虽以整体快速冷却为必要的形成条件，可是它的真正形成原因，却不在快速冷却(包括马氏体转变区内)本身，而是淬火件局部位置(由几何结构决定)；
在高温临界温度区内的冷却速度显著减缓，因而没有淬硬所致。产生在大型非淬透性件中的横断和纵劈，是由以热应力为主要成份的残余拉应力作用在淬火件中心，而在淬火件末淬硬的截面中心处，首先形成裂纹并由内往外扩展而造成的。
为了避免这类裂纹产生，往往使用水-油双液淬火工艺。在此工艺中实施高温段内的快速冷却，目的仅仅在于确保外层金属得到马氏体组织；而从内应力的角度来看，这时快冷有害无益。
其次，冷却后期缓冷的目的，主要不是为了降低马氏体相变的膨胀速度和组织应力值，而在于尽量减小截面温差和截面中心部位金属的收缩速度，从而达到减小应力值和最终抑制淬裂的目的。
参考资料来源：百度百科-热裂
参考资料来源：百度百科-热应力开裂
参考资料来源：百度百科-热应力
灰口铸铁的焊接性存在主要就是2点
1、容易白口化，焊接容易产生裂纹。
2、渗碳组织变硬。
3、热影响区明显变硬。
有条件可以用焊前预热处理，焊接后保温缓冷，或者选用抗裂性能优异的WEWELDING777铸铁焊条（简称威欧丁777）冷焊工艺焊接，适合现场没有热焊条件使用，尽量减少热量影响，使得成功率增加，特别是冷焊工艺的WEWELDING777特种铸铁焊条焊接。
焊接铸铁和普通铁如果是热焊预热和焊后保温处理可以用J506焊接，如果是抗裂性能要求高强度要求高就用WEWELDING777特种铸铁焊条这个是冷焊接工艺，就是省却了焊前预热和焊后保温的繁琐工艺。
WEWELDING777用于哪些方面
–将铸铁和钢焊接、不同铸铁的焊接 –传动齿轮箱体
–灰口铸铁、可锻铸铁或球墨铸铁 –下水管
铸铁焊补时产生白口的原因及预防措施。铸铁焊补时，往往会在焊缝和母材交界的熔合线处生成一层白口铸铁，严
如果用同材质焊接不会产生热裂纹，如果用碳钢或镍基焊材会产生热裂纹。这个问题怎么回答呢。不过还是选择（对）因为焊接灰铸铁是一般都用镍基焊材焊接的比较多。
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