当四个因素同时作用时，氢致开裂要么发生在热影响区微观结构中，要么发生在焊缝金属中。这些因素被定义为（1）氢的存在，（2）焊接应力，（3）易受影响的微观结构，以及（4）低温。在焊接过程中，可以从基底、焊接材料和外来污染物中获得氢气。在目前的炼钢工艺中，氢被降低到较低水平（尤其是在核工业的某些应用中，焊接材料中的氢含量受到严格控制），氢在起始金属材料中的存在已经减少，但并未消除。 然而，在一定程度上仍然存在从未适当干燥的焊剂中引入氢气的可能性。焊接应力不可避免地存在，只能在焊接前通过考虑接头几何形状、装配、外部约束和焊缝金属的屈服强度来最小化。热影响区微观结构取决于钢的成分和淬透性以及焊接后的冷却速度，而冷却速度又取决于焊接热输入、预热和厚度。最受制造控制的一个因素是焊接后的预热温度和保温时间。 因此，预热控制是焊接和热处理过程中降低氢浓度（如果存在）的有效手段。

Hydrogen-induced cracking occurs either in the heat-affected zone microstructure or in weld metal when four factors react simultaneously. These factors have been defined as (1) presence of hydrogen, (2) welding stresses, (3) a susceptible microstructure, and (4) a low temperature. Hydrogen can become available during welding from base and welding materials and extraneous contaminating matter. With the current processes of steel making where hydrogen is reduced to a low level (in particular for certain applications within the nuclear industry where the hydrogen content in weld material is closely controlled), the presence of hydrogen in the starting metallic materials has been diminished, but not eliminated. However, the possibility of introducing hydrogen still exists to some degree, for example, from welding fluxes that have not been properly dried. Welding stresses are inevitably present and can only be minimized prior to welding by consideration of joint geometry, fit-up, external restraint, and yield strength of the weld metal. The heat-affected zone microstructure is dependent upon the composition and hardenability of the steel and the cooling rate after welding, which, in turn, is governed by the weld heat input, preheat, and thickness. The one factor that is most subject to fabrication control is the preheat temperature and holding time after welding. Thus, dependence is placed on the control of preheat as an effective means of reducing hydrogen concentrations (if present) during welding and heat treatment.