焊接冷裂纹临界冷却时间判据t_（cr）的建立

本文采用平板刚性拘束裂纹试验（ＰＲＲＣ）研究了四种国产低合金高强钢焊接冷裂纹敏感性，探讨了焊接接头扩散氢含量、焊接线能量、局部预热温度、拘束度的大小及由于局部预热产生附加应力等对钢材冷裂纹敏感性的影响。在上述试验研究的基础上，建立了国产低合金高强钢的临界冷却时间判据ｔ＿（ｃｒ）。并通过实例验证这一判据是可靠的，对于评定现行工艺条件下是否产生冷裂纹及确定合理焊接工艺都具有重要的指导意义。

配方施肥对赤皮青冈容器苗生长的影响

通过对赤皮青冈容器苗进行N、P、K配比施肥试验,研究其不同施肥配方处理下的苗木苗高、地径、地上干质量、地下干质量和总干质量等特征的变化。结果表明:不同施肥处理对赤皮青冈容器苗木各项指标均存在显著差异,处理2(尿素5 g+过磷酸钙3 g+氯化钾5 g)对其幼苗生长的促进作用最大,为最优施肥处理;经过2次施肥后处理2的苗木苗高、地径、地上干质量、地下干质量、总干质量和净光合速率分别是对照组的126.59%、124.55%、191.57%、248.57%、202.19%、222.81%。

ESTABLISHMENT OF CRITICAL COOLING TIME CRITERION OF WELDING COLD CRACKING

The plate rigid restraint cracking tests (PRRC) have been used to study the welding cold cracking susceptibilities of four kinds of domestic HSLA steels and the effects of diffusive hydrogen content. In welded joints, welding heat input, local preheat temperature, restraint intensity and additional stress induced by local preheating on cold cracking susceptibility of steels have been discussed. On the basis of the above research, the critical cooling time criterion tcr of domestic HSLA steels is established. This criterion is proved to be reliable in real application, and has important significance to assess whether the cold cracking occurs under conditions of welding process.