Views: 3 Author: Site Editor Publish Time: 2016-10-17 Origin: Site
In order to avoid cold crack and improve the mechanical properties of welded joint, heat and welding after preheating, high temperature should be taken round the fire.
(1) preheating before welding
Welding of martensitic stainless steel, especially in use with parent metal components of welding material, in order to prevent cold cracking, needs preheating before welding. Preheat temperature generally choose in 20 ~ 320 ℃ (), it's best to transition temperature is not higher than martensite.Carbon content is the most important factors to determine the preheating temperature, carbon content is high, the preheating temperature should be higher.Other factors influence the selection of preheating temperature and material thickness, the type of filler metal, welding method, the constraint degree and so on.Carbon is less than 0.1%, not hot, also have recommended preheat to 200 ℃ with broken l t is 0.1% ~ 0.2%, 200 ~ 260 ℃.In particularly tough situation can use higher preheating temperature, such as pre 400 ~ 450 ℃, but pay attention to the negative influence of high temperature.When the ancient carbon amount is more than 0.2%, the welding is difficult, in addition to the preheating, need to keep the temperature between the layers.
(2) temperature before tempering after welding
Artifacts from the welding temperature directly after welding heat up to round the fire.Because in the process of welding austenitic may not completely change, such as falling in to immediately and tempering after welding, there will be a carbide along the smelly austenite grain boundary precipitation and smelly transformation from austenite to perlite, produce product grain bulky groups, severe lower toughness.So round weldment cooling should be brought before the fire, let the welding seam and heat affected OuDeAo austenite basic points to make up.The stiffness of small components may be cooling to room temperature before tempering. For large structure, the thickness of the special when carbon content is higher, need to use more complex process;Cold to 100 ~ 150 ℃ after welding, insulation 0.5 ~ 1.0 h, and then heated to round the fire temperature.
(3) the heat treatment after welding
Is to reduce the purpose of heat treatment after welding seam and heat affected zone hardness and improve its plasticity and toughness, while reducing welding residual stress.Heat treatment after welding including tempering and annealing completely. Only in in order to get the lowest hardness, such as the need to be machined after welding, only by full annealing, the annealing temperature is 830 ~ 880 ℃, 2 h after the furnace cooling to 595 ℃, and then air cooling.High chromium martensitic stainless steel in quenching tempering welding quenched and tempered condition, after the high temperature tempering treatment after welding, the welding joint has good rhyme mechanical properties 0 if in annealing state welding, after welding will still appear uneven martensite structure, the whole weldment need after tempering treatment, make the performance of the joint is uniform.