430铁素体不锈钢超窄间隙焊接试验

Welding process of 430 ferritic stainless steel ultra-narrow gap welding

铁素体不锈钢焊接时，需采用低热输入，以防止因热影响区晶粒粗化而导致的接头局部脆化。采用间隙宽度为3．2mm的焊剂带约束电弧超窄间隙焊接方法，对430热轧板进行焊接试验。利用底部衬条获得了熔合良好的根焊，该方法焊接热输入可低至0．32kJ／mm；热影响区窄，约为0．25mm；铁素体晶粒未严重粗化，晶粒度为5．5—6级。采用ER309焊丝，焊接接头焊缝组织为奥氏体＋板条状铁素体；在焊接热循环过程中，热影响区部分组织发生α→γ→M相变，最终组织为铁素体＋马氏体；快速冷却促使铁素体晶粒内优先析出M23C6或M23（C，N）6。焊缝与母材为高强匹配，热影响区冲击韧性与母材相当。

In order to avoid the embrittlement caused by coarse grain in welding of ferritic stainless steel,the low heat input is necessary.A series of experiments for the ultra-narrow gap welding with constrained arc by flux strip of 430 ferritic stainless steel were carried out,and the gap width was 3.2 mm.By using bottom steel bar,the root welding with good fusion is acquired.The heat input could be decreased to 0.32 kJ/mm in welding process.A narrow HAZ(heat-affected zone) with width of 0.25 mm is obtained..The ferrite grain has not grew up remarkably,with grain size of 5.5~6 grade.By using ER309 welding wire,the microstructure of the weld contains austenite and plate strip ferrite.During the welding thermal cycle,there is a phase transformation α→γ→M which takes place in the HAZ,so the final microstructure is ferrite and martensite.The rapid cooling conditions of welding would facilitate the formation of microphase precipitation M_(23)C_6 or M_(23)(C,N)_6 in the HAZ of the ferrite.The weld metal is found to be over matched.The impact toughness of HAZ is equal to parent metal.