Welding performance of 00Cr18Ni5Mo3Si2, 00Cr18Ni5Mo3Si2Nb steel

Welder and welding joints with the welded 00Cr18Ni5Mo3Si2 and 00Cr18Ni5Mo3Si2Nb can meet the requirements of 01Cr18Ni10Ti and 03Cr18Ni11Ti with higher strength, high toughness, good corrosion resistance and high temperature resistance. 00Cr18Ni5Mo3Si2 and 00Cr18Ni5Mo3Si2Nb are commonly used super austenitic stainless steel. (1) Welding Heat Input Control: Since austenitic stainless steel has a small thermal deformation capacity at high temperatures, it is necessary to limit the welding heat input to reduce the thermal deformation. The method adopted is to reduce the welding current or reduce the welding speed. (2) Shielding Gas Control: Shielding gas control is an important measure to assure the weldability of austenitic stainless steel. Use an argon-rich mixed gas, the mixed proportion of Argon : Carbon dioxide = 8:2. (3) Welding Material Selection: It is recommended to use 309L electrode or 625 electrode for welding austenitic stainless steel. It is not recommended to use 308L electrodes or 2209 electrodes. 309L electrodes or 625 electrodes contain higher niobium or niobium and titanium. Niobium can prevent grain growth and reduce the tendency of hot cracking. (4) Preheating: Before welding, it is recommended to preheat austenitic stainless steel below 20 mm in thickness to 150 ~ 200 ℃, above 20 mm in thickness to 200 ~ 350 ℃, prevent the welded joint structure transformation and cold crack due to too rapid cooling. After welding, the welded joint should be maintained at a temperature of 200 ~ 250 ℃ for 30 ~ 60 minutes. (5) Interlayer or Interpass Temperature Control: The maximum temperature for the interpass welds should be controlled below 350 ℃ and the minimum temperature should be controlled above 40 ℃. It is recommended that the temperature for the first pass should not exceed 250 ℃, and for the second and subsequent passes it should not exceed 200 ℃. (6) Stress Relief Ater Welding: After welding 0Cr18Ni5Mo3Si2 and 00Cr18N5Mo3Si2Nb stainless steel, it is necessary to conduct a stress relief annealing to eliminate the welding residual stress, avoid distortion and cracking. Stress relief annealing temperature should not exceed 420 ℃, time: 1.5 to 2.5 hours.

00Cr18Ni5Mo3Si2钢和00Cr18Ni5Mo3Si2Nb钢的焊接接头可以满足比01Cr18Ni10Ti和03Cr18Ni11Ti更高强度、高韧性和良好耐腐蚀性和耐高温性的要求。00Cr18Ni5Mo3Si2和00Cr18Ni5Mo3Si2Nb是常用的超奥氏体不锈钢。（1）焊接热量输入控制：由于奥氏体不锈钢在高温下的热变形能力小，因此必须限制焊接热量输入以减少热变形。采用的方法是减少焊接电流或降低焊接速度。（2）屏蔽气体控制：屏蔽气体控制是保证奥氏体不锈钢焊接性能的重要措施。使用氩富混合气体，氩：二氧化碳的混合比例为8：2。（3）焊材料选择：建议用309L电极或625电极焊接奥氏体不锈钢。不推荐使用308L电极或2209电极。309L电极或625电极含有较高的铌或铌和钛。铌可以防止晶粒增长和减少热裂纹的趋势。（4）预热：焊接前，建议将厚度小于20 mm的奥氏体不锈钢预热至150~ 200℃，厚度大于20 mm的奥氏体不锈钢预热至200~ 350℃，以防止焊接接头由于冷却过快而发生结构变形和冷裂纹。焊接后，应将焊接接头温度保持在200~ 250℃，30 ~60分钟。（5）层间或间隙温度控制：层间焊的最高温度应控制在350℃以下，最低温度应控制在40℃以上。建议第一道焊的温度不要超过250℃，第二道及以后的焊道温度不要超过200℃。（6）焊后应力释放：焊接0Cr18Ni5Mo3Si2和00Cr18N5Mo3Si2Nb不锈钢后，必须进行应力释放退火，以消除焊接残余应力，避免变形和开裂。应力释放退火温度不应超过420℃，时间：1.5至2.5小时。

00Cr18Ni5Mo3Si2 (TP347) and 00Cr18Ni5Mo3Si2Nb (TP347Nb) are austenitic stainless steel grades, both of which are commonly used in the manufacture of pressure vessels, piping systems and containers in high temperature environments. Both of these alloys have excellent corrosion resistance to acidic media and high temperature oxidation resistance.

Both 00Cr18Ni5Mo3Si2 an 00Cr18Ni5Mo3Si2Nb are easily weldable by conventional welding methods, such as gas arc welding, tungsten-inert gas welding (TIG) and electron beam welding. The solidification structure of the weld is austenitic and the strength of the weld is excellent. Before welding, preheating is not necessary and the interpass temperature should not exceed 350°F (177°C). The alloy should be protected from heat input by coatings during welding.

For 00Cr18Ni5Mo3Si2, the use of gas-tungsten arc or gas-metal arc welding with R309Mo and R309Si rods (matching filler metals) is recommended. Argon-based shielding gas and slow cooling should be used to prevent temper embrittlement. For 00Cr18Ni5Mo3Si2Nb, welding with R310NiMo and R347Si electrodes (matching filler metals) and also a shielding gas of argon is recommended. Slower cooling should be applied to both grades to reduce the hardness of the welds. For both steels, post-weld heat treatment at temperatures below 1300°F (704°C) is prohibited.

The weldability of 00Cr18Ni5Mo3Si2 and 00Cr18Ni5Mo3Si2Nb is excellent. The strength of the welding joint is high, and the effect of post-weld heat treatment on their strength is small. Both are easy to weld and can be used in a wide range of industrial applications.