特殊金属焊接技术要点

引言

镍基高温合金和高合金不锈钢在焊接时面临独特的挑战。它们的高合金含量、迟缓的熔池流动性以及对热裂纹的敏感性，都要求严格的工艺控制。

本指南涵盖三大材料家族的焊接关键变量：Hastelloy耐蚀合金、Inconel高温合金、以及奥氏体耐热钢。

焊材选择

默认策略是使用同质或稍高匹配的填充材料。Hastelloy C-276 使用 ERNiCrMo-4 焊丝；Inconel 625 使用 ERNiCrMo-3；310S 耐热钢使用 ER310 或 310S 同质焊丝。

偏离同质化学成分会导致焊缝区的电化学腐蚀或高温性能下降。当必须焊接异种金属时，应选择中间成分的填充材料，并通过腐蚀试验验证。

预热与层间温度

过高的层间温度会促进镍合金晶粒长大和不锈钢敏化。每道焊后使用红外测温仪监控。

保护气体策略

镍合金TIG（GTAW）焊接以纯氩为标准保护气。焊接厚板时可添加25–30%氦气以提高热输入和改善流动性。背面必须采用氩气背保护，防止根部氧化（"sugaring"）。

MIG（GMAW）工艺中，仅在指定时使用含1–2%氧气或CO₂的氩气混合气。镍合金对活性气体耐受性较差。

污染控制

硫、磷、铅、锌会在镍合金中引起灾难性热裂纹。焊接前用丙酮清洁所有坡口表面。使用专用于特定合金的不锈钢钢丝刷；严禁与碳钢工具交叉污染。

热输入与焊接速度

镍合金导热系数低、电阻率高，热量容易集中导致过热和变形。应采用窄焊道、适中电流、比碳钢更快的焊接速度。

推荐热输入：薄板0.5–1.2 kJ/mm；厚板1.0–1.8 kJ/mm。摆动宽度不超过焊丝直径的3倍。

焊后热处理

大多数固溶态镍合金在耐蚀应用中无需焊后热处理。但Inconel 718必须进行720°C/8h + 炉冷至620°C/8h的时效处理。310S组件有时在870–980°C进行消除应力处理。

联系我们的冶金团队获取焊接工艺支持和焊材供应

Key Techniques for Welding Special Metals

Introduction

Nickel-based superalloys and high-alloy stainless steels present unique welding challenges. Their high alloy content, sluggish weld pool behavior, and sensitivity to hot cracking demand disciplined process control.

This guide covers the essential variables for three material families commonly supplied: Hastelloy corrosion-resistant alloys, Inconel high-temperature alloys, and austenitic heat-resistant steels.

Filler Metal Selection

Matching or over-matching filler composition is the default strategy. For Hastelloy C-276, use ERNiCrMo-4 filler. For Inconel 625, use ERNiCrMo-3. For 310S heat-resistant steel, use ER310 or 310S filler wire.

Deviating from matching chemistry risks galvanic corrosion in the weld zone or reduced high-temperature properties. When dissimilar metals must be joined, select a filler with intermediate composition and verify with corrosion testing.

Preheating and Interpass Temperature

Excessive interpass temperature promotes grain growth in nickel alloys and sensitization in stainless steels. Use infrared thermometers to monitor every pass.

Shielding Gas Strategy

Pure argon is standard for TIG (GTAW) welding of nickel alloys. Add 25–30% helium to increase heat input and improve fluidity when welding thick sections. Back-purging with argon is mandatory to prevent sugaring (oxidation) on the root side.

For MIG (GMAW) processes, use argon with 1–2% oxygen or CO₂ only when specified. Nickel alloys do not tolerate aggressive active gases well.

Contamination Control

Sulfur, phosphorus, lead, and zinc cause catastrophic hot cracking in nickel alloys. Clean all joint surfaces with acetone before welding. Use stainless-steel wire brushes dedicated to the specific alloy; never cross-contaminate with carbon steel tools.

Oil, grease, and marking crayons must be completely removed. Even trace zinc from galvanized fixtures can initiate liquid-metal embrittlement cracks.

Heat Input and Travel Speed

Nickel alloys have low thermal conductivity and high electrical resistance. Heat tends to concentrate, causing overheating and distortion. Use stringer beads with moderate amperage and faster travel speed compared to carbon steel.

Recommended heat input: 0.5–1.2 kJ/mm for thin sheet; 1.0–1.8 kJ/mm for thick plate. Oscillation width should not exceed 3× wire diameter.

Post-Weld Heat Treatment

Most solution-annealed nickel alloys require no PWHT for corrosion applications. However, Inconel 718 must be aged at 720°C/8h + furnace cool to 620°C/8h to achieve design strength. Stress relief at 870–980°C is occasionally applied to 310S assemblies to redistribute residual stresses without sensitized microstructure.

Critical: Always refer to the latest ASME Section IX or AWS D10.18 procedures when qualifying welding procedures for pressure equipment.

Contact our metallurgical team for welding procedure support and filler metal supply at ay-alloy.com