Chemical Engineering - Chemical Engineering Basics - Discussion

Correct Answer: B. Electrical resistance

Explanation:
Chromium molybdenum steel (like 4130 or 4140) is a high-strength alloy steel that requires careful control during welding due to its hardenability and risk of cracking in the heat-affected zone (HAZ).

Thermit welding: This can be used on chromoly steel, especially in large cross-sections like railway tracks. It provides high heat, which can be beneficial if controlled properly.

Electrical resistance welding (like spot welding): Not suitable for chromium molybdenum steels due to their low electrical resistance and high thermal conductivity, which interferes with proper fusion and leads to brittle joints.

Oxy-acetylene welding: Although not ideal, it can be used if proper preheat and post-weld heat treatment are applied.

Any of these: This would be wrong because some of these methods can be used successfully.

Chromium-molybdenum steel has a low value of weldability factor for electrical resistance welding and hence cannot be welded using electrical resistance welding.

Chromium-molybdenum steel can not be welded using conventional welding methods such as oxy-acetylene welding or arc welding.
This is because the high carbon content and the presence of alloying elements such as chromium and molybdenum can cause cracking and brittleness in the heat-affected zone during welding.

Anyone can elaborate it?

Why we can't use electrical welding?

Whatever compound we have in chromium molybdenum steel. Steel is there & it is good conductor of electricity i.e why?

The main characteristics are strength (creep strength and room temperature), rigidity, harden ability, wear resistance, corrosion resistance, fairly good impact resistance (toughness), relative ease of fabrication.