By what means can the machinability rating of steel be improved___________________?
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Answer: B. phosphorous, lead and sulphur
Explanation
Machinability of steel is enhanced by adding free-machining additives such as sulfur, phosphorus, and lead, which promote chip breakage. These alloy additions form microscopic inclusions that interrupt continuous chip formation, reducing friction and tool wear. Shorter chips prevent tangling around cutting tools and allow for higher machining speeds and improved surface finishes. Machinability measures how easily a metal can be cut, shaped, and finished while maintaining acceptable tool life. Lead forms fine dispersed globules in steel, acting as a solid lubricant that decreases cutting forces during machining. Sulfur combines with manganese to create inclusions that make metal chips brittle and easy to shear off cleanly.
Silicon and aluminum act primarily as deoxidizers and grain refiners rather than serving as primary free-machining additives. Phosphorus and aluminum alone do not provide the combined lubricating and chip-breaking benefits of lead, sulfur, and phosphorus. Graphite is added to cast irons rather than standard steels to provide internal lubrication during machining operations.
- Subject
- Engineering
- Category
- Mechanical Engineering
- Topic
- —
- Difficulty
- medium
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