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HSLA, stainless and tool steels

Short answer

HSLA steels: low carbon, microalloyed with Nb, V, Ti; high strength, good weldability; used in bridges, pipelines. Stainless steels: ≥10.5% Cr; ferritic (BCC), austenitic (FCC, 18Cr-8Ni), martensitic (hardenable); corrosion resistant. Tool steels: high carbon with W, Mo, Cr, V; hard, wear-resistant; for cutting tools, dies.

Write short notes on (a) high-strength low-alloy (HSLA) steels, (b) stainless steels and their types, and (c) tool steels. Mention the composition, properties and uses.

Alloy steels contain elements such as Cr, Ni, Mo, V, Mn, Si added to plain carbon steel to improve strength, hardenability, toughness, corrosion or wear resistance.

(a) HSLA steels

  • Composition: low carbon (0.05-0.25% C), up to 2% Mn, small amounts (below 0.1%) of Nb, V, Ti, plus Cu, Cr, Ni.
  • Strengthening: fine grain size, precipitation of carbonitrides, and solid-solution strengthening.
  • Properties: yield strength 275-550 MPa (higher than mild steel), good weldability and toughness, better atmospheric corrosion resistance (weathering steels).
  • Uses: bridges, pressure vessels, pipelines, vehicle frames, and building structures, where lighter sections reduce weight.

(b) Stainless steels

Contain at least 10.5% Cr; a thin, self-healing film of Cr2_2O3_3 protects against corrosion.

TypeTypical compositionStructurePropertiesUses
Ferritic12-27% Cr, low CBCCMagnetic, moderate strength, not heat treatableAutomotive trim, kitchen equipment
Austenitic (304: 18Cr-8Ni)16-26% Cr, 6-22% NiFCCNon-magnetic, ductile, best corrosion resistance and weldabilityChemical plant, food and dairy equipment
Martensitic12-18% Cr, 0.1-1% CMartensiteHardenable, magnetic, strong, lower corrosion resistanceCutlery, turbine blades, surgical tools

Other types: duplex and precipitation-hardening stainless steels.

(c) Tool steels

  • Used to make cutting, forming and shearing tools; contain 0.6-1.5% C with W, Mo, Cr, V, Co that form hard carbides.
  • Properties: high hardness, wear resistance, hot hardness (red hardness), toughness.
  • Types: high-speed steel (18-4-1: 18% W, 4% Cr, 1% V), cold-work (die) steels, hot-work steels, shock-resisting steels.
  • Uses: drills, taps, lathe cutting tools, punches, and dies.

✓ Answer checked by Claude Opus 5.5 (high effort)

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