Heat Treatment Overview

Steel heat treatment methods · temperatures · hardness · typical materials

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Heat Treatment Methods 12

Hardness Scale Reference

Soft
0–20 HRC
Medium
20–40 HRC
Hard
40–55 HRC
Very Hard
55–70 HRC
HRC 20 ≈ HB 241
HRC 30 ≈ HB 286
HRC 40 ≈ HB 371
HRC 45 ≈ HB 421
HRC 50 ≈ HB 481
HRC 55 ≈ HB 543
HRC 60 ≈ HB 620
HRC 65 ≈ HB 721
Background — Steel Heat Treatment Principles

Why heat treat?

  • Hardening increases wear resistance and strength
  • Annealing relieves stresses and improves machinability
  • Surface treatments give a hard wear layer while keeping tough core
  • Thermochemical treatments enrich the surface with C or N

Carbon requirement

  • Quench hardening: requires > 0.30% C (typically 0.35–0.60%)
  • Carburising: used on low-C steels (0.10–0.25% C); surface C raised to 0.7–1.0%
  • Nitriding: no minimum C; uses Al, Cr, Mo alloying elements
  • Annealing: effective on all carbon steels

Typical Czech steels

  • 12 050 (C45): quenching, induction, 46–54 HRC
  • 14 220 (16MnCr5): carburising, 58–63 HRC surface
  • 19 312 (X38CrMoV5): tool steel, hot work
  • 14 109 (34CrAlNi7): nitriding steel, 900–1100 HV surface
  • 11 500 (S355): stress relief annealing only

Distortion and cracking

  • Quenching in water → higher hardness, more distortion/cracking risk
  • Oil quench → lower hardness, less distortion
  • Tempering always follows quenching to reduce brittleness
  • Through-hardening vs case hardening: thick sections may not harden fully through
  • Hardenability: described by Jominy end-quench test