440B: How Heat Treatment Shapes Its Final Mechanical Properties
440B Steel (also known as 90Cr18MoV, UNS S44003, 1.4112, X90CrMoV18, SUS440B) is a high-carbon, high-chromium martensitic stainless steel. With Cr content of 17.00–19.00 % and Mo content of 1.00–1.30 %, it delivers outstanding wear resistance, corrosion resistance and high tensile strength.
This grade is widely used for high-strength components requiring wear and corrosion resistance, including bearings, cutting tools, medical devices and valve parts. Its final mechanical properties strongly depend on applied heat treatment cycles. Details are outlined below.
– Heat Treatment Procedures
The core heat treatment workflow for 440B manipulates microstructure via annealing (softening), quenching (strengthening), and tempering (property stabilization) to achieve target mechanical properties.
1.Annealing (softening treatment):
Purpose: Reduce hardness to improve machinability, relieve forging or rolling residual stress, and homogenize carbide distribution to prepare the material for subsequent quenching.
Process parameters:
- Heating temperature: 800–920 ℃. Full austenitisation is required while preventing excessive carbide dissolution and grain coarsening.
- Holding time: 2–4 hours, adjusted according to workpiece thickness for uniform temperature penetration.
- Cooling method: Slow furnace cooling (≤50 ℃/h) down to below 600 ℃, followed by air cooling.
Microstructure & hardness after annealing: Pearlite plus carbides (predominantly Cr₂₃C₆). Hardness ≤25 HRC for easy machining.
2. Quenching (Strengthening Treatment)
Purpose: Form supersaturated martensitic microstructure to substantially boost hardness and strength. This step dissolves carbides into austenite sufficiently to secure subsequent corrosion and wear resistance.
Process parameters:
- Heating temperature: 1050–1075 ℃. This critical range prevents incomplete carbide dissolution at lower temperatures, and restricts grain coarsening or decarburization at excessive heat.
- Holding time: 30–60 minutes, to realise uniform austenitisation and eliminate local compositional variation.
- Cooling method: Oil quenching. 9Cr18MoV possesses good hardenability; oil cooling avoids cracking common with water quenching while enabling complete martensite transformation.
Post-quench microstructure & properties: Martensite, minor retained austenite and undissolved carbides. Hardness ≥60 HRC. High internal stress and brittleness remain, so tempering must follow promptly.
3. Tempering (Property Stabilization)
Purpose: Eliminate quenching residual stress and reduce brittleness; balance hardness and toughness; minimise retained austenite and stabilise component dimensions.
Process parameters: Heating temperature: Selected according to target performance, typical range 100–200 ℃. Cooling method: Air cooling.
Post-temper microstructure & hardness: Tempered martensite, minor carbides and retained austenite (≤5 %). Hardness can be tuned within 55–62 HRC.
– Properties After Heat Treatment
The final performance of 440B is governed by its post-heat-treatment microstructure. This grade features high hardness, excellent wear resistance and moderate corrosion resistance, detailed below.
1. Mechanical Properties
Hardness: After quenching plus low-temperature tempering (200–250 ℃), hardness reaches 58–62 HRC for maximum wear resistance. Medium-temperature tempering (300–400 ℃) lowers hardness to 55–58 HRC while delivering a notable toughness improvement.
Toughness: Its high-carbon high-chromium chemistry yields lower toughness compared with low-carbon stainless steels. Tempering at 300–400 ℃ improves this property, with impact toughness αk ≈15–30 J/cm²; toughness rises slightly as tempering temperature increases.
2.Corrosion Resistance
Base corrosion performance: With 17.00–19.00 % Cr and 1.00–1.30 % Mo, this grade outperforms ordinary carbon steel. It withstands corrosion from ambient air, fresh water, weak acids and bases, including food-grade service environments.
Process-related risk note: Incomplete quenching (undissolved carbides) or improper tempering (carbide precipitation along grain boundaries) raises susceptibility to intergranular corrosion. Tight control of quenching temperature and tempering cycles prevents carbide aggregation and mitigates this risk.
Wear Resistance: High hardness (58–62 HRC) plus evenly dispersed Cr₂₃C₆ carbides deliver exceptional wear resistance. It greatly outperforms austenitic stainless steels such as 304, suited for sliding friction applications including bearing parts and cutting edges.
3.Additional Properties
Low thermal conductivity (~20 W/(m·K)), roughly one-quarter that of carbon steel. Slow heating is required to prevent cracking induced by thermal stress. Large residual stress forms after quenching. Tempering must start promptly (delay ≤4 hours), otherwise distortion or cracking may occur.
– Summary
Heat treatment sequence: The full workflow of annealing (softening) → quenching (martensitic strengthening) → tempering (stress relief and property tuning) gives 440B a balanced combination of high hardness, outstanding wear resistance and moderate corrosion resistance. This grade serves high-strength components under wear and mild-corrosion service conditions.
Application tuning: Tempering temperature shall be adjusted according to practical working conditions such as impact resistance requirements, to strike a balance between hardness and toughness.
Material supply & certifications: Sichuan Super Metal Material Co., Ltd. maintains ready stock of 440B stainless steel rounds, squares, flats, hexagons, octagons and steel plates. Products are certified to GB/T 19001-2016/ISO 9001:2015 and GJB 9001C-2017 quality management standards. Inquiries from all industrial sectors are welcome.
