Stainless Steel – Grade 446 (UNS S44600)

Topics Covered

Introduction
Chemical Composition
Physical Properties
Mechanical Properties
Thermal Properties
Other Designations
Fabrication and Heat Treatment
Machinability
Welding
Forging
Hot Working
Cold Working
Annealing
Applications

Introduction

Stainless steels are known as high-alloy steels. They have excellent corrosion resistance in comparison with other steels as they contain more chromium.

Based on their crystalline structure, stainless steels are divided into three groups, namely, martensitic, austenitic and ferritic steels. A combination of martensitic and ferritic steels forms a fourth group known as precipitation-hardened steels.

The grade 446 stainless steel is a ferritic, non-heat treatable stainless steel that provides good resistance to high temperature oxidation and corrosion. The following datasheet provides more details of grade 446 stainless steel.

Chemical Composition

The chemical composition of grade 446 stainless steel is outlined in the following table.

Element Content (%)
Iron, Fe 73
Chromium, Cr 23.0 - 27.0
Manganese, Mn 1.50
Silicon, Si 1.0
Nickel, Ni 0.25
Carbon, C 0.20
Phosphorous, P 0.040
Sulfur, S 0.030

Physical Properties

The following table shows the physical properties of grade 446 stainless steel.

Properties Metric Imperial
Density 7.80 g/cm3 0.282 lb/in³

Mechanical Properties

The mechanical properties of grade 446 stainless steel are displayed in the following table.

Properties Metric Imperial
Tensile strength 550 MPa 79800 psi
Yield strength (@strain 0.200%) 345 MPa 50000 psi
Elastic modulus 200 GPa 29000 ksi
Poisson's ratio 0.27-0.30 0.27-0.30
Elongation at break 20% 20%
Hardness, Brinell (estimated from Rockwell B) 159 159
Hardness, Knoop (estimated from Rockwell B) 173 173
Hardness, Rockwell A (estimated from Rockwell B) 51.1 51.1
Hardness, Rockwell B 83 83
Hardness, Vickers (estimated from Rockwell B) 159 159

Thermal Properties

The thermal properties of grade 446 stainless steel are given in the following table.

Properties Metric Imperial
Thermal expansion co-efficient (@0-100°C/32-212°F) 10.4 µm/m°C 5.78 µin/in°F
Thermal conductivity 21.6 W/mK 150 BTU in/hr.ft².°F

Other Designations

Equivalent materials to grade 446 stainless steel are:

  • AISI 446
  • ASTM A176
  • ASTM A268
  • ASTM A276
  • ASTM A314
  • ASTM A473
  • ASTM A511
  • ASTM A815
  • DIN 1.4762
  • QQ S763
  • QQ S766
  • ASME SA268
  • ASTM A580
  • FED QQ-S-763
  • FED QQ-S-766
  • MIL SPEC MIL-S-862
  • SAE J405 (51446)

Fabrication and Heat Treatment

Machinability

Machinability of the grade 446 stainless steel is possible at slow speeds with positive feeds, rigid mounts and sharp tooling surfaces.

Welding

The grade 446 stainless steel can be easily welded using most of the traditional methods except oxyacetylene welding. Type 308 welding material can be used if required, but it will not exhibit scaling resistance equal to the base metal. Differences in coefficient of thermal expansion of base and weld metal has to be taken into consideration.

Forging

Forging can be started at 1149°C (2100°F) and completed at 871°C (1600°F). The last 10% of forging has to be performed below 871°C (1600°F) to gain grain refinement and room temperature embrittlement.

Hot Working

The hot working of grade 446 stainless steel is performed in between the ranges 1093- 1177°C (2000-2150° F). The last 10% of hot working has to be performed below 871°C (1600°F) to gain grain refinement

Cold Working

The grade 446 stainless steel is more difficult to cold work than other stainless steels due to the high level of chromium content.

Annealing

Annealing of the grade 446 stainless steel has to be soaked at 816°C (1500°F) and then water quenched. The temperature should not exceed 900°C (1650°F) at any time and slow cooling below 649°C (1200°F) can cause loss of ductility.

Applications

The grade 446 stainless steel can be used in the following products:

  • X-ray tube bases
  • Boiler baffles
  • Oil burner components
  • Annealing boxes
  • Industrial mufflers
  • Kiln linings
  • Glass molds
  • Furnace parts


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