Martensitic stainless steel have the highest strength but also the lowest corrosion resistance of the stainless steel. Martensitic steels with high carbon contents are used for tool steel. Due to their high strength in combination with somecorrosion resistance, martensitic steels are suitable for applications where the material is subjected to both corrosion and wear. An example is in hydroelectric turbines. Martensitic grades of stainless steel were developed in order to provide a group of stainless alloys that would be corrosion resistant and hardenable by heat treating. The martensitic grades are straight chromium steels containing no nickel. They are magnetic and can be hardened by heat treating. The martensitic grades are mainly used where hardness, strength, and wear resistance are required.
Martensitic stainless steel has a relatively high carbon content (0.1% – 1.2%) compared to other stainless steel. The martensitic steels are plain chromium steel containing between 12% and 18% chromium, can be heat treated to obtain high strength with good ductility. Martensitic stainless steel has very high hardenability. When only limited corrosion resistance or resistance to moderately elevated temperature scaling is required, can be used in the annealed condition, but its highest corrosion resistance is attained in the hardened and stress relieving (low temperature tempered) condition.
Type 410
Basic martensitic grade, containing the lowest alloy content of the three basic stainless steels (304, 430, and 410). Low cost, general purpose, heat treatable stainless steel. Used widely where corrosion is not severe (air, water, some chemicals, and food acids. Typical applications include highly stressed parts needing the combination of strength and corrosion resistance such as fasteners.
Type 410S
Contains lower carbon than Type 410, offers improved weldability but lower hardenability. Type 410S is a general purpose corrosion and heat resisting chromium steel recommended for corrosion resisting applications.
Type 414
Has nickel added (2%) for improved corrosion resistance. Typical applications include springs and cutlery.
Type 416
Contains added phosphorus and sulfur for improved machinability. Typical applications include screw machine parts.
Type 420
Contains increased carbon to improve mechanical properties. Typical applications include surgical instruments.
Type 431
Contains increased chromium for greater corrosion resistance and good mechanical properties. Typical applications include high strength parts such as valves and pumps.
Type 440
Further increases chromium and carbon to improve toughness and corrosion resistance. Typical applications include instruments.
The major alloying addition in martensitic stainless steel is chromium in the range of 11 to 17%. The carbon levels can vary from 0.10 to 0.65% in these alloys. This radically changes the behavior of the martensitic alloys relative to the ferritic 400 Series alloys. The high carbon enables the material to be hardened by heating to a high temperature, followed by rapid cooling (quenching). Martensitic types offer a good combination of corrosion resistance and superior mechanical properties, as produced by heat treatment to develop maximum hardness, strength and resistance to abrasion and erosion. The martensitic grades are usually sold in the soft state. This allows the customers to cut or form the parts before they are thermally hardened. End uses include cutlery, scissors, surgical instruments, wear plates, garbage disposal shredder lugs, and industrial knives. The AL 403 alloy is used to make vanes for steam turbines. Stainless Steel – MartensiticAlloy (UNS Designation) End UseComposition nominal wt%SpecificationsDensity lb/in3 (g/cm3)Tensile Strength ksi. (MPa)0.2% Yield Strength ksi. (MPa)Elong- ation %HardnessAL 403 S40300 Turbine blades, banding, strapping and hose clampsC 0.15 max, Mn 1.0 max, Si 0.5 max, Cr 11.5-13.0, Ni 0.6 max, P 0.04 max, S 0.03 max, Fe BalanceASTM A176 AMS QQ57630.280 (7.75)70 min (485 min)30 min (205 min)25 min96 Rockwell B max
410 S41000 Cutlery, dental and surgical instruments, nozzles, valve parts, hardened steel balls and seats for oil well pumps, separating screens and strainers, springs, shears, and wear surfacesC 0.08-0.15, Mn 1.0 max, P 0.04 max, S 0.03, Si 1.0, Cr 11.5-13.5, Ni 0.75 max, Fe BalanceASTM A2400.276 (7.65)65 min (450 min)30 min (205 min)20 min96RockwellB max (Annealed) 38-45 RC (Hardened)
416 S41600 Cutlery, dental & surgical instrumentsC 0.15 max, Mn 1.25 max, Si 1.0 max, Cr 12.0-14.0, P 0.06 max, S 0.15 min, Mo 0.60 max, Fe BalanceASTM A895 ASTM A194 AMMS 55610 SAE J4050.280 (7.74)75-90 (517-621)40-50 (276-345)15-3038-45 Rc (Hardened)
AL 418 SPL S41800 Engine braces, turbine exhaust components, exhaust struts, stiffeners, ductsC 0.15-0.20, Cr 12.0-14.0, Mn 0.50 max, Ni 1.8-2.2, P 0.04 max, S 0.03 max, Si 0.50 max, W 2.5-3.5, Fe BalanceAMS 55080.284 (7.87)130 (900)105 (725)2025-50 Rockwell C (Hardened)
420 S42000 Cutlery, Dental and surgical instruments, nozzles, valve parts, hardened steel balls and seats for oil well pumps, separating screens and strainers, springs, shears, and wear surfacesC 0.15 min, Mn 1.0 max, Si 1.0 max, Cr 12.0-14.0, Ni 0.75 max, Mo 0.5 max S 0.03 max, P 0.04 max, Fe BalanceASTM A1760.280 (7.74)85 (586)45 (310)2953-57 Rockwell C (Hardened)
440A S44002 Cutlery, dental and surgical instruments, nozzles, valve parts, hardened steel balls and seats fro oil well pumps, separating screens and strainers, springs, shears, and wear surfacesC 0.60-0.75, Mn 1.0 max, Si 1.0 max, Cr 16.0-18.0, Mo 0.75 max, S 0.03 max, P 0.04 max, Fe BalanceASTM A2760.279 (7.72)104 (717)62 (427)2057-60 Rockwell C (Hardened)
440C S44004 Bearings, valve parts, cutlery and industrial knivesC 0.95-1.20, Mn 1.0 max, Si 1.0 max, Cr 16.0-18.0, Mo 0.75 max, S 0.03 max, P 0.04 max, Fe BalanceASTM A276 AMS 5630 QQ-S-7630.277 (7.68)110 (760)65 (450)1558-61 Rockwell C (Hardened)
Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)
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