| Chemical Composition |
| | Min. % | Max % |
| *Carbon | 0.15 | 0.36 |
| Silicon | 0 | 1.00 |
| Manganese | 0 | 1.00 |
| *Nickel | 0 | 1.00 |
| Chromium | 12.00 | 14.00 |
| Phosphorous | 0 | 0.04 |
| Sulphur | 0 | 0.03 |
*Carbon range can vary considerably
*Nickel addition optional. |
| Mechanical Property Requirements For Material in the Annealed and Heat Treated - Condition R and Condition S To AS2837 - 1986 420 and BS970 Part3 1991 420S37 and *BS970 Part 4 1970/73 420S45 |
| Condition | Annealed | R | S |
| Tensile Strength Mpa | Min | | 700 | | 770 | |
| Max | | 850 | | 930 | |
| 0.2% Yield Strength Mpa | Min | | 495 | | 555 | |
| Elongation on 5.65√S0 % | Min | | 15 | | 13 | |
| Impact Izod J | Min | | 63 34 | 63 27 | 63 27 | 63 14 |
| Hardness HB | Min | | 201 | | 223 | |
| Max | 229 | 255 | | 277 | |
Material stocked generally in condition R or condition S.
NB. Check the mill certificate if critical for end use.
*Material supplied to BS970 Part4 1970/73 420S45 mechanical property requirements as above with the following exception:
Annealed condition - Hardness HB 241 Max. |
| Typical Mechanical Properties At Room Temperature - Annealed and *Hardened and Tempered to Condition R and Condition S |
| Condition | Annealed | R | S |
| Tensile Strength Mpa | 650 | 790 | 900 |
| 0.2% Yield Strength Mpa | 350 | 635 | 740 |
| Elongation in 50mm % | 25 | 19 | 18 |
| Impact Charpy J | | 50 | 40 |
| Hardness | HB | 196 | 240 | 270 |
| Rc | 15 | 24 | 29 |
| *Typical Hardening Temperatures | 950oC - 1020oC |
| *Typical Tempering Temperatures | 650oC - 750oC | Condition R |
| *Typical Tempering Temperatures | 600oC - 700oC | Condition S |
| Typical Mechanical Properties At Room Temperature - Hardened By Oil Quench at 980oC and Tempered as Indicated |
| Temperature oC | 150 | 200 | 300 | 425 | 500 | 600 | 650 |
| Tensile Strengt Mpa | 1630 | 1605 | 1570 | 1625 | 1450 | 1025 | 895 |
| 0.2% Yield Strength Mpa | 1385 | 1365 | 1360 | 1415 | 1240 | 800 | 675 |
| Elongation in 50mm % | 12 | 12 | 14 | 11 | 14 | 19 | 20 |
| Impact Charpy J | | 20 | 19 | *9 | *11 | 22 | 42 |
| Hardness | HB | 495 | 480 | 465 | 495 | 429 | 302 | 262 |
| Rc | 52 | 51 | 50 | 52 | 46 | 33 | 27 |
Section Size 30mm
*Note drop in impact properties.Tempering within the range 400oC - 550oC should be avoided. |
| Elevated Temperature Properties |
| 420 displays good resistance to scaling in continuous service up to 650oC. Its use however at these higher working temperatures results in a substantial drop in tensile strength and hardness, plus a reduction in corrosion resistance.It is therefore not recommended for use at working temperatures above 400oC. |
| Low Temperature Properties |
| 420 is also not recommended for use at sub-zero temperatures due to a substantial drop in impact properties consistent with most steels other than the austenitic steel types. |
| Cold Bending |
| In the hardened and tempered as supplied condition will be more difficult due to the high yield strength which must be taken into account. |
| Hot Bending |
| In the hardened and tempered as supplied condition it is not recommended due to its affect on the mechanical properties within the heat affected zone. |
| Corrosion Resistance |
| 420 has a corrosion resistance similar to 410 grade, better than 416 grade, but lower than 431 grade, also lower than most of the 400 series ferritic stainless steels and all of the 300 series austenitic stainless steels.NB. It has optimum corrosion resistance in the hardened and tempered, ground and polished condition, and is not therefore recommended for use in the annealed condition.It is most important that oxygen is always allowed to circulate freely on all stainless steel surfaces to ensure that a chrome oxide film is always present to protect it. If this is not the case, rusting will occur as with other types of non stainless steels. For optimum corrosion resistance surfaces must be free of scale and foreign particles.
Finished parts should be passivated. |
| Forging |
| Preheat to 760oC - 820oC, then heat uniformly to 1100oC - 1200oC, hold until temperature is uniform throughout the section and commence forging immediately.Do not overheat as this can cause a loss of toughness and ductility.Do not forge below 900oC Finished forgings should be cooled slowly in a furnace, warm dry lime or ashes to room temperature and annealed immediately. NB. Air cooling after forging may cause cracking. |
| Heat Treatment |
| Sub-Critical Annealing |
Heat uniformerly to 730oC - 790oC hold until temperature is uniform throughout the section.
*Soak as required, cool in air. |
| Annealing |
Heat uniformerley to 840oC - 900oC, hold until temperature is uniform throughout the section.
*Soak as required. Cool in furnace. |
| Hardening |
| Heat to 950oC - 1020oC, hold until temperature is uniform throughout the section. *Soak as required.Quench in oil or air cool. Temper immediately while still hand warm.Note: Hardening from 1020oC - 1060oC will give optimum corrosion resistance, but hardening from about 980oC will give the best combination of corrosion resistance and mechanical properties. |
| Nitriding |
| Prior to nitriding, the chrome oxide film which protects the surface must be broken down by pickling or fine sand blasting.Nitriding is carried out at 500oC - 550oC followed by slow cooling (no quench) reducing the problem of distortion.Parts can therefore be machined to near final size, leaving a grinding tolerance only. Always ensure that the tempering temperature employed during the initial heat treatment was higher than the nitriding temperature otherwise the core strength will be affected. |
| Tempering |
Condition R:
Heat to 650oC - 750oC, hold until temperature is uniform throughout the section. *Soak as required.
Cool in air.Condition S:
Heat to 600oC - 700oC, hold until temperature is uniform throughout the section. *Soak as required.
Cool in air.Tempering within the range 150oC - 200oC will give optimum corrosion resistance and maximum hardness - up to Rc52 depending upon section size. NB. Tempering however within the range 400oC - 550oC should be avoided due to temper brittleness, resulting in a considerable reduction in impact properties and loss of corrosion resistance. *Heating temperatures, rate of heating, cooling and soaking times will vary due to factors such as work piece size/shape, also furnace type employed, quenching medium and work piece transfer facilities etc. Please consult your heat treater for best results. |
| Machining |
| 420 machines best in the hardened and tempered as supplied condition R or condition S, and despite its relatively high carbon content is still regarded as having reasonable machinability with all operations such as drilling, turning etc. capable of being carried out as per machine manufacturers recommendations for suitable tool type, feeds and speeds. It does not work harden to the same extent as the 300 series austenitic stainless steels, but is more similar in this respect to the low alloy high tensile steels such as 4150 or 6150 etc. |
| Welding |
| 420 is not generally recommended for welding in either the annealed or hardened and tempered condition, due to its air hardening capability which can lead to the formation of brittle martensite, resulting in cold cracking due to contraction stresses within the weld and heat affected zone. The higher the carbon content the higher the hardening capability and the greater the risk of cracking.Pre heating and interpass temperature control during welding, plus very slow cooling and post-weld annealing is the best method to prevent cracking.The following welding procedure and post-weld heat treatment may be taken as a guide only if welding is necessary. |
| Welding Procedure |
| Welding electrodes or rods should be low hydrogen types 420 or *similar when strength is required or when post-weld hardening and tempering, otherwise an austenitic stainless electrode or rod such as 309 or *similar may be used to give a more ductile weld, when strength is not so critical and post-weld annealing is not possible or intended.Pre-heat at 200oC - 300oC and maintain a high heat input during welding. On completion of welding cool slowly as possible until hand warm and as required:Post-weld sub-critical anneal at 650oC - 750oC or full anneal and harden and temper as required. *Please consult your welding consumables supplier. |
