AISI 303 | 1.4305 | BS 303S31 | X8CrNiS18-9 | Austenitic stainless steel
AISI 303 is an austenitic stainless steel, also known by the designations 1.4305, BS 303S31 and X8CrNiS18-9. This steel is typically used for free-cutting applications and is also known as free-cutting steel. The material can be used at temperatures of up to 400 °C. As an additional alloying element, AISI 303 stainless steel contains 0.15–0.35% sulphur, which gives it very good machinability. However, this has a negative effect on its corrosion resistance, which is why it offers only moderate corrosion resistance and pitting corrosion (e.g. in contact with seawater) may occur. The PREN value lies between 17.0 and 20.7, although the influence of sulphur is not taken into account here. AISI 303 stainless steel has a tensile strength of 500 to 750 N/mm² and a hardness of ≤ 230 HB. The yield strength is ≥ 190 mm² and the density is 7.90 kg/dm³ (at 20 °C). The material is well suited to cold drawing but poorly suited to cold forming (cold upsetting and cold deformation). This material is poorly suited to welding and forging. Stainless steel AISI 303/1.4305 is very weakly magnetisable (magnetic properties μr ≤ 1.3) and cannot be polished. It is used in mechanical engineering, for decorative purposes or in the automotive industry. Processing options include automatic machining and conventional machining.
Product range for AISI 303 (1.4305) stainless steel wire and bars
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Data sheet in accordance with DIN EN 10088-3 for material number AISI 303 (BS 303S31)
Technical properties at a glance
Elongation at break (A): ≥ 35 %
Density: 7.9 kg/dm³
Hardness: ≤ 230
Cold forming: Poor
Cold heading: Not suitable
Corrosion resistance: Low
Magnetic: No
Magnetisability: Low
Polishability: Poor
PREN value: 17 - 20.7
Forgability: Medium
Weldability: Poor
Machinability: Excellent
Yield strength (Rp0.2): ≥ 190 MPa
Machinability: Excellent
Tensile strength: 500 - 750 N/mm²
Specifications and classification
EN material number: 1.4305
EN short name: X8CrNiS18-9
EN standard: 10088-3
Structure class: Austenite
Comparable standards and designations
AFNOR Z8CNF18-09
AISI 303
Alloy 303
AMS 5640
BS 303S31
ČSN 17243
JIS SUS303
RVS 303
SAE 303
SS 2346
UNE F.3508
UNS S30300
The chemical composition of stainless steel AISI 303 (1.4305, X8CrNiS18-9) is specified in accordance with DIN EN 10088-3 in mass percent as follows:
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Carbon (C): ≤ 0.10
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Silicon (Si): ≤ 1.00
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Manganese (Mn): ≤ 2.00
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Phosphorus (P): ≤ 0.045
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Sulphur (S): 0.15 - 0.35
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Nitrogen (N): ≤ 0.10
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Chromium (Cr): 17.0 - 19.0
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Nickel (Ni): 8.00–10.00
Mechanical properties at room temperature
The values given refer to the diameter range ≤ 160 (Ø in mm)*
Hardness in HB: ≤ 230
Yield strength Rp0.2 in Mpa: ≥ 190
Yield strength Rp1.0 in Mpa: ≥ 225
Tensile strength / strength Rm in Mpa: 500 - 750
Elongation A5 (longitudinal) in %: ≥ 35
* These figures refer to mechanical properties at room temperature (according to EN 10088-3)
Physical properties
Magnetisability: low
Density (kg/dm³): 7.9
Thermal conductivity (at up to 20°C): 15
Specific heat capacity (at 20°C) in J/(kg K): 500
Electronic resistance at room temperature (in Ω mm²/m): 0.73
Corrosion resistance of stainless steel AISI 303
Stainless steel AISI 303 (1.4305 / X8CrNiS18-9) has a medium corrosion resistance (PREN value = 17.0 – 20.7* ), especially in comparison to material AISI 304 /1.4301. Due to the sulphur content, stainless steel AISI 303 has only limited corrosion resistance in media containing acid and chloride. This can lead to pitting corrosion and pitting, for example in connection with seawater or salt (NaCl). It is not resistant to intergranular corrosion.
* Please note that the harmful influence of sulphur is not taken into account here
Due to the addition of sulphur, the stainless steel AISI 303 / BS 303S31 has poor welding properties. If possible, this material should not be welded, as this can lead to the formation of hot cracks.
Heat treatment and hot forming
Solution annealing (+AT) (cooling by air or water): 1000 - 1100 °C
Hot forming (cooling by air): 900 - 1200 °C
Forging
Stainless steel AISI 303 (1.4305 / X8CrNiS18-9) is relatively difficult to forge and requires high temperatures, which means that there is a risk of overheating and hot cracking. If forging is unavoidable, it should take place in the temperature range from 1150°C to 950°C. The subsequent cooling should take place in the air.
Machinability and machining
Due to its sulphur content, the austenitic stainless steel AISI 303 (1.4305, X8CrNiS18-9) possesses excellent machinability and is among the stainless steels that are easiest to machine. Chip formation is improved by the incorporated sulphides. However, during machining, the low thermal conductivity of austenitic stainless steels can lead to increased heat build-up in the cutting zone. The heat generated there is dissipated less effectively, thereby increasing the thermal load on the tool. The use of cooling lubricants and appropriate cutting parameters is therefore necessary.
Cold forming and cold heading
Cold forming: The austenitic stainless steel AISI 303 (1.4305, X8CrNiS18-9) is only suitable for cold forming to a limited extent. It can be processed by bending, edging, drawing and similar forming processes. Due to its austenitic microstructure, the material exhibits significant work hardening. Higher forces are therefore required for more severe forming operations.
Cold heading: Due to its elevated sulphur content, AISI 303 is only suitable to a limited extent for cold heading and cold extrusion processes. Although the precipitated sulphides improve machinability, they also reduce the material’s formability and toughness. This stainless steel can be used for simple cold heading applications; however, it is not recommended for high degrees of forming.