Type 303 stainless steel

Identity and product specification

Carpenter advises against welding its Type 303 because sulfur can contribute to hot cracking. Alleima gives a separate filler-metal route for Sanmac 4305, with heat input below 1.0 kJ/mm and interpass below 100°C. Confirm the actual stock and qualify the joint before applying producer guidance. Carpenter weldability, Alleima Sanmac 4305 welding

Type 303, UNS S30300, is an austenitic free-machining stainless steel. ATI describes sulfur addition to improve machining of the basic chromium-nickel composition; it cannot be hardened by heat treatment. Its technical sheet describes hot-rolled plate furnished annealed and associates that product with ASTM A895. ATI 303 technical data sheet

The same sheet lists chromium 17–19%, nickel 8–10% and sulfur 0.15% minimum, together with other controlled elements. Use the complete governing composition and delivered analysis rather than accepting a major-element match. A producer's data sheet is not an inspection certificate. ATI composition and forms

Carpenter's CarTech 303 and Alleima's Sanmac 4305 are named producer offerings. Carpenter also distinguishes its Project 70+ machining variant. Preserve those product identities rather than inferring identical processing, inclusion control or tool performance from a generic 303 label. Carpenter 303 product sheet, Alleima Sanmac 4305

A bounded mechanical example

ATI's technical sheet gives these typical room-temperature ranges for annealed plate:

These are reference ranges, not universal specification minima. The source does not provide a complete direction and specimen protocol with this table. Obtain the actual product requirements and sampling basis before using the values for acceptance or design. ATI mechanical-property table

For an illustrative nominal-stress calculation, a uniform 100 mm² section carrying 5,000 N has stress 50 MPa. Dividing by the lower end of the published typical yield range gives 50 / 207 ≈ 0.242. This original arithmetic is not a safety factor: it uses reference data and omits local geometry, actual properties, joint behavior, fatigue, corrosion loss and design rules.

Match condition, temperature, orientation, dimensions and test method when comparing candidates. Obtain cold-worked properties for cold-worked stock. A room-temperature tensile number does not establish impact performance, allowable pressure or life under repeated loading.

Machining and manufacturing sequence

ATI notes that 303 still work hardens and that machining practice must avoid glazing at the tool interface. Its published speed/feed tables are starting points for its stated material and equipment context, with modification required for the actual operation. ATI machining guidance

Plan stock condition, tool engagement, rigidity, chip handling, coolant and surface finish together. Qualify parameters on representative stock and the actual machine. Do not turn a relative machinability claim into a cutting-speed guarantee for every diameter, insert or operation.

For hollow stock, Alleima's Sanmac 4305 sheet specifies solution-annealed, white-pickled supply and distinguishes outside/inside dimensions from guaranteed component sizes after machining. That is a producer-specific supply basis, not permission to assume all nominal hollow-bar dimensions are finished dimensions. Alleima forms of supply

Place finished geometry inside a verified cleanup envelope, including surface removal, tolerance and straightness. Establish when critical dimensions are inspected relative to any joining, thermal treatment or finishing. Retain condition and lot identity when parts move between machining and outside processing.

Corrosion and surface finishing

ATI explains that free-machining additions slightly reduce corrosion resistance relative to unmodified grades. It also warns that bright machined surfaces may dull or etch during nitric-acid treatment. A familiar stainless designation does not qualify an unspecified passivation or cleaning process. ATI corrosion and surface-treatment guidance

Alleima warns that Sanmac 4305 may suffer pitting and crevice corrosion even at relatively low chloride content. Its guidance is expressly for its own product. Keep fluid composition, temperature, stress, crevice geometry and surface condition with a compatibility assessment. Alleima corrosion limitations

Include deposits, cleaning fluids and shutdown exposure in the service description. Validate the intended finish on representative parts, with the required appearance and corrosion criteria. A clean-looking surface does not demonstrate resistance in an inaccessible joint or establish a maintenance interval.

Welding is a selection constraint

Carpenter does not recommend welding its Type 303, identifying sulfur-related hot cracking and possible off-center weld behavior when joining lower-sulfur stainless material. Treat required welding as a material-selection issue before purchasing stock. Carpenter weldability guidance

Alleima separately describes carefully controlled filler-metal welding for Sanmac 4305, recommending heat input below 1.0 kJ/mm and interpass temperature below 100°C. These are instructions for that producer's material, not a generic qualified procedure for all S30300 supply. Alleima welding section

Resolve base material, joint, filler, shielding, thermal history and acceptance through a qualified procedure. Inspect the finished weld and affected regions for the intended function. Neither parent-metal properties nor an acceptable external bead establishes crack freedom, corrosion performance or joint life.

Carpenter also limits its product to moderate cold working. If a part needs severe forming or deformation during assembly, trial the actual stock, geometry and sequence or select a material supported for that route. Carpenter cold-working guidance

Release and source versions

Retain grade/specification, producer, heat/lot, delivered and final conditions, machining/finishing history and required inspection. Resolve substitutions against the complete drawing and service requirements. Application lists are discovery leads rather than qualification of a finished pressure, medical or load-bearing component.

ATI's sheet prints Version 1, 25 February 2013. The Alleima sheet prints an update date of 9 May 2025; its filename resolves the numeric date format. Carpenter's inspected sheet has no clear technical revision date used here. Obtain current controlled documents for contractual use. Review date: 2026-11-01, America/Los_Angeles.

Grades, tempers and conditions