630 stainless steel (also widely known as 17-4 PH or SUS630) is one of the most popular martensitic precipitation-hardening stainless steel grades in global industrial manufacturing. Renowned for its exceptional mechanical strength, outstanding toughness, reliable high-temperature performance, and superior corrosion resistance, it outperforms many conventional stainless steel grades for high-load and harsh-environment applications.

Widely adopted in chemical processing, automotive manufacturing, power generation, offshore engineering, and precision machinery, 630 stainless steel fills the performance gap between ordinary 304 stainless steel and high-cost specialty alloys. To help overseas engineers, procurement teams, and manufacturers with material selection and CNC machining processing, SMS — an ISO 9001 certified OEM manufacturing expert — delivers this comprehensive guide covering 630 stainless steel chemical composition, physical & mechanical properties, international standards, industrial applications, heat treatment skills, and professional machining & welding tips.

630 stainless steel is a martensitic precipitation-hardening stainless steel, universally recognized as 17-4 PH in the American standard and SUS630 in Japanese JIS standards. It features a unique alloy formula with 15–17.5% chromium and 3–5% nickel, plus targeted additions of copper and niobium.

Different from ordinary austenitic stainless steel like 304, 630 stainless steel achieves ultra-high strength and hardness through low-temperature precipitation hardening treatment, with minimal material deformation. It maintains stable mechanical properties at working temperatures up to 600°F (316°C), while retaining corrosion resistance comparable to 304 stainless steel. This unique balance of high strength and anti-corrosion capability makes it irreplaceable for high-strength precision industrial parts.

A core advantage of SUS630 steel is its flexible processing performance: it is supplied in solution-treated condition, allowing rapid age hardening for strength enhancement and convenient pre-hardening machining. Low-temperature aging treatment effectively avoids large-scale distortion, making it ideal for manufacturing long shafts and precision components that require no secondary straightening after heat treatment.

The excellent comprehensive performance of 630 stainless steel derives from its precise chemical alloy ratio. Chromium ensures corrosion resistance, nickel and copper enhance toughness and strength, and niobium optimizes structural stability. The strict standardized composition range complies with AISI, UNS, and JIS G4303 specifications, as shown in the table below:

The remaining composition is iron (Fe) and trace negligible impurities. The low carbon content effectively prevents intergranular corrosion, while the synergistic effect of copper and niobium significantly improves the steel’s hardening efficiency and structural stability after heat treatment.

The physical parameters of SUS630 / 17-4 PH stainless steel are stable and uniform, providing reliable data support for structural design, thermal processing, and CNC precision machining. All parameters comply with international industry standards:

The mechanical performance of 630 stainless steel varies significantly with different heat treatment processes. Solution-treated, H900, and H1150 conditions cover low to high strength requirements, adapting to diverse industrial scenarios. The standardized mechanical property data is listed below:

Overall, 630 stainless steel delivers excellent stress corrosion resistance and crevice corrosion resistance. When aged at 550°C or above, it shows far better stress corrosion cracking resistance than ordinary SUS304 austenitic stainless steel. Note that solution-treated Condition A has weaker corrosion resistance, so it is not recommended for high-corrosion working environments.

630 stainless steel corresponds to unified equivalent grades in global mainstream standards, facilitating international material procurement and cross-border manufacturing cooperation. The complete standard comparison is as follows:

Why is SUS630 called Grade 630? SUS is the material grade prefix defined by the Japanese JIS G4303 standard for hot-worked stainless steel bars. SUS630 and AISI 630 are completely consistent in chemical composition, physical and mechanical properties, just with different regional naming conventions.

630 stainless steel is supplied in diverse finished forms to meet different processing and application needs. The mainstream market specifications include:

Conventional dimensional range: Material thickness ranges from 1mm to 30mm, and width covers 700mm to 1500mm.SMS supports customized size processing and precision CNC machining for all specifications of 630 stainless steel parts.

Combining high strength, high-temperature resistance, and excellent corrosion resistance, 630 stainless steel is widely used in high-standard industrial fields worldwide:

: Engine core parts, transmission gearboxes, hydraulic pipeline components, high-load automotive structural parts

: Chemical processing equipment, power generation turbine components, industrial waste treatment facilities

: Offshore platform handling equipment, corrosion-resistant marine structural parts

: Plastic mold dies, industrial gears, control valves, long precision shafts

: Industrial detection instruments, medical precision equipment parts

630 stainless steel relies on high chromium and copper content to achieve excellent general corrosion resistance, stress corrosion resistance, and crevice corrosion resistance. Its anti-corrosion performance is further optimized after standardized heat treatment, basically matching the level of 304 stainless steel.

Common heat treatment processes for 630 stainless steel include solution treatment, quenching, tempering, and annealing. Different processes adjust the material’s hardness, toughness, and strength to adapt to diverse working conditions. Low-temperature aging treatment effectively avoids workpiece deformation, which is its biggest advantage over other high-strength stainless steels.

630 stainless steel has work-hardening characteristics, making it more challenging to machine than ordinary 304 steel. Hardening during cutting easily causes tool wear and dimensional deviation. Professional machining solutions adopted bySMS include:

Welding 630 stainless steel has strict process requirements. Without standardized treatment, welding cracks and performance attenuation are prone to occur. Standard welding processes require preheating treatment before welding and targeted post-weld heat treatment, which effectively eliminates welding stress, prevents cracking, and retains the material’s original mechanical and anti-corrosion properties.

SMS is a leading ISO 9001 certified OEM manufacturer, providing one-stop custom manufacturing solutions for 630 stainless steel (17-4 PH / SUS630) parts from prototype verification to mass production. With rich experience in processing precipitation-hardening stainless steel, our team masters professional heat treatment, CNC machining, and welding processes to solve the difficult processing problems of 630 steel.

We strictly control material standards and processing accuracy, providing high-precision custom parts for automotive, chemical, medical, and offshore engineering industries. Adhering to innovation, process optimization, and fine workmanship, SMS delivers cost-effective, high-quality metal machining services for global clients.

630 stainless steel (17-4 PH / SUS630) is a premium martensitic precipitation-hardening stainless steel with a perfect combination of high strength, high toughness, temperature resistance, and corrosion resistance. Its unique chemical composition and adjustable mechanical properties make it superior to ordinary stainless steel in high-load and harsh working environments.

Although 630 stainless steel has higher machining and welding difficulty, standardized processing and heat treatment can maximize its performance advantages. For industrial manufacturers, choosing professional suppliers like SMS for precision machining can fully leverage the value of 630 stainless steel and improve product durability and stability.