EN 1.7230 belongs to the chromium-molybdenum quenched and tempered steel family specified in the EN 10083 series, in which the 34CrMo4 type is the most widely produced grade. Nickel 600 is UNS N06600, a solid-solution nickel-chromium alloy with roughly 76 % nickel. Both are used for shafts, discs, fittings and pressure components, but they reach their strength by completely different routes and operate under very different environmental limits.
What EN 1.7230 Is
The EN 1.7230 designation identifies a chromium-molybdenum steel supplied in the quenched and tempered condition, with roughly 1 % chromium and 0.2 to 0.3 % molybdenum. The molybdenum addition raises hardenability so that thick sections through-harden on oil quenching and improves resistance to temper embrittlement. Typical delivery conditions are normalised, quenched and tempered to a specified property class, or soft annealed for subsequent machining. The grade is produced as bar, plate, forgings and seamless tube, and it is commonly specified with a guaranteed core property after hardening and tempering.
Chemical Composition
| Element, % | EN 1.7230 (34CrMo4 type) | Nickel 600 (N06600) |
|---|---|---|
| Carbon | 0.30-0.37 | 0.15 max |
| Silicon | 0.40 max | 0.50 max |
| Manganese | 0.60-0.90 | 1.00 max |
| Chromium | 0.90-1.20 | 14.0-17.0 |
| Molybdenum | 0.15-0.30 | - |
| Nickel | - | 72.0 min |
| Iron | balance | 6.0-10.0 |
| Phosphorus | 0.025 max | - |
| Sulfur | 0.035 max | 0.015 max |
The composition difference explains the property difference: 1.7230 is a hardenable steel whose strength comes from a martensitic microstructure, while Nickel 600 is austenitic and cannot be strengthened by heat treatment at all.
Heat Treatment
1.7230 is austenitised in the range of 850 to 880 °C, quenched in oil or polymer, and tempered in the 540 to 660 °C band depending on the required strength and toughness. Tempering below 400 °C should be avoided because it leaves the steel sensitive to temper embrittlement and low in impact energy. Nickel 600, by contrast, is annealed between 980 °C and 1065 °C and rapidly cooled to keep carbides in solution; it is softened by annealing and hardened only by cold work. Any attempt to quench-harden Nickel 600 will not raise its strength, and thermal treatment that holds it in the 480 to 800 °C range for too long can precipitate grain-boundary carbides and reduce its corrosion resistance.
Mechanical Properties
| Property | EN 1.7230, quenched and tempered | Nickel 600, annealed |
|---|---|---|
| Tensile strength | about 900-1100 MPa | about 550-690 MPa |
| 0.2 % yield strength | about 650 MPa min | about 240-345 MPa |
| Elongation, 5D | about 14 % min | 30-40 % |
| Impact energy at 20 °C | 27 J min typical for the class | high, no transition |
| Hardness | about 260-320 HBW | about 85 HRB |
In terms of pure strength, the quenched and tempered steel is the stronger material at room temperature. Its advantage disappears above about 400 °C, where tempering reactions accelerate and creep becomes the controlling damage mechanism.
Service Limits and Corrosion Behaviour
1.7230 is not a corrosion-resistant grade. It forms a loose oxide scale in air above about 500 °C and corrodes readily in acids, chlorides and wet sour gas unless it is coated or clad. Its strength and low cost make it suitable for shafts, gears, couplings, studs and pressure-retaining parts in dry, non-corrosive service up to roughly 450 to 500 °C. Nickel 600 resists oxidation in air to about 1100 °C, resists chloride stress corrosion cracking and caustic attack, and remains structurally useful in furnace and chemical process environments. Its penalty is a much higher price, lower machinability and a yield strength that cannot be raised by heat treatment.
Choosing Between the Two
The choice normally follows three questions. First, is the environment corrosive or chloride-bearing? If yes, the steel is eliminated. Second, is the service temperature above about 450 °C? If yes, the steel is again eliminated because of oxidation and creep. Third, is very high room-temperature strength with acceptable toughness the dominant requirement in a dry environment? If yes, 1.7230 is the economical answer. Where a design needs both strength and corrosion resistance, the usual solution is a corrosion-resistant alloy or a steel clad with one, rather than a heavier section of the quenched and tempered grade.
Frequently Asked Questions
Q: Can EN 1.7230 be welded?
A: It is weldable with a matching or slightly over-alloyed filler, but preheat and post-weld heat treatment are necessary for sections above about 25 mm to avoid cracking and hardness problems in the heat-affected zone.
Q: Is Nickel 600 stronger than quenched and tempered 1.7230?
A: No. In the quenched and tempered condition the steel develops higher tensile and yield strength at room temperature; Nickel 600 is chosen for temperature and corrosion resistance, not for strength.
Q: What is the maximum service temperature of each grade?
A: Nickel 600 is used in continuous service up to about 1100 °C in oxidising atmospheres, while 1.7230 is limited in practice to about 450 to 500 °C to avoid excessive oxidation and loss of temper.
Q: Which grade is more resistant to chloride stress corrosion cracking?
A: Nickel 600. Its high nickel content makes it essentially immune in the chloride and caustic condition where a low-alloy steel would crack or corrode rapidly.
Q: Does the molybdenum in 1.7230 provide corrosion resistance?
A: Only marginally. The molybdenum content is added for hardenability and temper resistance, not to give the steel resistance to acids or chloride pitting.
Q: How should each grade be specified on a purchase order?
A: State the grade designation, the delivery condition, the property class, the heat treatment parameters, the applicable product standard and the required test certificates; for Nickel 600 the applicable ASTM or EN standard for the product form should also be named.
