16Mo3, 13CrMo4-5 or 10CrMo9-10? Creep-Resistant Steels Compared

The choice of the right creep-resistant grade determines the operational safety, service life and economy of pressure vessels, boilers and piping. 16Mo3, 13CrMo4-5 and 10CrMo9-10 form a proven ladder for rising temperature requirements. This article places the three steels in a practical context and shows what matters in selection and processing.

What "creep-resistant" really means

Creep-resistant does not simply mean "strong at higher temperatures". Decisive is the long-term behavior under sustained load: at high temperatures, steel deforms slowly and progressively even below the yield strength – this creep leads to failure over the years. Decisive are therefore the creep rupture and creep strength, i.e. characteristic values for the sustainable stress over typical design periods of, for example, 100,000 hours.

The short-term hot strength, such as the hot yield strength, describes only part of the picture. For the design of components in continuous service, the creep rupture values from the relevant standards and data sheets are governing.

The role of molybdenum and chromium

The difference between the three grades is made above all by the alloying elements:

• Molybdenum raises the hot strength considerably and improves the creep resistance by stabilizing the strength of the matrix at temperature.
• Chromium increases the scaling and oxidation resistance and, through the formation of stable carbides, also contributes to the hot strength.

16Mo3 relies on molybdenum alone. 13CrMo4-5 and 10CrMo9-10 combine chromium and molybdenum to an increasing degree – with the tendency that higher chromium contents raise both the temperature limit and the resistance to scaling.

Application limits: a ladder

Qualitatively, a clear order of temperature suitability results:

• 16Mo3 – for moderate temperatures, the classic entry into the creep-resistant range.
• 13CrMo4-5 – for higher temperatures, when 16Mo3 reaches its limits.
• 10CrMo9-10 – for the highest requirements in this group, with the best creep and scaling resistance.

The exact permissible temperatures and stresses depend on component, design life and standard, and are to be taken from the respective data sheet and the design standard. Typical applications are boilers and boiler plates, steam and superheated-steam lines, headers, as well as apparatus and components in plant and power plant construction.

Standards and product forms

For procurement, two standards are central:

• EN 10028-2 – flat products made of pressure-vessel steels, i.e. plates for creep-resistant applications.
• EN 10216-2 – seamless steel tubes for pressure loading with defined hot yield strengths.

Both standards cover the grades mentioned and specify the chemical composition as well as the mechanical and creep properties. An inspection certificate 3.1 to EN 10204 with the specific heat values is available on request.

Welding and heat treatment

Creep-resistant Cr-Mo steels are weldable but require care. With rising alloy content – and thus from 16Mo3 through 13CrMo4-5 to 10CrMo9-10 – the hardening tendency in the heat-affected zone increases. In practice this means:

• Preheating before welding, depending on grade, wall thickness and process.
• Control of the interpass temperature.
• As a rule, a post-weld heat treatment (stress-relief annealing or tempering) to relieve residual stresses and to set the microstructure of the weld.

The specific parameters depend on the welding procedure specification (WPS) and the applicable codes.

When switching to the higher-alloyed grade is worthwhile

The step from 16Mo3 to 13CrMo4-5 or further to 10CrMo9-10 is worthwhile as soon as the operating temperature reaches the economic limit of the lower-alloyed grade – for example because the wall thicknesses would otherwise grow disproportionately, or the required service life in the creep range can no longer be safely achieved. Elevated requirements for scaling resistance also speak for the more chromium-rich variant. Conversely: where the temperature permits, the lower-alloyed grade is usually the more cost-effective choice and the simpler one in welding terms.

In short: 16Mo3, 13CrMo4-5 and 10CrMo9-10 form a ladder of rising creep strength and scaling resistance, carried by increasing chromium and molybdenum contents. Decisive for the design are the creep rupture values according to data sheet and standard – and in the workshop, the right welding sequence with preheating and post-weld heat treatment determines the quality. We are glad to support you in grade selection, product form and the 3.1 certificate.