Choosing a Reciprocating Grate Bar Grade: From RTSi5 to ZG35Cr24Ni4

Five grades are common for reciprocating grate bars, with service temperatures running from 800℃ to 1150℃ across two material systems, cast iron and cast steel. How a grade is written and whose temperature basis applies are the two things that get mixed up most easily, so they are taken separately here.

One: separate the two material systems first

RTSi5, RQTSi5 and RTCr16 are heat-resisting cast irons and follow GB/T 9437, Heat resistant iron castings. That standard states its scope plainly: iron castings working below 1100℃. The cast iron system therefore has a ceiling at 1100℃.

ZG35Cr24Ni4 is a heat-resisting steel casting and does not follow the iron standard; it is ordered within the GB/T 8492 system, Heat-resistant steel and alloy castings for general applications. Above 1100℃ both the grade system and the acceptance method change completely.

Two: spell the grade according to the standard

RQTSi5 is a high-silicon heat-resisting ductile iron. Read the grade apart: R for heat resisting, QT for ductile iron, Si5 for a nominal silicon content of about 5%. It follows GB/T 9437, where the 1988 edition wrote RQTSi5 and the 2009 edition rewrote it as QTRSi5 under the designation rules of GB/T 5612, and both spellings are still in circulation.

Put the edition into the technical agreement. The two editions differ in their figures, so writing RQTSi5 without an edition leaves room for argument at acceptance. GB/T 9437 also has a 2026 edition issued and effective 2026-11-01, so the editions overlap right now and stating the year matters more than usual.

Three: service temperature of the five grades

The service temperatures above come from the partner factory’s selection data and are not mandatory figures from the standards. How far a grade really goes also depends on the temperature swing of the bed, the number of thermal cycles and the bar’s own structure, so the same grade can last quite differently on two boilers.

Four: how to choose

First, set the grade by the temperature of the position, not of the whole grate. Preheating, main combustion and burnout zones do not run at the same temperature, and using different grades by zone on one grate costs less than upgrading everything.

Second, change system once 1100℃ is passed. The cast iron ceiling is there, and forcing cast iron into high temperature brings thinning and cracking quickly.

Third, split the work inside cast iron between the silicon and chromium families. The silicon grades (RTSi5, RQTSi5) resist heat well, resist oxidation only moderately and behave poorly under thermal shock, while the chromium grades (RTCr16, RTCr20) resist oxidation and corrosion better with lower toughness.

Put five things into the technical agreement when ordering: the standard number and year, the grade spelling, the service temperature, the acceptance method, and the measured dimensions of the old part. With those five stated, arguments over mismatched grades or two sets of temperature figures do not arise later.

Standards referred to in this article:

• GB/T 9437-2009, Heat resistant iron castings
• GB/T 9437-2026, Heat resistant iron castings, effective 2026-11-01
• GB/T 5612, Designation of cast irons
• GB/T 8492, Heat-resistant steel and alloy castings for general applications

We supply moving and fixed grate bars for reciprocating grates, dispatched from a partner factory, and we can check grade and applicable standard against your grate model and fuel.