{"id":7826,"date":"2026-09-26T06:16:22","date_gmt":"2026-09-26T06:16:22","guid":{"rendered":"https:\/\/chinametalfoundry.com\/?p=7826"},"modified":"2026-09-26T06:16:22","modified_gmt":"2026-09-26T06:16:22","slug":"cast-iron-vs-cast-steel","status":"publish","type":"post","link":"https:\/\/chinametalfoundry.com\/ru\/blog\/cast-iron-vs-cast-steel\/","title":{"rendered":"\u0427\u0443\u0433\u0443\u043d \u0438\u043b\u0438 \u043b\u0438\u0442\u0430\u044f \u0441\u0442\u0430\u043b\u044c: \u043a\u0430\u043a \u0432\u044b\u0431\u0440\u0430\u0442\u044c \u0441 \u0443\u0447\u0435\u0442\u043e\u043c \u043d\u0430\u0433\u0440\u0443\u0437\u043a\u0438, \u0443\u0434\u0430\u0440\u043e\u043f\u0440\u043e\u0447\u043d\u043e\u0441\u0442\u0438 \u0438 \u0441\u0442\u043e\u0438\u043c\u043e\u0441\u0442\u0438"},"content":{"rendered":"
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Every sourcing engineer hits the same wall sooner or later: the drawing calls for “cast steel” or “cast iron” with no grade, and the two quotes come back 40\u201390% apart. Choosing cast iron vs cast steel<\/strong> is not a matter of which one is “stronger” \u2014 it is a decision about impact load, service temperature, wall thickness, and how much the part is allowed to cost per kilogram.<\/p>\n<\/div>\n

This guide puts real numbers on the trade-off: tensile and Charpy data from the ASTM specifications buyers actually cite, carbon equivalents and weld preheat, melting and pouring temperatures, casting yield, machinability, and a 40 kg bracket worked out end to end. Where a rule of thumb is quoted, the underlying standard is named \u2014 including references from the \u0410\u043c\u0435\u0440\u0438\u043a\u0430\u043d\u0441\u043a\u043e\u0435 \u043e\u0431\u0449\u0435\u0441\u0442\u0432\u043e \u043b\u0438\u0442\u0435\u0439\u0449\u0438\u043a\u043e\u0432 (AFS)<\/a> \u0438 ASTM International<\/a> \u2014 so you can take it straight into an RFQ instead of arguing with a supplier. The short version of cast iron vs cast steel: iron buys damping, machinability and cost, while steel buys toughness, weldability and performance below zero.<\/p>\n

\"cast
Two families, one bench: graphite-bearing iron castings on the left, low-carbon steel castings on the right. The difference is not the colour \u2014 it is the carbon.<\/figcaption><\/figure>\n

What Actually Separates Cast Iron from Cast Steel<\/h2>\n

Both families start as iron plus carbon, but they sit on opposite sides of one line. Once that line is crossed, the carbon stops behaving like an alloying element and starts behaving like a defect \u2014 or like a built-in lubricant, depending on how you let it solidify. If you are still mapping the wider landscape, our \u0440\u0443\u043a\u043e\u0432\u043e\u0434\u0441\u0442\u0432\u043e \u043f\u043e \u043b\u0438\u0442\u044c\u044e \u043c\u0435\u0442\u0430\u043b\u043b\u043e\u0432<\/a> covers the full process-and-material tree before you narrow down to these two.<\/p>\n

The 2% carbon line<\/h3>\n
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Cast steel runs below roughly 2.0% carbon \u2014 most engineering castings sit between 0.15% and 0.50%. Cast iron runs above it, typically 2.5\u20134.0%, and that surplus carbon has nowhere to go. In grey iron it precipitates as graphite flakes; in ductile iron a magnesium treatment forces it into spheroids; in cast steel it stays chemically combined as pearlite, ferrite or cementite. This single fact drives almost every property difference that follows: damping, machinability, elongation, and weldability all trace back to whether free graphite is present.<\/p>\n\n\n\n\n\n\n\n\n\n\n\n
\u0424\u0430\u043a\u0442\u043e\u0440<\/th>\nGrey \/ ductile cast iron<\/th>\nCast carbon \/ low-alloy steel<\/th>\n<\/tr>\n<\/thead>\n
Carbon content<\/td>\n2.5\u20134.0% C, 1.0\u20133.0% Si<\/td>\n0.15\u20130.50% C, 0.30\u20130.80% Si<\/td>\n<\/tr>\n
Carbon form<\/td>\nFree graphite (flakes or nodules)<\/td>\nCombined (pearlite \/ ferrite \/ cementite)<\/td>\n<\/tr>\n
Common ASTM specs<\/td>\nA48 (grey), A536 (ductile), A897 (ADI)<\/td>\nA27 \/ A148 (structural), A216 WCB, A352 LCB<\/td>\n<\/tr>\n
Melting range<\/td>\n1150\u20131250 \u00b0C<\/td>\n1470\u20131520 \u00b0C<\/td>\n<\/tr>\n
Typical pouring temperature<\/td>\n1350\u20131450 \u00b0C<\/td>\n1540\u20131600 \u00b0C<\/td>\n<\/tr>\n
\u0423\u0441\u0430\u0434\u043a\u0430 \u043f\u0440\u0438 \u0437\u0430\u0442\u0432\u0435\u0440\u0434\u0435\u0432\u0430\u043d\u0438\u0438<\/td>\nGrey \u2248 0 (graphite expansion offsets it); ductile 4\u20136%<\/td>\n2.5\u20134.0%, always needs generous feeding<\/td>\n<\/tr>\n
Minimum castable wall<\/td>\n3\u20134 mm in sand castings<\/td>\n5\u20136 mm, thicker on large sections<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Cast Iron vs Cast Steel: Mechanical Properties Compared<\/h2>\n

Below are the numbers you will actually find on a mill certificate. One caveat that decides a lot of disputes: ASTM A48 grey iron classes are defined on a separately cast 30 mm test bar, not on the casting itself, so a 100 mm section of Class 35 will not deliver 241 MPa through its core. Cast steel behaves far more predictably across section thickness \u2014 which is exactly why thick, highly loaded parts migrate to steel.<\/p>\n\n\n\n\n\n\n\n\n\n\n\n
\u041d\u0435\u0434\u0432\u0438\u0436\u0438\u043c\u043e\u0441\u0442\u044c<\/th>\nGrey iron A48 Class 35<\/th>\nDuctile iron A536 65-45-12<\/th>\nCast steel A27 Gr 70-40<\/th>\n<\/tr>\n<\/thead>\n
Tensile strength, min<\/td>\n241 MPa (35 ksi)<\/td>\n448 MPa (65 ksi)<\/td>\n485 MPa (70 ksi)<\/td>\n<\/tr>\n
Yield strength, min<\/td>\nNot specified (breaks first)<\/td>\n310 MPa (45 ksi)<\/td>\n276 MPa (40 ksi)<\/td>\n<\/tr>\n
Elongation, min<\/td>\n<1% (effectively zero)<\/td>\n12%<\/td>\n22%<\/td>\n<\/tr>\n
Typical hardness<\/td>\n180\u2013220 HB<\/td>\n156\u2013217 HB<\/td>\n150\u2013190 HB<\/td>\n<\/tr>\n
Charpy V-notch at 20 \u00b0C<\/td>\nNot applicable<\/td>\n12\u201318 J<\/td>\n27\u201360 J<\/td>\n<\/tr>\n
Modulus of elasticity<\/td>\n100\u2013140 GPa<\/td>\n165\u2013170 GPa<\/td>\n200\u2013210 GPa<\/td>\n<\/tr>\n
Damping capacity<\/td>\n10\u201325\u00d7 that of steel<\/td>\n2\u20134\u00d7 that of steel<\/td>\nBaseline<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Read that table as a whole and the pattern is obvious. In the cast iron vs cast steel<\/strong> decision, tensile strength is nearly a tie \u2014 448 MPa against 485 MPa. The real gap is elongation and toughness: cast steel stretches 22% and absorbs 27 J or more, while grey iron does neither. If your part can fail by cracking, the choice is already made.<\/p>\n

Section sensitivity, weight and corrosion<\/h3>\n
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Section thickness separates the two families more quietly than any strength number. Grey iron is strongly section-sensitive: a Class 35 casting with 100 mm walls typically delivers 170\u2013210 MPa through the core rather than the 241 MPa printed on the certificate, so a drawing that simply says “ASTM A48 Class 35” is not a specification \u2014 you have to say where the properties are required. Ductile iron is better but still fades on heavy sections. Cast steel stays close to uniform, which is the practical reason thick structural parts move to steel even when the nominal loads would suit iron. Weight runs the other way: at 7.1\u20137.2 g\/cm\u00b3, iron is about 9% lighter than steel at 7.85 g\/cm\u00b3, which matters on freight and on unsprung mass. Neither material is corrosion-proof \u2014 grey iron can form a graphitic surface layer, steel rusts uniformly, and both need paint, galvanising or an alloy upgrade. Coating options are covered in our notes on sand casting corrosion resistance<\/a>, and the preparation that makes coatings stick is in the \u043e\u0442\u0434\u0435\u043b\u043a\u0430 \u043f\u043e\u0432\u0435\u0440\u0445\u043d\u043e\u0441\u0442\u0438 \u043e\u0442\u043b\u0438\u0432\u043a\u043e\u0432<\/a> guide. This is the least-discussed axis of the cast iron vs cast steel<\/strong> decision, and the one that most often surfaces in warranty claims.<\/p>\n

\"cast
Machined tensile and Charpy specimens cut from production castings \u2014 the only way to verify that the certificate matches the section you are actually buying.<\/figcaption><\/figure>\n

Where Cast Iron Wins<\/h2>\n

Iron is not the cheap fallback. For four out of five industrial castings it is the correct engineering answer, and here is the evidence. Before the list: cast iron vs cast steel is not a quality hierarchy, it is a load case.<\/p>\n