302HQ vs. 304 nerezová ocel

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Nerezová ocel 302HQ je standardní materiál používaný zejména při výrobě samorezných šroubů a lehkých mechanických šroubů. Používá se také v šroubech, závěsných šroubech, nitích a speciálních spojovacích prvcích. Název 302HQ není standardizovaný. ASTM jej uvádí jako UNS S30430, přičemž zahrnuje také „XM-7“, „304CU“ a „304HQ“. Nyní zcela nahradil ocel 384 a 305 pro účely studeného ohýbání. Norma ISO 3506, Standardní specifikace pro spojovací prvky z nerezové oceli, 302HQ jako vhodná součást pro spojovací prvky třídy „A2“; běžně se používá k výrobě spojovacích prvků v pevnosti A2-70 a A2-80. Stabilní austenitická struktura umožňuje použít 302HQ i po rozsáhlém tepelném zpracování bez magnetismu a zároveň udržovat vynikající houževnatost při teplotách až do bodu mrazu. Ve srovnání s nerezovou ocelí 304 může přidání 3 procent mědi v 302HQ výrazně snížit rychlost ztvrdnutí při tepelném zpracování. Chemické složení a fyzikální vlastnosti jsou uvedeny níže:

 

Ekvivalentní materiál

Zpětné hodnocení UNS No DIN EN JIS
302HQ S30430 1.4567 X3CrNiCu18-9-4 SUSXM7

 

Chemická kompozice (ASTM A493 S30430)

Zpětné hodnocení C Mn Si P S Cr Mo Ni Cu
302HQ 0.03 2.00 1.00 0.045 0.03 17.0-19.0 / 8.0-10.0 3.0-4.0

 

Mechanické vlastnosti

Síla v tahu 302HQ: Zkápnutí: 605, Mírné tváření: 660

Hustota: 7900 kg/m²

Modul pružnosti: 193 GPa

Průměrný koeficient tepelného rozpínání: 0–100 °C (um/m/°C) 17,2; 0–315 °C (um/m/°C); 0–538 °C (18,8)

Teplotní vodivost: 100 °C (W/M.K) 16,3; 500 °C (W/M.K) 21,5

Specifická teplota: 0–100 °C (J/kg.K) 500;

Odolnost: 720

 

Odolnost proti korozi

Jeho odolnost proti korozi je ekvivalentní nebo lepší než u nerezové oceli 304. V teplém chlorném prostředí se snadno vyskytuje vrzání a koroze v dírách, zatímco vřetení v napětí je citlivé při teplotách vyšších než asi 50 °C. 302HQ dokáže odolávat chloridu ve vodě pitné v množství přibližně 200 mg/l při pokojové teplotě a 150 mg/l při teplotě 60 °C.

 

Vysoká odolnost vůči teplotám

Dobrá oxidační odolnost, intermitentní provoz při teplotě až 870 °C, nepřetržitý provoz při teplotě až 925 °C. Vzhledem k nízkému obsahu uhlíku v materiálu 302HQ je vhodný pro nepřetržitý provoz (bez precipitace karbidů) v rozmezí teplot od 425 do 860 °C.

 

Ošetření horkým vzduchem

Léková úprava (zafouknutí) se zahřívá na teplotu 1010–1120 °C a rychle se ochlazuje. Lékárenské úpravy ho nezpevní.

 

Svařitelnost

Vynikající svařitelnost. K svařování lze použít všechny standardní metody fúze (ať už s plnivým kovem nebo bez něj). Použijte elektrodu 308L. Svařování obvykle není nutné, s výjimkou výroby šroubových spojovacích prostředků, kde se pro spojení drátů používá rezistivní spojovací proces butt welding.

 

Zpracování 

Modul 302HQ se jen zřídka obrábí. Tento typ materiálu má velmi nízký obsah síry, což pomáhá zlepšit jeho tvarovatelnost, ale snižuje jeho zpracovatelnost. Vylepšený modul 302HQ (UGIMA 4567) má velmi vysokou zpracovatelnost, o něco vyšší obsah síry a je také kalcium ošetřený pro použití vyžadující rozsáhlé opracování za studena a obrábění. Ocel 18/8.

 

Studená zpracování tvrdnutí

302HQ je nejnižší mírou tvrzení mezi běžnými třídami austenitických nerezových ocelí. Podle údajů o tváření drátu se pevnost v tahu zvýší o 8 MPa při snížení plochy pro studené zpracování o 1%). I po rozsáhlém studeném opracování zůstává značka v podstatě odolná vůči magnetům. Některé šrouby pro vysokou pevnost s studeným ohýbáním vyžadují nižší míru tvrzení, takže 304 nebo by se místo 302HQ mělo použít 304L (nebo speciální třída 304M); míra tvrzení těchto tříd je přibližně 10–12,5 MPa.

 

Typické aplikace

Všechny aplikace s tvrdým hřížením, včetně samorezných šroubů, střešních šroubů, mechanických šroubů, šroubů s montážním kroužkem, blindových nití apod.

Nerezová ocel 321 vs 347

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The property of 321 stainless steel and 347 stainless steel is similar in most cases, the 321 stainless steel is a kind of titanium – stabilization of 18/8 austenitic stainless steel (304), a small amount of titanium makes it in carbide precipitation temperature range, that’s 425-850℃, not appear intergranular corrosion after heating, with good strength, resistance to oxidation peeling and aqueous corrosion resistance.

The 321H is a high-carbon version of the 321 with higher high-temperature strength and is primarily used for high-temperature applications around 900°C. The disadvantage of 321 is that titanium has poor welding arc transition, so it cannot be used as welding material, while 347 containing niobium also plays the role of carbide stabilization, and can also be transferred through welding arc. 347 is standard welding material for 321 stainless steel welding and occasionally used as the base metal. Let’s see their chemical and mechanical comparison below:

 

Chemical composition comparison

Zpětné hodnocení C Mn Si P S Cr Ni Mo N Other
321 0.08 2.00 0.75 0.045 0.03 17.0-19.0 9.0-12.0 / 0.1 Ti=5(C+N)0.7
347 0.08 2.00 0.75 0.045 0.03 17.0-19.0 9.0-13.0 / / Nb=10(C+N)1.0

We can see that the difference between them is the addition of  Ti and Nb. Due to the addition of stabilized element titanium, 321 can resist the formation of chromium carbide at 426℃~815℃, so it has excellent intergranular corrosion resistance and high-temperature performance and has higher creep and stress fracture properties than 304 and 304L. In addition, 321 also has good low-temperature toughness and excellent formability and welding characteristics, without annealing after welding.

347 Stainless steel is a niobium-containing Austenitic stainless steel and 347H is its high carbon version. 347 can be seen as a niobium-adding version based on 304. Nb, a rare earth element, has a similar effect to titanium in refining grains,  can resist intergranular corrosion and promoting aging hardening.

 

Physical property comparison

Zpětné hodnocení Uzávěrnost, Mpa Síla v tahu, MPa Elongation(50mm) Tvrdost, HB
321 515 205 40 217
347 515 205 40 201

 

Typical applications

347&347H stainless steel has better high-temperature performance than 304 and 321. It is widely used in aviation, petrochemical, food, papermaking and other industries, such as exhaust pipe and branch pipe of aero engine, hot gas pipe of turbine compressor and parts working under low load and temperature not exceeding 850℃.

The addition of titanium to the 321 makes it more suitable for where need high temperature and good corrosion resisting applications. It is suitable for 304 sensitized and 304L applications with insufficient high-temperature strength. Typical applications include thermal expansion joints, bellows, aircraft exhaust system components, heating element sleeves, furnace components, and heat exchangers.

What’s the difference between 316L and 904L steel?

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Commonly known as “medical-grade steel”, 316L stainless steel is not only used to make jewelry and medical scalpels due to its low allergenic properties but also used by watch manufacturing companies to make watchbands. 904L stainless steel is Austenitic stainless steel made by Outokumpu Company in Finland based on 316L stainless steel, is a super Austenite with low carbon content and high alloying designed for corrosive environments such as dilute sulfuric acid.

904L stainless steel increases the content of chromium, nickel and molybdenum and adds a certain amount of copper, which will bring about a change in performance, making 904L stainless steel more wear-resistant and corrosion-resistant, but at the same time, there is not much difference between the two in hardness, let’s show their difference with the table below:

Zpětné hodnocení C Si Mn Cr Ni Mo P S Cu
316L ≤0.03 ≤0.1 ≤0.2 16-18 10-14 2-3 ≤0.04 ≤0.03 /
904L ≤0.02 ≤0.1 ≤0.2 19-23 23-28 4-5 ≤0.04 ≤0.03 1-2

 

It is not difficult to see that 904L alloy elements chromium, nickel, molybdenum is more than 1.6 times of 316L stainless steel, 1%-2% copper makes 904L stainless steel has stronger corrosion resistance and wear resistance than 316L stainless steel. The 904 has a lower carbon content (C), so the polished 904L steel pipe or sheet steel has a better surface, and the same volume of 904L stainless steel is much heavier than the 316L stainless steel. Their Rockwell strength (HRB) is less than 95, and the strength is almost 490MPa. So it is completely wrong to say that 904L stainless steel is harder than 316L stainless steel.

Rolex was the first company to put 904L into watch manufacturing. In 1985, Rolex produced the watch case made of 904L steel replaced 316L steel. 904L steel contains more chromium, which helps to form a corrosion-resistant coating on the surface of metal materials. And “anti-corrosion” is also the benefit of the Rolex watches we often mention, but here “anti-corrosion” does not have any practical significance, because 316L steel has been completely enough daily corrosion. 904L steel is indeed better in corrosion resistance than 316L steel, but it does not mean that 316L steel is not good. For consumers, as a watch case material,  904L steel’s “propaganda” effect is better than the actual role of “anti-corrosion” itself.

Not just in the watch industry, chemical fields shows more advantages., 904L offers better corrosion resistance than 316L and even 317L. The addition of 1.5% copper has excellent corrosion resistance to reducing acids such as sulfuric acid and phosphoric acid, and also has excellent intergranular corrosion resistance to stress corrosion, pitting corrosion and crevice corrosion caused by chloride ion. In the concentration range of 0-98% pure sulfuric acid, 904L can be used at temperatures up to 40 ℃. Of all the phosphoric acids, 904L is more resistant to corrosion than ordinary stainless steel. Ordinary Austenitic stainless steels may be sensitive to stress corrosion at temperatures above 60℃ in a chloride-rich environment, and this sensitivity can be reduced by increasing the nickel content of the stainless steels. Due to its high nickel content, 904L is highly resistant to stress corrosion cracking in chloride solutions, concentrated hydroxide solutions, and hydrogen sulfide-rich environments.

The difference between Stainless steel hot rolled plate and cold rolled plate

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Stainless steel has excellent corrosion resistance, processing, biocompatibility and strong toughness within a wide range of temperatures, has been widely used in the petrochemical industry, atomic energy, light industry, textile, food, household appliances and other fields. Hot rolling and cold rolling are the necessary processes for stainless steel plate forming. The hot rolled plate is the raw material of cold-rolled plate, both of them will affect the microstructure of the stainless steel plate.

The hot rolling process of stainless steel is made from the slab (mainly continuous casting slab), which is heated and made from a roughing mill and finishing mill group. The hot steel from the last finishing mill is cooled by laminar flow to the specified temperature and is rolled into coils by the coiler. The steel after cooling has an oxide surface, with a black color, commonly known as “stainless steel black coil”. After annealing and pickling, the oxidized surface is removed, that is, “stainless steel white roll”. Some hot rolled stainless steel products can be used directly and some need to be processed into cold-rolled products before being used.

Stainless steel cold-rolled plate is generally the product of stainless steel hot-rolled plate with a thickness of 3.0-5.5mm after being rolled and processed by cold rolling equipment (single stand cold rolling/multi-strand cold rolling). Different processing methods and reprocessing after cold rolling can make the surface of stainless steel plate have different grades of surface finish, grain and color. There are 2D, 2B, No.3, No.4, No.4, HL, BA, TR, embossing and other surface grades in the surface processing of cold-rolled stainless steel plates. A variety of deeply processed surfaces such as electroplating, electropolishing, directional pattern, etching, shot peening, coloring, coating and its combination can be further implemented on the basis of cold rolling, in addition, the no.1 surface and pattern plate after hot rolling pickling are also included. what’s the difference between of hot rolled and cold rolled stainless steel plate?

 

Different surface qualities

Stainless steel cold-rolled plate has good surface quality, no oxide scale, a variety of surface treatments are available. Stainless steel hot rolled plate is generally No 1 treatment, with oxide skin, gray-white (pickling) or black-brown (not electroplated). The smoothness of the cold-rolled plate after electroplating is higher than that of a hot rolled plate.

 

Different prices

The toughness and surface quality of the stainless steel cold-rolled plate is higher than the hot-rolled plate, and the price is higher than the hot-rolled plate.

 

Different applications

Stainless steel cold-rolled sheet is widely used in various civil and industrial fields, including architectural decoration, products, home appliances, rail transit transportation, automobiles, elevators, containers, solar energy, precision electronics, etc. 2D, 2B, BA and grinding surface can be directly used for most products in architectural decoration, elevator, container and other industries. The cold-rolled sheet after forming or re-processing can be used in places with higher surface quality requirements, such as home appliances, rail transportation, automobiles, solar energy, precision electronics, etc.

What is Ferritic stainless steel used for?

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Ferrite stainless steel refers to the stainless steel with 11%~30%Cr and cubic crystal ferrite structure. Its high chromium content is the main element that affects its performance. The advantages of Ferritic stainless steel include low cost (without nickel), good magnetic conductivity, excellent stress corrosion resistance; Small working hardening tendency, easy to cold heading and cutting; High thermal conductivity (1.5 times that of Austenitic steel), low linear expansion coefficient (60% of Austenitic steel), but also obvious disadvantages such as poor plasticity and low strength in post-processing, easy welding cracking. Ferritic stainless steel is mainly used in oxidizing medium and nitride medium, suitable for heat exchange and heat circulation purposes, provides a wide range of applications.

 

Architecture and structure applications

Ferritic stainless steel is used as the roof and curtain wall of buildings because of its good resistance to atmospheric corrosion. High-chromium ferritic stainless steels used in coastal areas have been developed, and atmospheric corrosion-resistant stainless steels contain high levels of chromium and molybdenum and are supplemented with small amounts of niobium and titanium. The steel actually contains 22% chromium and 1.2% molybdenum. Sufficient chromium and molybdenum are necessary to improve the pitting resistance of stainless steel. The rusting area of type 304 and Type 316 austenitic stainless steel increased significantly with the increase of the number of periodic corrosion test cycles. On the contrary, the rust area of type 444 ferritic stainless steel increased slightly during the first 600 test cycles and was saturated after longer tests.

 

Automobile industry

Type 409 or 410L stainless steel is used as a vehicle exhaust emission control system material such as front pipe, center pipe and muffler due to its excellent intergranular corrosion resistance, formability and heat resistance. In recent years, the design temperature of vehicle exhaust has increased because of the catalytic conversion rate and reduction of harmful gases such as NOx, SOx and hydrocarbon (HC) emissions. However, the increased temperature of chromium carbide will produce deposits on the silencer, i.e., temperatures of 400 ~ 500℃will lead to grain boundary corrosion. Because the weld area is particularly sensitive to intercrystalline corrosion, it is necessary to improve the corrosion resistance of Ferritic stainless steel containing 12% Cr. Therefore, a new Ferritic stainless steel was developed by adding niobium to steel containing 12% Cr. It is well known that reducing carbon and nitrogen content in steel is quite effective in preventing intercrystalline corrosion. In this way, the intercrystalline corrosion resistance can be further improved by adding niobium and titanium to steel. 409L stainless steel is used as the material for the exhaust manifold of automobiles, and the exhaust temperature is designed to be about 800℃. 430J1L stainless steel is recommended when the exhaust temperature is approximately 900℃.

 

Home appliances and kitchenware

400 series ferrite stainless steel has been widely accepted in the field of household appliances and kitchenware because of its unique aesthetic properties, corrosion resistance to cleaners and disinfectants, low thermal expansion coefficient and magnetism (suitable for electromagnetic cookers). Ferritic stainless steel greatly reduces weight compared with carbon steel. Ferritic stainless steels do not contain nickel and are far more price stable than Austenitic steels, making it easier for manufacturers to manage costs, purchase and sell. The use of ferritic stainless steel is so wide, each use of the required ferrite stainless steel performance is different. Typical applications include dishwashers, electric kettles, washing machines, dustbins, kitchen drains, ovens, gas appliances, coffee makers, microwave ovens, gas stoves, cold storage, restaurant trolleys.

 

Ferritic stainless steel is also used in transportation and other industrial applications. Because it has so many advantages over carbon steel and Austenitic stainless steel, it’s excellent formability like bending, cutting and drilling making it has a wide applications. Because there are many ferritic stainless steel grades, in order to obtain good corrosion resistance, good strength and lower price, you need to choose the right grade to meet customer requirements.

Zpětné hodnocení Chemical composition Characterize Applications
409L 11.3Cr-0.17Ti

Low C and N

 The added Ti making it has good high-temperature corrosion resistance and strength. Automobile exhaust pipes, heat exchangers, containers and other products without heat treatment after welding.
410L 13Cr

Low C

 Reduce the C based on 410, has good processing, welding deformation resistance, high-temperature oxidation resistance. Parts for mechanical construction, engine exhaust pipes, boiler combustor, burner.
430 16Cr Typical grades of ferrite steel, it has a low thermal expansion rate, excellent formability and oxidation resistance. Heat resistant appliances, burners, home appliances, tableware, kitchen sinks, external decorative materials, bolts, nuts, screen
430J1L 18-Cr0.5Cu-Nb

Low C&N

 Addition of Cu, Nb based on 430, good corrosion resistance, formability, weldability and high-temperature oxidation resistance. Building exterior decoration materials, auto parts, hot and cold water supply equipment.
436L 18Cr-1Mo-Ti、Nb、Zr

Low C&N

 Added Nb, Zr, excellent heat resistance and abrasion resistance, good processing and weldability. Washing machines, car exhausts, electronics, cooking POTS.